A combination of biomaterials and stem cells is being used to improve outcome in reparative medicine. Biomaterials interact with the stem cells through physical and chemical interactions which can change cell properties. The degree in which this affects cell characteristics and their ability to repair damaged tissue has not been investigated yet. The present project aims to determine the proteomic changes of human umbilical cord mesenchymal stem cells (hUC-MSC) encapsulated into collagen hydrogels. To do so, hUC-MSC were encapsulated into collagen hydrogels (2 mg/mL) for 1 week. Cell media was collected for exosome isolation and cells were harvested. Protein expression profiling was performed on 20 µg of total protein of either cells or exosomes via tryptic digestion and LC- MS/MS analysis (MaXis 5G (UHR ESI Qq-TOF)). A fraction of the exosomes was also analyzed by fluorescence activated cell sorting (FACS). First pilot studies aimed to optimize the protocol and maximize cell viability and exosome detection. Viability of the cells seemed to be affected by hydrogel production time and collagenase treatment before cell harvesting. Thus, hydrogels will be produced in smaller amounts and collagenase treatment will be reduced. The ability to detect exosomes is directly proportional to their concentration in the media and, hence, higher numbers need to be produced. Future studies will include the optimizations needed for FACS and LC-MS/MS analyses. Then, identified peptides will be analyzed with the MaxQuant MS/MS search program against Homo sapiens database. Gene ontology annotations and pathway analysis will be performed and changes in protein levels of collagen-encapsulated hUC-MSC will be investigated. Acknowledgements: The authors would like to thank Orbsen Therapeutics for training on hUC-MSC culture and exosome isolation. This project has been funded by the European Union Horizon 2020 Programme (H2020-MSCA-ITN-2015) under the Marie Skłodowska-Curie Innovative Training Networks and Grant Agreement No. 676408.