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Highlights • Effect of temperature on the contributions to fracture toughness of unidirectional composites. • Partial development of the matrix process zone in the composite verified. • Fibre bridging successfully modelled as a peeling of a bridging ligament. • Cohesive laws for fibre bridging were experimentally determined. Abstract The interlaminar fracture toughness, G Ic , of unidirectional carbon fibre composite laminates produced by infusion moulding with two different thermoplastic acrylic matrices, one plain and one rubber toughened, was studied. For the composite with the plain matrix fracture was dominated by failure at the fibre-matrix interface. With the toughened matrix, fracture occurred within the matrix-rich layer, although the matrix toughness could not be fully exploited due to the interaction of the fibres with the development of the process zone. A fibre bridging model based on experimentally derived cohesive laws was developed and it confirmed that fracture occurs within the matrix. [ABSTRACT FROM AUTHOR]

The present work focuses on application of an investigational approach to assess the hot-processability of pharmaceutical-grade polymers with a potential for use in the manufacturing of reservoir drug delivery systems via micromolding, and the performance of resulting molded barriers. An inert thermoplastic polymer, ethylcellulose (EC), widely exploited for preparation of prolonged-release systems, was employed as a model component of the release-controlling barriers. Moldability studies were performed with plasticized EC, as such or in admixture with release modifiers, by the use of disk-shaped specimens ≥ 200 µm in thickness. The disks turned out to be a suitable tool for evaluation of the dimensional stability and diffusional barrier performance of the investigated materials after demolding. The effect of the amount of triethyl citrate, used as a plasticizer, on hot-processability of EC was assessed. The rate of a model drug diffusion across the polymeric barriers was shown to be influenced by the extent of porosity from the incorporated additives. The investigational approach proposed, of simple and rapid execution, holds potential for streamlining the development of prolonged-release systems produced by micromolding in the form of drug reservoirs, with no need for molds and molding processes to be set up on a case-by-case basis. [ABSTRACT FROM AUTHOR]

In previous works, a finite element model of the shock absorbing characteristics of athletics tracks was developed, able to give sufficiently reliable predictions from laboratory tests performed on suitable material samples. The model proved to be effective in discriminating the effects of geometry (i.e. thickness) and material properties (essentially the elastic characteristics) on force reduction, thus allowing a first optimization of the tracks in view of their approval by the International Association of Athletics Federations (IAAF). This simplified 2D model neglected the real track structure, considering it as a single layer of material having homogenized properties. In the present study, a new 3D model was developed to accurately describe the structure of multi-layered tracks, with properties and geometrical construction (e.g. solid or honeycomb) differing from one layer to another. Several tracks having different combinations of top/bottom layers varying in both material formulation (i.e. chemical composition) and geometry were thus considered. Mechanical properties of the individual elements constituting the track were measured with small-scale laboratory tests, taking into account their strain-rate dependence. The 3D model allowed a complete representation of the loads acting on the track and it gave results which are in very good agreement with the experiments. This proves it to be a valuable tool for the purpose of optimizing the track in terms of material formulation as well as layer geometrical construction and arrangement: as an example, the effect of changing the cell size of the honeycomb pattern was investigated. [ABSTRACT FROM AUTHOR]

Abstract: The Force Reduction (FR) impact test, performed by means of an apparatus called artificial athlete, has been chosen by IAAF (International Association of Athletics Federations) as a standard to evaluate the performance of athletics tracks. The test procedure consists in dropping a mass on the sample, recording the evolution of the impact force and taking its maximum value normalized with respect to a reference one. In this work a Finite Element (FE) model of the FR test was developed to investigate the effects of sample thickness and material properties. Two athletics tracks and, for comparison, a sample of natural rubber were considered. Their mechanical behaviour was characterized, extrapolated to the strain rate of interest and modelled using hyperelastic constitutive equations. With data so derived a number of numerical (FE) simulations of the FR test on the three materials with varying thickness were performed. The FR values predicted by the simulations resulted to be in very good agreement with experimental FR data, particularly for thicknesses of practical interest. Finally, the suitability of an alternative model based on a linear elastic constitutive relationship was considered and results were discussed. [Copyright &y& Elsevier]

Abstract: Organic–inorganic hybrid coatings, obtained through the sol–gel chemistry from tetraethoxysilane and polyethylene–poly(ethylene glycol) block copolymer, have been prepared in different compositions and applied to untreated and plasma treated LDPE films by spin coating. The mechanical properties of the coatings and the adhesion between coating and substrate have been characterized by fragmentation test. An increase in coating strength, elongation at break and adhesion has been observed with increasing the organic fraction in the hybrid coating. A plasma treatment of the LDPE surface, just before the application of the coating, lead to an increase of the adhesion between coating and substrate (interfacial shear strength), leaving almost unaffected coating strength and strain at fragmentation onset. [Copyright &y& Elsevier]

The present paper aims at developing an integrated experimental/computational approach towards the design of shape memory devices fabricated by hot-processing with potential for use as gastroretentive drug delivery systems (DDSs) and for personalized therapy if 4D printing is involved. The approach was tested on a plasticized poly(vinyl alcohol) (PVA) of pharmaceutical grade, with a glass transition temperature close to that of the human body (i.e., 37 °C). A comprehensive experimental analysis was conducted in order to fully characterize the PVA thermo-mechanical response as well as to provide the necessary data to calibrate and validate the numerical predictions, based on a thermo-viscoelastic constitutive model, implemented within a finite element framework. Particularly, a thorough thermal, mechanical, and shape memory characterization under different testing conditions and on different sample geometries was first performed. Then, a prototype consisting of an S-shaped device was fabricated, deformed in a temporary compact configuration and tested. Simulation results were compared with the results obtained from shape memory experiments carried out on the prototype. The proposed approach provided useful results and recommendations for the design of PVA-based shape memory DDSs. [ABSTRACT FROM AUTHOR]

3D printing, and particularly fused deposition modeling (FDM), has rapidly brought the possibility of personalizing drug therapies to the forefront of pharmaceutical research and media attention. Applications for this technology, described in published articles, are expected to grow significantly in 2020. Where are we on this path, and what needs to be done to develop a FDM 2.0 process and make personalized medicines available to patients? Based on literature analysis, this manuscript aims to answer these questions and highlight the critical technical aspects of FDM as an emerging technology for manufacturing safe, high-quality personalized oral drug products. In this collaborative paper, experts from different fields contribute strategies for ensuring the quality of starting materials and discuss the design phase, printer hardware and software, the process, the environment and the resulting products, from the perspectives of both patients and operators. [ABSTRACT FROM AUTHOR]

The fracture behaviour of continuous unidirectional carbon fibre composite materials prepared adopting two, one plain and one rubber toughened, thermoplastic acrylic resins as matrices was investigated as a function of temperature and displacement rate. The contributions to fracture toughness of composites given by the matrix and the fibre related mechanisms was analysed by comparing results obtained at crack initiation and during crack propagation stages. It was verified that the transfer of matrix toughness into the composite is only partial when the matrix process zone size is comparable to the interlaminar matrix layer thickness. The effectiveness of fibre bridging mechanism was found to be related to the interfacial strength between the matrix and the fibre. [ABSTRACT FROM AUTHOR]

Nucleation of semi-crystalline polymers is very sensitive to perturbations of the melt state. In contrast to the case of flow, the influence of pressure changes on nucleation has been almost neglected so far. In this work we explore the effect of the pressure history on isotactic polypropylene crystallization by applying a brief step-like increase of pressure to the undercooled melt. Using dilatometry and synchrotron X-ray diffraction, an enhancement of crystallization kinetics proportional to the magnitude of the pressure pulse is revealed. This acceleration is linked to an increase of the number of active nuclei after the short term pressurization, as confirmed by ex-situ optical microscopy observations. Up to an order of magnitude increase in nucleation density is found, for pressure pulses around 600–700 bar. The pressure-induced nucleating effect is interpreted in the light of classical nucleation theory; although a non-classical “barrier-less” nucleation mechanism is also envisaged. [ABSTRACT FROM AUTHOR]

Strain induced molecular orientation effect on the fracture toughness of natural rubber based compounds was studied under biaxial loading conditions, using non-linear elastic fracture mechanics. The J -integral at fracture was evaluated using the finite element method. Fracture toughness can be severely influenced by strain induced molecular orientation up to a material dependent threshold, above which toughness becomes constant. The effect of the fracture phenomenology shown by two carbon black filled compounds, for which propagation is preceded by branching at the tip (sideways crack propagation), is shown to remove any significant stress concentration at the original crack tip, enhancing the apparent fracture resistance. [ABSTRACT FROM AUTHOR]

Capillary rheometry was used for measurement of the high rate steady-state flow properties of micro-filled high-density polyethylene (HDPE) melts, and the effects of the test geometry were investigated. Attention was paid to the influence of the die diameter. The micro-compounds examined had the same filler content (10 vol.% in the melt state), but differed in the nature and geometry of filler (glass beads, discontinuous glass fibres and talc). [ABSTRACT FROM AUTHOR]

3D printing, in particular the Polyjet technology, has been widely employed for the production of complex heterogeneous composites such as co-continuous architectures (the so-called Interpenetrating Phase Composites, IPCs). It is a manufacturing method in which discrete photopolymer droplets of different materials can be deposited on a build tray and cured by UV light lamp. Previous research already demonstrated how the characteristics of the interface between different photopolymers can vary if formed before or after UV curing process, with the formation of a narrow or broad interphase. In the present work, the dynamic-mechanical properties of multilayer bimaterial composites (made combining a glassy and a rubbery polymer) were investigated under tensile loading, which is relatively insensitive to the spatial arrangement of layers, as opposed to bending. The use of a simple parallel configuration allowed the development of an analytical model which incorporates the properties of the two photopolymers and their interphase, considering their effect on both elastic and dissipative behaviour of the composites; in particular, the interphase behaviour is quite close to that of the glassy polymer and even small quantities are sufficient to dramatically change the overall dissipative behaviour of the composite. It is demonstrated that reliable modelling of real co-continuous architectures as obtained by Polyjet printing (and similar techniques) should include the effect of the interphase. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The present paper is aimed at clarifying the dependence of the force reduction ability of sport surfaces used in athletic tracks on the material''s viscoelastic properties and on the geometry of the sample. The study is based on laboratory tests carried out with an “artificial athlete” apparatus and dynamic mechanical analysis. Seven different sport surfaces were tested; other polymeric materials were also examined in order to widen the property ranges covered. The results show a prominent effect of sample thickness on the measured value of force reduction; a method to relate it to the intrinsic properties of the material is proposed. [Copyright &y& Elsevier]

Graphical abstract Abstract The use of shape memory polymers exhibiting water-induced shape recovery at body temperature and water solubility was proposed for the development of indwelling devices for intravesical drug delivery. These could be administered via catheter in a suitable temporary shape, retained in the bladder for a programmed period of time by recovery of the original shape and eliminated with urine following dissolution/erosion. Hot melt extrusion and fused deposition modeling 3D printing were employed as the manufacturing techniques, the latter resulting in 4D printing because of the shape modifications undergone by the printed item over time. Pharmaceutical-grade poly(vinyl alcohol) was selected based on its hot-processability, availability in different molecular weights and on preliminary data showing water-induced shape memory behavior. Specimens having various original and temporary geometries as well as compositions, successfully obtained, were characterized by differential scanning calorimetry and dynamic-mechanical thermal analysis as well as for fluid uptake, mass loss, shape recovery and release behavior. The samples exhibited the desired ability to recover the original shape, consistent in kinetics with the relevant thermo-mechanical properties, and concomitant prolonged release of a tracer. Although preliminary in scope, this study indicated the viability of the proposed approach to the design of retentive intravesical delivery systems. [ABSTRACT FROM AUTHOR]

Processing conditions have a strong effect on the final mechanical properties of products made of polymeric materials. Relevant phenomena most commonly include thermal stresses, physical ageing, frozen-in strains and molecular orientation. In this work, two different high-impact polystyrenes, processed by thermoforming, were considered: a “standard” one and a grade specifically resistant to Environmental Stress Cracking (ESC). The main effect induced by thermoforming was molecular orientation. The local degree of orientation was measured on a thermoformed product and its effect on the material ESC behavior in sunflower oil was studied. A Fracture Mechanics approach was applied to evaluate the fracture resistance of the two materials. Results show that a higher degree of orientation increases the fracture resistance in air but has no effect on the (expectedly lower) resistance in the active oil environment. [ABSTRACT FROM AUTHOR]

The outcomes of the electrospinning of polyamide 6 (PA6) solutions in formic acid containing FeCl 3 are correlated with the extensional rheological behaviour of these fluids, which is investigated by the self-controlled capillary breakup of a filament. The rheological analysis enlightens a significant effect of the FeCl 3 content on the rheological behaviour, the viscous component becoming predominant over a certain salt content threshold. At this concentration, the electrospun fibres show the formation of severely inhomogeneous structures this indicating that an elastically dominated behaviour is necessary to yield defect-free fibres. Addition of FeCl 3 also decreases fibre crystallinity and fibres turn out to be completely amorphous above a critical concentration. Interestingly, this concentration coincides with the one at which the viscous component starts dominating the rheological behaviour. [ABSTRACT FROM AUTHOR]

Several diseases would benefit from prolonged drug release provided by systems retained in the stomach for extended time periods. Expandable gastroretentive devices are administered in a collapsed configuration enabling swallowing and regain in situ their native shape having larger spatial encumbrance, thus hindering voidance through the wide open pylorus. An expandable system for gastric retention was here proposed relying on the shape memory behavior of pharmaceutical-grade poly(vinyl alcohol). Different original configurations to be recovered upon exposure to aqueous fluids at 37 °C, potentially enabling gastric retention, were conceived. Prototypes containing allopurinol were directly manufactured by fused deposition modeling or shaped by purposely-designed templates from hot melt extruded rods immediately after production. Various temporary shapes, in principle suitable for administration, were programmed by manual deformation of samples by means of specific templates, under defined temperature conditions. In 0.1 N hydrochloric solution at 37 °C, the prototypes recovered their original shape, reaching the desired spatial encumbrance within few minutes. Release from the samples, although of relatively short duration, was independent of the original shape and processing undergone, and was noticeably slowed down by application of Eudragit® RS/RL-based coatings. Unlabelled Image [ABSTRACT FROM AUTHOR]