Viscoelastic to elastic transformation of soft polymer properties for accelerated materials selection based on tissue dynamics in tissue engineering applications

Abstract

Human tissues exhibit strain rate-dependent mechanical properties, adapting to various physical activities by altering their stiffness and elasticity. This dynamic behavior is critical for tissue functionality, influencing the design of biomaterials for tissue engineering. The current choice of tissue-specific biomaterials does not take into account the tissue dynamics nor the strain-dependent property variation. We propose a conceptual framework to overcome this challenge, considering soft tissues as a case in point and Thermoplastic polyurethanes (TPUs) as a suitable material, the chemistry of which can be controlled to develop them across a broad spectrum of mechanical properties to match those of the natural tissue. TPUs have attracted considerable interest in tissue engineering because of their versatility in biofabrication methods, tunable mechanical properties, and biocompatibility. However, characterizing such soft viscoelastic materials with a strong dependence of their properties on temperature and strain rate is a challenge and requires an elaborate test scheme over multiple strain rates and temperatures. The present study described a viscoelastic-elastic transform that can convert the frequency domain viscoelastic measurements to elastic constants over a wider range of test conditions using a single sample and substantially reduce the test regime. Tensile test measurements were used to validate the results of the transformation. The findings revealed that while some TPUs might be suitable for certain applications at specific strain rates, others are better suited when strain rates are varied to more accurately mimic human life conditions. Additionally, cytocompatibility tests, crucial for tissue engineering applications, confirmed that the TPU scaffolds support cell attachment and proliferation, with viability rates exceeding 80 % across all tested groups. Overall, this study highlights the versatility of the viscoelastic-elastic transform method in identifying suitable materials by characterizing their strain rate-dependent mechanical properties, thereby optimizing scaffold performance to more accurately replicate the dynamic conditions encountered in human tissues.

Keywords

• Dynamic mechanical analysis
• Elastic modulus
• Thermoplastic polyurethane TPU
• 3D printing
• Tissue engineering