Bioinspired micropatterned adhesive surfaces for medical applications: a numerical investigation of fibrillar adhesives and swellable microneedle arrays

Tarpey, Ruth
Traditional sutures and tissue adhesives can cause adverse effects, inflicting additional damage to the tissue, resulting in toxic chemical residues, and increasing the risk of infection. Bioinspired adhesives have demonstrated the potential of these alternate solutions to replace the use of sutures and tissue adhesives to meet the current clinical need. However, the underlying mechanics of how these micropatterned surfaces adhere in the context of more compliant biological tissues are poorly understood. The main aim of this thesis is to develop detailed computational frameworks models of bioinspired micropatterned surfaces and to improve the design of alternate adhesives to suit a multitude of medical applications. This work focuses on two adhesion mechanisms: (i) gecko-inspired fibrillar adhesives that adhere via intermolecular forces and (ii) parasitic-like swellable microneedles (MNs) that expand and interlock within tissue to cater for both dry skin and wetter internal environments. Fibrillar adhesion to more compliant substrates with similar moduli to biological tissues is simulated and the effects of fibril contact tip shape and substrate stiffness on detachment behaviour are evaluated, revealing that the detachment strength decreases as the substrate becomes more compliant relative to the fibril. The anisotropy of skin is incorporated into a 3D computational framework, and it is shown that the fibres cause a redistribution in interfacial stresses, similar to stiffening the substrate modulus, which has implications on the design of these fibrillar adhesives for clinical applications. Unlike standard MNs, the shape-changing capabilities of these swellable MNs must be explored, and parameters such as MN aspect ratio and swellable layer thickness are investigated to improve the mechanical interlocking abilities of the needle. The swelling of the entire surface coated in hydrogel when hydrated results in a swelling-mediated curvature at the array level, and a thermal strain analogy is sufficient to capture the free swelling of the MN array. A design platform is developed that can mitigate the unwanted curling observed when exposed to wet environments, to tune the array curvature to conform to specific surface topographies and improve the clinical feasibility of these MNs for wetter in vivo applications. The powerful predictive tools developed in this thesis illustrate the importance of detailed mechanical analysis to improve the design of bioinspired adhesive surfaces and eliminate the clinical need for sutures and tissue adhesives.
NUI Galway
Publisher DOI
Attribution-NonCommercial-NoDerivs 3.0 Ireland