Novel designs of bone-like scaffolds using topology optimisation and additive manufacturing

Around the world, fractures are a common reason for admission to hospitals. In England only, there were 2,489,052 fracture admissions between 2004 and 2014 [1]. As a result of these high rates of bone fractures, the field of bone tissue regeneration has extensively attracted researchers worldwide. The complex and hierarchical structure of bone tissue serves its diverse functions including mechanical, biological and chemical. This hierarchical structure of bone tissue is composed of optimised irregular arrangements of macrostructures (such as cortical and cancellous bone), microstructures (such as osteons and trabeculae), sub-microstructures (like lamellae), nanostructures (such as fibrillar collagen), and sub-nanostructures (such as minerals and collagen molecules)[2]. The mechanical function needs of bone tissue is supported by its component phases and the organisation of its hierarchical structure [3].

Extensive bone defects caused by trauma, tumour, and/or infection must be replaced by a functional alternative [3]. Autografts (bone tissue harvested from various sites of the patient body) has been widely accepted as the standard method for small defect reconstruction [4]. However, there are some limitations associated with autogenous bone grafting procedures, such as donor site morbidity, limited bone supply, anatomical, structural, and surgical limitations [5]. Other biological sources such as allograft (bone tissue harvested from one individual to another) and xenogenic (bone tissue harvested from another species) bone also been evaluated and used with varying clinical success for bone repair and regeneration. Hence, the use of synthetic materials is another way to repair and regenerate lost bone tissue [5]. However, it is still challenging to obtain synthetic bone substitutes that mimic the physical and biological properties of the healthy bone tissue more closely.

In bone tissue engineering, highly porous scaffold materials provide a pathway for cell attachment, bone in-growth, and vascularisation. To improve integration of porous scaffold material and the living bone tissue, material features like porosity, pore size, pore geometry and pore connectivity have to be controlled in a suitable range.

In this project, we propose using topology optimisation techniques to design cellular structures for bone-like scaffolds with different hierarchical levels made from hydroxyapatite submicron particles extracted from readily available molluscs shells and manufactured using Digital Light Processing (DLP) additive manufacturing technology. The shells are available in abundance with a global aquaculture production of approximately 15 million tonnes in 1 year and costing £88.95/tonne to landfill. These resulting bone-like scaffolds will offer mechanical properties that match the intended site for implantation and provides sufficient interconnectivity of the porous network that favour tissue integration and vascularisation. The resulting bone substitutes will demonstrate biocompatibility, osteogenic properties, and mechanical properties closer to those of natural bone tissues to avoid stress shielding which results in unwanted bone resorption and implant loosening.

1. Our primary impact will be by supplying the UK knowledge economy with skilled multidisciplinary researchers, equipped with the technical and transferable skills to establish the UK as pre-eminent in topology-based future technologies. The training they receive will make them proficient in the demands of the translation of academic science (with a broad background in condensed matter physics, materials science and applied electromagnetics) to industry, with direct experience from internship and industry engagement days. With their exposure to both theoretical research (including modelling and big data-driven problems) and experimental practice, our graduates will be ideally equipped to tackle research challenges of the future and communicate to a broad audience, ready to lead teams made up of diverse specialised components. The potential impact of our researchers will be enhanced by a broad programme of transferable skills, focusing on innovation, entrepreneurship and responsible research. Beneficiaries here will include the students themselves as they embark on future careers intertwining academic research and industry, as well as the other sectors listed below.

2. The research undertaken by students in the CDT will have impact on the future direction of topological science. Related disciplines, including physics, materials science, mathematics, and information technology will benefit from the cross-disciplinary fertilisation it will enable. The CDT will not only provide an interface between research in physical sciences and engineering, but also provide a route for academia to interact effectively with industry. This will help organise researchers from different disciplines to collaborate around the needs of future technology to design materials based on topological properties.

3. Our research will enable industries to set the direction of topological research around the needs of commercial research and development, leading to wealth generation for the UK, and to influence the mindset of the next generation of future technologists. Specifically, topological design has the promise to revolutionise devices and materials relevant to communications, microwave and terahertz technologies, optical information processing, manufacturing, and cybersecurity. Through partnership with organisations from the wider knowledge sector, we will deepen the relationship between academic research and disciplines including IP law and scientific software development.

4. Our CDT will also have impact on the wider academic community. New specialist courses and training in transferable skills will be developed utilising cutting-edge multimedia technologies. Our international research collaborators, including prominent global laboratories, will benefit from placements and research visits of the CDT students. Our interdisciplinary research, combining the needs of academia and industry will be an exemplar of the effectiveness of the CDT model on an international stage.

5. The wider community will benefit from our organised public engagement activities. These will include direct interaction activities, such as demonstrating at the Birmingham Thinktank Science Centre, the Royal Society Summer Exhibition, local schools and community centres.