Silicone based biomaterials are characterized with NMR. Bulk spin-lattice (T1) and spin-spin (T2) relaxation times are measured in polydimethylsiloxane (PDMS) model networks and various types of implants. The T2 results seem to indicate that crosslink densities of these biomaterials are lower than those of the PDMS model networks studied. 1H chemical shift NMR imaging techniques are developed to investigate the aging (e.g., migration of free polymer, rupture due to mechanical stress, etc.) of biomaterials in vivo.