John G. Lyons

Cell encapsulation and cryostorage in PVA–gelatin cryogels: incorporation of carboxylated ε‐poly‐L‐lysine as cryoprotectant

It is desirable to produce cryopreservable cell‐laden tissue‐engineering scaffolds whose final properties can be adjusted during the thawing process immediately prior to use. Polyvinyl alcohol (PVA)‐based solutions provide platforms in which cryoprotected cell suspensions can be turned into a ready‐to‐use, cell‐laden scaffold by a process of cryogelation. In this study, such a PVA system, with DMSO as the cryoprotectant, was successfully developed. Vascular smooth muscle cell (vSMC)‐encapsulated cryogels were investigated under conditions of cyclic strain and in co‐culture with vascular endothelial cells to mimic the environment these cells experience in vivo in a vascular tissue‐engineering setting. In view of the cytotoxicity DMSO imposes with respect to the production procedure, carboxylated poly‐L‐lysine (COOH–PLL) was substituted as a non‐cytotoxic cryoprotectant to allow longer, slower thawing periods to generate more stable cryogels. Encapsulated vSMC with DMSO as a cryoprotectant responded to 10% cyclic strain with increased alignment and proliferation. Cells were stored frozen for 1 month without loss of viability compared to immediate thawing. SMC‐encapsulated cryogels also successfully supported functional endothelial cell co‐culture. Substitution of COOH–PLL in place of DMSO resulted in a significant increase in cell viability in encapsulated cryogels for a range of thawing periods. We conclude that incorporation of COOH–PLL during cryogelation preserved cell functionality while retaining fundamental cryogel physical properties, thereby making it a promising platform for tissue‐engineering scaffolds, particularly for vascular tissue engineering, or cell preservation within microgels. Copyright

Review of Multifarious Applications of Poly (Lactic Acid)

ABSTRACT Poly (lactic acid) is considered to be a promising alternative to petroleum-based polymers due to its renewability, biodegradability, biocompatibility, and good mechanical properties. Because of the high cost, the applications of poly (lactic acid) were limited to the medical field. Over the past decade, improvements in polymerization allow the economical mass production of high molecular weight poly (lactic acid). Therefore, the applications of poly (lactic acid) have recently spread to domestic, commercial packaging, and textile applications. This review outlines the chemical, thermal characteristics of poly (lactic acid) and discusses the use of poly (lactic acid) in medical applications such as sutures, stents, drug carrier, orthopaedic devices, scaffolds, as well as commercial applications in textile and packaging fields with superior properties such as high wicking performance, good dyeability, antibacterial feature, good ultraviolet resistance, high water vapor transmission rates, shrink wrapping, and dead fold property. While the drawbacks of poly (lactic acid) utilized in these fields are also discussed. It is clear that the advantages of using poly (lactic acid) outlined in this review will ensure that the market for poly (lactic acid) products will continue to expand. GRAPHICAL ABSTRACT

Physical and Mechanical Properties of Blends Based on Poly (dl-lactide), Poly (l-lactide-glycolide) and Poly (ϵ-caprolactone)

Bioresorbable materials are extensively used for a wide range of biomedical applications. In this study, the common industrial processes of compression moulding and solvent casting were utilised for initial preparation of thin film blends based on Poly (dl-lactide), Poly (l-lactide-glycolide) and Poly (ϵ-caprolactone). Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), phosphate buffered saline adsorption, tensile testing and contact angle measurement were used as a means of investigating the physical and mechanical properties of the blends.

The effect of processing conditions for polylactic acid based fibre composites via twin-screw extrusion

Hemp, jute and lyocell fibres were incorporated into polylactic acid via twin-screw extrusion using three screw configurations, with varying lengths of mixing sections, in order to reduce the levels of shear and fibre attrition. When mixing zones were reduced, the measured fibre lengths increased and as a result the tensile properties of polylactic acid composites were improved. Similarly impact properties were observed to improve as fibre length increased. However, by increasing the fibre length in polylactic acid composites, fibre surface area within the composite was reduced and subsequently the rate of biodegradation decreased. Composites prepared using different extrusion temperature profiles were shown to have vastly different mechanical properties and in all cases composites produced using low temperature profiles exhibited superior properties to those produced at higher temperatures, indicating thermal degradation at the more elevated temperatures. For example, 50 wt% jute composites exhibited increases of 20.9% and 199% in tensile strength and flexural modulus, the greatest improvement of all composite types at that loading.

Effect of Compatibilizer Content on the Mechanical Properties of Bioplastic Composites via Hot Melt Extrusion

Polyhydroxybutyrate fiber biocomposites were prepared via twin screw extrusion. Results show mechanical properties of short natural fiber composites can be greatly improved with the addition of a compatibilizer. Compatibilizer composites exhibited an increased resistance to water absorption at low temperatures. A considerable increase in flexural modulus was also observed, in particular for the jute fiber composites. The dispersion of fibers was visibly improved as was observed using optical microscopy which allowed for a more even transfer of stress throughout the composite matrix. Lyocell composites however continued to display fiber agglomerates and although these were visibly reduced as PHB-g-MA content increased.

Material Considerations for Fused-Filament Fabrication of Solid Dosage Forms

Material choice is a fundamental consideration when it comes to designing a solid dosage form. The matrix material will ultimately determine the rate of drug release since the physical properties (solubility, viscosity, and more) of the material control both fluid ingress and disintegration of the dosage form. The bulk properties (powder flow, concentration, and more) of the material should also be considered since these properties will influence the ability of the material to be successfully manufactured. Furthermore, there is a limited number of approved materials for the production of solid dosage forms. The present study details the complications that can arise when adopting pharmaceutical grade polymers for fused-filament fabrication in the production of oral tablets. The paper also presents ways to overcome each issue. Fused-filament fabrication is a hot-melt extrusion-based 3D printing process. The paper describes the problems encountered in fused-filament fabrication with Kollidon® VA64, which is a material that has previously been utilized in direct compression and hot-melt extrusion processes. Formulation and melt-blending strategies were employed to increase the printability of the material. The paper defines for the first time the essential parameter profile required for successful 3D printing and lists several pre-screening tools that should be employed to guide future material formulation for the fused-filament fabrication of solid dosage forms.

Synthesis, characterisation and phase transition behaviour of temperature-responsive physically crosslinked poly (N-vinylcaprolactam) based polymers for biomedical applications

Poly (N-vinylcaprolactam) (PNVCL) is a polymer which offers superior characteristics for various potential medical device applications. In particular it offers unique thermoresponsive capabilities, which fulfils the material technology constraints required in targeted drug delivery applications. PNVCL phase transitions can be tailored in order to suit the requirements of current and next generation devices, by modifying the contents with regard to the material composition and aqueous polymer concentration. In this study, physically crosslinked Poly (N-vinylcaprolactam)-Vinyl acetate (PNVCL-VAc) copolymers were prepared by photopolymerisation. The structure of the polymers was established by Fourier transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography. The polymers were further characterised using differential scanning calorimetry and swelling studies. Determination of the LCST of the polymers in aqueous solution was achieved by employing four techniques; cloud point, UV-spectrometry, differential scanning calorimetry and rheometry. Sol-gel transition was established using tube inversion method and rheological analysis. This study was conducted to determine the characteristics of PNVCL with the addition of VAc, and to establish the effects on the phase transition. The PNVCL based polymers exhibited a decrease in the LCST as the composition of VAc increased. Sol-gel transition could be controlled by altering the monomeric feed ratio and polymer concentration in aqueous milieu. Importantly all copolymers (10wt% in solution) underwent gelation between 33.6 and 35.9°C, and based on this and the other materials properties recorded in this study, these novel copolymers have potential for use as injectable in situ forming drug delivery systems for targeted drug delivery.

Melt Processing of Bioplastic Composites via Twin Screw Extrusion and Injection Molding

Polymer composites composed of polyhydroxybutyrates and natural fibers were extruded to investigate the effect of varying screw speed and lubricant loadings. Optical microscopy results show that increasing screw speed can enhance the dispersion of fibers within the polymer composite. At high screw speeds this caused an exothermic reaction to occur within the barrel resulting in the fibers thermally degrading. In terms of mechanical properties considerable increases in flexural properties were observed with the increase in screw speed. However, impact and tensile properties were negatively affected, due in part to the level of fiber attrition.

Thermal, mechanical, dielectric, and morphological study of dielectric filler–based thermoplastic nanocomposites for electromechanical applications

Dielectric nanocomposite elastomers based on poly(styrene-ethylene/butylene-styrene) (SEBS) and SEBS-grafted-maleic anhydride (SEBS-g-MA) with barium titanate (BT) suitable for electroactive applications were successfully manufactured by using two corotating twin extrusion systems. The main purpose of the work was to investigate the thermal, mechanical, dielectric, and morphological effects of additives on SEBS and SEBS-g-MA to widen their applications for electroactive applications using fast and more cost-effective simple production process. The morphological characterization showed a good and bad dispersion of BT into SEBS-g-MA and SEBS with 34.9% and −3% dielectric permittivity change in SEBS-g-MA and SEBS upon addition of 10 wt% BT. In addition, dielectric permittivity change, thermal change (enthalpy relaxation and thermal transitions), and mechanical (Young’s modulus, hysteresis loss under multiple stress cycles, storage modulus, loss modulus, and tan δ) properties of elastomers were found to be a function of additive concentration, compatibility and interaction between elastomers and additive type, orientation of additives, and reinforcing factors of additives in elastomers. A simple and effective modeling technique was used to demonstrate the effects of dielectric properties on nanocomposites due to poor dispersion of additives.

Investigation of miscibility estimation methods between indomethacin and poly(vinylpyrrolidone-co-vinyl acetate)

Graphical abstract Figure. No Caption available. Abstract The investigation of the miscibility between active pharmaceutical ingredients (API’s) and polymeric excipients is of great interest for the formulation and development of amorphous solid dispersions, especially in the context of the prediction of the stability of these systems. Two different methods were applied to determine the miscibility between model compounds poly(vinylpyrrolidone‐co‐vinyl acetate) (PVPVA) and indomethacin (IND), viz. the measurement of the glass transition temperature (Tg) and the melting point depression method framed on the Flory‐Huggins theory. Measurement of the glass transition temperatures of the binary blends showed the formation of an amorphous single phase system between the PVPVA and the IND regardless of the composition. Variation of Tg with the composition was well described by the Gordon‐Taylor equation leading to the error of concluding lack of intermolecular interactions between the materials. Application of the Brostow‐Chiu‐Kalogeras‐Vassilikou‐Dova (BCKV) model shows a negative interaction parameter (a0) suggesting the presence of drug‐drug intermolecular interactions. Application of the melting point depression method within the framework of the Flory‐Huggins theory proved the miscibility of the system at temperatures close to the melting point of IND.