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Jose Ramon Sarasua and Aitor Larrañaga, researchers in the materials engineering department of the UPV/EHU-University of the Basque Country, have been studying new materials or implants that are of interest in medicine—particularly in helping to mend bones. They have, in fact, measured the effect that bioglass has on the thermal degradation of polymers currently used in medicine. The results1 were published in the journal Polymer Degradation and Stability.
Bones are capable of regenerating themselves if they suffer slight damage. But if the damage is above a certain degree, bone lacks the capability to mend itself. When breaks are too big, bones need to be helped. Metal nails or other components are often inserted to help these breaks to mend. However, once the bone has mended, a second operation has to be performed to extract these components. The aim of these new materials or implants is, among other things, to obviate the need for the second operation.
These materials or implants that are of interest in medicine have to meet a number of requirements before they can be used in therapeutic applications. Among other things, the materials have to be biocompatible; in other words, they must not damage the cells or the organism itself. At the same time, biodegradability—so that the body will easily convert the materials into metabolic products that are not toxic—is an interesting option. Other factors must be taken into consideration as well, including mechanical robustness and the straightforward nature of the production process.
With all this in mind, the UPV/EHU researchers are synthesising and shaping tailor-made bioimplants. The main component, on the whole, tends to be a biodegradable polymer; that is, one that will gradually disappear as the bone occupies its own place. Since the polymer is too soft, bioglass was added to the polymer in this piece of work. Bioglass is a bioactive agent and helps the bone to regenerate; what is more, it gives the polymer tough mechanical properties. The result is that the biodegradable polymer/bioglass composite system is stiffer and tougher than the polymer alone.
These composite systems can be manufactured by means of thermoplastic processes that use heat; thus, it is important to study how these materials respond to heat. In this work, the biodegradable polymer/bioglass composite systems were found to have a lower thermal stability compared with the systems without bioglass. In fact, a reaction occurs between the silicon oxide ions of the bioglass and the carbonyl groups in the polymers’ structure, and so the material degrades and adversely affects the properties of the end product.
When an implant is grafted into the body, it encourages the formation of bi-products that may be harmful for the cells. This would greatly restrict the application of these systems in medicine. That is why the UPV/EHU researchers are doing a lot of research to improve the thermal stability of these systems. They are proposing that a chemical transformation of the bioglass surface be made by means of plasma. By creating protective layers for the bioglass particles, the reaction to the polymer is prevented and the final product remains undamaged.
“These composites that have a biodegradable polymer base are candidates with a bright future in mending broken bones or in regenerating bone defects,” Sarasua said. In fact, after the material has temporarily substituted the bone and encouraged it to regenerate, it gradually disappears as the bone returns to its proper place.
“This obviates the need for the second operations required nowadays to remove nails and other parts that are inserted in order to somehow support the bones in major breaks above a critical size, with all the advantages that has from a whole range of perspectives,” he said.
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1. Larrañaga, A., Sarasua, Jose-Ramon, “Effect of Bioactive Glass Particles on the Thermal Degradation Behaviour of Medical Polyesters,” Polymer Degradation and Stability, 98:751-758 (2013).