Abstract
Development of biodegradable shape memory elastomers (SMEs) is driven by the growing need for materials to address soft tissue pathology using a minimally invasive surgical approach. Composition, chain length and crosslinking of biocompatible polymers like PCL and PLA have been investigated to control mechanical properties, shape recovery and degradation rates. Depending on the primary mechanism of degradation, many of these polymers become considerably stiffer or softer resulting in mechanical properties that are inappropriate to support the regeneration of surrounding soft tissues. Additionally, concerns regarding degradation byproducts or residual organic solvents during synthesis accelerated interest in development of materials from bioavailable monomers. We previously developed a biodegradable SME, poly(glycerol dodecanoate) (PGD), using biologically relevant metabolites and controlled synthesis conditions to tune mechanical properties for soft tissue repair. In this study, we investigate the influence of crosslinking density on the mechanical and thermal properties of PGD during in vitro and in vivo degradation. Results suggest polymer degradation in vivo is predominantly driven by surface erosion, with no significant effects of initial crosslinking density on degradation time under the conditions investigated. Importantly, mechanical integrity is maintained during degradation. Additionally, shifts in melt transitions on thermograms indicate a potential shift in shape memory transition temperatures as the polymers degrade. These findings support the use of PGD for soft tissue repair and warrant further investigation towards tuning the molecular and macromolecular properties of the polymer to tailor degradation rates for specific clinical applications.
Highlights
Regenerative therapies involving minimally invasive surgical procedures require materials to mechanically bridge tissue defects while allowing implant delivery through smaller incisions or via transcatheter approach
High cure poly(glycerol dodecanoate) (PGD) has a lower Ttrans compared to medium cure PGD and low cure PGD
Differential scanning calorimetry indicates a lower transition temperature for high cure PGD (hPGD) compared to lPGD and mPGD (Fig 1C and Table 1)
Summary
Regenerative therapies involving minimally invasive surgical procedures require materials to mechanically bridge tissue defects while allowing implant delivery through smaller incisions or via transcatheter approach. Hydrogels have been prone to migration and biodegradable polymers like PLGA, PLA and PCL predominantly undergo bulk degradation causing rapid changes in mechanical integrity during the degradation timeframe [5]. Biodegradable elastomers like polyglycerol sebacate(PGS) and poly-diol citrates have been increasingly studied for soft tissue repair applications [6,7,8,9]. These materials are synthesized from components of common metabolic pathways and break down into biologically compatible byproducts. The shape transition temperatures (7–42 ̊C), elasticity (300–500% strain at break) and tensile modulus (0.1–80 MPa) can be tuned to make these materials ideal for a wide range of soft tissue repair including but not limited to neural, cardiac and musculoskeletal pathologies [10]
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