Elsevier

Biomaterials

Volume 26, Issue 15, May 2005, Pages 2603-2610
Biomaterials

Electrospinning of nano/micro scale poly(l-lactic acid) aligned fibers and their potential in neural tissue engineering

https://doi.org/10.1016/j.biomaterials.2004.06.051Get rights and content

Abstract

Efficacy of aligned poly(l-lactic acid) (PLLA) nano/micro fibrous scaffolds for neural tissue engineering is described and their performance with random PLLA scaffolds is compared as well in this study. Perfectly aligned PLLA fibrous scaffolds were fabricated by an electrospinning technique under optimum condition and the diameter of the electrospun fibers can easily be tailored by adjusting the concentration of polymer solution. As the structure of PLLA scaffold was intended for neural tissue engineering, its suitability was evaluated in vitro using neural stem cells (NSCs) as a model cell line. Cell morphology, differentiation and neurite outgrowth were studied by various microscopic techniques. The results show that the direction of NSC elongation and its neurite outgrowth is parallel to the direction of PLLA fibers for aligned scaffolds. No significant changes were observed on the cell orientation with respect to the fiber diameters. However, the rate of NSC differentiation was higher for PLLA nanofibers than that of micro fibers and it was independent of the fiber alignment. Based on the experimental results, the aligned nanofibrous PLLA scaffold could be used as a potential cell carrier in neural tissue engineering.

Introduction

Tissue engineering is an emerging area in the contemporary human health care administration, in which the basic understanding of cellular biology and the application of bioengineering are harnessed together for developing feasible substitutes to aid in the clinical treatment associated with human nervous system. More precisely, the treatment of nerve tissue repair arising from the spinal cord injury requires an additional care or new medical therapy, because axons do not regenerate appreciably in their native environment. Fortunately, recent advances in the neural tissue engineering (NTE) provide optimism by creating a permissive environment for nerve regeneration [1], [2], [3], [4]. A variety of biomaterials, in particular polymers, have been investigated for their suitability in tissue engineering application. Among them, PLLA is a promising scaffold material due to its biocompatibility and biodegradability.

Recent studies focus on the use of scaffolds with various advanced techniques in order to create complex guidance channels, which precisely mimic a natural repairing process in the human body [5], [6], [7], [8]. Our previous investigation also demonstrated an elegant way to produce nanofibrous scaffolds using PLLA by a liquid–liquid phase separation method quite similar to natural extracellular matrix (ECM) and its efficacy in supporting the NSC differentiation and neurite outgrowth [9]. Though this method provided scaffolds for NTE, there were however difficulties encountered in controlling fiber diameter and alignment. As an alternative, a fiber spinning technique, the so-called electrospinning, has been developed and succeeded in fabricating fibrous scaffolds with required sizes and dimensions depending upon the field of application [10]. In general, the process of electrospinning is chiefly affected by (i) system parameters, such as polymer molecular weight, molecular weight distribution and solution properties (e.g. viscosity, surface tension, conductivity); (ii) process parameters, such as flow rate, electric potential, distance between capillary and collector, motion of collector, etc. [11], [12], [13]. Therefore, these parameters should be carefully optimized while controlling fiber diameter and its alignment. Our previous studies clearly demonstrated the feasibility of fiber spinning with controllable fiber diameter and alignment by varying polymer concentration and motion of the collector [10], [14]. However, as per literature survey, there is no report on the design of aligned synthetic polymeric scaffolds using an electrospinning technique, especially in the nano or submicron scale range, resembling natural ECM for purpose of NTE. As it is anticipated that the aligned fibers could provide better contact guidance effects on the neurite outgrowth, the present study of electrospinning of aligned PLLA fibrous scaffold was undertaken and its suitability in NTE was evaluated using NSC as a model cell line.

There is a growing research interest in NSC, in particular C17.2, which generates hope for the development of biomimetic cell therapy. This kind of cell line is the primordial, multipotent self renewing cells, which can be used as neuron precursors since they involve in the normal development of cerebellum, embryonic neocortex and other structures upon implantation [8], [15], [16]. Furthermore, C17.2 cells are capable of differentiating without the interaction with adhesion molecules (without coating), such as laminin, fibronectin, collagen, poly-l-lysine or MatrigelTM, which are generally required as permissive substrates in neurite outgrowth. This offers the convenience of investigating the physical effects of PLLA fibrous scaffolds because the coating of adhesive molecules will affect the surface topography of the scaffold. Based on the above reasons, we have made an attempt to fabricate an aligned PLLA nano fibrous scaffold by electrospinning and use C17.2 cells to assess its efficacy in promoting neuron differentiation and guiding neurite outgrowth in vitro.

Section snippets

Fabrication of PLLA scaffolds

Both aligned and random PLLA fibers were fabricated by electrospinning technique under optimum conditions [10], [14], [17]. Polymer solution was prepared by dissolving the PLLA (Mw=300,000, Polysciences, USA) into dichloromethane (DCM)/n,n-dimethyl-formamid (DMF) (70:30) at the concentrations of 1%, 2%, 3% and 5% w/w. From each concentration of the polymer solution, 10 g was fed into a 10-ml plastic syringe (B-D, Singapore), which was controlled by a syringe pump (KDS100, KD Scientific Inc., USA)

Electrospun PLLA fibrous scaffolds

The processing condition of fabricating aligned nanofibrous PLLA scaffold was optimized and it was found that their properties were strongly influenced by the concentration of the polymeric solution. The morphological structure of aligned electrospun PLLA fibers obtained from the 2% and 5% polymer solution are shown in Fig. 1. Both the fibrous scaffolds exhibited a high order of alignment, which was independent on the polymer concentration. The fiber diameter was determined for both the cases,

Conclusion

This study demonstrates the possibilities of fabricating aligned PLLA nano/micro fibrous scaffolds by electrospinning technique under optimum condition. It is obvious that the fiber diameter can easily be tailored by manipulating the processing parameters. The suitability of PLLA scaffolds for the NSC culture was studied in terms of their fiber alignment and dimension. It was found that the NSCs elongated and their neurite outgrew along with the fiber direction for the aligned scaffolds,

Acknowledgements

This study was supported by the Ministry of Education of Singapore, Office of Life Sciences, National University of Singapore and the Agency for Science, Technology and Research (A* STAR), Singapore.

Cited by (1659)

  • Silk fibroin-derived electrospun materials for biomedical applications: A review

    2024, International Journal of Biological Macromolecules
View all citing articles on Scopus
View full text