LYSOPHOSPHOLIPID-FUNCTIONALISED TITANIUM: A DUAL ACTION SURFACE SUPPORTING HUMAN OSTEOBLAST MATURATION WHILST DETERRING BACTERIAL ATTACHMENT

Summary Statement Developing titanium (Ti) surfaces that are biocompatible yet serve as deterrents for bacterial attachment and growth are particularly appealing in tackling the ongoing problem of sepsis-induced implant failures. Realising this could include coating Ti with the bioactive lipid, lysophosphatidic acid. Introduction Surgical revision for failed total joint replacements costs a staggering £300m/yr and approximately 20% of this burden is attributed to implant failure through bacterial infection. Producing biomaterials that deter microbial attachment as well as securing robust osseointegration continues to be a significant research challenge in contemporary bone biomaterials design. Steps to realising novel improvements are further compounded by the concerns raised over resistance of bacteria to many antimicrobial agents. Clearly this is a major constraint necessitating an entirely novel approach to minimising implant infection risk. We therefore turned our attention to certain lysophosphatidic acids (LPAs) for Ti functionalisation. We have found LPA to enhance calcitriol-induced human osteoblast (hOB) maturation. Of further significance is the discovery that LPA can directly inhibit the growth of certain bacteria and even co-operate with some antibiotics to bring about their demise. Herein we describe the fabrication of a hOB-compatible Ti surface with palmitoyl-LPA (P-LPA) which we also find hinders bacterial attachment. Methods We adopted a self-assembly strategy for the attachment of P-LPA to Ti. Briefly Ti discs (Corin Group, Cirencester, UK) were baked, overnight, at 160°C and then coated with octadecylphosphonic acid (ODP) which has a natural affinity for Ti oxide. Bound ODP provided a tethering point for P-LPA via hydrophobic interaction with the “tail” region perpendicular to the Ti surface. Modified Ti discs were subsequently seeded with hOBs to evaluate their maturation response to calcitriol. In addition modified Ti samples were exposed to either Staphylococcus epidermidis or methicillin-resistant Staphylococcus aureus and the extent of surface coverage determined via crystal violet staining following 24hr incubation. Results The development of P-LPA functionalised Ti provided a surface that secured hOB maturation in response to calcitriol, as supported by significant increases in total alkaline phosphatase activity, an enzyme expressed in greater abundance as hOBs progress to a more differentiated phenotype. In contrast this Ti substrate was not as attractive to bacteria as evaluated by crystal violet staining and dye recovery from the incubated specimens. Discussion Multifunctional bone biomaterials that combine host tissue biocompatibility with an antibacterial surface finish will represent the next-generation orthopaedic devices. The biologically active lysophospholipid, LPA, is assuming an emerging interest in hOB biology. This has partly arisen from our discovery that it co-operates with calcitriol to bolster the formation and maturation of hOBs. Another equally exciting property of LPA is the discovery that it can inhibit the growth of bacteria and, in some instances, co-operate with certain antibiotics in killing bacteria. The application of ODP for the attachment of P-LPA to Ti presented itself as a facile step towards developing a novel Ti surface finish. Collectively our preliminary investigations indicate that our modified Ti supports calcitriol-induced hOB maturation but that it deters bacteria.