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Polymer developments offer solutions to bio medical sector

Polymer developments offer solutions to bio medical sector

13-Jun-14

Modern day healthcare would have been difficult without the use of plastics. Besides replacing many old applications in medicine polymer have opened the door for new applications that no other material would permit, and replaced cost prohibitive procedures with lower cost alternatives. Plastics are robust and durable, and able to withstand frequent sterilisation. Polymers aid in design, synthesis and characterization in a vast range of biomedical applications. Two new developments are described:
The mechanical properties of natural joints are considered unrivalled. A cartilage coated with a special polymer layer allows joints to move virtually friction-free, even under high pressure. Using simulations on Julich's supercomputers, scientists from Forschungszentrum Julich and the Univ. of Twente have developed a new process that technologically imitates biological lubrication and even improves it using two different types of polymers. In joints, a thin, watery solution prevents friction. The thin film stays where it should thanks to a trick of nature. A polymer layer is anchored to the cartilage at the end of bones. Polymers are a string of densely packed, long-chain molecules. They protrude from the cartilage and form "polymer brushes" which attract the extremely fluid lubricant and keep it in place at the contact point. Over the last 20 years, numerous attempts have been made to imitate the natural model technically. But with no resounding success. The tentacle-like polymers on surfaces opposite each other tend to get tangled up in each other. They slow each other down and detach from the surfaces. In technical systems, individual polymers that become detached are difficult to replace as they do not possess the same self-healing mechanisms as in a natural organism. Julich physicist Prof. Martin Muser came up with the idea of using two different polymers at the contact point to prevent the polymers becoming entangled. "Using supercomputers, we simulated what would happen if we applied water-soluble polymers to one side and water-repellent polymers to the other side," says head of the NIC (John von Neumann Institute for Computing) group Computational Materials Physics at the Julich Supercomputing Centre (JSC)." This combination of water-based and oil-based liquids as a lubricant reduced the friction by two orders of magnitude - around a factor of 90 - compared to a system comprising just one type of polymer." Measurements with an atomic force microscope at the University of Twente in the Netherlands verified the results. "The two different phases of the liquid separate because they repel each other. This simultaneously holds the polymers back and prevents them from protruding beyond the borders," says Dr. Sissi de Beer, who recently moved from Muser group to the University of Twente. The low-friction two-component lubricant is interesting for numerous applications. One example are simple piston systems, like syringes, which are used to precisely administer even tiny amounts of a drug. Above all, the new process could provide low-friction solutions where high pressures and forces occur locally - for example, axle bearings and hinges.

When stem cells are used to regenerate bone tissue, many wind up migrating away from the repair site, which disrupts the healing process. But, a technique employed by a University of Rochester research team keeps the stem cells in place, resulting in faster and better tissue regeneration. The key, as explained in a paper published in Acta Biomaterialia, is encasing the stem cells in polymers that attract water and disappear when their work is done. The technique is similar to what has already been used to repair other types of tissue, including cartilage, but had never been tried on bone. This opens the door for complicated types of bone repair, enabling to pinpoint repairs within the periosteum - or outer membrane of bone material, says Assistant Prof. of Biomedical Engineering Danielle Benoit. The polymers used by Benoit and her teams are called hydrogels because they hold water, which is necessary to keep the stem cells alive. The hydrogels, which mimic the natural tissues of the body, are specially designed to have an additional feature that's vital to the repair process; they degrade and disappear before the body interprets them as foreign bodies and begins a defense response that could compromise the healing process. Because stem cells have the unique ability to develop into many different types of cells, they are an important part of the mechanism for repairing body tissue. At present, unadulterated therapeutic stem cells are injected into the bone tissue that needs to be repaired. Benoit believed hydrogels would allow the stem cells to finish the job of initiating repairs, then leave before overstaying their welcome.The research team tested the hypothesis by transplanting cells onto the surface of mouse bone grafts and studying the cell behavior both in vivo - inside the animal - and in vitro - outside the body. They started by removing all living cells from donor bone fragments, so that the tissue regeneration could be accomplished only by the stem cells.In order to track the progress of the research, the stem cells were genetically modified to include genes that give off fluorescence signals. The bone material was then coated with the hydrogels, which contained the fluorescently labeled stem cells, and implanted into the defect of the damaged mouse bone. At that point, the researchers began monitoring the repair process with longitudinal fluorescence to determine if there would be an appreciable loss of stem cells in the in vivo samples, as compared to the static, in vitro, environments. They found that there was no measurable difference between the concentrations of stem cells in the various samples, despite the fact that the in vivo sample was part of a dynamic environment - which included enzymes and blood flow - making it easier for the stem cells to migrate away from the target site. That means virtually all the stem cells stayed in place to complete their work in generating new bone tissue."Some types of tissue repair take more time to heal than do others," says Benoit. "What we needed was a way to control how long the hydrogels remained at the site."The team was able to manipulate the time it took for hydrogels to dissolve by modifying groups of atoms - called degradable groups - within the polymer molecules. By introducing different degradable groups to the polymer chains, the researchers were able to alter how long it took for the hydrogels to degrade.Benoit believes degradable hydrogels show promise in many research areas. For example, it may be possible to initiate tissue regeneration after heart attacks without having a patient undergo difficult, invasive surgery, but a great deal of additional research is required.

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