Different Degrees Of Stiffness Research Articles

Development of a Wearable Haptic Glove Presenting Haptic Sensation by Electrical Stimulation

Most haptic devices generate haptic sensation using mechanical actuators. However, the workload and limited workspace handicap the operator from operating freely. Electrical stimulation is an alternative approach to generate haptic sensations without using mechanical actuators. The light weight of the electrodes adhering to the body brings no limitations to free motion. Because a real haptic sensation consists of feelings from several areas, mounting the electrodes to several different body areas can make the sensations more realistic. However, simultaneously stimulating multiple electrodes may result in "noise" sensations. Moreover, the operators may feel tingling because of unstable stimulus signals when using the dry electrodes to help develop an easily mounted haptic device using electrical stimulation. In this study, we first determine the appropriate stimulation areas and stimulus signals to generate a real touch sensation on the forearm. Then, we propose a circuit design guideline for generating stable electrical stimulus signals using a voltage divider resistor. Finally, based on the aforementioned results, we develop a wearable haptic glove prototype. This haptic glove allows the user to experience the haptic sensations of touching objects with five different degrees of stiffness.

Implicit extensions of an explicit multirate Runge–Kutta scheme

We propose a new method that extends conservative explicit multirate methods to implicit explicit-multirate methods. We develop extensions of order one and two with different stability properties on the implicit side. The method is suitable for time-stepping adaptive mesh refinement PDE discretizations with different degrees of stiffness. A numerical example with an advection–diffusion problem illustrates the new method’s properties.

Avoiding tensional equilibrium in cells migrating on a matrix with cell-scale stiffness-heterogeneity

Intracellular stresses affect various cell functions, including proliferation, differentiation and movement, which are dynamically modulated in migrating cells through continuous cell-shaping and remodeling of the cytoskeletal architecture induced by spatiotemporal interactions with extracellular matrix stiffness. When cells migrate on a matrix with cell-scale stiffness-heterogeneity, which is a common situation in living tissues, what intracellular stress dynamics (ISD) emerge? In this study, to explore this issue, finite element method-based traction force microscopy was applied to cells migrating on microelastically patterned gels. Two model systems of microelastically patterned gels (stiff/soft stripe and stiff triangular patterns) were designed to characterize the effects of a spatial constraint on cell-shaping and of the presence of different types of cues to induce competing cellular taxis (usual and reverse durotaxis) on the ISD, respectively. As the main result, the prolonged fluctuation of traction stress on a whole-cell scale was markedly enhanced on single cell-size triangular stiff patterns compared with homogeneous gels. Such ISD enhancement was found to be derived from the interplay between the nomadic migration of cells to regions with different degrees of stiffness and domain shape-dependent traction force dynamics, which should be an essential factor for keeping cells far from tensional equilibrium.

Stiffness of the extracellular matrix affects apoptosis of nucleus pulposus cells by regulating the cytoskeleton and activating the TRPV2 channel protein

It is known that nucleus pulposus cells (NPs) play an important role in intervertebral disc degeneration (IVDD), and a previous study indicated that the stiffness of NP tissue changes during the degeneration process. However, the mechanism underlying the cellular response to ECM stiffness is still unclear. To analyze the effects of extracellular matrix (ECM) with different degrees of stiffness on NPs, we prepared polyacrylamide (PA) gels with different elastic moduli, and cells grown under different stiffness conditions were obtained and analyzed. The results showed that the spreading morphology of NPs changed significantly under increased ECM elastic modulus conditions and that TRPV2 and the PI3K / AKT signaling pathway were activated by stiffer ECM. At the same time, mitochondria released cytochrome c (Cyt c) and activated caspase proteins to promote the apoptosis of NPs. After TRPV2 was specifically knocked out, the activation of the PI3K / AKT signaling pathway decreased, and the release of Cyt c and NP apoptosis were reduced. These results indicate that TRPV2 is closely linked to the detection of extracellular mechanical signals, and that conversion of mechanical and biological signals plays an important role in regulating the biological behavior of cells. This study offers a new perspective on the cellular and biochemical events underlying IVDD which could result in novel treatments.

Assessing the Stiffness Perception of Acupressure Massage Beginning Learners: A Pilot Study

Visually impaired licensed therapists must have the ability to perceive stiffness through their fingertips in the school for the blind. The teachers strive to provide careful introductory education based on a quantitative assessment of new students’ basic stiffness perception. However, assessment materials to help teachers understand new students’ stiffness perception are lacking. This study aimed to develop suitable fundamental assessment materials that visually impaired licensed teachers could use to quantitatively assess the difference in the stiffness perception ability of beginning learners in the early stages of learning. They were asked to discriminate the presented materials one at a time, which consisted of thermoplastic elastomers with different degrees of stiffness. We used these materials to compare the beginning learners’ ability to perceive stiffness with that of teachers and found that teachers answered correctly at an overall significantly higher rate. Specifically, the teachers’ correct response rate (78.8%) for the stiffness perception of all presented stimuli was approximately 15% higher than the beginning learners’ correct response rate (64.2%). These results revealed areas of stiffness that are difficult for beginning learners to identify.

3D Cell Culture: Recent Development in Materials with Tunable Stiffness.

It is widely accepted that three-dimensional cell culture systems simulate physiological conditions better than traditional 2D systems. Although extracellular matrix components strongly modulate cell behavior, several studies underlined the importance of mechanosensing in the control of different cell functions such as growth, proliferation, differentiation, and migration. Human tissues are characterized by different degrees of stiffness, and various pathologies (e.g., tumor or fibrosis) cause changes in the mechanical properties through the alteration of the extracellular matrix structure. Additionally, these modifications have an impact on disease progression and on therapy response. Hence, the development of platforms whose stiffness could be modulated may improve our knowledge of cell behavior under different mechanical stress stimuli. In this review, we have analyzed the mechanical diversity of healthy and diseased tissues, and we have summarized recently developed materials with a wide range of stiffness.

Keloid disorder: Fibroblast differentiation and gene expression profile in fibrotic skin diseases.

Keloid disorder, a group of fibroproliferative skin diseases, is characterized by unremitting accumulation of the extracellular matrix (ECM) of connective tissue, primarily collagen, to develop cutaneous tumors on the predilection sites of skin. There is a strong genetic predisposition for keloid formation, and individuals of African and Asian ancestry are particularly prone. The principal cell type responsible for ECM accumulation is the myofibroblast derived from quiescent resident skin fibroblasts either through trans-differentiation or from keloid progenitor stem cells with capacity for multi-lineage differentiation and self-renewal. The biosynthetic pathways leading to ECM accumulation are activated by several cytokines, but particularly by TGF-β signalling. The mechanical properties of the cellular microenvironment also play a critical role in the cell's response to TGF-β, as demonstrated by culturing of fibroblasts derived from keloids and control skin on substrata with different degrees of stiffness. These studies also demonstrated that culturing of fibroblasts on tissue culture plastic in vitro does not reflect their biosynthetic capacity in vivo. Collectively, our current understanding of the pathogenesis of keloids suggests a complex network of interacting cellular, molecular and mechanical factors, with distinct pathways leading to myofibroblast differentiation and activation. Keloids can serve as a model system of fibrotic diseases, a group of currently intractable disorders, and deciphering of the critical pathogenetic steps leading to ECM accumulation is expected to identify targets for pharmacologic intervention, not only for keloids but also for a number of other, both genetic and acquired, fibrotic diseases.

Effects of Flow-Induced Microfluidic Chip Wall Deformation on Imaging Flow Cytometry.

Imaging flow cytometry is a powerful tool by virtue of its capability for high-throughput cell analysis. The advent of high-speed optical imaging methods on a microfluidic platform has significantly improved cell throughput and brought many degrees of freedom to instrumentation and applications over the last decade, but it also poses a predicament on microfluidic chips. Specifically, as the throughput increases, the flow speed also increases (currently reaching 10 m/s): consequently, the increased hydrodynamic pressure on the microfluidic chip deforms the wall of the microchannel and produces detrimental effects lead to defocused and blur image. Here, we present a comprehensive study of the effects of flow-induced microfluidic chip wall deformation on imaging flow cytometry. We fabricated three types of microfluidic chips with the same geometry and different degrees of stiffness made of polydimethylsiloxane (PDMS) and glass to investigate material influence on image quality. First, we found the maximum deformation of a PDMS microchannel was >60 μm at a pressure of 0.6 MPa, while no appreciable deformation was identified in a glass microchannel at the same pressure. Second, we found the deviation of lag time that indicating velocity difference of migrating microbeads due to the deformation of the microchannel was 29.3 ms in a PDMS microchannel and 14.9 ms in a glass microchannel. Third, the glass microchannel focused cells into a slightly narrower stream in the X-Y plane and a significantly narrower stream in the Z-axis direction (focusing percentages were increased 30%, 32%, and 5.7% in the glass channel at flow velocities of 0.5, 1.5, and 3 m/s, respectively), and the glass microchannel showed stabler equilibrium positions of focused cells regardless of flow velocity. Finally, we achieved the world's fastest imaging flow cytometry by combining a glass microfluidic device with an optofluidic time-stretch microscopy imaging technique at a flow velocity of 25 m/s. © 2019 International Society for Advancement of Cytometry.

Bearing capacity of composite ground with soil-cement columns under earth fills: Physical and numerical modeling

Soil-cement columns are widely used to improve soft ground, and the bearing capacity of the formed composite ground is a key design parameter. The currently employed design method was developed for composite grounds under rigid footings, whilst the bearing capacity behavior of composite grounds under earth fills with different degrees of stiffness has rarely been investigated. Hence, the present study attempts to fill this gap. In this investigation, 1-g laboratory model tests are conducted to compare the bearing capacity behavior of composite grounds under a rigid footing and under embankment fill, based on which a numerical model that can capture the strain-softening behavior of soil-cement columns is established. The calibrated numerical model is further employed to perform 144 analyses. The results indicate that the failure mode of composite grounds differs for different types of earth fills: soil failure occurs prior to column failure under soft clay and dredged slurry, whereas column failure is the primary failure mode for composite grounds under embankment fill. This difference in failure mode of composite grounds can be explained using soil arching theories. For different failure modes, different bearing capacity efficiency factors should be used in design.

Inter-layer bonding characterisation between materials with different degrees of stiffness processed by fused filament fabrication

One of the main benefits of material extrusion additive manufacturing, also known as fused filament fabrication (FFF) or 3D printing, is the flexibility in terms of printing materials. Locally reinforced components can be easily produced by selectively combining reinforced with unfilled tough thermoplastics. However, such multi-material composites usually lack sufficient weld strength in order to be able to withstand operation loads. The present study attempts to close this gap by characterising the cohesion between the strands of two materials with different stiffness, namely neat PLA and short carbon fibre reinforced PLA (CF-PLA), produced by FFF using advanced fracture mechanical techniques. The full set of engineering constants of both materials were obtained under the assumption of transverse isotropy from tensile tests in combination with digital image correlation. Double cantilever beam (DCB) and cracked round bar (CRB) tests were used to determine the critical energy release rate (GIc). Both tests were in good correlation with each other and revealed that the interlayer PLA/CF-PLA bonding was at least as tough as the interlayer CF-PLA/CF-PLA bonding.

Neutron star structure in the presence of nonminimally coupled scalar fields

We study the structure of neutron stars in scalar-tensor theories for the nonminimal coupling of the form $(1+\kappa \xi \phi^{2})\cal R$. We solve the hydrostatic equilibrium equations for two different types of scalar field potentials and three different equations of state representative of different degrees of stiffness. We obtain the mass-radius relations of the configurations and determine the allowed ranges for the term $\xi\phi^2$ at the center of the star and spatial infinity based on the measured maximum value of the mass for neutron stars and the recent constraints on the radius coming from gravitational wave observations. Thus we manage to limit the deviation of the model from general relativity. We examine the possible constraints on the parameters of the model and compare the obtained restrictions with the ones inferred from other cosmological probes that give the allowed ranges for the coupling constant only. In the case of the Higgs-like potential, we also find that the central value for the scalar field cannot be chosen arbitrarily but it depends on the vacuum expectation value of the field. Finally, we discuss the effect of the scalar field potential on the mass and the radius of the star by comparing the results obtained for the cases considered here.

Bacterial Adhesion on Soft Materials: Passive Physicochemical Interactions or Active Bacterial Mechanosensing?

The influence of mechanical stiffness of biomaterials on bacterial adhesion is only sparsely studied and the mechanism behind this influence remains unclear. Here, bacterial adhesion on polydimethylsiloxane (PDMS) samples, having four different degrees of stiffness with Young's modulus ranging from 0.06 to 4.52 MPa, is investigated. Escherichia coli and Pseudomonas aeruginosa are found to adhere in greater numbers on soft PDMS (7- and 27-fold increase, respectively) than on stiff PDMS, whereas Staphylococcus aureus adheres in similar numbers on the four tested surfaces. To determine whether the observed adhesion behavior is caused by bacteria-specific mechanisms, abiotic polystyrene (PS) beads are employed as bacteria substitutes. Carboxylate-modified PS (PS-COOH) beads exhibit the same adhesion pattern as E. coli and P. aeruginosa with four times more adhered beads on soft PDMS than on stiff PDMS. In contrast, amine-modified PS (PS-NH2 ) beads adhere in similar numbers on all tested samples, reminiscent of S. aureus adhesion. This work demonstrates for the first time that the intrinsic physicochemical properties associated with PDMS substrates of different stiffness strongly influence bacterial adhesion and challenge the previously reported theory on active bacterial mechanosensing, which provides new insights into the design of antifouling surfaces.

Crustal heating in accreting neutron stars from the nuclear energy-density functional theory

Context.X-ray observations of soft X-ray transients in quiescence suggest the existence of heat sources in the crust of accreted neutron stars. Heat is thought to be released by electroweak and nuclear processes triggered by the burying of ashes of X-ray bursts.Aims.The heating in the crust of accreting neutron stars is studied using a fully quantum approach taking consistently into account nuclear shell effects.Methods.To this end, we have followed the evolution of ashes made of56Fe employing the nuclear energy-density functional theory. Both the outer and inner crusts are described using the same functional, thus ensuring a unified and thermodynamically consistent treatment. To assess the role of accretion on the structure of the crust, we have employed the set of accurately calibrated Brussels–Montreal functionals BSk19, BSk20, and BSk21, for which the equations of state of nonaccreted neutron stars have been already calculated. These energy-density functionals were fitted to the same set of nuclear masses but were simultaneously adjusted to realistic neutron-matter equations of state with different degrees of stiffness at suprasaturation densities. For comparison, we have also considered the SLy4 functional.Results. Due to nuclear shell effects, the interior of fully accreted crust is found to be much less stratified than in previous studies. In particular, large regions of the inner crust contain clusters with the magic numberZ = 14. The heat deposited in the outer crust is tightly constrained by experimental atomic mass data. The shallow heating we obtain does not exceed 0.2 MeV per accreted nucleon and is therefore not enough to explain the cooling of some soft X-ray transients. The total heat released in the crust is very sensitive to details of the nuclear structure and is predicted to lie in the range from 1.5 MeV to 1.7 MeV per accreted nucleon.Conclusions.The evolution of an accreted matter element and therefore the location of heat sources are governed to a large extent by the existence of nuclear shell closures. Ignoring these effects in the inner crust, the total heat falls to ∼0.6 MeV per accreted nucleon.

The Soft Story Challenge to Architectural Design in Earthquake-Prone Areas

The stiffness of irregular configurations/soft storeys is the most frequent cause of structural failure in the irregular vertical part of a building when major earthquakes occur in Indonesia, leaving behind many victims. Soft storeys occur because the first floor of a building is usually more flexible than the other floors. When a strong earthquake occurs, the more flexible storey is not strong enough to withstand the force of the earthquake, and it will cause the building to break and collapse. This paper attempted to address the structural failure of the soft storey, particularly in Indonesia, with regard to its causes, and to find ways to evaluate it and to overcome it through architectural designs. Therefore, this can be taken into consideration by architects in their designing process. The research involved a literature review of topics on soft storeys from existing books and researches. Based on the study, the occurrence of soft storeys in Indonesia is due to inadequate shear column capacity, the presence of a weak storey, a significant difference in wall densities between the floors, the use of materials with different degrees of stiffness in the main structure, structural ductility and poor construction. To reduce the potency of soft storeys, several things can be done by architects in their designing processes such as avoiding direct contact between brick walls, columns and beams, increasing the shear capacity of columns by 2.5 times the normal calculation, using shear walls on the first floor, installing bracings and using seismic insulations

Many-body Forces in Magnetic Neutron Stars

Abstract In this work, we study in detail the effects of many-body forces on the equation of state and the structure of magnetic neutron stars. The stellar matter is described within a relativistic mean field formalism that takes into account many-body forces by means of a nonlinear meson field dependence on the nuclear interaction coupling constants. We assume that matter is at zero temperature, charge neutral, in beta equilibrium, and populated by the baryon octet, electrons, and muons. In order to study the effects of different degrees of stiffness in the equation of state, we explore the parameter space of the model, which reproduces nuclear matter properties at saturation, as well as massive neutron stars. Magnetic field effects are introduced both in the equation of state and in the macroscopic structure of stars by the self-consistent solution of the Einstein–Maxwell equations. In addition, the effects of poloidal magnetic fields on the global properties of stars, as well as density and magnetic field profiles, are investigated. We find that not only different macroscopic magnetic field distributions but also different parameterizations of the model for a fixed magnetic field distribution impact the gravitational mass, deformation, and internal density profiles of stars. Finally, we show that strong magnetic fields significantly affect the particle populations of stars.

Wide-range stiffness gradient PVA/HA hydrogel to investigate stem cell differentiation behavior

Although stiffness-controllable substrates have been developed to investigate the effect of stiffness on cell behavior and function, the use of separate substrates with different degrees of stiffness, substrates with a narrow range stiffness gradient, toxicity of residues, different surface composition, complex fabrication procedures/devices, and low cell adhesion are still considered as hurdles of conventional techniques. In this study, a cylindrical polyvinyl alcohol (PVA)/hyaluronic acid (HA) hydrogel with a wide-range stiffness gradient (between ∼20kPa and ∼200kPa) and cell adhesiveness was prepared by a liquid nitrogen (LN2)-contacting gradual freezing–thawing method that does not use any additives or specific devices to produce the stiffness gradient hydrogel. From an in vitro cell culture using the stiffness gradient PVA/HA hydrogel, it was observed that human bone marrow mesenchymal stem cells have favorable stiffness ranges for induction of differentiation into specific cell types (∼20kPa for nerve cell, ∼40kPa for muscle cell, ∼80kPa for chondrocyte, and ∼190kPa for osteoblast). The PVA/HA hydrogel with a wide range of stiffness spectrum can be a useful tool for basic studies related with the stem cell differentiation, cell reprogramming, cell migration, and tissue regeneration in terms of substrate stiffness. Statement of SignificanceIt is postulated that the stiffness of the extracellular matrix influences cell behavior. To prove this concept, various techniques to prepare substrates with a stiffness gradient have been developed. However, the narrow ranges of stiffness gradient and complex fabrication procedures/devices are still remained as limitations. Herein, we develop a substrate (hydrogel) with a wide-range stiffness gradient using a gradual freezing–thawing method which does not need specific devices to produce a stiffness gradient hydrogel. From cell culture experiments using the hydrogel, it is observed that human bone marrow mesenchymal stem cells have favorable stiffness ranges for induction of differentiation into specific cell types (∼20kPa for nerve, ∼40kPa for muscle, ∼80kPa for cartilage, and ∼190kPa for bone in our hydrogel system).

3D Scaffolds with Different Stiffness but the Same Microstructure for Bone Tissue Engineering.

A growing body of evidence has shown that extracellular matrix (ECM) stiffness can modulate stem cell adhesion, proliferation, migration, differentiation, and signaling. Stem cells can feel and respond sensitively to the mechanical microenvironment of the ECM. However, most studies have focused on classical two-dimensional (2D) or quasi-three-dimensional environments, which cannot represent the real situation in vivo. Furthermore, most of the current methods used to generate different mechanical properties invariably change the fundamental structural properties of the scaffolds (such as morphology, porosity, pore size, and pore interconnectivity). In this study, we have developed novel three-dimensional (3D) scaffolds with different degrees of stiffness but the same 3D microstructure that was maintained by using decellularized cancellous bone. Mixtures of collagen and hydroxyapatite [HA: Ca10(PO4)6(OH)2] with different proportions were coated on decellularized cancellous bone to vary the stiffness (local stiffness, 13.00 ± 5.55 kPa, 13.87 ± 1.51 kPa, and 37.7 ± 19.6 kPa; bulk stiffness, 6.74 ± 1.16 kPa, 8.82 ± 2.12 kPa, and 23.61 ± 8.06 kPa). Microcomputed tomography (μ-CT) assay proved that there was no statistically significant difference in the architecture of the scaffolds before or after coating. Cell viability, osteogenic differentiation, cell recruitment, and angiogenesis were determined to characterize the scaffolds and evaluate their biological responses in vitro and in vivo. The in vitro results indicate that the scaffolds developed in this study could sustain adhesion and growth of rat mesenchymal stem cells (MSCs) and promote their osteogenic differentiation. The in vivo results further demonstrated that these scaffolds could help to recruit MSCs from subcutaneous tissue, induce them to differentiate into osteoblasts, and provide the 3D environment for angiogenesis. These findings showed that the method we developed can build scaffolds with tunable mechanical properties almost without variation in 3D microstructure. These preparations not only can provide a cell-free scaffold with optimal matrix stiffness to enhance osteogenic differentiation, cell recruitment, and angiogenesis in bone tissue engineering but also have significant implications for studies on the effects of matrix stiffness on stem cell differentiation in 3D environments.

Application of approximate matrix factorization to high order linearly implicit Runge–Kutta methods

Linearly implicit Runge–Kutta methods with approximate matrix factorization can solve efficiently large systems of differential equations that have a stiff linear part, e.g. reaction–diffusion systems. However, the use of approximate factorization usually leads to loss of accuracy, which makes it attractive only for low order time integration schemes. This paper discusses the application of approximate matrix factorization with high order methods; an inexpensive correction procedure applied to each stage allows to retain the high order of the underlying linearly implicit Runge–Kutta scheme. The accuracy and stability of the methods are studied. Numerical experiments on reaction–diffusion type problems of different sizes and with different degrees of stiffness illustrate the efficiency of the proposed approach.

Neutron star structure in the presence of conformally coupled scalar fields

Neutron star models are studied in the context of scalar–tensor theories of gravity in the presence of a conformally coupled scalar field, using two different numerical equations of state (EoS) representing different degrees of stiffness. In both cases we obtain a complete solution by matching the interior numerical solution of the coupled Einstein-scalar field hydrostatic equations, with an exact metric on the surface of the star. These are then used to find the effect of the scalar field and its coupling to geometry, on the neutron star structure, particularly the maximum neutron star mass and radius. We show that in the presence of a conformally coupled scalar field, neutron stars are less dense and have smaller masses and radii than their counterparts in the minimally coupled case, and the effect increases with the magnitude of the scalar field at the center of the star.

Gait responses to modifying the spring stiffness of a dorsiflexion stopped ankle-foot orthosis in a polio survivor with plantar flexor weakness

Introduction and aim: In patients with post polio syndrome (PPS), gait is frequently hampered by excessive and/or abrupt ankle dorsiflexion, caused by weakness of the plantar flexors. This can lead to instability and fatigue due to a reduced walking efficiency [1]. To provide stability and increase walking efficiency, patients with plantar flexor weakness can be prescribed with a spring-like dorsiflexion stopped ankle-foot orthosis (DS-AFO). In patients with stroke and MS presenting spastic leg paresis, it has been shown that walking with such an AFO can optimize walking efficiency by choosing the correct ankle stiffness [2]. A similar principal might also apply to patientswith flaccid paresis. The aimof this studywas to evaluate the effect of different degrees of DS-AFO ankle stiffness on walking efficiency and gait biomechanics in patients with PPS and plantar flexor weakness. Patients/materials and methods: One male patient with PPS and mild plantar flexor weakness participated (age: 67 years, MRC score plantar flexors: 4+, gait pattern: excessive ankle range of motion combined with persistent knee flexion during stance). For this patient a custommade foot partwith calf casingwas fabricated, in which five interchangeable carbon leaf springs with a different degree of stiffness (k) could be placed (range: k1: 0.8Nm/deg to k5: 7.3Nm/deg, as measured with the BRUCE device [3]). The patient was first assessed for gait biomechanics (Vicon MX, AMTI force plates) at comfortable speed while walking with the DS-AFO (5 springs, tested in random order). Each measurement started after the patient indicated to be customized to the new spring. After each condition, satisfaction was rated with a visual analogue scale. Subsequently, walking efficiency was assessed (Cosmed) during a 6-min walk test for the most satisfying DS-AFO spring, the stiffest and themost compliant spring. Gait biomechanics andwalking efficiency were also assessed for the patients’ own DS-AFO and for walking with shoes alone. Results: The patient rated DS-AFO-k3 (2.5Nm/deg) asmost satisfying: ‘It supported, butdidnot constrain toomuch’.Walkingwith this DS-AFO resulted in the highest comfortable gait speed (10% higher compared to shoes alone) and it increasedwalking efficiency with 2.5% compared to walking with shoes alone and to walking with his ownDS-AFO (Fig. 1). However,most efficient gaitwas seen with the stiffest spring (k5 =7.3Nm/deg): +4.1% compared to walking with shoes alone. Regarding gait biomechanics, ankle range of motion (range: k1: 33◦ to k5: 19◦) and ankle power during push-off (range: k1: 2.1W/kg to k5: 1.2W/kg) reduced with increasing stiffness. Only the three stiffest springs resulted in a decreased knee flexion during terminal stance (all about −4.8◦), compared to the two most compliant springs. Discussion and conclusions: The results of this case study indicate that for this patient with PPS and plantar flexor weakness optimizing DS-AFO ankle stiffness was useful for improving gait with respect to walking efficiency. Walking with the stiffest DSAFO (k5 =7.3) resulted in the most efficient gait, and, although the improvements were small, gait efficiency and reduction of knee flexion seemed to be related. However, the most efficient DS-AFO wasnot considered themost satisfyingDS-AFO. Sinceplantar flexor weakness from themeasuredpatientwas onlymild, a high stiffness may not be optimal. This is the first result from an ongoing project; we expect that a broader range in plantar flexorweaknesswill yield more precise relations onhowDS-AFOmechanics andpatient characteristics interact towards gait performance. Ultimately, this will serve DS-AFO stiffness selection in patients with PPS.