In-situ development of self-defensive antibacterial biomaterials: phenol-g-keratin-EC based bio-composites with characteristics for biomedical applications

Recently, the development of highly inspired biomaterials with multi-functional characteristics has gained considerable attention, especially in biomedical, and other health-related areas of the modern world. It is well-known that the lack of antibacterial potential has significantly limited biomaterials for many challenging applications such as infection free wound healing and/or tissue engineering etc. In this perspective, herein, a series of novel bio-composites with natural phenols as functional entities and keratin-EC as a base material were synthesised by laccase-assisted grafting. Subsequently, the resulting composites were removed from their respective casting surfaces, critically evaluated for their antibacterial and biocompatibility features and information is also given on their soil burial degradation profile. In-situ synthesised phenol-g-keratin-EC bio-composites possess strong anti-bacterial activity against Gram-positive and Gram-negative bacterial strains i.e., B. subtilis NCTC 3610, P. aeruginosa NCTC 10662, E. coli NTCT 10418 and S. aureus NCTC 6571. More specifically, 10HBA-g-keratin-EC and 20T-g-keratin-EC composites were 100% resistant to colonisation against all of the aforementioned bacterial strains, whereas, 15CA-g-keratin-EC and 15GA-g-keratin-EC showed almost negligible colonisation up to a variable extent. Moreover, at various phenolic concentrations used, the newly synthesised composites remained cytocompatible with human keratinocyte-like HaCaT, as an obvious cell ingrowth tendency was observed and indicated by the neutral red dye uptake assay. From the degradation point of view, an increase in the degradation rate was recorded during their soil burial analyses. Our investigations could encourage greater utilisation of natural materials to develop bio-composites with novel and sophisticated characteristics for potential applications.

Fracture toughness determination of adhesive and co-cured joints in natural fibre composites

Adhesive bonding has become more efficient in the last few decades due to the adhesives developments, granting higher strength and ductility. On the other hand, natural fibre composites have recently gained interest due to the low cost and density. It is therefore essential to predict the fracture behavior of joints between these materials, to assess the feasibility of joining or repairing with adhesives. In this work, the tensile fracture toughness (Gc n) of adhesive joints between natural fibre composites is studied, by bonding with a ductile adhesive and co-curing. Conventional methods to obtain Gc n are used for the co-cured specimens, while for the adhesive within the bonded joint, the J-integral is considered. For the J-integral calculation, an optical measurement method is developed for the evaluation of the crack tip opening and adherends rotation at the crack tip during the test, supported by a Matlab sub-routine for the automated extraction of these quantities. As output of this work, an optical method that allows an easier and quicker extraction of the parameters to obtain Gc n than the available methods is proposed (by the J-integral technique), and the fracture behaviour in tension of bonded and co-cured joints in jute-reinforced natural fibre composites is also provided for the subsequent strength prediction. Additionally, for the adhesively- bonded joints, the tensile cohesive law of the adhesive is derived by the direct method.

An approach for reliability-based robust design optimisation of angle-ply composites

Variations of manufacturing process parameters and environmental aspects may affect the quality and performance of composite materials, which consequently affects their structural behaviour. Reliability-based design optimisation (RBDO) and robust design optimisation (RDO) searches for safe structural systems with minimal variability of response when subjected to uncertainties in material design parameters. An approach that simultaneously considers reliability and robustness is proposed in this paper. Depending on a given reliability index imposed on composite structures, a trade-off is established between the performance targets and robustness. Robustness is expressed in terms of the coefficient of variation of the constrained structural response weighted by its nominal value. The Pareto normed front is built and the nearest point to the origin is estimated as the best solution of the bi-objective optimisation problem.

Single-lap joints of similar and dissimilar adherends bonded with an acrylic adhesive

In this study, the tensile strength of single-lap joints (SLJs) between similar and dissimilar adherends bonded with an acrylic adhesive was evaluated experimentally and numerically. The adherend materials included polyethylene (PE), polypropylene (PP), carbon-epoxy (CFRP), and glass-polyester (GFRP) composites. The following adherend combinations were tested: PE/PE, PE/PP, PE/CFRP, PE/GFRP, PP/PP, CFRP/CFRP, and GFRP/GFRP. One of the objectives of this work was to assess the influence of the adherends stiffness on the strength of the joints since it significantly affects the peel stresses magnitude in the adhesive layer. The experimental results were also used to validate a new mixed-mode cohesive damage model developed to simulate the adhesive layer. Thus, the experimental results were compared with numerical simulations performed in ABAQUS®, including a developed mixed-mode (I+II) cohesive damage model, based on the indirect use of fracture mechanics and implemented within interface finite elements. The cohesive laws present a trapezoidal shape with an increasing stress plateau, to reproduce the behaviour of the ductile adhesive used. A good agreement was found between the experimental and numerical results.