Ryuji Inai

ALIGNED BIODEGRADABLE NANOFIBROUS STRUCTURE: A POTENTIAL SCAFFOLD FOR BLOOD VESSEL ENGINEERING

A unique biodegradable nanofibrous structure, aligned poly(L-lactid-co-epsilon-caprolactone) [P(LLA-CL)] (75:25) copolymer nanofibrous scaffold was produced by electrospinning. The diameter of the generated fibers was around 500 nm with an aligned topography which mimics the circumferential orientation of cells and fibrils found in the medial layer of a native artery. A favorable interaction between this scaffold with human coronary artery smooth muscle cells (SMCs) was demonstrated via MTS assay, phase contrast light microscopy, scanning electron microscopy, immunohistology assay and laser scanning confocal microscopy separately. Tissue culture polystyrene and plane solvent-cast P(LLA-CL) film were used as controls. The results showed that, the SMCs attached and migrated along the axis of the aligned nanofibers and expressed a spindle-like contractile phenotype; the distribution and organization of smooth muscle cytoskeleton proteins inside SMCs were parallel to the direction of the nanofibers; the adhesion and proliferation rate of SMCs on the aligned nanofibrous scaffold was significantly improved than on the plane polymer films. The above results strongly suggest that this synthetic aligned matrix combines with the advantages of synthetic biodegradable polymers, nanometer-scale dimension mimicking the natural ECM and a defined architecture replicating the in vivo-like vascular structure, may represent an ideal tissue engineering scaffold, especially for blood vessel engineering.

Structure and properties of electrospun PLLA single nanofibres

An electrospinning method was used to spin semi-crystalline poly(L-lactide) (PLLA) nanofibres. Processing parameter effects on the internal molecular structure of electrospun PLLA fibres were investigated by x-ray diffraction (XRD) and differential scanning calorimetry (DSC). Take-up velocity was found as a dominant parameter to induce a highly ordered molecular structure in the electrospun PLLA fibres compared to solution conductivity and polymer concentration, although these two parameters played an important role in controlling the fibre diameter. A collecting method of a single nanofibre by an electrospinning process was developed for the tensile tests to investigate structure-property relationships of the polymer nanofibres. The tensile test results indicated that higher take-up velocity caused higher tensile modulus and strength due to the ordered structure developed through the process.

Technological advances in electrospinning of nanofibers

Progress in the electrospinning techniques has brought new methods for the production and construction of various nanofibrous assemblies. The parameters affecting electrospinning include electrical charges on the emerging jet, charge density and removal, as well as effects of external perturbations. The solvent and the method of fiber collection also affect the construction of the final nanofibrous architecture. Various techniques of yarn spinning using solid and liquid surfaces as well as surface-free collection are described and compared in this review. Recent advances allow production of 3D nanofibrous scaffolds with a desired microstructure. In the area of tissue regeneration and bioengineering, 3D scaffolds should bring nanofibrous technology closer to clinical applications. There is sufficient understanding of the electrospinning process and experimental results to suggest that precision electrospinning is a real possibility.

Modified Halpin-Tsai Equation for Clay-Reinforced Polymer Nanofiber

In this paper, two sets of electrospun fibers—nylon-6 and montmorillonite (MMT)-reinforced nylon-6—are being investigated for their tensile modulus. Results show that a reduction of fiber diameter close to nano-scale range reveals increasing modulus due to greater alignment of polymeric molecules and increased influence of surface stresses as a result of increased surface-to-volume ratio. However, addition of MMT caused a reduction of modulus in spite its very high modulus. This anomalous phenomenon may well be attributed to the effect of small fiber radius for containing the MMT platelets width. By expressing the matrix modulus as a function of fiber diameter and by introducing a proportionality constant, we obtained a semi-empirical micromechanical model within the framework of the Halpin-Tsai equation—hence the modified Halpin-Tsai model. The result suggests that the fibers be shrunk for increasing its modulus without reinforcement. However, for cases where fillers are required to fulfill non-mechanical purposes (such as medical purposes), the modified Halpin-Tsai model is useful for informing the designer of the threshold weight or volume fraction of the inclusion to maintain the modulus above the required level.