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Aqueous microgels are distinct entities of soft matter with mechanical signatures that can be different from their macroscopic counterparts due to confinement effects in the preparation, inherently made to consist of more than one domain (Janus particles) or further processing by coating and change in the extent of crosslinking of the core. Motivated by the importance of the mechanical properties of such microgels from a fundamental point, but also related to numerous applications, we provide a perspective on the experimental strategies currently available and emerging tools being explored. Albeit all techniques in principle exploit enforcing stress and observing strain, the realization differs from directly, as, e.g., by atomic force microscope, to less evident in a fluid field combined with imaging by a high-speed camera in high-throughput strategies. Moreover, the accompanying analysis strategies also reflect such differences, and the level of detail that would be preferred for a comprehensive understanding of the microgel mechanical properties are not always implemented. Overall, the perspective is that current technologies have the capacity to provide detailed, nanoscopic mechanical characterization of microgels over an extended size range, to the high-throughput approaches providing distributions over the mechanical signatures, a feature not readily accessible by atomic force microscopy and micropipette aspiration.

Rotational culture promotes primary human osteoblasts (hOBs) to form three‐dimensional (3D) multicellular spheroids with bone tissue‐like structure without any scaffolding material. Cell‐based bone models enable us to investigate the effect of different agents on the mechanical strength of bone. Given that low dietary intake of both vitamin D and K is negatively associated with fracture risk, we aimed to assess the effect of these vitamins in this system. Osteospheres of hOBs were generated with menaquinone‐4 (MK‐4; 10μM) and 25‐hydroxyvitamin D3 [25(OH)D3; 0.01μM], alone and in combination, or without vitamins. The mechanical properties were tested by nanoindentation using a flat‐punch compression method, and the mineralized extracellular bone matrix was characterized by microscopy. The in vitro response of hOBs to MK‐4 and 25(OH)D3 was further evaluated in two‐dimensional (2D) cultures and in the 3D bone constructs applying gene expression analysis and multiplex immunoassays. Mechanical testing revealed that 25(OH)D3 induced a stiffer and MK‐4 a softer or more flexible osteosphere compared with control. Combined vitamin conditions induced the same flexibility as MK‐4 alone. Enhanced levels of periostin (p < 0.001) and altered distribution of collagen type I (COL‐1) were found in osteospheres supplemented with MK‐4. In contrast, 25(OH)D3 reduced COL‐1, both at the mRNA and protein levels, increased alkaline phosphatase, and stimulated mineral deposition in the osteospheres. With the two vitamins in combination, enhanced gene expression of periostin and COL‐1 was seen, as well as extended osteoid formation into the central region and increased mineral deposition all over the area. Moreover, we observed enhanced levels of osteocalcin in 2D and osteopontin in 3D cultures exposed to 25(OH)D3 alone and combined with MK‐4. In conclusion, the two vitamins seem to affect bone mechanical properties differently: vitamin D enhancing stiffness and K2 conveying flexibility to bone. These effects may translate to increased fracture resistance in vivo. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Collapse of the soft palate in the upper airway contributes to obstructive sleeping apnea (OSA). In this study, we investigate the influence of the adhesion from the tongue on the soft palate global response. This is achieved using a cohesive zone finite element approach. A traction-separation law is determined to describe the adhesion effect from the surface tension of the lining liquid between the soft palate and the tongue. According to pull-off experimental tests of human lining liquid from the oral surface of the soft palate, the corresponding cohesive properties, including the critical normal traction stress and the failure separation displacement, are obtained. The 3D patient-specific soft palate geometry is accounted for, based on one specific patient’s computed tomography (CT) images. The calculation results show that influence of the adhesion from the tongue surface on the global response of the soft palate depends on the length ratio between the cohesive length and the soft palate length. When the length of the cohesive zone is smaller than half of the soft palate length, the adhesion’s influence is negligible. When the adhesion length is larger than 70 percent of soft palate length, the adhesion force contributes to preventing the soft palate from collapsing towards to the pharynx wall, i.e. the closing pressure is more negative than in the no adhesion case. These results may provide useful information to the clinical treatment of OSA patients.

A Hill model-based phenomenological method for muscle activation was used to investigate defectiveness of the palatal muscle tone during sleep for obstructive sleep apnea (OSA) patients. Based on the stretch–stress characteristic of muscle activation when the eccentric contraction is considered, a specifically defined phenomenological strain-energy function was used, as well as the Holzapfel-type strain-energy function for the passive part. A continuum mechanical framework, including the stress tensor and elasticity tensor, was obtained, based on the defined strain-energy function. The model parameters were obtained by fitting the constitutive model to experimental test data. Three-dimensional patient-specific geometry was modeled, accounting for the muscle tissue layer and based on the quantitative histology study of the soft palate. Anatomically representative boundary conditions for the finite element calculation were also considered. Palatal muscle activation level (electromyographic data) versus the negative pressure was defined in the simulations, and the patients’ activation level was set to be lower than for the healthy people. The simulation results showed that reduced in activation level for the patients causes a less negative closing pressure, and this makes the soft palate more prone to collapse. In addition, if we account for the passive–active transfer displayed as the muscle contraction corresponding to the neurogenic reflex in the soft palate, the collapse is prevented. This numerical representation of the reduced activation for the OSA patients may provide increased understanding of OSA physiology.

Objective To evaluate the biomechanical properties of the soft palate and velopharynx in patients with obstructive sleep apnea (OSA) and nasal obstruction. Study design Prospective experimental study. Materials and methods Two finite element (FE) models of the soft palate were created in six patients undergoing nasal surgery, one homogeneous model based on CT images, and one layered model based on soft tissue composition. The influence of anatomy on displacement caused by a gravitational load and closing pressure were evaluated in both models. The strains in the transverse and longitudinal direction were obtained for each patient. Results The individual anatomy influences both its structural stiffness and its gravitational displacement. The soft palate width was the sole anatomical parameter correlated to the critical closing pressure, but the maximal displacement due to gravity may have a relationship to closing pressure of possibly an exponential order. The airway occlusion occurred mainly at the lateral attachments of the soft palate. The total transverse strain showed a strong correlation with maximal closing pressure. There was no relationship between the critical closing pressure and the preoperative AHI levels, or the change in AHI after surgery. Conclusion Hyperelastic FE models both in the homogeneous and layered model represent a novel method of evaluating soft tissue biomechanics of the upper airway. The obstruction occurs mainly at the level of the lateral attachments to the pharyngeal wall, and the width of the soft palate is an indicator of the degree of critical closing pressure. A less negative closing pressure corresponds to small total transverse strain. The effect of nasal surgery on OSA is most likely not explained by change in soft palate biomechanics. Level of Evidence NA.

Obstructive sleep apnea (OSA) affects a large percentage of the population and is increasingly recognized as a major global health problem. One surgical procedure for OSA is to implant polyethylene (PET) material into the soft palate, but its efficacy remains to be discussed. In this study, we provide input to this topic based on numerical simulations. Three 3 dimensional (3D) soft palate finite element models including mouth-close and mouth-open cases were created based on three patient-specific computed tomography (CT) images. A simplified material modeling approach with the Neo-Hookean material model was applied, and nonlinear geometry was accounted for. Young’s modulus for the implant material was obtained from uniaxial tests, and the PET implant pillars were inserted to the 3D soft palate model. With the finite element model, we designed different surgical schemes and investigated their efficacy with respect to avoiding the soft palate collapse. Several pillar schemes were tested, including different placement directions, different placement positions, different settings for the radius and the array parameters of the implant pillars, and different Young’s moduli for the pillars. Based on our simulation results, the longitudinal-direction implant surgery improved the stiffness of the soft palate to a small degree, and implanting in the transverse direction was evaluated to be a good choice for improving the existing surgical scheme. In addition, the Young’s modulus of the polyethylene material implants has an influence on the reinforcement efficacy of the soft palate.