Chemotactic penetration of keratocytes in ePTFE polymer in vitro

Layer-by-layer assembly of thin organic films on PTFE activated by cold atmospheric plasma

An air diffuse coplanar surface barrier discharge is used to activate the surface of polytetrafluoroethylene (PTFE) samples, which are subsequently coated with polyvinylpyrrolidone (PVP) and tannic acid (TAN) single, bi- and multilayers, respectively, using the dip-coating method. The surfaces are characterized by X-ray Photoelectron Spectroscopy (XPS), Attenuated Total Reflection – Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Atomic Force Microscopy (AFM). The XPS measurements show that with plasma treatment the F/C atomic ratio in the PTFE surface decreases, due to the diminution of the concentration of CF2 moieties, and also oxygen incorporation through formation of new C–O, C=O and O=C–O bonds can be observed. In the case of coated samples, the new bonds indicated by XPS show the bonding between the organic layer and the surface, and thus the stability of layers, while the gradual decrease of the concentration of F atoms with the number of deposited layers proves the creation of PVP/TAN bi- and multi-layers. According to the ATR-FTIR spectra, in the case of PVP/TAN multilayer hydrogen bonding develops between the PVP and TAN, which assures the stability of the multilayer. The AFM lateral friction measurements show that the macromolecular layers homogeneously coat the plasma treated PTFE surface.

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.

Covalent attachment of multilayers on poly(tetrafluoroethylene) surfaces

These studies demonstrate a new approach of producing multifunctionalized coatings on poly(tetrafluoroethylene) (PTFE) surfaces by covalent attachments of multilayers (CAM) of heparin (HP) and poly(ethylene glycol) (PEG). This process can be universally applied to other covalently bonded species and was facilitated by microwave plasma reactions in the presence of maleic anhydride which, upon ring-opening and hydrolysis, provided covalent attachment of COOH groups to PTFE. These studies showed that alternating layers of PEG and HP can be covalently attached to COOH-PTFE surfaces, and the volume concentration and surface density of PEG and HP on the PTFE surface achieved by the CAM were 7.02-6.04 × 10(-3) g/cm(3) (2.1-1.8 × 10(-7) g/cm(2)) and 9.3-8.7 × 10(-3) g/cm(3) (2.8-2.6 × 10(-7) g/cm(2)), respectively. The CAM process may serve numerous applications when the covalent modification of inert polymeric substrates is required and particularly where the presence of bioactive species for biocompatibility enhancement is desirable.

Antibacterial Surfaces on Expanded Polytetrafluoroethylene; Penicillin Attachment

Expanded polytetrafluoroethylene (ePTFE) was chemically modified to retard the growth of Staphylococcus aureus bacteria. This was accomplished by microwave plasma reactions in the presence of maleic anhydride (MA) to create acid functional groups on ePTFE surfaces, followed by esterification reactions with 200 and 600 molecular weight linear polyethylene glycol (PEG). Such surfaces were utilized for further reactions with penicillin (PEN) through etherification reactions to create anti-microbial surfaces. These reactions resulted in surface morphological changes, and spectroscopic analysis using attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT-IR) revealed the formation of ester linkages resulting from reactions between PEN and PEG functionalities. Antibacterial activities were evaluated by a series of experiments where PEN-modified ePTFE specimens were immersed in a liquid aureus culture, and the bacteria growth was quantified by measuring % absorbance of the suspension at 600 nm wavelength. The lowest absorbance was observed for the solution containing PEN-PEG-MA-ePTFE specimens, thus showing highly effective anti-bacterial activity toward gram-positive Staphylococcus aureus bacteria. To our best knowledge, this is the first study that shows PEN-ePTFE surface modifications that are effective against gram-positive aureus bacteria.

Growth factors in the anterior segment: role in tissue maintenance, wound healing and ocular pathology

A number of growth factors and their associated receptors, including epidermal growth factor, transforming growth factor-beta, keratinocyte growth factor, hepatocyte growth factor, fibroblast growth factor and platelet-derived growth factor have been detected in the anterior segment of the eye. On binding to cellular receptors, these factors activate signalling cascades, which regulate functions including mitosis, differentiation, motility and apoptosis. Production of growth factors by corneal cells and their presence in the tear fluid and aqueous humour is essential for maintenance and renewal of normal tissue in the anterior eye and the prevention of undesirable immune or angiogenic reactions. Growth factors also play a vital role in corneal wound healing, mediating the proliferation of epithelial and stromal tissue and affecting the remodelling of the extracellular matrix (ECM). These functions depend on a complex interplay between growth factors of different types, the ECM, and regulatory mechanisms of the affected cells. Imbalances may lead to deficient wound healing and various ocular pathologies, including edema, neovascularization and glaucoma. Growth factors may be targeted in therapeutic ophthalmic applications, through exogenous application or selective inhibition, and may be used to elicit specific cellular responses to ophthalmic materials. A thorough understanding of the mechanism and function of growth factors and their actions in the complex environment of the anterior eye is required for these purposes. Growth factors, their function and mechanisms of action as well as the interplay between different growth factors based on recent in vitro and in vivo studies are presented.