Material Design for Minimally Invasive Spinal Implant for Metastatic Bone Disease

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This PhD is part of the EPSRC Programme Grant, OncoEng project (www.oncoeng.org), which aims to develop a minimally invasive implant (MII) designed to support the vertebrae load and prevent fractures in people affected from metastatic bone disease (MBD). The primary focus of this PhD research involves the design and optimisation of the material for the creation of the MII. MBD denotes the infiltration of cancerous cells from primary tumours to the bone, and is a common complication of cancer with incidences reaching 70-95% in multiple myeloma, 65-90% in prostate cancer and approximately 65-75% in breast cancer. MBD occurs predominantly in the vertebrae and results in neurological compression symptoms, and in severe cases paraplegia. This condition can have a significant impact on patients, including pain, reduced weight-bearing capacity, limitations in daily activities and overall, substantially deteriorating the patient Quality of Life (QoL). Acknowledging the distinctive and personalized needs of terminally ill patients, the NHS Long Term Plan for Cancer hasemphasized the importance of new interventions regarding the improvement of their QoL. Consequently, there is a demand for the development of an implant capable of filling the void left by the removal of metastatic spinal lesions.The target profile of the MII entails its ability to be inserted into the spine with minimally invasive techniques, and seamlessly match the structure of the surrounding bone. In response, research has shifted towards developing a biocompatible, radiopaque material exhibiting the required mechanical properties to sustain the vertebral loads of the spine. Metamaterials, distinguished by non-natural or uncommon properties at a scale smaller than bulk phenomena, are deemed suitable for this purpose. The enhanced mechanical properties of metamaterials arise from the incorporation of micro-scale building blocks organized in a structured hierarchy. Thus, the challenge of the material design lies in achieving a complex geometric structure with a feature size on the order of 1 um, crucial for obtaining the desired homogeneity and emergent properties. No subtractive or forming manufacturing exists that can produce such feature resolution in 3D without significant geometric constraints. Consequently, additive manufacturing methods have been explored, with VAT photopolymerizationtechniques demonstrating promise in efficiently producing intricate lattices integral to the MII development.VAT photopolymerization is a 3D printing process which involves selectively curing a volume of photocurable material through light-activated polymerization. It has been shown to have the highest accuracy and resolution compared to other 3D printing technologies. A wide range of thermosetting photopolymers are available which are well suited to medical applications due to their smooth surface finish, versatile modification and viability for current sterilization protocols. Previous work by members of the research group has led to the development of 10 base formulations for the fabrication of the candidate material. The focus of this thesis will be to examine and optimise these formulations to achieve the target resolution and physical properties required for the development of the MII. VAT photopolymerization will be employed to print the material into the intricate geometrical structures required.