An electrochemical study of acrylate bone adhesive permeability and selectivity change during in vitro ageing: a model approach to the study of biomaterials and membrane barriers

This study assessed the solute permeability of a family of UV and moisture cured acrylates-based adhesives during in vitro ageing in pH 7.4 buffer. Acrylates have a potential role in bone fracture fixation, but their inability to allow microsolute exchange between the fractured bone surfaces may contribute to ineffective healing. Cyclic voltammetry and chronoamperometry were used to determine the diffusion coefficients for various electrochemically active probe molecules (O2, H2O2, acetaminophen, catechol, uric acid and ascorbic acid) at proprietary acrylic, urethane – acrylate and cyanoacrylate adhesives. All adhesives proved to be impermeable for up to 9 days ageing, following which a near-exponential increase in permeability resulted for all solutes. At 18 days, the diffusion coefficients were in the range of 10-5 cm2s-1 for O2 and H2O2 and 10-6 cm2s-1 for the organic solutes; no transport selectivity was seen between the latter. Adhesive joint strength showed a direct, inverse, correlation with permeability, with the more hydrophilic cyanoacrylates showing the greatest loss of strength. Adhesive permeabilisation does not appear to be compatible with the retention of bonding strength, but it serves as a new non-destructive predictor of adhesion strength change during ageing and practical use

Design against distortion for aerospace-grade additively manufactured parts - PADICTON

Collections: Brunel Composite CentreAdditive manufacturing (AM) is a computer-controlled 3D printing process with increasing demand in the aerospace sector. This manufacturing process offers the production of lighter components, design flexibility, reduced labour effort and material cost, as well as decreased waste generation compared with subtractive manufacturing. Additionally, AM can provide parts availability at the point of use, significantly improving the supply chain. However, producing advanced high-temperature AM thermoplastic components remains a challenging task as these require a high-temperature build chamber environment that is prone to producing parts with thermal stresses and warpage. PADICTON project aims to develop a tool capable of accurately and rapidly predicting and correcting such distortions, offering improved quality of the produced parts and minimising rejection rates. Creating this tool requires conducting a comprehensive mechanical and thermal characterisation campaign to optimise the print parameters and part geometry. In this study, the concept of the project and the findings of the initial mechanical and optical characterisation tests for two AM processes, namely fused deposition modelling and selective laser sintering, are presented and discussed.The authors would like to acknowledge the PADICTON partners, namely FDM Digital Solutions, e Xstream Engineering, part of Hexagon Manufacturing Intelligence, AMendate, as well as the Topic Manager of the project, Airbus, for their assistance and encouragement towards the realisation of the activities. In addition, the consortium would like to express its gratitude to EOS for their technical support. Furthermore, the activities of PADICTON project have received funding from the Clean Sky 2 Joint Undertaking under the European Union’s Horizon 2020 research and innovation programme under grant agreement number 86481

Laser Micro Welding of Nitinol for Cardiovascular Applications

Nitinol (NiTi), an equiatomic nickel-titanium alloy, is widely used in the medical field due to its unique properties such as superelasticity and shape memory effect. Nitinol alloy is sensitive to thermo-mechanical processing which leads to reduction in the superelasticity and shape memory effect at the joint. These thermo-mechanical processes are necessary in the manufacturing procedure which are involved in the construction of cardiovascular devices and implants. Most medical devices are currently obtained from lasercutting of nitinol tubes, or from assemblies of nitinol elements (e.g. wires) joined at specific locations by crimping. However, these approaches reduce the strength of the structure at the joints. The main objective of this study is to analyse the most common joining techniques adopted for nitinol-nitinol and optimise the joint. Preliminary experiments were conducted on superelastic nitinol wires of 0.44 mm diameter, employing resistance discharge welding and percussive arc welding processes. Successively, laser micro welding was tested, and resulted to provide superior joining properties, due to increased mechanical strength. Examination of the microstructure and microhardness of the welded specimens was carried out. The mechanical strength of the welded specimens was evaluated using tensile testing. An elemental study was performed using energy dispersive X-ray spectroscopy (EDS) to assess nickel and titanium concentration at the fusion zone. Differential scanning calorimeter (DSC) investigations was carried out to determine the phase transformation temperatures. The results suggest that the laser micro welding procedure preserves the pseudoelastic properties of laser welded specimens in comparison to the reference material. The proposed joining approach may enable further expansion in the use of the properties of nitinol in the medical area, and result in improvements in the safety and durability of cardiovascular implants

Laser Surface Modification of Poly(etheretherketone) to Enhance Surface Free Energy, Wettability and Adhesion

Enhancement of the surface wettability and surface free energy of thermoplastic materials is an effective way of improving their adhesion and consequently the adhesive joint strength. A nanosecond pulsed Nd:YAG laser was selected in this work to provide energetic treatment of PEEK surfaces, in order to investigate its effectiveness in increasing the performance of lap shear adhesive joints. The laser was used to irradiate the PEEK, by rastering a spot of ca. 1 mm diameter across a large area. The resulting surfaces were characterised using single lap shear testing, confocal laser scanning microscopy, contact angle analysis, FT-IR, XPS and ToF-SIMS. Single lap shear testing of PEEK joints showed that the strength of adhesively bonded joints is greatly improved by laser treatment, up to 13 times that of untreated PEEK. Confocal laser scanning microscopy showed that the higher laser powers intensities (≥ 107 W mm-2) disrupted the surface of the PEEK more than the lower laser powers intensities (< 107 W mm-2), but also showed that, as expected, only some of the surface is treated by the laser. Contact angle analysis showed a decrease in water contact angle with increasing laser power intensity, and the derived surface free energy increased accordingly. FT-IR in the specular reflectance mode showed no discernible change but XPS and ToF-SIMS did, suggesting that laser treatment only affects the near surface at the extremity of the 1-2 μm sampling depth. XPS showed a decrease in the carbon/oxygen ratio of PEEK on treatment, indicating that oxygen-containing functional groups were being created at the surface. XPS also suggested a cleaning mechanism at a laser intensity of 7.83 x 10⁶ W mm-², progressing to surface modification from a laser intensity of 107 W mm-² and above. ToF-SIMS confirmed that laser treatment cleans the surface of PEEK of extraneous material