Methods to image and assess the microstructure of polymer based biomaterials in liquid phase, for example cell culture medium, are well warranted. X-ray microtomography could provide a mean to visualize and analyze such structures. However, the density of such polymers is close to that of water and hence the X-ray contrast is poor. Moreover, if the biomaterials contain cells and are dried, the cell morphology may be distorted. In this paper we test phosphotungstic acid (PTA) staining to improve the contrast. We imaged collagen and PLA samples with μCT in air, water and alcohol. The methods were compared visually and with contrast to noise ratio calculated from the images. Our results demonstrate that with alcohol the PLA can be imaged also in liquid phase. PTA staining seems to be a good method to increase the contrast for collagen in μCT imaging.