Bioinspired micropatterned adhesive surfaces for medical applications: a numerical investigation of fibrillar adhesives and swellable microneedle arrays
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Date
2024-03-21Embargo Date
2025-03-20
Author
Tarpey, Ruth
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Abstract
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.