BackgroundThe design of foot and ankle orthoses is currently limited by the methods used to fabricate the devices, particularly in terms of geometric freedom and potential to include innovative new features. Additive manufacturing (AM) technologies, where objects are constructed via a series of sub-millimetre layers of a substrate material, may present the opportunity to overcome these limitations and allow novel devices to be produced that are highly personalised for the individual, both in terms of fit and functionality.Two novel devices, a foot orthosis (FO) designed to include adjustable elements to relieve pressure at the metatarsal heads, and an ankle foot orthosis (AFO) designed to have adjustable stiffness levels in the sagittal plane, were developed and fabricated using AM. The devices were then tested on a healthy participant to determine if the intended biomechanical modes of action were achieved.ResultsThe adjustable, pressure relieving FO was found to be able to significantly reduce pressure under the targeted metatarsal heads. The AFO was shown to have distinct effects on ankle kinematics which could be varied by adjusting the stiffness level of the device.ConclusionsThe results presented here demonstrate the potential design freedom made available by AM, and suggest that it may allow novel personalised orthotic devices to be produced which are beyond the current state of the art.

Purpose -The purpose of this paper was twofold: first, to determine if rotating bending could be used as an effective way of determining the fatigue behaviour of laser-sintered nylon, and second, to examine whether the fatigue behaviour of laser-sintered PA12 showed any significant anisotropy. Design/methodology/approach -Specimens were measured to obtain dimensional accuracy, density and surface roughness levels. Then, uniaxial tensile and rotating-bending fatigue tests were performed. A purpose-built test-jig has been used to subject hourglass-shaped specimens to reversed bending at two frequencies: 50 and 30 Hz. Additionally, thermal and microstructural analyses were performed to understand the underlying mechanisms of failure. Findings -The experiments suggest PA12 specimens will fail in fatigue following the conventional fatigue mechanisms observed in previous research with ductile polymers. Although high-frequency loading caused a heat build-up in the specimen, temperatures stabilised between 20 and 30°C, suggesting that rotating-bending fatigue at frequencies of up to 50 Hz is a valid way of determining the fatigue behaviour of laser-sintered PA12 specimens. Stresses below 20 MPa led to fatigue lives above 1 million cycles. Some anisotropic behaviour was observed in the fatigue test results, with specimens made orientated with the Z axis showing the lowest fatigue lives on average, but an endurance limit of approximately 15 MPa seems to be common for all specimens regardless of their build orientation. Practical implications -The observed endurance limit of 15 MPa did not depend significantly on the orientation at which a part was builtmeaning that it may be possible to guarantee a service life for a part which does not depend on part orientation within a build. Clearly, good-quality control will also be required to ensure performance, but this has important implications for the design of laser-sintered PA12 parts for realistic service conditions. Originality/value -To our knowledge, this is the first paper to present rotating-bending fatigue data for laser-sintered PA12 parts, and the first to identify an endurance limit which is independent of part orientation.

Continuous positive airway pressure (CPAP) therapy is a clinical treatment for moderate or severe obstructive sleep apnea (OSA). Commercial CPAP mask designs normally come in standard sizes and the configuration is not commonly tailored to the patients' characteristics such as face topology, skin sensitivity, and severity of OSA syndrome; however, an optimal mask/interface selection is a key factor influencing the compliance and effectiveness of CPAP treatment. Areas covered: This review investigates the conventional CPAP mask design, its effect on OSA treatment, and the related risk factors that can lead to skin damage after long-term repeated use. Through a literature search on common databases, Scopus, PubMed, and Google Scholar, we identified reported facts on the influence of the mask interface and current trends toward customized devices. Expert commentary: There is potential for optimizing the CPAP mask fit by adapting the interface to the patients' individual characteristics. This holds particularly true for users with abnormal features or simply outside conventional industry sizing standards. Enabling technologies for undertaking this adaptation include reverse engineering, computational modeling, and additive manufacturing. There is to date no integrated system that integrates those elements into a standard solution, but several studies have shown its effectiveness for specific cohorts.

This paper reports the results of a study into the fatigue behaviour of laser sintered Nylon 12 specimens in both reversed and rotating bending. Rotating bending tests are generally the most efficient in terms of test time, but reversed bending deformation explicitly promotes delamination, and so the main aim was to identify whether or not there was significant variation in fatigue behaviour between the two loading modes. The paper presents the first reversed bending fatigue test study on selective laser sintered Nylon parts and compares the results to fatigue behaviour from rotating bending. The results showed no significant variation in fatigue behaviour between the two loading modes and also showed an isotropic response in terms of fatigue behaviour in both test configurations.

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