Biomedical Materials

Current Projects: Past Projects:

Investigation of Load-Bearing Scaffolds for Critical-Size Bone Defects

Personnel: Weiting Deng (Ph.D. student in Medical Engineering)

Bone tissue possesses an innate regenerative capability to sufficiently heal small sites of damage, for instance some types of fractures. The reconstruction of large bone defects (typically >2cm, depending on the anatomical site) caused by trauma, disease or tumor resection is a fundamental challenge for orthopedic and plastic surgeons. This type of bone lesion requires clinical intervention if functional restoration and complete healing is to be achieved. Additive manufacturing (AM), also named 3D printing, is an emerging technology that permits the fabrication of complex-shaped structure with high precision using layer-by-layer printing. This freedom of design has allowed engineers to have an unprecedented control over a scaffold's structure and composition. Additive manufacturing offers the capability to fabricate customized bone scaffold without size limitation and meet the urgent requirement when implants are needed immediately. Significant progress has been made in developing biocompatible materials with AM, but challenges still remain in load-bearing scaffolds of matching the bone stiffness - due to the large heterogeneity in bone structure and difference across patients, and maintaining structural integrity.

To tackle this problem, rational designs are required through both material approach and structure approach. Vat photopolymerization was chosen as the fabrication method due to its ability to achieve high resolution. Techniques such as SLA and DLP can achieve micron level resolutions while two photon lithography can achieve sub-micron resolutions. Our central hypothesis is that stiffness matching between natural bone and scaffold could be achieved via modification of biocompatible photo-crosslinkable resins and scaffold design of spinodal structure.

Photopolymerization of a custom polymer resin to produce a bone-like scaffold

Past Projects

Designing Neural Probes for Long Term Neural Recording in Large Brains

Personnel: Dr. Luizetta Elliott (alumna)

Chronic reliability, and thus a reduced foreign body response, is key to realizing the promise of neural probe technology in applications such as brain-machine interfaces, connectome mapping and brain disorder investigations. A variety of flexible, low density probes with small footprints have been designed to minimize the foreign body response in mouse models. However, few are applicable to larger systems such as primate brains. Such implantations are challenging; probes must be inserted ~3cm into the brain, which could require ~100mN of force. Further, accurate targeting requires less than 2 degrees deflection and may involve repeated insertions during the up to 6 hour surgical procedure.

To enable the implantation of compliant probes with minimal diameter under these constraints, we aim to minimize the insertion load required for implantation. Past the initial 2mm of insertion where tissue penetration forces are dominant, continued load increases are attributed to friction between the implant and the surrounding tissue. We are therefore developing coating approaches to minimize this contribution in agarose and tissue models. Through decreasing loads attributable to friction by a factor of 6, we have improved targeting accuracy by 23%. Further experiments under realistic surgical conditions will enable accurate placement of minimally invasive probes in primate brains.

Experimental set-up for large scale neural probe insertion into lamb brain.

Stereolithographic Synthesis of Hydroxyapatite Bone Scaffolds

Personnel: Sammy Shaker (Ph.D. student in Biology and Biological Engineering)

Additively manufactured materials can exhibit a variety of microstructural and physical properties that differ from classically synthesized materials of the same composition. With regards to biomedical materials, these properties can have significant effects on the interaction of tissues and cells with implanted materials and devices. Bone scaffold materials provide a prime example of the importance of these interactions, and designing materials that provide effective cell integration as well as mechanical support is a significant challenge.

We attempt to address this challenge by using stereolithography to generate bone scaffold structures that are then calcined into a phase or phase mixture of our choice. In doing so, we hope to generate biosimilar phases whilst further examining the effects of microstructural and mechanical properties on the interaction between cells and the scaffold.