Samir Hamidi

Doctoral Researcher
Physical Sciences for Health CDT 

Thesis project - "Design & develop an injectable, light curable and resorbable material for intramedullary stabilisation of upper extremity fractures"

Supervisors:
Dr Will Palin, School of Dentistry
Professor Liam Grover, School of Chemical Engineering
Dr Iain Styles, School of Computer Science
Dr DJ Wilson, Smith & Nephew

Surgical repair of fractures in long bones such as humerus or tibia, rely upon the use of conventional fixation techniques such as intramedullary (IM) nails, extramedullary plates and fixators. Traditional IM systems are designed to provide longitudinal stabilisation with minimal bending moment, sufficient rigidity and compressive strength with adequate durability to promote bone healing.  However, these fixation devices are deemed inadequate for patients exhibiting autoimmune response towards metallic hardwares or suffering from metabolic bone diseases such as osteoporosis, which is particularly prevalent in the aging population. Complications further arise with prosthetic related infections, which are considered to be the leading cause of post clinical morbidity and mortality following surgical implantations [1]. It is suggested that the bone stabilisation system involving resorbable cement would address the aforementioned challenges currently faced within the field.

The proposed system will consist of a resorbable stent positioned over the fracture site from within the bone canal and expanded into place by inflation of a resorbable bio-balloon. The main focus of this PhD programme will be development of the novel light curable resorbable bioactive cement. The material will be injected percutaneously into the intramedullary canal that will conform to the unique canal geometry following a photo-polymerisation process. The crosslinked cement will be contained within the confines of the implanted bio-balloon as to eliminate the risk of extravasation. The bioactive cement implant will be designed to systematically degrade into biocompatible compounds that can either be excreted directly from the body or metabolised without the need for surgical removal of the device. The cement will be designed and formulated such that it provides sufficient mechanical stability and integrity necessary at load bearing points, during the early stages of healing process. The degradation of bioactive cement rate will coincide with the new tissue (bone) regeneration and remodelling process in a timely manner (< 2 years).

Aims and objectives
The overarching aim of this project is to develop a standalone bone stabilisation system consisting of a light curable and resorbable bioactive cement material that can be used as a fracture fixator during a minimally invasive percutaneous surgical procedure.

The majority of the project involves engineering and physical science; designing and formulating a novel injectable, light curable, bioactive and resorbable polymer composite. This will include characterisation of ceramic particle morphology (inorganic component) and how the particle size, shape and distribution will affect the overall rheological properties of the polymer composite and its infusion into the bone canal. More importantly, how this will affect the photopolymerisation process and subsequently the mechanical properties and stability of the cement mixture. Some of the methods that will be used for particle size characterisation include scanning electron microscopy, sieve analysis and laser diffraction. The project will also involve chemical modification of polymer and/or ceramic particles with groups amenable to photocrosslinking. The properties of a range of photoinitiator chemistries will be explored, including molar absorptivity, quantum yield and any possible cytotoxic effect of either the photoinitiator or the activation wavelength. Raman/FTIR spectroscopy will be used to determine the degree of crosslinking by photopolymerisation enabling spatial mapping of how deep the curing reaction reaches into the resin composite. The aim is to effectively photopolymerise greater than 3mm layer of cement mixture.

References

  1. Williams DF. Introduction: implantable materials and infection. Injury. 1996; 27:SC1-SC4.