Antibacterial surface modification of titanium implants in orthopaedics

Abstract

The use of biomaterials in orthopaedics for joint replacement, fracture healing and bone regeneration is a rapidly expanding field. Infection of these biomaterials is a major healthcare burden, leading to significant morbidity and mortality. Furthermore, the cost to healthcare systems is increasing dramatically. With advances in implant design and production, research has predominately focussed on osseointegration; however, modification of implant material, surface topography and chemistry can also provide antibacterial activity. With the increasing burden of infection, it is vitally important that we consider the bacterial interaction with the biomaterial and the host when designing and manufacturing future implants. During this review, we will elucidate the interaction between patient, biomaterial surface and bacteria. We aim to review current and developing surface modifications with a view towards antibacterial orthopaedic implants for clinical applications.

Keywords: Biomaterials; biofilms; orthopaedic implants; titanium; topography.

Figure 1.

Bacteria–material–host interaction. (a) Bacteria adhere on material surface and form a biofilm enhancing their proliferation and protecting themselves from immune response and antibiotic drugs. (b) Bacteria interact with host cells such as osteoblasts. Osteoblasts non-professionally internalise bacteria. This mechanism helps bacteria evade the immune system. Bacteria induce osteoblast apoptosis by toxin production.^, Infected osteoblasts also induce tumour necrosis factor–related apoptosis-induced ligand (TRAIL) via caspase-8. (c) Immune cells, both innate and adaptive, attack the planktonic bacteria to reduce bacterial numbers. Infected osteoblasts produce cytokines to activate immune response. (d) Infected osteoblasts produce RANKL, CXCL2 and CCL3 which enhance osteoclastogenesis resulting in bone resorption., OB: osteoblast; PAMPs: pathogen-associated molecular patterns; TLR: toll-like receptors.

Figure 2.

The four stages of biofilm development. (a) Initial bacterial attachment. (b) Bacteria start to produce multiple layers through cell aggregation and accumulation. (c) Biofilm development and matrix elaboration. (d) Bacteria start a new cycle of biofilm formation in different location.

Figure 3.

Three main features affect bacterial–material interaction. (a) Material features such as morphology and physicochemical cues. (b) Bacterial features including surface charge and hydrophobicity/hydrophilicity. (c) Environments such as temperature, pH, bacterial concentration and contact time as well as other factors such as serum and protein.

Figure 4.

Planktonic bacteria attach on material surface and form biofilms. (a) Various techniques were used as antibacterial strategies. Anti-adhesive surface coats using concepts of surface chemistry and functionality including ions and polymer coats. (b) Material surface can be coated with bactericidal substances such as antibiotics and silver. (c) Nanotopographic surface modifications were also effective strategies used as either anti-adhesives or bactericidal. (d) The examples of nanotopography, such as nanowires promoting osteoblastogenesis and have bactericidal effects. Other bactericidal topographies include nanotubes (permission from Yu et al.) and cicada wings (permission from Ivanova et al.).