Nanofibers and their applications in tissue engineering

Abstract

Developing scaffolds that mimic the architecture of tissue at the nanoscale is one of the major challenges in the field of tissue engineering. The development of nanofibers has greatly enhanced the scope for fabricating scaffolds that can potentially meet this challenge. Currently, there are three techniques available for the synthesis of nanofibers: electrospinning, self-assembly, and phase separation. Of these techniques, electrospinning is the most widely studied technique and has also demonstrated the most promising results in terms of tissue engineering applications. The availability of a wide range of natural and synthetic biomaterials has broadened the scope for development of nanofibrous scaffolds, especially using the electrospinning technique. The three dimensional synthetic biodegradable scaffolds designed using nanofibers serve as an excellent framework for cell adhesion, proliferation, and differentiation. Therefore, nanofibers, irrespective of their method of synthesis, have been used as scaffolds for musculoskeletal tissue engineering (including bone, cartilage, ligament, and skeletal muscle), skin tissue engineering, vascular tissue engineering, neural tissue engineering, and as carriers for the controlled delivery of drugs, proteins, and DNA. This review summarizes the currently available techniques for nanofiber synthesis and discusses the use of nanofibers in tissue engineering and drug delivery applications.

Figure 1

(a) Schematic of the electrospinning process. (b) Scanning electron micrograph of poly(lactic-co-glycolic acid) (PLGA) nanofibers synthesized using the electrospinning technique (scale bar = 10 μm). Source for 1b: Katti DS, Robinson KW, Ko FK, et al. 2004. Bioresorbable nanofiber based systems for wound healing and drug delivery: optimization of fabrication parameters. J Biomed Mater Res, 70B:286–96. Copyright © 2004 J Wiley. Reprinted with permission of John Wiley&Sons Inc.

Figure 2

Transmission electron micrograph (TEM) of nanofibers formed from peptide amphiphile molecules (N terminus – C₁₀H₁₉O and Peptide – CCCCGG GS^(PO4)RGD) that self-assembled by drying directly onto a TEM grid without adjusted pH (negatively stained with phosphotungstic acid). The morphology of the nanofibers was similar to that observed by pH-induced self-assembly. Source: Hartgerink JD, Beniash E, Stupp SI. 2002. Peptide-amphiphile nanofibers: a versatile scaffold for the preparation of self-assembling materials. Proc Natl Acad Sci U S A, 99:5133–8. Copyright © 2002 National Academy of Sciences, USA. Reprinted with permission of the National Academy of Sciences, USA.

Figure 3

Scanning electron micrograph of poly(l-lactic acid) (PLLA) nanofibrous foam synthesized from 2.5% (wt/v) PLLA/tetrahydrofuran solution at a gelation temperature of 8°C using the phase separation technique (image 500 ×). Source: Ma PX, Zhang R. 1998. Synthetic nano-scale fibrous extracellular matrix. J Biomed Mater Res, 46:60–72. Copyright © 1998 J Wiley. Reprinted with permission of John Wiley&Sons Inc.

Figure 4

High magnification scanning electron micrograph of carbon nanofiber compacts. The carbon nanofibers were prepared using a chemical vapor deposition technique with a pyrolitic aromatic hydrocarbon outer layer (PR-1 AG [nanophase]). The resulting carbon nanofibers were compacted serially in a steel-tool die via a uniaxial pressing cycle (0.2–0.4 GPa over a 5-minute period) at room temperature and the resulting carbon fiber compacts were used in the cell experiments (scale bar = 1 μm). Source: Elias KL, Price RL, Webster TJ. 2002. Enhanced function of osteoblasts on nanometer diameter carbon fibers. Biomaterials, 23:3279–87. Copyright © 2002. Reprinted with permission of Elsevier.