A Method of Calibration for the Distortion of LiDAR Integrating IMU and Odometer.

To improve the motion distortion caused by LiDAR data at low and medium frame rates when moving, this paper proposes an improved algorithm for scanning matching of estimated velocity that combines an IMU and odometer. First, the information of the IMU and the odometer is fused, and the pose of the LiDAR is obtained using the linear interpolation method. The ICP method is used to scan and match the LiDAR data. The data fused by the IMU and the odometer provide the optimal initial value for the ICP. The estimated speed of the LiDAR is introduced as the termination condition of the ICP method iteration to realize the compensation of the LiDAR data. The experimental comparative analysis shows that the algorithm is better than the ICP algorithm and the VICP algorithm in matching accuracy.

[Study on the mechanical properties of sutures in the process of suturing].

Suture broken, knot slipping and tissue tearing are the main reasons of wound closure failure in clinical operation. Based on this, we simulated the suturing and healing operation by using a biological materials testing machine and investigated the tensile properties before and after knotting, relaxation property and friction property of three common sutures: silk, polyglactin 910 and polypropylene. Results show that the tensile property decreased after knotting. The tensile strength of polyglactin 910 and elongation of polypropylene were the largest. During the relaxation process, the sutures relaxed the most in the first 2 hours. The relaxation from less to more was: polyglactin 910, silk and polypropylene. Coating or monofilament could obviously reduce the surface roughness of sutures, and thus reduce the friction force of the suture-suture interface. The friction force of the suture-suture interface increased with the increasing load but did no change with the increasing velocity. The results can provide an important theoretical basis for the optimizations of suture design and knotting operation.

New model to explain tooth wear with implications for microwear formation and diet reconstruction.

Paleoanthropologists and vertebrate paleontologists have for decades debated the etiology of tooth wear and its implications for understanding the diets of human ancestors and other extinct mammals. The debate has recently taken a twist, calling into question the efficacy of dental microwear to reveal diet. Some argue that endogenous abrasives in plants (opal phytoliths) are too soft to abrade enamel, and that tooth wear is caused principally by exogenous quartz grit on food. If so, variation in microwear among fossil species may relate more to habitat than diet. This has important implications for paleobiologists because microwear is a common proxy for diets of fossil species. Here we reexamine the notion that particles softer than enamel (e.g., silica phytoliths) do not wear teeth. We scored human enamel using a microfabrication instrument fitted with soft particles (aluminum and brass spheres) and an atomic force microscope (AFM) fitted with silica particles under fixed normal loads, sliding speeds, and spans. Resulting damage was measured by AFM, and morphology and composition of debris were determined by scanning electron microscopy with energy-dispersive X-ray spectroscopy. Enamel chips removed from the surface demonstrate that softer particles produce wear under conditions mimicking chewing. Previous models posited that such particles rub enamel and create ridges alongside indentations without tissue removal. We propose that although these models hold for deformable metal surfaces, enamel works differently. Hydroxyapatite crystallites are "glued" together by proteins, and tissue removal requires only that contact pressure be sufficient to break the bonds holding enamel together.

[Security research of laparoscopic graspers during tissue clamping operation].

The large force applied by laparoscopic grasper during clamping operation can cause tissue damage and induce various complications. In this research, the security of graspers with different radii of curvature and teeth were evaluated by using experimental investigation, finite element simulation and tissue damage assessment method based on in vivo compression tests with rabbit large intestines models. Results showed that the most serious tissue damages appeared in areas that were in contact with the jaw edges, which were the regions of stress concentration. The increase in radii of curvature of the edges or teeth could alleviate the tissue damages. The results could provide basic data for choosing and designing noninvasive graspers.

Technical note: An in vitro study of dental microwear formation using the BITE Master II chewing machine.

Dental microwear has been used for decades to reconstruct the diets of fossil hominins and bioarchaeological populations. The basic theory has been that hard-brittle foods (e.g., nuts, bone) require crushing and leave pits as they are pressed between opposing cheek-tooth surfaces, whereas soft-tough foods (e.g., grass blades, meat) require shearing and leave scratches as they are dragged along opposing surfaces that slide past one another. However, recent studies have called into question the efficacy of microwear as an indicator of diet. One issue has been the limited number of in vitro studies providing empirical evidence for associations between microwear pattern and chewing behavior. We here describe a new study using a chewing simulator, the BITE Master II, to examine the effects of angle of approach between opposing teeth and food consistency on microwear surface texture. Results indicate that opposing teeth that approach one another: 1) perpendicular to the occlusal plane (crushing) result in pits; 2) parallel to the occlusal plane (shearing) result in striations in the direction of movement; and 3) oblique to the occlusal plane (45°) result in both striations and pits. Results further suggest that different food types and abrasive loads affect the propensity to accumulate microwear features independent of feature shapes.

Temperature-Responsive, Femtosecond Laser-Ablated Ceramic Surfaces with Switchable Wettability for On-Demand Droplet Transfer.

Reversible wettability transition has drawn substantial interest because of its importance for widespread applications, but facile realization of such transition on ceramic surfaces, which is promising for achieving on-demand droplet manipulation under harsh conditions, remains rare. Herein, superhydrophobic zirconia ceramic surfaces that can reversibly and repeatedly transit between superhydrophobicity and superhydrophilicity after alternate heating treatments have been fabricated using a femtosecond laser. The underlying mechanisms of the complex wettability transitions on the laser-ablated zirconia surfaces are elucidated. Hydrophilic polished zirconia surfaces immediately become superhydrophilic after laser ablation, which is mainly attributed to the amplification effect of the laser-induced micro/nanostructures and has no obvious relationship with oxygen vacancies. The obtained superhydrophilic surfaces are transformed into superhydrophobic surfaces because of rapid adsorption of airborne organic compounds driven mainly by physical interaction under heating conditions. With the alternate removal and re-adsorption of organic compounds, reversible and repeatable wettability transition between superhydrophobicity and superhydrophilicity happens on the zirconia surfaces. The laser-induced micro/nanostructures also contribute to the wettability transitions. Furthermore, utilizing the superhydrophobic zirconia surfaces with switchable wettability, on-demand transfer of strong acid droplet in air and oil droplet under strong acid solution has been achieved. This work will inspire the environmentally friendly fabrication of switchable superhydrophobic ceramic surfaces and their multifunctional applications under harsh conditions.

Heterogeneous hardening of enamel surface by occlusal loading: Effect of nanofiber orientation.

Human tooth enamel is composed of enamel rods and surrounding inter-rod enamel. As the fundamental block of enamel, hydroxyapatite (HAP) nanofibers are mostly longitudinally aligned in the rods but inclined in the inter-rod enamel. The surface hardening of enamel by occlusal loading is reportedly a result of hydroxyapatite nanofiber fragmentation and rearrangement and plays an important role in the anti-wear performance of enamel, but little is known about the effect of HAP nanofiber orientation on enamel surface hardening. In this study, the occlusal loading-induced surface hardening behaviors of enamel at different zones (rod and inter-rod) and different orientations (occlusal and axial) were investigated in vitro using impact treatment and a nanoindentation technique, aiming to reveal the effect of nanofiber orientation on enamel surface hardening. It was found that surface hardening by occlusal loading occurs in the rod and inter-rod areas, but the former shows a greater hardening degree than the latter, leading to an increase in the mechanical heterogeneity of enamel surface. Under the same loading condition, the HAP nanofibers in the inter-rod enamel are more likely to tilt into transverse nanofibers than those in the rods. Compared with longitudinal nanofibers, transverse nanofibers fragment into more transverse crystal particles, but the transverse particles impair the compactness of the hardening layer and decrease its hardening degree. In sum, inherent non-uniform nanofiber orientation endows the enamel with the ability to undergo heterogeneous surface hardening upon occlusal loading, which is critical for providing and maintaining its surface mechanical heterogeneity. These findings extend the understanding of the relationship between microstructure and mechanical properties of dental enamel and provide valuable insights into the bionic design of engineering materials.

Calcium release-mediated adsorption and lubrication of salivary proteins on resin-based dental composites.

The lack of wear resistance is always a challenge for clinical applications of resin-based dental composites (RBDCs). In this study, the role of the calcium release from RBDCs in the adsorption and lubrication of salivary proteins was investigated, aiming to provide useful insights concerning the development of high-performance RBDCs. Three experimental RBDCs with distinct calcium-releasing capabilities were prepared using calcium phosphate particles as inorganic fillers. Salivary protein adsorption and film-forming on RBDC surfaces were characterized by atomic force microscopy, while the mechanical properties and lubricating effect of salivary pellicle were examined using nano-indentation/scratch techniques. Results showed that calcium release from RBDCs plays a crucial role in mediating the electrostatic interaction between salivary proteins and composite surface, thereby promoting the formation of salivary pellicle with a multi-layer structure. The mechanical properties and lubricating effect of the pellicle are positively related to the level of calcium release. In sum, for RBDCs with robust calcium release, saliva provides effective lubrication to resist composite wear. Incorporating calcium compounds is a promising way to improve the wear resistance of RBDCs in the oral cavity.

Modeling the initial-volume dependent approximate compressibility of porcine liver tissues using a novel volumetric strain energy model.

Experimental observations in the open literature indicate that soft tissues are slightly compressible, and this characteristic affects not only their overall elastic response but also their damage evolution and failure mechanism. In this study, we find that the compressibility of liver tissues is also closely related to the initial specimen volume according to the confined compression tests: the samples with smaller initial volume exhibit more compressible behavior compared to the larger ones. To include this initial-volume dependent effect, we developed a novel volumetric strain energy model with two variables, i.e., the bulk modulus and the compressibility factor. A detailed scheme was proposed as well to identify these two parameters, and the relationship between the bulk modulus and the initial volume was clarified. Findings from this study will help to deepen the understanding of the biomechanical properties of soft tissues. STATEMENT OF SIGNIFICANCE: Liver is a highly vascular organ and traditionally assumed to be an incompressible medium. However, through the confined compression tests, we found that the samples with smaller initial volumes exhibit more compressible behavior. Hence, we developed a novel strain energy density model to characterize the initial-volume dependent hyperelastic response, and found that the bulk modulus of liver tissues is positively related to the initial volume. Our results suggest that the compressibility of liver tissues should be considered in the future study of liver biomechanics.

Patient-specific finite element analysis of frictional behavior in different esophageal regions during endoscopy.

PURPOSE: Endoscopy is a common and effective method to treat digestive system diseases. Not only can it detect the physiological state of the digestive tract, but also can conduct clinical operations. As a result, it's of great significance to make clear the relationship between the clinical operation and the complications. METHODS: Considering the difficulty in measuring the contact force and determining the stress distribution in real time during endoscopy, a specific-patient finite element model for the frictional behavior at the endoscope-esophagus interface was built in current study. By collecting the CT data of the patient, a 3D esophagus model was built and divided into three characteristic regions (narrow region, thoracic region and abdominal region) according to the physiological structure. RESULTS: Results showed that the radius of the narrowest position was the dominant factor for the maximum von Mises stress when the endoscope passed through the narrow region. For abdominal region and thoracic region, with the increasing coefficient of friction (COF) and amplitude, the total force duo to frictional force (CFSM), frictional dissipation (FD), strain energy (SE) and maximum von Mises stress (Max) all increased correspondingly. Meanwhile, the region of stress concentration gradually approached the initial contact stage. CONCLUSIONS: The results can provide theoretical basis and technical support for clinical application and offer some suggestions for medical workers during endoscopy as well.

Wear mechanism of human tooth enamel: The role of interfacial protein bonding between HA crystals.

Human tooth enamel, the most mineralized tissue in body, contains less than 2 wt% protein. Consequently, the importance of the protein to enamel mechanical response has always been overlooked. In this study, the role of minor protein in providing enamel microstructure and mechanical performance, especially tribological properties, were studied using deproteinization treatment and nano-indentation/scratch technique. Via the change from the original to the deproteinated conditions, a nanostructure degeneration from the assembly of hydroxyapatite (HA) crystals into nano-fibers to crystal aggregation has been found between the high-wear-resistance and low-wear-resistance on the enamel surface. Correspondingly, an energy dissipation to cause a unit volume of wear on enamel surface decreases by 50%, and wear volume increases by 80%. With the presence of protein, the occurrence of enamel wear requires to break the interfacial protein bonding between the HA crystals in nano-fibers and the break dissipates considerable energy, which benefits the enamel to resist wear. Thus, the protein in enamel, although of a very low content, is essential to resisting wear by mediating the assembly of rigid HA crystals via interfacial protein bonding. Replicating functions of the protein component will be critical to the successful development of bio-inspired materials that are designed for wear-resistance.

Surface Hardening Behavior of Enamel by Masticatory Loading: Occurrence Mechanism and Antiwear Effect.

Previous studies have suggested that surface hardening occurs in human tooth enamel under certain loading conditions. However, the occurrence mechanism and significance remain unclear. In this study, the surface hardening behavior of enamel under masticatory loading was studied in vitro using impact treatment and the nanoindentation/scratch technique to identify the mechanism and antiwear effect. The fundamental block of enamel is made of hydroxyapatite (HAP) nanofibers, which consist of fine nanoparticles held together by protein. These fibers respond to masticatory loading in two ways: bending deflection at low loads and fragmentation at high loads. When the contact pressure exceeds the bonding strength between the nanoparticles, the HAP fibers split into fine nanoparticles and then form a surface layer consisting of tightly packed nanoparticles. This results in surface hardening dominated by an increased hardness and elastic modulus. The maximum degree and depth of surface hardening were determined as approximately 60% and 100 nm, respectively. With the occurrence of surface hardening, the wear resistance of the enamel is enhanced, which is manifested by a reduced friction coefficient and wear volume. In summary, the surface hardening of enamel induced by masticatory loading is a result of HAP nanoparticle rearrangement as a response of the enamel hierarchical structure to high chewing loads. It is adaptive overload protection derived from the enamel hierarchical structure and plays a critical role in resisting excessive wear induced by high chewing loads.

Friction-induced nanofabrication on monocrystalline silicon.

Fabrication of nanostructures has become a major concern as the scaling of device dimensions continues. In this paper, a friction-induced nanofabrication method is proposed to fabricate protrusive nanostructures on silicon. Without applying any voltage, the nanofabrication is completed by sliding an AFM diamond tip on a sample surface under a given normal load. Nanostructured patterns, such as linear nanostructures, nanodots or nanowords, can be fabricated on the target surface. The height of these nanostructures increases rapidly at first and then levels off with the increasing normal load or number of scratching cycles. TEM analyses suggest that the friction-induced hillock is composed of silicon oxide, amorphous silicon and deformed silicon structures. Compared to the tribochemical reaction, the amorphization and crystal defects induced by the mechanical interaction may have played a dominating role in the formation of the hillocks. Similar to other proximal probe methods, the proposed method enables fabrication at specified locations and facilitates measuring the dimensions of nanostructures with high precision. It is highlighted that the fabrication can also be realized on electrical insulators or oxide surfaces, such as quartz and glass. Therefore, the friction-induced method points out a new route in fabricating nanostructures on demand.

Influence of clamping parameters on the trauma of rabbit small intestine tissue.

BACKGROUND: During clamping operation for minimally invasive intestinal surgery, patients often suffer from small intestine trauma. This phenomenon will lead to various complications, increase recovery time and cause pain for patients. METHODS: In this paper, preliminary simulations of small intestine clamping operations in the minimally invasive surgery were made by conducting compression tests under different clamping stresses, durations and loading rates. A pathological grading system was designed after microscope observation to quantitatively evaluate the trauma of small intestine tissue. FINDINGS: Results showed that different traumas: inflammatory cell infiltration, hyperemia, hemorrhage and rupture between serosa and muscularis, as well as villi destruction could be observed on the clamping sites of the small intestine tissue. When the clamping parameters (clamping stress, duration and loading rate) increased, the degree of the tissue trauma increased. There existed safe thresholds for clamping operations, at which severe trauma of small intestine tissues could be avoided in the clamping process. INTERPRETATION: As the clamping parameters increased, the strain, that is the deformation of the small intestine tissue increased. The increase in the deformation would induce the aggravation of trauma degree.

Correction to: 'Comment on van Casteren et al. (2018): softer metallic spheres do abrade harder enamel'.

[This corrects the article DOI: 10.1098/rsos.181376.].

Effect of calcium ions on the adsorption and lubrication behavior of salivary proteins on human tooth enamel surface.

The aim of this study is to investigate the effect of calcium ions on the adsorption and lubrication behavior of salivary proteins on human tooth enamel. Human whole saliva was collected from healthy donors. Three testing groups were calcium ion-enhanced saliva samples with an increased ion concentration of 1 mmol/L, 5 mmol/L, and 10 mmol/L, respectively. Normal saliva was used as a control. The adsorption behavior was tested using quartz crystal microbalance with dissipation (QCM-D), while the mechanical properties and lubricating behavior of salivary pellicle were examined by nano-indentation/scratch technique. Results show that the increased calcium ion concentration in the saliva weakens the electrostatic interaction between the salivary proteins and enamel surface, but causes increases in the thickness and viscoelasticity of the salivary pellicle formed on enamel surface. Therefore, the load-bearing and anti-shear capacity of the pellicle is improved, and then the anti-wear and friction-reducing effect of the pellicle is enhanced. In sum, the addition of calcium ion in saliva can contribute to the formation of the salivary pellicle with enhanced lubrication performance and help to alleviate the excessive tooth wear of xerostomia patients.

Research of the role of microstructure in the wear mechanism of canine and bovine enamel.

The relationship between the microstructure and tribological behavior of mammalian tooth enamel has not been fully understood. In this paper, the microstructure, mechanical properties, and tribological behavior of canine (carnivore) and bovine (herbivore) enamel are studied using scanning electronic microscopy and nano-indentation/scratch technique, aiming to reveal the contribution of enamel microstructure to its mechanical and tribological properties. Canine enamel has a microstructure of hard keyhole-like rods embedded in soft inter-rod enamel, and its surface exhibits high resistance against both micro-crack initiation and crack-induced delamination during friction and wear process. Bovine enamel with the microstructure consisting of the hydroxyapatite (HAP) nano-fibers in decussation has higher surface hardness and better capabilities of resisting wear and encumbering crack propagation, as compared to canine enamel. In sum, the soft inter-rod enamel in the canine enamel contributes to high load tolerance and then protects enamel surface from brittle damage, while the staggered arrangement of HAP nano-fibers benefits hard bovine enamel in crack propagation resistance and then help resist wear and fatigue. The findings suggest that there exists a self-adaptation in enamel microstructure and tribological performance of mammals with their feeding habits, which will promote and assist the bionic design of high-performance materials.

Load distribution measurement instrument for oscillating follower cam mechanism.

Cam mechanism is widely applied in industry because it can help achieve various complex motions of the follower via the cam contour design. However, its performance is significantly affected by the wear condition. This study proposes a load distribution measurement instrument to assist the study on friction and wear regularities of oscillating follower cam mechanisms through obtaining the normal pressure (F) and friction force (Ff) distributions along the cam profile. In the instrument, F and Ff are automatically calculated via a MATLAB program based on the geometry and the measured rotary resistance torque and rotary angle of the cam. The latter two parameters are obtained through a static torque sensor and a rotary encoder built in servo motor in real time, respectively. An experimental test was conducted and the cam morphology after service was observed using scanning electron microscopy. Results show that the wear condition of the cam is significantly related to the corresponding F and Ff. Complex load parameters of oscillating follower cam mechanisms can be provided by this instrument, which is crucial in understanding the friction and wear behaviors of cams and finding the vulnerable position.

[Effects of frictional properties on traumas of rabbit skin].

Simulative experiments on skin traumas between prosthetic socket materials and residual limb skin were investigated by using the means of tribology, histology and animal experiment. Healthy adult rabbits were used as animal model and their denuded back skin was selected as experimental position to simulate residual limb skin. The effects of different normal load and reciprocal sliding frequency on rabbit skin trauma grade were investigated by using a reciprocal sliding skin friction testing apparatus to simulate prosthesis gait. The traumatic subcutaneous tissue slice was stained with hematoxylineosin and the morphology was observed under the optical microscope. The scab thickness of traumatic skin was measured under x 10 object lens. The inflammatory cells were counted in a given visual field under x 20 object lens. The statistical significance analysis of scab thickness and inflammatory cells were carried out to assess the effect of different frictional conditions on skin pathological traumas. The results showed: the greater normal load and higher reciprocal sliding frequency applied on the rabbit skin, the more serious injury to skin and more inflammatory cells in the subcutaneous tissue at the same time. The findings provide a theoretical basis of comfortized prosthesis design and gait analysis for the amputee.

[The skin frictional properties of 4 kinds of commonly used prosthetic materials].

Skin frictional properties of four kinds of prosthetic materials in common use have been researched. Experiments are carried out on residual limb and on normal tibia. Surface roughness and the hydrophobic/hydrophilic of the skin and materials are also tested. Under normal load 0.3 N and 0.7 N, the friction coefficient of silicon rubber and skin has the maximum value among all the materials due to the surface property of silicon rubber (containing oil). There is remarkable difference in friction coefficient between normal skin and amputee skin when they are in contact with silicon rubber (P<0.05). Other materials show "the higher the hydrophobia tendency of surface, the lower the friction coefficient". There are no significant differences (P>0.05) in friction coefficient between amputee skin and normal skin when they are in contact with all materials under normal load 8 N.