"The body's dynamic is often forgotten"

Photo: Smiling man with brown hair_Michael Doser

Today biomaterial has to fulfil high standards and requirements. But some essential question still remain: What is already state-of-the-art? Which kind of material can be transformed to the "ideal biomaterial" and which branches of research have a future?

COMPAMED.de spoke with Professor Michael Doser, Development Director Biomedical Engineering and Deputy Director of the Institute of Textile and Process Engineering of the German Institutes for Textile and Fibre Research Denkendorf.

COMPAMED.de: Professor Doser, Biomaterials are increasingly the focus of scientific research. What new materials have gained entry into medical technology by now?

Michael Doser: Many projects are being expedited in biomaterials research but ultimately only very few of them are being put into practice. Initially many materials were being used, that were primarily developed for technical applications. Today special materials are being developed for medical applications. Biomaterials can be used in very different areas, ranging from wound dressing to materials that are implanted into the body. At this point in many cases synthetic materials are replacing static materials such as metals, since they are more biocompatible. They adapt better to the elastic substances of the body.

COMPAMED.de:Which functions do these materials already take on in practice?

Doser: There is an interesting example for this: the cages. Cages are molds that are placed between vertebras, for instance for spinal disk or general vertebral body issues. This way two neighboring vertebras can fuse via so-called cages. Ever since titanium has been known as a biocompatible material, the cages are made from this material. Today there are more and more cages made of polyetheretherketone (PEEK).

Another interesting example is the development of hernia meshes. These are mostly two-dimensional, wide-meshed nets made of monofilament polypropylene fibers that are being used for hernia repairs. In parts already absorbable, partially absorbable or self-fixating hernia mesh is being produced. Titanium-coated mesh is also a new development. One process that’s called PACVD (Plasma Activated Chemical Vapor Deposition) leads to a titanium surface that is being accepted and better tolerated by the tissue than the hydrophobic synthetic fabric polypropylene. We were able to demonstrate improved cell attachement which produces many fewer inflammatory reactions with titanium mesh than with traditional mesh.

COMPAMED.de: What measures have to be taken to optimally prepare biomaterials such as polymer or ceramics for use as medical devices?

Doser: Needless to say, biocompatibility is a prerequisite for these materials. Based on the definition by Professor Williams from Liverpool, biocompatible material not only has to be nonhazardous, but also has to produce an appropriate response in the tissue. This means that all materials that are being used in the body or that have direct contact with the body evoke a reaction. There are no inert biomaterials. In fact, we must try to control these reactions and while doing so avoid toxicity or infections. Most biomaterial developers however forget that the body is extremely dynamic. This can be especially well seen in the connective tissue of the skin which constantly changes the matrix.

Cells only adhere to implanted material in punctiform and they never adhere directly, but always through a matrix they produce, for instance one made of collagen. If you closely examine the adhesion, very specific sequences can be discovered on these matrix materials to which they adhere. That is for example a RGD peptide sequence, an amino acid sequence of the three amino acids arginine, glycine and asparagine. This sequence particularly occurs in the extracellular matrix (connective tissue). Researchers have tried binding this RGD-sequence to the biomaterial. But this makes no sense in my opinion. Although the cell recognizes it and also adheres for a short time, since it is extremely dynamic however just like the tissue, it will eventually detach from the static material. In biomaterials research, this body dynamic is often forgotten.



COMPAMED.de: What procedures are used to check biocompatibility and the biochemical and biological interactions of these materials?

Doser: Sometimes you cannot figure out in advance what effect a material will have on the human tissue. As a matter of principle however, we have to check on questions of biocompatibility through the appropriate in-vitro testing. There is a set of standards for this, the ISO 10993 series. With these sets of standards, biocompatibility of different materials can be checked very well – starting with cytotoxicity, blood compatibility all the way to degradation behavior. In the majority of cases we then conduct an animal experiment to test whether the material can also achieve the functionality we expect from it. Ultimately, the results are backed up by a clinical trial.

COMPAMED.de: New biomaterials can also have a positive influence on the risk of infection. How should we picture this? What risks are possibly involved in this?

Doser: Lately, materials that contain silver and emit silver ions are increasingly hitting the market. They are supposed to destroy so-called biofilms containing microorganisms that can form under certain conditions or prevent the development of these biofilms. On the one hand we know that silver ions can be effective in killing off bacteria, on the other hand they barely cause resistances. If it is released in small amounts, metallic silver barely exhibits cytotoxicity.

COMPAMED.de: Which biomaterials are still in the research stage and what criteria do they still need to meet in the future for the use in the field?

Doser: Regenerative medicine is the future of medical science. However, the biggest problem is the integration of newly cultured tissue into the existing health tissue. That’s why today we know in regenerative medicine that we have to use biomaterials that control the regenerative process in the body. In the future, it will be the “guided tissue regeneration“ that systematically controls regeneration. This can be achieved through a combination of biomaterials and active mediators like for example growth factors. Carrier materials will also be of larger interest in the future. The significance of natural materials such as collagen, fibrin and carbohydrate-based biomaterials like alginate, cyclodextrin and cytosan will increase. These substances are currently very intensely being tested for different applications.

The interview was conducted by Diana Posth and translated by Elena O'Meara.