Modelling composition-solubility relationships in bio-active phosphate glasses

The manufacture of biocompatible materials for tissue replacement is a central theme in the fields of biomedicine and tissue engineering research. Natural sources of bone graft material are compromised by availability and cost, both from the individual patient as autograft and from other donors as allograft. "Third generation" bioactive implant materials, which play an active role in tissue regeneration and degrade after the tissue has healed, have been remarkably successful in many clinical applications, especially in dental and orthopaedic fields. Among the third-generation biomedical materials, phosphate-based bio-active glasses (PBGs) are becoming increasingly popular owing to their unique properties: (i) their composition is chemically related to the surrounding tissue; (ii) they dissolve completely in aqueous media; (iii) their dissolution rate can be controlled by changing the composition of the phosphate-sodium-calcium glass. The solubility of the PBGs, which is arguably their most important property to be exploited in biomedical applications, can thus be tailored to suit the end application. As the solubility of a glass is linked to its atomic-level structure, insight into the P2O5 network structure at the molecular level; the effect of varying concentrations of calcium and sodium and other cations on the network; and the dominant surface and dissolution processes, are of fundamental interest to the design of phosphate glass compositions for applications in tissue engineering. However, a common problem in the investigation of these materials, generally related to their amorphous nature, is the lack of detailed information on the microscopic structure of the glasses and how this structure is affected by the different ions making up the glass composition. This research proposal therefore aims to develop robust models to provide quantitative insight at the atomic level into the structures, physico-chemical properties and solubilities of a range of phosphate-based bioglasses as a function of their composition.

The types of materials investigated and developed in this project are used as soluble scaffolds for soft tissue replacement materials (collagen), in dental implants and maxillofacial surgery and for the controlled delivery of drugs, antimicrobial agents and nutrients (for livestock). This project and its outcomes will therefore have undoubted impact on:

* Society, by developing science to contribute to the Nation's health and improve the quality of life;
* The Economy, through the design of new benign materials for biomedical applications. The biomaterials market in the USA alone is worth approximately $10 billion annually, which is easily tripled globally. Any improvement on existing materials clearly could have significant economic impact;
* Knowledge, both academic and commercial, as the new models will deliver significant advances in the predictive simulations of amorphous materials;
* People, through the technical expertise developed by the researcher during the project, the training received by a number of researchers in societal and ethical issues and the transferable skills developed in engagement with the media, the general public, policy makers and legislators.

In addition to the obvious benefits to academic researchers in the field (summarised in the Academic Beneficiaries section), the research will benefit in particular (i) the general public, but also (ii) the public sector, (iii) the UK and global commercial sector and, more speculatively (iv) voluntary workers and charities.

(i) The general public
Our society increasingly needs to cope with a rapidly ageing population with all its associated illnesses and other medical problems. However, we also expect to retain an active lifestyle well into old age and, indeed, need to remain mobile and self-sufficient for much longer now than has been the case historically. The materials developed in this project will benefit the general public, by (i) leading to better designed and more benign implant materials, which are closer to our natural tissue than current alternatives, thus avoiding the leaching and retention of harmful species in our body, and (ii) providing "smart" carriers to deliver and ration the dosage of pharmaceuticals at specific locations, thus avoiding the need for high doses or indiscriminate delivery.

(ii) Commercial sector
The development of materials for the controlled delivery of pharmaceuticals and nutrients will benefit both the pharmaceutical industry, which is an exceptionally strong sector in the UK, and also companies providing feed for livestock to combat nutrient deficiencies. In addition, healthcare companies providing implant materials, for example collagen scaffolds for soft tissue replacement or bioglass-based materials for maxillofacial surgery will profit from the development of materials better-tailored for individual applications. More generally, glass manufacturers will benefit from the generic models developed in this project, which are widely applicable to glass systems and amorphous materials.

(iii) Government/public sector
To improve the health of an ageing population is not only of interest to the individuals concerned, but also to public services, as any materials which improve health and limit the necessity for invasive (repreat) surgery will reduce demands on the medical infrastructure and the cost of healthcare.

(iv) Third sector
More speculative beneficiaries of this research are charities and voluntary organisations, who work with patients and victims of accidents. More natural, benign materials lead to fewer side-effects and shorter recuperation periods.