Seeding of Corneal Wounds by Epithelial Cell Transfer from Micropatterned PDMS Contact Lenses

Hybrid Materials with Antimicrobial Properties Based on Hyperbranched Polyaminopropylalkoxysiloxanes Embedded with Ag Nanoparticles

New hybrid materials based on Ag nanoparticles stabilized by a polyaminopropylalkoxysiloxane hyperbranched polymer matrix were prepared. The Ag nanoparticles were synthesized in 2-propanol by metal vapor synthesis (MVS) and incorporated into the polymer matrix using metal-containing organosol. MVS is based on the interaction of extremely reactive atomic metals formed by evaporation in high vacuum (10−4–10−5 Torr) with organic substances during their co-condensation on the cooled walls of a reaction vessel. Polyaminopropylsiloxanes with hyperbranched molecular architectures were obtained in the process of heterofunctional polycondensation of the corresponding AB2-type monosodiumoxoorganodialkoxysilanes derived from the commercially available aminopropyltrialkoxysilanes. The nanocomposites were characterized using transmission (TEM) and scanning (SEM) electron microscopy, X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD) and Fourier-transform infrared spectroscopy (FTIR). TEM images show that Ag nanoparticles stabilized in the polymer matrix have an average size of 5.3 nm. In the Ag-containing composite, the metal nanoparticles have a “core-shell” structure, in which the “core” and “shell” represent the M0 and Mδ+ states, respectively. Nanocomposites based on silver nanoparticles stabilized with amine-containing polyorganosiloxane polymers showed antimicrobial activity against Bacillus subtilis and Escherichia coli.

Antibacterial Properties of Silver Nanoclusters with Carbon Support on Flexible Polymer

Here, we aimed at the preparation of an antibacterial surface on a flexible polydimethylsiloxane substrate. The polydimethylsiloxane surface was sputtered with silver, deposited with carbon, heat treated and exposed to excimer laser, and the combinations of these steps were studied. Our main aim was to find the combination of techniques applicable both against Gram-positive and Gram-negative bacteria. The surface morphology of the structures was determined by atomic force microscopy and scanning electron microscopy. Changes in surface chemistry were conducted by application of X-ray photoelectron spectroscopy and energy dispersive spectroscopy. The changes in surface wettability were characterized by surface free energy determination. The heat treatment was also applied to selected samples to study the influence of the process on layer stability and formation of PDMS-Ag or PDMS-C-Ag composite layer. Plasmon resonance effect was determined for as-sputtered and heat-treated Ag on polydimethylsiloxane. The heating of such structures may induce formation of a pattern with a surface plasmon resonance effect, which may also significantly affect the antibacterial activity. We have implemented sputtering of the carbon base layer in combination with excimer laser exposure of PDMS/C/Ag to modify its properties. We have confirmed that deposition of primary carbon layer on PDMS, followed by sputtering of silver combined with subsequent heat treatment and activation of such surface with excimer laser, led to the formation of a surface with strong antibacterial properties against two bacterial strains of S. epidermidis and E. coli.

High-Throughput Methods in the Discovery and Study of Biomaterials and Materiobiology

The complex interaction of cells with biomaterials (i.e., materiobiology) plays an increasingly pivotal role in the development of novel implants, biomedical devices, and tissue engineering scaffolds to treat diseases, aid in the restoration of bodily functions, construct healthy tissues, or regenerate diseased ones. However, the conventional approaches are incapable of screening the huge amount of potential material parameter combinations to identify the optimal cell responses and involve a combination of serendipity and many series of trial-and-error experiments. For advanced tissue engineering and regenerative medicine, highly efficient and complex bioanalysis platforms are expected to explore the complex interaction of cells with biomaterials using combinatorial approaches that offer desired complex microenvironments during healing, development, and homeostasis. In this review, we first introduce materiobiology and its high-throughput screening (HTS). Then we present an in-depth of the recent progress of 2D/3D HTS platforms (i.e., gradient and microarray) in the principle, preparation, screening for materiobiology, and combination with other advanced technologies. The Compendium for Biomaterial Transcriptomics and high content imaging, computational simulations, and their translation toward commercial and clinical uses are highlighted. In the final section, current challenges and future perspectives are discussed. High-throughput experimentation within the field of materiobiology enables the elucidation of the relationships between biomaterial properties and biological behavior and thereby serves as a potential tool for accelerating the development of high-performance biomaterials.

Paradigm shifts, peregrinations and pixies in ophthalmology

Human ingenuity is challenged by defending vision, our highest bandwidth sense. Special challenges are presented by the replacement or repair of highly specialized but scarce tissue within the constraints of transparency, tissue shape and alignment, tissue borders and pressure maintenance. Many, mostly destructive, surgical procedures were developed prior to an understanding of underlying pathophysiology. For a number of conditions, both reconstructive and destructive procedures co-exist, yet there are few guidelines as to the better approach. Because the consequences of these procedures may take many years to surface (consistent with a stem cell role in long-term tissue maintenance), guidance may be provided by the elucidation of underlying principles from these approaches. Illustrative examples from clinical, basic research and biotechnology, particularly relating to pterygium, ocular surface squamous neoplasia, dry-eye syndrome, corneal rehabilitation and replacement, cataract surgery, strabismus surgery and bionic eye research, are described. An unexpected consequence of bionic device development has been an appreciation of the sophistication of tissues being replaced, given the limitations of available biomaterials. Examples of how this has provided insights into ocular disease will be illustrated. Stem cell and biomaterial technologies are starting to impact at a time when cost-effectiveness is under scrutiny. Both efficacy and cost will need to be considered as these interventions are introduced. It appears that the paradigm shift rate is accelerating and there is evidence of this in ophthalmology. Lessons learned from the areas of destructive versus reconstructive surgery and the limitations of development of bionic replacements will be used to illustrate how new procedures and technologies can be developed.

Development of ciprofloxacin-loaded contact lenses using fluorous chemistry

In this work, we developed a simple method to load drugs into commercially available contact lenses utilizing fluorous chemistry. We demonstrated this method using model compounds including fluorous-tagged fluorescein and antibiotic ciprofloxacin. We showed that fluorous interactions facilitated the loading of model molecules into fluorocarbon-containing contact lenses, and that the release profiles exhibited sustained release. Contact lenses loaded with fluorous-tagged ciprofloxacin exhibited antimicrobial activity against Pseudomonas aeruginosa in vitro, while no cytotoxicity towards human corneal epithelial cells was observed. To mimic the tear turnover, we designed a porcine eye infection model under flow conditions. Significantly, the modified lenses also exhibited antimicrobial efficacy against Pseudomonas aeruginosa in the ex vivo infection model. Overall, utilizing fluorous chemistry, we can construct a drug delivery system that exhibits high drug loading capacity, sustained drug release, and robust biological activity.

Expert Views on Innovative Future Uses for Contact Lenses

Over the past 10 to 15 years, the availability of new materials and technologies has resulted in revolutionary concepts for contact lenses being proposed that go well beyond correcting vision. These novel uses include their prescribing to deliver topical ocular and systemic drugs, assist with ocular surface disease management, and limit the progression of myopia and novel methods to display visual information. How likely are these concepts to become commercially available, how successful will they be, and what are the potential issues to consider for them to come to market? To answer these questions, a panel of four experts were invited to discuss the benefits and pitfalls of these technologies and what challenges lay ahead of these concepts before their availability. Their responses provide a fascinating insight for the clinician into the likelihood of such revolutionary contact lenses being available in a clinical setting.

Small-molecule detection in thiol-yne nanocomposites via surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) is generally performed on planar surfaces, which can be difficult to prepare and may limit the interaction of the sensing surface with targets in large volume samples. We propose that nanocomposite materials can be configured that both include SERS probes and provide a high surface area-to-volume format, i.e., fibers. Thiol-yne nanocomposite films and fibers were fabricated using exposure to long-wave ultraviolet light after the inclusion of gold nanoparticles (AuNPs) functionalized with thiophenol. A SERS response was observed that was proportional to the aggregation of the AuNPs within the polymers and the amount of thiophenol present. Overall, this proof-of-concept fabrication of SERS active polymers indicated that thiol-yne nanocomposites may be useful as durable film or fiber SERS probes. Properties of the nanocomposites were evaluated using various techniques including UV-vis spectroscopy, μ-Raman spectroscopy, dynamic mechanical analysis, differential scanning calorimetry, thermogravimetric analysis, and transmission electron microscopy.

Transparent and flexible supercapacitors with single walled carbon nanotube thin film electrodes

We describe a simple process for the fabrication of transparent and flexible, solid-state supercapacitors. Symmetric electrodes made up of binder-free single walled carbon nanotube (SWCNT) thin films were deposited onto polydimethylsiloxane substrates by vacuum filtration followed by a stamping method, and solid-state supercapacitor devices were assembled using a gel electrolyte. An optical transmittance of 82% was found for 0.02 mg of SWCNTs, and a specific capacitance of 22.2 F/g was obtained. The power density can reach to 41.5 kW · kg(-1) and shows good capacity retention (94%) upon cycling over 500 times. Fabricated supercapacitors will be relevant for the realization of transparent and flexible devices with energy storage capabilities, displays and touch screens in particular.

Cultivation of limbal epithelial cells on electrospun poly (lactide-co-glycolide) scaffolds for delivery to the cornea

In delivering tissues to the body, both natural and synthetic materials have been used. Currently, a natural membrane, the human amniotic membrane (AM), is used to deliver limbal epithelial cells (LEC) to the cornea. AM presents inherent problems with structural variation and requires extensive serological screening before use. Therefore alternatives are required to improve the predictability in clinical outcomes and economic costs associated with the use of this biological substrate. In this chapter, we describe the development of an alternative, structurally simple, synthetic biodegradable electrospun scaffold based on poly(lactide-co-glycolide) (PLGA: materials used in dissolvable sutures) to replace AM.

Screening of rat mesenchymal stem cell behaviour on polydimethylsiloxane stiffness gradients

Substrate stiffness is emerging as an effective tool for the regulation of cell behaviours such as locomotion, proliferation and differentiation. In order to explore the potential application of this biophysical tool, material platforms displaying lateral and continuously graded stiffness are advantageous since they allow the systematic exploration of adherent cell response to substrate stiffness and the tuning of the material to elicit the desired cell behaviour. Here, we demonstrate a simple approach towards the fabrication of polydimethylsiloxane (PDMS) stiffness gradients (with an indentation modulus of 190 kPa-3.1 MPa across a 12 mm distance) by means of a temperature gradient during curing. We then apply these stiffness gradients to the screening of osteogenic differentiation in rat mesenchymal stem cells (rMSCs). Our proof-of-principle results show that mineralization of rMSCs is strongly dependent on the PDMS substrate stiffness, but is also influenced by the display of extracellular matrix proteins preadsorbed on the gradients. This screening capability holds tremendous potential for the design of improved implant materials and tissue engineering scaffolds.

Tissue-regenerating, vision-restoring corneal epithelial stem cells

The cornea, the most anterior segment of the eye, provides us with exquisite vision. Unlike other vital tissues, it is poorly protected from the environment and is thus reliant on a self-renewal program to preserve integrity. This function is reserved for corneal epithelial stem cells located in the basal layer of the limbus, a narrow transition zone that segregates the peripheral cornea from the adjacent conjunctiva. Under physiological conditions, these cells replenish the corneal epithelium when mature or traumatized cells are lost. However, when the limbus is extensively damaged, stem cell activity is compromised, resulting in a condition known as limbal stem cell deficiency (LSCD). This disease is characterized by corneal neovascularization and persistent epithelial defects which impair vision. Over the past 20 years a myriad of treatment options have been developed for LSCD, most of which incorporate stem cell transplantation. Due to the disadvantages associated with the use of allogeneic and xenogeneic material, researchers are currently focusing on refining techniques involving autologous limbal tissue transplantation and are delving into the possibility that stem cells found in other organs can provide an alternative source of corneal epithelium. Determining where donor stem cells reside on the recipient's ocular surface and how long they remain viable will provide further insights into improving current therapeutic options for patients with LSCD.

Using poly(lactide-co-glycolide) electrospun scaffolds to deliver cultured epithelial cells to the cornea

Aims: To assess the potential of electrospun poly(lactide-co-glycolide) membranes to provide a biodegradable cell carrier system for limbal epithelial cells. Material & methods: 50:50 poly(lactide-co-glycolide) scaffolds were spun, sterilized and seeded with primary rabbit limbal epithelial cells. Cells were cultured on the scaffolds for 2 weeks and then examined by confocal microscopy, cryosectioning and scanning-electron microscopy. The tensile strength of scaffolds before and after annealing and sterilization was also studied. Results: The limbal cells had formed a continuous multilayer of cells on either side of the scaffold. Scaffolds with cells showed signs of the onset of degradation within 2 weeks in culture media at 37°C. Scaffolds that were annealed resulted in a more brittle and stiff mat. Conclusions: We suggest this carrier membrane could be used as a replacement for the human amniotic membrane in the treatment of limbal stem cell deficiency, lowering the risk of disease transmission to the patient.

Use of human mesenchymal cells to improve vascularization in a mouse model for scaffold-based dermal regeneration

All engineered bioartificial structures developed for tissue regeneration require oxygen and nutrients to establish proper physiological functions. Aiming to improve vascularization during dermal regeneration, we combined the use of a bioartificial collagen scaffold and a defined human mesenchymal cell (MC) line. This cell line, termed V54/2, exhibits typical morphologic and immunohistochemical characteristics of MC. V54/2 cells seeded in the scaffold were able to survive, proliferate, and secrete significant amounts of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) during 2 weeks in vitro. To induce dermal regeneration, scaffolds with or without cells were transplanted in a nude mice full skin defect model. After 2 weeks of transplantation, scaffolds seeded with V54/2 cells showed more vascularization during the dermal regeneration process than controls, and the presence of human cells in the regenerating tissue was detected by immunohistochemistry. To confirm if local presence of angiogenic growth factors is sufficient to induce neovascularization, scaffolds were loaded with VEGF and bFGF and used to induce dermal regeneration in vivo. Results showed that scaffolds supplemented with growth factors were significantly more vascularized than control scaffolds (scaffolds without growth factors). The present work suggests that combined use of MC and bioartificial scaffolds induces therapeutic angiogenesis during the scaffold-based dermal regeneration process.

Surface modification of polydimethylsiloxane (PDMS) induced proliferation and neural-like cells differentiation of umbilical cord blood-derived mesenchymal stem cells

Stem cell-based therapy has recently emerged for use in novel therapeutics for incurable diseases. For successful recovery from neurologic diseases, the most pivotal factor is differentiation and directed neuronal cell growth. In this study, we fabricated three different widths of a micro-pattern on polydimethylsiloxane (PDMS; 1, 2, and 4 microm). Surface modification of the PDMS was investigated for its capacity to manage proliferation and differentiation of neural-like cells from umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs). Among the micro-patterned PDMS fabrications, the 1 microm-patterned PDMS significantly increased cell proliferation and most of the cells differentiated into neuronal cells. In addition, the 1 microm-patterned PDMS induced an increase in cytosolic calcium, while the differentiated cells on the flat and 4 microm-patterned PDMS had no response. PDMS with a 1 microm pattern was also aligned to direct orientation within 10 degrees angles. Taken together, micro-patterned PDMS supported UCB-MSC proliferation and induced neural like-cell differentiation. Our data suggest that micro-patterned PDMS might be a guiding method for stem cell therapy that would improve its therapeutic action in neurological diseases.