Fabrication of electrospun biocomposites comprising polycaprolactone/fucoidan for tissue regeneration

Abstract

In this study, we designed a new biocomposite comprising electrospun polycaprolactone (PCL)/fucoidan, in which the fucoidan has various beneficial biological functions, including anticoagulant, antiviral, and immunomodulatory activity. To obtain the composite scaffolds, a mixture of PCL and fucoidan was electrospun using various compositions (1, 2, 3, and 10 wt.%) of fucoidan powders. The resultant electrospun composites exhibited improved tensile modulus and strength for limited weight fractions (<10 wt.%) of fucoidan when compared with the pure PCL fiber mats. In addition, the biocomposites showed dramatic hydrophilic properties at >3 wt.% of fucoidan in the PCL/fucoidan. The biocompatibility of the electrospun mats was examined in vitro using osteoblast-like cells (MG63). Total protein content, alkaline phosphatase activity, and calcium mineralization were assessed. Scanning electron microscopic images showed that the cells were distributed more widely and were agglomerated on PCL/fucoidan mats compared with pure PCL mats. In addition, total protein content, alkaline phosphatase activity, and calcium mineralization were higher with PCL/fucoidan mats than with pure PCL mats. These observations suggest that fucoidan-supplemented biocomposites would make excellent materials for tissue-engineering applications.

Introduction

Tissue engineering is a well known interdisciplinary research field that combines engineering, material science, and life sciences, including pharmacy, medical science, physiology, and others. The goal of tissue engineering is to replace or regenerate various tissues or organs that may have been damaged by trauma, tumors, or abnormal defects with various alternative substitutes (scaffolds). Recently, these scaffolds have been widely researched because they can significantly affect cell growth and differentiation, and the scaffolds have been combined with various drug delivery systems (Hirose et al., 1987, Hubbell and Langer, 1995, Nerem and Sambanis, 1995, Ratner et al., 1996, Yang et al., 2001, Yoo and Lee, 1998, Zeltinger et al., 2001).

Ideal biomedical scaffolds should induce high cellular activities, have a large surface area to provide good attachment and proliferation of cells, have low toxicity, have low inflammatory properties, and have proper mechanical properties. In addition, they should be biodegradable to allow for replacement with neo-tissues and should be biocompatible during the degradation process (Chen et al., 2002, Hollister, 2005, Hutmacher, 2001, Kretlow and Mikos, 2008, Langer and Vacanti, 1993, Langer and Vacanti, 1995, Li et al., 2002, Sachlos and Czernuszka, 2003).

One of the techniques used to fabricate biomedical scaffolds, electrospinning, is a typical electrohydrodynamic process that generates micro/nanofibers from various polymeric solutions under electric field conditions. This technique has several advantages, such as simplicity, ease, low cost of equipment, widely selective materials, and easy injection of various additives compared with other techniques (Ma et al., 2005a, Teo and Ramakrishna, 2006, Yoshimoto et al., 2003). In addition, as a biomedical scaffold, electrospun micro/nanofibers are promising materials because their size and morphology are similar to components of the extracellular matrix (ECM), which functions to support a combination of tissues and has a high surface area and good mechanical properties to support neo-tissues. For these reasons, studies on electrospun micro/nanofibers mimicking the ECM have been widely conducted (Ma et al., 2005b, Shin et al., 2004).

Poly(ɛ-caprolactone) (PCL) has been widely applied to fabricate biomedical scaffolds because of its controllable biodegradability, biocompatibility, easy processability, and good mechanical properties, but it has low initial cell attachment and proliferation because of its hydrophobicity and low inclusion of various cell growth factors (Glowacki & Mizuno, 2008). To overcome these deficiencies of PCL, we accommodated a new natural material, fucoidan, which is extracted from brown algae. Fucoidan is an anionic polysaccharide comprising fucose and sulfate ester groups (Li, Lu, Wei, & Zhao, 2008) as a reinforcing component of cellular activities for bone regeneration. In general, fucoidan can induce FGF-2 activity, assist fibrillar collagen matrix formation, enhance fibroblastic proliferation, and stimulate in vitro and in vivo angiogenesis (Luyt et al., 2003, Nakamura et al., 2008, Senni et al., 2003). As reported in several studies, although fucoidan may strongly affect cellular activities, one major obstacle is that it is very difficult to fabricate structured scaffolds because it is very soluble in water.

For these reasons, we aimed to fabricate micro/nanofibrous scaffolds comprising PCL and fucoidan using an electrospinning process. We studied the electrospinability, which can vary with the weight fraction of fucoidan, and measured the mechanical and hydrophilic properties of various weight fractions (1, 2, 3, and 10 wt.%) of fucoidan. Finally, to observe the cellular behavior of the PCL/fucoidan fibrous mat as a bone tissue regeneration scaffold, total protein content, alkaline phosphatase (ALP) activity, and an alizarin red assay were determined in osteoblast-like cells (MG63).