The quest for surfaces capable of preventing bacterial colonisation and adhesion in the area surrounding the implant "is a subject of undoubted interest, borne out by the huge number of publications that have been developed in this field," explained Beatriz Palla, researcher in the Biomaterials Group of the UPV/EHU's Department of Polymer Science and Technology. The fact is that "about 10% of implants have to be removed due to osseointegration problems or to the onset of infections," she added.
When it comes to designing strategies to combat these problems, one has to bear in mind the challenge posed by providing the surface of titanium implants with antibacterial properties, and at the same time, by the tremendous resistance that bacterial strains are capable of developing to conventional therapies with antibiotics.
That was the challenge that the UPV/EHU group, which has for some time been developing materials geared towards dental implants, was keen to tackle. "We had already obtained coatings that facilitate the generating of bone around the implant and thus facilitate anchoring to the bone. In a bid to go a step further, we looked at how to turn these coatings into bactericides," said the researcher.
The method they used for this was sol-gel synthesis. Sol-gel synthesis is based on the preparation of a precursor solution (sol) that when left on its own for a while turns into a gel that can be used to coat the surface of the titanium screw, and after heat treatment at a high temperature in the kiln ends up finally being adhered to the screw that will be implanted. "We used silica as the precursor, because in many studies this compound has been shown to be osteoinductive, so it facilitates one of the objectives we wanted to achieve. What is more, to provide the materials with antibacterial characteristics, we added various antibacterial agents".
Three prototypes, one of them a trade secret
In the study carried out, Palla developed three types of coatings depending on the various antibacterial agents chosen; each one had a mechanism to tackle bacterial infections, either prophylactically by preventing the bacteria from becoming adhered initially and the subsequent infection, or else by eliminating it once it has developed.
What was needed in the case of prophylactic coatings was "a material with a very long degradation time so that it would remain adhered to the screw and work for as long as possible preventing bacteria from becoming adhered," said Palla. In the coatings designed to eradicate an infection that has already taken hold, however, "a rapidly degrading material is needed so that it can release the antibacterial agent as quickly as possible to attack the infection". What is more, one of the coatings developed for this purpose "is designed to be used in situ, at the dentist's surgery itself, on the infected screw without any need to extract the implant from the patient. This new material is in the process of being patented and remains a trade secret," pointed out the researcher.
In view of the results, Palla believes that "it is possible to confirm that coatings with an antibacterial capability and which do not affect the proper integration of the implant into the jawbone have been developed". She also admits, however, that there is still a long way to go until they can be applied and used at dentists' surgeries: "Apart from all the trials that remain to be carried out, it would also be advisable to pursue the research a little further to optimize the results more".
Beatriz Palla-Rubio (San Sebastian, 1989) conducted this study as part of her PhD thesis entitled Recubrimientos antibacterianos basados en silicio para implantes dentales [Silica-based antibacterial coatings for dental implants] supervised by Mariló Gurruchaga-Torrecilla and Isabel Goñi-Echave, both UPV/EHU professors. Various partnerships assisted her throughout her research: firstly, part of the research was conducted at the Jaume I University in Castellón (Valencian region) where discs were coated with titanium and later studied in vitro; secondly, the CSIC (National Research Council) in Madrid carried out the trials using cells. At the same time, the supply of implants was offered by the company Ilerimplant SL, of Lleida (Catalonia).
Bibliographic referenceControl of the degradation of silica sol-gel hybrid coatings for metal implants prepared by the triple combination of alkoxysilanes. Journal of Non-Crystalline Solids, 453, 66-73.