Antimicrobial Nitric Oxide-Releasing Electrospun Dressings for Wound Healing Applications.

Nonhealing and chronic wounds represent a major problem for the quality of life of patients and have cost implications for healthcare systems. The pathophysiological mechanisms that prevent wound healing are usually multifactorial and relate to patient overall health and nutrition, vascularity of the wound bed, and coexisting infection/colonization. Bacterial infections are one of the predominant issues that can stall a wound, causing it to become chronic. Successful wound healing often depends on weeks or months of antimicrobial therapy, but this is problematic given the rise in multidrug-resistant bacteria. As such, alternatives to antibiotics are desperately needed to aid the healing of chronic, and even acutely infected wounds. Nitric oxide (NO) kills bacteria through a variety of mechanisms, and thus, bacteria have shown no tendency to develop resistance to NO as a therapeutic agent and therefore can be a good alternative to antibiotic therapy. In this paper, we report on the development of NO-releasing electrospun membranes fabricated from polycaprolactone (PCL)/gelatin blends and optimized to reduce bacterial infection. The NO payload in the membranes was directly related to the number of amines (and hence the amount of gelatin) in the blend. Higher NO payloads corresponded with a higher degree of antimicrobial efficacy. No cytotoxicity was observed for electrospun membranes, and an in vitro wound closure assay demonstrated closure within 16 h. The results presented here clearly indicate that these NO-releasing electrospun membranes hold significant promise as wound dressings due to their antimicrobial activity and biocompatibility.

Characterization of Tunable Poly-ε-Lysine-Based Hydrogels for Corneal Tissue Engineering.

A family of poly-ε-lysine hydrogels can be synthesized by crosslinking with bis-carboxylic acids using carbodiimide chemistry. In addition to creating hydrogels using a simple cast method, a fragmented method is used to introduce increased porosity within the hydrogel structure. Both methods have created tunable characteristics ranging in their mechanical properties, transparency, and water content, which is of interest to corneal tissue engineering and can be tailored to specific cellular needs and applications. With a worldwide shortage of cornea donor tissue available for transplant and limitations including rejection and potential infection, a synthetic material that can be used as a graft, or a partial thickness corneal replacement, would be an advantageous treatment method. These hydrogels can be tuned to have similar mechanical and transparency properties to the human cornea. They also support the attachment and growth of corneal epithelial cells and the integration of corneal stromal cells.

Multivalent Presentations of Glycomimetic Inhibitor of the Adhesion of Fungal Pathogen Candida albicans to Human Buccal Epithelial Cells.

Candida albicans causes some of the most prevalent hospital-acquired fungal infections, particularly threatening for immunocompromised patients. C. albicans strongly adheres to the surface of epithelial cells so that subsequent colonization and biofilm formation can take place. Divalent galactoside glycomimetic 1 was found to be a potent inhibitor of the adhesion of C. albicans to buccal epithelial cells. In this work, we explore the effect of multivalent presentations of glycomimetic 1 on its ability to inhibit yeast adhesion and biofilm formation. Tetra-, hexa-, and hexadecavalent displays of compound 1 were built on RAFT cyclopeptide- and polylysine-based scaffolds with a highly efficient and modular synthesis. Biological evaluation revealed that the scaffold choice significantly influences the activity of the lower valency conjugates, with compound 16, constructed on a tetravalent polylysine scaffold, found to inhibit the adhesion of C. albicans to human buccal epithelial cells more effectively than the glycomimetic 1; however, the latter performed better in the biofilm reduction assays. Interestingly, the higher valency glycoconjugates did not outperform the anti-adhesion activity of the original compound 1, and no significant effect of the core scaffold could be appreciated. SEM images of C. albicans cells treated with compounds 1, 14, and 16 revealed significant differences in the aggregation patterns of the yeast cells.

Material Characterisation and Stratification of Conjunctival Epithelial Cells on Electrospun Poly(ε-Caprolactone) Fibres Loaded with Decellularised Tissue Matrices.

The conjunctiva, an under-researched yet incredibly important tissue, plays key roles in providing protection to the eye and maintaining homeostasis of its ocular surface. Multiple diseases can impair conjunctival function leading to severe consequences that require surgical intervention. Small conjunctival defects can be repaired relatively easily, but larger defects rely on tissue grafts which generally do not provide adequate healing. A tissue engineering approach involving a biomaterial substrate capable of supporting a stratified epithelium with embedded, mucin-secreting goblet cells offers a potential solution. As a first step, this study aimed to induce stratification of human conjunctival epithelial cells cultured on electrospun scaffolds composed from poly(ε-caprolactone) (PCL) and decellularised tissue matrix (small intestinal submucosa (SIS) or urinary bladder matrix (UBM)) and held at the air/liquid interface. Stratification, up to 5 cell layers, occurred more frequently on scaffolds containing PCL + UBM. Incorporation of these decellularised tissue matrices also impacted material properties, with significant changes occurring to their fibre diameter, tensile properties, and chemical composition throughout the scaffold structure compared to PCL alone. These matrix containing scaffolds warrant further long-term investigation as a potential advanced therapy medicinal product for conjunctiva repair and regeneration.

Plasma Polymer Coatings To Direct the Differentiation of Mouse Kidney-Derived Stem Cells into Podocyte and Proximal Tubule-like Cells.

Kidney disease is now recognized as a global health problem and is associated with increased morbidity and mortality, along with high economic costs. To develop new treatments for ameliorating kidney injury and preventing disease progression, there is a need for appropriate renal culture systems for screening novel drugs and investigating the cellular mechanisms underlying renal pathogenesis. There is a need for in vitro culture systems that promote the growth and differentiation of specialized renal cell types. In this work, we have used plasma polymerization technology to generate gradients of chemical functional groups to explore whether specific concentrations of these functional groups can direct the differentiation of mouse kidney-derived stem cells into specialized renal cell types. We found that amine-rich (-NH2) allylamine-based plasma-polymerized coatings could promote differentiation into podocyte-like cells, whereas methyl-rich (CH3) 1,7-octadiene-based coatings promoted differentiation into proximal tubule-like cells (PTC). Importantly, the PT-like cells generated on the substrates expressed the marker megalin and were able to endocytose albumin, indicating that the cells were functional.

Biomaterials for Regenerative Medicine Approaches for the Anterior Segment of the Eye.

The role of biomaterials in tissue engineering and regenerative medicine strategies to treat vision loss associated with damage to tissues in the anterior segment of the eye has been studied for several years. This has mostly involved replacement and support for the cornea and conjunctiva. These are complex tissues with specific functional requirements for different parts of the tissue. Amniotic membrane (AM) is used in clinical practice to transplant autologous or allogenic cells to the corneal surface. Fibrin gels have also progressed to clinical use under specific conditions. Alternatives to AM such as collagen gels, other natural materials, for example keratin and silks, and synthetic polymers have received considerable attention in laboratory and animal studies. This experience is building a body of evidence to demonstrate the potential of tissue engineering and regenerative medicine in corneal and conjunctival reconstruction and can also lead to other applications in the anterior segment of the eye, for example, the trabecular meshwork. There is a real clinical need for new procedures to overcome vision loss but there are also opportunities for developments in ocular applications to lead to biomaterials innovations for use in other clinical areas.

Matching seed to site by climate similarity: Techniques to prioritize plant materials development and use in restoration.

Land management agencies are increasing the use of native plant materials for vegetation treatments to restore ecosystem function and maintain natural ecological integrity. This shift toward the use of natives has highlighted a need to increase the diversity of materials available. A key problem is agreeing on how many, and which, new accessions should be developed. Here we describe new methods that address this problem. Our methods use climate data to calculate a climate similarity index between two points in a defined extent. This index can be used to predict relative performance of available accessions at a target site. In addition, the index can be used in combination with standard cluster analysis algorithms to quantify and maximize climate coverage (mean climate similarity), given a modeled range extent and a specified number of accessions. We demonstrate the utility of this latter feature by applying it to the extents of 11 western North American species with proven or potential use in restoration. First, a species-specific seed transfer map can be readily generated for a species by predicting performance for accessions currently available; this map can be readily updated to accommodate new accessions. Next, the increase in climate coverage achieved by adding successive accessions can be explored, yielding information that managers can use to balance ecological and economic considerations in determining how many accessions to develop. This approach identifies sampling sites, referred to as climate centers, which contribute unique, complementary, climate coverage to accessions on hand, thus providing explicit sampling guidance for both germplasm preservation and research. We examine how these and other features of our approach add to existing methods used to guide plant materials development and use. Finally, we discuss how these new methods provide a framework that could be used to coordinate native plant materials development, evaluation, and use across agencies, regions, and research groups.