martes, 30 de abril de 2013

Copy and nanopaste - bioactive bone filler

Researchers at the University of Duisburg-Essen, Germany, have developed a bioactive nanopaste from seashells that can be injected into bone defects. 
Mussels and seashells make calcium carbonate from seawater to repair their shells, and calcium phosphate can be used to re-mineralise teeth. Having observed these phenomena, researchers at the University of Duisburg-Essen, Germany, have developed a bioactive nanopaste that can be injected into bone defects.   

After severe fractures, tumour extraction and in areas around implanted prosthetics, bone defects can occur, which must be filled to encourage bone repair. At the moment, surgeons transplant existing bone from the iliac crest on the pelvis into the problem areas, but it is difficult to gather enough of this material to complete the job.  

Some researchers have looked to materials based on calcium phosphate – a mineral found in human bones and teeth – to solve this shortage. While these materials work well, they fall short in terms of resorbability and mechanical stability.  

The team has developed a material to stimulate bone growth by inducing the surrounding cells to form proteins. Lead researcher Dr Matthias Epple explains, ‘The nanopaste consists of calcium phosphate nanoparticles that are coated with a biodegradable polymer (carboxymethyl cellulose) and DNA. All these materials are highly biocompatible and are well accepted by the body. Calcium phosphate is the mineral of human bone, therefore it is highly biocompatible and – in the form of nanocrystals – also biodegradable.’  

To form the paste, calcium phosphate nanocrystals are precipitated in water. A biodegradable polymer covers the surface to restrict growth, while some of the nanocrystals are coated with DNA. After freeze-drying and adding water, a substance is formed with a toothpaste-like viscosity. ‘The individual particles are coated to prevent their growth to larger crystals and to assure good dispersability,’ Epple says. ‘The nucleic acid (DNA) covers the nanocrystals. We have shown in cell culture experiments that cells take up the nanoparticles together with DNA. After uptake they start to synthesise the protein, which is encoded by the DNA (its genetic code). The proteins stimulate bone growth (bone morphogenetic protein) or vascularisation around the implantation site.’  
SEM image of calcium phosphate nanorods, 
which form the basis of the nanopaste.SEM image of calcium phosphate nanorods, 
which form the basis of the nanopaste.
The researchers assume that the body will resorb the paste, and that the bioactive nanoparticles will be released continuously. As yet, however, the technology has only been demonstrated in vitro using chemical and cell biological tests. The process may be simple and cost-effective, but Epple notes that they still need to investigate the amount of DNA needed to create the desired bioactivity. He says, ‘We plan to carry out the necessary in vivo experiments, together with colleagues from trauma surgery. Then we will see whether the outcome is as good as predicted.’   

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