Replicating the intrinsic biomechanical characteristics of connective tissue: An exploration into the design and manufacture of PVA cryogel

Crolla, Joseph Patrick (2023). Replicating the intrinsic biomechanical characteristics of connective tissue: An exploration into the design and manufacture of PVA cryogel. University of Birmingham. Ph.D.

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Abstract

Damage and disease of connective tissue (CT) pose a risk to an increasing percentage of the population, and the ability to develop biocompatible polymers that better replicate the intrinsic properties of CT would aid in improving the function of CT replacements. Poly(Vinyl Alcohol) (PVA) cryogel is a particularly versatile biomaterial because it has `tuneable' mechanical properties which can mimic a wide range of soft tissues. PVA is compatible with magnetic resonance (MR) imaging; allowing tissue implants to be monitored non-invasively. PVA is compatible with novel sub-zero temperature additive manufacturing (AM) techniques, which provides considerably greater freedom in the design process, as well as social and economical benefits to implant manufacture.
The overarching aim of this thesis is to explore the design for additive manufacture, and intrinsic material properties of PVA cryogels, with respect to their use as physical models of connective tissue.

Viscoelastic and MR T2 characterisation was conducted to assess the relationship between PVA composition and its viscoelastic behaviour under dynamic loading,representing physiological conditions, and the relationship between composition and MR T2 relaxation time. The AM of PVA has been progressed through a bio-inspired approach to control the 3D printing toolpath, allowing for the introduction of anisotropic and functionally graded material behaviour. This has been achieved through the analysis of key AM process parameters, and the development of a parametric method to vary the infill geometry, and in turn the mechanical properties of AM PVA.

This thesis establishes a composition-dependent correlation between the viscoelastic moduli and MR T2 relaxation time. This thesis has also shown that AM PVA samples exhibit pronounced orthotropic properties; with the smallest nozzle size tested showing a 30% decrease in viscoelastic moduli when tested perpendicular to the print direction. Samples with custom infill geometries were successfully manufactured, and the empirically derived relationships have been shown between parameters used to define the toolpath shape, and hyperelastic mechanical properties.

Critically, this thesis has explored the design and manufacture of PVA cryogels; for the first to time assessing its viscoelastic properties under physiological loading, and defining bio-inspired AM methods to introduce and control orthotropic and functional graded properties intrinsic to CT.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):