DUTCH PROGRAMME FOR TISSUE ENGINEERING
Esther Middelkoop, Association of Dutch Burn Centres (ADBC),
Beverwijk, The Netherlands

CARTILAGE from the lab, an artificial liver from cultured liver cells? It should be possible within
ten years, according to scientist Dr Ruud Bank from TNO Prevention and Health Care; ‘Technically and scientifically there is impressive progress’. Dr Bank is vicepresident of the DPTE consortium. Aims of the programme are not only to reach further scientific improvements in cell cultures, but also to apply tissue engineered artificial organs in the clinic.

Tissue engineering has been surrounded by many promises from the very start of this discipline in science. To make new tissues which mimic the original ones in the body is an appealing concept leading to many new perspectives in medical practice. Medical specialists are confronted with worn-out body parts and limited replacement possibilities on a daily basis. Artificial materials hardly meet the needs and quality of the originals, donor organs are limited in availability and may be immunologically rejected. So what could be better than to produce replacement organs based on biological materials, with living cells, if necessary at the site of injury in the body?

Figure 1: DPTE is a consortium of research groups from almost all Dutch universities and academic
hospitals, joined by pioneering companies and supporting organizations.
The objective of DPTE is to build a strong, coordinated knowledge infrastructure that
integrates new knowledge, stimulates collaborations and facilitates utilization of Tissue Engineering products.
More information on this programme and contributors can be found on: www.dpte.nl

These goals are defined within the three technological platforms stem cells, biomaterials and bioreactors. Each of these platforms contains several scientific projects, in which scientists from different universities and research institutes
collaborate. Furthermore, translational projects have started for bone, cartilage, skin and blood vessels. For these areas the goal is to reach clinically applicable products at the end of the project.

Tissue engineering starts from individual cells. These may be stem cells, which can differentiate into many cell
types, or specialized cells. In general two processes are of importance: proliferation and, in case of stem cells, differentiation into the necessary cell type. ‘Proliferation of stem cells in general is not difficult to achieve. But if you do not create the correct circumstances, they may lose their ability to differentiate and thus their stem cell characteristics.

Above: Dr Esther Middelkoop, research director of the
Association of Dutch Burn Centres (ADBC).

An important research question is how, by which growth factors or hormones, this can be avoided.’ Also the multiplication of specialized cells may be cumbersome. ‘Cartilage cells will become skin cells after two cell divisions in
a culture flask. This is a very interesting phenomenon in itself, one specialized cell transforming into another specialized cell. Fifteen years ago we would have thought this was impossible. Therefore we need to find out under which culture conditions cells will keep their specific characteristics.

Above: The research group of Skin Tissue Engineering in DPTE:
Association of Dutch Burn Centres, Beverwijk; Matrix Biology, Radboud University, Nijmegen; Department
of Dermatology, Radboud University, Nijmegen; Department of Dermatology, VU Medical Centre, Amsterdam.

A large number of research groups are involved in this type of research.’ Bioreactors can create the correct culture conditions. Research groups in Twente and Eindhoven universities are developing monitoring systems which allow measurements during the culturing process. ‘In this way you can follow the culture process without having to stop it’, explains biochemist Ruud Bank. Isolated cells are helpless. They need a medium or scaffold for growth and correct function. This is comparable to the physiological situation. For example, only 5% of cartilage consists of cells. The other 95% is made of collagen and other proteins. These proteins exert a crucial influence on the cartilage cells. This is further illustrated by the observation that a stem cell can differentiate into a liver cell when cultured on a specific polymer. This finding was done with the help of a TE-Arrray technique: such an array contains some thousand different
biomaterials. ‘With such a system the behavior of cells on all those different biomaterials can be tested in one single
experiment.’ This allows for a substantial speed-up of the biomaterial research, which is concentrated in Nijmegen, Utrecht, Enschede and Amsterdam.

The consortium is particularly devoted to clinical application of the findings: ‘You can do wonderful fundamental
research, but at the end of the day findings need to be practically feasible. Therefore it is important to involve clinicians early in the projects: how do you want this to work, what are your needs’, according to Ruud Bank, who is head of the Tissue Repair department at TNO. He cooperates with the Orthopedic Department of the Free University in Amsterdam on repair of cartilage damage in intervertrebral discs. ‘We want to do that with a fluid matrix containing cartilage cells. This socalled hydrogel is injected in the closed compartment between the discs, where the gel solidifies. Without the input of the orthopedic surgeons we would have started with a solid matrix. But a liquefied gel is much easier to
get into place.’ In the skin DPTE project the Burn Centre of the Red Cross Hospital in Beverwijk cooperates with the Radboud University of Nijmegen (Departments of Matrix Biology and Dermatology) and the free University of Amsterdam
(VU Medical Centre, Department of Dermatology) on a project aiming at the development of skin substitutes. Biochemist Dr Esther Middelkoop (Board Member of the ETRS) coordinates this project: ‘Severe burns lead to considerable scar formation. At the moment one of the few available skin substitutes consists of only artificial dermis, which can be transplanted with an epidermal component from the patient him/herself only after several weeks. This approach is not ideal. The risk of wound infection is considerable and two operations are required. We mean to improve this by applying a skin substitute in a single stage procedure. In this project our knowledge of clinical problems is an immediate input for the fundamental and applied research concerning biomaterials and cell culture techniques. All participants find this a very stimulating experience.’

Clinical applications are the aim, but industrial activity around tissue engineering is still rather limited. However, the worldwide market for tissue engineered products is estimated at two hundred billion euro in ten years time. One of the limitations for increased industrial activity may be the lack of uniform and clear European legislation. ‘The requirements for tissue-engineered products have not been defined yet. If a company would market a product as medical device and in the near future it would be classified as a drug, that would be the immediate end of the product. Therefore, we urgently need guidelines from Brussels’ says Ruud Bank. ‘It is equally important to pay attention to the social acceptability. Stem cell research may be scary to some people. We should make clear that what we are doing is not an imitation of Frankenstein. Our goal is to help patients and gain knowledge with which we can make biological tissues. I am sure this programme will give us that knowledge.’