A new generation of plastics forms the basis of caring implants
Photo: HZG/Christian Schmid
Plastics have been used in medicine for a long time – for example, as small-meshed nets to stabilise tissue after a hernia. But only rarely were they developed specifically for use in the body – generally polymers are used, which were initially designed for completely different purposes. A striking exception are sutures that no longer have to be removed once a wound has healed, because they automatically dissolve. The Helmholtz-Zentrum Geesthacht is developing new types of polymers for medicine, particularly for implants, at its Institute of Biomaterial Science in Teltow. In future, these should help to regenerate tissue in a controlled manner, expand narrowed heart vessels and release correct doses of medication over extended time periods.
Gel sponge to assist at the start
The samples are also examined under a lightoptical microscope. Photo: HZG/Frank Bierstedt
One example is the development of an artificial gel sponge that can promote the formation of bone tissue. The starting point is the biopolymer gelatine, a natural component of the body. On the one hand, it contains nano-structures that allow bone-building cells to specifically dock on to the gelatine. On the other hand, it can be degraded by the body without any problems, and the degradation products even appear to stimulate the regeneration process.
However, the biopolymer is a challenging material. Gummy bears, which consist to a large extent of gelatine, can swell in water to many times of their original size – a highly undesirable property in an implant. This is why the scientists had to develop special foaming procedure to stabilise the shape of the gelatine. At the same time, an inner structure had to be formed that attracts initial cells, so-called precursor cells, and makes them construct the required tissue type.
The result: a sponge-like, open-porous gel. It is inserted into damaged tissue and dissolves after a few weeks – once it has fulfilled its function as a start-up assistant. Pre-clinical studies have shown that the concept appears to bear fruit: a bone defect in a rat was healed within a few weeks; the body tolerated the material well.
Releasing medication into the body
Micro-particulate carrier systems with a porous internal structure can encapsulate bioactive substances. Photo: HZG/Institute of Biomaterial Science
In a further project, the experts at Teltow are researching new types of release systems for pharmaceuticals. Many medications have to be administered regularly over long periods. But occasionally swallowing tablets does not help much – simply too small a dose reaches the actual site of action. For these cases, researchers are relying on another strategy: they pack larger quantities of a bioactive substance into small polymer carriers. These are deposited in close proximity. These are deposited immediately adjacent to the site of action to gradually release the medication there: either the polymer disintegrates over time or the bioactive substance gradually diffuses, or seeps through the polymer.
Within the framework of a Collaborative Research Centre, the HZG researchers are currently working on delivering active substances into the hair follicles. Hair follicles are small channels in the skin in which hair grows and which can become inflamed. Conventional ointments do not always achieve the required result and sometimes their effect does not last long enough. This is why the experts in Teltow are developing new types of polymer particles that settle in the hair follicles for a longer period and there by slowly but continuously release an anti-inflammatory substance – which should assist healing.
Cardiovascular implants made from plastic
Photo: HZG/Frank Bierstedt
The composition of the material is also important for other research fields, for example for cardiovascular implants. So far, a complex intervention was required when a heart valve had to be replaced: the surgeon had to open the ribcage and stitch in a new heart valve. For several years now there has been a gentler, minimallyinvasive alternative: here, doctors push a folded implant through the blood vessels to the heart using a catheter. At its destination, the implant is unfolded and anchored so that it can fulfill its function.
For these implants, the HZG experts are working with shape-memory materials made from polymer; in future, this will also be used for stents, to hold blood vessels open. Scientists are currently researching how compatible the polymers are for this purpose, and what the design should look like – and the first prototypes have already been produced.
Biomaterials for clinical practice
In-vitro tests in the laboratory. Photo: HZG/Christian Schmid
The use of biomaterials requires purity and compatibility. One challenge is to produce large quantities of a new polymer in a highly-pure, sterile form. Thanks to technologies such as upscaling procedures and certified clean rooms, synthesis and processing can be carried out in Teltow according to qualityassurance directives.
In addition, the materials have to be tested for biocompatibility, in order to identify well in advance whether or not a substance is unsuitable or even harmful. For this purpose, HZG scientists are examining the biological environment for interactions between cells and materials, with the aim of mimicking nature to a certain extent. Skills from the fields of materials science, chemistry, biology, physics, engineering and medicine have to be combined in order to translate fundamental research into clinical applications as soon as possible.
An important partner facility is the Berlin-Brandenburg Centre for Regenerative Therapies (BCRT): a joint translational centre of the Charité-Universitätsmedizin Berlin and the Helmholtz-Zentrum Geesthacht. Here BCRT employees provide early advice to research groups additional continuous support ranging from business development, through regulatory matters to health economics. In this way, results from fundamental research can be passed quickly into practice.
Locked by the touch of a hand
The plastic closure device at 20°C and 37°C. Photo: HZG/Institut für Biomaterialforschung.
Shape-memory polymers are also suitable for application outside the body. Experts have developed a polymer that changes its shape when switching between room and body temperatures. Thanks to its ability to switch back and forth numerous times, the new material could be suitable for a novel application – a mechanism that can be used to simply tie and untie shoe closures that even older people could operate easily. Instead of a hook and loop closure, the shoes would have a type of plastic buckle that contracts at 20 degrees Celsius and relaxes at 37 degrees Celsius.
The shoe could be opened by placing a hand on it, and it would close elegantly when the hand is removed. Using a demonstrator, researchers have already been able to show that this principle works reliably.