Reporting matrix metalloproteinase (MMP) activity directly from the extracellular matrix (ECM) may provide critical insights to better characterize 2D and 3D cell culture model systems of inflammatory diseases and potentially leverage in vivo diagnosis. In this proof-of-concept study, we designed MMP-sensors, which were covalently linked onto the ECM by co-administration of the activated transglutaminase factor XIIIa (FXIIIa). Elements of the featured MMP-sensors are the D-domain of insulin-like growth factor I (IGF-I) through which co-administered FXIIIa covalently links the sensor to the ECM followed by an MMP sensitive peptide sequence and locally reporting on MMP activity, an isotopically labeled mass tag encoding for protease activity, and an affinity tag facilitating purification from fluids. All sensors come in identical pairs, other than the MMP sensitive peptide sequence, which is synthesized with l-amino acids or d-amino acids, the latter serving as internal standard. As a proof of concept for multiplexing, we successfully profiled two MMP-sensors with different MMP sensitive peptide sequences reporting MMP activity directly from an engineered 3D ECM. Future use may include covalently ECM bound diagnostic depots reporting MMP activity from inflamed tissues.

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BACKGROUND: The incidence of conversion total hip arthroplasty (cTHA) following reduction and fixation for proximal femur fractures will increase in parallel to the aging population worldwide. OBJECTIVE: The goal of this study is to report the frequency of bacterial detection and the outcome of cTHA at the authors’ institution and to analyze preoperative factors that correlate with higher rates of bacterial growth and septic revision. METHODS: 48 patients who had been converted to THA after osteosynthesis of a proximal femur fracture either by a one- or two-stage procedure were included. Septic failure rate and the frequency of bacterial detection at the time of fixation device removal were calculated. The influence of different preoperative factors was examined by the odds ratio. A receiver operating characteristic curve of c-reactive protein (CRP) for detection of bacterial growth at the time of fixation device removal was calculated. RESULTS: 18.8% patients showed positive bacterial cultures, with Staph. epidermidis being the most frequent pathogen (33.3%). Septic failure after cTHA occurred in 4.2%. Fixation with cephalomedullary nails and complications with the internal fixation showed higher odds for bacterial growth at time of cTHA. CRP for predicting bacterial growth had an area under the curve of 0.661. Implant survival was worse when temporary spacers were used. CONCLUSION: Bacterial detection rate at the time of cTHA is high, whereas septic failure rates are low. Isolated evaluation of inflammatory blood markers without other diagnostic modalities for infection is not decisive and does not justify a two-stage approach with implantation of a temporary spacer.

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