the use of colloidal particles with hollow 
 interiors has been considered promising for the controlled release 
 of drugs and biological molecules , for immune isolation and protection 
 of biomolecules and of biologically active species , and for waste 
 removal due to their high surface area and hollow interior for loading and 
 templating . the fabrication of porous hollow particles is commonly reported 
 using template - based synthesis approaches with materials such as vesicular 
 solution , colloids , emulsion droplets , and polymers as templates for 
 forming a layer of target material or its precursor . the core material 
 is subsequently removed by methods such as calcination and dissolution 
 to generate the hollow shell . however , a flexible fabrication 
 approach that allows for the synthesis of hollow particles with a 
 broad range of precise size and specific dual porosity has yet to 
 be developed . with the existing methods , porosity is primarily 
 defined by the shell material resulting in pores of up to a few nanometers 
 in size . this results in relatively low permeability , preventing 
 the diffusion of macromolecules such as enzymes , proteins , or larger 
 biologically active materials . other 
 approaches exist to create mesoporous particles reaching porosities 
 of several tens of nanometers ; however these techniques lack precise 
 control of the pore size and are not applicable to nanopore diameters . such approaches typically use a specific property of a given material 
 to create porosity and do not provide a generalized method that can 
 be applied to a large selection of materials . therefore , a generalized 
 fabrication technique for synthesizing porous particles with any desired 
 specific dimensions , materials and porosity is needed to further expand 
 the potential applications of these particles . nanomasking is 
 a template - based approach that can potentially use 
 a variety of materials to prepare hollow particles with monodisperse 
 sizes ranging from 10 to 20 nm to micrometers and with surface pores 
 of controllable sizes from a few nanometers to tens of nanometers . 
 with nanomasking method , shms can be manufactured with a precise control 
 in size and permeability in a wide range of scales with various materials . 
 in this approach , blocking materials prevent the growth reaction on 
 parts of the surface and concomitantly create mesopore features on 
 the surface . the diameter of the pores can be adjusted 
 by varying the size of the masking particle , and the number of mesopores 
 on the particle surface is controlled by the relative molar concentration 
 of template and masking particles . silica was selected as a 
 suitable and practical material to demonstrate 
 shms and shels because of its biodegradability , biocompatibility and 
 low toxicity thus making it suitable for in vivo applications . in addition , silica has adjustable porosity , thermal 
 and mechanical stability , low density , and high specific surface area . for silica shms , amine - functionalized polystyrene nanoparticles 
 are used as templates for nucleating growth of the nanoporous silica 
 solgel network . tetramethoxysilane ( tmos ) 
 is hydrolyzed in aqueous solution to give silicic acid , which acts 
 as a precursor for the polycondensation reaction on the particle s 
 surface . the initial chemistry of the process is shown below the synthesis approach is demonstrated in figure 2 . in order to generate the shms structure , carboxy - functionalized 
 polystyrene latex nanoparticles as nanomasks are first mixed with 
 larger templates ( figure 2a.1 ) . particles with 
 oppositely charged surface functional groups attract each other in 
 solution , causing aggregation ( figure 2a.2 ) . amine - functionalized polystyrene nanoparticles 
 ( templates ) and carboxy - functionalized polystyrene nanoparticles ( nanomasks ) 
 are mixed in solution . the silica polycondensation reaction occurs on the basic 
 template surface while nanomasks block the reaction at the point of 
 contact with the templates . polymer templates and nanomasks are 
 removed by calcination or dissolution to generate shms structure . ( b ) scanning electron micrograph of aggregated templates and nanomasks . 
 ( c ) scanning electron micrograph of silica shms . figure 2b shows a scanning electron 
 micrograph 
 ( sem ) micrograph of the framework for shms synthesis made up of 500 
 nm templates and 100 nm nanomasks . the basic nature of the amine - functionalized 
 surface creates a more efficient nucleation site for base - catalyzed 
 silica gel growth compared to the acidic carboxy functionalized surface . 
 at the point of contact once the silica layer is formed with 
 the desired thickness , the 
 polystyrene particles are removed by dissolution or calcination leaving 
 the silica shms structure ( figure 2a.4 ) . later , the shms are resuspended and dispersed in water using vortex 
 mixing and gentle sonication . the final particle diameter after calcination 
 is about 85% of the diameter of the initial 500 nm template nanoparticles , 
 which may be related to partial dehydration of the silica gel hydroxyl 
 groups during heating or extraction with anhydrous solvents . the structural properties of shms higher - resolution electron 
 micrographs taken using 
 the secondary electron mode of a scanning transmission electron microscope 
 ( stem ) and a transmission electron microscope ( tem ) are presented 
 in figure 3a , b , respectively , revealing the 
 structure of the generated holes . silica formation is blocked around 
 the point of contact between two particles , and the curvature of the 
 nanomask surface is reflected by the surface topography of the resultant 
 particle ( figure 3a ) . the synthesis using 500 
 nm templates with a tmos - to - template - weight ratio of 3:1 results in 
 silica shells with a thickness of 25 nm . the open - hole structure 
 throughout the shell and the thickness of the shell are illustrated 
 by the scanning electron micrograph of a cracked shms from the interior 
 perspective in figure 3c . ( a  e ) electron 
 micrographs of silica synthetic hollow mesoporous 
 nanospheres ( shms ) made from 500 nm templates and 100 nm . ( a ) electron 
 micrograph revealing the surface topography of shms taken with secondary 
 electron mode of scanning transmission electron microscope ( stem ) . ( c ) scanning electron 
 microscope ( sem ) image of a cracked shms showing the holes from the 
 interior perspective . ( d ) shms made by 500 nm templates and 100 nm 
 nanomasks with the particle number ratio of 1:30 and ( e ) 1:15 . shms 
 made by ( f ) 500 nm templates and 60 nm nanomaks , ( g ) 200 nm templates 
 and 40 nm nanomasks , ( i ) 100 nm templates and 20 nm nanomasks . this fabrication procedure can 
 be applied to particles with different 
 features in a wide range of sizes from 10 to 20 nm to several micrometers . there are three main degrees of freedom in the fabrication of shms : 
 the number of mesopores on the surface ( figure 3d , e ) , diameter of the mesopores ( figure 3f ) , 
 and overall particle size ( figure 3g the average number of mesopores on the surface is controlled by the 
 relative molar concentration of templates and nanomasks . sem micrographs 
 in figure 3e , f show the mesopore distribution 
 on the surface when the template - to - nanomask molar ratios in solution 
 are 1:30 and 1:15 , respectively . these ratios result in 2530 
 holes per particle for the 1:30 ratio ( figure 3e ) and 1015 holes per particle for the 1:15 ratio ( figure 3f ) . the size of the holes created on the surface 
 can be adjusted by selecting nanomasks with different diameters independently 
 of the overall diameter of the shms . figure 3e , f shows mesopores created using nanomasks with diameters of 100 
 nm , and figure 3 g shows particles created using 
 nanomasks with 60 nm diameters , all on 500 nm templates . the use of 
 100 nm nanomasks produces mesopores of 30  4 nm in diameter , 
 and the use of 60 nm nanomasks produces mesopores of 20  3 nm 
 in diameter at the point of contact . nanomasks down to 20 nm in diameter 
 are available commercially , theoretically yielding mesopores down 
 to several nanometers with high accuracy . the overall size of the 
 shms depends on the template particle size , and templates can be obtained 
 in a wide range of sizes . all template and nanomask particle 
 combinations resulted in mesopores 
 about 2535% of the diameter of the initial nanomasks , decreasing 
 slightly with smaller dimensions . the slight decrease for smaller 
 nanomasks might be related to the particles increasing surface 
 curvature , resulting in a smaller point of contact . the diameter of 
 the mesopores formed on the shms fabricated using the 200 nm template/40 
 nm nanomask pair is 12  2 nm ( figure 3h ) , whereas the diameter of the mesopores formed on the shms fabricated 
 using the 100 nm template/20 nm nanomask pair is 5  3 nm ( figure 3i ) . removal of the core by calcination results in 
 an isotropic shrinking of hydrated shms . the fabrication approach 
 results in monodisperse and uniform particles for all three sizes , 
 as shown in the electron micrographs in figure 3g  i ; the particles monodispersity in suspension was 
 validated by dynamic light scattering ( see supporting 
 information , figure s1 ) . dynamic light scattering measurements 
 yield average hydrodynamic radii of 110  5 , 221  8 , and 
 534  13 nm for particles made with 100 , 200 , and 500 nm templates , 
 respectively . their polydispersity indexes end up 0.120  0.011 , 
 0.134  13 , 0.111  22 , respectively . shms are loaded 
 by diffusion of macromolecules through their mesopores ( figure 4.a ) . as the mesopores are relatively large ( typically 
 > 5 nm ) compared to many enzymes , enzymes can diffuse freely and 
 quickly 
 into the structure to equilibrate the concentration inside and outside 
 of shms ( figure 4.b ) . later , a new layer of 
 nanoporous material is formed around the particle surface , closing 
 the mesopores within the nanoporous surface ( figure 4.c ) . in the case of silica , a positively charged 
 polymer such as poly - l - lysine is added to adsorb to the surface 
 of the particles and change the surface charge to positive . tmos is 
 then added to grow new silica on the surface and close the mesopores 
 of shms , converting them to shels . this reaction occurs in near - neutral 
 buffer conditions and does not damage the enzyme . once the mesopores 
 are closed , the load is encapsulated within shels and can not escape 
 ( figure 4.d ) . however , the load can still interact 
 with small molecules in the surrounding environment via diffusion 
 through nanopores . ( b ) high concentration of enzyme is added to the shms 
 suspension and diffuses into the hollow interior of shms . the inset 
 shows a blowup of a part of shms , depicting an enzyme diffusing through 
 a mesopore . ( d ) shms are coated with another layer of porous material sealing 
 enzymes within the particle . this capability provides two unique benefits , as discussed 
 in the 
 next section . first , the enzyme is essentially hidden from the immune 
 system because antibodies are too large to pass through the nanopores . therefore , the enzyme is protected from the immune system and from 
 digesting enzymes , such as proteases , while remaining completely active . second , shels can be coated with passivating and targeting ligands 
 without any chemical modification of the payload , making them a simple 
 yet effective vehicle for in vivo applications . penicillinase from bacillus cereus is a member of the family of beta - lactamases that catalyze the hydrolysis 
 of the beta - lactam ring.b . cereus penicillinase was selected for the characterization of shels because 
 it is the preferred beta - lactamase for enzyme - prodrug based therapies , and sensitive chromogenic and 
 fluorogenic assays are available . the 
 latter used the substrate ccf2 , which contains a coumarin linked to 
 fluorescein via a cephalosporin group . before cleavage by penicillinase , 
 excitation of the coumarin at 409 nm causes efficient fluorescence 
 resonance energy transfer ( fret ) to fluorescein , resulting in green 
 emission peaking around 520 nm . penicillinase cleaves the cephalosporin 
 group , separating fluorescein from coumarin and disrupting fret , so 
 that the same excitation produces blue 447 nm emission from coumarin . ccf2 is sold commercially as an acetoxymethyl ( am ) ester , which rapidly 
 reverts to ccf2 on exposure to esterases in rodent plasma and serum , 
 as well as inside cells . figure 5.a shows activity of penicillinase ( mw = 28 kda ) 
 enzyme encapsulated within shels . all samples were exposed to proteinase - k , 
 which digests proteins ( see supporting information , figure s2 ) ; therefore , sustained activity of the encapsulated enzyme 
 after exposure to proteinase - k demonstrates protection of the enzyme 
 against proteolysis by encapsulation in shels . ( a ) activity comparison 
 for shels with encapsulated penicillinase 
 and ccf2-am as substrate in normal serum . from the left : first group , 
 hollow silica nanospheres ( shs ) ; second group , shms ; third group , 
 sealed shs ; fourth group , shels . dark blue bars represent the fluorescence 
 from alexa 488 with streptavidin that can attach antibody molecules 
 with biotin . ( right ) penicillinase encapsulated within silica 
 shels , which was incubated with proteinase - k followed by successive 
 washing before measurement . error bars correspond to standard deviation of at least three replicate 
 experiments . in figure 5.a , the left - most bar represents 
 silica synthetic hollow nanospheres ( shs ) fabricated by sol  gel 
 templation over 200-nm templates without mesopores on the surface . therefore , enzymes can only be adsorbed on the 
 surface ( figure 5.c ) . the second bar from the 
 left represents shms made with 200-nm templates and 40-nm nanomasks 
 ( figure 5.d ) . both shs and shms were incubated 
 with 26.4 m b. cereus penicillinase solution . the third and fourth bars from the left ( figure 5.e ) represent particles similar to shs and shms , respectively , except 
 that the sealing reaction was performed after enzyme incubation , thereby 
 encapsulating enzymes within the structure . later , all four groups 
 were washed successively , removing unbound and free enzymes , and subsequently 
 incubated with proteinase - k to remove the enzyme molecules stuck on 
 the surface . shs and shms exhibit no or very little activity 
 ( figure 5.a ) , which is expected after exposure 
 to proteinase - k . 
 sealed shs show about a 2-fold increase in activity over shs ; this 
 is brought about by the protection provided by the second layer of 
 silica over the enzymes stuck on the surface and thereby supporting 
 the protective effect of the additional sealing silica layer . however , 
 there is a significant increase in activity in shels ( outlined in 
 red ) . the 10-fold activity increase of shels over sealed shs indicates 
 that the increase is not due to the enzyme covering the surface but 
 rather is caused by the enzyme molecules filling the hollow interior . this dramatic difference between shms and shels clearly establishes 
 the superiority of using shels , as both samples have gone through 
 the same process except for the additional sealing step on shels . with the current protocol , comparing with the standard curve of 
 free b. cereus penicillinase ( see supporting information , figure s3 ) , the measured activity 
 corresponds to 6  10 international units 
 ( iu ) from a single 200 nm shels corresponding to 67 enzyme 
 molecules per particle ( see supporting information , figure s4 ) . during enzyme loading , shms were initially incubated 
 with 26.4 m enzyme solution . the assayed concentration of enzyme 
 within a single shels corresponds to 26 m , resulting 
 in a 98100% match with the exterior loading concentration . this result also shows that there is no measurable loss of activity 
 of enzyme during the loading and sealing process or by hindered diffusion 
 of substrate through the nanoporous shell in this interior concentration 
 of enzyme . with this procedure , we have shown that it is feasible 
 to achieve > 1500 mg / g enzyme entrapment capacity in silica shels 
 using b. cereus penicillinase ( mw 28 kda ) ( see supporting information , figures s5 and s6 ) . the 
 evaluation 
 of entrapment capacity for different enzymes with varying molecular 
 weights needs further investigation . figure 5.b evaluates antibody access to 
 the enzyme encapsulated in shels . for this demonstration , the penicillinase 
 was fluorescently labeled with cy5 , and its accessibility was probed 
 with a rabbit polyclonal biotinylated antibody against penicillinase , 
 detected by alexa488 labeled streptavidin . the dark blue bar on the 
 left - hand side depicts fluorescence from enzyme molecules adsorbed 
 on the surface of shs , while the dark blue bar on the right - hand side 
 depicts fluorescence from penicillinase enzymes encapsulated within 
 shels . both sets were incubated with proteinase - k to remove any enzyme 
 that might have been stuck on the surface and were washed several 
 times to remove unbound enzymes . the light blue bars are alexa488 
 fluorescence intensities that represent antibody binding . in the case 
 of surface - adsorbed penicillinase , however , when penicillinase is encapsulated within shels , 
 no such antibody binding is observed . although the amount of encapsulated 
 penicillinase within shels is about 2.5 times more than surface - absorbed 
 penicillinase on hollow shells , the lack of antibody binding demonstrates 
 the prevention of antibody access to the enzymes encapsulated within 
 shels . to determine the effect of serum containing neutralizing 
 antibodies 
 on the encapsulated enzyme within shels in figure 6a we compared the activity of the free penicillinase and penicillinase 
 encapsulated within shels on nitrocefin ( 50 g / ml ) in the presence 
 of serial dilutions of serum obtained from immunized mice with penicillinase 
 ( see supporting information for immunization 
 protocol ) the activity of each group was adjusted to 2.5 iu / ml in 
 preimmunization serum , and the neutralization is reported as the ratio 
 of the activity in serums post- to preimmunization . there were around 
 4  10 particles in the shels set , making around 
 4.5 g of silica . free penicillinase activity decayed rapidly 
 after dilutions of less than 1:10  000 , with activity reduced 
 to less than 5% for all dilutions less than 1:1000 . however , even 
 in neat immunized serum , the activity of shels was greater than 50% , 
 demonstrating the protection of enzymes against neutralizing antibodies 
 by shels encapsulation . the gradual reduction in shels activity as 
 serum dilutions decreased may be due to opsonins coating the surface 
 of shels , thereby reducing the diffusion of substrate through the 
 nanoporous shell . this result clearly shows the protection of enzymes 
 against neutralizing antibodies by shels encapsulation . the ratios 
 of activity on nitrocefin ( 50 g / ml ) in serums post- to preimmunization 
 are used as the vertical axis . circles , free penicillinase ; diamonds , 
 penicillinase encapsulated shels with bare silica surface . ( b ) sustained 
 activity of penicillinase loaded shels for 15 days with the presence 
 ( triangles ) and without the presence ( squares ) of proteinase - k in 
 serum from mice immunized with penicillinase previously . ( c ) demonstration 
 of in vivo activity of gaussia princeps luciferase 
 encapsulated in shels labeled with cyanine 7 ( cy7 ) dye . fifty microliters 
 of gaussia princeps luciferase ( galuc ) enzyme encapsulated 
 shels solution with a concentration of 4  10 particles / ml was injected subcutaneously into 
 balb / c mice , followed by lateral tail vein injection of 150 g 
 native - coelenterazine after 5 min . ( d ) localization of intramuscularly 
 injected penicillinase loaded shels labeled with cy7 at days 0 , 15 , 
 30 , and 45 . free elspar ( circles ) 
 and shels - elspar ( diamonds ) were injected intramuscularly 
 into nave mice with equivalent units of activity . serum l - asparagine level pre and post injection up to 8 days was measured . free elspar ( circles ) and shels - elspar ( diamonds ) were injected intramuscularly to passively immunized 
 mice with equivalent units of activity . serum l - asparagine 
 level pre and post injection up to 8 days was measured . error bars 
 correspond to standard deviation of at least three replicate experiments . to determine whether the protection 
 from neutralization was transient , 
 penicillinase - encapsulated shels with 10 iu / ml activity were incubated 
 for 14 days in neat serum obtained from mice immunized with penicillinase . moreover , the addition of proteinase - k 
 did not affect the activity level , indicating that encapsulated enzymes 
 were still protected during the experiment ( figure 6b ) . to determine whether enzymes encapsulated in shels 
 are in a free 
 state within the hollow interior , embedded within the shell , or adsorbed 
 on the interior of the shell , the kinetic parameters of encapsulated and free escherichia colil - asparaginase were compared ; ( see supporting information , figure s7 ) both free and encapsulated l - asparaginase followed similar michaelis substrate 
 system at the saturating substrate concentration , vmax , was 0.3087 m / min for the encapsulated enzyme 
 and 0.3108 um / min for free enzyme . the michaelis constant , km , was calculated as 0.001838 mm for encapsulated l - asparaginase and 0.001989 mm for free l - asparaginase . the turnover number , kcat , was derived 
 as 108.8 for the encapsulated enzyme and 109.6 for free enzyme . this 
 similar behavior as verified using multiple constants might indicate 
 that the majority of the encapsulated enzyme is at a free state within 
 the nanoparticle s hollow interior . to confirm the feasibility 
 of enzymatic therapies with shels , protection 
 against neutralization and sustained activity in the presence of serum 
 opsonins and other serum proteins are shown next , in addition to in 
 vivo activity and in - tissue - residence of particles . to demonstrate 
 such activity in vivo , gaussia princeps luciferase 
 encapsulated in shels ( 4 10 particles / ml ) labeled with cyanine 7 ( cy7 ) dye were injected subcutaneously 
 into balb / c mice , followed by lateral tail vein injection of 150 g 
 native - coelenterazine after 5 min ( figure 6c ) . luminescence from galuc ( figure 6c right panel ) 
 was colocalized with the cy7 fluorescence from shels ( figure 6c left panel ) proving the in vivo activity of encapsulated 
 galuc . instability of galuc at body temperature prevented the detection 
 of in vivo enzymatic activity at later time points ( see supporting information , figure s8 ) . the 
 residence time of shels in tissue is important for potential 
 applications such as amino acid depletion therapy . cy7-labeled shels 
 were injected intramuscularly ( figure 6d ) and 
 repeatedly imaged over 2 months . a gradual clearance extending to 
 2 months was observed . finally , to illustrate the activity of 
 shels in a therapeutically 
 relevant setting , l - asparaginase - loaded shels were prepared . for over 40 years , l - asparaginase from escherichia 
 coli has been used to treat acute lymphoblastic leukemia 
 ( all ) in order to deplete circulating l - asparagine , which , 
 unlike normal cells , can not be synthesized by leukemic cells . l - asparagine is converted into aspartic acid and ammonia by l - asparaginase s selective starving of leukemic cells , 
 causing cell death . immune responses generated 
 against the l - asparaginase are a significant clinical problem 
 and can cause rapid neutralization and clearance of the enzyme as 
 well as significant side effects such as hypersensitivity reactions 
 and anaphylaxis . because 
 an extended residence time in tissue was observed with intramuscular 
 injection previously , this route of administration was chosen for 
 testing the systemic depletion of l - asparagine with either 
 free enzyme or shels containing the enzyme . in both cases , the clinically 
 approved enzyme , brand name elspar , was used , and 
 the same total enzyme activity ( 5 iu ) was administered to all mice . the duration of l - asparagine depletion by equivalent amounts 
 of elspar in either nave ( figure 6e ) or passively immunized ( figure 6f ) mice was determined . in nave mice , free enzyme 
 rapidly depleted the serum l - asparagine and kept it at undetectable 
 levels for at least two days . by day five , elspar given in shels ( shels - elspar ) produced a more durable l - asparagine depletion 
 of greater than five days ( figure 6e ) . when 
 neutralizing anti - l - asparaginase antibodies ( verified in supporting information , figure s9 ) were given 
 before free elspar , l - asparagine depletion 
 was not observed ( figure 6f ) . however , shels - elspar was completely unaffected by the prior introduction 
 of neutralizing antibodies ( figure 6f ) verifying 
 the protected operation of enzymes in therapeutically relevant in 
 vivo setting . functionalization of shels particle surface to 
 improve tissue retention , 
 reduce cell uptake , and protein binding without affecting encapsulated 
 enzyme activity might further prolong the in vivo activity . in summary , 
 shels are shown to be a promising platform for encapsulating functional 
 biomolecules , such as enzymes acting on small molecule substrates 
 that can freely diffuse in and out through particles pores . shels can be manufactured in large quantities with sizes and characteristics 
 that can be tightly controlled , thus maximizing entrapment capacity 
 and enzymatic activity . the experimental results show that this porous 
 shell effectively encapsulates the enzyme payload without affecting 
 enzyme activity . the shell also protects the payload from specific 
 and nonspecific interference from large biomolecules in vivo . in addition , 
 surface modifications of shels should be able to enhance circulation 
 and targeting in vivo without the need for modification of the payload . 
 as nanomasking provides flexible fabrication of shels with control 
 of particle dimensions and permeability , , the utilization 
 of a hollow nanostructure reduces the amount of carrier material introduced 
 into the body . it has also been shown that the shels technology prevents 
 the neutralization of nonhuman enzymes by antibodies in vivo and can 
 be used to achieve systemic effects even while these particles remain 
 localized . the shels fabrication approach is general and should 
 be applicable to many other materials . shels made of different materials 
 can be envisioned being used in a variety of applications , including 
 nonbiomedical ones such as biocatalysis . for medical applications , however , toxicity and quantification 
 of the immune response on shels will need further study . the effect 
 of surface modifications on the activity of the payload remains to 
 be tested . indeed , for systemic delivery applications the surface 
 of shels can be further functionalized for targeting and improved 
 circulation half - life , thereby eliminating the need for chemical modification 
 of the enzymic payload . under these conditions , stealth shels should 
 allow continuous and controlled access of the substrate to the native 
 enzyme cargo , which makes this a promising therapeutic platform for 
 treating metastatic disease . in addition , shels could be applicable 
 to in vivo medical diagnostics and monitoring . enzyme - prodrug therapy 
 and enzymatic depletion of tumor nutrients are among the most promising 
 applications of shels .
although enzymes of nonhuman origin 
 have been studied for a variety 
 of therapeutic and diagnostic applications , their use has been limited 
 by the immune responses generated against them . 
 the described dual - porosity 
 hollow nanoparticle platform obviates immune attack on nonhuman enzymes 
 paving the way to in vivo applications including enzyme - prodrug therapies 
 and enzymatic depletion of tumor nutrients . 
 this platform is manufactured 
 with a versatile , scalable , and robust fabrication method . 
 it efficiently 
 encapsulates macromolecular cargos filled through mesopores into a 
 hollow interior , shielding them from antibodies and proteases once 
 the mesopores are sealed with nanoporous material . 
 the nanoporous 
 shell allows small molecule diffusion allowing interaction with the 
 large macromolecular payload in the hollow center . 
 the approach has 
 been validated in vivo using l - asparaginase to achieve l - asparagine depletion in the presence of neutralizing antibodies .