Smart Manufacturing of Medical Devices for soft tissue fixation

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We will research smart manufacturing routes, which impart controllable enhancement of properties and functionality of polymers and polymer composites whilst achieving precision geometry products. These will be relevant to a range of potential medical devices, selected with our industry partners, Zmith * Nephew, Wittman Battenfeld and Corbion Purac, particularly those exploiting shape memory functionality and surface feature control. The initial focus is for soft tissue fixation to bone (e.g. rotator cuff and anterior cruciate ligament (ACL) repairs); longer-term goals include fixations for fracture (including intermedullary nails) and knee joint replacements.Solid phase orientation processing of polymers at temperatures above their glass transition point, but below their melting point, provides the major route to imparting a wide range of polymer molecular orientation, from low up to very high levels. This can be utilized to create dynamic devices which change shape in-situ on exposure to temperature or, potentially, body fluid, allowing the device to adapt to the surrounding bone topology. Protype devices will be manufactured from known resorbable or inert polymers, inorganic particles and suitable plasticisers all having known clinical history. The devices will be programmed to mechanically function and then degrade to expose known inorganic salts/scaffolds which can then be used to promote osteogenesis. In the case of medical implants such as tissue fixations, the recovery typically needs to take place at an appropriate temperature to avoid tissue damage (so less than ~50C), or (more challenging) be driven by exposure to body fluids, and to occur in an acceptable timescale to the operating clinicians (e.g. less than 15 s), and to retain fixation strength over required timescales (months for bioresorbables, permanent for non-resorbables). In addition to the solid phase orientation processing route, a range of melt processing techniques can be used to obtain (in general) lower levels of orientation but which may have other advantages in terms of manufacturing, including net shape processing. Novel variants of these are explored in the Research Programme,including: (a) micromoulding (single shot property gradient products, or over-moulded products, and surface feature control), (b) micro-extrusion (for precision preforms for die drawing, or controlled surface continuous products), and (c) hybrid processing, such as a novel injection-drawing process.Manufacturing challenges to be addressed include (i) the overall goal of 'Smart Manufacturing', defined here as the effective control of property levels through processing, simultaneous with achieving precision geometry products at economic production rates for shape memory polymers; (ii) materials and additives suitability, combined with processability for the complex requirements for bioresorbable fixations; (iii) formation of starting materials suited to manufacturing routes, and (iv) refined modelling for developed understanding of solid and melt phase processing, vital in developing understanding of the processes and process design.