Development of new Bombyx mori silk fibroin membranes for periodontal guided tissue regeneration

Abstract

Periodontitis is one of the most common inflammatory diseases and a leading cause of tooth loss in adults, being characterized by progressive destruction of the tooth-supporting apparatus. Guided Tissue Regeneration (GTR) and Guided Bone Regeneration (GBR) procedures were established as basic techniques in periodontal regenerative medicine due to its promising results. These procedures are based, typically, on a membrane, that is placed between the gingiva and the alveolar bone in which the regenerative process will take place. However, the commercial available membranes present limitations at structural, mechanical and biofunctional level demonstrating the need for developing clinically effective materials. In this work a new generation of GTR/GBR membranes is presently being proposed using a natural-based material. Bombyx mori silk fibroin(SF)-based membranes have been developed using glycerol (GLY) and poly (vinyl alcohol) (PVA) as plasticizers to improve the flexibility and enhanceSF stabilization. The developed membranes, designed to be in contact with the gingiva, aim at providing an effective solution for mild periodontitis (the most prevalent form worldwide) by helping to restore the anatomy and function of lost or damaged periodontal tissues. Purified SF solution was mixed with GLYor PVA at weight ratios of 0, 10, and 30%. The membranes were obtained by casting the final solutions into Petri dishes and dried at 85 ºC in the oven for 6 hours some and 12 hours others for further characterization. A comparative study was undertaken using the pure SF membrane as control. The SF-based membranes were characterized in terms of their morphology, physical integrity, chemical structure, mechanical and thermal properties, swelling capability and in vitro degradation behavior. Membranes dried for 6 and 12 hours presented similar aspect and microstructure. Scanning electronmicroscopy (SEM) micrographs suggested that GLY is well distributed in SF matrix while PVA presented phase separation between the two polymers. Atomic force microscopy (AFM) revealed that the surface nanotopography and the average roughness of the SF-based membranes are affected by the exposure time and by the percentage of additive content. Contact angle measurements showed a decrease of water contact angle with GLY and PVA increasing, indicating that the surfaces become more hydrophilic. Attenuated infrared spectroscopy (ATR-FTIR) analysis demonstrated that the thermal treatment induced SF b-sheet conformation for both exposure periods. However, only the membranes dried for 12 hours were water stable for more than 24 hours. These membranes reached equilibrium hydration degree after 3 hours. With the addition of the synthetic polymers, the hydration capacity increased together with the weight loss both in PBS and PBS with enzyme. The mechanical properties revealed that GLY and PVA had a plasticizing effect on the membrane which became more ductile without compromising its mechanical strength. The developed membranes demonstrated to be promising systems to be used in a guided tissue regeneration approach for periodontal regeneration.

Date of Award	28 Apr 2017
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Ana Leite Oliveira (Supervisor) & Joaquim Miguel Oliveira (Co-Supervisor)