Development of multiphasic scaffolds for tissue engineering of bone- ligament interface

Thesis

Due to their low cell density and low nutrient and oxygen requirements, ligaments have a poor regeneration capacity and injuries frequently lead to persistent impairment of joint function. The integration of ligament into bone occurs at a specialised interface known as the enthesis, which is designed to allow smooth transfer between tissues of vastly different mechanical properties. Healthy enthesis exhibits a continuous gradient of interfacial tissue classified into four distinct zones, with varying cellular compositions, mechanical properties, and functions. Current reconstructive treatment methods are unable to recreate the natural smooth transition that typifies the original attachment site. Therefore, the aim of this research was to capture the biological and mechanical behaviour of natural entheses by developing multiphase collagen- based scaffolds which could be used to regenerate the compositionally complex interface and facilitate functional graft-to-bone integration.

Although enthesis regeneration has increasingly become a subject of intense interest within the field of orthopaedic and tissue engineering research, the development of a successful technique has been hindered by a lack of understanding of the structure and composition of the enthesis. Therefore, the first part of this thesis reports the composition and mechanical behaviour of the entheses of pig knees. The gradient of stiffness through the enthesis was presented by utilising a nanoindentation technique. Dry and wet nanoindentation tests were performed on the anterior cruciate ligament (ACL) to tibia insertions to measure the elastic modulus of each region and observe the time-dependent behaviour of biological material.

The second part of this thesis reports the development of various collagen-based scaffolds utilising monomeric forms of the protein. Extruded collagen fibres were developed and used to reinforce porous scaffolds which typically have less than optimal mechanical strength. Composite scaffolds exhibited superior mechanical properties and strong fibre-matrix bonds were formed. Furthermore, highly porous (>97%) collagen-based constructs were created to mimic the various regions of the enthesis: a soft tissue layer composed of Type I collagen; an uncalcified fibrocartilage layer composed of Type II collagen and chondroitin sulphate (CS); a calcified layer composed of Type I collagen and hydroxyapatite (HAp). These scaffolds were then used to fabricate two-phase scaffolds with great integration of layers. Preliminary in vitro studies on the single-layer porous scaffolds showed the biocompatible nature of the scaffolds and their viability as an implantable device for tissue growth.

Authors: Karadag, IM

• DOI: 10.5287/ora-qze2k6nvp
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: enthesis; collagen-based scaffolds; ligament-bone interface; tissue engineering
• Subjects: Tissue engineering