Synthetic Poly(Vinylalcohol)-Based Membranes for Cartilage Surgery and Repair.

Cell-based therapies for cartilage repair are continually being developed to treat osteoarthritis. The cells are either introduced directly by intra-articular injection or via a cell-seeded matrix scaffold. Here, poly(vinylalcohol)-based membranes are developed to be used for mesenchymal stem cell implantation in cartilage repair procedures, having controllable physicochemical properties such as porosity, mechanical strength, and permeability, and a unique self-sealing property. The membranes possess a bilayer structure with a less porous layer providing mechanical strength and selective permeability, exhibit an elastic modulus of between 0.3 and 0.9 MPa, and are permeable to molecules <40 kDa, which is in the range of cartilage permeability. Three different peptide ligands with the sequences Ac-GCGYGRGDSPG, Ac-GCG(OPG)4REGOFG(OPG)4, and Ac-GCG(OPG)7, respectively, are conjugated to the membranes and subject to in vitro cell adhesion and differentiation assays. Col I/Col II gene expression ratios indicated that the collagen-mimetic peptide, Ac-GCG(OPG)7, best supported mesenchymal stem cell differentiation into the chondrogenic lineage. Although low retention of the membrane is observed in vivo in a rabbit knee model, results suggest that the membrane was able to facilitate mesenchymal stem cell implantation and differentiation to chondrocytes. These PVA-based membranes provide a feasible, synthetic, off-the-shelf material for the delivery of stem cells, and can be modified for other surgical applications.

CHITIN--a promising biomaterial for tissue engineering and stem cell technologies.

Chitin, after cellulose, is the second most abundant natural polymer. With a 200-year history of scientific research, chitin is beginning to see fruitful application in the fields of stem cell and tissue engineering. To date, however, research in chitin as a biomaterial appears to lag far behind that of its close relative, chitosan, due to the perceived difficulty in processing chitin. This review presents methods to improve the processability of chitin, and goes on further to discuss the unique physicochemical and biological characteristics of chitin that favor it as a biomaterial for regenerative medicine applications. Examples of the latter are presented, with special attention on the qualities of chitin that make it inherently suitable as scaffolds and matrices for tissue engineering, stem cell propagation and differentiation.

Modified polyelectrolyte complex fibrous scaffold as a matrix for 3D cell culture.

The paradigm of scaffold tissue engineering relies on the provision of an appropriate environment for cell growth, which includes both structural support and the presentation of cellular signals. In terms of biosignal presentation, fibrous scaffolds by interfacial polyelectrolyte complexation (IPC) offer a clear advantage over other scaffold types as IPC scaffolds are formed using an aqueous-based, room-temperature process compatible with the incorporation of biological molecules. This paper establishes two primary methods for the chemical and biochemical modification of these scaffolds: (i) physical entrapment of the bioactive component, and (ii) covalent binding of the bioactive component. For the first method, extracellular matrix (ECM) proteins, collagen, fibronectin and laminin were drawn into the IPC fiber. For the second method, the cell adhesion peptide, RGD, was chemically conjugated to a thiol-active maleimidylated form of the scaffold. Immobilization of the bioactive components was characterized by confocal fluorescence microscopy, scanning electron microscopy (SEM) and BCA protein assay. The ECM proteins were distributed throughout the bulk and surface of the fiber. The ratio of covalently bound to physisorbed RGD was approximately 2:3. The performance of the various scaffolds as a matrix to maintain the differentiated function of primary hepatocytes showed that albumin levels in the supernatant were in the order of RGD-modified scaffold>collagen Type I-modified scaffold>fibronectin- or laminin-modified scaffold>unmodified scaffold>plate, while no clear trend in urea production could be discerned. Thus, IPC scaffolds offered a promising platform for the presentation of signals to cells, in this case, to influence their differentiated function.

The use of a polyelectrolyte fibrous scaffold to deliver differentiated hMSCs to the liver.

Liver transplantation as a therapy for liver failure is often hampered by a shortage of donor tissue. The delivery of liver-differentiated human mesenchymal stem cells (hMSCs) is a potential therapy to aid in liver regeneration. In this study, an RGD-modified chitosan-alginate polyelectrolyte complex (PEC) fibrous non-woven scaffold was employed to deliver differentiated hMSCs in vivo. Bone marrow-derived hMSCs were differentiated in vitro by a combination of extracellular matrix (ECM) and conditioned medium and seeded onto the RGD-modified chitosan-alginate fibrous scaffolds. The cell/scaffold construct was then implanted into the livers of a rat model, where 70% of the liver had been removed. Post-implantation analysis of the cell/scaffold constructs showed positive periodic acid-Schiff (PAS) staining for glycogen, and expression of the hepatic markers, AFP, CK19, CK18, albumin, HNF-3beta and MRP-2 by immunofluorescence labeling. In addition, human albumin was detectable in the rat serum by spot blot. These findings demonstrated that the RGD-modified chitosan-alginate fibrous scaffold was useful for delivering transdifferentiated hMSCs into the liver and maintaining the differentiated phenotype of the cells.

Polyelectrolyte complex membranes for specific cell adhesion.

The presentation of bioactive ligands on biomaterial surfaces is often confounded by the adsorption of proteins present in the biological milieu, rendering any type of cellular response nonspecific. We have engineered a polyelectrolyte complex membrane that demonstrates specific adhesion of various cell types for both two-dimensional (2D) and three-dimensional (3D) cell culture systems. Specific cell adhesion is achieved by a three-tiered structure: a silica cross-linked polycation as the bottom (first) tier, a nonfouling polyanion-poly(ethylene glycol) (PEG) conjugate as the intermediate (second) tier, and the cell-adhesion ligand as the top (third) tier. Each tier of the membrane was characterized in terms of chemical composition and dimensions. Epithelial cells (primary human cortical renal cells and a hepatocellular carcinoma cell line) cultured on the membranes exhibited little cell attachment on the polyanion-PEG second tier and good cell adhesion on the RGD-modified third tier. Thus, the second tier allowed the effect of cell adhesion due to the ligand (third tier) to be isolated and distinguished from nonspecific cell attachment to the first tier. For the culturing of cells in three dimensions, the three-tiered membrane system was applied using a highly swellable chitosan membrane as the first tier. The resulting cell-membrane construct was uniformly dispersed and centrifuged to form a matrix that interacted intimately with cells in the form of a pellet. Presentation of RGD in the latter format enhanced the viability of human mesenchymal stem cells (hMSCs) over controls without RGD.