Space charge occurs in a dielectric material when the rate of charge accumulation is different from the rate of removal, which arises due to moving or trapped charges. Inevitably, the local electric field is increased at some point within the material, which then leads to faster degradation and premature failure. The determination of space charge behavior has seen wide implementation in characterizing novel dielectric materials, especially in connection with the newly emerging field of nanocomposites. In this paper, we report on an investigation into space charge dynamics in silica-based polyethylene nanocomposites. The various systems differed with respect to the amount of filler and its surface chemistry; the pulsed electro-acoustic (PEA) technique was used to evaluate the space charge distribution in each. Experimental results indicate that the incorporation of nanosilica into polyethylene results in a significant amount of homocharge development near both electrodes. With appropriate surface treatment of the nanofiller, homocharge formation was successfully suppressed, indicating less severe space charge development in the nanocomposite materials. The mechanisms leading to the observed space charge development and direct current (DC) breakdown properties of the nanocomposites are discussed.

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Bioengineering neocartilage grafts of human articular chondrocytes in a custom-built microfluidic perfusion bioreactor with integrated ultrasound standing wave trap.

This work reported the thermomechanical and morphological properties of polyvinyl alcohol (PVA) nanocomposites reinforced with nanosilica and oil palm empty fruit bunches derived nanocellulose. The nanocomposites were characterized by mechanical, thermal, XRD, optical, and morphological studies. Uniformity dispersion of the nanofillers at a 3 wt% concentration has been shown by scanning electron microscopy, whereas the changes in crystallinity were demonstrated by X-ray diffraction analysis. Addition of nanosilica resulted in increased thermal stability of PVA/nanocellulose composites due to the reduction in mobility of the matrix molecules. Visible light transmission showed that the addition of 0.5 wt% nanosilica only slightly reduced the light transmission of PVA/nanocellulose composites with 3 wt% nanocellulose. The addition of a small concentration of nanosilica successfully improved the tensile and modulus properties of PVA/nanocellulose composite films. The increases in tensile strength and thermal stability were evidence of a nanosilica contribution in PVA/nanocellulose composites, inducing reinforcement, as detected by the thermomechanical properties.

Extensive employment of biomaterials in the areas of biomedical and microbiological applications is considered to be of prime importance. As expected, oil based polymer materials were gradually replaced by natural or synthetic biopolymers due to their well-known intrinsic characteristics such as biodegradability, non-toxicity and biocompatibility. Literature on this subject was found to be expanding, especially in the areas of biomedical and microbiological applications. Introduction of porosity into a biomaterial broadens the scope of applications. In addition, increased porosity can have a beneficial effect for the applications which exploit their exceptional ability of loading, retaining and releasing of fluids. Different applications require a unique set of pore characteristics in the biopolymer matrix. Various pore morphologies have different characteristics and contribute different performances to the biopolymer matrix. Fabrication methods for bio-based porous materials more related to the choice of material. By choosing the appropriate combination of fabrication technique and biomaterial employment, one can obtain tunable pore characteristic to fulfill the requirements of desired application. In our previous review, we described the literature related to biopolymers and fabrication techniques of porous materials. This paper we will focus on the biomedical and microbiological applications of bio-based porous materials.

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Articular cartilage defects, when repaired ineffectively, often lead to further deterioration of the tissue, secondary osteoarthritis and, ultimately, joint replacement. Unfortunately, current surgical procedures are unable to restore normal cartilage function. Tissue engineering of cartilage provides promising strategies for the regeneration of damaged articular cartilage. As yet, there are still significant challenges that need to be overcome to match the long-term mechanical stability and durability of native cartilage. Using electrospinning of different blends of biodegradable poly(3-hydroxybutyrate)/poly(3-hydroxyoctanoate), we produced polymer scaffolds and optimised their structure, stiffness, degradation rates and biocompatibility. Scaffolds with a poly(3-hydroxybutyrate)/poly(3-hydroxyoctanoate) ratio of 1:0.25 exhibit randomly oriented fibres that closely mimic the collagen fibrillar meshwork of native cartilage and match the stiffness of native articular cartilage. Degradation of the scaffolds into products that could be easily removed from the body was indicated by changes in fibre structure, loss of molecular weight and a decrease in scaffold stiffness after one and four months. Histological and immunohistochemical analysis after three weeks of culture with human articular chondrocytes revealed a hyaline-like cartilage matrix. The ability to fine tune the ultrastructure and mechanical properties using different blends of poly(3-hydroxybutyrate)/poly(3-hydroxyoctanoate) allows to produce a cartilage repair kit for clinical use to reduce the risk of developing secondary osteoarthritis. We further suggest the development of a toolbox with tailor-made scaffolds for the repair of other tissues that require a 'guiding' structure to support the body's self-healing process.

Recently, surface functionality and thermal property of the green nanomaterials have received wide attention in numerous applications. In this study, microcrystalline cellulose (MCC) was used to prepare the nanocrystalline celluloses (NCCs) using acid hydrolysis method. The NCCs was treated with TEMPO [(2,2,6,6-tetramethylpiperidin-1-yl)oxy radical]-oxidation to prepare TEMPO-oxidized NCCs. Cellulose nanofibrils (CNFs) also prepared from MCC using TEMPO-oxidation. The effects of rapid cooling and chemical treatments on the thermo-structural property studies of the prepared nanocelluloses were investigated through FTIR, thermogravimetric analysis-derivative thermogravimetric (TGA-DTG), and XRD. A posteriori knowledge of the FTIR and TGA-DTG analysis revealed that the rapid cooling treatment enhanced the hydrogen bond energy and thermal stability of the TEMPO-oxidized NCC compared to other nanocelluloses. XRD analysis exhibits the effect of rapid cooling on pseudo 2 helical conformation. This was the first investigation performed on the effect of rapid cooling on structural properties of the nanocellulose.