Browsing by Author "Mitchell, Geoffrey R."
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- Additive manufactured Poly("-caprolactone)-graphene scaffolds: Lamellar crystal orientation, mechanical properties and biological performancePublication . Biscaia, Sara; Silva, João C.; Moura, Carla; Viana, Tânia; Tojeira, Ana; Mitchell, Geoffrey R.; Pascoal-Faria, Paula; Ferreira, Frederico Castelo; Alves, NunoUnderstanding the mechano–biological coupling mechanisms of biomaterials for tissue engineering is of major importance to assure proper scaffold performance in situ. Therefore, it is of paramount importance to establish correlations between biomaterials, their processing conditions, and their mechanical behaviour, as well as their biological performance. With this work, it was possible to infer a correlation between the addition of graphene nanoparticles (GPN) in a concentration of 0.25, 0.5, and 0.75% (w/w) (GPN0.25, GPN0.5, and GPN0.75, respectively) in three-dimensional poly("-caprolactone) (PCL)-based scaffolds, the extrusion-based processing parameters, and the lamellar crystal orientation through small-angle X-ray scattering experiments of extruded samples of PCL and PCL/GPN. Results revealed a significant impact on the scaffold’s mechanical properties to a maximum of 0.5% of GPN content, with a significant improvement in the compressive modulus of 59 MPa to 93 MPa. In vitro cell culture experiments showed the scaffold’s ability to support the adhesion and proliferation of L929 fibroblasts (fold increase of 28, 22, 23, and 13 at day 13 (in relation to day 1) for PCL, GPN0.25, GPN0.5, and GPN0.75, respectively) and bone marrow mesenchymal stem/stromal cells (seven-fold increase for all sample groups at day 21 in relation to day 1). Moreover, the cells maintained high viability, regular morphology, and migration capacity in all the different experimental groups, assuring the potential of PCL/GPN scaffolds for tissue engineering (TE) applications.
- Biomaterials for In Situ Tissue Regeneration: A ReviewPublication . Abdulghani, Saba; Mitchell, Geoffrey R.This review focuses on a somewhat unexplored strand of regenerative medicine, that is in situ tissue engineering. In this approach manufactured scaffolds are implanted in the injured region for regeneration within the patient. The scaffold is designed to attract cells to the required volume of regeneration to subsequently proliferate, differentiate, and as a consequence develop tissue within the scaffold which in time will degrade leaving just the regenerated tissue. This review highlights the wealth of information available from studies of ex-situ tissue engineering about the selection of materials for scaffolds. It is clear that there are great opportunities for the use of additive manufacturing to prepare complex personalized scaffolds and we speculate that by building on this knowledge and technology, the development of in situ tissue engineering could rapidly increase. Ex-situ tissue engineering is handicapped by the need to develop the tissue in a bioreactor where the conditions, however optimized, may not be optimum for accelerated growth and maintenance of the cell function. We identify that in both methodologies the prospect of tissue regeneration has created much promise but delivered little outside the scope of laboratory-based experiments. We propose that the design of the scaffolds and the materials selected remain at the heart of developments in this field and there is a clear need for predictive modelling which can be used in the design and optimization of materials and scaffolds.
- Biopolymers based on rosinPublication . Mitchell, Geoffrey R.; Mahendra, Vidhura; Sousa, DoraRosin is a material, which can be obtained from pine resin using a green technology with no waste output. It is a mixture of terpenes with a functionality that make them a rich chemical resource. Rosin is a material which has been available for hundreds of years and has developed many niche applications some old, some new. The authors review the potential of this material for preparing sustainable biopolymers and composites by identifying the reaction paths. The authors conclude that foams and composites may be the most effective route to high volume applications based on rosin.
- Direct Digital Manufacturing of NanocompositesPublication . Mohan, Saeed D.; Nazhipkyzy, Meruyert; Carreira, Pedro; Santos, Cyril dos; Davis, Fred J.; Mateus, Artur; Mitchell, Geoffrey R.Additive manufacturing has surged in popularity as a route to designing and preparing functional parts. Depending on the parts function, certain attributes such as high mechanical performances may be desired. We develop a route for improving the mechanical properties of polymer devices, fabricated through additive manufacturing by combining electrospinning and stereo-lithography into one automated process. This process utilises the impressive mechanical properties of carbon nanotubes by encapsulating and aligning them in electrospun fibres. Composite fibres will be incorporated into polymer resins prepared with stereo-lithography, thereby providing resins that benefit from the composite fibres properties, enhancing their overall mechanical properties.
- Effect of Hydrodynamic Forces on meso‐(4‐Sulfonatophenyl)‐Substituted Porphyrin J‐Aggregate Nanoparticles: Elasticity, Plasticity and BreakingPublication . El‐Hachemi, Zoubir; Balaban, Teodor Silviu; Campos, J. Lourdes; Cespedes, Sergio; Crusats, Joaquim; Escudero, Carlos; Kamma‐Lorger, Christina S.; Llorens, Joan; Malfois, Marc; Mitchell, Geoffrey R.; Tojeira, Ana; Josep M. RibóThe J aggregates of 4‐sulfonatophenylmeso‐substituted porphyrins are non‐covalent polymers obtained by self‐assembly that form nanoparticles of different morphologies. In the case of high aspect‐ratio nanoparticles (bilayered ribbons and monolayered nanotubes), shear hydrodynamic forces may modify their shape and size, as observed by peak force microscopy, transmission electron microscopy of frozen solutions, small‐angle X‐ray scattering measurements in a disk‐plate rotational cell, and cone–plate rotational viscometry. These nanoparticles either show elastic or plastic behaviour: there is plasticity in the ribbons obtained upon nanotube collapse on solid/air interfaces and in viscous concentrated nanotube solutions, whereas elasticity occurs in the case of dilute nanotube solutions. Sonication and strong shear hydrodynamic forces lead to the breaking of the monolayered nanotubes into small particles, which then associate into large colloidal particles.
- Electrospinning of food-grade nanofibres from whey proteinPublication . Zhong, Jie; Mohan, Saeed D.; Bell, Alan; Terry, Ann; Mitchell, Geoffrey R.; Fred, DavisIn this study, electrospinning has been employed to produce micro to nano scale fibres of whey protein in order to investigate their potential for use in the food industry. Initially, spinning of purewhey protein proved challenging; so in order to facilitate the spinning of freshly prepared aqueous solutions, small amounts of polyethylene oxide (as low as 1% w/w in solution) were incorporated in the spinning solutions. The electrospun composite polyethylene-oxide/whey fibres exhibited diameters in the region of 100 to 400 nm, showing the potential to build fibre bundles from this size up. Time-dependent examinations of pure whey protein aqueous solutions were conducted using rheometery and small angle neutron scattering techniques, with the results showing a substantial change in the solution properties with time and stirring; and allowing the production of fibres, albeit with large diameters,without the need for an additive. The spinability is related to the potential of thewhey protein composites to form aggregate structures, either through hydration and interaction with neighbouring proteins, or through interaction with the polyethylene oxide.
- Ferronematic liquid crystal polymers and elastomersPublication . Reeves, Sarah J.; Davis, Fred J.; Mitchell, Geoffrey R.Liquid crystal polymers, through covalent bonding, combine the spontaneous long range orientational order of the liquid crystal state with the entropically driven random coil configurations of the skeletal polymer chains in a single material [1]. [...]
- Measuring in-situ X-ray scattering of natural rubber biaxial deformation: A new equipment for polymer studiesPublication . Silva, Daniel P. da; Lamolinara, Barbara; Costa, André; Gameiro, Fábio; Pascoal-Faria, Paula; Mateus, Artur; Martinez, Juan Carlos; Phinyocheep, Pranee; Amornsakchai, Taweechai; Mitchell, Geoffrey R.Understanding biaxial deformation is essential for a more realistic evaluation of rubber elasticity compared to the more usual uniaxial deformation. To study crystallisation occurring during biaxial deformation of natural rubber films, a new simple equipment has been designed and assembled. The equipment, mounted in the beamline of ALBA synchrotron light source facility, allowed the in-situ measurement of X-ray scattering of natural rubber during biaxial deformation. This work provides, for the first time, quantitative information on crystallisation during biaxial extension.
- Microwave Treatment of Polyacrylonitrile Powder Method Development and Effects of Surface Modification Porosity for Supercapacitor Devices or other Mobile ApplicationsPublication . Koutsonas, Spiridon; Mitchell, Geoffrey R.; Davis, Fred J.The aim of this article is to develop a method in order to investigate the surface modifications of degraded polyacrylonitrile powders under microwave treatment in air. Microwave treatment of polyacrylonitrile powders in air recorded two stages of degradation firstly an exothermic reaction that started in the range of (86-117)°C. Secondly the Thermal runway here the weight loss reached a peak value between 80-90 percent with the small quantity of 0.25g polyacrylonitrile and in the ashes with a bigger quantity 1g of polyacrylonitrile. Scanning electron microscopy analysis technique revealed the morphological characteristics and the porosity of the carbon compound that may play an important role in the construction of high porosity area and so in electrochemical supercapacitor devices with high performances.
- Morphology Development During Micro Injection Moulding of ThermoplasticsPublication . Mitchell, Geoffrey R.; Carreira, Pedro; Gomes, Sara; Mateus, Artur; Saeed MohanMicro injection moulding is a key process in the field of micro manufacturing especially in the production of medical devices. Micro injection molding technology involves the injection of the whole material with the result of a high degree of efficiency due to the material saving process. In comparison with conventional large injection moulding, the volume of material is very much reduced and as a consequence the flow and temperature profiles are considerable different to macro injection moulding. This work focuses on the impact on the structure, morphology and properties of parts prepared using micro injection moulding of these changes flow and temperature profiles. We have used small-angle X-ray Scattering techniques to evaluate the semicrystalline morphology and we have discovered that the nature of the process has led to changes in the morphology. We have supplemented the small angle scattering technique with wide-angle x-ray scattering as well differential scanning calorimetry.