gms | German Medical Science

Objectives: Cell therapy and tissue engineering have become core elements of regenerative medicine. Delivery of antibiotics and liquids to their intended site of action is difficult as these fluids are easily washed away during surgery or removed via natural processes. Future treatments involving cell therapy and tissue engineering products mandate suitable carriers for efficient retention of cells and fluids in situ.

Here, the absorption capacity and antibiotic release kinetics of carrier grafts were assessed. Different human bone allografts were compared including the novel fibrous allograft Fiberfill^®, a specifically designed high absorption and high surface area carrier-graft consisting of demineralised cortical fibers and granulated cancellous bone.

Methods: Different possible carrier grafts were analysed comprising three groups of fibrous allografts (rehydration rate: 2.7, 4 and 8 ml/g), demineralized bone matrix (DBM), cortical granules, different densities of mineralized cancellous bone and demineralized cancellous bone (all produced by the DIZG, Germany). Absorption capacity was assessed after rehydrated with phosphate-buffered saline (PBS) to a final volume of 0.4 cc. Rehydrated samples were centrifuged in a sieve to separately determine the total and matrix-linked absorption capacities. Rehydration with Gentamicin (40 mg/ml, to a final volume of 0.4 cc) was done to determine the antibiotic elution kinetics. To evaluate gentamicin elution, samples were taken over 21 days for analysis (GENT2, Roche GmbH). Antimicrobial activity of the eluted samples was detected via a zone of inhibition (ZOI) test with S. aureus.

Results and conclusion: Interstitial space: Demineralized cancellous bone absorbed the most fluid in the interstitial spaces (0.712 ± 0.071 ml/cc).

Matrix absorption: The largest absorption capacity of the tissue matrix was observed with fibrous allograft (88.82±2.99 %) while low-density cancellous bone displayed the smallest matrix-linked absorption capacity (0.95±1.07 %).

Antibiotic elution kinetics: Fibrous allograft with rehydration rate of 8 ml/g showed a burst release, while allografts with rehydration rate 2.7 and 4 ml/g release gentamicin more constantly and at higher amounts compared to DBM and cancellous bone within the first 3 days. Varying the incubation time from 5-30 min had only minor effect on the absorption and release kinetics.

ZOI: The 1-hour elution samples from all grafts showed the largest ZOI. The ZOI decreased with an increase in elution time confirming the findings of the gentamicin quantification. After 21 days, fibrous grafts still showed detectable gentamicin in the inhibition test with S. aureus.

Carrier grafts are a valuable addition to the regenerative medicine toolkit. Fibrous allograft may act as an appropriate carrier graft for septic surgery due to its high matrix absorption capabilities. It provides a suitable option for keeping liquids at the intended target site such as antibiotics for septic orthopaedic indications.