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The impact of bone variables, including density, geometry, angle of femoral torsion, and thickness of the femoral cortices, on the formation of bone micro-damage following THA was investigated. Using CT images of avascular necrosis patients, we developed 28 intact femoral bone models with ages ranging from 19 to 87 years to explore the relationship between age and bone density. Among these 28 femur models, 10 models were selected for implantation with the Zweymuller stem, divided into two groups based on the highest and lowest bone mineral density (BMD). After proper stem insertion into the femoral bone canal, finite element analyses with nonlinear damage analysis were performed on the THA models under three boundary conditions: stance, lateral bending, and torsion. Using the Pearson’s correlation coefficient, the study revealed a strong correlation between bone density and fracture load in the 10 THA models, which remained consistent across all three boundary conditions: stance (r = 0.74), lateral bending (r = 0.79), and torsion (r = 0.88). However, a moderate correlation was observed between bone density and the number of solid element failures, which also remained consistent across all boundary conditions: stance (r = -0.40), lateral bending (r = -0.51), and torsion (r = -0.48). It was found that femoral models with a bent shape of the femoral shaft and thin cortices experienced greater bone damage compared to models with normal geometry. Additionally, THA models with retroversion stem placement resulted in higher bone damage compared to models with normal anteversion placement.

Previously, we have developed a novel porous hydroxyapatite/poly l-lactic-co-caprolactone (HA/PLCL) composite sandwich beam as a new scaffold material for bone regeneration. This work presents the study of bending fracture mechanisms and microdamage of porous hydroxyapatite/poly L-lactic-acid (HA/PLLA) sandwich beam, in comparison to the previous developed HA/PLCL sandwich beam. Both beams were fabricated using the sandwich method in which the single porous composite beams were layered in between two porous polymer layers of their kind. Three-point bending tests were performed to assess their mechanical properties, and their microstructures along with the damage mechanisms were examined using field emission-scanning electron microscope (FE-SEM). Their crystalline structures and thermal properties were analyzed using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) analysis, and differential scanning calorimetry (DSC) measurements. The microdamage and fracture mechanisms were then characterized by stepwise crack formations. It was found that HA/PLLA composite sandwich beam possessed higher mechanical properties compared to HA/PLCL sandwich beam, resulting from higher stiffness of PLLA polymer. PLCL layer showed a vast ductile fracture, with elongated PLCL strips, while the fracture surfaces observed on the PLLA layer have a relatively brittle fracture pattern with some polymeric pores that were still visible. Three stages of damage were observed on both beams with different locations of crack initiation, indicating that different polymer materials do affect the fracture behavior of each beam.

The purpose of the present study was to mechanically verify after vertebral augmentation (AVA) scores using a finite element method (FEM) with accurate material constants of balloon kyphoplasty (BKP) cement. Representative cases with AVA scores of 1 (case 1), 3 (case 2), and 5 (case 3) among patients with vertebral body fractures who underwent BKP were analyzed. A FEM model consisting of 5 vertebral bodies was created, including the injured vertebral body in each case. The amount of displacement for each load (up to 4000 N) between the upper and lower vertebral bodies of each model was measured. Young modulus of the BKP cement was calculated from actual measurements using the EZ-Test EZ-S (Shimadzu Corporation, Kyoto, Japan). In all cases, the number of shell elements (209,296–299,876), solid elements (1913,029–2417,671), and nodes (387,848–487,756) were similar, indicating that FEM modeling was comparable among the cases. Young modulus of BKP cement, calculated using EZ-Test EZ-S, was 572 MPa. Fractures were detected by compressive forces of 3300 N (upper) and 3300 N (lower), 3000 N (upper) and 3100 N (lower), and 1200 N (upper) and 1200 N (lower) in cases 1, 2, and 3, respectively. The AVA scoring system was mechanically verified using the accurate material constants of BKP cement. A multicenter survey and external validation are therefore required for the clinical implementation of the AVA score.

Scaffold engineering has attracted significant attention for three-dimensional (3D) growth, proliferation and differentiation of stem cells in vitro. Currently available scaffolds suffer from issues such as poor ability for cell adhesion, migration and proliferation. This paper addresses these issues with 3D porous chitosan scaffold, fabricated and functionalized with cysteine-terminated Arg-Gly-Asp (Cys-RGD) tri-peptide on their walls. The study reveals that the compressive moduli of the scaffold is independent to RGD functionalization but shows dependence on the applied freezing temperature (TM) during the fabrication process. The low freezing TM (-80°C) produces scaffold with high compressive moduli (14.64 ± 1.38 kPa) and high TM (-30°C) produces scaffold with low compressive moduli (5.6 ± 0.38 kPa). The Cys-RGD functionalized scaffolds lead to significant improvements in adhesion (150%) and proliferation (300%) of human mesenchymal stem cell (hMSC). The RGD-integrin coupling activates the focal adhesion signaling (Paxillin-FAK-ERK) pathways, as confirmed by the expression of p-Paxillin, p-FAK and p-ERK protein, and results in the observed improvement of cell adhesion and proliferation. The proliferation of hMSC on RGD functionalized surface was evaluated with scanning electron microscopy imaging and distribution though pore was confirmed by histochemistry of transversely sectioned scaffold. The hMSC adhesion and proliferation in scaffold with high compressive moduli showed a constant enhancement (with a slope value 9.97) of compressive strength throughout the experimental period of 28 days. The improved cell adhesion and proliferation with RGD functionalized chitosan scaffold, together with their mechanical stability, will enable new interesting avenues for 3D cell growth and differentiation in numerous applications including regenerative tissue implants.

Porous scaffolds comprising natural polymers and bioceramic particles have recently been used in tissue engineering. Collagen is one such natural polymer providing favorable biological conditions; for example, it stimulates the generation and differentiation of cells as an extracellular matrix. α-Tricalcium phosphate (α-TCP) and β-tricalcium phosphate (β-TCP) have also been widely used in bone tissue engineering owing to their favorable osteoconductivity, cellular adhesion, accelerated differentiation, and mechanical properties. In the present study, collagen scaffolds with different bioceramic particles were successfully fabricated by varying the ratio of α-TCP and β-TCP particles. Our results indicate that material properties, such as compressive modulus, swelling behavior, and porosity, can be controlled by varying the ratio of α-TCP and β-TCP particles.

Recently, many researchers focus on the nanoscale fillers to enhance electrical properties of composite due to the uniqueness of material. In this study, polyimide/barium titanate (BaTiO3) nanofibers films were prepared by incorporating electrospun BaTiO3 nanofibers with polyimide derived from 2,2-Bis [4-(4-aminophenoxy) phenyl] propane (BAPP) and 3,3',4,4'-Biphenyl tetracarboxylic dianhydride (BPDA). The obtained nanofibers were modified with (3-Glycidyloxypropyl) trimethoxysilane as coupling agent before integrating into the polyimide matrix. Microstructure and dielectric properties of BaTiO3 nanocomposites were investigated. The results showed BaTiO3 nanofibers were successfully produced at nanoscale regime and well dispersed in the hybrid film after modification and ultrasonication method. Dielectric constant of the nanofibers films were improved and increased with increasing of BaTiO3 nanofibers concentration while dielectric loss remains relative low.

Recently, human iPS cells derived cardiomyocytes (hiPS-CM) have been utilized as the power source of biological actuators. However, the detailed mechanical properties of hiPS-CM have not been well understood yet. The primary aim of this study was to characterize and compare the stress–strain responses of two-dimensional hiPS-CM sheet and three-dimensional tube structure under self-contractive deformation. Firstly, their pulsation behaviors were examined as the time variation of brightness using a high-speed imaging system. Then, the minimum principal strain values on the surfaces of the sheet and tube were measured using the digital correlation method with the consecutive digital images. The theoretical strain was fund to coincide with the experimental strain vey well, indicating the validity of the developed theoretical models. The stress–strain responses of the sheet and tube were then constructed using the active stress model and the experimental strain. It was found that both the stress–strain responses clearly exhibited viscoelastic behaviors characterized by the hysteresis loop. It was thus concluded that the mechanical responses of hiPS-CM structures could be characterized using the viscoelastic theory along with the active stress model.

Poly (L-lactic) Acid (PLLA) is one type of degradable polymer which mostly used for bioplastic. PLLA has strength and modulus comparable with another commercial polymer and not degrade in general environment, however PLLA exhibits brittle fracture. In the present study, blending between PLLA with other polymers was carried out to improve the brittleness of PLLA resin. Polymers that been used in the blending process are synthetic rubber, waste rubber, acrylonitrile butadiene styrene (ABS) and polylactic acid microsphere. Blend ratio (98/2) was considered in the study . The tensile properties and morphology was investigated using tensile testing and field emission scanning electron microscope (FE-SEM). It was found that the addition of PLA microsphere shows the highest tensile strength and elongation at break and good Youngs modulus. While waste rubber and synthetic rubber exhibit the lowest tensile properties. In general, it is found that the toughness of PLLA can be improved by blending method.

Continuous porous hydroxyapatite (HA) scaffold has been considered to be used in bone tissue engineering. However, the low fracture property of HA scaffold has been a problem to be solved. In the present study, polycaprolactone (PCL) was introduced as a secondary phase into the porous structure of HA scaffold to improve the low fracture property. HA scaffolds were firstly fabricated using the template method. The HA scaffolds were then coated with PCL by changing the solution concentration from 1 to 5 wt%. Compression tests and SEM were done to examine the mechanical properties and the morphology of the two-phase composite scaffolds. It was found that the compression strength and modulus increased with increasing PCL concentration. It is also noted that PCL coating can greatly improve the brittleness of pure HA scaffolds. XRD test was also done to study the phase stability of HA and the two-phase scaffolds. There was no chemical reaction between PCL and HA observed by the XRD results. On the overall, these results indicated that PCL coating can effectively improve the low fracture property of pure HA scaffold and the two-phase scaffold could be a potential candidate for bone regeneration.

Characterizing the relative performance between mobile bearing and fixed bearing knee prosthesis remains seen as a difficult task as the previous short-term and mid-term clinical studies disable to observe any evidence of superiority of one design over another. The aim of the present study is to characterize the mechanics comparison between both designs of prosthesis during deep flexional motion with tibial rotation. Three dimensional (3D) FE model of clinically used mobile bearing posterior stabilized (PS) prosthesis was developed from its CAD data. Explicit finite element model was used to simulate the dynamic loaded deep flexional motion from 0 to 135° with neutral and 10° tibial rotation. Fixed bearing prosthesis was represented by fixing the tibial insert to the tibial component. The fixed bearing design was found relatively sensitive to flexion motion and tibial rotation in terms of contact area and maximum shear stress as compared to the mobile bearing design. Tibial rotation increased the peak value of maximum shear stress up to 58 MPa for the fixed bearing, on the contrary, the mobile bearing maintained the peak value of maximum shear stress at 31 MPa even with tibial axial rotation. The influence of post-cam design was also discussed in this study. The mobile bearing has an ability to maintain conformity and relatively low shear stress during very deep flexion with tibial axial rotation in comparison to the fixed bearing.

Hydroxyapatite (HA) scaffold was fabricated using template method. Secondary phase of poly (ε-caprolactone) (PCL) was then introduced into the porous structure of the HA scaffold by the freeze drying method or the room drying process. Compression test and SEM were done to examine the mechanical properties and the microstructural morphology of the composite scaffolds. It was found that the compressive strength and modulus tend to increase with increasing PCL concentration. HA/PCL scaffolds fabricated under the room drying process exhibited higher compression strength and modulus than HA/PCL scaffolds prepared by the freeze drying method because the porous HA surfaces were completely covered by PCL in the room drying scaffolds. XRD test was also used to study the phase stability of the scaffolds. It was confirmed that there was no chemical reaction between PCL and HA. On overall, the results indicated that the introduction of secondary PCL phases into the porous HA scaffold can improve the low strength and toughness of the pure HA scaffold and the HA/PCL composite scaffolds might be a potential candidate in bone tissue engineering.

Knee joint implants developed by western companies have been imported to Korea and used for Korean patients. However, many clinical problems occur in knee joints of Korean patients after total knee joint replacement owing to the geometric mismatch between the western implants and Korean knee joint structures. To solve these problems, a method to determine the representative dimension parameter values of Korean knee joints is introduced to aid in the design of knee joint implants appropriate for Korean patients. Measurements of the dimension parameters of 88 male Korean knee joint subjects were carried out. The distribution of the subjects versus each measured parameter value was investigated. The measured dimension parameter values of each parameter were grouped by suitable intervals called the “size group,” and average values of the size groups were calculated. The knee joint subjects were grouped as the “patient group” based on “size group numbers” of each parameter. From the iterative calculations to decrease the errors between the average dimension parameter values of each “patient group” and the dimension parameter values of the subjects, the average dimension parameter values that give less than the error criterion were determined to be the representative dimension parameter values for designing knee joint implants for Korean patients.

Purpose. To assess the effect of each step of medial soft-tissue releases on the joint gap angle during posterior-stabilised total knee arthroplasty (TKA).Methods. 82 women and 9 men (mean age, 72 years) with medial osteoarthritic knees underwent 100 posterior-stabilised TKAs, in which release of superficial fibres of the medial collateral ligament (MCL) were required using the gap control technique. The order of releases was the superficial MCL, the pes anserinus, and then the semi-membranosus. The superficial MCL was released selectively. The effect of each step of medial soft-tissue releases in full extension and in 90° flexion was compared.Results. After all medial soft-tissue releases, the mean joint gap angles decreased from 8.7° to 3.8° varus in flexion and from 4.4° to 1.4° varus in extension. The total effect of medial soft-tissue releases was significantly larger in flexion than in extension (4.9°±3.2° vs. 3.0°±2.0°, p<0.0001), except for the release of posterior fibres of the superficial MCL. The effect of release of the semi-membranosus in flexion was largest.Conclusion. The release effect was significantly greater in flexion than in extension during posterior-stabilised TKA; the joint gap technique may be more reliable in medial osteoarthritic knees with moderate and severe varus instability.

For normal healthy teeth, the percussive energy generated by mastication is attenuated by the periodontal ligament at the healthy bone/natural tooth interface. However, when a natural tooth must be replaced by an implant because of damage or disease, the ligament is lost and the implant will transmit the percussive forces to the bone directly. Studies have evaluated the deformation distribution of the alveolar bone in the vicinity of implants using finite element analysis and photoelasticity. However, finite element analysis requires clinical verification or a determination of material properties, and photoelastic materials generally have material properties and structure quite different from those of actual bone. Therefore, this study examined the deformation distribution around dental implants in cortical/cancellous bone experimentally using sawbone cortical/cancellous bone models. Dental implants were placed in the bone models and the displacement distribution was measured using the digital image correlation method, and the strain distribution was visualized under a compressive load that simulated the occlusion force.

Novel reinforcements such as beam, film, and porous frame were developed to improve the mechanical properties of poly(L-lactide) (PLLA) scaffolds. A solid-liquid phase separation method was used to fabricate porous structures such as core portions and porous frame of reinforced scaffolds. The beam and film reinforcements were also fabricated from PLLA pellets by applying the thermal-press technique. In the standard scaffold, the localized deformation was characterized as buckling of the pore structures. On the contrary, the primary microstructural deformation mechanism in the beam and the film reinforced scaffolds was characterized as buckling deformation and interfacial failure of the matrix and the reinforcement respectively. It is also seen that the inner porous structure could maintain the initial structure without local buckling of the pore structure. The compressive mechanical properties of the reinforced scaffolds were dramatically improved by about 2 ~ 5 times compared to the standard scaffold.

PLA/PCL and PLA/PCL/LTI blends were developed to improve the fracture properties of biodegradable PLA. LTI was blended to improve the miscibility of PLA and PCL. It was shown that the fracture toughness values were dramatically increased due to LTI addition. SEM results also exhibited that PCL spherulites decreases due to LTI addition and therefore, void formation is reduced and local stress concentration is suppressed, resulting in the improvement of the toughness values. The improved miscibility is also closely related to the enhancement of ductile deformation; as a result, the fracture toughness is increased.

Attempts have been made to improve the impact resistance[removed info] of biodegradable thermoplastic polymer, PLA. A ductile biodegradable polymer, PCL, has been used to improve such property of PLA by using blending technique. Details of the impact fracture properties and mechanisms of PLA/PCL blends, however, have not fully been understood yet. Recently, it was also found that LTI can improve the immiscibility between PLA and PCL. In this study, PLA/PCL and PLA/PCL/LTI blends were prepared, and their impact fracture toughness values were measured[removed info]to assess the effect of PCL content and LTI addition on the impact resistance. Fracture mechanisms of the polymer blends were also characterized by scanning electron microscopy.

Thermal deformation behaviors of electronic packages, stacked-MCP (multi chip package) and SOJ (small outline J-leaded package) were measured by phase-shifting moiré interferometry. This method was developed using a wedged glass plate as a phase shifter to obtain displacement fields with a sensitivity of nanometer scale. Digital image processing was also introduced to determine the strain distributions quantitatively. In stacked-MCP, thermal loading was applied from room temperature 25°C to two elevated temperatures (75 and 100°C), and thermal strains were then examined at these two elevated temperatures. The results showed that the normal strain εxx concentrated at the ends of two silicon chips, and the transverse strain εyy increased between the two silicon chips. The shear strain γxy increased at the end of the lower silicon chip to 0.30% from 0.17% when the temperature increased by 25°C. In SOJ, the thermal strains were investigated with the two packages before and after mounted on PWB (printed wiring board). The results showed that the strains increased by about 50% when the SOJ was mounted on the PWB.

The in situ polymerization synthesis and properties of methyl methacrylate-butadiene-styrene resin (MBS resin) with bimodal rubber particle size distribution were investigated. MBS resin was prepared by bulk-suspension polymerization of styrene and methyl methacrylate in the presence of the styrene-butadiene block copolymer, and bimodal rubber particle size distribution was observed during bulk polymerization and cooling. During bulk polymerization and cooling, size distribution was regulated by the viscosity of the prepolymer or shearing for the prepolymer. The formative mechanisms of the bimodal distribution were presumed to be increase of small rubber particles by shearing and delay in changing to small rubber particles according to the difference in the inside structure of large rubber particles. MBS resin with the bimodal distribution was obtained by suspension polymerization using the prepolymer with bimodal distribution. The resin was superior with regard to balance of impact resistance and transparency.

Effect of mixing process on the fracture behavior of HA/PLLA Composites were investigated. Fracture toughness values of HA/PLLA composites prepared under different mixing time and rotor speed were measured. The fracture surface morphology was also examined by scanning electron microscopy. It was found that the fracture toughness of HA/PLLA composite decreases due to decrease of ductile deformation of PLLA matrix and debonding of interfaces with increase of the rotor speed and mixing time. Effect of mixing process on neat PLLA was also assessed, and it was found that the fracture toughness of PLLA decreases due to such pocess. Disappearance of multiple craze formation and thermal degradation were found to be the primary mechanisms of the toughness degradation.

Microscopic studies on the toughening mechanism of rubber-toughened PMMA (RTPMMA) were carried out using a polarizing optical microscope (POM) and a transmission electron microscope (TEM). POM result showed that in a typical RT-PMMA, a damage zone was developed in the vicinity of crack-tip, and therefore, it was considered that energy dissipation due to the damage zone development was the primary toughening mechanism. TEM result exhibited that the damage zone was a crowd of micro-crazes generated around rubber particles in the vicinity of notch-tip. Finite element analysis was then performed to simulate such damage formations in crack-tip region. Macro-scale and micro-scale models were developed to simulate damage zone formation and micro-crazing, respectively, with use of a damage model. It was shown that the damage model introduced was successfully applied to predict such kind of macro-damage and micro-craze formations.

Effect of annealing on the fracture behavior of poly(lactic acid) (PLA) was investigated. Fracture toughness of PLA samples prepared under different annealing conditions was measured under static and dynamic loadings. Microstructure and crack growth behavior were characterized by polarizing microscopy (POM). Crystallinity was determined by DSC analysis. Fracture surface morphology was also studied by scanning electron microscopy. It was shown that the static fracture toughness increased with increase of crystallinity, while the dynamic toughness increased as crystallinity increased. POM exhibited that craze formation played an important role in the fracture mechanism of amorphous samples. Macroscopic fracture toughness and microscopic crack growth mechanism were correlated on the basis of these experimental results, and effect of annealing on the toughness and mechanism were discussed.

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Effects of moisture absorption on the dynamic mode II interlaminar fracture behavior of two different kinds of carbon/epoxy composites at a low impact rate of 0.9 m/s were studied. ENF specimens were preconditioned under three different environmental conditions, that is, dry, 80°C-90% RH and 80°C-wet. Mode II interlaminar fracture toughnesses, GIIC, of the composites were then evaluated under quasi-static and dynamic loading. The results showed that moisture absorption had an influence on the GIICvalues of the composites. The experimental results also exhibited that the impact loading condition tended to decrease the GIIcvalues. Scanning electron micrography was also performed to characterize the micromechanisms of mode II interlaminar fracture. Effects of moisture absorption on the mode II interlaminar fracture behavior were then discussed on the basis of the results of the interlaminar fracture testing and microscopic studies.

Tensile testing of plain-weave-cloth-reinforced polyamide composites has been carried out at various strain rates ranging from 1×10−2to 4×101s−1in a servohydraulic testing apparatus. Four different polyamide composites studied were composed of two kinds of reinforcements, carbon fibre (CF) and glass fibre (GF), and two kinds of matrices, polyamide-6 (PA6) and modified polyamide-6 (mPA6). The experimental results showed that the tensile strength and failure strain of the composites tend to increase with increase in strain rate except in the case of GF/mPA6 whose fracture properties were stabilized at high rates (1×100s−1). Damaged regions of the fractured specimens were observed in order to study the micromechanisms of tensile failure by means of polarized optical and scanning electron microscopes. The microscope studies showed that in the composites with the mPA6 matrix, extensive microcracking occurred in the matrix and transverse threads region prior to the final failure. The effects of strain-rate on the tensile fracture behaviour of these types of composite systems are discussed on the basis of these experimental results.

Mode II interlaminar fracture tests of continuous fiber reinforced polyamide-6 composites were carried out at a quasi-static and a dynamic loading rate. Loadingrate dependence on the mode II interlaminar fracture toughness was investigated, and two different kinds of the composites, carbon fiber cloth reinforced polyamide-6 and glass fiber cloth reinforced polyamide-6, exhibited different loading-rate dependencies on the frao. ture toughness. Micromechanisms of the mode II interlaminar fracture were also studied using a scanning electron microscope. Loading-rate effects on the mode II interlaminar fracture behavior of the composites are discussed on the basis of the experimental results.

Dynamic mode II and mixed-mode interlaminar fracture toughnesses of CFRP laminates were measured using an instrumented impact testing system at a low impact speed (0.9 m/s). The system consisted of an instrumented drop weight impact tester and dynamic displacement measuring apparatus constructed from an optical fiber, position sensing detector and laser light source. The results showed that if dynamic interlaminar fracture toughness is estimated on the basis of load data obtained from a strain gage signal measured on the falling dart, the dynamic toughness could be overestimated, resulting in an erroneous understanding of the experimental results. It was also shown that the dynamic toughness can be evaluated accurately on the basis of the displacement data measured by the dynamic displacement measuring apparatus. It is thus concluded that the displacement-based analysis is more accurate and reliable than the load-based analysis in the measurement of the dynamic interlaminar fracture toughness of FRP laminates.

In this work, porous composite beams of HA/PLLA and HA/PLCL were developed using a combination of the template and freeze-drying methods. Their compositions were examined using Fourier transform infrared spectroscopy and X-ray diffraction spectroscopy. Their bending mechanical and fracture properties were characterized under the three-point bending condition. Their microstructures and the micro mechanisms of deformation and fracture were also examined by scanning electron microscopy. It was confirmed that the presence of polymer material did not affect the crystal structure of HA, and the diffraction pattern of both beams remained the same after sintering. Both composite beams showed dramatically improved flexural mechanical properties compared to a pure HA beam. Their bending fracture behavior was characterized as a crack initiation and growth accompanied by microdamage formation at the center. It was determined that microdamage formation and the subsequent deformation and fracture of the polymer phase was initiated by microfracture of HA struts. It was also found that the addition of PLLA results in a higher modulus and fracture strength, while the addition of PLCL results in a higher fracture energy due to ductile elongation.