Characterization of tissue scaffolds using optics and ultrasound

Abstract

Tissue scaffolds are an integral part of the tissue engineering process, assisting in the culturing of cells in three dimensions. It is important to understand both the properties of the scaffold and the growth of cells within the scaffold. This paper describes a system to characterise scaffolds using acoustic techniques alone and the development of an ultrasound modulated optical tomography system to study the growth of cells within the scaffolds. Our interest is in characterising the properties of gel-based and polymer foam-based scaffolds. Results from a purely acoustic system have been used to investigate the properties of foam scaffolds manufactured from synthetic polyesters poly(lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) via a supercritical fluid process. As these are porous materials, they are particularly challenging acoustically as the pores scatter sound significantly. However, it is demonstrated that acoustic signals are detectable through a 6mm thick scaffold. Although acoustics alone can be used to characterize many properties of the scaffolds, useful information can also be obtained from optical techniques e.g. monitoring the growth of cells within the scaffold via optical absorption or fluorescence techniques. Light scattering is of course a significant problem for relatively thick engineered tissue (~5mm). The acoustic approach has been extended to include laser illumination and detection of the ultrasound modulated optical pulse. Images of optically-absorbing materials embedded in gel-based tissue phantoms will be presented demonstrating that a lateral resolution of 250μm and an axial resolution of ~90μm can be achieved in scattering samples.