Title: Fluorophosphonate biofunctionalisation of biomaterials for orthopaedic applications
Funder: Department of Health and Social Care

Abstract: In realising the development of next-generation orthopaedic devices we request support to fully optimise and characterise our novel biomaterials. Detailed below are the main areas that will form the basis of the project: Optimising the surface finish. Having established that our FHBP-Ti/HA-Ti enhances VD3-induced hOB maturation (q.v. supporting documentation) research must now proceed to optimising the functionalisation process under ambient conditions, i.e., the most pragmatic and appealing to device manufacturers. In the first instance this will necessitate time and concentration-dependent studies to assess how best to modify Ti/HA-Ti surfaces. Once established, a second phase of the study will require an examination of device stability when stored under ambient conditions for a period of up to 18 months, a condition suggested by Corin, our industrial collaborator. Batches of bio-modified samples will be evaluated every 3 months for their ability to support hOB maturation during the course of the study. Corin has also recommended we utilise their &ldquo;premature ageing&rdquo; facility wherein bio-functionalised materials, in accordance with ASTM F2003, are subject to 70&deg; C, 503 kPa (73 psi, 5 atmospheres) of pure oxygen for 14 days. Another important part of this work package examines device stability to routine sterilisation procedures; pilot data are attached (supporting documentation) which show stability of FHBP-Ti to autoclaving but it will also be important to examine resistance to gamma irradiation. We have found that LPA withstands 35kilograys of gamma-irradiation as a solid in glass but we need to extend our research to FHBP-functionalised biomaterials. Evidence supporting retention of FHBP bioactivity for each of the procedures examined will be obtained through tracking total alkaline phosphatase (ALP) activity of hOBs seeded onto surfaces just as we detailed previously (II-FS-0510-15049). Heightened ALP reflects greater hOB maturation a key event in providing a mechanically competent, mineralised bone tissue at the implant surface. Microbiological evaluation. In addition to supporting a desirable maturation response in hOBs is our recent discovery that FHBP-Ti deters the attachment and growth of bacteria (qv supporting documentation). This particular area of research is still in its infancy and we will need to better ascertain the biological basis of the anti-adherent properties we have found for our FHBP-modified Ti and extend these studies to FHBP-HA-Ti. Thus far we have examined the responses of S.aureus but research must reach out to other bacteria implicated in implant failures through infection. We will further investigate the antiadherence properties of FHBP-tethered surfaces using vital stains combined with epifluorescence microscopy and conventional viable counting. Sessile organisms exercise their pathogenicity through localised damage; exoenzyme (e.g. lipase, protease and coagulase) and toxin (e.g. haemolysin, alpha-toxin) production will be followed by SDS-PAGE and ELISA, respectively. Our goal will be to demonstrate the potential for surface-tethered FHBP to limit staphylococcal attachment, biofilm growth and virulence behaviours. Physicochemical characterisation. Having identified the best strategy towards FHBP-Ti/HA-Ti modification the following surface techniques will be utilised to fully characterise our optimised functionalised surfaces. A typical analytical regime includes microscopy techniques, specifically scanning electron microscopy (SEM) and atomic force microscopy (AFM) to determine surface morphology and roughness. Morphology and phase images (from AFM) will provide local information on the thickness and % surface coverage, as well as information on molecular packing and local organisation; a combination of Infrared (IR) spectroscopy, X-ray photoelectron spectrometry (XPS) and Auger will provide surface elemental composition of control and functionalised surfaces. They also provide insight into the degree of local functionalisation (e.g., through ratios of Ti, F, and P, typically probing 1-10nm into the surface of the device). Contact angle measurements will provide quantitative data on surface energies consequent to surface functionalisation.

Lay abstract: Many implants used in surgery are made from titanium. These include joint replacements, screws and plates for fixing broken bones and dental implants. The patient's own bone joins onto the titanium using the body's own natural healing processes. When formed properly this join is extremely strong, however in many cases the patient's bone fails to join firmly to the titanium and therefore the prosthesis works loose and ultimately fails. Ten percent of all joint replacements fail due to loosening. We have discovered that a naturally occurring molecule called lysophosphatidic acid (LPA) acts alongside vitamin D to promote bone forming cell maturation. Vitamin D is vital for bone health because it enhances the maturation process. Therefore agents that can co-operate with vitamin D could find place as a coating on titanium to encourage better bonding to the patient's bone. We have found ways of joining LPA onto titanium using a rather simple chemical process which we can perform at room temperature. Simple procedures for modifying titanium are the most appealing to the companies that manufacture bone implants in order to keep costs to a minimum. We have found that our LPA-modified titanium works with vitamin D to support bone cell maturation. Recently we discovered that our novel coating also hindered the attachment of bacteria, this is particularly exciting as it means we have a potential dual-action titanium implant material. At present no bone implant materials that work in the ways we describe have been reported. We therefore have a potential unique clinical advantage. These are very promising developments but we need to optimise the titanium coating to support the different responses we observe. We also need to examine how robust and stable our coatings are and that they can withstand the rigours of storage, sterilisation and the physical forces they will experience when implanted into the body.

Research activity codes: 5.3 MEDICAL DEVICES
Health categories: MUSCULOSKELETAL