INTRODUCTION: Platelet lysate (PL) has shown outstanding properties as an inexpensive source of growth factors, cytokines and extracellular matrix precursors (e.g. fibrinogen) currently being explored in several tissue engineering strategies. However, the proposed PL-based formulations show limited ability to retain/protect biological active biomolecules from degradation, exhibit extremely low mechanical properties and structural stability, as well as fast in vitro/in vivo degradation rates.¹ In order to overcome these limitations and further enabling the use PL not only as a source of growth factors but also as a scaffolding biomaterial, we propose here reinforcing its protein content with cellulose nanocrystals (CNC). Using this strategy, we have been able to develop injectable hydrogels, bioinks and sponges, with unprecedented biomimetic and biofunctional characteristics with high potential in tissue engineering applications.

METHODS: CNC were modified to present surface aldehyde groups.PL/CNC materials were produced using standard double barrel syringes promoting the in situ PL-clotting via thrombin and calcium activation along with the CNC/protein covalent crosslinking.² While the sponges were obtained by freeze-drying of the injectable hydrogels, the bioink was 3D printed inside a support microparticles bath. Human adipose tissue-derived stem cells (hASCs) were used for all the tests.

RESULTS: The inclusion of CNC allowed to avoid extensive clot retraction typical from plain PL gels while remaining biocompatible. Furthermore, the CNC markedly increased the bulk hydrogels mechanical properties up to an impressive 2 orders of magnitude higher storage modulus compared to plain PL gels, while allowing to control growth factor release and to tune hASCs behaviour. In addition, using the bioink formulation, we were able to 3D print complex freeform cell-laden constructs with outstanding biomimetism of the native tissues fibrillar extracellular matrix and unprecedented biofunctionality, which promoted fast cellularization and remodelling of the printed constructs. Regarding the PL/CNC sponges, they were biocompatible and showed better haemostatic properties than commercial gelatin sponges in vivo.

DISCUSSION & CONCLUSIONS: The combination of PL, a clinical-derived product, with CNC, the nature’s “carbon nanotubes”, has allowed to produce biomimetic biomaterials that explore the outstanding biological properties of PL for a wide range of applications in tissue engineering and regenerative medicine.