Nano functional scaffolds for tissue engineering

Abstract

Scaffolds for tissue engineering should have good biocompatibility and antibacterial properties to reduce the risk of infection and improve healing. Poly-L-Lactide (PLLA), which is biocompatible, biodegradable, and an immunologically inert synthetic polymer was selected for the fabrication of tissue engineering scaffolds in this study. Silver and its compounds have been studied for many years because of their strong antibacterial activity and low toxicity. It has been found that its toxicity was related to the individual silver species rather than total silver concentration. Furthermore the toxicity of silver mainly depends on the active, free Ag+ concentration. Therefore, the cytotoxicity and antibacterial property of PLLA scaffolds composed with silver nanoparticles (Ag/PLLA scaffolds) were studied. Wool keratin has been reported as being suitable for long-term cell cultivation with a high cell density. Therefore the cytotoxicity and cell proliferation of PLLA/keratin (Pk) scaffolds composed with wool keratin were explored as well. In this study, PLLA scaffolds were prepared in two forms, films and electrospun fibrous membranes. Films were prepared with nano silver particles with weight ratios of nano silver particles to PLLA of 0.5%, 2.5%, 5%, 7.5% and 10% produced by an evaporation method. Fibrous membranes were fabricated from PLLA with silver nanoparticles or wool keratin by an electrospinning technique. In vitro cytotoxicity, cell proliferation and antibacterial tests were performed. The results implied that Ag/PLLA scaffolds can be used as non-toxic scaffolds for tissue engineering with antibacterial property. On the other hand, PLLA/keratin membranes were fabricated with different weight ratios at 2:1, 1:1, 1:2, 1:4 and 1:8 (Pk21, Pk11, Pk12, Pk14 and Pk18). The physical properties and degradability of the PLLA/keratin membranes were firstly tested. It was found that, although the tensile strength and elongation decreased, after being composited with keratin particles, the PLLA/keratin membranes became more hydrophilic than thepure PLLA membranes. This result suggested that the proportion of keratin particles within the membranes can affect the hydrophilicity of PLLA/keratin membranes. Furthermore, the releasing rate of keratin from the membranes was detected by fourier transform infrared (FTIR) after the PLLA/keratin membranes were degraded in PBS up to 4 weeks. Although more than half of the keratin was removed from the PLLA/keratin membrane in the first few hours of degradation, some keratin particles were still embedded in the PLLA fibers which were expected to enhance cell attachment and their proliferation on the PLLA. Then, cytotoxicity and cell proliferation of PLLA/keratin membranes were studied. High concentrations of wool keratin showed cytotoxicity, and the concentration of the wool keratin particles significantly influenced the cell adhesion on the PLLA/keratin membranes. Pk21 increased cell proliferation compared to PLLA, while the other PLLA/keratin membranes decreased it. Furthermore, the cytotoxicity of the Pk membranes had a close relationship with the tensile property and moisture content of the scaffolds, as, basically, it was most correlated to the wool keratin concentration. So, the raw materials and the properties of the scaffolds are two main factors which affect the cytotoxicity, but the specific mechanism of the scaffold cytotoxicity still needs further study. It can be concluded that Ag/PLLA is a good matrix for containing and gradually releasing antibacterial substance, while PLLA/keratin membranes can give good support for cell proliferation. Therefore, Ag/PLLA scaffolds can be used as non-cytotoxic antibacterial scaffolds for tissue engineering. PLLA/keratin fibrous membranes can provide a good matrix for cell proliferation. Combining these two kinds of compositions may produce antibacterial TE scaffolds with biomechanical properties that would enable them to play an important role as a skin substitute in the wound healing process.