Non-Invasive Ultrasonic Assessment of the Mechanical Properties of Hydrogels

R. M. IRASTORZA; E. BLANGINO; B. DROUIN; D. MANTOVANI

Chengdu

Congreso; 9th World Biomaterials Congress (WBC); 2012

National Engineering Research Center for Biomaterials Sichuan University, Chengdu, China.

Natural macromolecules represent a well-founded and rational choice for the design of scaffolds for tissue engineering. Collagen hydrogel biomaterials have been proposed for a wide range of biomedical applications. However, insufficient mechanical properties have severely limited the use of these hydrogels for loadbearing applications such as Vascular Tissue replacement (VTR). Bioreactors are useful to improve mechanical and functional properties of constructors (scaffold+cells), in this context, non-destructive techniques to evaluate phisical properties are higly desirable. Gels, made with Type-I collagen obtained from rat tail tendons, were prepared using three concentrations (1.6, 2.0 and 2.4 g/L). Disk-shaped geometry was chosen because it facilitates simultaneous ultrasonic testing and unconfined compression characterisation. The unconfined compression tests were made with a micro-tester (Instron 5848) using Teflon plates. The upper moving plate, attached to a 10N Load cell contained the ultrasonic probe. All tests were performed at .5 mm /min speed, and samples were maintained at a constant temperature by a thermoelectric device. All tests implied a monotonic compression to ~ 60 % strain followed by as many as 8 cycles (~ 40 to 60% strain). This presentation will summarise the ongoing effort done in our labs to gain an in-depth understanding of the mechanical properties of collagen hydrogels. One of the goals of this research is to propose a non-destructive method based on ultrasonic propagation of longitudinal waves to investigate the elastic properties of the collagen gels. Results, ultrasonic as well as mechanical, indicate huge differences between the monotonic and cyclic compression modes. Analysis of the results using widely accepted viscoelastic mechanical models (e.g. Maxwell, Voigt or Kelvin) will be discussed as well as the ones used to analyse propagation of ultrasonic longitudinal waves. Testing of collagen gels scaffolds with ultrasonic techniques can provide a fast and non-destructive way of predicting the mechanical properties. This technique is also useful for real time monitoring of evolution of these properties, while scaffold plus cells are inserted in a bioreactor . These simultaneous mechanical and ultrasonic tests are essential steps to achieve this goal.