Polydimethylsiloxane Scaffold Research Articles

Plasma-Activated Polydimethylsiloxane Microstructured Pattern with Collagen for Improved Myoblast Cell Guidance.

We focused on polydimethylsiloxane (PDMS) as a substrate for replication, micropatterning, and construction of biologically active surfaces. The novelty of this study is based on the combination of the argon plasma exposure of a micropatterned PDMS scaffold, where the plasma served as a strong tool for subsequent grafting of collagen coatings and their application as cell growth scaffolds, where the standard was significantly exceeded. As part of the scaffold design, templates with a patterned microstructure of different dimensions (50 × 50, 50 × 20, and 30 × 30 μm2) were created by photolithography followed by pattern replication on a PDMS polymer substrate. Subsequently, the prepared microstructured PDMS replicas were coated with a type I collagen layer. The sample preparation was followed by the characterization of material surface properties using various analytical techniques, including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). To evaluate the biocompatibility of the produced samples, we conducted studies on the interactions between selected polymer replicas and micro- and nanostructures and mammalian cells. Specifically, we utilized mouse myoblasts (C2C12), and our results demonstrate that we achieved excellent cell alignment in conjunction with the development of a cytocompatible surface. Consequently, the outcomes of this research contribute to an enhanced comprehension of surface properties and interactions between structured polymers and mammalian cells. The use of periodic microstructures has the potential to advance the creation of novel materials and scaffolds in tissue engineering. These materials exhibit exceptional biocompatibility and possess the capacity to promote cell adhesion and growth.

Enhancing Nasopharyngeal Carcinoma Cell Separation with Selective Fibronectin Coating and Topographical Modification on Polydimethylsiloxane Scaffold Platforms.

The extracellular matrix (ECM) serves as a complex scaffold with diverse physical dimensions and surface properties influencing NPC cell migration. Polydimethylsiloxane (PDMS), a widely used biocompatible material, is hydrophobic and undesirable for cell seeding. Thus, the establishment of a biomimetic model with varied topographies and surface properties is essential for effective NPC43 cell separation from NP460 cells. This study explored how ECM surface properties influence NP460 and NPC43 cell behaviors via plasma treatments and chemical modifications to alter the platform surface. In addition to the conventional oxygen/nitrogen (O2/N2) plasma treatment, O2 and argon plasma treatments were utilized to modify the platform surface, which increased the hydrophilicity of the PDMS platforms, resulting in enhanced cell adhesion. (3-aminopropyl)triethoxysilane and fibronectin (FN) were used to coat the PDMS platforms uniformly and selectively. The chemical coatings significantly affected cell motility and spreading, as cells exhibited faster migration, elongated cell shapes, and larger spreading areas on FN-coated surfaces. Furthermore, narrower top layer trenches with 5 µm width and a lower concentration of 10 µg/mL FN were coated selectively on the platforms to limit NP460 cell movements and enhance NPC43 cell separation efficiency. A significantly high separation efficiency of 99.4% was achieved on the two-layer scaffold platform with 20/5 µm wide ridge/trench (R/T) as the top layer and 40/10 µm wide R/T as the bottom layer, coupling with 10 µg/mL FN selectively coated on the sidewalls of the top and bottom layers. This work demonstrated an innovative application of selective FN coating to direct cell behavior, offering a new perspective to probe into the subtleties of NPC cell separation efficiency. Moreover, this cost-effective and compact microsystem sets a new benchmark for separating cancer cells.

High-dielectric porous CaCu3Ti4O12/reduced graphene oxide/polydimethylsiloxane foam for wearable, breathable and low crosstalk capacitive pressure sensor

High-dielectric porous CaCu3Ti4O12 (CCTO)/reduced graphene oxide (rGO)/polydimethylsiloxane (PDMS) foam is prepared through a simple sacrificial salt-templating method. By introducing CCTO and rGO fillers into the porous PDMS scaffold, a three-dimensional porous CCTO/rGO/PDMS foam with large dielectric constant of 107.8 is obtained. The CCTO/rGO/PDMS foam also has a low Young’s modulus of 0.007 MPa as well as a high water vapor transmission (WVT) rate of 14 mg/cm2·h (0.5 mm thickness). A wearable, breathable and low crosstalk capacitive pressure sensor based on CCTO/rGO/PDMS foam and porous Ag nanowires (NW)/thermoplastic polyurethane (TPU) electrodes has been fabricated. The sensor displays fast response speed (<48 ms), excellent sensitivity (3.5 kPa−1), superior cyclic repeatability and stability (11,000 cycles), as well as high gas permeability (WVT rate of 13 mg/cm2·h). The sensor can be attached to different body positions to monitor diverse physiological activities including breathing, vocal cord vibration and finger touch pressure. Moreover, the pressure sensor array integrated by multiple sensor units with low crosstalk is fabricated to detect spatial pressure distribution.

Biomimetic approach to articular cartilage tissue engineering using carbon nanotube-coated and textured polydimethylsiloxane scaffolds.

There is a significant need to understand the complexity and heterogeneity of articular cartilage to develop more effective therapeutic strategies for diseases such as osteoarthritis. Here, we show that carbon nanotubes (CNTs) are excellent candidates as a material for synthetic scaffolds to support the growth of chondrocytes—the cells that produce and maintain cartilage. Chondrocyte morphology, proliferation, and alignment were investigated as nanoscale CNT networks were applied to macroscopically textured polydimethylsiloxane (PDMS) scaffolds. The application of CNTs to the surface of PDMS‐based scaffolds resulted in an up to 10‐fold increase in cell adherence and 240% increase in proliferation, which is attributable to increased nanoscale roughness and hydrophilicity. The introduction of macroscale features to PDMS induced alignment of chondrocytes, successfully mimicking the cell behavior observed in the superficial layer of cartilage. Raman spectroscopy was used as a noninvasive, label‐free method to monitor extracellular matrix production and chondrocyte phenotype. Chondrocytes on these scaffolds successfully produced collagen, glycosaminoglycan, and aggrecan. This study demonstrates that introducing physical features at different length scales allows for a high level of control over tissue scaffold design and, thus, cell behavior. Ultimately, these textured scaffolds can serve as platforms to improve the understanding of osteoarthritis and for early‐stage therapeutic testing.

Molecular characterization of hematopoietic stem cells after in vitro amplification on biomimetic 3D PDMS cell culture scaffolds

Hematopoietic stem cell (HSC) transplantation is successfully applied since the late 1950s. However, its efficacy can be impaired by insufficient numbers of donor HSCs. A promising strategy to overcome this hurdle is the use of an advanced ex vivo culture system that supports the proliferation and, at the same time, maintains the pluripotency of HSCs. Therefore, we have developed artificial 3D bone marrow-like scaffolds made of polydimethylsiloxane (PDMS) that model the natural HSC niche in vitro. These 3D PDMS scaffolds in combination with an optimized HSC culture medium allow the amplification of high numbers of undifferentiated HSCs. After 14 days in vitro cell culture, we performed transcriptome and proteome analysis. Ingenuity pathway analysis indicated that the 3D PDMS cell culture scaffolds altered PI3K/AKT/mTOR pathways and activated SREBP, HIF1α and FOXO signaling, leading to metabolic adaptations, as judged by ELISA, Western blot and metabolic flux analysis. These molecular signaling pathways can promote the expansion of HSCs and are involved in the maintenance of their pluripotency. Thus, we have shown that the 3D PDMS scaffolds activate key molecular signaling pathways to amplify the numbers of undifferentiated HSCs ex vivo effectively.

Engineering a macroporous oxygen-generating scaffold for enhancing islet cell transplantation within an extrahepatic site

Insufficient oxygenation is a serious issue arising within cell-based implants, as the hypoxic period between implantation and vascularization of the graft is largely unavoidable. In situ oxygen supplementation at the implant site should significantly mitigate hypoxia-induced cell death and dysfunction, as well as improve transplant efficacy, particularly for highly metabolically active cells such as pancreatic islets. One promising approach is the use of an oxygen generating material created through the encapsulation of calcium peroxide within polydimethylsiloxane (PDMS), termed OxySite. In this study, OxySite microbeads were incorporated within a macroporous PDMS scaffold to create a single, streamlined, oxygen generating macroporous scaffold. The resulting OxySite scaffold generated sufficient local oxygenation for up to 20 days, with nontoxic levels of reaction intermediates or by-products. The benefit of local oxygen release on transplant efficacy was investigated in a diabetic Lewis rat syngeneic transplantation model using a clinically relevant islet dosage (10,000 IEQ/kg BW) with different isolation purities (80%, 90%, and 99%). Impure islet preparations containing pancreatic non-islet cells, which are common in the clinical setting, permit examination of the effect of increased overall oxygen demand. Our transplantation outcomes showed that elevating the oxygen demand of the graft with decreasing isolation purity resulted in decreased graft efficacy for control implants, while the integration of OxySite significantly mitigated this impact and resulted in improved graft outcomes. Results highlight the superior clinical translational potential of these off-the-shelf OxySite scaffolds, where islet purity and the overall oxygen demands of implants are increased and highly variable. The oxygen-generating porous scaffold further provides a broad platform for enhancing the survival and efficacy of cellular implants for numerous other applications. Statement of significanceHypoxia is a serious issue within tissue engineered implants. To address this challenge, we developed a distinct macroporous scaffold platform containing oxygen-generating microbeads. This oxygen-generating scaffold showed the potential to support clinically relevant cell dosages for islet transplantation, leading to improved treatment efficacy. This platform can also be used to mitigate hypoxia for other biomedical applications.

Engineering an Macroporous Oxygen-Generating Scaffold for Enhancing Islet Cell Transplantation within an Extrahepatic Site

Insufficient oxygenation is a serious issue arising within cell-based implants, as the hypoxic period between implantation and vascularization of the graft is largely unavoidable. In situ oxygen supplementation at the implant site should significantly mitigate hypoxia-induced cell death and dysfunction, as well as improve the transplant efficacy, particularly for highly metabolically active cells such as pancreatic islets. One promising approach is the use of an oxygen generating material created through the encapsulation of calcium peroxide within polydimethylsiloxane (PDMS), termed OxySite. In this study, OxySite microbeads were incorporated within a macroporous PDMS scaffold to create a single, streamlined, oxygen generating macroporous scaffold. The resulting OxySite scaffold generated sufficient local oxygenation for up to 20 days, with nontoxic levels of reaction intermediates or by-products. The benefit of local oxygen release on transplant efficacy was investigated in a diabetic Lewis rat syngeneic transplantation model containing clinically relevant islet isolation purities (80%, 90%, and 99%). Transplantation outcomes showed that elevating the oxygen demand of the graft with decreasing isolation purity resulted in decreased graft efficacy for control implants, while the integration of OxySite significantly mitigated this impact and resulted in significantly improved graft outcomes. Results highlight the superior clinical translational potential of these off-the-shelf OxySite scaffolds, where islet purity and the overall oxygen demands of implants are increased and highly variable. The oxygen-generating porous scaffold further provides a broad platform for enhancing the survival and efficacy of cellular implants for numerous other applications.

Development of polydimethylsiloxane-based biomimetic scaffolds with cylinder micropillars for retinal pigment epithelial cell cultivation.

Background:Age-related macular degeneration (AMD) is one of the leading causes of vision loss. Once the retinal pigment epithelium (RPE) layers are destroyed, the poor visual acuity and recognition are generally irreversible. Cell therapy that possesses enormous potential in regenerative medicine may provide an alternative treatment for several incurable diseases such as AMD. In this study, we developed an innovative polydimethylsiloxane (PDMS)-based biomimetic scaffolds with cylinder micropillars for the cultivation of induced pluripotent stem cell–derived RPEs (iPSC-RPEs). RPEs were cultured on the PDMS-based biomimetic scaffolds and validated the cells gene expression.Methods:The biomimetic PDMS scaffold was fabricated through spin coating and lithography method. It was further modified on surface with biomolecules to improve cell affinity and stability. The iPSC-RPEs were seeded on the scaffold and analyzed with characteristic gene expression.Results:PDMS biomimetic scaffold was analyzed with Fourier transform infrared spectroscopy and proved its chemical composition. iPSC-RPEs demonstrated confluent cell monolayer on the scaffold and maintained RPE-specific gene expression, which proved the PDMS-based biomimetic scaffold to be supportive for iPSC-RPEs growth.Conclusion:The PDMS interface allowed regular growth of iPSC-RPEs and the design of cylinder micropillars further provided the bioscaffold high motion resistance may improve the engraftment stability of iPSC-RPEs after transplantation. Taken together, this innovative PDMS-based biomimetic scaffold may serve as an ideal interface for in vitro iPSC-RPE cultivation and subsequent transplantation in vivo. This novel device exhibits better bioavailability than conventional injection of donor cells and may be an alternative option for the treatment of AMD.

Development of Thermo-Responsive Polycaprolactone-Polydimethylsiloxane Shrinkable Nanofibre Mesh.

A thermally activated shape memory polymer based on the mixture of polycaprolactone (PCL) and polydimethylsiloxane (PDMS) was fabricated into the nanofibre mesh using the electrospinning process. The added percentages of the PDMS segment in the PCL-based polymer influenced the mechanical properties. Polycaprolactone serves as a switching segment to adjust the melting temperature of the shape memory electro-spun PCL–PDMS scaffolds to our body temperature at around 37 °C. Three electro-spun PCL–PDMS copolymer nanofibre samples, including PCL6–PDMS4, PCL7–PDMS3 and PCL8–PDMS2, were characterised to study the thermal and mechanical properties along with the shape memory responses. The results from the experiment showed that the PCL switching segment ratio determines the crystallinity of the copolymer nanofibres, where a higher PCL ratio results in a higher degree of crystallinity. In contrast, the results showed that the mechanical properties of the copolymer samples decreased with the PCL composition ratio. After five thermomechanical cycles, the fabricated copolymer nanofibres exhibited excellent shape memory properties with 98% shape fixity and above 100% recovery ratio. Moreover, biological experiments were applied to evaluate the biocompatibility of the fabricated PCL–PDMS nanofibre mesh. Owing to the thermally activated shape memory performance, the electro-spun PCL–PDMS fibrous mesh has a high potential for biomedical applications such as medical shrinkable tubing and wire.

Permeability and mechanical properties of gradient porous PDMS scaffolds fabricated by 3D-printed sacrificial templates designed with minimal surfaces

In the present study, polydimethylsiloxane (PDMS) porous scaffolds are designed based on minimal surface architectures and fabricated through a low-cost and accessible sacrificial mold printing approach using a fused deposition modeling (FDM) 3D printer. The effects of pore characteristics on compressive properties and fluid permeability are studied. The results suggest that radially gradient pore distribution (as a potential way to enhance mechanically-efficient scaffolds with enhanced cell/scaffold integration) has higher elastic modulus and fluid permeability compared to their uniform porosity counterparts. Also, the scaffolds are fairly strain-reversible under repeated loading of up to 40% strain. Among different triply periodic minimal surface pore architectures, P-surface was observed to be stiffer, less permeable and have lower densification strain compared to the D-surface and G-surface-based pore shapes. The biocompatibility of the created scaffolds is assessed by filling the PDMS scaffolds using mouse embryonic fibroblasts with cell-laden gelatin methacryloyl which was cross-linked in situ by UV light. Cell viability is found to be over 90% after 4 days in 3D culture. This method allows for effectively fabricating biocompatible porous organ-shaped scaffolds with detailed pore features which can potentially tailor tissue regenerative applications. Statement of SignificancePrinting polymers with chemical curing mechanism required for materials such as PDMS is challenging and impossible to create high-resolution uniformly cured structures due to hard control on the base polymer and curing process. An interconnected porous mold with ordered internal architecture with complex geometries were 3D printed using low-cost and accessible FDM technology. The mold acted as a 3D sacrificial material to form internally architected flexible PDMS scaffolds for tissue engineering applications. The scaffolds are mechanically stable under high strain cyclic loads and provide enough pore and space for viably integrating cells within the gradient architecture in a controllable manner.

Generation and Initial Characterization of 3D Cortical Collecting Ducts (CCDs)‐on‐a‐Chip

Hydrodynamic forces, including fluid shear stress (FSS), circumferential stretch and drag/torque on apical cilia, regulate ion transport in the CCD of the kidney. Studies aimed at examining pathways and regulation of transepithelial transport in this nephron segment are largely limited to experiments in 2D cell culture monolayers, while renal tubular epithelia grown in their native 3D geometry provide a more physiologically relevant environment. Cell doming is a characteristic unique to epithelial cell monolayers and has previously been described by others to reflect cellular differentiation and vectorial transport of salt and water. We describe the doming characteristics of cells grown in a novel in vitro 3D microphysiological model that recapitulates the in vivo geometry of the CCD. 3D CCD‐like tubules were generated using a pin pullout technique to generate a 500 μm hollow lumen through a fibrin/gelatin extracellular matrix (ECM) enclosed within a polydimethylsiloxane scaffold. The lumen was seeded with mpkCCD cells x 24 hr then continuously perfused with cell culture media via a peristaltic pump in a closed loop circuit at a unidirectional FSS of 0.1 dyn/cm2. By 7 d of culture/perfusion, a confluent monolayer of cells lined the channel. Epithelial integrity was demonstrated using widefield microscopy by retention of a continuously perfused 70 kDa FITC‐dextran (25 μM) in the lumen for 5 hr. Confocal microscopy of 50 μm sections of tubules labeled with target‐specific antibodies revealed ENaC, Na‐K‐ATPase and laminin expression. Cell doming was observed after about 30 minutes of stopping flow (no flow) in all tubules. We quantitatively measured doming characteristics by live‐cell differential interference contrast video microscopy in a 1 mm tubule segment at the inlet of each chip after a 1 hr period of no flow, in the absence (control) or presence of 10 μM benzamil (BZ), an inhibitor of ENaC. Interestingly, domes were observed in only 1 of the benzamil treated tubules. Dome dimensions were measured and volume was estimated using the formula for a segment of a sphere. Data are presented as X ± SEM from individual experiments. Significance of differences was tested by unpaired Student t‐test and statistical significance was defined as P values &lt;0.05. The mean dome volume was ~3.1 ± 0.5 nl in 3 tubules in the absence vs. ~0.04 ± 0.01 nl in the 1 tubule that demonstrated doming in the presence of BZ (P=0.01). In summary, we generated and initially characterized a 3D CCD‐on‐achip that promises to provide a relevant model for studying transport physiology and addressing a variety of clinically important questions. The mechanism(s) underlying dome formation remains to be determined.Support or Funding InformationNIH grants T32DK007757 (JLR), R01DK038470 (LMS) and the NIDDK (Re)Building A Kidney Consortium grant U01DK107350 (LMS). Microscopy was performed at the Microscopy CoRE at the Icahn School of Medicine at Mount Sinai.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Conductive Polymer Coated Scaffold to Integrate 3D Cell Culture with Electrochemical Sensing.

Remarkable progresses have been made in electrochemical monitoring of living cells based on one-dimensional (1D) or two-dimensional (2D) sensors, but the cells cultured on 2D substrate under these circumstances are departed from their three-dimensional (3D) microenvironments in vivo. Significant advances have been made in developing 3D culture scaffolds to simulate the 3D microenvironment yet most of them are insulated, which greatly restricts their application in electrochemical sensing. Herein, we propose a versatile strategy to endow 3D insulated culture scaffolds with electrochemical performance while granting their biocompatibility through conductive polymer coating. More specifically, 3D polydimethylsiloxane scaffold is uniformly coated by poly(3,4-ethylenedioxythiophene) and further modified by platinum nanoparticles. The integrated 3D device demonstrates desirable biocompatibility for long-term 3D cell culture and excellent electrocatalytic ability for electrochemical sensing. This allows real-time monitoring of reactive oxygen species release from cancer cells induced by a novel potential anticancer drug and reveals its promising application in cancer treatment. This work provides a new idea to construct 3D multifunctional electrochemical sensors, which will be of great significance for physiological and pathological research.

Culturing melanocytes and fibroblasts within three-dimensional macroporous PDMS scaffolds: towards skin dressing material.

In the present study, we propose a platform for topical wound dressing material using a polydimethylsiloxane (PDMS) scaffold in order to enhance the skin healing process. In vitro co-culture assessment of epidermal-origin mouse B16-F10 melanocyte cells and mouse L929 fibroblast cells in three-dimensional polymeric scaffolds has been carried out towards developing bio-stable, interconnected, highly macroporous, PDMS based tissue-engineered scaffolds, using the salt leaching method. To determine a suitable ratio of salt to PDMS pre-polymer in the scaffold, two different samples with ratios 2:1 and 3:1 [w/w], were fabricated. Effective pore sizes of both scaffolds were observed to lie in the desirable range of 152-165μm. In addition, scaffolds were pre-coated with collagen and investigated as a podium for culturing the chosen cells (fibroblast and melanocyte cells). Experimental results demonstrate not only a high proliferative potential of the skin tissue-specific cells within the fabricated PDMS based scaffolds but also confirm the presence of several other essential attributes such as high interconnectivity, optimum porosity, excellent mechanical strength, gaseous permeability, promising cell compatibility, water absorption capability and desired surface wettability. Therefore, scaffolds facilitate a high degree of cellular adhesion while providing a microenvironment necessary for optimal cellular infiltration and viability. Thus, the outcomes suggest that PDMS based macroporous scaffold can be used as a potential candidate for skin dressing material. In addition, the fabricated PDMS scaffolds may also be exploited for a plethora of other applications in tissue engineering and drug delivery.

Fabrication and Characterization of 3D Graded PDMS Scaffolds Using Vacuum-Assisted Resin Transfer Moulding

Graded porous scaffold can be applied to study the interactions between cells and scaffold with different pore sizes. Polydimethylsiloxane (PDMS) scaffold with an axial pore size grade was successfully manufactured via vacuum-assisted resin transfer moulding (VARTM) and particle leaching technologies. The properties of graded PDMS scaffolds, including porosity, water absorption, interconnectivity, compression modulus, as well as compression strength were investigated. The results showed that the smaller the size of the NaCl particles is, the higher the porosity and water absorption of graded PDMS scaffolds would be. The graded PDMS scaffold fabricated had a compressive modulus and a compressive strength of 19.69±1.42 kPa and 4.76±0.22 kPa, respectively. Moreover, the graded chitosan (CS)-coated PDMS scaffolds were prepared by using dip-coating technique under low vacuum and their hydrophilicity was examined. It is found that the water contact angle (WCA) will decrease with an increase in the CS solution concentration and the coating time, which indicates that CS-coated PDMS scaffolds exhibit noticeable hydrophilicity compared with graded PDMS scaffold.

Development of a Graphene Oxide-Incorporated Polydimethylsiloxane Membrane with Hexagonal Micropillars.

Several efforts have been made on the development of bioscaffolds including the polydimethylsiloxane (PDMS) elastomer for supporting cell growth into stable sheets. However, PDMS has several disadvantages, such as intrinsic surface hydrophobicity and mechanical strength. Herein, we generated a novel PDMS-based biomimetic membrane by sequential modifications of the PMDS elastomer with graphene oxide (GO) and addition of a hexagonal micropillar structure at the bottom of the biomembrane. GO was initially homogenously mixed with pure PDMS and then was further coated onto the upper surface of the resultant PDMS. The elastic modulus and hydrophilicity were significantly improved by such modifications. In addition, the development of hexagonal micropillars with smaller diameters largely improved the ion permeability and increased the motion resistance. We further cultured retinal pigment epithelial (RPE) cells on the surface of this modified PDMS biomembrane and assayed its biocompatibility. Remarkably, the GO incorporation and coating exhibited beneficial effect on the cell growth and the new formation of tight junctions in RPE cells. Taken together, this GO-modified PDMS scaffold with polyhexagonal micropillars may be utilized as an ideal cell sheet and adaptor for cell cultivation and can be used in vivo for the transplantation of cells such as RPE cells.

Chondrogenic differentiation of embryonic stem cells using mechanotransductive 3-D PDMS scaffolds

Embryonic stem cells (ESCs) are an ideal source for cell therapy and regenerative medicine. ESCs must be differentiated prior to their use for therapeutic applications. However, homogeneous differentiation of ESCs in vitro has proven to be challenging. We hypothesized that both biological and mechanical cues contribute to the specific differentiation of ESCs in vivo . This was tested by mimicking the in vivo microenvironment to differentiate ESCs into chondrogenic lineage using highly elastic polydimethylsiloxane (PDMS) scaffolds and the application of mechanical compression in vitro . ESCs seeded in PDMS scaffolds subjected to static compressive stress resulted in significant upregulation of genes, Sox9, Col2, and Acan , involved in early chondrogenic differentiation . However, the compressive stress did not affect expression of the late hypertrophic markers, Runx2 , Col10, and Mmp13 , signifying induction of ESCs into early chondroprogenitors. Application of mechanical stress increased expression of mechanical signaling genes, Rhoa , Yap, and Taz . The chondroinductive role of Rhoa was confirmed by the inhibition of RhoA signaling by CCG-1423, which resulted in decreased transcriptional and translational expression of chondrogenic markers. Based on these findings, we proposed a strategy for compression induced chondrogenic differentiation in mechanotransductive 3-D PDMS scaffolds.

Effect of an oxygen-generating scaffold on the viability and insulin secretion function of porcine neonatal pancreatic cell clusters.

Islet encapsulation techniques have shown limited success in maintaining islet survival and function because encapsulation decreases oxygen supply. In this study, an oxygen-generating scaffold was fabricated to prevent hypoxic cell damage and improve the viability and insulin secretion of islets. We fabricated an oxygen-generating scaffold by mixing calcium peroxide (CaO2 ) with polydimethylsiloxane (PDMS). We evaluated the effects of the oxygen-generating PDMS+CaO2 scaffold on viability, caspase-3 and caspase-7 activity, oxygen consumption rate (OCR), glucose-stimulated insulin secretion (GSIS), hypoxic cell marker expression, and reactive oxygen species (ROS) levels in porcine neonatal pancreatic cell clusters (NPCCs). We also fabricated a microfluidic device that allowed measuring the effects of the oxygen-generating scaffold on viability. Oxygen generation by the PDMS+CaO2 scaffold was sustained for more than 24hours in vitro. NPCCs encapsulated in PDMS+CaO2 showed higher viability than NPCCs in PDMS scaffolds and control NPCCs grown without a scaffold. PDMS+CaO2 -encapsulated NPCCs showed lower caspase-3 and caspase-7 activity, hypoxic cell expression, and ROS levels, and higher OCR and GSIS than those in PDMS or control cells. Using the microfluidic device, we observed that the viability of PDMS+CaO2 -encapsulated NPCCs was higher than that of PDMS-encapsulated NPCCs. NPCCs in PDMS+CaO2 scaffolds show higher viability and insulin secretion than do NPCCs in PDMS scaffolds and control cells. Therefore, this oxygen-generating scaffold has potential for application in future islet transplantation studies.

Study on the regulation of focal adesions and cortical actin by matrix nanotopography in 3D environment

Matrix nanotopography plays an important role in regulating cell behaviors by providing spatial as well as mechanical cues for cells to sense. It has been proposed that nanoscale topography is possible to modulate the tensions which direct the formation of cytoskeleton and the organization of the membrane receptor within the cell, which in turn regulate intracellular mechanical and biochemical signaling. With current studies on this topic being performed mainly in 2D platforms, the question on how nanotopography can influence cell bahaviors in 3D environments has yet to be addressed. In this paper, we explored this question by placing cells in 3D hollow spherical polydimethylsiloxane scaffolds. After culturing rat embryonic fibroblast cells in two kinds of scaffold, one with smooth surface and the other with numerous nano-spikes, we observed that cells in the smooth scaffold have more anchoring sites and more focal adhesions than in the etched scaffold. Moreover, we found the presence of correlation between cortical actin, the important component for supporting cell attachment, and local cell geometry.

Local delivery of fingolimod from three-dimensional scaffolds impacts islet graft efficacy and microenvironment in a murine diabetic model.

The local delivery of immunosuppressive agents could significantly promote the success of islet transplantation for the treatment of Type 1 diabetes. Fingolimod, a clinically-approved sphingosine-1-phosphate receptor agonist, has been found to dampen allograft islet rejection in rodent models when delivered systemically. Herein, we engineered a platform for the local delivery of fingolimod by incorporating it within a macroporous polydimethylsiloxane (PDMS) scaffold specifically designed for islet transplantation. In vitro drug release studies quantifying kinetics confirmed sustained release within targeted dose levels for >7 days. Fingolimod-PDMS scaffolds containing syngeneic islets were subsequently transplanted into diabetic mice for examination of the effect of local fingolimod release on engraftment. Surprisingly, either delayed or abrogated efficacy was observed when scaffolds contained a dosage of fingolimod >0.5% w/w; despite drug release rates estimated at ~80-fold less than published systemic delivery reports where no detrimental effects were noted. Histological analysis of explants indicated a dose-dependent modulation of cellular migration and phenotype at the graft site, with high doses impairing host infiltration and engraftment while lower doses promoted leucocyte migration. Mechanistic in vivo and in vitro studies observed unique host and islet responses to local fingolimod delivery, with impairment of murine islet viability and function. Overall, this study confirmed the ability to modulate local delivery of fingolimod in a sustained-release manner using a three-dimensional PDMS scaffold; however, the observed detrimental impacts at the site of islet transplantation do not support further investigation of local delivery at the graft site in murine models.

A sugar-template manufacturing method for microsystem ion-exchange membranes

In this work, we report on a novel method for producing ion-exchange membranes that can be integrated directly into polydimethylsiloxane-based micro devices. Ionomers such as NafionTM, a copolymer with high conductivity and selectivity to small cations, are generally incompatible with common micro device materials due to the chemical inertness of the tetrafluoroethylene-based skeleton and the swelling in aqueous solutions. Hence, we introduce a microfabrication concept where we use consolidated sugar granules as a template to produce a porous polydimethylsiloxane scaffold. Ionomer and scaffold are combined to a composite membrane where the cohesion of these incompatible materials is of rather mechanical nature; i.e. the ionomer is physically entrapped in the scaffold. Electrochemical impedance spectroscopy measurements reveal the excellent membrane conductivity for the upper electrolyte concentrations tested in this work.