Enhancement of the soft tissue seal around transcutaneous implants and inhibition of bacterial colonisation
Lead Research Organisation:
University College London
Department Name: Institute of Orthopaedics
Abstract
Amputees are traditionally fitted with artificial limbs which are attached to amputation stumps by strapping or using suction sockets. The use of these artificial limbs may be complicated by sweating, rashes, ulceration and pressure sores due to uneven pressure distribution on the soft tissues of the stump. Osseointegrated prostheses used for amputees are bone-anchored metal implants that project through the skin to directly attach artificial limbs to the skeleton. Overall, amputees report improved quality of life, comfort, mobility and sensory awareness with these prostheses. However, infection is a significant problem as little attention has been paid to the seal between the soft tissues and the implant. The Intraosseous Transcutaneous Amputation Prosthesis (ITAP) is an exciting innovation developed at University College London that is designed to promote a tight soft tissue seal to prevent infection. This study aims to create a more robust seal by mimicking nature using a porous metal implant coated with hydroxyapatite (the mineral component in bone) and fibronectin (a naturally occurring protein) to enhance soft tissue attachment. Silver will be incorporated into the coating as it is known to reduce bacterial growth. The effect of these surfaces on skin cell attachment and bacterial growth will be tested.
Technical Summary
The Intraosseous Transcutaneous Amputation Prosthesis (ITAP) is an osseointegrated titanium implant which projects through the skin and provides attachment for an external prosthetic device. It results in improved quality of life for amputees by avoiding soft tissue complications associated with traditional prostheses and by allowing improved function due to increased sensory feedback (Figure 1). However, there is a significant risk of infection if a successful seal is not achieved at the skin-implant interface. The goal of ITAP is to create a tight soft tissue seal which prevents epithelial downgrowth and infection. A successful seal is dependent on a race between soft tissue attachment and bacterial colonisation. The longer the interface is kept sterile and the faster the seal is established, the lower the risk of infection.
Figure 1: A-C: Near-normal motion with a transhumeral ITAP. This patient was unable to use conventional prostheses due to restricted motion. D: The skin-implant interface at 740 days. E: A radiograph of the ITAP.
My research aims to decrease infection associated with ITAP by improving soft tissue ingrowth and decreasing bacterial colonisation. Porous titanium, hydroxyapatite (HA) and fibronectin (Fn) are known to individually increase cell attachment. Silver (Ag) has a broad spectrum of antimicrobial activity. I will investigate whether these surfaces can act synergistically to prevent infection of ITAP by testing the hypothesis that porous titanium will promote soft tissue ingrowth and that the seal will be further enhanced and bacterial colonisation inhibited by coating the surface with HA, Ag and Fn (HA-Ag-Fn).
The study consists of two parts. Firstly, an in vitro assessment will determine concentrations of HA-Ag-Fn that inhibit bacterial colonisation without inducing cytotoxicity. A number of assays will be used to assess the antibacterial effects of HA-Ag-Fn, fibroblast attachment, fibroblast viability and the release kinetics of Ag and Fn. Secondly, an established in vivo ovine transcutaneous pin model will be used to assess soft tissue ingrowth and bacterial colonisation around porous titanium coated with HA-Ag-Fn. Surfaces will be prepared by electrodepositing HA-Ag onto titanium (Figure 2). (This method is able to produce uniform coatings inside porous titanium). Fn will be adsorbed onto the HA-Ag.
This study will select surfaces that will be applied clinically to enhance the seal around ITAP.
Figure 2: Scanning electron micrograph showing electrodeposited HA-Ag
Figure 1: A-C: Near-normal motion with a transhumeral ITAP. This patient was unable to use conventional prostheses due to restricted motion. D: The skin-implant interface at 740 days. E: A radiograph of the ITAP.
My research aims to decrease infection associated with ITAP by improving soft tissue ingrowth and decreasing bacterial colonisation. Porous titanium, hydroxyapatite (HA) and fibronectin (Fn) are known to individually increase cell attachment. Silver (Ag) has a broad spectrum of antimicrobial activity. I will investigate whether these surfaces can act synergistically to prevent infection of ITAP by testing the hypothesis that porous titanium will promote soft tissue ingrowth and that the seal will be further enhanced and bacterial colonisation inhibited by coating the surface with HA, Ag and Fn (HA-Ag-Fn).
The study consists of two parts. Firstly, an in vitro assessment will determine concentrations of HA-Ag-Fn that inhibit bacterial colonisation without inducing cytotoxicity. A number of assays will be used to assess the antibacterial effects of HA-Ag-Fn, fibroblast attachment, fibroblast viability and the release kinetics of Ag and Fn. Secondly, an established in vivo ovine transcutaneous pin model will be used to assess soft tissue ingrowth and bacterial colonisation around porous titanium coated with HA-Ag-Fn. Surfaces will be prepared by electrodepositing HA-Ag onto titanium (Figure 2). (This method is able to produce uniform coatings inside porous titanium). Fn will be adsorbed onto the HA-Ag.
This study will select surfaces that will be applied clinically to enhance the seal around ITAP.
Figure 2: Scanning electron micrograph showing electrodeposited HA-Ag