“Degradable” osteosynthesis –
optimising bone regeneration through stability-driven implant absorption using absorbable light metals
Project description:
The aim of this subproject is to develop optimal resorbable implants, made of magnesium alloys, for osteosynthesis applications in weight-bearing bone. These resorbable light metals are of significantly higher strength than the polymers previously used as resorbable implant material. Initial findings indicate that they allow, by means of corrosion, degradation that is controllable over time. This enables them to have a stabilising effect that is tailored to the strength of the healing bone.
This research project has set itself the aim of developing optimal implants made of resorbable, magnesium-based light metals in order to achieve “intelligent” osteosynthesis. During the first funding period, the project largely centred around in vivo studies, using a rabbit model, into physiological processes during bone healing, in order to calculate the demands made on the resorbable implant in the course of bone healing using the finite-element method (FEM). Furthermore, in conjunction with the R1 project, investigations will be conducted to find suitable alloys, as well as to study degradation behaviour and how the biocompatibility of simple intramedullary implants made of various magnesium alloys compares with that of titanium and resorbable polymers. When determining intramedullary blood flow, it was revealed that ostectomy initially led to depression - and later to a marked increase - of blood flow in the vicinity of the ostectomy site above the level of the intact bone. The implantation of intramedullary titanium or polymer implants led to an increase in blood flow. When magnesium implants were used, however, this led initially to depression of the blood flow and, towards the end of the experimental period, to an increase. Measurements of rigidity revealed an initial increase, regardless of whether or not an intramedullary implant had been put in; thereafter it stagnated or even declined before recovering at the end. Investigations to find the right alloy involved testing four magnesium alloys (MgCa0.8, WE43, LAE442 and LACe442). The material LACe442 proved unsuitable for implantation, whereas the other three alloys were very well tolerated. X-ray imaging revealed that density decreased over time, without gas formation. Micro-computed tomography (micro-CT) showed that the degradation of the implants and reformation of the endosteal bone was relatively uniform. Histological analysis demonstrated good biocompatibility as well as both endosteal and periosteal remodelling. On the surface of all implants, corrosion with cell adhesion was evident. All three magnesium alloys showed a marked reduction in weight and volume over time. Unlike We43, the implants made of MgCa0.8 and LAE442 showed a favourable trend over time in the reduction in mechanical stability. MgCa0.8 showed unchanged ductility and the progression of volume reduction was satisfactory, with LAE442 exhibiting greater strength and higher flexural stress. The second funding period will see continuation of pure research aimed at characterising the biomechanical parameters of magnesium-based materials, geometries, biocompatibility and biological principles in the healing progression of bone. As MgCa0.8 and LAE442 have different benefits in terms of their mechanical properties, the aim in the second funding period is to test - in addition to LAE442 – a combination of magnesium, calcium and lithium. Furthermore, rotationally stable, intramedullary implants promoting stable osteosynthesis are to be developed and, in a rabbit model, tested on osteotomised and fractured tibia under standardised conditions. Bone healing, and both the degradation behaviour and growth of regenerated material into the implants, are to be assessed using in vivo micro-CT. Additionally, and as in the first funding period, various port-mortem investigations of the implants and the bone-implant composite are to be carried out. As well as research into local cellular response, the trends in local pH value and the occurrence of various growth factors and osteocalcin when using Mg implants are to be investigated. In addition, the transferability of the results to other long bones (such as the humerus and femur) is to be investigated in a rabbit model. It is expected that, towards the end of the second funding period and at the start of the third, the tested implants will be clinically used in cases of spontaneous fracture in veterinary patients. The implant design and its range of indications will be reviewed frequently as to their applicability, and enhanced with a view to later use in humans.
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