Development of a facile fluorophosphonate-functionalised titanium surface for potential orthopaedic applications.

BACKGROUND: Aseptic loosening of total joint replacements (TJRs) continues to be the main cause of implant failures. The socioeconomic impact of surgical revisions is hugely significant; in the United Kingdom alone, it is estimated that £137 m is spent annually on revision arthroplasties. Enhancing the longevity of titanium implants will help reduce the incidence and overall cost of failed devices. METHODS: In realising the development of a superior titanium technology, we exploited the natural affinity of titanium for phosphonic acids and developed a facile means of coating the metal with (3S)1-fluoro-3-hydroxy-4-(oleoyloxy)butyl-1-phosphonate (FHBP), a phosphatase-resistant analogue of lysophosphatidic acid (LPA). Importantly LPA and selected LPA analogues like FHBP synergistically cooperate with calcitriol to promote human osteoblast formation and maturation. RESULTS: Herein, we provide evidence that simply immersing titanium in aqueous solutions of FHBP afforded a surface that was superior to unmodified metal at enhancing osteoblast maturation. Importantly, FHBP-functionalised titanium remained stable to 2 years of ambient storage, resisted ∼35 kGy of gamma irradiation and survived implantation into a bone substitute (Sawbone™) and irrigation. CONCLUSION: The facile step we have taken to modify titanium and the robustness of the final surface finish are appealing properties that are likely to attract the attention of implant manufacturers in the future. THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE: We have generated a functionalised titanium (Ti) surface by simply immersing Ti in aqueous solutions of a bioactive lipid. As a facile procedure it will have greater appeal to implant manufacturers compared to onerous and costly developmental processes.

Polydopamine-Lysophosphatidate-Functionalised Titanium: A Novel Hybrid Surface Finish for Bone Regenerative Applications.

Aseptic loosening of total joint replacements (TJRs) continues to be the main cause of implant failures. The socioeconomic impact of surgical revisions is hugely significant; in the United Kingdom alone, it is estimated that £135m is spent annually on revision arthroplasties. Enhancing the longevity of titanium implants will help reduce the incidence and overall cost of failed devices. In realising the development of a superior titanium (Ti) technology, we took inspiration from the growing interest in reactive polydopamine thin films for biomaterial surface functionalisations. Adopting a "one-pot" approach, we exposed medical-grade titanium to a mildly alkaline solution of dopamine hydrochloride (DHC) supplemented with (3S)1-fluoro-3-hydroxy-4-(oleoyloxy)butyl-1-phosphonate (FHBP), a phosphatase-resistant analogue of lysophosphatidic acid (LPA). Importantly, LPA and selected LPA analogues like FHBP synergistically cooperate with calcitriol to promote human osteoblast formation and maturation. Herein, we provide evidence that simply immersing Ti in aqueous solutions of DHC-FHBP afforded a surface that was superior to FHBP-Ti at enhancing osteoblast maturation. The facile step we have taken to modify Ti and the biological performance of the final surface finish are appealing properties that may attract the attention of implant manufacturers in the future.

Development and biological evaluation of fluorophosphonate-modified hydroxyapatite for orthopaedic applications.

There is an incentive to functionalise hydroxyapatite (HA) for orthopaedic implant use with bioactive agents to encourage superior integration of the implants into host bone. One such agent is (3S) 1-fluoro-3-hydroxy-4-(oleoyloxy) butyl-1-phosphonate (FHBP), a phosphatase-resistant lysophosphatidic acid (LPA) analogue. We investigated the effect of an FHBP-HA coating on the maturation of human (MG63) osteoblast-like cells. Optimal coating conditions were identified and cell maturation on modified and unmodified, control HA surfaces was assessed. Stress tests were performed to evaluate coating survivorship after exposure to mechanical and thermal insults that are routinely encountered in the clinical environment. MG63 maturation was found to be three times greater on FHBP-modified HA compared to controls (p < 0.0001). There was no significant loss of coating bioactivity after autoclaving (P = 0.9813) although functionality declined by 67% after mechanical cleaning and reuse (p < 0.0001). The bioactivity of modified disks was significantly greater than that of controls following storage for up to six months (p < 0.001). Herein we demonstrate that HA can be functionalised with FHBP in a facile, scalable manner and that this novel surface has the capacity to enhance osteoblast maturation. Improving the biological performance of HA in a bone regenerative setting could be realised through the simple conjugation of bioactive LPA species in the future. Depicted is a stylised summary of hydroxyapatite (HA) surface modification using an analogue of lysophosphatidic acid, FHBP. a HA surfaces are simply steeped in an aqueous solution of 2 µM FHBP. b The polar head group of some FHBP molecules react with available hydroxyl residues at the mineral surfaces forming robust HA-O-P bonds leaving acyl chain extensions perpendicular to the HA surface. These fatty acyl chains provide points of integration for other FHBP molecules to facilitate their self-assembly. This final surface finish enhanced the human osteoblast maturation response to calcitriol, the active vitamin D3 metabolite.

The impact of ageing reveals distinct roles for human dentate gyrus and CA3 in pattern separation and object recognition memory.

Both recognition of familiar objects and pattern separation, a process that orthogonalises overlapping events, are critical for effective memory. Evidence is emerging that human pattern separation requires dentate gyrus. Dentate gyrus is intimately connected to CA3 where, in animals, an autoassociative network enables recall of complete memories to underpin object/event recognition. Despite huge motivation to treat age-related human memory disorders, interaction between human CA3 and dentate subfields is difficult to investigate due to small size and proximity. We tested the hypothesis that human dentate gyrus is critical for pattern separation, whereas, CA3 underpins identical object recognition. Using 3 T MR hippocampal subfield volumetry combined with a behavioural pattern separation task, we demonstrate that dentate gyrus volume predicts accuracy and response time during behavioural pattern separation whereas CA3 predicts performance in object recognition memory. Critically, human dentate gyrus volume decreases with age whereas CA3 volume is age-independent. Further, decreased dentate gyrus volume, and no other subfield volume, mediates adverse effects of aging on memory. Thus, we demonstrate distinct roles for CA3 and dentate gyrus in human memory and uncover the variegated effects of human ageing across hippocampal regions. Accurate pinpointing of focal memory-related deficits will allow future targeted treatment for memory loss.