Study of corneal biomechanical properties in patients with childhood glaucoma

AIM:To study of corneal biomechanical properties and intraocular pressure(IOP)measured with Corvis Scheimpflug Technology(ST)in patients with childhood glaucoma(CG).METHODS:Cross-sectional study in which 89 eyes were included 56 of them with CG.Only one eye per patient was included.The following variables were obtained from the clinical history and the ophthalmological examination:age,sex,IOP,number of surgeries,and the cup/disc ratio(CDR).The following parameters were recorded using Corvis ST:corrected by biomechanics IOP(b IOP),not corrected IOP(nct IOP),central corneal thickness(CCT),maximum concavity[radius,peak distance(PD)and deformation amplitude],applanation 1 and 2(length and velocity).The mean age was 23±14.55 and 33±19.5 years old for the control group and CG group,respectively.Totally 36 were males and 53 were females.In the CG group,7 patients were controlled only with medical treatment.Sixteen had at least one previous goniotomy,19 had at least one trabeculectomy,and 11 had an Ahmed implant.RESULTS:A significant and positive intraclass correlation coefficient was found between Goldman IOP and the IOP measured by Corvis in both groups.No differences were found between the IOP measured with Corvis and Goldman using a student t-test.Regarding biomechanical parameters,there were differences in the applanation length 2(A-L2),in the applanation velocity 2(A-V2)and in the PD.By sex,only the applanation length 1(A-L1)was found to be different in control group.A positive and significant Pearson correlation was found between CDR and the A-L1.CONCLUSION:Corneal biomechanical properties have shown differences between CG and healthy subjects and also between men and women.

Effect of biometric characteristics on biomechanical properties of the cornea in cataract patient

AIM： To determine the impact of biometric characteristics on the biomechanical properties of the human cornea using the ocular response analyzer （ORA） and standard comprehensive ophthalmic examinations before and after standard phacoemulsificaUon. METHODS： This study comprised 54 eyes with cataract with significant lens opacification in stages I or II that underwent phacoemulsification （2.8 mm incision）. Corneal hysteresis （CH）, corneal resistance factor （CRF）, Goldmann-correlated intraocular pressure （IOPg）, and corneal-compensated intraocular pressure （IOPcc） were measured by ORA preoperatively and at lmo postoperatively. Biometric characteristics were derived from corneal topography [TMS-5, anterior equivalent （EQTMS） and cylindric （CYLTMS） power], corneal tomography [Casia, anterior and posterior equivalent （EQaCASC, EQpCASIA） and cylindric （CYLaCASIA, CYLpCASIA） power], keratometry [IOLMaster, anterior equivalent （EQIOL） and cylindric （CYL,oL） power] and autorefractor [anterior equivalent （EQAR）]. Results from ORA were analyzed and correlated with those from all other examinations taken at the same time point. RESULTS： Preoperatively, CH correlated with EQpCASIA and CYLpCASIA only （P=0.001, P=0.002）. Postoperatively, IOPg and IOPcc correlated with all equivalent powers （EQTMS, EQIOL, EQAR, EQaCASIA, and EQpCASIA）（P=0.001, P=0.007, P=0.001, P= 0.015, P=0.03 for IOPg and P〈0.001, ,0=0.003, P〈0.001, P= 0.009, P=0.014 for IOPcc）. CH correlated postoperatively with EQaCASIA and EQpCASIA only （P=0.021, P=0.022）. CONCLUSION： Biometric characteristics may significantly affect biomechanical properties of the cornea in terms of CH, IOPcc and IOPg before, but even more after cataract surgery.

Microtubule Biomechanical Properties under Deformation and Vibration

Microtubules (MT) are of great engineering importance due to their potential applications as sensors, actuators, drug delivery, and others. The MT properties/mechanics are greatly affected by their biomechanical environment and it is important to understand their biological function. Although microtubule mechanics has been extensively studied statically, very limited studies are devoted to the biomechanical properties of microtubule undergoing deformation and vibration. In this study, we investigate the biomechanical properties of the microtubule under bending deformation and free vibration using 3D finite element analysis. Results of force-deformation and vibration frequencies and mode shapes obtained from the finite element analysis are presented. The results indicate that the force-deformation characteristics vary with time/phases and become non-linear at higher time intervals. The modes of MT vibration and frequencies are in the GHz range and higher modes will involve combined bending, torsion and axial deformations. These higher modes and shapes change their deformation which might have implications for physiological and biological behavior, especially for sensing and actuation and communication to cells. The bending force-deformation characteristics and vibration modes and frequencies should help further understand the biomechanical properties of self-assembled microtubules.

Discrete element modeling and parameter calibration of safflower biomechanical properties

Understanding the biomechanical properties of safflowers is essential for appropriately designing harvesting machinery and optimizing the harvesting process.Safflower is a flexible crop that lacks a basis for relevant simulation parameters,which causes difficulties in designing harvesting machinery.In this study,a calibration method for safflowers was proposed.First,a discrete element model was established by measuring the intrinsic parameters of a safflower,such as its geometric parameters,density,Poisson’s ratio,and modulus of elasticity.Second,the contact and bonding parameters were calibrated using a combination of physical and simulation tests.In the contact parameter tests,the Hertz-Mindlin(no-slip)model was implemented for the stacking angle tests conducted regarding the safflower filament.A regular two-level factorial design was used to determine the important factors and perform the steepest climb test.Moreover,the Box-Behnken design was adopted to obtain the optimal contact parameters.In the bonding parameter tests,the Hertz-Mindlin model with bonding contact was applied for the safflower shear simulation tests;moreover,the optimum bonding parameters were obtained through the central composite design test.The results demonstrated that the relative errors between the simulated and measured stacking angles and maximum shear were 3.19%and 5.29%,respectively.As a result,the safflower simulation parameters were accurately calibrated,providing a reference for appropriately setting the simulation parameters and designing key mechanical components.

Biomechanical behavior of grass roots at different gauge lengths

Gauge length influences the biomechanical properties of herbaceous roots such as tensile resistance,tensile strength and Young’s modulus.However,the extent to which and how these biomechanical properties of herbaceous roots are influenced remain unknown.To better understand the behavior of roots in tension under different conditions and to illustrate these behaviors,uniaxial tensile tests were conducted on the Poa araratica roots as the gauge length increased from 20 mm to 80 mm.Subsequently,ANOVA was used to test the impact of the significant influences of gauge length on the biomechanical properties,nonlinear regression was applied to establish the variation in the biomechanical properties with gauge length to answer the question of the extent to which the biomechanical properties are influenced,and Weibull models were subsequently introduced to illustrate how the biomechanical properties are influenced by gauge length.The results reveal that(1)the variation in biomechanical properties with root diameter depends on both the gauge length and the properties themselves;(2)the gauge length significantly impacts most of the biomechanical properties;(3)the tensile resistance,tensile strength,and tensile strain at cracks decrease as the gauge length increases,with values decreasing by 20%-300%,while Young’s modulus exhibits the opposite trend,with a corresponding increase of 30%;and(4)the Weibull distribution is suitable for describing the probability distribution of these biomechanical properties;the Weibull modulus for both tensile resistance and tensile strain at cracks linearly decrease with gauge length,whereas those for tensile strength and Young’s modulus exhibit the opposite trend.The tensile resistance,tensile strength,and tensile strain at the cracks linearly decrease with increasing gauge length,while the tensile strength and Young’s modulus linearly increase with increasing gauge length.

Effect of robot-assisted gait training on the biomechanical properties of burn scars:a single-blind,randomized controlled trial

Background:Robot-assisted gait training(RAGT)is more effective in the range of motion(ROM)and isometric strength in patients with burns than conventional training.However,concerns have been raised about whether RAGT might negatively affect the scars of patients with burns.Therefore,we investigated the effects of RAGT-induced mechanical load on the biomechanical properties of burn scars.Methods:This was a single-blind,randomized clinical trial conducted on inpatients admitted to the Department of Rehabilitation Medicine between September 2020 and August 2021.RAGT was conducted for 30 min per day,five days a week for 12 weeks and the control group received conventional gait training for 12 weeks.The pre-training ROM of lower extremity joints was evaluated and the levels of melanin,erythema,trans-epidermal water loss,scar distensibility and elasticity were assessed before training and at 4 and 12 weeks after training.Finally,19 patients in the gait assistance robot(GAR)group and 20 patients in the control group completed the 12-week trial and all evaluations.Results:There were no significant differences in the epidemiologic characteristics,pre-training ROM of joints and pre-training biomechanical properties of the burn scar between the groups(p>0.05 for all).None of the patients experienced skin abrasion around the burn scar where the fastening belts were applied or musculoskeletal or cardiovascular adverse events during the training.Scar thickness significantly increased in both groups(p=0.037 and p=0.019)and scar distensibility significantly decreased in the control group(p=0.011)during the training.Hysteresis was significantly decreased in the GAR group during the training(p=0.038).The GAR and control groups showed significant difference in the change in the values of hysteresis between pre-training and 12 weeks after training(p=0.441 and p=0.049).Conclusions:RAGT significantly decreased hysteresis in hypertrophic burn scars and did not cause a significant decrease in skin distensibility.Moreover,no skin complications around the burn scars were detected during RAGT.

Biomechanical Properties and Modeling of Skin with Laser Influence

This paper studied experimentally and theoretically the biomechanical properties of skin with laser influence. Different types of tensile tests of the porcine skin in vitro were conducted to study effect of the laser, tensile strength, stress-strain relationship, influence of skin's anisotropy and different regions, repetitive loading and stress-relaxation. A modeling of skin was developed according to the experimental results. The modeling provided insights into the important structure-function relationship in skin tissue with the laser effect. The nonlinear and anisotropic mechanical responses of skin are largely due to varying degree of fiber undulation which is effected by laser and outside forces. By introducing the laser factor into the constitutive modeling, the skin's biomechanical properties and the mechanism of the skin repair with laser were discussed.

Biomechanical properties of four dermal substitutes

Many kinds of cell-free dermal substitutes have been developed during the past several years, however,their biomechanical properties, including hysteresis, stress relaxation, creep, and non-linear stress-strain, are still unknown. In this study, we tested these biomechanical characteristics of four dermal substitutes, and compared them with those of fresh human skin （FHS）.

Comparison of Biomechanical Properties and Hemodynamics of Three Different Vena Cava Filters

The interaction mechanism of three types of vena cava filters(VCFs) with blood vessels and their influence on the bloodstream during the process of implantation are investigated by finite element method and computational fluid dynamics. The VCF models are set up with Solidworks software. Using ABAQUS software,we simulate the working conditions of the VCFs in the vessel to analyze the stress distribution and radial support stiffness of the vessel wall and the filter surface. Using FLUENT software, we simulate and analyze the velocity,pressure and shear stress distributions of blood flow when the VCFs are at their working conditions. For the retrievable VCF(R-VCF), the peak stress at the working conditions of the VCF is the highest, the peak stress toward the vessel wall is the lowest, and the support stiffness is the lowest. For the permanent VCF(P-VCF), the peak stress at the working conditions of the VCF is the highest, the peak stress toward the vessel wall is the lowest,and the support stiffness is the highest. Because of the structure of scaffolding support units and the tendency to form intimal hyperplasia on their support units, both the convertible VCF(C-VCF) and the P-VCF can embed their support units in the hyperplasia skin. This effectively prevents them from harming blood veins through filter damage at the pulse load conditions. As the biomechanical property of the C-VCF is between those of the R-VCF and the P-VCF, it has smaller obstacle to blood flow after conversion and has some fragmentation effects on the thrombus. The results show that different types of VCFs differ in their biomechanical and hemodynamic properties after implantation. Therefore, the simulative analysis can provide a reference basis for filter design and clinical decision making.

Human umbilical cord blood stem cells and brainderived neurotrophic factor for optic nerve injury: a biomechanical evaluation

Treatment for optic nerve injury by brain-derived neurotrophic factor or the transplantation of human umbilical cord blood stem cells has gained progress, but analysis by biomechanical indicators is rare. Rabbit models of optic nerve injury were established by a clamp. At 7 days after injury, the vitreous body received a one-time injection of 50 μg brain-derived neurotrophic factor or 1 × 10^6 human umbilical cord blood stem cells. After 30 days, the maximum load, maximum stress, maximum strain, elastic limit load, elastic limit stress, and elastic limit strain had clearly improved in rabbit models of optical nerve injury after treatment with brain-derived neurotrophic factor or human umbilical cord blood stem cells. The damage to the ultrastructure of the optic nerve had also been reduced. These findings suggest that human umbilical cord blood stem cells and brain-derived neurotrophic factor effectively repair the injured optical nerve, improve biomechanical properties, and contribute to the recovery after injury.

Local treatment of osteoporosis with alendronate-loaded calcium phosphate cement

Background A new treatment strategy is to target specific areas of the skeletal system that are prone to clinically significant osteoporotic fractures.We term this strategy as the ＂local treatment of osteoporosis＂.The study was performed to investigate the effect of alendronate-loaded calcium phosphate cement （CPC） as a novel drug delivery system for local treatment of osteoorosis.Methods An in vitro study was performed using CPC fabricated with different concentrations of alendronate （ALE,0,2,5,10 weight percent （wt％））.The microstructure,setting time,infrared spectrum,biomechanics,drug release,and biocompatibility of the composite were measured in order to detect changes when mixing CPC with ALE.An in vivo study was also performed using 30 Sprague-Dawley rats randomly divided into six groups：normal,Sham （ovariectomized （OVX） ＋ Sham）,CPC with 2％ ALE,5％ALE,and 10％ ALE groups.At 4 months after the implantation of the composite,animals were sacrificed and the caudal vertebrae （levels 4-7） were harvested for micro-CT examination and biomechanical testing.Results The setting time and strength of CPC was significantly faster and greater than the other groups.The ALE release was sustained over 21 days,and the composite showed good biocompatibility.In micro-CT analysis,compared with the Sham group,there was a significant increase with regard to volumetric bone mineral density （BMD） and trabecular number （Tb.N） in the treated groups （P ＜0.05）.Trabecular spacing （Tb.Sp） showed a significant increase in the Sham group compared to other groups （P ＜0.01）.However,trabecular thickness （Tb.Th） showed no significant difference among the groups.In biomechanical testing,the maximum compression strength and stiffness of trabecular bone in the Sham group were lower than those in the experimental groups.Conclusions The ALE-loaded CPC displayed satisfactory properties in vitro,which can reverse the OVX rat vertebral trabecular bone microarchitecture and biomechanical properties in vivo.

Potential Application of Entangled Porous Titanium Alloy Metal Rubber in Artificial Lumbar Disc Prostheses

Entangled Porous Titanium Alloy Metal Rubber(EPTA-MR)was used as a nucleus pulposus material in the design of non-fusion intervertebral disc prosthesis for the first time.A novel artificial lumbar intervertebral disc prosthesis was designed by reconstructing the lumbar model with reverse engineering technology,and the biomechanical behavior of the prosthesis was simulated under varied working conditions.The nucleus pulposus size was determined by the actual size of human prosthesis.EPTA-MR samples with different densities were prepared by medical titanium alloy wire experimental studies were conducted on static stiffness,damping energy consumption,and fatigue life.The results indicated that the static stiffness of EPTA-MR could reach approximately 1500 N mm and its loss factor remained higher than 0.2,and the variation range was relatively small,with excellent vibration damping capacity and bearing capacity.Among them,the overall performance of EPTA-MR with a density of 2.5 g em 3 was closer to that of the physiologic intervertebral disc.A macro experiment of five million fatigue vibration tests combined with microstructure observation exhibited a wear rate of only 0.9396 g-MC with no noticeable change in the internal micro-morphology.Therefore,the EPTA-MR has a broad application prospect as the nucleus pulposus material of artificial intervertebral disc prosthesis.