Putting the pieces together One route to improving the delivery of existing drugs is by encapsulation inside a protective but slowly degrading shell. Such slow-release capsules improve drug availability in vivo, reduce side effects, and allow for more constant dose delivery. McHugh et al. leverage a number of existing fabrication techniques to make tiny (∼400-µm), hollow injectable microparticles that can be filled with fluid containing the therapeutic agent. By adjusting the degradation rate of the microparticle material (in this case, a lactic/glycolic copolymer), the cargo in the internal reservoir can be released at a desired time, ranging from a few days to 2 months. Science, this issue p. 1138 
 
 Abstract Three-dimensional (3D) microstructures created by microfabrication and additive manufacturing have demonstrated value across a number of fields, ranging from biomedicine to microelectronics. However, the techniques used to create these devices each have their own characteristic set of advantages and limitations with regards to resolution, material compatibility, and geometrical constraints that determine the types of microstructures that can be formed. We describe a microfabrication method, termed StampEd Assembly of polymer Layers (SEAL), and create injectable pulsatile drug-delivery microparticles, pH sensors, and 3D microfluidic devices that we could not produce using traditional 3D printing. SEAL allows us to generate microstructures with complex geometry at high resolution, produce fully enclosed internal cavities containing a solid or liquid, and use potentially any thermoplastic material without processing additives. 
 
 Three-dimensional (3D) microstructures have potential use in a wide array of biomedical (tissue engineering and drug delivery), microelectromechanical (sensors and actuators), energy, and environmental applications (1–4). Although a number of extrusion, sintering, and light-based additive manufacturing processes (i.e., 3D printing) have been developed to create these devices, each of these methods has advantages and disadvantages that make it applicable to only a subset of microstructures. Therefore, the most appropriate fabrication technique is typically selected by considering the size, shape, and composition of the desired microdevice because each technique has limitations in spatial resolution, device geometry, material compatibility, and/or throughput (5, 6). For example, stereolithography and fused deposition modeling, which have emerged as leaders in the field of custom manufacturing, are subject to a trade-off between resolution and the materials that can be printed (7). High-resolution stereolithographic 3D printing can produce nanoscale features but requires photoactive processing additives (some of which have unknown safety profiles in humans) and is not compatible with materials relevant for biomedical applications, such as poly(lactic-co-glycolic acid) (PLGA) and polycaprolactone (8–10). These processes also rely on liquid polymerization or cross-linking and may not be compatible with the encapsulation of drugs or other sensitive molecules owing to the presence of the liquid prepolymer solution that could denature or solubilize the cargo. Alternatively, heat-based fused deposition modeling, although theoretically compatible with any thermoplastic polymer, lacks the control needed to create microstructures with high resolution (11). Single-step micromolding processes, such as particle replication in nonwetting templates (PRINT), are attractive for their nanoscale resolution and throughput. However, these approaches are limited to single-layer geometries that can be released from a mold, which makes it difficult to fabricate structures that have internal architecture or a “top-narrowing” 3D shape (12, 13). 
 
 We have developed a bottom-up, high-resolution microstructure fabrication technique to create microdevices with complex geometries using a variety of commercially relevant materials, including lactide-glycolide copolymers, the most widely used biodegradable polymers for human applications. This approach, termed StampEd Assembly of polymer Layers (SEAL), combines the technology used for computer chip manufacturing with soft lithography and an aligned sintering process to produce small (≤400 μm) polymeric structures (movie S1 and fig. S1). Two or more silicon molds with complementary patterns are etched by standard microfabrication techniques (fig. S1, A to J). Polydimethylsiloxane (PDMS) is then cured on the surface of each silicon wafer to produce inverse elastomeric molds (fig. S1, K and L). A polymer is heated and pressed into the PDMS molds to produce the laminar microstructure components of interest. The first layer is then delaminated onto a separate surface, such as glass, by heat-assisted microtransfer molding. Subsequent layers of the final structure are assembled by a layer-by-layer sintering process under microscopic alignment to produce a large array of microstructures (Fig. 1). This process draws on elements from existing technology, including laminated object manufacturing (14), microfabrication-based surface patterning (15), and thermal bonding of PLGA (16) to create discrete polymeric microdevices with well-defined geometry. 
 
 Fig. 1 Assembly of 3D microstructures using the SEAL process. (A) Microstructures are fabricated by pressing and heating polymer into a patterned PDMS base mold and delaminating these structures onto a substrate to create the first layer. A second layer is then formed by using a similar molding process against a Teflon surface, which allows the features to remain in the PDMS mold after cooling. The second layer is aligned, placed into contact with the first layer, and sintered by using a mild heating step. (B) Schematic depicting the alignment and sintering equipment, consisting of a mask aligner retrofitted with a Peltier heater. A glass slide containing the first layer is suspended upside down from a fixed mask holder by means of a vacuum while the second layer, still in the PDMS mold, is placed on the wafer chuck, aligned using the stage rotation and translation knobs, put into contact, and heated until they fuse. This approach can be used to create a variety of microstructures, including (C and D) stars, (E and H) letters spelling “MiT,” (F and I) two-layered tables, and (G and J) three-layered chairs. Scale bars indicate 200 μm for scanning electron microscopy (SEM) images and 1 mm for optical images. Optical images were stitched together from multiple images to enable a better depth of focus. The interfaces between images are denoted by thin red lines. 
 
 To ensure high-fidelity microdevice fabrication, we have developed a technique to align layers during sintering with high precision. This approach uses a photomask aligner (MA4, Karl Suss, Sunnyvale, California) retrofitted with a Peltier heater, temperature controller, relay, and voltage source to enable simultaneous alignment and thermal bonding (Fig. 1B). The mask holder vacuum was applied to hold a glass slide containing the first microstructure layer facing down while the next layer, still in the PDMS mold, was held on the wafer chuck. After optically aligning adjacent features with the mask aligner’s microscope and alignment knobs, the layers were brought into contact and heated to just above the polymer’s glass transition temperature (table S1) for up to 3 min. The sealing process was continuously monitored during this time by observing the disappearance of light diffraction patterns (movie S2). As two layers came into contact, the small air gap between them produced diffraction that resolved when the heated polymer flowed to close the gap. After cooling samples to room temperature, the PDMS micromold containing the second layer was peeled off to yield a multilayered microstructure. Individual devices were then removed from the glass slide. This process was used to create large arrays of microstructures, including a 3D star, two-layered letters spelling “MiT,” a two-layer table with high–aspect-ratio supports, and a three-layer chair (Fig. 1, C to J). Mechanical characterization of the PLGA microstructures indicated that the adhesion strength of adjacent layers was of similar magnitude as that of the corresponding bulk material (fig. S2). 
 
 SEAL enables the fabrication of complex 3D microstructures that are otherwise challenging to generate, especially with materials such as PLGA. Our initial motivation for developing this process was based on our desire to create a PLGA microparticle platform to deliver timed pulses of antigens for essentially any vaccine in a single injection. To create these microparticles, fillable bases were molded using thermoplastic polymers and transferred to a glass slide to expose the empty particle core (Fig. 2A). Particle cores were filled with a model drug solution by using a BioJet Ultra picoliter dispensing apparatus (BioDot, Irving, California) (Fig. 2B and movie S3), aligned with capping polymer lids, pressed together, and briefly heated to seal the particles (Fig. 2C). Images of these particles after each stage of the fabrication process are shown in Fig. 2, D to K. 
 
 Fig. 2 SEAL-fabricated controlled-release microparticles. Particles are fabricated by (A) heating and pressing polymer between a patterned PDMS base mold and a Teflon surface, (B) transferring these bases to a new substrate and filling them with a model drug of interest, then (C) aligning an array of particle caps with drug-filled bases and briefly applying a low amount of heat to sinter the two layers. SEM images of (D) a single particle, (E) the core of a particle, and (F) a sealed particle. (G) A cross section of a single particle and (H) an array of sealed particles. Optical images of (I) an array of bases, (J) an array of filled particles, and (K) a side view of a single filled particle. 
 
 These core-shell particles are potentially useful for biomedical applications because they are sufficiently small to be injected, can be created with fully biodegradable materials, and induce only a minimal foreign body reaction (fig. S3). Each particle weighs ~60 μg and has a theoretical loading of about 2%; however, much higher loading can be achieved by varying the wall thickness to yield larger cores (fig. S4). Unlike emulsion-based processes (17), loading and kinetics can be decoupled. These devices—or similar encapsulating structures—could be used for controlled release of a drug after an appropriate stimulus. Because our initial interest was in creating pulsatile release for single-injection immunizations, we studied the release kinetics of a model antigen from PLGA microparticles. In this approach, multiple particles with different compositions could be coinjected at the time of initial immunization, degrade over time, and release antigen in discrete pulses at time points that match typical vaccination schedules (Fig. 3A). 
 
 Fig. 3 Single-injection vaccination concept and release from SEAL-fabricated PLGA microparticles. (A) Schematic of a syringe containing multiple micromolded particles sufficiently small to pass through an 18-gauge needle that each produce a discrete, delayed pulse of antigen release to mimic current bolus vaccination regimens. (B) In vitro and in vivo pulsatile release of encapsulated Alexa Fluor 680–labeled 10-kD dextran from SEAL-fabricated particles composed of PLGA1, PLGA2, and PLGA3, respectively, from left to right. The top row shows the in vitro cumulative release of fluorescently labeled dextran at 37°C (normalized average, n = 10 particles). Graphs in the second row depict the in vivo cumulative release (normalized average, n = 7 to 10 particles). Note that this yields a broader release curve even though each particle exhibits a sharp pulse because the onset of release can differ slightly in each animal. Error bars indicate the standard error of the mean. The third row shows representative images of mice collected with an in vivo imaging system after injection of a single SEAL-fabricated PLGA particle containing fluorescently labeled dextran. 
 
 We fabricated microparticles using three PLGA polymers with varying properties (table S1) and filled the microparticles with fluorescently labeled dextran to observe release kinetics. Particles composed of PLGA1, PLGA2, or PLGA3 released in vitro at 10 ± 0, 15 ± 0, and 34 ± 1 days, respectively (Fig. 3B, first row). No measurable leakage was observed prior to release, indicating that this platform releases its contents as a sharp pulse after degradation of the polymer barrier. A similar trend was observed when particles were subcutaneously injected into mice, as PLGA1, PLGA2, and PLGA3 particles released after 9 ± 2, 20 ± 1, and 41 ± 3 days in vivo, respectively (Fig. 3B, second row), as indicated by an ~50-fold increase in fluorescence upon release (fig. S5). Particles could also be lyophilized or frozen at –20°C without altering release kinetics (fig. S6). These results are especially exciting because they enable the production of various injectable microparticles that release their payloads in distinct, delayed bursts without prior leakage. Although a number of groups have created layered microparticles using microfluidic and other approaches (18, 19), these methods produce particles with continuous release, whereas we show rapid drug release after a material-dependent delay. 
 
 We examined the compatibility of the SEAL process with biologics, including the trivalent inactivated polio vaccine (IPV), one of the most thermolabile vaccines in use today (20), and ovalbumin (OVA), a commonly studied model antigen. A formulation consisting of IPV, sucrose, monosodium glutamate, and magnesium chloride was dispensed into each PLGA1 particle core and dried spontaneously within seconds after filling. Particles were then exposed to the sealing process to determine if brief heating (~60 s at 42°C) had any effect on IPV stability. IPV D-antigenicity, a surrogate for the seroprotection-conferring antigen conformation used to evaluate clinical formulations (21), remained statistically similar before and after the sealing process, suggesting that the sealing step is relatively harmless to the encapsulated biologic (fig. S7). Type 1 IPV retained 98.1 ± 11.4% of D-antigenicity after filling, type 2 IPV retained 99.6 ± 7.8%, and type 3 IPV retained 103.8 ± 11.9% relative to filled, unsealed particles. Overall, the stability of the biologic during sealing in PLGA1 was much higher than what is typically reported for microsphere encapsulation with an emulsion-based process (22, 23), likely due to the elimination of organic solvents, emulsification stressors, and washing, which can lead to substantial losses. After encapsulating and sealing IPV in PLGA microparticles, additional excipients may be needed to stabilize IPV against thermal and acidic pH stressors that it will encounter during long-term storage in the body (24, 25). To achieve very long time points with this system, it may be necessary to use PLGA with different end groups, copolymer ratios, and/or molecular weights. Maintaining a low sealing temperature to minimize stress on the antigen can be achieved by using an ester end cap, which increases hydrophobicity and thus delays the onset of release. 
 
 OVA was then used to assess the potential of this platform as a single-injection vaccine. Mice received a single injection of 25 PLGA1 particles containing 10 μg of endotoxin-free OVA (EndoFit, Invivogen, San Diego, California) and 25 PLGA3 particles containing 10 μg of endotoxin-free OVA, for a total of 20 μg. The corresponding bolus controls were injected to match the time at which 25 coinjected microparticles of each PLGA1 and PLGA3 released fluorescent 10-kD dextran (fig. S8). Mice receiving OVA-filled core-shell particles achieved peak titers (20 ± 1 on a log 2 scale) that were significantly higher than those in mice receiving two dose-matched boluses at 6 and 36 days (12 ± 4, P < 0.01). The experimental group was also statistically similar to mice receiving empty particles along with the two bolus injections (peak titer of 18 ± 5), suggesting that the PLGA particles themselves have an adjuvant effect, consistent with what has been previously reported (26). In addition, it appears that this adjuvant effect is sufficient to achieve approximately twofold dose sparing, because peak titers in the experimental group were statistically similar to those of two bolus injections containing double the antigen dose, indicating that this single-injection strategy could potentially be used to replace multiple injections and enable the use of lower antigen doses. Longitudinal and peak antibody titers can be seen in Fig. 4, A and B, respectively. Additionally, storage did not affect the release or stability of OVA, as particles stored dry for 1 month at 4°C released similar amounts of enzyme-linked immunosorbent assay (ELISA)–reactive OVA compared to freshly prepared particles (Fig. 4C). These experiments demonstrate that one injection of core-shell particles can induce a long-term antibody response, outperform multiple time-matched injections, and achieve twofold dose sparing. 
 
 Fig. 4 Ovalbumin (OVA) vaccination and storage stability. (A) Longitudinal geometric mean antibody titers and (B) peak antibody titers achieved by mice treated with a single injection of OVA-containing particles or two bolus injections of OVA in solution (n = 5 mice). All peak titer groups were significantly different from those of the control group receiving only methyl cellulose (MC; P < 0.001), but significance markers are not shown for clarity. All other differences are indicated by *P < 0.05 and **P < 0.01. These results show that a single injection of core-shell particles can induce an immune response that is not only noninferior to two dose-matched boluses, but also noninferior to two boluses with double the cumulative dose. (C) Core-shell particles stored desiccated for 30 days at 4°C release the same amount of ELISA-reactive OVA as freshly prepared particles (n = 4 particles). Error bars indicate standard error of the geometric mean in (A) and (B) and standard error of the mean in (C). 
 
 Overall, the ability to fabricate an internal compartment alone could enable a broad array of new applications with potential utility in biomedicine, sensing, actuation, and environmental monitoring. Stimuli-responsive materials could be used in environmental applications to detect harmful conditions and release a molecule that either serves as a warning signal, neutralizes the harmful agent, or protects a sensitive payload until it reaches the desired target for release (27, 28). To examine this capability, we created a microscale pH sensor consisting of fluorescent dye encapsulated in a particle composed primarily of Eudragit FS 30 D (Evonik Industries, Essen, Germany), a pH-sensitive polymer that remains solid at low pH but rapidly dissolves at neutral pH. When subjected to a near-neutral environment (pH 7.5), these particles quickly released their contents, signaling that a change in pH had occurred (fig. S9, A to E). These particles were also able to protect a biologic from low-pH insult. OVA encapsulated in FS 30 D was released at neutral pH after incubation in a pH 1.2 solution at 37°C for 18 hours and retained 95 ± 8% of ELISA reactivity (fig. S9F). When fed to mice, these particles did not release their fluorescent payload in the low pH of the stomach; release occurred only after particles reached the desired target of the more neutral intestines (fig. S9, G to I). Other polymers that demonstrate the opposite behavior, such as Eudragit E PO (Evonik Industries), could be used in parallel for precise regulation of environmental conditions. We also demonstrate the ability of SEAL to create 3D microfluidic channels with a cross-sectional area of 50 μm by 50 μm using a three-layered PLGA structure that was embedded in PDMS and removed via dissolution in organic solvent (fig. S10, A to C). The resulting structure was a vertically serpentine hollow channel in PDMS that was subsequently bonded to glass and subjected to flow (fig. S10, D and E, and movie S4). These channels are optically transparent and smaller than the minimum reliable resolution produced by 3D printing, which has been reported to be 60 μm by 108 μm or 200 μm (29, 30), while avoiding the bonding issues associated with multiple PDMS layers (31). 
 
 Supplementary Materials www.sciencemag.org/content/357/6356/1138/suppl/DC1 Materials and Methods Figs. S1 to S10 Table S1 Movies S1 to S4 Reference (32) 
 
 This is an open-access article distributed under the terms of the Creative Commons Attribution license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ||||| KidStock/Getty 
 
 It might be small, but it packs a mighty punch. By cramming vaccines into microscopic containers that release their loads after a preset amount of time, we may have found a way to deliver a vaccine and a booster shot all in one injection. 
 
 Kevin McHugh at the Massachusetts Institute of Technology and his colleagues have come up with a way of making drug-carrying particles that allow multiple doses of a vaccine to be delivered over weeks or even months. 
 
 Until now, this has been out of reach. “Vaccines are notoriously unstable,” says McHugh, and they often don’t last long at body temperature. 
 
 To make the microparticles, McHugh filled silicon cube moulds with a polymer that’s already used in implants and other medical devices. These cubes – which measure just a few hundred micrometres on each side – are then filled with tiny amounts of vaccine before a lid is fitted and the whole thing is heated slightly to seal it. 
 
 The polymer breaks down when in contact with water, but you can extend the time it takes to degrade by altering the structure of the particles in the polymer. 
 
 Shrink to fit 
 
 McHugh and his team gave five mice a single injection of a mix of microparticles designed to release their contents at different times. Each was filled with a protein that stimulates a similar kind of immune response as vaccines. In tests, they found that the protein was released within the mice 9, 20 and 41 days after the injection, just as the team planned. 
 
 “This is a novel method for making microparticles,” says Moein Moghimi at Durham University, UK. It could make it possible to deliver a vaccine and a booster in one go – which would be particularly useful for delivering vaccines in the developing world, where it can be hard to make sure that people get the boosters required to give lasting protection. They’re already working on versions of the particles that can last for 100 or 200 days before releasing their contents. 
 
 But Moghimi says that, in their current form, these microparticles are still too big to inject in the same way that we normally inject vaccines – deep into the muscle. At the moment they can only be injected just below the skin. McHugh is already working working to halve the size of the particles so they can be injected into muscle. 
 
 The technology could eventually be used to create “omni-vaccines” that protect against a whole host of diseases in one shot, says Kevin McHugh. 
 
 Journal reference: Science, DOI: 10.1126/science.aaf7447 
 
 Read more: Lyme disease is set to explode and we still don’t have a vaccine; Refusing boys HPV vaccine saves the NHS cash but is bad science ||||| A new technique allowing drugs or vaccines to be encapsulated within tiny biodegradable particles could see an end booster jabs 
 
 New technology could allow multiple vaccines to be delivered in single jab 
 
 Multiple injections for vaccinations could become a thing of the past, according to scientists who have developed an approach for delivering many doses of different substances in just one jab. 
 
 The technology involves encapsulating drugs or vaccines within tiny particles made of biodegradable polymers. Depending on their makeup, these polymers break down at different points in time, releasing their contents into the body. 
 
 Researchers say the approach could allow multiple vaccines to be delivered at once and remove the need for booster jabs. It may also prove handy in treatments for allergies, diabetes and even cancer where multiple injections are needed. 
 
 Dissolvable patch offers radical pain-free alternative to flu injection, study finds Read more 
 
 Researchers say it could prove valuable in developing countries, potentially allowing all childhood vaccines and their boosters to be given in one shot. 
 
 “One of the main limitations there is access to vaccines and the fact that you have to come back several times in order to get immunity from the pathogen,” said Ana Jaklenec, co-author of the research from the Massachusetts Institute of Technology. “A child or a baby is usually seen once, sometime around the birth time by some sort of healthcare worker.” 
 
 Writing in the journal Science, Jaklenec and colleagues describe how they developed the novel technique using biodegradable polymers already approved for use in humans. 
 
 The process, they reveal, involves making tiny silicone moulds – rather like ice cube trays – into which the biodegradable polymers are pressed and removed to form an array of box-like structures, each about 400 micrometres across. These are then filled with the required drug or vaccine and allowed to dry. 
 
 A lid, made from the same polymer, is then lined up on top of each micro-box and the system is briefly heated to seal it and prevent the drug or vaccine from leaking out. 
 
 When injected into the body, the boxes remain sealed until the polymer disintegrates – an event which occurs rapidly, with the timing dependant on the makeup of the polymer itself. 
 
 “What’s novel here is that the sharpness of how quickly the drug releases from the particle and the fact there is no leakage at all from the particle until [then],” said Jaklenec. 
 
 To test the approach, the team injected mice with microparticles made from one of three different polymers, each filled with a fluorescent substance. Using imaging techniques, the fluorescent substance was seen to be released at about nine days, 20 days or 41 days, depending on the polymer used. 
 
 The team also produced microparticles filled with a polio vaccine and exposed them to an antibody test to see if the vaccine’s potency was affected by the heat sealing: no such problem was detected. 
 
 Finally, mice were injected with two sets of microparticles made from different polymers – one designed to break down after about one week and the other after about five weeks – with both containing a protein found in egg white. The animals’ immune response was tracked for 16 weeks. 
 
 
 
 The results reveal that the filled microparticles triggered a response greater than two regular injections of the same dose of protein spaced four weeks apart. Indeed, the response was on a par with that from two regular injections each with twice the dose – probably down to the microparticles themselves boosting the immune response. 
 
 Einstein-inspired Isobar vaccine cooling system wins UK James Dyson award Read more 
 
 The team say the approach could have myriad applications in medicine and beyond. “ You could use pH sensitive materials [or] you can fill with any type of drug, or therapeutic or sensing drug, so we think it has a lot more application than just vaccines,” said Jaklenec. 
 
 But, she added, challenges remain, not least that vaccines are normally stored in refrigerators: “[We] have to stabilise all of these vaccines in the body for a long period of time at elevated temperature,” she said. 
 
 
 
 Andrew Pollard, professor of paediatric infection and immunity at the University of Oxford, was optimistic, although he noted it was early days. 
 
 “Technologies which allow slow or timed release of a dose and thus reduce the ‘needle burden’ of an immunisation programme without compromising protection would be welcomed by healthcare workers, parents and their offspring,” he said. 
 
 
 
 David Goldblatt, professor of vaccinology and immunology at University College London, said the approach was sophisticated. 
 
 
 
 But, he warned, hurdles remain, noting that it removed the chance to modify vaccines between doses and that there was no way to adjust the timing of vaccine release after injection. “We prefer to avoid immunising when you might have an active viral infection,” he said. “[What happens] if a child has malaria on the day that the [vaccine dose] is released automatically?” 
 
 Nevertheless, he said, the approach could prove revolutionary in helping children in developing countries to receive adequate vaccination. “It could be a game changer for that,” he said. 
 
 ||||| MIT engineers have invented a new 3-D fabrication method that can generate a novel type of drug-carrying particle that could allow multiple doses of a drug or vaccine to be delivered over an extended time period with just one injection. 
 
 The new microparticles resemble tiny coffee cups that can be filled with a drug or vaccine and then sealed with a lid. The particles are made of a biocompatible, FDA-approved polymer that can be designed to degrade at specific times, spilling out the contents of the “cup.” 
 
 “We are very excited about this work because, for the first time, we can create a library of tiny, encased vaccine particles, each programmed to release at a precise, predictable time, so that people could potentially receive a single injection that, in effect, would have multiple boosters already built into it. This could have a significant impact on patients everywhere, especially in the developing world where patient compliance is particularly poor,” says Robert Langer, the David H. Koch Institute Professor at MIT. 
 
 Langer and Ana Jaklenec, a research scientist at MIT’s Koch Institute for Integrative Cancer Research, are the senior authors of the paper, which appears online in Science on Sept. 14. The paper’s lead authors are postdoc Kevin McHugh and former postdoc Thanh D. Nguyen, now an assistant professor of mechanical engineering at the University of Connecticut. 
 
 After the lids are deposited onto the cups, the particles are heated slightly to form a tight seal between the lids and cups. (Courtesy of the Langer lab) 
 
 Sealed cups 
 
 Langer’s lab began working on the new drug delivery particles as part of a project funded by the Bill and Melinda Gates Foundation, which was seeking a way to deliver multiple doses of a vaccine over a specified period of time with just one injection. That could allow babies in developing nations, who might not see a doctor very often, to get one injection after birth that would deliver all of the vaccines they would need during the first one or two years of life. 
 
 Langer has previously developed polymer particles with drugs embedded throughout the particle, allowing them to be gradually released over time. However, for this project, the researchers wanted to come up with a way to deliver short bursts of a drug at specific time intervals, to mimic the way a series of vaccines would be given. 
 
 To achieve their goal, they set out to develop a sealable polymer cup made from PLGA, a biocompatible polymer that has already been approved for use in medical devices such as implants, sutures, and prosthetic devices. PLGA can also be designed to degrade at different rates, allowing for the fabrication of multiple particles that release their contents at different times. 
 
 Conventional 3-D printing techniques proved unsuitable for the material and size that the researchers wanted, so they had to invent a new way to fabricate the cups, drawing inspiration from computer chip manufacturing. 
 
 Using photolithography, they created silicon molds for the cups and the lids. Large arrays of about 2,000 molds are fit onto a glass slide, and these molds are used to shape the PLGA cups (cubes with edge lengths of a few hundred microns) and lids. Once the array of polymer cups has been formed, the researchers employed a custom-built, automated dispensing system to fill each cup with a drug or vaccine. After the cups are filled, the lids are aligned and lowered onto each cup, and the system is heated slightly until the cup and lid fuse together, sealing the drug inside. 
 
 “Each layer is first fabricated on its own, and then they’re assembled together,” Jaklenec says. “Part of the novelty is really in how we align and seal the layers. In doing so we developed a new method that can make structures which current 3-D printing methods cannot. This new method called SEAL (StampEd Assembly of polymer Layers) can be used with any thermoplastic material and allows for fabrication of microstructures with complex geometries that could have broad applications, including injectable pulsatile drug delivery, pH sensors, and 3-D microfluidic devices.” 
 
 Leon Bellan, an assistant professor of mechanical engineering and biomedical engineering at Vanderbilt University, says the approach offers an impressive level of control for constructing 3-D microparticles. 
 
 “It’s a new take on a 3-D printing process, and an elegant solution to building macroscopic 3-D structures out of materials that are relevant for biomedical applications,” says Bellan, who was not involved in the research. 
 
 An automated dispensing system can be used to load drugs into the 3-D microparticles. (Courtesy of the Langer lab) 
 
 Long-term delivery 
 
 The molecular weight of the PLGA polymer and the structure of the polymer molecules’ “backbone” determine how fast the particles will degrade after injection. The degradation rate determines when the drug will be released. By injecting many particles that degrade at different rates, the researchers can generate a strong burst of drug or vaccine at predetermined time points. “In the developing world, that might be the difference between not getting vaccinated and receiving all of your vaccines in one shot,” McHugh says. 
 
 In mice, the researchers showed that particles release in sharp bursts, without prior leakage, at 9, 20, and 41 days after injection. They then tested particles filled with ovalbumin, a protein found in egg whites that is commonly used to experimentally stimulate an immune response. Using a combination of particles that released ovalbumin at 9 and 41 days after injection, they found that a single injection of these particles was able to induce a strong immune response that was comparable to that provoked by two conventional injections with double the dose. 
 
 The researchers have also designed particles that can degrade and release hundreds of days after injection. One challenge to developing long-term vaccines based on such particles, the researchers say, is making sure that the encapsulated drug or vaccine remains stable at body temperature for a long period before being released. They are now testing these delivery particles with a variety of drugs, including existing vaccines, such as inactivated polio vaccine, and new vaccines still in development. They are also working on strategies to stabilize the vaccines. 
 
 “The SEAL technique could provide a new platform that can create nearly any tiny, fillable object with nearly any material, which could provide unprecedented opportunities in manufacturing in medicine and other areas,” Langer says. These particles could also be useful for delivering drugs that have to be given on a regular basis, such as allergy shots, to minimize the number of injections. 
 
 Other authors on the paper are Allison Linehan, David Yang, Adam Behrens, Sviatlana Rose, Zachary Tochka, Stephanie Tzeng, James Norman, Aaron Anselmo, Xian Xu, Stephanie Tomasic, Matthew Taylor, Jennifer Lu, and Rohiverth Guarecuco.
– Potential good news for kids—and the parents who hate to watch them squirm when faced with a needle. Researchers at the Massachusetts Institute of Technology have developed a technology that could allow childhood vaccines—for everything from polio to measles, mumps, and rubella—to be combined into a single injection, reports the BBC. The idea is that one shot would inject microscopic capsules of vaccine into a person, and those capsules would be designed to break down and release their contents at different times, per the Science study. A simpler application would be to deliver one vaccine and its necessary booster shots at one time. In tests on mice, researchers were able to time the release of the booster doses to exactly nine, 20, and 41 days after the initial shot. The concept has not been tested in humans yet. "For the first time, we can create a library of tiny, encased vaccine particles, each programmed to release at a precise, predictable time, so that people could potentially receive a single injection that, in effect, would have multiple boosters already built into it," MIT's Robert Langer says in a release. In the developing world especially, this "might be the difference between not getting vaccinated and receiving all of your vaccines in one shot," adds study author Kevin McHugh, whose research was funded by the Bill and Melinda Gates Foundation. Much work remains: For one thing, scientists would need to figure out how to keep the doses, normally refrigerated, stable in a warm body, per the Guardian. They also are trying to further shrink the capsules so they can be injected directly into muscle, per New Scientist. (A vaccine for the common cold is in the works.)