Micromolding-Assisted Production of SERS-Active Microcylinders for Size- and Charge-Selective Molecular Detection

Surface-enhanced Raman scattering (SERS) is an effective technique for amplifying the Raman signal of molecules by using metal nanostructures. However, these metal surfaces are susceptible to contamination by undesirable adhesives in complex mixtures, typically necessitating a time-consuming and costly sample pretreatment. In order to circumvent this, metal nanoparticles have been uniformly embedded within microgels by using microfluidics. In this work, we introduce a simple, scalable micromolding method for creating SERS-active cylindrical microgels designed to eliminate the need for pretreatment. These microcylinders are created through the simultaneous photoreduction and photo-cross-linking of precursor solutions. These solutions are optimized for consistent, high-intensity Raman signals as well as molecular size and charge selectivity. A sequential micromolding method is employed to design dual-compartment microcylinders, offering additional functionalities such as optical encoding, magnetoresponsiveness, and dual-charge selectivity. These SERS-active microcylinders provide robust Raman signals of small molecules, even in the presence of adhesive proteins, without compromising sensitivity. To demonstrate this capability, we directly detect pyocyanin in saliva and tartrazine in whole milk without any need for sample pretreatment.

Rapid Micromolding of Sub-100 µm Microfluidic Channels Using an 8K Stereolithographic Resin 3D Printer

Engineering microfluidic devices relies on the ability to manufacture sub-100 micrometer fluidic channels. Conventional lithographic methods provide high resolution but require costly exposure tools and outsourcing of masks, which extends the turnaround time to several days. The desire to accelerate design/test cycles has motivated the rapid prototyping of microfluidic channels; however, many of these methods (e.g., laser cutters, craft cutters, fused deposition modeling) have feature sizes of several hundred microns or more. In this paper, we describe a 1-day process for fabricating sub-100 µm channels, leveraging a low-cost (USD 600) 8K digital light projection (DLP) 3D resin printer. The soft lithography process includes mold printing, post-treatment, and casting polydimethylsiloxane (PDMS) elastomer. The process can produce microchannels with 44 µm lateral resolution and 25 µm height, posts as small as 400 µm, aspect ratio up to 7, structures with varying z-height, integrated reservoirs for fluidic connections, and a built-in tray for casting. We discuss strategies to obtain reliable structures, prevent mold warpage, facilitate curing and removal of PDMS during molding, and recycle the solvents used in the process. To our knowledge, this is the first low-cost 3D printer that prints extruded structures that can mold sub-100 µm channels, providing a balance between resolution, turnaround time, and cost (~USD 5 for a 2 × 5 × 0.5 cm3 chip) that will be attractive for many microfluidics labs.

Effect of Collagen and GelMA on Preservation of the Costal Chondrocytes' Phenotype in a Scaffold in vivo

The aim of the study was to compare type I collagen-based and methacryloyl gelatin-based (GelMA) hydrogels by their ability to form hyaline cartilage in animals after subcutaneous implantation of scaffolds.

Materials and Methods

Chondrocytes were isolated from the costal cartilage of newborn rats using 0.15% collagenase solution in DMEM. The cells was characterized by glycosaminoglycan staining with alcian blue. Chondrocyte scaffolds were obtained from 4% type I porcine atelocollagen and 10% GelMA by micromolding and then implanted subcutaneously into the withers of two groups of Wistar rats. Histological and immunohistochemical studies were performed on days 12 and 26 after implantation. Tissue samples were stained with hematoxylin and eosin, alcian blue; type I and type II collagens were identified by the corresponding antibodies.

Results

The implanted scaffolds induced a moderate inflammatory response in both groups when implanted in animals. By day 26 after implantation, both collagen and GelMA had almost completely resorbed. Cartilage tissue formation was observed in both animal groups. The newly formed tissue was stained intensively with alcian blue, and the cells were positive for both types of collagen. Cartilage tissue was formed among muscle fibers.

Conclusion

The ability of collagen type I and GelMA hydrogels to form hyaline cartilage in animals after subcutaneous implantation of scaffolds was studied. Both collagen and GelMA contributed to formation of hyaline-like cartilage tissue type in animals, but the chondrocyte phenotype is characterized as mixed. Additional detailed studies of possible mechanisms of chondrogenesis under the influence of each of the hydrogels are needed.

Dissolvable Carboxymethylcellulose Microneedles for Noninvasive and Rapid Administration of Diclofenac Sodium

The aim of this study is to prepare dissolvable biopolymeric microneedle (MN) patches composed solely of sodium carboxymethylcellulose (CMC), a water-soluble cellulose derivative with good film-forming ability, by micromolding technology for the transdermal delivery of diclofenac sodium salt (DCF). The MNs with ≈456 µm in height displayed adequate morphology, thermal stability up to 200 °C, and the required mechanical strength for skin insertion (>0.15 N needle^-1 ). Experiments in ex vivo abdominal human skin demonstrate the insertion capability of the CMC_DCF MNs up to 401 µm in depth. The dissolution of the patches in saline buffer results in a maximum cumulative release of 98% of diclofenac after 40 min, and insertion in a skin simulant reveals that all MNs completely dissolve within 10 min. Moreover, the MN patches are noncytotoxic toward human keratinocytes. These results suggest that the MN patches produced with CMC are promising biopolymeric systems for the rapid administration of DCF in a minimally invasive manner.

Robust and Reliable Fabrication of Gelatin Films Containing Micropatterned Opal Structures via Evaporative Deposition and Thermal Gelation

Biopolymeric hydrogel materials containing tunable optical properties such as micropatterned artificial opal structures hold significant potential in various applications. Despite recent advances in fabrication techniques, simple, reliable, and tunable production of stimuli-responsive micropatterned opal hydrogels under mild conditions remains challenging. We report a simple micromolding-based evaporative deposition-thermal gelation technique for gelatin films that capture uniform opal micropatterns, aided by a potent aminopolysaccharide chitosan (CS) that provides binding affinity and structural stability. Our results show reliable, tunable, and high-fidelity fabrication of gelatin hydrogel films containing CS-opal micropatterns, while the as-prepared films show responsiveness to pH, ionic strength, and water content indicating a robust nature. Uniform CS-opal microparticles can also be readily prepared via removal of the gelatin through various simple routes, illustrating the crucial roles of CS and gelatin. We envision that this robust, reliable, and simple evaporative deposition-thermal gelation technique can be readily extended to prepare responsive biopolymeric materials for various applications.

Early Braking of Overwarmed Lithium-Ion Batteries by Shape-Memorized Current Collectors

In the context of the constant impending energy crisis, the lithium-ion battery as a burgeoning energy storage means is showing extraordinary talents in many energy relevant investigations. However, fire and explosion would probably occur when the battery is encountered with overheating, at which the shrinking of the separator routinely causes an internal short circuit. Herein, we develop a kind of novel shape-memorized current collector (SMCC), which can successfully brake battery thermal runaway at the battery internal overheating status. Unlike traditional current collectors made of commercial copper foils, SMCC is made of a micropatterned shape memory micron-sized film with copper deposition. SMCC displays ideal conductivity at normal temperatures and turns to be insulative at overheating temperatures. Following this principle, the battery consisting of an SMCC can run normally at temperatures lower than 90 °C, while it quickly achieves self-shutdown before the occurrence of battery combustion and explosion.

Low Cost, Ease-of-Access Fabrication of Microfluidic Devices Using Wet Paper Molds

Rapid prototyping methods enable the widespread adoption of microfluidic technologies by empowering end-users from non-engineering disciplines to make devices using processes that are rapid, simple and inexpensive. In this work, we developed a liquid molding technique to create silicone/PDMS microfluidic devices by replica molding. To construct a liquid mold, we use inexpensive adhesive-backed paper, an acetate backing sheet, and an off-the-shelf digital cutter to create paper molds, which we then wet with predetermined amounts of water. Due to the immiscibility of water and PDMS, mold patterns can be effectively transferred onto PDMS similarly to solid molds. We demonstrate the feasibility of these wet paper molds for the fabrication of PDMS microfluidic devices and assess the influence of various process parameters on device yield and quality. This method possesses some distinct benefits compared to conventional techniques such as photolithography and 3D printing. First, we demonstrate that the shape of a channel's cross-section may be altered from rectangular to semicircular by merely modifying the wetting parameters. Second, we illustrate how electrical impedance can be utilized as a marker for inspecting mold quality and identifying defects in a non-invasive manner without using visual tools such as microscopes or cameras. As a proof-of-concept device, we created a microfluidic T-junction droplet generator to produce water droplets in mineral oil ranging in size from 1.2 µL to 75 µL. We feel that this technology is an excellent addition to the microfluidic rapid prototyping toolbox and will find several applications in biological research.

Robust, Long-Term, and Exceptionally Sensitive Microneedle-Based Bioimpedance Sensor for Precision Farming

Precision farming has the potential to increase global food production capacity whilst minimizing traditional inputs. However, the adoption and impact of precision farming are contingent on the availability of sensors that can discern the state of crops, while not interfering with their growth. Electrical impedance spectroscopy offers an avenue for nondestructive monitoring of crops. To that end, it is reported on the deployment of impedimetric sensors utilizing microneedles (MNs) that can be used to pierce the waxy exterior of plants to obtain sensitive impedance spectra in open-air settings with an average relative noise value of 3.83%. The sensors are fabricated using a novel micromolding and release method that is compatible with UV photocurable and thermosetting polymers. Assessments of the quality of the MNs under scanning electron microscopy show that the replication process is high in fidelity to the original design of the master mold and that it can be used for upward of 20 replication cycles. The sensor's performance is validated against conventional planar sensors for obtaining the impedance values of Arabidopsis thaliana. As a change is detected in impedance due to lighting and hydration, this raises the possibility for their widespread use in precision farming.

Melt Electrospinning Writing of Magnetic Microrobots

The magnetic microrobots actuated by an external magnetic field can access distant, enclosed, and small spaces under fuel-free conditions, which is apromising technology for manipulation and delivery under microenvironment; however, the complicated fabrication method limits their applications. Herein, three techniques including melt electrospinning writing (MEW), micromolding, and skiving process are combined to successfully mass-produce tadpole-like magnetic polycaprolactone/Fe3O4 (PCL/Fe3O4) microrobot. Importantly, the tadpole-like microrobots under an external magnetic field can achieve two locomotions: rolling mode and propulsion mode. The rolling motion can approach the working destination quickly with a speed of ≈2 mm s-1. The propulsion motion (0-340 µm s-1) can handle a microcargo. Such a simple and cost-effective production method shows a great potential for scale-up fabrication of advanced shape-design, mass-production, and multifunctionality microrobot.

Characterization of Gelatin Hydrogels Cross-Linked with Microbial Transglutaminase as Engineered Skeletal Muscle Substrates

Engineered in vitro models of skeletal muscle are essential for efficiently screening drug safety and efficacy. However, conventional culture substrates poorly replicate physical features of native muscle and do not support long-term culture, which limits tissue maturity. Micromolded gelatin hydrogels cross-linked with microbial transglutaminase (gelatin-MTG hydrogels) have previously been shown to induce C21C2 myotube alignment and improve culture longevity. However, several properties of gelatin-MTG hydrogels have not been systematically characterized, such as changes in elastic modulus during incubation in culture-like conditions and their ability to support sarcomere maturation. In this study, various gelatin-MTG hydrogels were fabricated and incubated in ambient or culture-like conditions. Elastic modulus, mass, and transmittance were measured over a one- or two-week period. Compared to hydrogels in phosphate buffered saline (PBS) or ambient air, hydrogels in Dulbecco’s Modified Eagle Medium (DMEM) and 5% CO₂ demonstrated the most stable elastic modulus. A subset of gelatin-MTG hydrogels was micromolded and seeded with C2C12 or primary chick myoblasts, which aligned and fused into multinucleated myotubes with relatively mature sarcomeres. These data are important for fabricating gelatin-MTG hydrogels with predictable and stable mechanical properties and highlight their advantages as culture substrates for engineering relatively mature and stable muscle tissues.

A New Edible Film to Produce In Vitro Meat

In vitro meat is a novel concept of food science and biotechnology. Methods to produce in vitro meat employ muscle cells cultivated on a scaffold in a serum-free medium using a bioreactor. The microstructure of the scaffold is a key factor, because muscle cells must be oriented to generate parallel alignments of fibers. This work aimed to develop a new scaffold (microstructured film) to grow muscle fibers. The microstructured edible films were made using micromolding technology. A micromold was tailor-made using a laser cutting machine to obtain parallel fibers with a diameter in the range of 70-90 µm. Edible films were made by means of solvent casting using non-mammalian biopolymers. Myoblasts were cultured on flat and microstructured films at three cell densities. Cells on the microstructured films grew with a muscle fiber morphology, but in the case of using the flat film, they only produced unorganized cell proliferation. Myogenic markers were assessed using quantitative polymerase chain reaction. After 14 days, the expression of desmin, myogenin, and myosin heavy chain were significantly higher in microstructured films compared to the flat films. The formation of fiber morphology and the high expression of myogenic markers indicated that a microstructured edible film can be used for the production of in vitro meat.

Fabrication of Gelatin Methacrylate (GelMA) Scaffolds with Nano- and Micro-Topographical and Morphological Features

The design of biomimetic biomaterials for cell culture has become a great tool to study and understand cell behavior, tissue degradation, and lesion. Topographical and morphological features play an important role in modulating cell behavior. In this study, a dual methodology was evaluated to generate novel gelatin methacrylate (GelMA)-based scaffolds with nano and micro topographical and morphological features. First, electrospinning parameters and crosslinking processes were optimized to obtain electrospun nanofibrous scaffolds. GelMA mats were characterized by SEM, FTIR, DSC, TGA, contact angle, and water uptake. Various nanofibrous GelMA mats with defect-free fibers and stability in aqueous media were obtained. Then, micropatterned molds produced by photolithography were used as collectors in the electrospinning process. Thus, biocompatible GelMA nanofibrous scaffolds with micro-patterns that mimic extracellular matrix were obtained successfully by combining two micro/nanofabrication techniques, electrospinning, and micromolding. Taking into account the cell viability results, the methodology used in this study could be considered a valuable tool to develop patterned GelMA based nanofibrous scaffolds for cell culture and tissue engineering.

Fabrication of alignment polycaprolactone scaffolds by combining use of electrospinning and micromolding for regulating Schwann cells behavior

In the present study, a new approach for fabricating micropatterned polycaprolactone (PCL) scaffolds with ridge/groove structure on the surface was developed by combining use of electrospinning and micromolding method. A series of physicochemical properties, including morphology, wettability, component, crystal pattern and mechanical properties, of prepared PCL scaffolds were characterization, respectively. Stability of the micropatterned PCL scaffolds was measured using phosphate buffer solution immersion for a certain period. Then, the regulating effects of the micropatterned PCL scaffolds on attachment, orientation and normal biological function of Schwann cells were evaluated. And the protein adsorption behavior in various PCL scaffolds was also detected. The results showed that the micropatterned PCL scaffolds demonstrated a porous micro/nano complex structure with enhanced hydrophobicity and mechanical properties as a function of electrospun flow-rate of PCL solution. The micropatterned PCL scaffolds possessed good stability and could effectively regulate the attachment and orientation of Schwann cells at the early stage after cell culture. Importantly, the electrospun flow-rate of PCL solution was found to play an important role in scaffold properties, cell behavior and protein adsorption. The micropatterned scaffolds with a flow-rate of PCL solution at 0.12 mL h^-1 demonstrated the better regulation on Schwann cells attachment and alignment without negatively affect the normal biological function of the cells. To the best of our knowledge, this is the first report of combining use of electrospinning and micromolding method for preparing artificial nerve implants. The study is anticipated to have potential application in peripheral nerve and other tissue engineering. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 3123-3134, 2018.

Microneedles containing cross-linked hyaluronic acid particulates for control of degradation and swelling behaviour after administration into skin

Microneedles (MN) containing cross-linked hyaluronic acid (X-linked HA) particulates were prepared to control the degradation and swelling behaviour after transdermal drug delivery. The X-linked HA particulates were prepared by cross-linking HA chains and then passing the particulates through a sieve. Then, microneedles were prepared by micromolding method. The rheological properties of X-linked HA were studied. The penetration success rate, mechanical failure and dissolution rate of microneedles containing only hyaluronic acid (HA MN) and microneedles containing X-linked HA were compared. The delivery of fluorescein into the skin with X-linked HA MN was also observed using a confocal microscope. The size of the pulverised particulates in water ranged between 29 and 82 μm in diameter. The HA MN and X-linked HA MN were 270 μm in length. X-linked HA MN with fluorescein was inserted to a depth of 90% of the microneedle length successfully. There was no decrease in the penetration success rate for MN with up to 20% content of X-linked HA particulates. X-linked HA MN with up to 20% of particulate content did not change the dissolution time. Delay in degradation of HA, sustained drug release, and swelling behaviour of the skin layer can be obtained by X-linked HA MN.

Solvent-Assisted Micromolding of Biohybrid Hydrogels to Maintain Human Hematopoietic Stem and Progenitor Cells Ex Vivo

Array-format cell-culture carriers providing tunable matrix cues are instrumental in current cell biology and bioengineering. A new solvent-assisted demolding approach for the fabrication of microcavity arrays with very small feature sizes down to single-cell level (3 µm) of very soft biohybrid glycosaminoglycan-poly(ethylene glycol) hydrogels (down to a shear modulus of 1 kPa) is reported. It is further shown that independent additional options of localized conjugation of adhesion ligand peptides, presentation of growth factors through complexation to gel-based glycosaminoglycans, and secondary gel deposition for 3D cell embedding enable a versatile customization of the hydrogel microcavity arrays for cell culture studies. As a proof of concept, cell-instructive hydrogel compartment arrays are used to analyze the response of human hematopoietic stem and progenitor cells to defined biomolecular and spatial cues.

Bistable Solid-State Fluorescence Switching in Photoluminescent, Infinite Coordination Polymers

Photo-functional infinite coordinated polymers (ICPs) were synthesized that consist of the photochromic dithienylethene (DTE) and a luminescent bridging unit to give enhanced fluorescence in the solid state. We could fabricate well-ordered micropatterns of these ICPs by a soft-lithographic method, which repeatedly showed high contrast on-off fluorescence switching.

Fabrication of a Microlens Array with Controlled Curvature by Thermally Curving Photosensitive Gel Film beneath Microholes

A rapid method is developed for fabricating low-cost and high-numerical-aperture photosensitive-gel microlens arrays (MLAs) with well-controlled curvatures. An UV-curable photosensitive-gel film beneath the microholes of a silicon mold can be flexibly deformed by thermally manipulating the surface tension of the photosensitive gel and the pressure difference across the air-photosensitive-gel interface. The concave interface is then solidified through UV curing, forming a MLA with a concave curvature. MLAs with a focal length ranging from 51.4 to 71.9 μm and a numerical aperture (NA) of 0.49 were fabricated. The photocured MLA has high mechanical and thermal strength and is suitable as a master mold for the further production of convex MLAs. The fabricated microlenses have uniform shapes and smooth surfaces. In a demonstration of imaging and focusing performance, clear and uniform images and focused light spots were observed using concave and convex MLAs.

Three-Dimensional Soft Material Micropatterning via Direct Laser Lithography of Flexible Molds

Three-dimensionally micropatterned surfaces are attracting increasing interest in soft robotics owing to the potential of mimicking natural morphologies at the micro/nanoscale. We employ direct laser lithography to fabricate molds with complex three-dimensional (3D) micrometric features, in a positive photoresist on flexible substrates, to pattern curved macroscopic soft surfaces with shapes not achievable with standard methods (e.g., reentrant angles). We present several 3D intricate microstructures in poly(dimethylsiloxane) (PDMS) and show a soft cylinder patterned with 3D microstructures with one molding process. Finally, we deform PDMS-based 3D architectures and show soft microgripping capability, indicating the potentiality of this approach for future application in soft robotics.

Control of Reversible Self-Bending Behavior in Responsive Janus Microstrips

Here, we demonstrate a simple method to systematically control the responsive self-bending behavior of Janus hydrogel microstrips consisting of a polymeric bilayer with a high modulus contrast. The Janus hydrogel microstrips could be easily fabricated by a simple micromolding technique combined with an initiated chemical vapor deposition (iCVD) coating, providing high flexibility in controlling the physical and chemical properties of the microstrips. The fabricated Janus hydrogel microstrip is composed of a soft, pH-responsive polymer hydrogel layer laminated with a highly cross-linked, rigid thin film, generating a geometric anisotropy at a micron scale. The large difference in the elastic moduli between the two layers of the Janus microstrips leads to a self-bending behavior in response to the pH change. More specifically, the impact of the physical and chemical properties of the microstrip on the self-bending phenomena was systematically investigated by changing the thickness and composition of two layers of the microstrip, which renders high controllability in bending of the microstrips. The curvature of the Janus microstrips, formed by self-bending, highly depends on the applied acidity. A reversible, responsive self-bending/unbending exhibits a perfect resilience pattern with repeated changes in pH for 5 cycles. We envision that the Janus microstrips can be engineered to form complex 3D microstructures applicable to various fields such as soft robotics, scaffolds, and drug delivery. The reliable responsive behaviors obtained from the systematic investigation will provide critical information in bridging the gap between the theoretical mechanical analysis and the chemical properties to achieve micron-scale soft robotics.

Insertion Process of Ceramic Nanoporous Microneedles by Means of a Novel Mechanical Applicator Design

Arrays of microneedles (MNAs) are integrated in an out-of-plane fashion with a base plate and can serve as patches for the release of drugs and vaccines. We used soft-lithography and micromolding to manufacture ceramic nanoporous (np)MNAs. Failure modes of ceramic npMNAs are as yet poorly understood and the question remained: is our npMNA platform technology ready for microneedle (MN) assembly into patches? We investigated npMNAs by microindentation, yielding average crack fracture forces above the required insertion force for a single MN to penetrate human skin. We further developed a thumb pressure-actuated applicator-assisted npMNA insertion method, which enables anchoring of MNs in the skin by an adhesive in one handling step. Using a set of simple artificial skin models, we found a puncture efficiency of this insertion method a factor three times higher than by applying thumb pressure on the npMNA base plate directly. In addition, this new method facilitated zero MN-breakage due to a well-defined force distribution exerted onto the MNs and the closely surrounding area prior to bringing the adhesive into contact with the skin. Owing to the fact that such parameter space exists, we can conclude that npMNAs by soft lithography are a platform technology for MN assembly into a patch.

Microneedles from Fishscale-Nanocellulose Blends Using Low Temperature Mechanical Press Method

Fish scale biopolymer blended with nanocellulose crystals is used for production of microneedles applying mechanical press microfabrication and the effect of nanocellulose on microfabrication, water absorption, moisture stability and mechanical properties of the microneedles is reported. The results show that microneedles produced from the nanocellulose loaded fish scale biopolymer requires higher temperature for micromolding (80 ± 5 °C) than microneedles from only fish scale biopolymer, which were moldable at 50 ± 5 °C. The mechanical properties of the fish scale biopolymer-nanocellulose (FSBP-NC) films showed that the addition of nanocellulose (NC) resulted in lower elongation and higher tensile stress compared to fish scale biopolymer (FSBP) films. The nanocellulose also prevented dissolution of the needles and absorbed up to 300% and 234% its own weight in water (8% and 12% w/w NC/FSBP), whereas FSBP films dissolved completely within 1 min, Indicating that the FSBP-NC films can be used to produce microneedles with prolonged dissolution rate. FTIR spectrometry of the FSBP films was compared with the FSBP-NC films and the NC gels. The FTIR showed typical peaks for fish scale polymer and nanocellulose with evidence of interactions. SEM micrographs showed relatively good dispersion of NC in FSBP at both NC contents corresponding to 8% and 12% w/w NC/FSBP respectively.

Controlled Fabrication of Microparticles with Complex 3D Geometries by Tunable Interfacial Deformation of Confined Polymeric Fluids in 2D Micromolds

Polymeric microparticles with complex shapes have attracted substantial attention in many application areas because particle shape is a critical parameter to impart programmable functionalities. The formation of specific three-dimensional (3D) microstructures in a simple, scalable, and controllable manner is difficult. Here, we report the controlled fabrication of microparticles with complex 3D shapes based on the simple tuning of mold swelling and capillarity. Specifically, a photocurable solution loaded in micromolds is spatially deformed into complex shapes depending on the degree of molding swelling and capillarity, thereby producing polymeric microparticles with controlled 3D shapes upon photopolymerization. The results show that highly uniform microparticles with controlled two-dimensional (2D) and 3D shapes were fabricated from identical 2D micromolds via the simple tuning of the wetting fluids. This technique can be extended to produce highly complex microarchitectures with controlled 3D geometric domains via 2D mold designs. Finally, multicompartment microparticles with independently controlled 3D shapes for each compartment are produced by a simple combination of fabrication sequences. We envision that this strategy of producing 3D microarchitectures from easily designed simple micromolds could provide a path to new materials and new properties.

Lateral flow through a parallel gap driven by surface hydrophilicity and liquid edge pinning for creating microlens array

This letter proposes a surface-energy driven process for economically creating polymer microlens array (MLA) with well controllable curvatures. When a UV-curable prepolymer flows into a cell constructed by multiple holes on a top template and a flat substrate, since the edge pinning of the contact line, an array of curved air/prepolymer interface forms around each microhole of the template. Then a UV-radiation of the bulk prepolymer leads to a solid microlens array. The curvature of the air/prepolymer interface can be controlled by choosing materials with different interface free energy or varying the gap height mechanically.

Hollow microneedles for intradermal injection fabricated by sacrificial micromolding and selective electrodeposition

Limitations with standard intradermal injections have created a clinical need for an alternative, low-cost injection device. In this study, we designed a hollow metal microneedle for reliable intradermal injection and developed a high-throughput micromolding process to produce metal microneedles with complex geometries. To fabricate the microneedles, we laser-ablated a 70 μm × 70 μm square cavity near the tip of poly(lactic acid) (PLA) microneedles. The master structure was a template for multiple micromolded poly(lactic acid-co-glycolic acid) (PLGA) replicas. Each replica was sputtered with a gold seed layer with minimal gold deposited in the cavity due to masking effects. In this way, nickel was electrodeposited selectively outside of the cavity, after which the polymer replica was dissolved to produce a hollow metal microneedle. Force-displacement tests showed the microneedles, with 12 μm thick electrodeposition, could penetrate skin with an insertion force 9 times less than their axial failure force. We injected fluid with the microneedles into pig skin in vitro and hairless guinea pig skin in vivo. The injections targeted 90 % of the material within the skin with minimal leakage onto the skin surface. We conclude that hollow microneedles made by this simple microfabrication method can achieve targeted intradermal injection.

The Effects of Geometry on Skin Penetration and Failure of Polymer Microneedles

Microneedles are small-scale devices that may be used for drug delivery and biosensing. In this study, the forces required for mechanical failure, the modes of mechanical failure, as well as the mechanisms for microneedle penetration into porcine skin were examined. Microneedles produced from the acrylate-based polymer e-Shell 200 using an indirect rapid prototyping approach involving two-photon polymerization and poly(dimethylsiloxane) micromolding were found to possess sufficient strength for penetration of porcine skin. The failure forces were an order of magnitude greater than the forces necessary for full insertion into the skin. Bending was the most common form of failure; an increasing aspect ratio and a decreasing tip diameter were associated with lower failure forces. Video captured during skin penetration revealed that microneedle penetration into the skin occurred by means of a series of insertions and not by means of a single insertion event. Images obtained during and after skin penetration confirmed microneedle penetration of skin as well as transdermal delivery of lucifer yellow dye. These findings shed insight into the mechanisms of microneedle penetration and failure, facilitating design improvements for polymer microneedles.

Microscale Strategies for Generating Cell-Encapsulating Hydrogels

Hydrogels in which cells are encapsulated are of great potential interest for tissue engineering applications. These gels provide a structure inside which cells can spread and proliferate. Such structures benefit from controlled microarchitectures that can affect the behavior of the enclosed cells. Microfabrication-based techniques are emerging as powerful approaches to generate such cell-encapsulating hydrogel structures. In this paper we introduce common hydrogels and their crosslinking methods and review the latest microscale approaches for generation of cell containing gel particles. We specifically focus on microfluidics-based methods and on techniques such as micromolding and electrospinning.

An electrically active microneedle array for electroporation

We have designed and fabricated a microneedle array with electrical functionality with the final goal of electroporating skin's epidermal cells to increase their transfection by DNA vaccines. The microneedle array was made of polymethylmethacrylate (PMMA) by micromolding technology from a polydimethylsiloxane (PDMS) mold, followed by metal deposition, patterning using laser ablation, and electrodeposition. This microneedle array possessed sufficient mechanical strength to penetrate human skin in vivo and was also able to electroporate both red blood cells and human prostate cancer cells as an in vitro model to demonstrate cell membrane permeabilization. A computational model to predict the effective volume for electroporation with respect to applied voltages was constructed from finite element simulation. This study demonstrates the mechanical and electrical functionalities of the first MEMS-fabricated microneedle array for electroporation, designed for DNA vaccine delivery.