Vascular endothelial growth factor-releasing scaffolds enhance vascularization and engraftment of hepatocytes transplanted on liver lobes

Intestinal smooth muscle cell maintenance by basic fibroblast growth factor

Intestinal tissue engineering is a potential therapy for patients with short bowel syndrome. Tissue engineering scaffolds that promote smooth muscle cell proliferation and angiogenesis are essential toward the regeneration of functional smooth muscles for peristalsis and motility. Since basic fibroblast growth factor (bFGF) can stimulate smooth muscle proliferation and angiogenesis, the delivery of bFGF was employed to stimulate proliferation and survival of primary intestinal smooth muscle cells. Two methods of local bFGF delivery were examined: the incorporation of bFGF into the collagen coating and the encapsulation of bFGF into poly(D,L-lactic-co-glycolic acid) microspheres. Cell-seeded scaffolds were implanted into the omentum and were retrieved after 4, 14, and 28 days. The seeded cells proliferated from day 4 to day 14 in all implants; however, at 28 days, significantly higher density of implanted cells and blood vessels was observed, when 10 microg of bFGF was incorporated into the collagen coating of scaffolds as compared to scaffolds with either no bFGF or 1 microg of bFGF in collagen. Microsphere encapsulation of 1 microg of bFGF produced similar effects as 10 microg of bFGF mixed in collagen and was more effective than the delivery of 1 microg of bFGF by collagen incorporation. The majority of the implanted cells also expressed alpha-smooth muscle actin. Scaffolds coated with microsphere-encapsulated bFGF and seeded with smooth muscle cells may be a useful platform for the regeneration of the intestinal smooth muscle.

Liver cell transplantation for Crigler-Najjar syndrome type I: Update and perspectives

Liver cell transplantation is an attractive technique to treat liver-based inborn errors of metabolism. The feasibility and efficacy of the procedure has been demonstrated, leading to medium term partial metabolic control of various diseases. Crigler-Najjar is the paradigm of such diseases in that the host liver is lacking one function with an otherwise normal parenchyma. The patient is at permanent risk for irreversible brain damage. The goal of liver cell transplantation is to reduce serum bilirubin levels within safe limits and to alleviate phototherapy requirements to improve quality of life. Preliminary data on Gunn rats, the rodent model of the disease, were encouraging and have led to successful clinical trials. Herein we report on two additional patients and describe the current limits of the technique in terms of durability of the response as compared to alternative therapeutic procedures. We discuss the future developments of the technique and new emerging perspectives.

The effect of cross-linking of collagen matrices on their angiogenic capability

The poor vascularization rate of matrices following cell invasion is considered to be one of the main shortcomings of scaffolds used in tissue engineering. In the past decade much effort has been directed towards enhancing the angiogenic potential of biomaterials. A great many studies have appeared reporting about enhancement of vascularization by immobilizing angiogenic factors, such as vascular endothelial growth factor (VEGF) and basic fibroblast growth factor-2 (FGF-2). We have also tried to achieve this goal by modifying collagen matrices by covalent incorporation of heparin into the matrices and loading them with VEGF. We and others have observed that loading angiogenic factors to heparinized materials markedly increases angiogenic capacity. In the present paper we also investigated the angiogenic properties of collagen matrices which were only cross-linked, i.e. in the absence of heparin. The angiogenic capacity of the modified matrices was evaluated using the chorioallantoic membrane assay. Differences in angiogenic potential were deduced from macroscopic and microscopic analyses of the chorioallantoic membrane, as well as from dry weight changes. Cross-linked only matrices and matrices both cross-linked and heparinized appeared to show a significantly larger angiogenic potential than unmodified matrices. As previously observed, loading VEGF to these matrices further stepped up angiogenic potential. Quite surprisingly, cross-linking had a substantial impact on angiogenic potential. In terms of magnitude, this effect was similar to the effect of loading VEGF to heparinized matrices. Both modification procedures resulted in an increase of average pore size within the collagen matrices, and this observation may explain the more rapid invasion of mouse fibroblasts into cross-linked and heparinized matrices. Form changes of the implants were also monitored during the in vivo contacts: cross-linked and heparinized matrices showed far better resistance against contraction, as compared to unmodified matrices. Results from the chorioallantoic membrane assay experiments were compared with data obtained from rat model experiments, which confirmed the results from the chorioallantoic membrane assay. This relatively simple assay was again shown to be extremely helpful in evaluating and predicting the angiogenic capabilities of biomaterials for use in tissue engineering and wound healing.

Stem cells for liver tissue repair: Current knowledge and perspectives

Stem cells from extra- or intrahepatic sources have been recently characterized and their usefulness for the generation of hepatocyte-like lineages has been demonstrated. Therefore, they are being increasingly considered for future applications in liver cell therapy. In that field, liver cell transplantation is currently regarded as a possible alternative to whole organ transplantation, while stem cells possess theoretical advantages on hepatocytes as they display higher in vitro culture performances and could be used in autologous transplant procedures. However, the current research on the hepatic fate of stem cells is still facing difficulties to demonstrate the acquisition of a full mature hepatocyte phenotype, both in vitro and in vivo. Furthermore, the lack of obvious demonstration of in vivo hepatocyte-like cell functionality remains associated to low repopulation rates obtained after current transplantation procedures. The present review focuses on the current knowledge of the stem cell potential for liver therapy. We discuss the characteristics of the principal cell candidates and the methods to demonstrate their hepatic potential in vitro and in vivo. We finally address the question of the future clinical applications of stem cells for liver tissue repair and the technical aspects that remain to be investigated.

Stem cells and scaffolds for vascularizing engineered tissue constructs

The clinical impact of tissue engineering depends upon our ability to direct cells to form tissues with characteristic structural and mechanical properties from the molecular level up to organized tissue. Induction and creation of functional vascular networks has been one of the main goals of tissue engineering either in vitro, for the transplantation of prevascularized constructs, or in vivo, for cellular organization within the implantation site. In most cases, tissue engineering attempts to recapitulate certain aspects of normal development in order to stimulate cell differentiation and functional tissue assembly. The induction of tissue growth generally involves the use of biodegradable and bioactive materials designed, ideally, to provide a mechanical, physical, and biochemical template for tissue regeneration. Human embryonic stem cells (hESCs), derived from the inner cell mass of a developing blastocyst, are capable of differentiating into all cell types of the body. Specifically, hESCs have the capability to differentiate and form blood vessels de novo in a process called vasculogenesis. Human ESC-derived endothelial progenitor cells (EPCs) and endothelial cells have substantial potential for microvessel formation, in vitro and in vivo. Human adult EPCs are being isolated to understand the fundamental biology of how these cells are regulated as a population and to explore whether these cells can be differentiated and reimplanted as a cellular therapy in order to arrest or even reverse damaged vasculature. This chapter focuses on advances made toward the generation and engineering of functional vascular tissue, focusing on both the scaffolds - the synthetic and biopolymer materials - and the cell sources - hESCs and hEPCs.

Induced differentiation and maturation of newborn liver cells into functional hepatic tissue in macroporous alginate scaffolds

The present work explores cell cultivation in macroporous alginate scaffolds as a means to reproduce hepatocyte terminal differentiation in vitro. Newborn rat liver cell isolates, consisting of proliferating hepatocytes and progenitors, were seeded at high cell density of 125 x 10(6)/cm(3) within the scaffold and then cultivated for 6 wk in chemically defined medium. Within 3 days, the alginate-seeded cells expressed genes for mature liver enzymes, such as tryptophan oxygenase, secreted a high level of albumin, and performed phase I drug metabolism. The cells formed compacted spheroids, establishing homotypic and heterotypic cell-to-cell interactions. By 6 wk, the spheroids developed into organoids, with an external mature hepatocyte layer covered by a laminin layer encasing inner vimentin-positive cells within a laminin-rich matrix also containing collagen. The hepatocytes presented a distinct apical surface between adjacent cells and a basolateral surface with microvilli facing extracellular matrix deposits. By contrast, viable adherent cells within collagen scaffolds presenting the identical porous structure did not express adult liver enzymes or secrete albumin after 6 wk. This study thus illustrates the benefits of cell cultivation in macroporous alginate scaffolds as an effective promoter for the maturation of newborn liver cells into functional hepatic tissue, capable of maintaining prolonged hepatocellular functions.

Vascular endothelial growth factor and dexamethasone release from nonfouling sensor coatings affect the foreign body response

Vascular endothelial growth factor (VEGF) and dexamethasone (DX) release from hydrogel coatings were examined as a means to modify tissue inflammation and induce angiogenesis. Antibiofouling hydrogels for implantable glucose sensor coatings were prepared from 2-hydroxyethyl methacrylate, N-vinyl pyrrolidinone, and polyethylene glycol. Microdialysis sampling was used to test the effect of the hydrogel coating on glucose recovery. VEGF-releasing hydrogel-coated fibers increased vascularity and inflammation in the surrounding tissue after 2 weeks of implantation compared to hydrogel-coated fibers. DX-releasing hydrogel-coated fibers reduced inflammation compared to hydrogel-coated fibers and had reduced capsule vascularity compared to VEGF-releasing hydrogel-coated fibers. Hydrogels that released both VEGF and DX simultaneously also showed reduced inflammation at 2 weeks implantation; however, no enhanced vessel formation was observed indicating that the DX diminished the VEGF effect. At 6 weeks, there were no detectable differences between drug-releasing hydrogel-coated fibers and control fibers. From this study, hydrogel drug release affected initial events of the foreign body response with DX inhibiting VEGF, but once the drug depot was exhausted these effects disappeared.

Membrane Bioreactor for Cell Tissues and Organoids

Progresses in polymeric membrane preparation and in the understanding and control of their transport properties make possible the design of novel membranes to be used for cell culture (e.g., hepatocytes, lymphocytes, pancreatic islets) in biohybrid systems such as therapeutic device or as in vitro model systems for studying the effects of various drugs and chemicals on cell metabolism. Special attention is paid to the design of the membrane with defined microstructure and physicochemical properties as well as to the importance of transport and physicochemical properties of the membrane in contact with the cells. The development of new biomaterials and bioreactors able to activate a specific response of the cells and to maintain cell differentiation for a long time is one of the most pertinent issues in the field of tissue engineering and regenerative medicine. Polymeric membranes are attractive for their selectivity and biostability characteristics in the use of biohybrid systems for cell culture. Semipermeable membranes act as a support for the adhesion of anchorage-dependent cells and allow the specific transport of metabolites and nutrients to cells and the removal of catabolites and specific products. Moreover, new membrane systems that have been recently realized as the membrane contactors might also potentially contribute to regenerative medicine and tissue engineering.

N/A

N/A

Scaffolds for liver tissue engineering

This review focuses on the expanding role for biomaterials and polymer scaffolds in liver tissue engineering. Studies are subdivided into in vitro and in vivo approaches. The in vitro section of the review discusses the challenges specific to liver tissue engineering, and how the choice of scaffold and its structure influences the success of the regenerative medicine strategy. The in vivo section evaluates early attempts to stimulate liver repair with cell and growth factor therapies, their failings and how current approaches aim to solve these problems.