Biodegradable PLA-ZnO nanocomposite biomaterials with antibacterial properties, tissue engineering viability, and enhanced biocompatibility

Polylactic acid (PLA) is a well-known biomaterial on account of its biocompatibility and biodegradability. Zinc oxide (ZnO) nanofillers may endow PLA with advantageous antibacterial and tissue regenerative properties, but may also compromise the biocompatibility of PLA. Several strategies have been developed to improve the biomedical practicality of such composites. The importance of surface properties on amplifying the therapeutic properties and safety of a material enables two potential strategies: (i) surface modification of ZnO nanoparticles, and (ii) surface engineering of the PLA/ZnO composites. Moreover, the controllable biodegradation of PLA allows a third possible strategy: (iii) biodegradation-controlled release of ZnO. The first part of this review introduces the controllable degradation of PLA and the mechanisms of therapeutic properties and cytotoxicity of ZnO. Following this, the paper highlights current research trends regarding the biomedical application of PLA-based ZnO nanocomposites. The final section of this review discusses the potential use of ZnO in tuning the degradation rate of PLA, and the possibility of manipulating the surface properties of ZnO nanoparticles and PLA/ZnO composites in order to optimize the therapeutic properties and safe usage of PLA/ZnO composites in the biomedical field

Immobilization and stabilization of alcohol dehydrogenase on polyvinyl alcohol fibre

A polyvinyl alcohol (PVA) fibrous carrier has been chemically modified for the immobilization of yeast alcohol dehydrogenase (ADH) with an aim to increase its stability over a wide pH range, prolong its activity upon storage, and enhance its reusability. The strategy for immobilization involved functionalization of the fibrous carrier with chloropropinoyl chloride followed by amination with ethylenediamine. Tethering of the ADH enzyme to the PVA scaffold was achieved with glutaraldehyde. The activity profile of the immobilized enzyme was compared to soluble enzyme as a function of pH, temperature and reusability. The immobilization of ADH on PVA fibrous carrier shifted the optimal reaction pH from 7 to 9, and improved the thermostability at 60 °C. Furthermore, the immobilized enzyme retained 60% of its original activity after eight cycles of reuse. These results demonstrate that PVA based textiles can serve as a flexible, reusable carrier for enzyme immobilization. Keywords: Polyvinyl alcohol fibre, Alcohol dehydrogenase (ADH), Enzyme immobilizatio

Open challenges in tensile testing of additively manufactured polymers: A literature survey and a case study in fused filament fabrication

Additive manufacturing (AM, also commonly termed 3D printing) is progressing from being a rapid prototyping tool to serving as pillar of the Industry 4.0 revolution. Thanks to their low density and ease of printing, polymers are receiving increasing interest for the fabrication of structural and lightweight parts. Nonetheless, the lack of appropriate standards, specifically conceived to consistently verify the tensile properties of polymer parts and benchmark them against conventional products, is a major obstacle to the wider uptake of polymer AM in industry. After reviewing the standardisation needs in AM with a focus on mechanical testing, the paper closely examines the hurdles that are encountered when existing standards are applied to measure the tensile properties of polymer parts fabricated by fused filament fabrication (FFF, aka fused deposition modeling, FDM), which is presently the most popular material extrusion AM technique. Existing standards are unable to account for the numerous printing parameters that govern the mechanical response of FFF parts. Moreover, the literature suggests that the raster- and layer-induced anisotropic behaviour and the complicated interplay between structural features at different length scales (micro/meso/macro-structure) undermine pre-existing concepts regarding the specimen geometry and classical theories regarding the size effect, and ultimately jeopardise the transferability of conventional tensile test standards to FFF parts. Finally, the statistical analysis of the tensile properties of poly(lactic acid) (PLA) FFF specimens printed according to different standards (ASTM D638 type I and ASTM D3039) and in different sizes provides experimental evidence to confirm the literature-based argumentation. Ultimately, the literature survey, supported by the experimental results, demonstrates that, until dedicated standards become available, existing standards for tensile testing should be applied to FFF with prudence. Whilst not specified in conventional standards, set-up and printing parameters should be fully reported to ensure the repeatability of the results, rectangular geometries should be preferred to dumbbell-like ones in order to avoid premature failure at the fillets, and the size of the specimens should not be changed arbitrarily

Thermochromic composite fibres containing liquid crystals formed via melt extrusion

A three-layered composite fibre has been generated via a modified wire-coating melt co-extrusion process. The continuous fibre consists of a thermochromic liquid crystalline (TLC) layer encapsulated between a transparent polypropylene outer sheath and a black polyether ether ketone inner core. The fibres exhibit clear thermochromic behaviour consistent with the behaviour of unincorporated TLCs, and have been formed into a textile. The presence of the black inner core was found to be the key for the clear retention of colour within the fibres against both white and black backgrounds. The temperature-sensitive fibres and textiles can be applied to a variety of thermal mapping applications, such as in the medical and engineering fields, due to the tunable nature of TLCs.</p

Fabrication and characterisation of polypropylene nanofibres by meltblowing process using different fluids

In nonwoven industry, meltblowing has been widely used as an important technique for the production of nonwoven webs consisting of microfibres, suitable for various applications. Recently, great attention is being paid to fabricate nonwoven webs consisting of nanofibres, commonly known as nanowebs. In this paper, polypropylene has been successfully used for the fabrication of nanowebs by meltblowing process with the injection of different fluids (such as air and water) at the vent port of commercial meltblowing equipment. The lowest average fibre diameters achieved were 755 and 438 nm by the use of air and water, respectively. Differential scanning calorimetry results showed the presence of single melting peaks in the first heating cycle and double melting peaks in the second, due to the re-crystallisation and re-organisation by heating during the experiments. The results obtained from thermo gravimetric analysis and intrinsic viscosity studies showed thermal degradation of the nanofibres during meltblowing. X-ray diffraction studies showed that all the meltblown polypropylene fibres produced with the injection of the fluids contained low degrees of crystallinity and monoclinic α-form crystals. The crystallinity was increased with annealing. Similar Fourier transform infrared spectra of the polymer and the fibres indicated no change to the chemical functionality of the nanofibres by the application of the fluids and high temperature during meltblowing.</p

Electrospun Polyacrylonitrile/β-Cyclodextrin Composite Membranes for Simultaneous Air Filtration and Adsorption of Volatile Organic Compounds

Simultaneous capture of different air pollutants including aerosols and volatile organic compound (VOC) is demonstrated using composite polyacrylonitrile (PAN)/β-cyclodextrin (β-CD) nanofiber membrane. Aerosol filtration along with VOCs adsorption in one step remains a challenge due to differences in the physical and chemical properties of these air pollutants. PAN/β-CD composite electrospun nanofiber membranes (ENMs) were produced with different concentrations of β-CD. The surface modification of the composite ENM was confirmed by X-ray photoelectron spectroscopy (XPS), field emission-scanning electron microscopy (FE-SEM) and water contact angles. PAN/β-CD composite ENMs showed excellent air filtration performance (>95% filtration efficiency with a relatively low pressure drop of 112 Pa). Formaldehyde (HCHO) adsorption was determined using a simple jar method and xylene adsorption by UV spectroscopy. HCHO and xylene adsorption found better by 66% and 73%, respectively, compared to pristine PAN ENM despite a reduction in fiber surface area. The composite ENMs were found to be nontoxic to human lung cell line, suggesting that it is a good candidate for respiratory filter media for simultaneous air filtration and VOC adsorption