Cell-type-specific adhesion onto polymer surfaces from mixed cell populations

Collagen--emerging collagen based therapies hit the patient

The choice of biomaterials available for regenerative medicine continues to grow rapidly, with new materials often claiming advantages over the short-comings of those already in existence. Going back to nature, collagen is one of the most abundant proteins in mammals and its role is essential to our way of life. It can therefore be obtained from many sources including porcine, bovine, equine or human and offer a great promise as a biomimetic scaffold for regenerative medicine. Using naturally derived collagen, extracellular matrices (ECMs), as surgical materials have become established practice for a number of years. For clinical use the goal has been to preserve as much of the composition and structure of the ECM as possible without adverse effects to the recipient. This review will therefore cover in-depth both naturally and synthetically produced collagen matrices. Furthermore the production of more sophisticated three dimensional collagen scaffolds that provide cues at nano-, micro- and meso-scale for molecules, cells, proteins and bulk fluids by inducing fibrils alignments, embossing and layered configuration through the application of plastic compression technology will be discussed in details. This review will also shed light on both naturally and synthetically derived collagen products that have been available in the market for several purposes including neural repair, as cosmetic for the treatment of dermatologic defects, haemostatic agents, mucosal wound dressing and guided bone regeneration membrane. There are other several potential applications of collagen still under investigations and they are also covered in this review.

A high throughput micro-array system of polymer surfaces for the manipulation of primary pancreatic islet cells

We developed a high throughput micro-arrayed polymer system for the study of polymer surfaces for islet cell culture. A micro-arrayed library with 496 different polymers was synthesized and used to examine attachment and insulin expression of islet cells. While most polymers were not supportive, several related polymers were identified as suitable ("hit's"). The "hit" arrays composed of "hit" polymers with 36 replicates were fabricated to confirm their capacities to support the attachment of islet cells, and these capacities were further validated in large surfaces. Notably, the attachment of islet cells on these synthetic polymeric films has been found to be as supportive as 804G supernatant coated tissue culture polystyrene dishes, one of the most extensively used substrates for the islet cell attachment. Interestingly, the polymeric surfaces optimal for a different cell type, hES derived cells, were distinct, highlighting the utility of these approaches for identifying cell type specific surfaces.

Surface characterization of extracellular matrix scaffolds

Extracellular matrix (ECM) scaffolds prepared from different tissue sources or using different methods have been demonstrated to have distinctive effects upon cell adhesion patterns and the ability to support and maintain differentiated phenotypes. It is unknown whether the molecular composition or the ultrastructure of the ECM plays a greater role in determining the phenotype of the cells with which it comes into contact. However, when implanted, the topology and ligand landscape of the material will determine the host molecules that bind and the type and behavior of cells that mediate the host response. Therefore, a comprehensive understanding of surface characteristics is essential in the design of scaffolds for specific clinical applications. The surface characteristics of ECM scaffolds derived from porcine urinary bladder, small intestine, and liver as well as the effects of two commonly used methods of chemical cross-linking upon UBM were investigated. Electron microscopy and time of flight secondary ion mass spectroscopy were used to examine the surface characteristics of the scaffolds. The results show that ECM scaffolds have unique morphologic and structural properties which are dependant on the organ or tissue from which the scaffold is harvested. Furthermore, the results show that the surface characteristics of an ECM scaffold are changed through chemical cross-linking.

Novel membranes and surface modification able to activate specific cellular responses

The design of new polymeric biomaterials together with new strategies to modify membrane surface are crucial to optimise cell-biomaterial interactions in vivo and in vitro biohybrid systems. In this study we report on the novel semipermeable membranes synthesised from a polymeric blend of modified polyetheretherketone and polyurethane able to support the long-term maintenance and differentiation of human liver cells and on the surface modification of polyethersulfone membranes by plasma polymerisation of acrylic acid monomers and by immobilization of arginine-glycine-aspartic acid (RGD) peptide through a hydrophilic "spacer arm" molecule. The performance of the modified and unmodified membranes was tested by evaluation of the liver function expression of primary human hepatocytes in terms of albumin production, protein secretion and drug biotransformation.

Effect of isoliquiritigenin on viability and differentiated functions of human hepatocytes maintained on PEEK-WC–polyurethane membranes

In this study, we tested the ability of microporous membranes synthesised from a polymeric blend of modified polyetheretherketone (PEEK-WC) and polyurethane (PU) to support long-term maintenance and differentiation of human liver cells. The effect of isoliquiritigenin (ISL), which is a component of liquorice extract, exhibiting growth stimulatory and antiproliferative dose-dependent effect was investigated by comparing cultures treated with ISL with those untreated. To this purpose, flat-sheet membranes were prepared by a blend of PEEK-WC and PU polymers by phase inverse technique. The morphological and physico-chemical properties were characterised, respectively, by scanning electron microscopy and water contact angle measurements. Human hepatocytes cultured on PEEK-WC-PU membranes were constant up to 1 month albumin production and urea synthesis as well as the synthesis of total proteins. The liver-specific functions were expressed at high levels when cells were cultured on membranes with respect to collagen. Also the biotransformation functions were maintained for all culture periods: the ISL elimination rate increased during the culture time and high values were measured up to 22 days. Thereafter, a decrease was observed. ISL stimulated the proliferation of hepatocytes cultured on both substrata but did not affect their liver-specific functions. Hepatocytes cultured on PEEK-WC-PU membranes responded very well to ISL and expressed high levels of P450 cytochrome. These results demonstrated that long-term maintenance of human liver differentiation can be achieved on PEEK-WC-PU membranes. The incubation with ISL at the investigated concentration could stimulate the proliferation of human hepatocytes in biohybrid systems.

Surface modification of biodegradable polyesters with fatty acid conjugates for improved drug targeting

We describe a general method for incorporating target ligands into the surface of biocompatible polyester poly(lactic-co-glycolic acid) (PLGA) 50/50 materials using fatty acids. Avidin-fatty acid conjugates were prepared and efficiently incorporated into PLGA. Avidin was chosen as an adaptor protein to facilitate the attachment of a variety of biotinylated ligands. We show that fatty acid preferentially associates with the hydrophobic PLGA matrix, rather than the external aqueous environment, facilitating a prolonged presentation of avidin over several weeks. We successfully applied this approach in both microspheres encapsulating a model protein, bovine serum albumin, and PLGA scaffolds fabricated by a salt-leaching method. Because of its ease, generality and flexibility, this strategy promises widespread utility in modifying the surface of PLGA-based materials for applications in drug delivery and tissue engineering.