There is provided a photostable and synergistically enhanced topical sunscreen composition. There is further provided a method of enhancing the photostability of a sunscreen active in a topical sunscreen composition. There is further still provided a method of synergistically enhancing the UV absorbance of a sunscreen active in a topical sunscreen composition. The preferred compositions and methods of the present invention use a dibenzoylmethane sunscreen active, an extract of Kaempferia Galanga, and a cosmetically acceptable vehicle.

1. Field of the Invention
The present invention relates to the use of Kaempferia Galanga extract to photostabilize a topical sunscreen composition and synergistically enhance the UV absorbency of a sunscreen composition. More particularly, the present invention relates to a sunscreen composition having a sunscreen active, particularly dibenzoylmethane and/or its derivatives, and an extract of Kaempferia Galanga, particularly from the root thereof. The present invention also relates to a method of photostabilizing a sunscreen active in the topical sunscreen composition. The present invention further relates to a method of synergistically enhancing the UV absorbance of a sunscreen active in the topical sunscreen composition.
2. Description of the Prior Art
Commercial sunscreen compositions commonly employ a sunscreen active, such as a dibenzoylmethane derivative, e.g. butylmethoxydibenzoylmethane (avobenzone).
A common problem associated with some sunscreen compositions is a tendency of sunscreen actives, including dibenzoylmethane and/or derivatives thereof, to photodegrade over time from exposure to UV (ultraviolet) light. This results in an alteration of the UV absorbance of the composition and, thus, a diminution in sunscreen protection for the user during extended exposure to sunlight.
U.S. Pat. No. 5,952,391 relates to sunscreen compositions having dibenzoylmethane sunscreen actives. The compositions have flavone or flavanone derivatives to stabilize the dibenzoylmethane actives.
An extract of Kaempferia Galanga is disclosed in Naturally Occurring Isoamyl p-Methoxycinnamate, Cosmetics and Toiletries magazine, vol. 112, pp. 74-77, Jan. 1997, which is incorporated herein by reference thereto. Topical compositions having the extract are disclosed in Japanese Application Nos. 8157346A2, 61291515A2, S61-291515 and 9030948A2. The extract has been disclosed as useful as a sunscreen, anti-inflammatory agent, skin lightening agent and food ingredient.
It would be desirable to have a sunscreen composition that is photostable and affords the claimed sunscreen protection for an extended period of time. It would be further desirable to have a photostable sunscreen composition that has a dibenzoylmethane and/or derivative thereof (hereafter collectively xe2x80x9cdibenzoylmethanexe2x80x9d). It would be still further desirable to have a photostable sunscreen composition that affords an enhanced degree of sunscreen protection.
It is an object of the present invention to provide a topical sunscreen composition having a photostable sunscreen active.
It is another object of the present invention to provide a topical sunscreen composition affording enhanced photostability for a dibenzoylmethane sunscreen active.
It is still another object of the present invention to provide a topical sunscreen composition that exhibits synergistic UV absorbance benefits upon prolonged exposure to sunlight.
These and other objects and advantages of the present invention are achieved by a topical sunscreen composition having a sunscreen active, a photostabilizing and/or UV absorbance enhancing amount of an extract of Kaempferia Galanga, and a cosmetically acceptable vehicle.
There is also provided a method of enhancing the photostability of a sunscreen active in a topical sunscreen composition. An extract of Kaempferia Galanga is introduced into the composition in an amount sufficient to enhance the photostability of the sunscreen active.
There is also provided a method of synergistically enhancing the UV absorbance of a topical sunscreen composition having a sunscreen active. An extract of Kaempferia Galanga is introduced into the composition in an amount sufficient to synergistically enhance UV absorption.
It was found surprising and unexpected that the photostability of a topical sunscreen composition having a sunscreen active, particularly dibenzoylmethane and/or derivatives thereof, could be enhanced by the introduction of an extract of Kaempferia Galanga, particularly from the root thereof. It was also found surprising and unexpected that UV absorption capability of such a composition was synergistically enhanced by the introduction into the composition of the extract of Kaempferia Galanga.
The present composition has one or more active sunscreens. Such sunscreen actives may be organic or inorganic and water-soluble or oil-soluble. Such actives include those for UVA and UVB protection (290 to 400 nanometer solar radiation). Such sunscreen actives include, but are not limited to, one or more of the following: dibenzoylmethane, oxybenzone, sulisobenzone, dioxybenzone, menthyl anthranilate, para aminobenzoic acid (PABA), octyl methoxycinnamate, DEA methoxycinnamate, octocrylene, drometrizole trisiloxane, octyl salicylate, homomenthyl salicylate, octyl dimethyl PABA, TEA salicylate, 4-methyl benzilidene camphor, octyl triazone, terephthalydiene dicamphor sulfonic acid, phenyl benzimidazole sulfonic acid, ethyl PABA, hydroxy methylphenyl benzotriazole, methylene bis-benzotriazoyltetramethylbutylphenol, bis-ethylhexyloxyphenol methoxyphenol triazine, titanium dioxide, zinc oxide, or any derivatives or any combinations thereof. Other useful sunscreen actives include those disclosed in U.S. Pat. No. 5,000,937, which is incorporated herein by reference.
Sunscreen actives of the present invention may be present at up to about 70 percentage by weight (wt %), of the total weight of the composition. Preferably, sunscreen actives are present from about 0.05 wt % to about 50 wt %, more preferably about 0.1 wt % to about 30 wt %, and most preferably about 0.5 wt % to about 20 wt %, based on the total weight of the composition. For example, octyl methoxycinnamate is present in an amount about 2 wt % to about 10 wt %, octyl salicylate in an amount about 3 wt % to about 5 wt %, and oxybenzone in an amount about 2 wt % to about 6 wt %.
The preferred sunscreen active is dibenzoylmethane and derivatives thereof. The dibenzoylmethane sunscreen active preferably conforms to the structure:
wherein R1 and R2 are alkyl groups having 1-36 carbons. The dibenzoylmethane sunscreen active includes, but is not limited to, butylmethoxydibenzoylmethane (avobenzone) and 4-isopropyldibenzoylmethane. The most preferred active is butylmethoxydibenzoylmethane.
The dibenzoylmethane sunscreen active is present at up to about 20 wt %, of the total weight of the composition. Preferably, the dibenzoylmethane sunscreen active is present from about 0.05 wt % to about 10 wt %, and most preferably about 0.5 wt % to about 3 wt %, based on the total weight of the composition.
The amount of sunscreen active employed will depend on the level of protection desired. Although not to be construed as limiting, compositions will typically range in level of sunscreen protection factor (SPF) from about 2 up to about 100, preferably about 2 to about 70, more preferably about 4 to about 30, and most preferably about 15 to about 30.
The present composition has an extract of Kaempferia Galanga. The extract is a crystalline solid obtained from the Kaempferia Galanga plant, also referred to as the Spice Lilly. The extract may be obtained from any part of the plant, such as the leaves, flowers, stem, bark and, most preferably, the root. The essential oil can include among its components the following: p-methoxycinnamic acid ethyl ester, p-methoxycinnamic acid methyl ester, cinnamic acid ethyl ester, n-pentadecane, 3-Carene borneol and 1,8-cineole.
The weight ratio of the extract of Kaempferia Galanga to the sunscreen active is 0.01:3 to 3:0.01. This ratio is preferably 0.01 to 0.5:1, more preferably 0.05:3, even more preferably 0.02 to 0.2:1, and most preferably 1.5:1.
Although an extract of Kaempferia Galanga is known to be useful as a sunscreen active, the effects observed in the present invention upon combination with other sunscreen actives, particularly dibenzoylmethane and/or derivatives thereof, is surprising and unexpected. First, the extract enhances or improves the photostability of the sunscreen active. The enhancement or improvement in photostability of the sunscreen active lengthens the period of time in which photoprotection by the sunscreen composition is provided. Thus, users of sunscreen compositions having the extract can be protected from sunlight for longer periods of time as compared to sunscreen compositions that do not have the extract. Second, the extract synergistically enhances or increases the level of sun protection typically provided by a sunscreen composition. In other words, the level of sunscreen protection afforded by, for example, butylmethoxy dibenzoylmethane and Kaempferia Galanga root extract is synergistically greater than the additive effect of these ingredients. This synergistic enhancement permits the use of lower levels of the sunscreen active. Thus, this effect reduces the need for reapplication. A preferred embodiment of the present invention comprises butlylmethoxy dibenzoylmethane, octyl methoxycinnamate and Kaempferia Galanga root extract.
The present composition may include any cosmetic vehicle known in the art. Suitable vehicles include, but are not limited to, one or more of the following: vegetable oils; esters such as octyl palmitate, isopropyl myristate and isopropyl palmitate; ethers such as dicapryl ether and dimethyl isosorbide; alcohols such as ethanol and isopropanol; fatty alcohols such as cetyl alcohol, stearyl alcohol and behenyl alcohol; isoparaffins such as isooctane, isododecane and isohexadecane; silicone oils such as dimethicones, cyclic silicones, and polysiloxanes; hydrocarbon oils such as mineral oil, petrolatum, isoeicosane and polyisobutene; polyols such as propylene glycol, ethoxydiglycol, glycerin, butylene glycol, pentylene glycol and hexylene glycol; as well as water, or any combinations of the foregoing.
The amount of cosmetically acceptable vehicle in the present composition will vary considerably based upon product form, but typically will range from about 30 wt % to about 99.95 wt % and preferably about 50 wt % to about 99 wt %, based upon the total weight of the composition.
The present composition may take the form of an emulsion. The emulsion may be, for example, anhydrous water-in-oil, oil-in-water, water-in-silicone, or multiple emulsions. The present composition, when in emulsion form, preferably has one or more emulsifiers. Emulsifiers that can be used in the composition of the present invention include, but are not limited to, one or more of the following: sorbitan esters dimethicone copolyols; polyglyceryl-3-diisostearate; such as sorbitan monooleate and sorbitan monostearate; glycerol esters such as glycerol monostearate and glycerol monooleate; polyoxyethylene phenols such as polyoxyethylene octyl phenol and polyoxyethylene nonyl phenol; polyoxyethylene ethers such as polyoxyethylene cetyl ether and polyoxyethylene stearyl ether; polyoxyethylene glycol esters; polyoxyethylene sorbitan esters; dimethicone copolyols; polyglyceryl-3-diisostearate; or any combinations thereof. Additional useful emulsifiers and co-emulsifiers are provided in U.S. Pat. Nos. 5,162,378 (column 4) and 5,344,665 (Table 1), which are incorporated herein by reference.
When in emulsion form, the present composition preferably has an amount of emulsifier about 0.1 wt % to about 35 wt % and most preferably about 1 wt % to about 25 wt %, based upon the total weight of the composition.
Optionally, the present composition may include one or more of the following ingredients: anesthetics, anti-allergenics, antifungals, antimicrobials, anti-inflammatories, antiseptics, chelating agents, botanical extracts, colorants, depigmenting agents, emollients, exfollients, film formers, fragrances, humectants, insect repellents (especially ethyl butylacetylaminopropionate (IR3535)), lubricants, moisturizers, pharmaceutical agents, preservatives, skin protectants, skin penetration enhancers, stabilizers, surfactants, thickeners, viscosity modifiers, vitamins, or any combinations thereof. Film formers are particularly preferred.
The present compositions may also contain one or more insect repellent actives. Such actives include, but are not limited to, N,N diethyl-m-toluamide (DEET), ethyl butylacetylaminopropionate (IR3535 by Merck Co.), hydroxyethyl isobutyl piperidine carboxylate (1-piperidine carboxylic acid) (Bayer KBR 3023), oil of citronella, soy bean oil, lemon grass oil, geranium/geraniol oil, neem oil and other natural essential oils, p-menthane-3,8-diol, or any mixtures thereof. Other useful actives are disclosed in U.S. Pat. Nos. 5,130,136 and 5,698,209, which patents are incorporated herein by reference. Preferred insect repellent actives are DEET, IR3535, p-menthane-3,8-diol and oil of citronella.
The insect repellent active is present in an amount about 0.05 wt % to about 60 wt %, and preferably about 5 wt % to about 30 wt %, based on the total weight of the composition.
Suitable film formers may include poly(vinyl pyrrolidone/1-triacontene) (Tricontonyl PVP), added at about 3 wt %. This compound contributes film forming and water-proofing qualities to the composition. An example of such a compound is GANEX.RTM. WP 660, a film-forming waterproofing agent distributed by International Specialty Products, Co. Primarily, it is used for high quality waterproofing sunscreen formulations. Other film formers known in the art can be used advantageously in the composition. These include acrylate copolymers, acrylic C12-22 alkyl methacrylate copolymer, acrylate/octylacrylamide copolymers, acrylate/VA copolymer, amodimethicone, AMP/acrylate copolymers, behenyl beeswax, behenyl/isostearyl, beeswax, butylated PVP, butyl ester of PVM/MA copolymers, calcium/sodium PVM/MA copolymers, dimethicone, dimethicone copolyol, dimethicone/mercaptopropyl methicone copolymer, dimethicone propylethylenediamine behenate, dimethicolnol ethylcellulose, ethylene/acrylic acid copolymer, ethylene/MA copolymer, ethylene/VA copolymer, fluoro C2-8 alkyldimethicone, hexanediol beeswax, C30-38 olefin/isopropyl maleate/MA copolymer, hydrogenated styrene/butadiene copolymer, hydroxyethyl ethylcellulose, isobutylene/MA copolymer, laurylmethicone copolyol, methyl methacrylate crosspolymer, methylacryloyl ethyl betaine/acrylates copolymer, microcrystalline wax, nitrocellulose, octadecene/MA copolymer, octadecene/maleic anhydride copolymer, octylacrylamide/acrylate/butylaminoethyl methacrylate copolymer, oxidized polyethylene, perfluoropolymethylisopropyl ether, polyacrylic acid, polyethylene, polymethyl methacrylate, polypropylene, polyquaternium-10, polyquaternium-11, polyquaternium-28, polyquaternium-4, PVM/MA decadiene crosspolymer, PVM/MA copolymer, PVP, PVP/decene copolymer, PVP/eicosene copolymer, PVP/hexadecene copolymer, PVP/MA copolymer, PVP/VA copolymer, silica, silica dimethyl silylate, sodium acrylate/vinyl alcohol copolymer, stearoxy dimethicone, stearoxytrimethylsilane, stearyl alcohol, stearylvinyl ether/MA copolymer, styrene/DVB copolymer, styrene/MA copolymer, tetramethyl tetraphenyl trisiloxane, tricontanyl trimethyl pentaphenyl trisiloxane, trimethylsiloxysilicate, VA/crotonates copolymer, VA/crotonates/vinyl proprionate copolymer, VA/butyl maleate/isobornyl acrylate copolymer, vinyl caprolactam/PVP/dimethylaminoethyl methacrylate copolymer, and vinyldimethicone.
The film former is present in an amount about 1 wt % to about 5 wt % of the total weight of the composition. Preferably, the film former is present in an amount about 3 wt % of the total weight of the composition.
The composition can be made into any suitable product form. Such product forms include, but are not limited to, an aerosol, balm, cream, gel, lotion, mousse, patch, pomade, pump spray, roll-on, solution, stick or towelette.

Photostable sunscreen compositions and methods of stabilizing


The invention relates to a process for preparing a porous ceramic body, which process is based on a negative replica method. The invention further relates to a ceramic body obtainable by said method and to its use as a scaffold for tissue engineering.

The invention relates to a method of preparing a porous ceramic body and to a body obtainable by said method. The invention further relates to the use of said body as a scaffold in tissue engineering.
Regeneration of skeletal tissues has been recognized as a new means for reconstruction of skeletal defects arising from abnormal development, trauma, tumors and other conditions requiring surgical intervention. Autologous bone grafting is considered the gold standard of bone transplantation with superior biological outcomes. However, autologous bone stocks are limited and often insufficient, particularly when large skeletal defects are encountered. Allografts are used as alternative materials but are associated with immunologically mediated complications and risks of disease transmission. Additional disadvantages of autograft and allograft materials include their limited potential for molding or shaping to achieve an optimum fit with bone voids.
As surgical techniques and medical knowledge continue to advance, there is an increasing demand for synthetic bone replacement materials, resulting from the limited supply of autograft materials and the health risks associated with the use of allografts. Hydroxyapatite has been investigated for use in the osseous environment for over 20 years, and the biocompatibility of the ceramic and its osteoconductive behavior is well established. Since porous HA is more resorbable and more osteoconductive than dense HA, there is an increasing interest in the development of synthetic porous hydroxyapatite (HA) bone replacement materials for the filling of both load-bearing and non-load-bearing osseous defects. Such technology could have the potential for restoration of vascularization and complete penetration of osseous tissue throughout the repair site.
Variation of the scaffold design as three-dimensional superstructures has been demonstrated as an approach to optimize the functionality of bone regeneration materials so that these materials may be custom designed for specific orthopedic applications in the form of void fillers, implants, or implant coatings. In attempt to develop a skeletal cell and tissue carrier, which could provide optimal spatial conditions for cell migration and maintenance by the arrangement of structural elements such as pores and fibers, the feasibility of using xe2x80x9clivexe2x80x9d material is under investigation. Such live material could take the form of an open-porous implant system together with living tissue. In other words, this is so-called hard tissue engineering.
The most traditional way of preparing a porous HA ceramic is to use a foaming agent like hydrogen peroxide (H2O2). In detail, an HA slurry is made by mixing HA powder with water and a H2O2 solution. Then, samples of the slurry are put in oven, under elevated temperature. H2O2 decomposes and O2 is released from the bulk material, leaving a porous structure. Until today, this technique is still widely used in both clinical applications and research areas. However, porous ceramics made by this H2O2 method has an intrinsic shortcoming: it possesses only xe2x80x9claminar porosityxe2x80x9d. In other words, the pores are interconnected mostly in a laminar way, so there is no truly three-dimensional interconnected structure.
Slip-casting is another way of synthesizing porous ceramics. The manufacturing route comprises preparing an HA slurry (slip) by mixing HA powder under stirring with water, a deflocculant and binder agents. In this slurry, a kind of foam (sponge) is immersed and pressed. As a result, the slurry will be sucked into the foam. A layer of ceramic will be coated on all the struts of the sponge after removing the extra slurry by squeezing the samples. Then the samples will be dried in microwave oven and finally sintered in a furnace. This method is often referred to as a positive replica method.
Slip-casted materials are highly porous; they have a reticulate structure. However, due to the inner flaws in the ceramic, which are left after the sponge is burnt off, the strength of the material can not be increased to meet the requirement of tissue engineering application.
Meanwhile, coral HA has gained a wide interest in biomaterial spheres. An example of such a material is Interpore(copyright), which has a high porosity and excellent microporous surface structure. However, it is an expensive material and, more importantly, its mechanical strength is insufficient for tissue engineering applications.
In summary, there are several known methods of preparing porous ceramics. However, there are specific requirements for porous ceramic which are to be used for skeletal regeneration, hard tissue repairing, and even for hard tissue engineering purpose. For bony tissue ingrowth, it is accepted that the pore size should be in the range of 100 to 300 microns, and the pores should be fully interconnected. This specification gives rise to a desire for a more suitable porous ceramic (tissue carrier or 3-D scaffold).
The present invention provides an improved method for preparing a porous ceramic body. The method leads to a ceramic body having interconnected pores of a controllable pore size. Furthermore, the mechanical properties of the ceramic body are superior to those of ceramic bodies prepared by the above discussed, known methods. Particularly its compressive strength is much higher.
A process for preparing a porous ceramic body according to the invention is based on a negative replica method. More in detail, the present method comprises the steps of:
1) preparing an aqueous slurry of a ceramic material;
2) mixing the slurry with a liquid, viscous organic phase to obtain a dough, wherein the organic phase is substantially insoluble in water, and is thermally decomposable into gaseous residues;
3) drying the dough; and
4) removing the organic phase by thermal decomposition.
The features of various preferred embodiments are discussed below with reference to the accompanying figures in which:
FIG. 1 shows the heating profile used in one embodiment to heat and sinter a body produced in accordance with a preferred embodiment.
FIG. 2 shows a microscopic photograph (magnification of 26.4) of a body produced in accordance with the embodiment of FIG. 1.
FIG. 3 shows a microscopic photograph (magnification of 1250) of a body produced in accordance with the embodiment of FIG. 1.
FIG. 4 shows a microscopic photograph (magnification of 2500) of a body produced in accordance with the embodiment of FIG. 1.
As has been mentioned, the present method has the advantage that a ceramic body is obtained which has a porous structure consisting of interconnected pores. Moreover, a particularly high porosity can be achieved while maintaining superior mechanical properties.
In addition, it has been found that a ceramic body obtainable by the present method possesses a specific microporous surface inside the macropores. In other words, the surface of the ceramic body, including the surface within the pores, has a certain advantageous rugosity. By virtue of this feature, a good attachment of cells is obtained when cells are seeded onto the body, e.g. in tissue engineering applications. Also, by virtue of this feature the ceramic body may give rise to osteoinduction. The above described ceramic materials prepared by a slip-casting method have been found not to have this feature.
The ceramic material of which the slurry is prepared can in principle be any material of which it is desired to prepare a porous body of. In other words, the choice for a particular ceramic material will depend on the objective application of the final product. In view of the envisaged application of the porous body as a scaffold in tissue engineering, in accordance with the invention it is preferred that the ceramic material is a calcium phosphate. Highly preferred calcium phosphates may be chosen from the group of octacalcium phosphate, apatites, such as hydroxyapatite and carbonate apatite, whitlockites, xcex1-tricalcium phosphate, xcex2-tricalcium phosphate, sodium calcium phosphate, and combinations thereof.
Under certain circumstances it may be desired to incorporate an additive in the aqueous slurry. Examples of such additives are binders, surfactants, pH controlling agents, deflocculants, and the like. As binder, a water soluble polymer may be used, such as a cellulose derivative (e.g. carboxymethylcellulose) may be used, preferably in an amount of between 0.05 and 0.5 wt. %, based on the weight of the slurry. A pH controlling agent may suitably be employed to control the solubility of the ceramic material. It will be clear that it is to be avoided that (a significant amount of) the ceramic material dissolves in the aqueous phase. The skilled person will be able to determine whether there is a need for the use of a certain additive, based on his general knowledge.
The concentration of the ceramic material in the slurry will depend on the solubility of the chosen ceramic material in water. Generally, said concentration will be chosen between 50 and 80 wt. %, preferably between 55 and 75 wt. %, based on the weight of the slurry. The slurry may be prepared by admixing water and the ceramic material under stirring until a homogeneous slurry is obtained.
As has been mentioned above, the slurry is mixed with an organic phase, which does not dissolve in the slurry (i.e. is substantially insoluble in water) and does not react chemically with the ceramic material in the slurry.
In order to enable a homogeneous distribution of the organic phase throughout the slurry, the organic phase needs to be in a liquid form at the time of mixing. Further, in order to ensure that the resultant mixture has the form of a moldable dough, allowing shaping of the resulting ceramic body, the organic phase should be viscous. It is also possible that the viscosity of the organic phase is relatively low at the time of mixing with the slurry, but increases upon drying.
Another requirement that has to be met by the organic phase is that it should be removable from the dough by thermal decomposition. It is preferred that the organic phase decomposes into volatile and/or gaseous residues upon exposure to temperatures above 200xc2x0 C. or 400xc2x0 C. Depending on the envisaged application of the ultimate ceramic body, it is desirable that substantially no charred or tar-like residues are formed upon thermal decomposition, respectively remain within the porous structure of the ceramic body after sintering.
Suitable examples of materials that can be used to form the organic phase will readily be identified by the skilled person, based on the considerations presented above. Depending on the material chosen, an organic solvent may or may not be present. It will be clear that, if an organic solvent is to be used, it should be chosen such that it does not substantially interfere with the characteristics of the organic phase recited above.
Without wishing to be exhaustive, the following suitable materials for use in the organic phase can be mentioned: waxes, shellac, fatty acids, fats, epoxy resins, polyurethane resins, polyester resins, poly(meth)acrylate resins and combinations thereof. Particular good results have been obtained using a poly(meth)acrylate resin. Such a resin can be a homo- or a copolymer of various acrylate and/or methacrylate monomers. Preferably, the resin is polymethylmethacrylate.
When a synthetic polymer is used in the organic phase, it has been found advantageous to incorporate a small amount of monomeric material. This monomeric material may polymerize in situ in-the dough formed by mixing the organic phase with the aqueous slurry of the ceramic material, thereby beneficially affecting the formation of interconnected pores in the final ceramic body. The monomeric material may be included in a ratio of up to 3:1, with respect to the weight of the polymer. Preferred ratios range from 1:1 to 1:2.5 with respect to the weight of the polymer. If necessary, a small amount of a suitable catalyst or initiator enabling the polymerization may be present.
In case it is desired to prepare a ceramic body having a particularly high porosity, a foaming agent may conveniently be included in the organic phase. The foaming agent may be present in the organic phase in amounts of up to 10 wt. %. By use of a foaming agent, it has been found possible to achieve a porosity of about 60%. A preferred example of a foaming agent is a combination of sodium bicarbonate and citric acid, which agents may suitably be employed in a weight ratio of between 1:2 and 1:5. Advantageously, this specific foaming agent substantially only acts when brought into contact with water (i.e. with the aqueous slurry of ceramic material). This has the effect that the organic phase will swell to a certain extent, while said phase will maintain its continuity, so that the mechanical properties of the ceramic body that is being prepared are substantially not adversely affected as a result of the use of a foaming agent.
In another embodiment, combustible particulate matter, such as pine tree branches or rigid polymeric fibers, are incorporated in the organic phase, in the slurry of ceramic material or in the mixture of the organic phase and said slurry. This matter is meant to decompose when the organic phase is removed by thermal decomposition. As a result, a ceramic body is obtained which has discrete cavities in its structure which have the shape and size of the particulate matter that has been removed. Such cavities may advantageously have the shape of tunnels, of channels, which facilitates the flow of culture medium through the ceramic body when it is used as a scaffold in tissue engineering and cells seeded onto it are being cultured.
The aqueous slurry of ceramic material and the organic phase are preferably mixed in a volume ratio of between 1:2 and 3:1, more preferably between 1:1 and 2:1. The dough will preferably comprise at least 35 vol. % of the organic phase, remainder preferably being the aqueous slurry. Both components of the dough may be mixed in any manner, taking care to obtain a homogeneous mixture.
The dough is subsequently dried. It is at this stage that a polymerization reaction may take place in the organic phase, as such is aimed at. Preferably the drying is carried out for a duration of at least 5 hours at atmospheric conditions. If a more thorough drying is desired, a microwave can be used for this purpose. It is further preferred that the dough is molded into a desired shape prior to drying. To this end, the dough may be brought into a mold, which can for instance be a polypropylene or polyethylene mold, or any other material that can be removed by burning substantially without release of toxic gases.
The dried dough is subsequently placed in a furnace in order to thermally decompose, and remove, the organic phase. Suitable conditions will depend on the nature of the organic phase. Typically, thermal decomposition will be achieved at a temperature between 200 and 800xc2x0 C. In order to ensure that the organic phase substantially completely disappears, the heating may be prolonged for a duration of up to 24 or even 36 hours.
After the thermal decomposition step, a porous ceramic body is obtained which may find application in itself. For many applications, however, it is preferred that the ceramic body is sintered. Sintering may be performed at a temperature between 800 and 1400xc2x0 C., preferably between 1000 and 1300xc2x0 C.
The thus obtained ceramic body has superior mechanical properties. In particular, it has a very high strength. The compressive strength will preferably be at least 10 MPa. Furthermore, the ceramic body has a porosity of a very advantageous configuration. The pores are interconnected and preferably have a mean diameter ranging from 400 to 4000 xcexcm. The lower limit of the porosity of the ceramic body may be 40%, or even as high as 50% or 70%.
The above properties make the ceramic body highly suitable for use as a scaffold in tissue engineering. In this regard, the term tissue engineering is intended to refer to any process wherein cells are seeded onto the scaffold material and cultured there, either in vitro or in vivo, to form tissue of a desired type. For the formation of tissue, cells of various types may be used ranging from stem cells to all sorts of differentiated cells. Due to its mechanical properties, the present porous ceramic body is particularly useful for tissue engineering bone tissue or for repair of defects at non-load bearing sites, but also at load bearing sites.
It has furthermore been found that the present ceramic body may be crushed to form a granulate of a desired porous structure. The granulate so obtained may find application in for example oral surgery and plastic surgery of the face, as well as in spine surgery and orthopedics. Preferably, the mean diameter of the particles of the granulate are between 2 and 3.5 mm.
The invention will now be elucidated by the following, non-restrictive example.


A novel toner system is provided employing a photodegradable toner. These toners are photodegradable during the fixing step in electrophotographic processes when they are exposed to light and then pressure or in the opposite sequences. This system provides excellent fixing of toner images at lower energy levels than is found in composition fixing systems.

This invention relates to electrostatography and more particularly to improved electrostatographic developing materials fixing systems and the use thereof.
In electrostatography, more specifically recited in U.S. Pat. No. 2,297,691, a uniform electrostatic charge is placed on a photoconductive insulating layer, selectively exposed, and the resulting latent electrostatic image is developed to provide a visible reproduction of an original by depositing on the image a finely divided electroscopic marking material referred to in the art as "toner." Toner is normally attracted to those areas of the layer which retain a charge thereby forming a toner image corresponding to the electrostatic latent image. The image so produced may be transferred to a support surface or otherwise processed. The image may then be permanently affixed to the support surface employing conventional fixing methods such as heating or application of a suitable solvent.
Toner alone or in combination with a suitable carrier and additives, where appropriate, may be applied employing a number of development techniques among which are cascade, more fully defined in U.S. Pat. No. 2,618,552 to E. N. Wise; magnetic brush, more fully defined in U.S. Pat. No. 2,874,063; powder cloud, more fully defined by Carlson in U.S. Pat. No. 2,221,776; or touch-down development, as disclosed by Gundlach in U.S. Pat. No. 3,166,432; among others.
When fixing the final image by application of heat, problems in adapting such a technique to high-speed machines in view of the energy required to raise the temperature of the toner to the desired level, charring or combustion, and specifically adapting toner materials to these parameters for use in high-speed electrostatographic copying machines has resulted in the requirement for additional complex machinery and process techniques. The development of an appropriate toner material which will fuse under high-speed machine conditions and avoid blocking or caking, process readily and exhibit the appropriate triboelectric properties under changes in the ambient humidity has become a rather critical and demanding art in and of itself. Other characteristics and properties that must be controlled or eliminated in a desirable toner include the effects of impaction on the triboelectric properties the abrasive nature of the toner, and bead sticking which is the adherence of carrier beads to a reusable photoconductor surface.
Toner particles are usually comprised of thermoplastic resins selected to have melting points significantly above any ambient temperature that might be encountered during electrostatic deposition. In addition to the developing power or toner materials described in U.S. Pat. No. 2,297,691 a number of additional toner materials have been developed especially for use in the newer development techniques including the cascade development technique described above. Generally speaking, these new toner materials have comprised various improved resins mixed with different pigments such as carbon black and other colorants. Some examplary patents along this line include U.S. Pat. No. 2,659,670 to Copley which describes a toner resin as rosin modified phenyl formaldehyde, U.S. Pat. No. Re. 25,136 to Carlson which describes an electrostatographic toner employing a resin of polymerized styrene and U.S. Pat. No. 3,079,342 to Insalaco describing a plasticized copolymer resin in which the comonomers are styrene and a methacrylate selected from the group consisting of butyl, isobutyl, ethyl, propyl, and iso-propyl.
Generally, these toners have been prepared by thoroughly mixing a heat softened resin and a colorant to form a uniform dispersion as by blending these ingredients in a rubber mill or the like and then pulverizing this material after cooling to form it into small particles. These toners, though they result in excellent image reproductions, do exhibit some disadvantages such as a rather wide range of particle sizes and the ability of the colored resin to be sufficiently pliable for high-speed pulverizing which results in an even wider range of particle sizes during pulverization. Other requirements of electrostatographic developers or toners including the requirements that they be stable in storage, non-agglomerative, have the proper triboelectric properties for developing and have a low melting point for heat fusing are only compounded by the additional requirements imposed by this toner forming process. It is, therefore, found that some developer materials, such as those containing toner particles made from low molecular weight resins though possessing desirable properties such as proper triboelectric characteristics are unsuitable because they tend to cake, bridge, and agglomerate during handling and storage. Another significant problem in the case of conventional toners is the high energy requirements for heat fusing sources employed with these toners.
Electrostatographic developer materials which are pressure fixable have been considered in view of the above stated difficulties. However, it is found that the toner requirements for good machine performance tend to be diametrically opposed to the requirements for pressure fixing. That is, low toner impaction requires a high toner softening temperature and good mechanical strength while pressure fixing requires softening and viscous flow at room temperature. In addition, one of the problems with potential pressure fixable toners is the need to gently handle these materials prior to pressure fusion to paper or other suitable support medium so that these materials will not prefuse and cause impaction in the development chamber. Therefore, a balance must generally be made between a material which will pressure fix onto paper at low pressure but not yet impact in the development chamber. A major cause of such prefusion is the abrasive action of the tumbling carrier beads on the toner both in normal cascade development and magnetic brush development.
Electrostatographic toner materials which are capable of pressure fixing are desirable and advantageous since unencapsulated materials which undergo cold flow tend to form tacky images on the copy sheet which often offset to other adjacent sheets. Toner particles containing unencapsulated materials which undergo cold flow, tend to bridge, cake, and block during production and in the shipping container as well as in the electrostographic imaging machine. Of course, the toner material should be capable of accepting a charge of the correct polarity such as when brought into rubbing contact with the surface of carrier materials in cascade, magnetic brush, or touch-down development systems. Further, it is found that some toner materials which possess many properties as aforementioned which would ordinarily be desirable in electrostatographic toners dispense poorly and cannot be used in automatic copying and duplicating machines. Still other toners dispense well but form images which are characterized by low density, poor resolution, or high background. Still other toners are suitable for processes where electrostatic transfer is employed.
In addition to pressure fix systems, other systems of a so-called hybrid nature have been employed such as pressure-vapor fix system wherein both pressure and a solvent vapor are applied to accomplish fixing or other combinations of heat, pressure and solvent fixing. Because of the energy requirements associated with heat fusing and the handling of an enviromental problem associated with vapor fusing there is a demonstrated need for improved toner fixing systems.
It is, therefore, an object of this invention to provide a toner fixing system which is devoid of the above noted deficiencies.
Another object of this invention is to provide a toner fixing system which employs substantially reduced energy levels.
Again another object of this invention is to provide a novel toner system.
Yet another object of this invention is to provide a toner which is stable at toner fusing conditions in high-speed copying and duplicating machines.
Still another object of this invention is to provide an impaction resistant toner material.
Again, another object of this invention is to provide a toner material which is resistant to smearing, agglomeration, and may be fused readily with less heat energy.
Yet still another object of this invention is to provide a toner which reduces mechanical abrasion of electrostatic imaging surfaces and is effective at low initial electrostatic surface potentials to provide dense toner images.
Again another object of this invention is to provide a toner which allows toner fixing at higher rates with less pressure.
These and other objects of the present invention are accomplished generally speaking by providing a photodegradable toner system. More specifically novel toner compositions are provided which comprise photodegradable polymers so that when employed in a xerographic process these toners may be applied to render a latent electrostatic image visible employing conventional techniques and thereafter be fixed employing a hybrid fixing system which utilizes the photodegradability of the toner material itself. The toner of the instant invention is therefore, applied either by itself or in connection with a carrier in the form of a developer during the developing step in a conventional electrophotographic process. Thereafter it is fixed e.g. by exposure to activating radiation which degrades the photodegradable polymer relieving the stress of the polymer and thereby allowing it to become affixed to the substrate on which it is deposited, followed by the application of pressure. In employing such a hybrid e.g., a combination of light and then pressure stress relief fixing system, substantially lower energy levels may be employed than is found in conventional pressure fix systems and in addition the solvent vapor step with its accompanying drawbacks is eliminated as found in other hybrid systems. Although pressure followed by light exposure may be employed to obtain satisfactory fixing the sequence of light exposure followed by application of pressure yield more desirable results. Photo fixing has certain advantages to normal heat fusing among which are the utilization of lower energy requirements, less fire hazard in electrophotographic imaging machines and the possibility of employing less complicated types of paper stocks. Polymer degradation may, therefore, be employed of the free radical type which involves decomposition by random chain scissions as well as depolymerization to monomer to effect efficient hybrid flash-pressure fixing. This may either be accomplished by providing a toner material wherein a solvent which effects the stress relaxation is formed in situ by photochemical process or alternatively a photodegradable polymer is allowed to degrade to lower "mers" which will simultaneously lower the viscosity and plasticize undegraded polymer thereby enhancing fixability in the hybrid fixing mode.
The present toner system comprises a degradable polymeric composition containing segments characterized by the formula: ##STR1## where R may be H, an alkyl(group) of 1 to 6 carbon atoms, a chlorine or fluorine substituted radical of 1 to 6 carbon atoms or a cyano substituted aliphatic hydrocarbon radical of 1 to 5 carbon atoms; a halogenated polymer; and a photoactive agent which upon activation is capable of abstracting a hydrogen atom from the polymer backbone of said degradable polymeric composition and halogenated polymer.
Suitable degradable polymers for use in the toner system of the instant invention can be prepared by the polymerization of aldehydes to give polymers which correspond to the formula previously set out. When aldehydes which contain alkyl groups of 1 to 6 carbon atoms attached to the carbonyl carbon atom are polymerized, polymers result in which the R moiety corresponds to the alkyl group of the aldehyde. Examples of aldehydes which contain such moieties include acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, valeraldehyde and heptaldehyde. The R moiety may also be hydrogen as is the case with poly(formaldehyde).
Alternatively, the aldehyde may contain a chlorinated or fluorinated hydrocarbon radical of from 1 to 6 carbon atoms to provide a polyaldehyde in which the R moiety corresponds to the group attached to the carbonyl carbon of the aldehyde. Examples of such aldehydes include chloroacetaldehyde, dichloroacetaldehyde, chloropropionaldehyde, chlorobutyraldehyde, chlorovaleraldehyde, chloroheptaldehyde, trifluoroacetaldehyde, trifluoropropionaldehyde, chloro-difluoroacetaldehyde and fluoroheptaldehyde.
In addition, aldehydes which contain cyano substituted aliphatic hydrocarbon radicals containing from 1 to 5 carbon atoms attached to the carbonyl carbon can be polymerized to form degradable polymers useful in the process of the instant invention. Examples of these aldehydes include cyanoacetaldehyde, beta-cyanopropionaldehyde and 5-cyanopentaldehyde.
When homopolymers of the above-described aldehydes are used in the process, the degradable polymer can be represented by the formula: ##STR2## wherein R is as defined above and n is a number representing the degree of polymerization. The degree of polymerization of the homopolymer may be quite low as in the case of oligomers or as high as the realities of the polymerization of the aldehyde permit. In general, those polyaldehydes characterized by the foregoing formula in which n is a number within the range of from 50 to 50,000 are preferred for use in the instant invention.
In addition to homopolymers of the desired aldehydes, copolymers containing degradable segments characterized by the foregoing formula can be employed in the process of the instant invention. For example, copolymers and block copolymers may be prepared from one or more of the aldehydes previously described and other polymerizable constituents such as styrene, isoprene, .eta.-methylstyrene, methylmethacrylate, phenyl isocyanate and ethyl isocyanate. In addition, the degradable segments may occur as side chains appended from the backbone of another polymer.
Suitable halogenated polymers are those which conform to the formula: ##STR3##
In the above formula, X is chlorine or bromine, Y and Y' are X or hydrogen and Z is Y or an alkyl, aryl or alkaryl constituent containing from 1 to 8 carbon atoms.
The symbols n and m represent numbers which designate the relative mole percent composition of the individual units in the polymer and can vary from 0 to 100 with the sum of n% and m% being 100. Thus, when Y is hydrogen and n is 100, the formula depicts a poly(vinylhalide), e.g., poly(vinylchloride), when X is chlorine. When Y' is X, Z is H and m is 100, a poly(vinylidenehalide) is depicted. When Y and Y' are as defined above, and n and m are numbers between 0% and 100%, a copolymer of a vinylhalide and a vinylidenehalide is depicted. These polymers can be substituted with organic constituents such as when Z is an alkyl, aryl or alkylaryl radical. Examples of organic constituents which Z represents include methyl, ethyl, propyl, n-butyl, isobutyl, octyl, phenyl, substituted phenyl, e.g., methylphenyl and ethylphenyl. Polymers containing units corresponding to the above formula which are copolymerized with other monomeric units such as vinylacetate, ethylene, propylene, methylacrylate, ethylacrylate, methylmethacrylate, ethylmethacrylate, styrene, .eta.-methylstyrene, ring substituted styrenes and acrylonitrile are also useful.
Useful photoactive agents include those compounds which, upon activation, are capable of abstracting a hydrogen atom from the backbone of the degradable polymers. While the process of the instant invention is not predicated upon any particular theory of operation, it is believed that upon irradiation the photoreactive reagent may abstract an H atom from the polyaldehyde backbone thereby forming a free radical species on a carbon atom. At this point, chain cleavage occurs as the result of the rearrangement of electrons in a carbon-oxygen sigma bond and polymer degradation occurs whereby the molecular weight of the polymer is greatly reduced. Simultaneously, the photoactive reagent removes an H atom from the halogenated polymer resulting in the formation of hydrogen halide which causes further degradation of the polyaldehyde.
A preferred class of photoactive agents is made up of those compositions which, when subjected to activating radiation, assume a .sup.3 (n,.pi.*) or .sup.1 (n,.pi.*) state. Many compositions are available which are capable of assuming such a state and are thereby able to abstract a hydrogen atom from the polymer backbone. In general, five classes of compounds are capable of assuming such an excited state and abstracting a hydrogen atom. These classes are:
1. Carbonyl compounds with reactive .sup.3 (n,.pi.*) states such as for example, benzophenone, 2-tert-butylbenzophenone, 4-aminobenzophenone, and 4-phenylbenzophenone; substituted acetophenones, e.g., 4-methoxyacetophenone, and aldehydes, e.g., benzaldehyde and anisaldehyde. PA1 2. Thiocarbonyl compounds such as for example, thiobenzophenone, 4,4'-dimethoxythiobenzophenone, substituted thiobenzophenones, thioacetophenone and substituted thioacetophenones. PA1 3. Aromatic nitro compounds having reactive .sup.3 (n,.pi.*) states such as nitrobenzene and 1,2-dinitro-3,4,5,6-tetramethylbenzene. PA1 4. Arylimines and alkylimines having reactive .sup.3 (n,.pi.*) states such as N-alkylbenzophenoneimine and benzophenone-N-hexylimine. PA1 5. Aromatic amines having reactive .sup.1 (n,.pi.*) states such as acridine and phenazine.
Another class of photoactive agents useful in the invention is that of organic peroxides such as for example, dibenzoylperoxide, tert-butylperoxide, 2,4-dichlorobenzoylperoxide and cumylperoxide. In general, those organic peroxides which form free radicals and thereby are able to abstract hydrogen atoms are useful.
An additional class of hydrogen abstracting compounds which can be used in the invention is made up of organic halides, for example, alkyl halides such as carbon tetrachloride, chloroform, carbon tetrabromide and bromoform.
The relative concentrations of degradable polymer, halogenated polymer and photoactive agent may vary widely. The degradable polymer is employed in an effective amount, i.e., that amount which when degraded will produce sufficient stress relaxation to allow fixing of the toner. Preferably, the degradable polymer will make up from 1 to 49 weight percent of the composition. The photoactive agent should be present in an effective amount, i.e., that amount which will increase the rate of degradation of the degradable polymer to a noticeable extent. A preferred concentration of photoactive agent is from 0.01 to 5 weight percent of the composition. Larger amounts can be used but are not preferred for economic reasons. In addition, too large a concentration of photoactive reagent will result in phase separation due to its crystallization. The balance of the composition is made up of the halogenated polymer and optionally additional elements which do not destroy the basic and novel characteristics of the composition.
Activating radiation, as used herein, is intended to refer to electromagnetic radiation having wavelengths within the range which will excite the photoactive reagent. In most cases, the radiation will be in the ultraviolet region, however, certain photoactive reagents such as the thiocarbonyl compounds are excited by light in the visible or near ultraviolet part of the spectra. When benzophenone is used as the photoactive reagent, irradiation in the ultraviolet range is employed with UV light having wavelengths from 250 to 370 nm being preferred.
The exposure time will vary widely depending on the relative concentrations of halogenated polymer, polyaldehyde and photoreactive agent in the toner and the intensity and wavelength of the activating radiation. Thus, optimum exposure time for a given toner in order to achieve the desired degree of polymer degradation may require some routine experimentation, but would not require the application of inventive skill. In general irradiation at a minimum of 0.1 watt-sec./cm.sup.2 should be employed, while irradiation sufficient to provide 0.5 watt-sec./cm.sup.2 is found to perform satisfactorily. If one were to employ a conventional P.E.K. Inc. 100 watt high pressure compact point source mercury arc, at least a 5 second exposure would be required. If a conventional Xenon Corporation flash lamp such as the Novatron 213-A were to be employed and operated at a 300 watt input with pulses having 10.sup.-5 -10.sup.-4 second pulse durations, the necessary exposure energy could occur in 10.sup.-3 second total exposure time.
It is found that the degree of fix obtained for these toner materials is related to light exposure, sensitizer loading, carbon black distributions and toner particles (ability to absorb light for a flash fusing) and pressure roll speeds.
The photodegradable polymeric material is described above is admixed with a suitable colorant such as, for example, carbon black and a suitable electrophotographic resin especially when this toner material is to be employed in a multiphase form as in an encapsulated toner composition to provide a toner material. Thus the toner could be fabricated of photodegradable polymer which would pressure fix and subsequently partially photodegrade giving the hybrid fix desired or it could be employed in a combination, for example a polyblend or encapsulated toner block copolymeric composition or other form with standard toner polymeric materials for example styrene/alkylmethacrylate compositions etc. In the case of encapsulated toners and other multiphase toners the weight % of photodegradable polymer based on the total weight of composition is from 1 to 49. When polymers are combined, the criterion for the monomer obtained through photodegradation would be that it relaxes the stressed photolytically inert matrix polymer for example, by solvolysis, plasticization, or other mechanistic means. Thus, for example, a toner material comprising polystyrene encapsulated polyacetaldehyde and benzophenone and a carbon black colorant may be provided by conventional spray drying techniques to provide toner particles having a diameter of for example, 15 to 20 microns on the average having dispersed therein smaller domains of polyacetaldehyde for example 0.5 microns diameter and carbon black. This toner material may then be mixed with a conventional carrier and applied to an electrostatic latent image formed through a conventional process including the steps of charging an electrophotographic member and exposing said member. The resulting visible image may then be fixed by a hybrid fixing step including the steps of applying pressure followed by application of activating radiation resulting in the properly fixed xerographic image.

Hybrid fix system incorporating photodegradable polymers


The invention relates to an RF coil system for an open MR apparatus. The system includes a plurality of resonator elements which are arranged at the area of a patient (102) positioned in the examination volume of an MR apparatus. The resonator elements are constructed at least partly as solenoid elements (104) whose conductor elements form open turns which are arranged around the patient (102). It is thus achieved that the RF field generated in the transmission mode and the sensitivity profile in the detection mode are limited as strictly as possible to the examination volume of interest. At the same time RF field strengths that are adequate for medical imaging can be generated without exposing the patient to an unacceptable load.

The invention relates to an RF coil system for an open MR apparatus, which system includes a plurality of resonator elements which are arranged at the area of a patient positioned in the examination volume of an MR apparatus, the resonator elements having at least one conductor element and at least one capacitor.
During MR imaging the nuclear magnetization in the examination volume is localized by means of temporally varying, spatially inhomogeneous magnetic fields (magnetic field gradients) which are superposed on a steady, as homogeneous as possible magnetic field. For the formation of images the magnetic resonance signal in the form of a voltage induced in the RF coil system of the MR apparatus is picked up under the influence of a suitable sequence of RF and gradient pulses in the time domain. The actual image reconstruction is then performed by Fourier transformation of the time signals. The sampling of the reciprocal k space is defined by the number, the distance in time, the duration and the strength of the gradient pulses used; this k space defines the volume to be imaged (FOV or field of view) as well as the image resolution. The number of phase encoding steps, and hence the duration of the imaging sequence, is defined by the requirements imposed on the image format and the image resolution. Contemporary MR apparatus aim to form images with an as high as possible quality and in an as short as possible period of time. Consequently, special requirements are imposed on the gradient system and the RF system of the MR apparatus.
In conventional MR apparatus the steady magnetic field, the RF fields and the magnetic field gradients are generated by essentially cylindrical coils which fully enclose the patient to be examined. In most cases cylindrical coil systems are also used for the detection of the MR signals. The RF system of customary MR apparatus includes a transmission and receiving coil such as, for example, an integrated body coil which can be used for volume imaging of the examination volume. The body coils used for the excitation as well as the detection of MR signals customarily are so-called birdcage resonators (birdcage coils). Such coils have a plurality of conductor rods which are arranged around the examination volume and extend parallel to the direction of the main field, said conductor rods being connected to one another via loop conductors at the extremities of the coil. The resonance behavior of the body coil is governed by capacitor elements which interconnect the conductor elements so as to form a network.
The steady magnetic field in a conventional MR system normally extends horizontally and parallel to the longitudinal axis of the cylindrical coil system. Granted, the cylindrical configuration enables high field strengths to be generated with a field distribution that can be suitably controlled. However, such a configuration has the drawback that the access to the examination volume and the patient present therein is strongly impeded. Because of the poor accessibility of the patient, the cylindrical geometry severely impedes or even inhibits interventional examinations. The narrow closed cylindrical tube of the MR apparatus, moreover, often gives rise to claustrophobic reactions of the patient.
For the above reasons so-called open MR apparatus have recently been developed; the examination volume therein is suitably accessible both for the patient and for a physician performing an examination. Some of the open MR apparatus utilize two disc-shaped magnet elements which are arranged at opposite sides of the examination volume and produce a vertically directed, steady magnetic field. The coils for generating the magnetic field gradients and the RF coils in such a system are customarily also constructed so as to be flat and disc-shaped, said coils being integrated in the pole faces of the main field magnet.
The flat construction of the RF coil system in open MR apparatus has the drawback that it is difficult to generate a suitably homogeneous RF field in the examination volume. Particularly strong inhomogeneities occur in the vicinity of the pole faces in which the conductor elements of the RF coils are integrated. The same holds for the sensitivity during the detection of the MR signals as this sensitivity disadvantageously also strongly dependent on the distance from the pole faces of the magnet in the open systems. A further problem resides in the fact, unlike in the conventional systems, no RF shielding is provided laterally around the examination volume in open MR apparatus. Therefore, the RF field strength decreases only slowly outside the examination volume and the spatial sensitivity profile during the detection also extends into areas far outside the examination volume. Consequently, outside the region of interest there are generated MR signals which, because of aliasing effects, become visible as undesirable artifacts in the selected FOV of the image formed.
Furthermore, flat RF coils in open MR apparatus are substantially more ineffective for the generating of RF fields than cylindrical coils. Therefore, open systems require a significantly higher transmission power in comparison with the conventional closed systems. Apart from the fact that stronger and hence more expensive power amplifiers are required, the level of the specific RF load whereto the patient to be examined is exposed is significantly higher than in customary MR apparatus. Because the conductor elements of the coil system at the area of the pole faces of the magnet are arranged very near to the body of the patient, the high RF field strengths may cause hazardous injuries (burnings) due to the absorption of the field energy in the body tissue. In order to avoid such risks, the transmission power must be limited in open MR systems. However, such limiting has an adverse effect on the imaging quality.
An alternative for the RF coils integrated in the pole faces of the main field magnet is the use of surface coils or systems with several surface coils, for example, as known from WO 99/27381. In conformity with the cited document, a plurality of surface coils, arranged notably at the area of the extremities of the patient to be examined, can operate in parallel in order to combine the respective detected MR signals so as to form an overall image. It is particularly advantageous that the limited spatial sensitivity range of the surface coils yields a larger signal-to-noise ratio. The combining of several surface coils for imaging is also known as SYNERGY.
However, the known arrangements of surface coils cannot be simply used in open MR apparatus. On the one hand, it should be noted that the orientation of the surface coils relative to the steady magnetic field has a decisive effect on the sensitivity upon detection. As has already been stated, the steady magnetic field is directed vertically in open MR systems. In this case surface coils which are arranged in a flat position on or underneath the patient have a minimum sensitivity only, because the nuclear magnetization which performs a precessional motion perpendicularly to the steady magnetic induces practically no voltage in such a coil system. However, surface coils which have each time a vertically oriented coil plane and are arranged to the side of the patient will be suitable. Unfortunately, however, it is a drawback that the sensitivity of surface coils decreases strongly in the direction from the coil plane to the volume to be examined. The high sensitivity inside the coil is not used.
Birdcage coils which are arranged around the patient are not suitable either for open MR apparatus. This is because these coils produce a circularly polarized RF field in a vertical plane. Because of the vertically oriented steady magnetic field, however, a horizontally oriented RF field which extends perpendicularly thereto is required.
Considering the foregoing, the present invention has for its object to provide an RF coil system for open MR apparatus in which the RF field generated in the transmission mode and the spatial sensitivity profile in the detection mode are limited as much as possible to the examination volume of interest. A high sensitivity should be obtained in the detection mode and it should notably be possible to generate the RF field strengths which satisfy the imaging requirements while the load whereto the patient is exposed should remain acceptable nevertheless.
This object is achieved in accordance with the invention in an RF coil system of the kind set forth in that at least one of the resonator elements is a solenoid element whose conductor element forms at least one open turn which is arranged around the patient.
Constructing one or more of the resonator elements as turns arranged around the patient in accordance with the invention offers a number of advantages. On the one hand, such solenoid elements generate a horizontally oriented, linearly polarized RF field which, because of the vertical direction of the main field, is well suitable for the excitation of MR signals in the examination volume of an open MR system. Therefore, a suitable sensitivity is also obtained in the detection mode. It is also feasible to arrange a plurality of solenoid elements around the patient so that they extend at an angle relative to one another, thus enabling operation in the quadrature mode. On the other hand, it is also advantageous that the patient is situated within the solenoid elements in the arrangement in accordance with the invention, that is, at the area where the RF field or the sensitivity profile is homogeneous to a high degree.
Unlike the flat RF coils integrated in the pole faces of the magnet, the solenoid elements have a spatial sensitivity profile which is more or less strictly limited to the area of the patient to be examined. Arranging the turns of the solenoid elements so as to extend at a short distance from and around the patient has a positive effect on the signal-to-noise ratio. Moreover, only comparatively small transmission powers are required for the excitation of MR signals.
It is advantageously possible to associate separate receiving channels with the individual resonator elements of the coil system in accordance with the invention, the detected MR signals then being applied, via said separate receiving channels, to a receiving unit for further processing. On the one hand volume imaging can thus be carried out with an as large as possible FOV by combining the MR signals detected by means of the individual resonator elements. Alternatively, sub-images can be formed from the separately detected MR signals, which sub-images are subsequently combined so as to form an overall image. This may be advantageous on the one hand to improve the signal-to-noise ratio, the individual resonator elements then being used as synergy coils. It is also possible to combine the individual images on the basis of the spatial sensitivity profiles associated with the individual resonator elements, thus saving measuring time during the imaging (SENSE method, sensitivity encoding). It is advantageous that the suitably defined spatial sensitivity profiles of the solenoid elements can be utilized for this purpose.
In the RF coil system in accordance with the invention it is advantageous to orient the plane of at least one solenoid element so as to extend perpendicularly to the longitudinal axis of the patient in conformity with claim 2. This enables the turns of the relevant solenoid elements to be arranged as closely as possible around the patient, resulting in a maximum sensitivity and an optimum signal-to-noise ratio. Notably an advantageous embodiment of the coil system claimed in claim 3 can thus be implemented; this embodiment a plurality of solenoid elements with a variable dimension of the turns can be arranged axially one behind the other. A parallel imaging method enables a large FOV to be covered in that the relevant regions of interest of the patient are enclosed by individual solenoid elements. The size of the turns is then adapted to the posture of the patient in that each turn is arranged closely around the patient. The sensitive area is thus strictly limited to the regions of interest; this has a favorable effect on the image quality.
An advantageous further embodiment of the coil system in accordance with the invention is obtained in conformity with claim 4 in that at least one of the resonator elements is a surface coil which is oriented in such a manner that the RF magnetic field generated by the surface coil has a component which extends perpendicularly to the longitudinal axis of the patient. The combination of solenoid elements around the patient and additional surface coils enables a further improvement of the receiving quality (improved signal-to-noise ratio, higher resolution) to be achieved. Considering the foregoing, for optimum sensitivity it is necessary to orient the surface coil in an open MR apparatus in such a manner that the nuclear magnetization which precesses in the horizontal plane induces a detectable voltage. It is notably when the plane of the surface coil used extends perpendicularly to the solenoid elements that the spatial sensitivity profiles of the relevant resonator elements strongly deviate from one another; this is advantageous for image reconstruction by means of the SENSE method. For example, it is feasible to arrange surface coils, together with solenoid elements, on a common cylinder surface which encloses the patient. Depending on the position relative to the main magnetic field, the surface coils are constructed as ring coils or as so-called butterfly coils. This enables the formation of systems which are all optimally suited for the imaging of the head or the body or notably for the imaging of the head/neck region.
For parallel imaging methods the individual resonator elements of the RF coil system in accordance with the invention should be decoupled from one another. In conformity with claim 5 such decoupling can be particularly simply realized by means of capacitances or inductances arranged between the conductor elements. When the capacitance or inductance values are suitably chosen, it is ensured that no resonant coupling exists between the various resonator elements. It may then make sense to provide decoupling networks (consisting of capacitances and inductances) between the conductor elements of neighboring resonator elements as well as of more remote resonator elements.
The coil system in accordance with the invention can be employed in an open MR apparatus as claimed in the claims 6 and 7. For the execution of parallel imaging methods (SYNERGY, SENSE) a separate receiving channel of the receiving unit is then advantageously associated with each resonator element.
An advantageous further embodiment of such an MR apparatus is obtained in conformity with claim 8 in that a separate transmission channel of a transmission unit is associated with each resonator element, the phase and/or the amplitude of the RF power supply being individually selectable for each resonator element by means of the transmission unit.
Because a separate transmission channel is associated with each resonator element in the open MR apparatus in accordance with the invention, the field distribution in the examination volume can be advantageously controlled completely. This is because any imaginable current distribution can be realized in the arrangement of the conductor elements by selecting the amplitude and phase for the individual transmission channels. The variation in time of the RF supply can also be selected so as to be different for each individual transmission channel. The amplitude and the phase of each individual transmission channel can be controlled by the software of the MR apparatus, thus enabling direct interactive control of the field distribution (RF shimming). For example, it is possible to integrate fully automatic control of the RF field homogeneity in the examination volume in the imaging sequence so as to compensate variable effects on the field distribution, for example, effects which are due to the different dielectric properties of the patients to be examined.
Because the spatial distribution of the RF field in the examination volume can be chosen at random, a series of further fields of application becomes feasible. For example, gradients in the RF field can be generated in different directions in space. The selection of spatially and temporally variable RF field patterns enables location codes to be impressed on the excited nuclear magnetization distribution; such codes can be used for fast volume imaging (Transmit SENSE method). It is also feasible to carry out a spatially selective pre-saturation of the nuclear magnetization in the examination volume.
A particularly simple implementation is obtained in conformity with claim 9 in which each transmission channel is connected to an output of a connection network (combiner hybrid) associated with the relevant resonator element, which connection network distributes the power of a transmission amplifier among the individual resonator elements. The connection network then defines the phase and the amplitude of the relevant supplied RF signal for each resonator element. This embodiment offers the advantage that the RF supply requires only a single power transmitter whose output is distributed among the individual resonator elements by means of the combiner hybrid. The distribution advantageously takes place in such a manner that an as homogeneous as possible RF field distribution is produced in the examination volume.


An embodiment of a well bore servicing apparatus includes a housing having a through bore and at least one high pressure fluid aperture in the housing, the fluid aperture being in fluid communication with the through bore to provide a high pressure fluid stream to the well bore, and a removable member coupled to the housing and disposed adjacent the fluid jet forming aperture and isolating the fluid jet forming aperture from an exterior of the housing. An embodiment of a method of servicing a well bore includes applying a removable member to an exterior of a well bore servicing tool, wherein the removable member covers at least one high pressure fluid aperture disposed in the tool, lowering the tool into a well bore, exposing the tool to a well bore material, wherein the removable cover prevents the well bore material from entering the fluid aperture, removing the removable member to expose a fluid flow path adjacent an outlet of the high pressure fluid aperture, and flowing a well bore servicing fluid through the fluid aperture outlet and flow path.

Hydrocarbon-producing wells often are stimulated by hydraulic fracturing operations, wherein a fracturing fluid may be introduced into a portion of a subterranean formation penetrated by a well bore at a hydraulic pressure sufficient to create or enhance at least one fracture therein. Stimulating or treating the well in such ways increases hydrocarbon production from the well.
In some wells, it may be desirable to individually and selectively create multiple fractures along a well bore at a distance apart from each other. The multiple fractures should have adequate conductivity, so that the greatest possible quantity of hydrocarbons in an oil and gas reservoir can be drained/produced into the well bore. When stimulating a reservoir from a well bore, especially those well bores that are highly deviated or horizontal, it may be difficult to control the creation of multi-zone fractures along the well bore without cementing a casing or liner to the well bore and mechanically isolating the subterranean formation being fractured from previously-fractured formations, or formations that have not yet been fractured.
To avoid explosive perforating steps and other undesirable actions associated with fracturing, certain tools may be placed in the well bore to place fracturing fluids under high pressure and direct the fluids into the formation. In some tools, high pressure fluids may be "jetted" into the formation. For example, a tool having jet forming nozzles, also called a "hydrojetting" or "hydrajetting" tool, may be placed in the well bore near the formation. Hydrojetting may also be referred to as a process of controlling high pressure fluid jets with surgical accuracy. The jet forming nozzles create a high pressure fluid flow path directed at the formation of interest. In another tool, which may be called a casing window, a stimulation sleeve, or a stimulation valve, a section of casing includes holes or apertures pre-formed in the casing. The casing window may also include an actuatable window assembly for selectively exposing the casing holes to a high pressure fluid inside the casing. The casing holes may include jet forming nozzles to provide a fluid jet into the formation, causing tunnels and fractures therein.

Apparatus for isolating a jet forming aperture in a well bore servicing tool