New biomaterials are all the rage – especially in the Department of Oral Biotechnology, which was established at the Dental School and Hospital at the Freiburg University Medical Centre in 2008. The department’s laboratory manager, Prof. Dr. Thorsten Steinberg, takes an approach that is inspired by clinical application and aimed at developing biomaterials that support the wound healing process. This approach must, of necessity, include basic research, especially when it comes to determining the parameters that contribute to the enhanced feeling of well-being in the target tissue. Steinberg uses these parameters for developing biomaterials that are suitable for covering defects in the oral mucosa or the cornea.
Prof. Dr. Thorsten Steinberg transferred from Heidelberg to Freiburg with the department’s director, Prof. Dr. Pascal Tomakidi, to establish the Department of Oral Biotechnology at the Freiburg University Medical Centre. The department plans to use regenerative approaches for developing biomaterials tailored to the requirements of different body tissues. This requires Steinberg and Tomakidi to work closely with researchers from other disciplines, including colleagues from the fields of biology, materials research and development as well as regenerative medicine.
“Initially, we need to study the tissues and find out what requirements the tissues and their cells have,” says Steinberg, going on to add, “then we use this information as a basis for the development of new biomaterials.” The department’s laboratory is a GLP (good laboratory practice) certified laboratory, and is only one of two such GLP-accredited laboratories in Baden-Württemberg (the other is at the University of Tübingen). Only GLP-certified laboratories are entitled to conduct tests for assessing the safety or efficacy of medical products. This assures regulatory authorities that the data is generated from tests that have been carried out in accordance with certain quality standards and can thus be relied upon when making risk and safety assessments of medical products for which marketing authorisation has been sought. Steinberg believes that GLP accreditation is beneficial for academic laboratories seeking industry contracts.
A number of wound healing materials are already on the market, but there is a lack of bio-inspired materials for the regeneration and replacement of soft tissue. In addition to having a high regenerative potential, i.e. being able to heal rapidly, such tissues also need to fulfil clinical surgical standards requirements. Amongst other things, Steinberg is planning to develop a biomaterial for the effective treatment of periodontal diseases, periodontitis for example. The type of biomaterial Steinberg has in mind must be suitable for the treatment of deep wounds and stimulate the self-healing process.The Department of Oral Biotechnology not only focuses on the development of oral tissue replacements. Steinberg and Tomakidi have already established 3D culture systems that enable them to study the growth of new biomaterials under in vitro conditions. The scientists are able to grow equivalents of human skin, oral mucosa and cornea. “It goes without saying that the skin model cannot 100% reflect the in vivo situation, but we are able to achieve stratification, i.e. the formation of different skin layers, as well as the differentiation of the skin epithelium and the underlying connective tissue.”
The in vivo-like culture systems consist of a type I collagen carrier matrix. Type I collagen is also a component of human connective tissue and the fibroblasts that are embedded in this material feel very comfortable and thrive very well. The scientists use this collagen-fibroblast matrix to grow human keratinocytes, cells that are found in the skin epithelium and the oral mucosa. “The keratinocytes and fibroblasts communicate with each other by way of the growth factors that they release,” explains Steinberg. The researchers use immortal keratinocytes. This means that the keratinocytes are genetically modified using viral HPV type 16 oncogenes, which interfere with cell cycle control. Normal keratinocytes have a specific replicative lifespan whereas immortal keratinocyte variants continue to divide whilst maintaining their normal differentiation behaviour, which is a prerequisite for 3D culture systems that seek to transfer the biomaterial test results to the in vivo situation. Steinberg and his colleagues already have an oral mucosal system that has the potential for commercial application, for example for the production of human skin and cornea equivalents.
Three-dimensional cell cultures are the basis for validating new biomaterials before they can be used for the treatment of patients. “We have identified basic research parameters that tell us the exact environment in which the cells feel comfortable enough to divide and differentiate, both in in vitro and in vivo wound healing situations. Epithelia will only grow when the conditions, and hence environment, is right. And this is what our research is all about,” Steinberg said.
Steinberg and the group of experts with whom he is working have already developed two different biomaterials – a hydrogel and a wound healing membrane – that are suitable for covering tissue defects. They have also assessed the biocompatibility of the biomaterials with 3D cell cultures. The polymer hydrogel has been developed for use in tissue holes resulting from disease or surgery, e.g. holes where teeth have been removed. The biologically absorbable gel was developed by Prof. Dr. Wilfried Weber’s team at the BIOSS Centre for Biological Signalling Studies at the University of Freiburg and has already undergone preclinical testing in the laboratory of the Department of Oral Biotechnology. It has been shown to have a volume-maintaining effect and also to mediate cell adhesion during the healing process. The researchers have equipped the gel surface with cell-adhesion sequences that are also found in collagen. These sequences enable many cell types to adhere to the hydrogel surface. The biochemical and biomechanical properties of a material are very important for boosting the tissue’s regenerative ability. “We need to make sure that the biomaterial and the body tissue adhere to each other so that the cells at the edge of the wound can migrate and divide.”
Steinberg is also working with Prof. Dr. Rolf Mülhaupt at the Institute of Macromolecular Chemistry at the University of Freiburg on the development of a wound healing membrane. The different membrane layers are produced by electrospinning, which uses an electrical charge to draw solid nanoscale fibres from a liquid that are then collected on a substrate. The wound healing membrane consists of a network of thick and thin synthetic and natural polymer threads with a diameter of between 90 nanometres and one micrometre. And what is the trick? “Cells located at the edges of wounds can migrate into this membrane and divide, thus producing a matrix that fills the wound from inside with the body’s own cells,” explains Steinberg. He has already successfully reconstituted 3D cultures of oral mucosal cells on this membrane. The membrane system is excellently suited for treating large defects such as large wounds of the skin or oral mucosa. The hydrogel can also be configured as a membrane or combined with a membrane for application to wounds where it is necessary to maintain the volume and cover a large area. “We can produce almost any kind of shape,” said Steinberg.
Further information:Prof. Dr. Thorsten SteinbergHead of Laboratory - Department of Oral BiotechnologyDental School and Hospital Freiburg University Medical CentreHugstetterstr. 5579106 FreiburgTel.: +49 (0)761 / 270 - 47460Fax.: +49 (0)761 / 270 - 47440E-mail: thorsten.steinberg(at)uniklinik-freiburg.de