Materials used in contact with the human body are called biomaterials. Depending on the intended purpose, these materials should be inert, i.e. they should not cause any reactions of the surrounding tissue, or they should specifically direct the surrounding cells in a predetermined direction. We are investigating cell/biomaterial interactions to identify and optimize suitable combinations for bone replacement and cardiovascular tissue engineering. The biomaterials used are mainly polymers and ceramics. As main cell type we use adult multipotent mesenchymal stem cells, which differentiate into bone and smooth muscle cells. In addition, mesenchymal stem cells produce cytokines and growth factors that support wound healing and regeneration processes.

Mesenchymal stem cells

Mesenchymal stem cells (MSC) are adult, multipotent stem cells which can be isolated out of diverse tissue, such as bone marrow, umbilical cord Wharton´s Jelly, adipose tissue or placenta. They possess a self-renewal and a differentiation potential and can be differentiated in vitro e.g. towards bone, cartilage and adipose cells. Besides proliferation and differentiation, MSC release cytokines involved in diverse processes (angiogenesis, fibrosis, extracellular matrix remodelling) and they can direct immune responses. Thus, MSC are a promising cell type for Regenerative Medicine and Tissue Engineering.

Biomaterials

Classical biomaterials are ceramics, metals and polymers. There is a huge variety of biomaterials for medical funcions. Biocompatibility is very important for each biomaterial. This means that it has to comply with a specific function at a very specific area within or on the body, that it is non-toxic for adjacent cells and does not induce inflammation or rejection. So biocompatibility is related to in vivo situations, while in vitro, only cytocompatibility or cytotoxicity can be analyzed. Analyses are in accordance with the ISO 10993-5 „Prüfung auf in vitro-Zytotoxizität“.

The impact of biomaterials on a specific cell type can be induced or directed by diverse parameters, e.g. biomaterial chemistry, physical properties like the wettability, surface charge, and electrical conductivity. Besides, the surface topography has a strong impact on adherend cells.

Stem Cell/Biomaterial Interactions

There are two main goals in the focus of stem cell direction via biomaterial properties: stem cell proliferation or directed differentiation without additional differentiation factors. Besides iterative analyses of cell behaviour on single biomaterials, high-throughput analyses are developed in the last decade to investigate cell/biomaterial interactions. Nowadays, biomaterial arrays are suitable tools to analyze large sample sizes in parallel with the aim to identify cell/biomaterial combinations for tissue engineering applications.

Tissue Engineering

Tissue Engineering is an interdisciplinary research field combining the principles of natural and engineering science to develop biological substitutes to restore, maintain or improve tissue function (Langer und Vacanti, 1993). In most cases, a tissue engineering construct is composed of three main components, the biomaterial (scaffold), the cells and biochemical factors. It is of importance to understand the influence of a biomaterial on cell behaviour and to investigate their interaction in in vivo models.

Further Reading