Modulating nonlinear elastic behavior of biodegradable shape memory elastomer and small intestinal submucosa(SIS) composites for soft tissue repair.

ABSTRACT

Structural repair of soft tissue for regenerative therapies can be advanced by developing biocompatible and bioresorbable materials with mechanical properties similar to the tissue targeted for therapy. Developing new materials modeling soft tissue mechanics can mitigate many limitations of material based therapies, specifically concerning the mechanical stress and deformation the material imposes on surrounding tissue structures. However, many elastomeric materials used in soft tissue repair lack the ability to be delivered through minimally invasive surgical (MIS) or transcatheter routes and require open surgical approaches for placement and application. We have developed a biocompatible and fully biodegradable shape memory elastomer, poly-(glycerol dodecanedioate) (PGD), which fulfills the requirements for hyperelasticity and exhibits shape memory behavior to serve as a novel substrate material for regenerative therapy in minimally invasive clinical procedures. Our previous work demonstrated control over the tangent modulus at 12.5% compressive strain between 1 and 3 MPa by increasing the crosslinking density in the polymer. In order to improve control over a broader range of mechanical properties, nonlinear behavior, and toughness, we 1) varied PGD physical crosslink density, 2) incorporated sheets of porcine small intestinal submucosa (SIS, Cook Biotech, Inc.) with varying thickness, and 3) mixed lyophilized SIS particulates into PGD at different weight percentages. Tensile testing (ASTM D412a) revealed PGD containing SIS sheets of were stiffer than controls (p < 0.01). Incorporating lyophilized SIS particulates into PGD increased the strain to failure (p < 0.001) compared to PGD controls. Test specimens with 1 ply sheets had greater tear strength (ASTM D624c) compared to PGD tear specimens prepared control specimens (p < 0.001). However, incorporating SIS particulates decreased tear strength of PGD-SIS 0.5 wt% particulate composites (p < 0.01) compared to PGD controls. Incorporating 2 ply and 4 ply sheets and 0.5 wt% particulates into PGD decreased the fixity and recovery of composite materials compared to controls (p < 0.01). Nonlinear modeling of stress strain curves under uniaxial tension demonstrated tunability of PGD-SIS composite materials to model various nonlinear soft tissues. These findings support the use of shape memory PGD-SIS composite materials towards the design of implantable devices for a variety of soft tissue regeneration applications by minimally invasive surgery.