Patch augmentation strategies receive great attention as the basis for the development of novel biomaterials aiming at tendon regeneration. Platelet lysate (PL), a cocktail of bioactive molecules, hold a strong potential for regenerative medicine. This pool of supra-physiological concentrations of growth factors (GFs) can be obtained in autologous or allogeneic set-ups and may potentially recapitulate the wound-healing cascade during regenerative processes.

Herein, we assessed PL-membranes as prospective bioinstructive patches under the hypothesis that tendon cells respond to PL-derived biochemical signals, modifying their behavior. For this purpose, PL-membranes were fabricated and characterized in terms of degradation and protein release profile. Human tendon-derived cells (hTDCs) were seeded on PL-membranes and their behavior was investigated regarding proliferation, GF secretion and extracellular matrix (ECM) production up to 21 days in culture. Additionally, to evaluate the antibacterial potential of these membranes as implantable patches in a clinical setting, the adhesion and viability of Staphylococcus aureus, a common pathogen in orthopedic surgical site infections, was assessed up to 72h.

Main results from the present work showed that membranes remained stable for up to 30 days. The release profile of PL proteins followed a typical controlled release

pattern, confirming what has been described in previous studies (1). Regarding biological performance, proliferation of hTDCs seeded in PL-membranes was controlled over time, possibly avoiding an extensive proliferative phase, which leads to scar formation in vivo during tendon repair. Besides, these bioinstructive membranes were able to modulate the secretion of relevant GFs, like basic fibroblast GF (bFGF), platelet derived GF (PDGF)-BB, which were produced by cultured hTDCs. Cells deposited tendon-related ECM proteins, including collagen type 1 and tenascin-C. Furthermore, PL-membranes exhibited a lower adherence of S. aureus when compared to controls. Also, the formation of bacterial biofilm on PL- membranes was not detected, thus demonstrating their antibacterial potential.

In summary, PL-membranes were fabricated through a very simple and reproducible method by crosslinking PL proteins. These membranes can modulate cellular activity in situ, acting as a reservoir of bioactive molecules derived from PL, which supports their application as bioinstructive and protective patches for tendon regeneration.

(1) Babo et al., 2014, Inflammation and Regeneration, 34:33-44.

Acknowledgements The authors thank Portuguese funds through FCT–Fundação para a Ciência e a Tecnologia in the framework of FCT-POPH-FSE, the PhD grant SFRH/BD/96593/2013 of R.C-A, and the Post-Doctoral grant SFRH/BPD/100760/2014 of ARF.