In-bioreactor ultrasonic monitoring of 3D culture human engineered cartilage

Abstract

Engineered cartilage tissue is one of the most promising treatments for articular cartilage defects. In this study, a bioreactor was designed to implement a non-invasive real-time monitoring of the neo-cartilage tissue formation processes through ultrasonic signal analysis. Polylactic acid (PLA) scaffolds were printed and seeded with human chondrocytes. Then, they were cultured in an ultrasound (US)-integrated bioreactor. The readings from the ultrasonic sensors were analyzed by numerical models of the ultrasound-tissue interaction and by a stochastic treatment to infer the extracellular matrix (ECM) evolution. To reconstruct the velocity and attenuation from the recorded signals, a genetic-algorithm based inverse problem (IP) was combined with an iterative computational propagation. The ultrasonic data were validated against evolution measurements of the in vitro 3D chondrocyte cultures assessed by proliferation and morphological observations, qualitative and quantitative biochemical parameters and gene expression analysis. Parameters reconstructed from the ultrasonic monitoring (p-wave velocity, attenuation, density changes in the culture layer) were proved useful to indirectly determine cell culture proliferation parameters in a non-invasive manner. The significant correlation shown between glycosaminoglicans (GAG) and collagen II (Col II) expression with the elastic damping evolution of the novo ECM (R = 0.78; p < 0.001) and (R = 0.57; p < 0.01), respectively, reinforces the feasibility of using ultrasound to evaluate chondrocyte functionality. Consequently, US can be used to monitor chondrocyte proliferation and ECM formation in the context of 3D cartilage engineering.