1 Platelet Lysate-Loaded Photo-cross-linkable Hyaluronic Acid 2 Hydrogels for Periodontal Endogenous Regenerative Technology 3 Pedro S. Babo, †,‡ Ricardo L. Pires, †,‡ Lívia Santos, †,‡ Albina Franco, †,‡ Fernando Rodrigues, ‡,§ 4 Isabel Leonor, †,‡ Rui L. Reis, †,‡ and Manuela E. Gomes* ,†,‡ 5 † 3B’s Research Group-Biomaterials, Biodegradables and Biomimetics, University of Minho, Avepark-Zona Industrial da Gandra, 6 4806-017 Barco GMR, Portugal 7 ‡ ICVS/3B’s-PT Government Associate Laboratory, University of Minho, Braga/Guimarã es 4710-057, Portugal 8 § Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho, Braga 4710-057, Portugal 9 ABSTRACT: The integrity and function of the periodontium can be 10 compromised by traumatic injuries or periodontitis. Currently available 11 clinical therapies are able to stop the progression of periodontitis and 12 allow the healing of periodontal tissue. However, an optimal strategy 13 capable of restoring the anatomy and functionality of the lost periodontal 14 tissue is still to be achieved. Herein is proposed the development of an 15 injectable hydrogel system able to release a growth factors and cells to the 16 periodontal defect. This injectable system is based on a photo-cross- 17 linkable hydrogel, prepared from methacrylated hyaluronic acid (me-HA) 18 and incorporating platelet lysate (PL). The delivery of growth factors and 19 cells in situ is expected to enhance regeneration of the periodontium. 20 Various formulations of me-HA containing increasing PL concentrations 21 were studied for achieving the formation of stable photo-cross-linkable 22 hydrogels. The produced hydrogels were subsequently characterized to 23 assess mechanical properties, degradation, protein/growth factor release profile, antimicrobial activity and response toward 24 human Periodontal Ligament fibroblasts (hPDLFs). The results demonstrated that it was possible to obtain stable photo-cross- 25 linkable hydrogels incorporating different amounts of PL that can be released in a sustained manner. Furthermore, the 26 incorporation of PL improved (p < 0.02) the viscoelastic properties of the hydrogels and enhanced their resilience to the 27 degradation by hyaluronidase (HAase). Additionally, the PL was shown to provide antimicrobial properties. Finally, hPDLFs, 28 either seeded or encapsulated into the developed hydrogels, showed enhanced proliferation over time (p < 0.05), proportionally 29 to the increasing amounts of PL present in the hydrogel formulations. 30 KEYWORDS: photo-cross-linkable hydrogels, platelet lysate, hyaluronic acid, periodontal ligament, endogenous regenerative technology 31 ■ INTRODUCTION 32 The periodontium is a complex and dynamic oral structure 33 comprising soft and hard tissues, the cementum, a functionally 34 oriented periodontal ligament, alveolar bone and gingiva The 35 main function of this structure is anchoring the teeth to the jaw 36 bones, while withstanding the forces originated by the 37 masticatory process. 1 The integrity and function of the 38 periodontium can be compromised by trauma or disease, 39 such as periodontitis, an inflammatory disease predominantly 40 caused by Gram-negative bacteria that causes the destruction of 41 these tooth supportive tissues potentially leading to tooth 42 loss. 1,2 43 Current therapeutic options, which include the implantation 44 of autografts, synthetic bone fillers and guided tissue 45 regeneration (GTR), are not able to fully regenerate 46 periodontium morphology and function. In recent years 47 endogenous regenerative technology (ERT) has arisen as a 48 new paradigm in periodontal regeneration. This new concept 49 has its foundations in tissue engineering and aims to induce or 50 encourage periodontal regeneration by superimposing specific 51 chemical (e.g., growth factors) and biophysical cues. 3 These 52 signals are expected to encourage homing of stem and 53 progenitor cells, leading to the formation of new periodontal 54 ligament and cementum. 3 55 Platelet-rich hemoderivatives (PRHds), namely platelet-rich 56 plasma and platelet-rich fibrin, have been widely investigated 57 for periodontal ERT as important sources of autologous growth 58 factors and provisional fibrin matrices. 1,3 Nevertheless, the 59 traditional PRHds clots retract, impairing the needed stability 60 for periodontal tissue ingrowth. 4 In this research work we 61 propose the development of photo-cross-linkable hyaluronic 62 acid hydrogels enriched with platelet lysate as a stable system Special Issue: Biomimetic Bioactive Biomaterials: The Next Gen- eration of Implantable Devices Received: August 31, 2016 Accepted: December 20, 2016 Published: December 20, 2016 Article pubs.acs.org/journal/abseba © XXXX American Chemical Society A DOI: 10.1021/acsbiomaterials.6b00508 ACS Biomater. Sci. Eng. XXXX, XXX, XXX-XXX clp00 | ACSJCA | JCA10.0.1465/W Unicode | research.3f (R3.6.i12 HF01:4457 | 2.0 alpha 39) 2016/10/28 09:46:00 | PROD-JCAVA | rq_7663590 | 12/30/2016 11:33:07 | 11 | JCA-DEFAULT