Multiscale photoacoustic microscopy of single-walled carbon nanotube-incorporated tissue engineering scaffolds

Three-dimensional polymeric scaffolds provide structural support and function as substrates for cells and bioactive molecules necessary for tissue regeneration. Noninvasive real-time imaging of scaffolds and/or the process of tissue formation within the scaffold remains a challenge. Microcomputed tomography, the widely used technique to characterize polymeric scaffolds, shows poor contrast for scaffolds immersed in biological fluids, thereby limiting its utilities under physiological conditions. In this article, multiscale photoacoustic microscopy (PAM), consisting of both acoustic-resolution PAM (AR-PAM) and optical-resolution PAM (OR-PAM), was employed to image and characterize single-walled carbon-nanotube (SWNT)-incorporated poly(lactic-co-glycolic acid) polymer scaffolds immersed in biological buffer. SWNTs were incorporated to reinforce the mechanical properties of the scaffolds, and to enhance the photoacoustic signal from the scaffolds. By choosing excitation wavelengths of 570 and 638 nm, multiscale PAM could spectroscopically differentiate the photoacoustic signals generated from blood and from carbon-nanotube-incorporated scaffolds. OR-PAM, providing a fine lateral resolution of 2.6 microm with an adequate tissue penetration of 660 microm, successfully quantified the average porosity and pore size of the scaffolds to be 86.5%±1.2% and 153±15 microm in diameter, respectively. AR-PAM further extended the tissue penetration to 2 mm at the expense of lateral resolution (45 microm). Our results suggest that PAM is a promising tool for noninvasive real-time imaging and monitoring of tissue engineering scaffolds in vitro, and in vivo under physiological conditions.