Engineering functional partial joint replacement: a soft solution to a hard problem

Arthritis is a common problem and typically treatment includes replacing the articular surfaces with hard metal on both sides of the joint with intervening plastic or ceramic. Although successful, with time these fail and further surgery is extensive with unpredictable outcomes. In a significant proportion of cases, the arthritis starts as a focal area on one side of the joint and in such cases, the replacement of one of the contacting articular cartilage surfaces is possible. This is less invasive and allows the patient to return to day to day activities quicker. Currently, these treatment options (known as hemiarthroplasty) include replacing the soft articular cartilage with a hard metallic surface, and are common in the treatment of joint problems secondary to trauma and/or arthritis. Hemiarthroplasty devices for hip, knee, ankle and shoulder currently exist but with somewhat unpredictable results. In vitro studies have shown that replacing the relatively compliant cartilage-covered native surface with a stiff, metallic, axisymmetrical hemiarthroplasty implant can reduce joint contact area by up to two thirds compared with the native joint and cause higher peak contact stress. The abnormal contact mechanics may promote degeneration and erosion of the native cartilage leading to persistent pain, stiffness, and loss of function. Without a doubt, the interactions occurring at the device-cartilage interface are key to successful implantation.

At Leeds, we have recently developed a novel two step method for the surface initiated functionalisation of idealised metallic and polymer biomaterials. This exploits soft matter materials concepts to produce a materials system similar in structure and chemistry to a phospholipid bilayer. These gel-type layers have enabled us to produce a relatively thick (~ 3 micrometers) and soft lubricious surface layer (micro < 0.01), although with a single moduli and limited load bearing capacity (effective up to contact pressures of ~ 20 MPa). However with this methods, the properties of these layers can be varied easily through synthesis parameters and are easily translatable to lower moduli biomaterials (ie PEEK). This presents tremendous opportunities for future devices and application where contact of implant interfaces need to be compliant with cartilage or soft tissues.

Objectives of this studentship include:

1. Develop a robust multi-moduli soft - aqueous based interface capable of withstanding common joint reaction forces observed in the aforementioned applications when slid against articular cartilage. This will be completed on 2D surfaces (PEEK & CoCrMo) and characterised using a range of surface sensitive (FTIR, XPS, cryo-SEM), mechanical (AFM, Nano-indentation) and functional assessments (Tribology, Corrosion).
2. Investigate the feasibility of adding therapeutic agents for the targeted treatment of infection or localised arthritis (gentamicin sulphate or glucosamine sulphate, respectively).
3. Translate and demonstrate the functionality of the proposed technology on clinically relevant components. The durability of these devices will be determined using the suite of joint simulators.