University of Cambridge
Additive Manufacturing of Functional Materials for Biomedical Devices
Abstract
dc:description.abstractBiomedical devices have revolutionised modern healthcare by enabling more precise and effective treatment, which has profoundly improved patient care and quality of life. Among these devices, protective wearable medical devices can offer continuous and non-invasive protection in everyday life, and thus have been widely used. However, common drawbacks, including a lack of bespoke design, low user comfort due to their bulk and rigidity, and a heavy weight, prevent protective wearable devices from unleashing their full potential. Rapid advancements in materials, manufacturing, and structural design are making personalised, comfortable, and lightweight medical devices possible. In this thesis, material extrusion additive manufacturing is used to enhance the functionality of polymers for the improvement of medical devices, including bespoke ankle braces, impact resistance protective paddings, and biomedical surfaces for the regulation of cell growth. Anisotropic, self-assembling, and self-reinforcement hierarchical liquid crystal polymer (LCP) are 3D printed with the form of fibres into macroscopic non-linear strain-hardening metamaterials to fabricate lightweight and flexible ankle braces. Printed LCP fibres presented high mechanical performance (Young’s modulus of 23.6 ± 3.36 GPa, ultimate tensile strength of 336.96 ± 39.7 MPa). Sinusoidal wave patterns enable a mechanical response to transition from a low stiffness to a high stiffness, therefore satisfying the biomechanics requirements for both free ankle motion and stiffening for effective protection from ankle inversion. By adjusting the period length and the amplitudes of wave patterns, the range of free motion can be customised for bespoke design. The effectiveness of this LCP ankle brace is further validated in the gait lab, presenting a weight reduction of 67%, compared to a commercial lace-up. Transitioning from the microscopic LCP fibres to the macroscopic single-wall LCP film. The periodic meso-scale textures were discovered for the first time on the LCP surface, driven by the unique viscoelasticity and anisotropy of LCP melt. The tunability of surface morphology (313 to 1137 m in length, 96 to 384 m in width, and 3 to 20 per mm2 in number of beads) is achieved through the control of processing parameters without requiring complex toolpath designs. The resulting meso-textures offer functional utility on direct nerve cell alignment for new possibilities on biomedical implants and terahertz wave manipulation for photonic devices. This showcases a new understanding of LCP manufacturing and demonstrates other potential applications of LCP. A flexible impact-resistance device that can soften and stiffen in response to external stimuli is developed. Shear-stiffening gels are 3D-printed into thin fibres with interstitial spaces filled with polydimethylsiloxane elastomer. The composites achieve the mechanical integrity with shear-stiffening behaviour featuring shear-rate dependent stiffness and shape recovery, which is desired for wearable anti-impact devices: composites are soft and flexible with fixed-shape at rest but get rigid when they are subjected to external impact. The composite exhibits effective impact-resistance (impact force decreased from 16.5 to 2.74 kN) and shape recovery. Composite mechanics can also be modulated by tuning the infill percentages to selectively vary part stiffness and therefore aid motion and wearer comfort with damping performance.
Degree
thesis:*- Level dc:type.qualificationlevel
- Doctoral
- Grantor dc:publisher.institution
- University of Cambridge
- Year dc:date.issued
- 2025
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Zou, Miaomiao
- Advisor dc:contributor.advisor
-
- Pattinson, Sebastian
Subjects
dc:subject × 11Rights
dc:rightsIdentifiers
dc:identifier.*- DOI dc:identifier.doi
- https://doi.org/10.17863/CAM.125260
- OAI identifier oai:identifier
- oai:www.repository.cam.ac.uk:1810/395911