EGF-grafted PDMS surfaces in artificial cornea applications

Multifiller-based polymer composites for shielding high energy ionising radiation

Polydimethyl silicone rubber-based polymer composites filled with molybdenum and bismuth were fabricated using simple open mold cast technique. The physical and chemical structure and gamma shielding parameters like attenuation coefficient, half-value layer (HVL) thickness and relaxation length have been investigated for the said novel materials using X-ray diffraction (XRD), Fourier transform Infrared spectroscopy (FTIR) and gamma ray spectrometer. XRD study reveals the crystalline nature of the composites. It is evident from FTIR studies that there is no chemical interaction between the polymer matrix and filler particles. The results of attenuation studies reveal that the linear attenuation coefficient increases with addition of Bi and Mo and is found to be 0.653, 1.341 and 1.017, 1.793 and 0.102, 0.152 cm-1 for 1MMB and 2MMB polymer composites at 80, 356 and 662 keV gamma rays, respectively. The HVL thickness of the materials is found to be 1.06, 0.51 and 0.68, 0.38 and 6.73, 4.532 cm for 1MMB (20Mo + 10Bi phr) and 2MMB (40Mo + 20Bi phr) at these energies, respectively. The mass attenuation coefficient of the novel composites 1MMB and 2MMB is found to be higher than the conventional materials like lead and barite for 356 keV gamma rays. In addition, the material is found to be light weight and flexible enabling to be molded in required forms, thus being a substitute for the material lead that is known to be heavy and toxic by nature.

Biofabrication paradigms in corneal regeneration: bridging bioprinting techniques, natural bioinks, and stem cell therapeutics

Corneal diseases are a major cause of vision loss worldwide. Traditional methods like corneal transplants from donors are effective but face challenges like limited donor availability and the risk of graft rejection. Therefore, new treatment methods are essential. This review examines the growing field of bioprinting and biofabrication in corneal tissue engineering. We begin by discussing various bioprinting methods such as stereolithography, inkjet, and extrusion printing, highlighting their strengths and weaknesses for eye-related uses. We also explore how biological tissues are made suitable for bioprinting through a process called decellularization, which can be achieved using chemical, physical, or biological methods. The review then looks at natural materials, known as bioinks, used in bioprinting. We focus on materials like gelatin, collagen, fibrin, chitin, chitosan, silk fibroin, and alginate, examining their mechanical and biological properties. The importance of hydrogel scaffolds, particularly those based on collagen and other materials, is also discussed in the context of repairing corneal tissue. Another key area we cover is the use of stem cells in corneal regeneration. We pay special attention to limbal epithelial stem cells and mesenchymal stromal cells, highlighting their roles in this process. The review concludes with an overview of the latest advancements in corneal tissue bioprinting, from early techniques to advanced methods of delivering stem cells using bioengineered materials. In summary, this review presents the current state and future potential of bioprinting and biofabrication in creating functional corneal tissues, highlighting new developments and ongoing challenges with a view towards restoring vision.

Squishy matters - Corneal mechanobiology in health and disease

The cornea, as a dynamic and responsive tissue, constantly interacts with mechanical forces in order to maintain its structural integrity, barrier function, transparency and refractive power. Cells within the cornea sense and respond to various mechanical forces that fundamentally regulate their morphology and fate in development, homeostasis and pathophysiology. Corneal cells also dynamically regulate their extracellular matrix (ECM) with ensuing cell-ECM crosstalk as the matrix serves as a dynamic signaling reservoir providing biophysical and biochemical cues to corneal cells. Here we provide an overview of mechanotransduction signaling pathways then delve into the recent advances in corneal mechanobiology, focusing on the interplay between mechanical forces and responses of the corneal epithelial, stromal, and endothelial cells. We also identify species-specific differences in corneal biomechanics and mechanotransduction to facilitate identification of optimal animal models to study corneal wound healing, disease, and novel therapeutic interventions. Finally, we identify key knowledge gaps and therapeutic opportunities in corneal mechanobiology that are pressing for the research community to address especially pertinent within the domains of limbal stem cell deficiency, keratoconus and Fuchs' endothelial corneal dystrophy. By furthering our understanding corneal mechanobiology, we can contextualize discoveries regarding corneal diseases as well as innovative treatments for them.

Immobilization of Growth Factors to Collagen Surfaces Using Pulsed Visible Light

In the treatment of traumatic injuries, burns, and ulcers of the eye, inadequate epithelial tissue healing remains a major challenge. Wound healing is a complex process involving the temporal and spatial interplay between cells and their extracellular milieu. It can be impaired by a variety of causes including infection, poor circulation, loss of critical cells, and/or proteins, and a deficiency in normal neural signaling (e.g., neurotrophic ulcers). Ocular anatomy is particularly vulnerable to lasting morbidity from delayed healing, whether it be scarring or perforation of the cornea, destruction of the conjunctival mucous membrane, or cicatricial changes to the eyelids and surrounding skin. Therefore, there is a major clinical need for new modalities for controlling and accelerating wound healing, particularly in the eye. Collagen matrices have long been explored as scaffolds to support cell growth as both two-dimensional coatings and substrates, as well as three-dimensional matrices. Meanwhile, the immobilization of growth factors to various substrates has also been extensively studied as a way to promote enhanced cellular adhesion and proliferation. Herein we present a new strategy for photochemically immobilizing growth factors to collagen using riboflavin as a photosensitizer and exposure to visible light (∼458 nm). Epidermal growth factor (EGF) was successfully bound to collagen-coated surfaces as well as directly to endogenous collagen from porcine corneas. The initial concentration of riboflavin and EGF as well as the blue light exposure time were keys to the successful binding of growth factors to these surfaces. The photocrosslinking reaction increased EGF residence time on collagen surfaces over 7 days. EGF activity was maintained after the photocrosslinking reaction with a short duration of pulsed blue light exposure. Bound EGF accelerated in vitro corneal epithelial cell proliferation and migration and maintained normal cell phenotype. Additionally, the treated surfaces were cytocompatible, and the photocrosslinking reaction was proven to be safe, preserving nearly 100% cell viability. These results suggest that this general approach is safe and versatile may be used for targeting and immobilizing bioactive factors onto collagen matrices in a variety of applications, including in the presence of live, seeded cells or in vivo onto endogenous extracellular matrix collagen.

Tethering Growth Factors to Collagen Surfaces Using Copper-Free Click Chemistry: Surface Characterization and in Vitro Biological Response

Surface modifications with tethered growth factors have mainly been applied to synthetic polymeric biomaterials in well-controlled, acellular settings, followed by seeding with cells. The known bio-orthogonality of copper-free click chemistry provides an opportunity to not only use it in vitro to create scaffolds or pro-migratory tracks in the presence of living cells, but also potentially apply it to living tissues directly as a coupling modality in situ. In this study, we studied the chemical coupling of growth factors to collagen using biocompatible copper-free click chemistry and its effect on the enhancement of growth factor activity in vitro. We verified the characteristics of modified epidermal growth factor (EGF) using mass spectrometry and an EGF/EGF receptor binding assay, and evaluated the chemical immobilization of EGF on collagen by copper-free click chemistry using surface X-ray photoelectron spectroscopy (XPS), surface plasmon resonance (SPR) spectroscopy, and enzyme-linked immunosorbent assay (ELISA). We found that the anchoring was noncytotoxic, biocompatible, and rapid. Moreover, the surface-immobilized EGF had significant effects on epithelial cell attachment and proliferation. Our results demonstrate the possibility of copper-free click chemistry as a tool for covalent bonding of growth factors to collagen in the presence of living cells. This approach is a novel and potentially clinically useful application of copper-free click chemistry as a way of anchoring growth factors to collagen and foster epithelial wound healing.

Nanomaterials-Tools, Technology and Methodology of Nanotechnology Based Biomedical Systems for Diagnostics and Therapy

Nanomedicine helps to fight diseases at the cellular and molecular level by utilizing unique properties of quasi-atomic particles at a size scale ranging from 1 to 100 nm. Nanoparticles are used in therapeutic and diagnostic approaches, referred to as theranostics. The aim of this review is to illustrate the application of general principles of nanotechnology to select examples of life sciences, molecular medicine and bio-assays. Critical aspects relating to those examples are discussed.

Human corneal epithelial cell response to substrate stiffness

It has been reported that mechanical stimulus can affect cellular behavior. While induced differentiation in stem cells and proliferation and directional migration in fibroblasts are reported as responses to mechanical stimuli, little is known about the response of cells from the cornea. In the present study, we investigated whether changes in substrate stiffness (measured by elastic modulus) affected the behavior of human corneal epithelial cells (HCECs). Polyacrylamide substrates with different elastic moduli (compliant, medium and stiff) were prepared and HCECs were cultured on them. HCECs responses, including cell viability, apoptosis, intercellular adhesion molecule-1 (ICAM-1) expression, integrin-α3β1 expression and changes in cytoskeleton structure (actin fibers) and migratory behavior, were studied. No statistically significant cell activation, as measured by ICAM-1 expression, was observed. However, on compliant substrates, a higher number of cells were found to be apoptotic and disrupted actin fibers were observed. Furthermore, cells displayed a statistically significant lower migration speed on compliant substrates when compared with the stiffer substrates. Thus, corneal epithelial cells respond to changes in substrate stiffness, which may have implications in the understanding and perhaps treatment of corneal diseases, such as keratoconus.

Functional fabrication of recombinant human collagen-phosphorylcholine hydrogels for regenerative medicine applications

The implant-host interface is a critical element in guiding tissue or organ regeneration. We previously developed hydrogels comprising interpenetrating networks of recombinant human collagen type III and 2-methacryloyloxyethyl phosphorylcholine (RHCIII-MPC) as substitutes for the corneal extracellular matrix that promote endogenous regeneration of corneal tissue. To render them functional for clinical application, we have now optimized their composition and thereby enhanced their mechanical properties. We have demonstrated that such optimized RHCIII-MPC hydrogels are suitable for precision femtosecond laser cutting to produce complementing implants and host surgical beds for subsequent tissue welding. This avoids the tissue damage and inflammation associated with manual surgical techniques, thereby leading to more efficient healing. Although we previously demonstrated in clinical testing that RHCIII-based implants stimulated cornea regeneration in patients, the rate of epithelial cell coverage of the implants needs improvement, e.g. modification of the implant surface. We now show that our 500μm thick RHCIII-MPC constructs comprising over 85% water are suitable for microcontact printing with fibronectin. The resulting fibronectin micropatterns promote cell adhesion, unlike the bare RHCIII-MPC hydrogel. Interestingly, a pattern of 30μm wide fibronectin stripes enhanced cell attachment and showed the highest mitotic rates, an effect that potentially can be utilized for faster integration of the implant. We have therefore shown that laboratory-produced mimics of naturally occurring collagen and phospholipids can be fabricated into robust hydrogels that can be laser profiled and patterned to enhance their potential function as artificial substitutes of donor human corneas.

Progress in the development of a corneal replacement: keratoprostheses and tissue-engineered corneas

Rapid progress has been made in the past 5 years in the development of corneal replacements. Traditionally they are divided into two categories, keratoprostheses and tissue-engineered corneal equivalents, as replacement tissues are increasingly in demand worldwide. There are currently several different keratoprosthesis models in clinical use around the world. The most popular and most widely publicized is the AlphaCor model, which has enjoyed significant clinical success. However, improvements remain to be made, and the aim of most of the current research is to better understand the interactions between a synthetic material and the surrounding biology on a more fundamental level. This improved understanding will no doubt lead to improvements in current models and to the development of new models in the near future. While tissue-engineered corneal equivalents have been under investigation for considerably less time, there is growing evidence to suggest that a tissue-engineered corneal equivalent comprised of primarily natural materials will exist in the not too distant future. Research groups have reported strong in vitro and in vivo results. The strength of the collagen matrix and its ability to support cell infiltration have been the primary avenues of research. Various collagen crosslinking techniques have been used. Infiltration of three major cells of the cornea has been observed. Most importantly, the ability of these materials to support nerve ingrowth has been demonstrated. While challenges remain with both types of corneal replacements, the considerable progress in the recent past suggests that reliable implants for the treatment of a variety of corneal diseases will be available. This review will provide an overview of recent results, and will provide insight into the future of research on corneal replacements.

Tissue engineering of the corneal endothelium: a review of carrier materials

Functional impairment of the human corneal endothelium can lead to corneal blindness. In order to meet the high demand for transplants with an appropriate human corneal endothelial cell density as a prerequisite for corneal function, several tissue engineering techniques have been developed to generate transplantable endothelial cell sheets. These approaches range from the use of natural membranes, biological polymers and biosynthetic material compositions, to completely synthetic materials as matrices for corneal endothelial cell sheet generation. This review gives an overview about currently used materials for the generation of transplantable corneal endothelial cell sheets with a special focus on thermo-responsive polymer coatings.

The promotion of angiogenesis by growth factors integrated with ECM proteins through coiled-coil structures

An appropriate method to bind extracellular matrix (ECM) proteins and growth factors using advanced protein engineering techniques has the potential to enhance cell proliferation and differentiation for tissue regeneration and repair. In this study we developed a method to co-immobilize non-covalently an ECM protein to three different types of growth factors: basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and single-chain vascular endothelial growth factor (scVEGF121) through a coiled-coil structure formed by helixA/helixB in order to promote angiogenesis. The designed ECM was established by fusing two repeats of elastin-derived unit (APGVGV)(12), cell-adhesive sequence (RGD), laminin-derived IKVAV sequence and collagen-binding domain (CBD) to obtain CBDEREI2. HelixA was fused to each growth factor and helixB to the engineered ECM. Human umbilical vein endothelial cells (HUVECs) were cultured on engineered ECM and growth factors connected through the coiled-coil formation between helixA and helixB. Cell proliferation and capillary tube-like formation were monitored. Moreover, the differentiated cells with high expression of Ang-2 suggested the ECM remodeling. Our approach of non-covalent coupling method should provide a protein-release control system as a new contribution in biomaterial for tissue engineering field.

Effects of a cell-imprinted poly(dimethylsiloxane) surface on the cellular activities of MG63 osteoblast-like cells: preparation of a patterned surface, surface characterization, and bone mineralization

To understand the relationship between surface patterns and cellular activities, various types of pattern models have been investigated. In this study, we suggest a new surface pattern model, which replicates proliferated cells. We used osteoblast-like cells (MG63) as a target cell pattern and constructed various cell-imprinted surfaces using an electric field assisted casting method for different culturing times (4 h and 7 and 14 days). On the basis of scanning electron microscopy images and three-dimensional topographical optical images, we acquired the cells' unique patterns and used them for replicating patterned substrates. We then cultured MG63 cells in the patterned surfaces for 7 and 14 days to observe various cellular activities, cell viability, alkaline phosphatase (ALP) activity, and mineralization. Higher cellular activities were observed on the roughened surface as compared with the smooth surface. In particular, we obtained the most appropriate roughness value (R(a) = 702 ± 87 nm) from proliferated cells cultured over 14 days. On the basis of these findings, we demonstrate a new biomimical surface model that enhances cellular activities at the cell-substrate interface.

Surface modification and drug delivery for biointegration

Biointegration refers to the interconnection between a biomedical device and the recipient tissue. In many implant devices, the lack of proper biointegration can cause device failure and potentially serious medical problems. This review summarizes the recent progress in surface chemistry, drug delivery and antifouling methods to improve the biointegration of implants. Much progress has been made as our understanding of biological systems and material properties expands and as new technologies become available. This article addresses methods of enhancing biointegration by means of modifying implant surface chemistry and by drug-delivery approaches.

Regenerative approaches as alternatives to donor allografting for restoration of corneal function

A range of alternatives to human donor tissue for corneal transplantation are being developed to address the shortfall of good quality tissues as well as the clinical conditions for which allografting is contraindicated. Classical keratoprostheses, commonly referred to as artificial corneas, are being used clinically to replace minimal corneal function. However, they are used only as last resorts, as they are associated with significant complications, such as extrusion/rejection, glaucoma, and retinal detachment. The past few years have seen significant developments in technologies designed to replace part or the full thickness of damaged or diseased corneas with materials that encourage regeneration to different extents. This review describes selected examples of these corneal substitutes, which range from cell-based regenerative strategies to keratoprostheses with regenerative capabilities via tissue-engineered scaffolds pre-seeded with stem cells. It is unlikely that one corneal substitute will be best for all indications, but taken together, the various approaches may soon be able to supplement the supply of human donor corneas for transplantation or allow restoration of diseased or damaged corneas that cannot be treated by currently available techniques.

PREPARATION OF GELATIN NANOPARTICLES WITH EGFR SELECTION ABILITY VIA BIOTINYLATED-EGF CONJUGATION FOR LUNG CANCER TARGETING

Lung cancer is the most malignant cancer today, and specific drug delivery has been developed for superior outcome. In this study, gelatin nanoparticles (GPs) were firstly employed as native carriers. Second, NeutrAvidinFITC was then grafted on the particle surface (GP-Av); finally much more amount of biotinylated EGF were able to be conjugated with NeutrAvidinFITC forming ligand- binding nanoparticles (GP-Av-bEGF) to enhance the targeting efficiency. These nanoparticles were applied as EGFR-seeking agents to detect lung cancer cells.

Results of particle characterization show that the modification process had no influence on size (230 nm). Round and smooth nanoparticles were observed by AFM. The surface property of nanoparticles was characterized by surface plasmon resonance (SPR) and flowcytometry analysis as well as by examining the interaction of the modified EGF on particle surface with the ability to recognize EGFR.

The binding ability of GPs with or without EGF modification is different. SPR assay showed that EGF-conjugated particles (GP-Av-bEGF) have stronger and faster bonding signal than the unmodified one (GP-Av). Free EGF competition results from SPR and A549 cell (lung adenocarcinoma cells) culture also confirmed the EGF receptormediated endocytosis mechanism for nanoparticles with EGF-modified binding. The in vitro targeting ability was confirmed by the uptake rate of different cells via flow cytometry assay. GP-Av-bEGF resulted in higher entrance efficiency on A549 than on normal lung cells (HFL1) and U2-OS (osteosarcoma cells) due to A549 possessing more amounts of EGFR. The targeting ability of GP-Av-bEGF nanoparticles with specific EGFR tracing ability was proved, which holds promise for further anticancer drug applications.

Dose-dependent and synergistic effects of proteoglycan 4 on boundary lubrication at a human cornea-polydimethylsiloxane biointerface

OBJECTIVES

Proteoglycan 4 (PRG4), also known as lubricin, is a boundary lubricating mucin-like glycoprotein present on several tissue surfaces in the body. The objectives of this study were to (1) implement and characterize an in vitro boundary lubrication test at a human cornea-polydimethylsiloxane (PDMS) biointerface and (2) determine the dose-dependent and synergistic effects of PRG4, with hyaluronan (HA), on ocular surface boundary lubrication using this test.

METHODS

Human corneas and model PDMS material were articulated against each other, at effective sliding velocities v(eff) between 0.3 and 30 mm/sec under physiologic loads of approximately 8 to 25 kPa. Samples were tested serially in (1) saline, PRG4 at 30, 100, 300 μg/mL resuspended in saline, then saline again or (2) saline, AQuify Comfort Eye Drops (containing 0.1% HA), 300 μg/mL PRG4 in saline, 300 μg/mL PRG4 in AQuify, then saline again. Both static and kinetic friction coefficients were calculated.

RESULTS

PRG4 effectively lowered friction at the cornea-PDMS biointerface, both alone in a dose-dependent manner and in combination with HA. PRG4 reduced kinetic friction coefficients, <μ(kinetic, Neq)>, from approximately 0.30 in saline, to approximately 0.30, 0.24, and 0.17 in 30, 100, and 300 μg/mL PRG4, respectively. Values of <μ(kinetic, Neq)> in AQuify, approximately 0.32, were similar to those in saline; however, when combined with 300 μg/mL PRG4, values of <μ(kinetic, Neq)> were reduced to approximately 0.15.

CONCLUSIONS

PRG4 functions as an effective ocular surface boundary lubricant, both alone in a dose-dependent manner and in combination with HA.

Corneal epithelial cell adhesion and growth on EGF-modified aminated PDMS

Growth factor tethering has significant potential to mediate cellular responses in biomaterials and tissue engineering. We have previously demonstrated that epidermal growth factor (EGF) can be tethered to polydimethylsiloxane (PDMS) substrates and that these surfaces promoted interactions with human corneal epithelial cells in vitro. The goal of the current work was to better understand the specific effects of the tethered growth factor on the cells. The EGF was reacted with a homobifunctional N-hydroxysuccinimide (NHS) polyethylene glycol (PEG) derivative, and then bound to allyamine plasma-modified PDMS. Human corneal epithelial cells were seeded on the surfaces and cultured in serum-free medium for periods of up to 5 days. Cell growth was monitored and quantified by trypsinization and counting with a Coulter counter. Expression of matrix proteins and alpha(6)-integrins was assessed by immunostaining and confocal microscopy. A centrifugation assay was used to determine cell adhesion under an applied detachment force. Binding of EGF was found to significantly increase cell numbers and coverage across the surfaces at 5 days of culture in vitro. Immunofluorescence experiments indicate increased expression of fibronectin, laminin, and alpha(6)-integrins on the EGF-modified surfaces, and expression is localized at the cell-material interface as observed by confocal microscopy. In accordance with these results, the highest quantity of adherent cells is found on the EGF-modified subtrates at 5 days of culture. The results provide initial evidence that binding of EGF may be used to improve the epithelialization of and the adhesion of the cells on a polymeric artificial cornea device.

An integrated microfluidic system for studying cell-microenvironmental interactions versatilely and dynamically

We presented an integrated microfluidic system for dynamical study of cell-microenvironmental interactions. We demonstrated its precisely spatio-temporal control in the flow direction and the multi-site staying of the fluids by groups of monolithic microfabricated valves through digital operation, aside from the regulated communication between two loci based on real-time microenvironment transition. Using this system, a series of functional manipulations, including specific delivery, addressable surface treatment, positional cell loading and co-culture were performed quickly and efficiently for biological applications. Sequentially, we carried out the potential utility of this system in the research of dynamic microenvironmental influence to cells using a patho-physiological interaction during cancer initiation and progression. Our results exhibit the passive role but collaborative response of NIH 3T3 fibroblasts to the soluble signals from hepatocellular carcinoma cells, and also the variable behaviors of carcinoma cells under different environmental stimulation. This system can facilitate the in vitro investigation of cell-microenvironmental interactions occurred in numerous biological and pathogenic processes.

Controlling cellular activity by manipulating silicone surface roughness

Silicone elastomers exhibit a broad range of beneficial properties that are exploited in biomaterials. In some cases, however, problems can arise at silicone elastomer interfaces. With breast implants, for example, the fibrous capsule that forms at the silicone interface can undergo contracture, which can lead to the need for revision surgery. The relationship between surface topography and wound healing--which could impact on the degree of contracture--has not been examined in detail. To address this, we prepared silicone elastomer samples with rms surface roughnesses varying from 88 to 650 nm and examined the growth of 3T3 fibroblasts on these surfaces. The PicoGreen assay demonstrated that fibroblast growth decreased with increases in surface roughness. Relatively smooth (approximately 88 nm) PDMS samples had ca. twice as much fibroblast DNA per unit area than the 'bumpy' (approximately 378 nm) and very rough (approximately 604 and approximately 650 nm) PDMS samples. While the PDMS sample with roughness of approximately 650 nm had significantly fewer fibroblasts at 24h than the TCP control, fibroblasts on the smooth silicone surprisingly reached confluence much more rapidly than on TCP, the gold standard for cell culture. Thus, increasing the surface roughness at the sub-micron scale could be a strategy worthy of consideration to help mitigate fibroblast growth and control fibrous capsule formation on silicone elastomer implants.

Biocompatible, hyaluronic acid modified silicone elastomers

Although silicones possess many useful properties as biomaterials, their hydrophobicity can be problematic. To a degree, this issue can be addressed by surface modification with hydrophilic polymers such as poly(ethylene glycol), but the resulting structures are usually not conducive to cell growth. In the present work, we describe the synthesis and characterization of covalently linked hyaluronic acid (HA) (35 kDa) to poly(dimethylsiloxane) (PDMS) elastomer surfaces. HA is of interest because of its known biological properties; its presence on a surface was expected to improve the biocompatibility of silicone materials for a wide range of bioapplications. HA was introduced with a coupling agent in two steps from high-density, tosyl-modified, poly(ethylene glycol) tethered silicone surfaces. All materials synthesized were characterized by water contact angle, ATR-FTIR, XPS and (13)C solid state NMR spectroscopy. Biological interactions with these modified silicone surfaces were assessed by examining interactions with fibrinogen as a model protein as well as determining the in vitro response of fibroblast (3T3) and human corneal epithelial cells relative to unmodified poly(dimethylsiloxane) controls. The results suggest that HA modification significantly enhances cell interactions while decreasing protein adsorption and may therefore be effective for improving biocompatibility of PDMS and other materials.

Microfabricated arrays for high-throughput screening of cellular response to cyclic substrate deformation

Mechanical forces play an important role in regulating cellular function and have been shown to modulate cellular response to other factors in the cellular microenvironment. Presently, no technique exists to rapidly screen for the effects of a range of uniform mechanical forces on cellular function. In this work, we developed and characterized a novel microfabricated array capable of simultaneously applying cyclic equibiaxial substrate strains ranging in magnitude from 2 to 15% to small populations of adherent cells. The array is versatile, and capable of simultaneously generating a range of substrate strain fields and magnitudes. The design can be extended to combinatorially manipulate other mechanobiological culture parameters in the cellular microenvironment. As a first demonstration of this technology, the array was used to determine the effects of equibiaxial mechanical strain on activation of the canonical Wnt/beta-catenin signaling pathway in cardiac valve mesenchymal progenitor cells. This high-throughput approach to mechanobiological screening enabled the identification of a novel co-dependence between strain magnitude and duration of stimulation in controlling beta-catenin nuclear accumulation. More generally, this versatile platform has broad applicability in the fields of mechanobiology, tissue engineering and pathobiology.

Bioactive interpenetrating polymer network hydrogels that support corneal epithelial wound healing

The development and characterization of collagen-coupled poly(ethylene glycol)/poly(acrylic acid) (PEG/PAA) interpenetrating polymer network hydrogels is described. Quantitative amino acid analysis and FITC-labeling of collagen were used to determine the amount and distribution of collagen on the surface of the hydrogels. The bioactivity of the coupled collagen was detected by a conformation-specific antibody and was found to vary with the concentration of collagen reacted to the photochemically functionalized hydrogel surfaces. A wound healing assay based on an organ culture model demonstrated that this bioactive surface supports epithelial wound closure over the hydrogel but at a decreased rate relative to sham wounds. Implantation of the hydrogel into the corneas of live rabbits demonstrated that epithelial cell migration is supported by the material, although the rate of migration and morphology of the epithelium were not normal. The results from the study will be used as a guide toward the optimization of bioactive hydrogels with promise in corneal implant applications such as a corneal onlay and an artificial cornea.