Erdal Karamuk

Matrices for tissue engineering-scaffold structure for a bioartificial liver support system

This study proposes a new composite scaffold system. A woven polyethylenterephtalate (PET) fabric was coated on one side with a biodegradable PLGA film, in order to obtain a geometrically polarized scaffold structure for an bioartificial liver support system. The composite structure ensures the stability of the membrane during degradation of the membrane polymer. The mesh size of the composite does not significantly influence the degradation behavior. Hepatocyte culturing studies reveal that the formation of aggregates depends on the mesh size and on the pretreatment: The largest aggregates could be observed after 48 h when PVLA coating, large mesh size and EGF were combined. Thus, the combination of a geometrically structured, partially degradable scaffold with receptor-mediated cell attachment sites offers promising possibilities in liver tissue engineering.

Nondestructive three-dimensional evaluation of biocompatible materials by microtomography using synchrotron radiation

Microtomography based on synchrotron radiation sources is a unique technique for the 3D characterization of different materials with a spatial resolution down to about 1 micrometers . The interface between implant materials (metals, ceramics and polymers) and biological matter is nondestructively accessible, i.e. without preparation artifacts. Since the materials exhibit different x-ray absorption, it can become impossible to visualize implant material and tissue, simultaneously. Here, we show that coating of polymer implants, which are invisible in bone tissue, does not only improve the interfacial properties but also allows the imaging of the interface in detail. Titanium implants, on the other hand, absorb the x-rays stronger than bone tissue. The difference, however, is small enough to quantify the bone formation near interface. Another advantage of microtomography with respect to classical histology is the capability to examine samples in a hydrated state. We demonstrate that ceramic hollow spheres can be imaged before sintering and fibroblasts marked by OsO4 are visible on polymer textiles. Consequently, scaffolds of different materials designed for tissue engineering and implant coatings can be optimized on the basis of the tomograms.

Hydrogel-coated textile scaffolds as three-dimensional growth support for human umbilical vein endothelial cells (HUVECs): possibilities as coculture system in liver tissue engineering.

Three-dimensional (3-D) scaffolds offer an exciting possibility to develop cocultures of various cell types. Here we report chitosan–collagen hydrogel-coated fabric scaffolds with defined mesh size and fiber diameter for 3-D culture of human umbilical vein endothelial cells (HUVECs). These scaffolds did not require pre-coating with fibronectin and they supported proper HUVEC attachment and growth. Scaffolds preserved endothelial cell-specific cobblestone morphology and cells were growing in compartments defined by the textile mesh. HUVECs on the scaffold maintained the property of contact inhibition and did not exhibit overgrowth until the end of in vitro culture (day 6). MTT assay showed that cells had preserved mitochondrial functionality. It was also noted that cell number on the chitosan-coated scaffold was lower than that of collagen-coated scaffolds. Calcein AM and ethidium homodimer (EtD-1) dual staining demonstrated presence of viable and metabolically active cells, indicating growth supportive properties of the scaffolds. Actin labeling revealed absence of actin stress fibers and uniform distribution of F-actin in the cells, indicating their proper attachment to the scaffold matrix. Confocal microscopic studies showed that HUVECs growing on the scaffold had preserved functionality as seen by expression of von Willebrand (vW) factor. Observations also revealed that functional HUVECs were growing at various depths in the hydrogel matrix, thus demonstrating the potential of these scaffolds to support 3-D growth of cells. We foresee the application of this scaffold system in the design of liver bioreactors wherein hepatocytes could be cocultured in parallel with endothelial cells to enhance and preserve liver-specific functions.

Hydrogel-coated textile scaffolds as candidate in liver tissue engineering: II. Evaluation of spheroid formation and viability of hepatocytes.

In this study we evaluate the performance of primary rat hepatocytes and HepG2 cells on chitosan-collagen hydrogel-coated textile scaffolds. Light microscopy and electron microscopic observations showed attachment and aggregate formation tendency of hepatocytes on the scaffolds. As tested by the tetrazolium reduction (MTT) assay it was evident that cells had preserved mitochondrial functionality. It was also observed that pure collagen and collagen blended scaffolds allowed higher cell growth than pure chitosan scaffold. Fluorescent live/dead staining showed a metabolically active, viable cell population on all scaffold compositions with occurrence of few dead cells. Cell functionality was confirmed by secretion of albumin, which was maintained throughout culture period. Take collectively our results suggests that hydrogel-coated textile scaffolds could be promising for tissue-engineering applications, as they allow favorable hepatocyte attachment, spheroid formation and maintenance of function. These scaffolds could be useful for co-culturing hepatocytes and nonparenchymal endothelial cells in bioartificial liver support systems.

Embroidery Technology for Medical Textiles

Textile structures are widely used as medical implants to replace and support soft and load bearing tissues and they serve as scaffolds in tissue engineering applications. In this study the potential of embroidery technology is investigated for the development of textile scaffold structures for tissue engineering and for medical applications. In a comparative experimental study the influence of ingrowing tissue on the mechanics of the thereby formed vital-avital composite has been investigated. An interlock knitted fabric has been compared to a specially designed embroidered fabric and a gelatine matrix has been used to simulate the ingrown tissue. It could be shown that due to the specific structure of the embroidery, stiffening effects known from other textiles i.e. woven and knitted fabrics could be inhibited. This observation together with the potential structural variety of embroidered fabrics, makes them interesting candidates for medical textiles applied to mechanically stressed tissues.