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Hygro-thermal ageing of composite materials introduces a modification in the material properties of its constituents and the development of stresses that can lead to severe local damage like fracture of the reinforcing fibers and de-bonding of the latter from the matrix. The study of the complex stress field generated by this induced damage is helpful in designing more resistant materials. Modelling strain-stress filed in the vicinity of these discontinuities has led to the development of different analytical models like for instance shear lag models based on simplification assumptions. Recently the development of embedded optical sensors allowed to shed light on the assumptions made, since they can be used, at the same time, as reinforcement and sensors and thus being capable to give information on the strain distributions during the evolution of the damage. In this work a single fiber composite, whose reinforcement is an optical sensor, is used in order to investigate the complex strain field generated by the fiber fracture caused by the matrix swelling during water uptake.

Humanitarian actors involved in physical rehabilitation, such as the International Committee of the Red Cross (ICRC), usually provide their beneficiaries with lower-limb prostheses comprising Solid Ankle Cushion Heel (SACH) feet as these are considered appropriate (price, durability, low profile to fit a majority of patients, appearance) and reliable for all ambulation levels. However, individuals in low-resource settings having higher ambulation abilities would greatly benefit from dynamic prosthetic feet with improved biomechanics and energy storage and release. Some attempts tried to address this increasing need (e.g. Niagara Foot) but most products proposed by large manufacturers often remain unaffordable and unsuitable to the context of low-resource settings. The design requirements and a price target were defined in partnership with the ICRC according to their initial assessment and used as a starting point for the development process and related technological choices. Numerical simulation and modeling were used to work on the design and to determine the required materials properties (mechanical, chemical, wear), and a cost modeling tool was used to select suitable materials and relevant processing routes (price vs. performance). A prosthetic foot comprising an internal keel made of composite materials, a filling foam, and a cosmetic shell with a foot shape was developed. Manufacturing processes meeting the cost criteria were identified and prototype feet were produced accordingly. These were successfully tested using a compression testing system before gait analyses were performed in the laboratory with non-amputees wearing testing boots. After validation in laboratory conditions, the prototype foot was tested in the field (Vietnam) with 11 trans-tibial unilateral amputees, who showed an increased mobility compared with the SACH foot. The collaboration of different research fields led to the development of a prosthetic foot which met the technical requirements determined by the ICRC's specific needs in its field of operation. The materials and selected production processes led to a manufacturing cost of less than 100 USD per part., Competing Interests: The authors have declared that no competing interests exist.

Long term durability of osseointegrated implants depends on bone adaptation to stress and strain occurring in proximity of the prosthesis. Mechanical overloading, as well as disuse, may reduce the stability of implants by provoking bone resorption. However, an appropriate mechanical environment can improve integration. Several studies have focused on the definition of numerical methods to predict bone peri-implant adaptation to the mechanical environment. Existing adaptation models differ notably in the type of mechanical variable adopted as stimulus but also in the bounds and shape of the adaptation rate equation. However, a general comparison of the different approaches on a common benchmark case is still missing and general guidelines to determine physically sound parameters still need to be developed. This current work addresses these themes in two steps. Firstly, the histograms of effective stress, strain and strain energy density are compared for rat tibiae in physiological (homeostatic) conditions. According to the Mechanostat, the ideal stimulus should present a clearly defined, position and tissue invariant lazy zone in homeostatic conditions. Our results highlight that only the octahedral shear strain presents this characteristic and can thus be considered the optimal choice for implementation of a continuum level bone adaptation model. Secondly, critical modeling parameters such as lazy zone bounds, type of rate equation and bone overloading response are classified depending on their influence on the numerical predictions of bone adaptation. Guidelines are proposed to establish the dominant model parameters based on experimental and simulated data., (Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.)

Objectives: (i) To assess the effects of mechanical overloading on implant integration in rat tibiae, and (ii) to numerically predict peri-implant bone adaptation., Materials and Methods: Transcutaneous titanium implants were simultaneously placed into both tibiae of rats (n = 40). After 2 weeks of integration, the implants of the right tibiae were stimulated daily for 4 weeks with loads up to 5N (corresponding to peak equivalent strains of 3300 ± 500 με). The effects of stimulation were assessed by ex vivo mechanical tests and quantification of bone mineral density (BMD) in selected regions of interests (ROIs). Specimen-specific finite element models were generated and processed through an iterative algorithm to mimic bone adaptation., Results: Bilateral implantation provoked an unstable integration that worsened when mild (2-4N) external loads were applied. In contrast, a stimulation at 5N tended to "counterbalance" the harmful effects of daily activity and, if applied to well-integrated specimens, significantly augmented the implants' resistance to failure (force: +73% P < 0.01, displacement: +50% P < 0.01 and energy: +153% P < 0.01). Specimen-specific numerical predictions were in close agreement with the experimental findings. Both local and overall BMD variations, as well as the implants' lateral stability, were predicted with small errors (0.14 gHA/cm 3 and 0.64%, respectively)., Conclusions: The rats' daily activity detrimentally affects implant integration. Conversely, external stimulations of large magnitudes counterbalance this effect and definitively improve integration. These changes can be predicted using the proposed numerical approach., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Implanted rat bones play a key role in studies involving fracture healing, bone diseases or drugs delivery among other themes. In most of these studies the implants integration also depends on the animal daily activity and musculoskeletal loads, which affect the implants mechanical environment. However, the tissue adaption to the physiological loads is often filtered through control groups or not inspected. This work aims to investigate experimentally and numerically the effects of the daily activity on the integration of implants inserted in the rat tibia, and to establish a physiological loading condition to analyse the peri-implant bone stresses during gait. Two titanium implants, single and double cortex crossing, are inserted in the rat tibia. The animals are caged under standard conditions and divided in three groups undergoing progressive integration periods. The results highlight a time-dependent increase of bone samples with significant cortical bone loss. The phenomenon is analysed through specimen-specific Finite Element models involving purpose-built musculoskeletal loads. Different boundary conditions replicating the post-surgery bone-implant interaction are adopted. The effects of the gait loads on the implants integration are quantified and agree with the results of the experiments. The observed cortical bone loss can be considered as a transient state of integration due to bone disuse atrophy, initially triggered by a loss of bone-implant adhesion and subsequently by a cyclic opening of the interface., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Biomaterials are constructed from limited sets of building blocks but exhibit extraordinary and versatile properties, because hierarchical structure formation lets them employ identical supramolecular motifs for different purposes. Here we exert a similar degree of structural control in synthetic supramolecular elastomers and thus tailor them for a broad range of thermomechanical properties. We show that oligopeptide-terminated polymers selectively self-assemble into small aggregates or nanofibrils, depending on the length of the oligopeptides. This process is self-sorting if differently long oligopeptides are combined so that different nanostructures coexist in bulk mixtures. Blends of polymers with oligopeptides matching in length furnish reinforced elastomers that exhibit shear moduli one order of magnitude higher than the parent polymers. By contrast, novel interpenetrating supramolecular networks that display excellent vibration damping properties are obtained from blends comprising non-matching oligopeptides or unmodified polymers. Hence, blends of oligopeptide-modified polymers constitute a toolbox for tailored elastomers with versatile properties.

The authors propose a protocol to derive finite element (FE) models from micro computer tomography scans of implanted rat bone. A semi-automatic procedure allows segmenting the images using specimen-specific bone mineral density (BMD) thresholds. An open-source FE model generator processes the segmented images to a quality tetrahedral mesh. The material properties assigned to each element are integrated from the BMD field. Piecewise, threshold-dependent density-elasticity relationships are implemented to limit the effects of metal artefacts. A detailed sensitivity study highlights the coherence of the generated models and quantifies the influence of the modelling parameters on the results. Two applications of the protocol are proposed. The stiffness of bare and implanted rat tibiae specimens is predicted by simulating three-point bending and inter-implant displacement, respectively. Results are compared with experimental tests. The mean value and the variability between the specimens are well captured in both tests.

Purpose: To assess the effect of external mechanical microstimuli of controlled magnitude on the microarchitecture of the peri-implant bone beds in rat tibiae., Materials and Methods: Tibiae of forty rats were fitted with two transcutaneous titanium cylinders. After healing, the implants were loaded to 1 to 3 N, five days/week for four weeks. These force levels translated into intraosseous strains of 700 ± 200 με, 1400 ± 400 με, and 2100 ± 600 με. After sacrifice, the implants' pullout strength was assessed. Second, the bone's microarchitecture was analyzed by microcomputed tomography (μCT) in three discrete regions of interest (ROIs). Third, the effect of loading on bone material properties was determined by nanoindentation., Results: The trabecular BV/TV significantly increased in an ROI of 0.98 mm away from the test implant in the 1 N versus the 3 N group with an opposite trend for cortical thickness. Pull-out strength significantly increased in the 2 N relatively to the nonstimulated group. Higher values of E-modulus and hardness were observed in the trabecular bone of the 2 N group., Conclusion: The in vivo mechanical loading of implants induces load-dependent modifications in bone microarchitecture and bone material properties in rat tibiae. In pull-out strength measurements, implant osseointegration was maximized at 2 N (1400 ± 400 με).

Objective: To miniaturize the "loaded implant" model to permit its application to small rodents. In this model, two titanium implants are placed 8 mm apart with their heads protruding from the skin and are forced together by a dedicated actuator. To assess the effect of (i) the post-implantation healing period and the duration of stimulation and (ii) the intratissular strain level on the microtomographical bone parameters BV/TV, Tb.N., Tb.Th. and BIC., Materials and Methods: Implants, 1 × 8 mm, were machined, inserted into the tibiae of rats and activated. A total of 123 animals were used. In series 1, the implants were left to heal for 2/4 weeks and then loaded to generate intratissular strains of 1125 ± 5% με for 4/8 weeks. Series 2 had their implants loaded to 750, 1500 and 2250 ± 5% με, respectively., Results: Bone to implant contact increased upon loading. In series 1, no difference was observed regarding the duration of healing or the stimulation period. In series 2, at 750 με, the bone parameters did not differ from baseline. At 1500 με, all four parameters increased. At 2250 με, three of four parameters decreased relative to 1500 με., Conclusions: (i) The loaded implant model can be miniaturized to the millimeter range; (ii) in the present model, implant activation beyond 4 weeks did not affect the bone parameters; (iii) mechanical stimulation increased bone to implant contact by up to 20%; (iv) the results obtained are consistent with the concept of an anabolic effect from 750 to 1500 με and deleterious effects at strains in the 2250 με range; and (v) strains at 2250 με did not lead to implant dis-integration., (© 2011 John Wiley & Sons A/S.)

Hydrogels are promising materials for bioengineering applications, and are good model materials for the study of hydrated biological tissues. As these materials often have a structural function, the measurement of their mechanical properties is of fundamental importance. In the present study gelatin gels reinforced with ceramic microspheres are produced and their poroviscoelastic response in spherical indentation is studied. The constitutive responses of unreinforced gels are determined using inverse finite element modeling in combination with analytical estimates of material parameters. The behavior of composite gels is assessed by both analytical and numerical homogenization. The results of the identification of the constitutive parameters of unreinforced gels show that it is possible to obtain representative poroviscoelastic parameters by spherical indentation without the need for additional mechanical tests. The agreement between experimental results on composite gelatin and the predictions from homogenization modeling show that the adopted modeling tools are capable of providing estimates of the poroviscoelastic response of particle-reinforced hydrogels., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Harmonic tension-compression tests at 0.1, 0.5 and 1 Hz on hydrated bovine periodontal ligament (PDL) were numerically simulated. The process was modeled by finite elements (FE) within the framework of poromechanics, with the objective of isolating the contributions of the solid- and fluid phases. The solid matrix was modeled as a porous hyperelastic material (hyperfoam) through which the incompressible fluid filling the pores flowed in accordance with the Darcy's law. The hydro-mechanical coupling between the porous solid matrix and the fluid phase circulating through it provided an apparent time-dependent response to the PDL, whose rate of deformation depended on the permeability of the porous solid with respect to the interstitial fluid. Since the PDL was subjected to significant deformations, finite strains were taken into account and an exponential dependence of PDL permeability on void ratio - and therefore on the deformation state - was assumed. PDL constitutive parameters were identified by fitting the simulated response to the experimental data for the tests at 1 Hz. The values thus obtained were then used to simulate the tests at 0.1 and 0.5 Hz. The results of the present simulation demonstrate that a porohyperelastic model with variable permeability is able to describe the two main aspects of the PDL's response: (1) the dependency on strain-rate-the saturated material can develop volumetric strains by only exchanging fluid and (2) the asymmetry between tension and compression, which is due to the effect of both the permeability and the elastic properties on deformation., (Copyright © 2010 Elsevier Ltd. All rights reserved.)