Scaffold Generation via Melt Electrowriting for Tendon Tissue Engineering

Abstract

Tissue engineering offers a promising solution to treat Achilles Tendon (AT) injuries, healing, and regeneration. Native human AT was recently shown to demonstrate auxetic behaviour within the normal range of motion, indicated essential in its highly dynamic loading environment. Melt electrowriting (MEW) has garnered much attention to realize functional tissue engineering scaffolds as it enables highly precise control over fibre deposition and scaffold architectures that mimic native tissue fibrous extracellular matrix (ECM). This thesis focused on the MEW fabrication of auxetic scaffolds and its influence on the mechanically induced response from seeded native tenocytes towards ECM formation and regeneration. The scaffold design employed a crimped fibre architecture with a sinusoidal wave morphology, pre-established as a significant contributor to tendon tissue regeneration. To test our hypothesis on the influence of scaffold architecture on mechanically loaded tenocytes, a high molecular weight poly(caprolactone) CAPA 6500 was employed using MEW. The bi-directionally crimped scaffolds exhibited a Poisson’s ratio of -1.5 and a tensile modulus of ~ 250 MPa. Native primary rabbit AT tenocytes under dynamic loading (4% strain at 1 Hz for 1h/day) for 2 weeks post 1 week of pre-culture, demonstrated higher cell proliferation and higher collagen deposition on bi-directionally crimped scaffolds in comparison to uniaxially crimped scaffold controls and static cell culture. This thesis also explored alternate material choices for MEW to expand the current selection of melt-processable materials. Photocrosslinking of polymers to manipulate the mechanical performance through covalent bond formation under light illumination has gathered attention as an alternative to PCL. Herein, random copolymers based on a carbonate monomer, MUM (((5-(4-methylumbelliferyloxymethyl)-5methyl-1,3-dioxan-2-one)) that includes a thermally stable photodimerizing coumarin pendant group were formulated. MEW processability of the synthesized copolymers with varying ratios of MUM were demonstrated. The copolymers possessed bulk tensile modulus values as high as 200 – 650 MPa. Moreover, the photocrosslinked linear micro-periodic MEW copolymer structures that showed cytocompatibility with both 3T3 fibroblasts and primary rabbit AT tenocyte-like fibroblasts. These rational polymer design approaches representing readily adaptable material solutions can help fabricate chemically modifiable polymeric structures with scaffold geometries beyond those studied here to achieve native tissue microarchitecture and biomechanics.