Mass spectrometry imaging is a promising technique for evaluating the biocompatibility of polymer scaffolds used for drug delivery and tissue engineering, according to a study (Anal. Chem., DOI: 10.1021/ac100837n). Ron M. A. Heeren of the Amsterdam-based Institute for Atomic & Molecular Physics and coworkers used time-of-flight secondary ion mass spectrometry (TOF-SIMS) to collect images of hydrogel drug delivery carriers implanted in the kidney of rats. In the images, which also include the cells surrounding the hydrogel, polymer fragment ions appear in the implant and are found to be distributed in newly formed tissue. The researchers identified markers associated with different phenotypes of macrophages, a type of immune cell, but are not yet able to distinguish definitively between the phenotypes. Such markers could reveal information about different stages of the foreign-body immune response. “Being able to simultaneously visualize information from a polymeric hydrogel, cellular material into which the gel was implanted, and macrophages that are attacking the implant breaks new ground, not only for bioanalysis but also for TOF-SIMS itself,” notes Nicholas Winograd, a TOF-SIMS imaging expert at Pennsylvania State University.