Changes in corneal biomechanics and posterior corneal surface elevation after FS-LASIK

AIM:To investigate the changes in corneal biomechanics and posterior corneal surface elevation after femtosecond laser-assisted in situ keratomileusis(FS-LASIK).METHODS:Totally 197 eyes of 100 patients who underwent the FS-LASIK from April 2022 to November 2022 were included.They were divided into three groups according to the ratio of residual corneal stroma thickness/corneal thickness(RCST/CT):Group I(50%≤RCST/CT<55%,63 eyes of 32 patients),Group II(55%≤RCST/CT<60%,67 eyes of 34 patients),and Group III(RCST/CT≥60%,67 eyes of 34 patients).The intraocular pressure(IOP),corneal compensated IOP(IOPcc),corneal hysteresis(CH)and corneal resistance factor(CRF)were measured immediately,1,and 3mo postoperatively by ocular response analyzer(ORA)and the posterior elevation difference(PED)was measured by Pentacam.RESULTS:After operation,IOP,CH,CRF,and PED were statistically different among the three groups(F=12.99,31.148,23.998,all P<0.0001).There was no statistically significant difference in IOPcc among the three groups(F=0.603,P>0.05).The IOP,IOPcc,CH,and CRF were statistical changed after surgery(F=699.635,104.125,308.474,640.145,all P<0.0001).The PED of Group I was significantly higher than that of Group II(P<0.05),and Group II was significantly higher than that of Group III(P<0.05).The PED value of 3mo after surgery decreased in each group compared with 1mo after surgery,but there was no statistical difference(Group I:t=0.82,P=0.41;Group II:t=0.17,P=0.87;Group III:t=1.35,P=0.18).The correlation analysis of corneal biomechanical parameter changes with PED at 1mo and 3mo after surgery showed thatΔIOP,ΔIOPcc,ΔCH,andΔCRF were not correlated with PED value in three groups(P>0.05).CONCLUSION:The smaller the RCST/CT,the greater effect on corneal biomechanics and posterior surface elevation.There is no correlation between changes in corneal biomechanics and posterior corneal surface elevation in the range of RCST/CT≥50%.

Pregnancy-Induced Changes in Ocular Biomechanics Are Related to Maternal Hormone Levels in Healthy Chinese Pregnant Women

Background: To explore the changes in ocular biomechanics during pregnancy and the postpartum period and their association with maternal hormone level changes. Methods: In a prospective cohort study, 24 eyes of 12 pregnant women were enrolled and monitored throughout pregnancy and after delivery (6 weeks). Intraocular pressure (IOP), central corneal thickness (CCT), corneal endothelium cell (CEC), axial length (AL), corneal curvature (K1, K2), anterior chamber depth (ACD), central subfield thickness (CST), macular volume (MV), cube average thickness (CAT), retinal nerve fibre layer (RNFL), tear meniscus height (TMH), and breaking up time (BUT) were measured throughout pregnancy, and blood plasma levels of maternal hormones were determined at the same time points. Results: A gradual decrease in IOP values was observed as gestation progressed, and there was a statistically significant difference in IOP between the 3rd trimester and the 1st and 2nd trimester and postpartum (p = 0.002, p = 0.006, p = 0.050). There was a significant difference between the 1st and 2nd trimesters in terms of MV (p = 0.023). The difference in RNFL in the 3rd trimester and postpartum was significant (p = 0.011). The levels of the β-hCG showed a significant correlation with K2, ACD, and TMH only in the 2nd trimester (r = 0.588, p = 0.045;r = - 0.740, p = 0.006;r = 0.642, p = 0.024). Regarding luteinizing hormone, there was a negative correlation with MV in the 1st and 2nd trimesters (r = - 0.598, p = 0.040;r = - 0.672, p = 0.017) and CAT in the 1st and 2nd trimesters (r = - 0.599, p = 0.040;r = - 0.655, p = 0.021). Luteinizing hormone levels were correlated with ACD (r = - 0.702, p = 0.011) in the 2nd trimester and K2 (r = 0.585, p = 0.046) in the 3rd trimester. A correlation was found between follicle-stimulating hormone levels and CEC, MV and CAT in the 1st trimester (r = - 0.677, p = 0.016;r = - 0.602, p = 0.039;r = - 0.584, p = 0.046) and AL in the 3rd trimester (r = - 0.618, p = 0.032). The correlation between oestradiol and CST in the 1st trimester (r = - 0.621, p = 0.031) and RNFL (r = 0.594, p = 0.041) in the postpartum. A statistically significant correlation between progesterone and MV (r = 0.583, p = 0.047) and TMH (r = 0.762, p = 0.004) was observed in the 1st trimester. No significant intergroup correlation was observed postpartum (p > 0.05). Conclusion: Ophthalmological parameters showed physiological changes induced by hormone levels in pregnancy and returned to baseline levels after delivery.

Effect of cervical spine surgery on the biomechanics of the cervical spine

In clinical practice,cervical spine surgery inevitably alters the original physiological structure of the cervical spine,thus causing changes in the original biomechanical properties of the cervical spine.The biomechanical properties of the cervical spine are particularly significant as it is an essential structure that supports the head and connects the trunk.Different cervical spine surgery options can have different effects on the biomechanics of the cervical spine.Therefore,this review will discuss recent research advances on the effects of cervical spine surgery on cervical spine biomechanics.We hope that this review will provide some theoretical basis for future studies on the biomechanical effects of cervical spine surgery on the cervical spine.

Acellular allogeneic nerve grafting combined with bone marrow mesenchymal stem cell transplantation for the repair of long-segment sciatic nerve defects:biomechanics and validation of mathematical models

We hypothesized that a chemically extracted acellular allogeneic nerve graft used in combination with bone marrow mesenchymal stem cell transplantation would be an effective treatment for long-segment sciatic nerve defects.To test this,we established rabbit models of 30 mm sciatic nerve defects,and treated them using either an autograft or a chemically decellularized allogeneic nerve graft with or without simultaneous transplantation of bone marrow mesenchymal stem cells.We compared the tensile properties,electrophysiological function and morphology of the damaged nerve in each group.Sciatic nerves repaired by the allogeneic nerve graft combined with stem cell transplantation showed better recovery than those repaired by the acellular allogeneic nerve graft alone,and produced similar results to those observed with the autograft.These findings confirm that a chemically extracted acellular allogeneic nerve graft combined with transplantation of bone marrow mesenchymal stem cells is an effective method of repairing long-segment sciatic nerve defects.

Micro air vehicle-motivated computational biomechanics in bio-flights:aerodynamics,flight dynamics and maneuvering stability

Aiming at developing an effective tool to unveil key mechanisms in bio-flight as well as to provide guidelines for bio-inspired micro air vehicles（MAVs） design,we propose a comprehensive computational framework,which integrates aerodynamics,flight dynamics,vehicle stability and maneuverability.This framework consists of（1） a Navier-Stokes unsteady aerodynamic model;（2） a linear finite element model for structural dynamics;（3） a fluidstructure interaction（FSI） model for coupled flexible wing aerodynamics aeroelasticity;（4） a free-flying rigid body dynamic（RBD） model utilizing the Newtonian-Euler equations of 6DoF motion;and（5） flight simulator accounting for realistic wing-body morphology,flapping-wing and body kinematics,and a coupling model accounting for the nonlinear 6DoF flight dynamics and stability of insect flapping flight.Results are presented based on hovering aerodynamics with rigid and flexible wings of hawkmoth and fruitfly.The present approach can support systematic analyses of bio- and bio-inspired flight.

Effect of femtosecond and microkeratome flaps creation on the cornea biomechanics during laser in situ keratomileusis： one year follow-up

AIM： To compare the corneal biomechanical outcomes at one year after laser in situ keratomileusis（LASIK） with the flaps created by Ziemer and Moria M2 microkeratome with 110 head and -20 blade.METHODS： Totally 100 eyes of 50 consecutive patients were enrolled in this prospective study and divided into two groups for corneal flaps created by Ziemer Femto LDV and Moria M2 microkeratome with 110 head and -20 blade.Corneal biomechanical properties including cornea resistance factor（CRF） and cornea hysteresis（CH） were measured before and 1,3,6,12 mo after surgery by ocular response analyzer.Central cornea thickness and corneal flap thickness were measured by optical coherence tomography.RESULTS： The ablation depth（P=0.693）,residual corneal thickness（P=0.453）,and postoperative corneal curvature（P=0.264） were not significant different between Ziemer group and Moria 110-20 group after surgery.The residual stromal bed thickness,corneal flap thickness,CH and CRF at 12 mo after surgery were significant different between Ziemer group and Moria 110-20 group（P〈0.01）; Ziemer group gained better corneal biomechanical results.The CRF and CH increased gradually from 1 to12 mo after surgery in Ziemer group,increased from 1 to 6 mo but decreased from 6 to 12 mo in Moria 110-20 group.Both CRF and CH at one year after surgery increased with the increasing of residual cornea thickness; pre-LASIK CRF,CRF also increased with residual stromal bed thickness,while CH decreased with the increasing of pre-LASIK intraocular pressure and cornea flap thickness（P〈0.01）.CONCLUSION： In one year follow-up,femtosecond laser can provide better cornea flaps with stable cornea biomechanics than mechanical microkeratome.

Biomechanics of the anterior cruciate ligament:Physiology,rupture and reconstruction techniques

The influences and mechanisms of the physiology,rupture and reconstruction of the anterior cruciate ligament(ACL)on kinematics and clinical outcomes have been investigated in many biomechanical and clinical studies over the last several decades.The knee is a complex joint with shifting contact points,pressures and axes that are affected when a ligament is injured.The ACL,as one of the intra-articular ligaments,has a strong influence on the resulting kinematics.Often,other meniscal or ligamentous injuries accompany ACL ruptures and further deteriorate the resulting kinematics and clinical outcomes.Knowing the surgical options,anatomic relations and current evidence to restore ACL function and considering the influence of concomitant injuries on resulting kinematics to restore full function can together help to achieve an optimal outcome.

Optimal Design of Bicycle Frame Parameters Considering Biomechanics

With the development of technology and the change of market demands,the trend in middle and high grade bicycle manufacturing is developed toward small-volume,multi-species,and customer-oriented production.Therefore,human element should be fully considered in design so that the bicycle has the best cycling performance for the specific rider.Currently,customized design is difficult to achieve since feature parameters of the rider are not included in the design.The design of bicycle frame is the most important in bicycle design.The relative positions among the saddle,handlebar and central axis are defined as the bicycle three-pivot,they are the main parameters in bicycle frame design.In conventional bicycle design,frame parameters are merely relevant to bicycle types.On the basis of the principles of biomechanics and ergonomics knowledge,this paper presents a design method for bicycle three-pivot considering feature parameters of the rider by dynamic simulation.Firstly,a dynamic model of rider-bicycle system is built for a special rider,and a serial of simulation experiments is designed by uniform test method.Then,a mathematical model is built between the three-pivot position and the square of lower limb muscle stress by using simulation and regression analysis of the rider-bicycle system.The optimal three-pivot position parameters are obtained by setting the minimal of the square of the lower limb muscle stress as the objective.Therefore,the optimal parameters are gained for the specific rider.Finally,various results are gained for different riders based on the same design process.The function between feature parameters of the rider and the optimum three-pivot position parameters is built by regression.Bicycle design considering biomechanics can be divided into three main steps：calculating the three-pivot position,designing the geometrical structure of the bicycle frame and analyzing frame strength,and selecting appropriate parts and assembling the bicycle.Bicycle design considering biomechanics changes the conventional bicycle design and realizes customized design by considering human element in the design process.

Interactions of primary insult biomechanics and secondary cascades in spinal cord injury： implications for therapy

The complex and variable nature of traumatic spinal cord inju- ry （SCI） presents a unique challenge for translational research. SCI is not bound by any demographic nor is it limited to specific injury biomechanics.

Biomechanics of sclera crosslinked using genipin in rabbit

AIM：To strengthen the biomechanics of collagen by crosslinking rabbit scleral collagen with genipin to develop a new therapy for preventing myopic progression. METHODS：Ten New Zealand rabbits were treated with 0.5 mmol/L genipin injected into the sub-Tenon＇s capsule in the right eyes. Untreated contralateral eyes served as the control. The treated area was cut into scleral strips measuring 4.0 mm×10.0 mm for stress-strain measurements（n=5）. The remaining five treated eyes were prepared for histological examination.RESULTS：Compared to the untreated scleral strips,the genipin-crosslinked scleral strips showed that the ultimate stress and Young＇s modulus at 10% strain were increased by the amplitude of 130% and 303% respectively,ultimate strain was decreased by 24%. There had no α-smooth muscle actin（α-SMA）positive cells in control and treated sclera. Histologically,there was no sign of apoptosis in the sclera,choroid,and retina; and no side effects were found in the peripheral cornea and optic nerve adjacent to the treatment area.CONCLUSION：Genipin induced crosslinking of collagen can increase its biomechanical behavior by direct strengthening of the extracellular matrix in rabbit sclera,with no α-SMA expression seen in the myofibroblasts. As there is no evidence of cytotoxicity in the scleral,choroidal,and retinal cells,genipin is likely a promising agent to strengthen the weakened sclera to prevent myopic progression.

Comparison of corneal biomechanics in Sjogren's syndrome and non-Sjogren's syndrome dry eyes by Scheimpflug based device

AIM：To compare the corneal biomechanics of Sj？gren＇s syndrome（SS） and non-SS dry eyes with Corneal Visualization Scheimpflug Technology（CorV is ST）.METHODS：Corneal biomechanics and tear film parameters, namely the Schirmer I test value, tear film break-up time（TBUT） and corneal staining score（CSS） were detected in 34 eyes of 34 dry eye patients with SS（SSDE group） and 34 dry eye subjects without SS（NSSDE group） using CorV is ST. The differences of the above parameters between the two groups were examined, and the relationship between corneal biomechanics and tear film parameters were observed. RESULTS：The differences in age, sex, intraocular pressure（IOP） and central corneal thickness（CCT） were not significant between the two groups（P〉0.05）. The tear film parameters had significant differences between the SSDE group and NSSDE group（all P〈0.05）. Patients in the SSDE group had significantly lower A1-time and HC-time, but higher DA（P=0.01, 0.02, and 0.02, respectively） compared with the NSSDE group. In the SSDE group, DA was negatively correlated with TBUT（rho=-0.38, P=0.03）; HC-time was negatively correlated with CSS（rho=-0.43, P=0.02）. In the NSSDE group, HC-time was again negatively correlated with CSS（rho=-0.39, P=0.02）.CONCLUSION：There are differences in corneal biomechanical properties between SSDE and NSSDE. The cornea of SSDE tends to show less ＂stiffness＂, as seen by a significantly shorter A1-time and HC-time, but larger DA, compared with the cornea of NSSDE. Biomechanical parameters can be influenced by different tear film parameters in both groups.

Biomechanics of the sclera and effects on intraocular pressure

Accumulating evidence indicates that glaucoma is a multifactorial neurodegenerative disease characterized by the loss of retinal ganglion cells （RGC）, resulting in gradual and progressive permanent loss of vision. Reducing intraocular pressure （IOP） remains the only proven method for preventing and delaying the progression of glaucomatous visual impairment. However, the specific role of IOP in optic nerve injury remains controversial, and little is known about the biomechanical mechanism by which elevated IOP leads to the loss of RGC. Published studies suggest that the biomechanical properties of the sclera and scleral lamina cribrosa determine the biomechanical changes of optic nerve head, and play an important role in the pathologic process of loss of RGC and optic nerve damage. This review focuses on the current understanding of biomechanics of sclera in glaucoma and provides an overview of the possible interactions between the sclera and IOP. Treatments and interventions aimed at the sclera are also discussed.

Numerical Modeling of Human Middle Ear Biomechanics Using Finite Element Method

An accurate finite element (FE) model of the human middle ear can provide better understanding of the mechanics of middle ear, and can be used for aiding the design of the implantable middle ear hearing devices. In this paper, a three-dimensional (3D) FE model of the human middle ear was constructed, including the tympanic membrane, ossicular bones, and middle ear suspensory ligaments/muscles. This model was constructed based on a complete set of computerized tomography section images of a healthy volunteer's left ear by reverse engineering technology. The validity of this model was confirmed by comparing the motions of the tympanic membrane and stapes footplate obtained by this model with published experimental measurements on human temporal bones. The result shows that the model is reasonable in predicting the biomechanics of the human middle ear.

Optimal Design of Mountain Bicycle Based on Biomechanics

To achieve better cycling performance and vibration comfort of mountain bicycle, the optimization of frame structural parameters and rear suspension scale parameters is investigated based on biomechanics.Firstly, the quadratic sum of rider lower limb muscles stresses is presented as the evaluation criterion of muscle fatigue.By taking the criterion as the objective function, the relative positions of three pivot points of frame are optimized to ensure that the frame structural parameters match the stature of riders.Secondly, the vibration performance is evaluated referring to the ISO 2631-1 Mechanical Vibration and Shock Evaluation of Human Exposure to Whole-Body Vibration.According to this evaluation, the mapping relationship between the vibration performance and rider's weight as well as structural parameters of rear suspension is revealed.Results show that the length of side link has no significant effect on vibration comfort, while rider's weight is important in the design of mountain bicycle.

Osteoarthritis and Articular Cartilage: Biomechanics and Novel Treatment Paradigms

Background: Osteoarthritis is a widespread highly painful disabling age-related disease with no known cure. Although novel strategies for ameliorating osteoarthritic damage abound, it is likely that none will be successful over time if the entire spectrum of the disease and the effects of joint biomechanics on joint tissues are not carefully considered. Objectives: 1) To detail the structure of healthy articular cartilage, the key tissue affected by osteoarthritis. 2) To detail what aspects of cartilage damage best characterize osteoarthritis. 3) To consider the role of biomechanical factors in developing solutions to treat osteoarthritic joint damage. Methods: Literature sources from 1980 onwards that have contributed to our knowledge of the topics relevant to this paper were accessed and retrieved. The data were categorized into four predominant themes and conclusions about the state of our knowledge and future directives were formulated. Conclusions: Osteoarthritis prevalence remains high, and a cure appears elusive. A rich body of data has helped us to better understand the key tissue involved, and suggests a repair process might be feasible, if the basic collective information on the role of biomechanics in mediating or moderating articular cartilage integrity and function is forthcoming.

Changes in corneal biomechanics and intraocular pressure following Femto-LASIK using Goldman applanation tonometry and ocular response analyzer

AIM:To compare intraocular pressure(IOP)measurements before and after laser in situ keratomileusis(LASIK)with a femtosecond laser for flap creation using ocular response analyzer(ORA)and Goldmann applanation tonometry,and to identify factors that may influence the preoperative and postoperative IOP.METHODS:A prospective study conducted on myopic patients who underwent LASIK using a femtosecond laser for flap fashioning.Enrolled patients were evaluated preoperatively,6 wk and 3 mo postoperatively for manifest refraction(MR),keratometric(K)readings and central corneal thickness(CCT)using a scheimpflug-based topography.Corneal resistance factor(CRF),corneal hysteresis(CH),Goldmann correlated IOP(IOPg)and corneal compensated IOP(IOPcc)were measured using ORA besides IOP assessment by Goldman applanation tonometry(GAT).RESULTS:There was a statistically significant decrease in measures of IOPg by 3.35±0.83 mm Hg,followed by GAT which decreased by 2.2±0.44 mm Hg,and the least affected by operation was IOPcc which decreased only by 0.87±0.1 mm Hg after 6 wk.After 3 mo follow up there was a statistically significant decrease in IOPcc which decreased only by 0.76±0.4 mm Hg,followed by IOP GAT by 1.6±0.5 mm Hg,and the most affected by operation was IOPg which decreased by 2.3±0.3 mm Hg.Correspondingly,there was a statistically significant decrease in CH and CRF after 6 wk and 3 mo.At 3 mo,the preoperative MR and preoperative GAT were prominent significant predictors of the postoperative GAT changes.The prediction equation was subsumed.CONCLUSION:IOP measurements and corneal biomechanical factors reduce significantly after LASIK with a femtosecond laser for flap creation.The IOPcc values are less influenced by changes in corneal properties than IOPg and GAT,indicating that IOPcc may provide the most reliable measurement of IOP after this procedure.

The structural basis of oscillation damping in plant stems-biomechanics and biomimetics

Oscillations and their damping were investigated for plant stems of Cyperus alternifolius L., Equisetum hyemale L., Equisetum fluviatile L., Juncus effuses L., Stipa gigantea Link, and Thamnocalamus spathaceus (Franch.) Soderstr. With the exception of T. spathaceus, mechanical damping of the oscillation of individual plant stems, even without side organs, leaves or inflorescences, is quite effective. Our experiments support the hypothesis that embedding stiff sclerenchymatous elements in a more compliant parenchymatous matrix provides the structural basis for the dissipation of mechanical energy in the plant stem. As an application the naturally occurring structures were mimicked in a compound material made from hemp fabrics em- bedded in polyurethane foam, cured under pressure. Like its natural model it shows plastic deformability and viscoelastic be- haviour. In particular the material is characterized by a remarkably high shock absorption capacity even for high impact loads.

Effects of Custom-made Insoles on Plantar Biomechanics and Upper Extremity Muscle Performance

Objective:To investigate the effectiveness of molding custom-made insoles for female patients with foot pain.Methods:The study included 20 patients whose insoles were prescribed according to biomechanical evaluations and molded by repositioning the subtalar joint in its neutral position using a simple set of tools.

Studies on morphology and biomechanics of the coronary arteries

Morphology and biomechanics of the coronary arteries have been studied in the human and common experimental animals since 1979. The types of the coronary distribution, the artery-vein relationship,and the intramural vascular changes and the coronary colla