Metallic bioresorbable orthopaedic implants based on magnesium, iron and zinc-based alloys that provide rigid internal fixation without foreign-body complications associated with permanent implants have great potential as next-generation orthopaedic devices. Magnesium (Mg) based alloys exhibit excellent biocompatibility. However, the mechanical performance of such implants for orthopaedic applications is contingent on limiting the rate of corrosion in vivo throughout the bone healing process. Additionally, the surgical procedure for the implantation of internal bone fixation devices may impart plastic deformation to the device, potentially altering the corrosion rate of the device. The primary objective of this study was to develop a computer-based model for predicting the in vivo corrosion behaviour of implants manufactured from a Mg-1Zn-0.25Ca ternary alloy (ZX10). The proposed corrosion model was calibrated with an extensive range of mechanical and in vitro corrosion testing. Finally, the model was validated by comparing the in vivo corrosion performance of the implants during preliminary animal testing with the corrosion performance predicted by the model. The proposed model accurately predicts the in vitro corrosion rate, while overestimating the in vivo corrosion rate of ZX10 implants. Overall, the model provides a “first-line of design” for the development of new bioresorbable Mg-based orthopaedic devices.Statement of SignificanceBiodegradable metallic orthopaedic implant devices have emerged as a potential alternative to permanent implants, although successful adoption is contingent on achieving an acceptable degradation profile. A reliable computational method for accurately estimating the rate of biodegradation in vivo would greatly accelerate the development of resorbable orthopaedic implants by highlighting the potential risk of premature implant failure at an early stage of the device development. Phenomenological corrosion modelling approach is a promising computational tool for predicting the biodegradation of implants. However, the validity of the models for predicting the in vivo biodegradation of Mg alloys is yet to be determined. Present study investigates the validity of the phenomenological modelling approach for simulating the biodegradation of resorbable metallic orthopaedic implants by using a porcine model that targets craniofacial applications.

All-cellulose composites (ACC) have been investigated as a high-strength bio-based alternative to commodity plastics. However, plastic products frequently demand complex 3D geometries as part of their functionality. Hence, a critical factor in the broader application of ACCs is the production of dimensionally-accurate 3D forms. Interestingly, there have been no attempts in the literature to produce 3D geometries based on all-cellulose composites. In the present work, the production of ACCs with 3D geometries is explored for the first time using conventional vacuum and compression moulding procedures. The level of 3D complexity possible in ACCs was examined using a closed mould design that incorporated a range of geometric shapes and angles of varying intricacy. The dimensional accuracy of the final 3D forms was analysed via 3D laser scanning of the surfaces of the as-moulded ACCs. The choice of coagulant type was found to strongly influence the dimensional accuracy of the as-moulded ACCs.

Canola protein is used to produce novel, mesoporous, plant-based aerogels through a salt-induced gelation technique and supercritical carbon dioxide drying. The use of calcium chloride in formulation permits the preservation of gel monoliths during solvent exchange processing, customarily a major challenge in aerogel preparation. The gels could be successfully converted to aerogels by supercritical drying using accessible, off-the shelf instrumentation, rather than the purpose-built systems commonly used in aerogel research. The use of calcium chloride represents a novel approach to canola protein gelation, achieving crosslinking via an environmentally-friendly approach. The first-ever supercritically-dried canola aerogels are shown to be mesoporous with an approximate density and specific surface area of 0.2 g/cm(3) and 113 m(2)/g, respectively. The typical low-densities (0.03 - 0.5 g/cm(3)) and high surface areas (50 - 600 m(3)/g) of bioaerogels lend themselves to novel pharma-and nutraceutical applications, with canola aerogels now another addition to this family of advanced materials.

Tuning the coefficients of thermal expansion (CTE) of polymeric materials through a combination of zinc cyanide and ionic liquid.

The biocompatibility and mechanical performance of biodegradable metals (e.g. magnesium, iron, and zinc-based alloys) in orthopaedic-targeted applications are contingent on limiting the rate of corrosion in vivo throughout the bone healing. Concurrently, the surgical procedure for the implantation of internal bone fixation devices may impart plastic deformation to the device, potentially altering the corrosion rate of the device. However, the potential effect of the surgical implantation procedure on the mechanochemical performance of metallic degradable orthopaedic devices in vivo remains largely unresolved. The objective of the present study is to develop a robust technique that permits the quantification of the strain introduced due to surgical implantation of degradable orthopaedic devices. Specifically, a novel combined experimental-modelling approach based on 3D laser scanning in situ and the finite element method is utilised to quantify the plastic strain introduced to a bone fixation plate following surgical implantation in a cadaveric porcine model where the plate is based on a ternary magnesium-zinc-calcium alloy (ZX10). The magnitude of plastic strains determined by the above approach for the Mg craniofacial miniplate confirms that the surgical procedure itself has the potential to enhance the corrosion rate of the Mg alloy in an accelerated and potentially localised manner. STATEMENT OF SIGNIFICANCE: Biodegradable metallic orthopaedic implant devices have emerged as a potential alternative to permanent implants, although successful adoption is contingent on achieving an acceptable degradation profile. Plastic strain that is introduced to the device during surgical implantation may influence the resulting degradation behaviour of the implant. In the present work, 3D laser scanning is combined with computer simulation to estimate the level and distribution of surgically-induced plastic strain in a magnesium alloy (ZX10). Subsequently, clinically-relevant pre-strain is shown to influence the rate of corrosion of ZX10 in vitro, indicating the value of such an approach in the design of biodegradable metallic devices under multiaxial loading.

The behaviour of regenerated cellulose composites produced from rayon (Cordenka™), dissolved using either ionic liquids or sodium hydroxide (common cellulose solvent) was investigated to determine in vivo biocompatibility. Cellulose-dissolving ionic liquids (1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, and four triaminocyclopropenium cation salts) and sodium hydroxide were examined in vitro using rat fibroblast-like cells to determine the most cytocompatible ionic liquid. The selected ionic liquid and sodium hydroxide were used to prepare regenerated cellulose constructs. The prepared cellulose constructs and ultra-high-molecular-weight polyethylene controls were implanted subcutaneously into adult male Sprague–Dawley rats. Post-surgery, implants were processed into a resin. Degradation properties were determined, and morphometric analysis was performed on resin sections stained with Haematoxylin & Eosin, Toluidine blue and Verhoeff’s van Giessen. The implants presented excellent biocompatibility. However, the cellulose implants showed a rapid infiltration of several mature fibroblasts and collagen fibres. A steady increase was observed in the granulation tissue ingrowth between the cellulose fibres by 14 days, increasing a further 35% by 28 days. This study indicates that non-derivatized cellulose regenerated using ionic liquids has the potential to be used as a biocompatible alternative to proteinaceous biomaterials like keratin for biomedical applications.

In this study, the influence of microstructure and buffer system on the corrosion behaviour of Mg-1 wt. % Zn is examined. The grain size of the alloy was refined from 700 µm to under 15 µm by rolling with varying reduction percentages per pass. The effects of the rolling procedure on the resulting corrosion profile were analysed with immersion and electrochemical methods. Though the rolling procedure resulted in significant grain refinement, the as-cast samples had the lowest corrosion rate of 2.8 mm/yr, while those of the rolled samples were as high as 15.8 mm/yr. The HEPES buffer system did not control the pH or support the formation of insoluble precipitates as well as the NaHCO3/CO2 buffer system, leading to more severe localised pitting corrosion in samples immersed in HEPES buffered media. While reducing grain size generally corresponds to a lower corrosion rate in Mg alloys, this study provides evidence that other factors such as texture and buffer system must also be considered to accurately test candidate alloys for biodegradable orthopaedic applications.

The potential for a facile aqueous-based solvent processing route for the synthesis of all-cellulose composites (ACCs) is explored using aqueous solutions containing tertabutylphosphonium hydroxide (TBPH). Specifically, ACC laminates are prepared via the partial dissolution of a woven textile of cellulose II using aqueous TBPH solutions. The dissolved cellulose was then regenerated to reform a cellulose II matrix phase in situ that acts to bond the original undissolved fibres. The hygroscopic behaviour and dissolution analysis of the solvent system showed wide range in the choice of processing conditions suited to the production of ACC laminates via TBPH. The effect of solvent concentration on the microstructure, crystallinity and tensile properties of ACCs is reported. The use of TBPH enables reductions in the processing cycle time and improved control over the properties of ACCs, indicative of a promising solvent system for the upscaled production of ACCs and their laminates.

Novel bio-aerogels produced via the gelation of protein extracts from canola seed meal (CSM) are described for the first time, representing a new class of advanced materials that are derived from plant-based biotechnology. The bio-aerogels were synthesised by firstly manipulating the pH of the protein solution to form a gel, followed by freeze drying to form an aerogel with an average pore size and density of 75 µm and 0.13 g cm−3, respectively. The resulting protein-based structures were observed to have pores sizes down to the meso-scale. The mechanical behaviour of CSM-derived protein aerogels was investigated using static compressive testing. The average compressive elastic moduli and strength of the aerogels were 0.97 ± 0.32 MPa and 0.055 ± 0.011 MPa, respectively. The CSM-derived protein aerogels had compressive mechanical properties up to 196% of soy protein composite aerogels. The mechanical properties could also be manipulated by altering the pH and temperature during gelation. Gels held at ambient temperature during processing were revealed to have the highest elastic moduli (2.0 ± 0.6 MPa) and compressive strength (0.096 ± 0.014 MPa) at a pH of 8. In contrast, gels that were heated at 90 °C demonstrated the highest compressive modulus and strength at a pH of 10 (133% and 140%, respectively, as compared to the gel at pH 8 prepared at ambient temperature). The tunability of the mechanical properties using simple aqueous chemistry suggests this novel system of bio-aerogels has potential uses in a range of food and biopharmaceutical applications.

Single-polymer composites based on cellulose I and/or II (aka all-cellulose composites) are emerging as a class of high-performance bio-based composite materials with mechanical properties suited to structural applications. There are various synthesis routes for the preparation of all-cellulose composites. However, little has been reported on the optimization of the processing variables affecting the properties of all-cellulose composites. In the present work, a range of all-cellulose composites were produced as single laminae via solvent infusion processing using a precursor of cellulose II fibers that were assembled as a woven 2D textile. The effects of dissolution time, dissolution temperature, and compaction pressure during hot pressing on the properties of the laminae were then systematically examined using a Taguchi design of experiment approach in order to identify the critical control factors. The tensile properties, fiber volume fraction, and crystallinity of the laminae were determined. Statistical analysis of variance and the signal-to-noise ratio were used to rank the importance of key control factors.

All-cellulose composites were produced by partial dissolution of two cellulosic sources in a mixture of sodium hydroxide and urea at low temperature. Filter paper (FP) and microfibrillated cellulose (MFC) were used to examine the role of the fiber dimensions of the initial reinforcing network on the final mechanical properties of thin self-reinforced all-cellulose composites. The dissolution time was used to control the extent of the transformation. The initial fiber structure was progressively transformed into a thoroughly consolidated composite material. X-ray diffraction and Fourier-transform infrared spectroscopy were able to show that the initial cellulose I allomorph was replaced with a cellulose II allomorph. FP underwent a fast crystallinity loss and transformation to cellulose II. In contrast, the crystallinity of MFC decreased slowly after dissolution. This result was also correlated with a slower allomorphic transformation. The crystallinity of MFC decreased to a level comparable to that of FP after 40 min and it remained comparatively unaffected at extended dissolution times. Comparison between powder and transmission XRD measurements demonstrated that the cellulose II present in all films after dissolution was strongly textured with its (1\(\bar{1}\)0) plane lying parallel to the sample surface despite fibrous microstructural features remaining from the initial substrates. The tensile strength and elastic modulus of FP increased significantly (+690 and +528 %, respectively) after only 20 min, while that of MFC remained relatively unaltered as a function of the dissolution time.

Electrospinning is recognised as an easily implementable method for the production of submicron-diameter polymer fibres. However, electrospinning is problematic for polymers such as biologically derived materials because of their higher viscosity. In this study, a new spinneret design applies shear forces to the polymer solution just prior to electrospinning. The efficacy of shear-electrospinning is proven using concentrated poly(vinyl alcohol) (PVOH) solutions as a model, with solutions designed around the various concentration regimes of PVOH, initially identified via rheological studies. Conventional electrospinning of solutions up to 16.8 wt% PVOH and viscosity in the order of 101 Pa s leads to the formation of ribbon-like fibres. In contrast, shear-electrospinning produces fibres finer in diameter, rounder in cross-section and smoother. Finally, fibre formation from solutions that are non-electrospinnable under conventional electrospinning is shown for the first time to be achievable via shear-electrospinning as demonstrated for a 30 wt% PVOH solution.

This paper presents complementary data corresponding to characterization tests done for our research article entitled "Uniaxially aligned electrospun fibers for advanced nanocomposites based on a model PVOH-epoxy system" (Karimi et al., 2016) [1]. Poly(vinyl alcohol) and epoxy resin were selected as a model system and the effect of electrospun fiber loading on polymer properties was examined in conjunction with two manufacturing methods. A novel electrospinning technology for production of uniaxially aligned nanofiber arrays was used. A conventional wet lay-up fabrication method is compared against a novel, hybrid electrospinning-electrospraying approach. The structure and thermomechanical properties of resulting composite materials were examined using scanning electron microscopy, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, and tensile testing. For discussion of obtained results please refer to the research paper (Karimi et al., 2016) [1]. (C) 2015 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/40).

Lignocellulosic fibres harvested from different plant types exhibit variations in mechanical properties that are associated with their chemical composition and physical features. This diversity indicates that plant fibres could be selected based on their physio-chemical properties for tailored applications such as enhanced vibration damping. In this study, bast, leaf, and mesocarp fibre bundles were investigated to understand correlations between their physiochemical characteristics and their mechanical properties with a particular focus on their vibrational damping ability. Due to the interrelations between the investigated variables such as cellulose content and microfibril angle, a multivariate analysis (principal component analysis) was applied to elucidate trends. The stiffness and strength of the fibre bundles were found to be positively correlated to high cellulose content and low microfibril angle while high toughness was correlated with fibre bundles of high lignin content and high microfibril angle. Conversely, the damping coefficient was found to be positively correlated to fibres containing high level of hemicelluloses, such as those extracted from leafy plants.

Four sources of cellulose with different molecular weights were dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate at 100 °C over a 10 h period. The solution densities were determined and these results were subsequently utilised to access the influence of dissolved cellulose on surface tension properties of cellulose/ionic liquid solutions. Surface tension measurements revealed increasing molecular weight and concentration reduced surface tension while temperature increases showed the opposite effect. These results are consistent with that of repulsive polymer-wall interactions near the interface in good solvent conditions. The semi-flexible nature of this carbohydrate in solution can help explain deviations of these results when compared to ideal flexible chains.

Event Abstract Back to Event Buffer-induced in vitro corrosion of magnesium alloys: considerations for standardisation of in vitro testing Ryan Wilkes1, 2*, Jay Waterman1* and Mark P. Staiger1, 2* 1 University of Canterbury, Mechanical Engineering, New Zealand 2 MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand Magnesium and its alloys have the potential to set a new standard for biodegradable orthopaedic implants. The unique combination of mechanical properties and biocompatibility exhibited by this family of alloys make them promising candidates as biodegradable metallic implants. A potential first step in assessing the suitability of biodegradable magnesium alloys is through the use of in vitro electrochemical corrosion tests. In vitro biodegradation tests have the potential to provide invaluable information about the degradation profile of the alloy in question as well as give insight to how the alloy may react when placed in an in vivo environment. However, in vitro tests seldom replicate the observed in vivo degradation behaviour largely due to the complexity of the in vivo environment that is difficult to artificially mimic. Additionally, standardisation of in vitro testing of Mg alloys is yet to be developed, making it difficult to accurately compare and contrast previously collected data. A pH of approximately 7.4 to 7.6 is constantly maintained in vivo, and as such pH control via a buffer system is an important factor in the development of in vitro test protocol. However, the selection of the buffer system for in vitro biodegradation testing has been largely overlooked in the vast majority of in vitro studies. In the present work, the effect of the buffer system on the corrosion behaviour of pure magnesium and binary alloys are examined as function of both the corrosion medium and microstructure. Potentiodynamic polarisation tests showed that the buffer system and grain size could play a role in altering the degradation rate of the materials. The more biologically realistic buffering system of carbonate buffers within a partial-CO2 atmosphere affected the corrosion rate differently than the zwitterion-based buffer system. Samples with different grain sizes also exhibited dissimilar degradation rates. Furthermore, the relationship between the buffer systems used, the grain sizes of the samples, and the degradation profiles was analysed. This systematic study provides useful background information for the development of a standardised in vitro corrosion testing that will assist with developing biodegradable Mg orthopaedic implant devices. Keywords: in vitro, corrosion, Biodegradable metal, biodegredation Conference: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016. Presentation Type: Poster Topic: Biomaterials in musculoskeletal orthopeadics and tissues Citation: Wilkes R, Waterman J and Staiger MP (2016). Buffer-induced in vitro corrosion of magnesium alloys: considerations for standardisation of in vitro testing. Front. Bioeng. Biotechnol. Conference Abstract: 10th World Biomaterials Congress. doi: 10.3389/conf.FBIOE.2016.01.01271 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Mar 2016; Published Online: 30 Mar 2016. * Correspondence: Dr. Ryan Wilkes, University of Canterbury, Mechanical Engineering, Christchurch, New Zealand, Email1 Dr. Jay Waterman, University of Canterbury, Mechanical Engineering, Christchurch, New Zealand, Email2 Dr. Mark P Staiger, University of Canterbury, Mechanical Engineering, Christchurch, New Zealand, mark.staiger@canterbury.ac.nz Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Ryan Wilkes Jay Waterman Mark P Staiger Google Ryan Wilkes Jay Waterman Mark P Staiger Google Scholar Ryan Wilkes Jay Waterman Mark P Staiger PubMed Ryan Wilkes Jay Waterman Mark P Staiger Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

This work demonstrates the potential of aligned electrospun fibers as the sole reinforcement in nanocomposite materials. Poly(vinyl alcohol) and epoxy resin were selected as a model system and the effect of electrospun fiber loading on polymer properties was examined in conjunction with two manufacturing methods. A proprietary electrospinning technology for production of uniaxially aligned electrospun fiber arrays was used. A conventional wet lay-up fabrication method is compared against a novel, hybrid electrospinning–electrospraying approach. The structure and thermomechanical properties of resulting composite materials were examined using scanning electron microscopy, dynamic mechanical analysis, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, and tensile testing. The results demonstrate that using aligned electrospun fibers significantly enhances material properties compared to unreinforced resin, especially when manufactured using the hybrid electrospinning–electrospraying method. For example, tensile strength of such a material containing only 0.13vol% of fiber was increased by ∼700%, and Young’s modulus by ∼250%, with concomitant increase in ductility.

AbstractIn this work, the production of continuous submicron diameter saccharide fibres is shown to be possible using the electrospinning process. The mechanism for the formation of electrospun polymer fibres is usually attributed to the physical entanglement of long molecular chains. The ability to electrospin continuous fibre from a low molecular weight saccharides was an unexpected phenomenon. The formation of sub-micron diameter “sugar syrup” fibres was observed in situ using highspeed video. The trajectory of the electrospun saccharide fibre was observed to follow that typical of electrospun polymers. Based on initial food grade glucose syrup tests, various solutions based on combinations of syrup components, i.e. mono-, di- and tri-saccharides, were investigated to map out materials and electrospinning conditions thatwould lead to the formation of fibre. Thiswork demonstrated that sucrose exhibits the highest propensity for fibre formation during electrospinning amongst the various types of saccharide solutions studied. The possibility of electrospinning low molecular weight saccharides into sub-micron fibres has implications for the electrospinability of supramolecular polymers and other biomaterials.

In present study, the influence of calcium content on the microstructure, mechanical properties and corrosion behavior of quaternary Mg-6Zn-0.8Mn-xCa alloys, where x = 1, 1.5, 3 or 4.5 wt.% Ca, was examined. The grain structure of this quaternary alloy system became more refined with increasing additions of Ca. In addition to α-Mg, the Ca2Mg6Zn3 phase was found to be present in Mg-6Zn-0.8Mn-1Ca and Mg-6Zn-0.8Mn-1.5Ca according to microstructural and thermal analysis (TA). In addition to the α-Mg and Ca2Mg6Zn3 phases, the Mg2Ca phase was found to be present in the Mg-6Zn-0.8Mn-3Ca and Mg-6Zn-0.8Mn-4.5Ca alloys. Alloys with 1 or 1.5 wt.% Ca led to increases in the tensile strength of Mg-6Zn-0.8Mn, although further Ca additions had a deleterious effect. The TA of Mg-6Zn-0.8Mn-xCa during its solidification indicates that the fraction of liquid phase increases with increasing Ca content at the dendrite coherency point, leading to an increase in secondary phases and increased corrosion rate of Mg-6Zn-0.8Mn-xCa alloys.