Photopolymerization is a common tool to harden materials initially in a liquid state. A surgeon can directly trigger the solidification of a dental implant or a bone or tissue filler. Traditionally, photopolymerization has been used mainly in dentistry. Over the last decade advances in material development including a wide range of biocompatible gel- and cement-systems open up a new avenue for in-situ photopolymerization for musculoskeletal, cardiovascular or neurosurgical applications. However, at the device level, surgical and endoscopic probes need to be developed to deliver the liquid photopolymer, harden it by light and to monitor that the hardened material has the appropriate property. Here we present a miniaturized light probe where a photoactive material can be 1) mixed, pressurized and injected 2) photopolymerized or photoactivated and 3) monitored during the chemical reaction. The device enables surgeries to be conducted through a hole smaller than 1 mm in diameter. Beside basic injection mechanics, the tool consists of an optical fiber guiding the light required for photopolymerization and also for chemical analysis. Using fluorescence spectroscopy, the current state of the photopolymerization is inferred and monitored in real time. Biocompatible and highly tunable Poly-Ethylene-Glycol (PEG) based hydrogels were used as injected material. The device was tested on a model for intervertebral disc replacement and hydrogels were successfully implanted into a bovine caudal model. These in-situ photopolymerized implants were evaluated at the tissue level (tissue integration and mechanical properties), at the cellular level (biocompatibility and cytotoxicity) and ergonomic level (sterilization procedure and feasibility study) and thus seem to be a promising alternative to traditionally used tissue and bone fillers. Currently further promising applications are under investigation. The results will be presented at WC2015.