Construction of a biodegradable scaffold with enhanced biocompatibility for bone tissue engineering

Injuries, accidents or diseases may cause deformity or loss of human body tissues that require critical medical intervention to facilitate their recovery process, regeneration or replacement. Conventional synthetic scaffolds which are made of polymers, ceramics and metals, in which the construction does not regard the native structure and characteristics of cell and tissue, leads mechanical mismatch and/or poor integration. Tissue engineering is an alternative for these treatment methods, aiming to regenerate functional tissues and/or organs. New biofunctional scaffolds with recreated geometry and porosity for treatment of bone, which is a highly vascularized and dynamic tissue, are promising but also presents significant challenges to be overcome. The aim of this study is to evaluate the effects of a natural biopolymer, silk fibroin, as a coating material for bone tissue engineering. For this, a nanofibrous scaffold prepared by electrospinning of PCL (poly-ε-caprolactone) / PLLA (poly-l-lactic acid) blend was coated with silk fibroin solution and the constructs were characterized. PCL/PLLA solutions of different concentrations (9 to 11 %w/v) were prepared with 1:1 polymer ratio, in methanol/chloroform mixture (1:3 v/v). Scanning electron microscopy (SEM) micrographs demonstrated that uniform nanofibers were obtained by each PCL/PLLA concentration. The average fiber diameter prepared from PCL/PLLA (10 %w/v) solution was 998.1 ± 246.0. PCL/PLLA (10 %w/v) chosen considering many studies which include fibers having a diameter less than 1 µm are broadly regarded as nanofiber and having great potential in medical applications. To obtain silk fibroin in solution form, firstly proteins that cause immune reaction were eliminated, by an extraction method. The scaffold was coated with silk fibroin solution as 1 layer, 2 layers and 3 layers applying dip coating technique. Three layers of silk fibroin coated PCL/PLLA (10 %w/v) nanofibers prepared with 24 h mixing was chosen for cell culture. Methanol treatment was applied to induce conformational transition and obtain β-sheet crystalline state of fibroin which is more stable. The effect of methanol treatment on the silk fibroin conformational structure was evaluated by FTIR analysis. β-sheet conformation partially observed in silk fibroin proteins. Neverthless, silk fibroin coating did not cause any conformational change on PCL/PLLA (10 %w/v) blend nanofibers. For biological evaluation, the proliferation of human osteoblast cells (hfOB) were seeded on prepared scaffolds and MTS analysis was applied at 1st, 4th and 7th days to examine the proliferation of cells on different surfaces. Surface wettability has a significant effect on cell adhesion and proliferation. Cell culture studies showed that silk fibroin coated scaffolds (with or without methanol treatment) led less cell proliferation. A correlation is observed between water contact angle measurements and decreased cell attachment with the increasing hydrophilicity. Highest cell proliferation was observed on hydrophobic PCL/PLLA nanofiber mats (136°). Silk fibroin coated (86°) and further methanol treated substrates (79°) demonstrated improved hydrophilicity but cell proliferation was decreased with increasing hydrophilicity.