Fabrication of a multi-layered decellularized amniotic membranes as tissue engineering constructs.

As a promising approach in tissue engineering, decellularization has become one of the mostly-studied research areas in tissue engineering thanks to its potential to bring about several advantages over synthetic materials since it can provide a 3-dimensional ECM structure with matching biomechanical properties of the target tissue. Amniotic membranes are the tissues that nurture the embryos during labor. Similarly, these materials have also been proposed for tissue regeneration in several applications. The main drawback in using amniotic membranes is the limited thickness of these materials since most tissues require a 3D matrix for an enhance regeneration. In order to prevent this limitation, here we report a facile fabrication methodology for multilayered amniotic membrane-based tissue constructs. The amniotic membranes of Wistar albino rats were first decellularized with the physical and chemical methods and utilized as scaffolds. Secondly, the prepared decellularized membranes were sutured to form a multilayered 3D structure. Within the study, 7 groups including control (PBS), were prepared based on physical and chemical decellularization methods. UV exposure and freezing techniques were used as a physical decellularization methods while hypertonic medium and SDS (sodium dodecyl sulfate) protocols were used as chemical decellularization methods. The combinations of both protocols were also used. In groups, A was the control and group B was applied just UV. In group C was applied UV and freezing. In addition to UV and freezing, in group D was applied hypertonic solution while group E was applied SDS (0.03 %). In group F was applied UV, freezing, hypertonic solution and SDS (0.03 %). In group G was applied UV, hypertonic solution, SDS (0.03 %) and freezing, respectively. Based on the histological and quantitative analyses, F and G groups were found as the most efficient decellularization protocols in rat amniotic membranes. Then, group F and G decellularized amniotic membranes were used to form scaffolds and thus-formed matrices were further characterized in vitro cell culture studies and mechanical tests. Cytotoxicity analyses performed using MTT showed a good cell viability in F and G groups scaffolds. The percentage viability rate was higher in G group (81.3 %) compared to F (75.33 %) and also cell viability in G group was found more meaningful according to p value which was obtained 0.007. Cellular adhesions after in vitro cell culture and morphology of scaffolds were evaluated by scanning electron microscopy (SEM). It was observed that the cells cultivated in equal amounts of tissue scaffolds were higher in the F compared to that observed in group G. The mechanical testing with 40 N force revealed 0.77 mm displacement in group F while it was 0.75 mm in group G. Moreover, according to force-controlled test, 2.9 mm displacement of F group and 1.2 mm displacement of G group was measured. As a result, this study shows that the multilayered decellularized amniotic membrane scaffolds support cell survival and adhesion and can form a flexible biomaterial with desired handling properties.

The Relationship Between Arthroplasty Surgeons' Experience Level and Optimal Cable Tensioning in the Fixation of Extended Trochanteric Osteotomy.

INTRODUCTION: In this study, our aim was to examine the relationship between the arthroplasty surgeons' experience level and their aptitude to adjust the cable tension to the value recommended by the manufacturer when asked to provide fixation with cables in artificial bones that underwent extended trochanteric osteotomy (ETO). MATERIALS AND METHODS: A custom-made cable tensioning device with a microvoltmeter was used to measure the tension values in Newtons (N). An ETO was performed on 4 artificial femur bones. Surgeons at various levels of experience attending the IXth National Arthroplasty Congress were asked to fix the osteotomized fragment using 1.7-mm cables and the tensioning device. The participants' demographic and experience data were investigated and recorded. The surgeons with different level of experience repeated the tensioning test 3 times and the average of these measurements were recorded. RESULTS: In 19 (35.2%) of the 54 participants, the force applied to the cable was found to be greater than the 490.33 N (50 kg) value recommended by the manufacturer. No statistically significant difference was determined between the surgeon's years of experience, the number of cases, and the number of cables used and the tension applied over the recommended maximum value (P = .475, P = .312, and P = .691, respectively). CONCLUSIONS: No significant relationship was found between the arthroplasty surgeon's level of experience and the adjustment of the cable with the correct tension level. For this reason, we believe that the use of tensioning devices with calibrated tension gauges by orthopedic surgeons would help in reducing the number of complications that may occur due to the cable.

Knotless anchors offer better prevention of meniscal excursion than knotted anchors: An experimental study of the bovine knee.

OBJECTIVE: Due to the biomechanical importance of the meniscal root ligament, several surgical techniques have been defined in order to treat meniscal root tear. Different application techniques have different levels of difficulty. We aimed to find a stronger and simpler repair technique. METHODS: Sixteen bovine knee joints were prepared. The posterior root of the medial meniscus was dissected and repaired with one of two different techniques. The knees in group 1 ("knotted group") were repaired with the knotted suture anchor technique, and the knees in group 2 ("knotless group") were repaired using the knotless suture anchor technique. The strength of the repairs was tested biomechanically. RESULTS: Cyclic loading tests were done. On the 0-20 N one-cycle test, the knotted anchor group's equivalent stiffness average was 5.28 N/mm, and the knotless anchor group's equivalent stiffness average was 5.48 N/mm. The 5-20 N two-cycle test results were 8.29 N/mm for the knotted group and 8.66 N/mm for the knotless group. On the 5-20 N 100-cycle test, the equivalent stiffness averages were 8.59 N/mm for the knotted group and 10.18 N/mm for the knotless group. Elongation was 5.83 mm for the knotted group and 4.86 mm for the knotless group. After performing load-to-failure tests, the failure forces were recorded as 237.83 N for the knotted group and 204.90 N for the knotless group. The failure test elongation values were 26.83 mm for the knotted group and 18.70 mm for the knotless group. The failure energies were 3.87 J for the knotted group and 1.83 J for the knotless group. Except for elongation until failure (p=0.009), there were no significant differences between the two groups tested (p>0.05). The average elongation was significantly less in group 2, showing that the knotless anchor had an advantage, with less meniscal excursion compared to the sutured anchor. CONCLUSION: Knotless anchors have a mechanical advantage over knotted anchors for preventing meniscal excursion. When thought together with technical simplicity during arthroscopic surgery, knotless anchors could be used safely for the fixation of the meniscal root ligament.

3D printed poly(ε-caprolactone) scaffolds modified with hydroxyapatite and poly(propylene fumarate) and their effects on the healing of rabbit femur defects.

A large variety of approaches have been used to treat large and irregular shaped bone defects with less than optimal success due to material or design issues. In recent years patient specific constructs prepared by additive manufacturing provided a solution to the need for shaping implants to fit irregular defects in the surgery theater. In this study, cylindrical disks of poly(ε-caprolactone) (PCL) were printed by fused deposition modeling and modified with nanohydroxyapatite (HAp) and poly(propylene fumarate) (PPF) to create a mechanically strong implant with well-defined pore size and porosity, controllable surface hydrophilicity (with PPF) and osteoconductivity (with HAp). Cytotoxicity, irritation and inflammation tests demonstrated that the scaffolds were biocompatible. PCL/HAp and PCL/HAp/PPF scaffolds were implanted in the femurs of rabbits with and without seeding with rabbit Bone Marrow Stem Cells (BMSC) and examined after 4 and 8 weeks with micro-CT, mechanically and histologically. BMSC seeded PCL/HAp/PPF scaffolds showed improved tissue regeneration as determined by bone mineral density and micro-CT. Compressive and tension stiffness values (394 and 463 N mm-1) were significantly higher than those of the healthy rabbit femur (316 and 392 N mm-1, respectively) after 8 weeks of implantation. These 3D implants have great potential for patient-specific bone defect treatments.

Mechanical design, analysis, and laboratory testing of a dental implant with axial flexibility similar to natural tooth with periodontal ligament.

At the interface between the jawbone and the roots of natural teeth, a thin, elastic, shock-absorbing tissue, called the periodontal ligament, forms a cushion which provides certain flexibility under mechanical loading. The dental restorations supported by implants, however, involve comparatively rigid connections to the jawbone. This causes overloading of the implant while bearing functional loading together with neighboring natural teeth, which leads to high stresses within the implant system and in the jawbone. A dental implant, with resilient components in the upper structure (abutment) in order to mimic the mechanical behavior of the periodontal ligament in the axial direction, was designed, analyzed in silico, and produced for mechanical testing. The aims of the design were avoiding high levels of stress, loosening of the abutment connection screw, and soft tissue irritations. The finite element analysis of the designed implant revealed that the elastic abutment yielded a similar axial mobility with the natural tooth while keeping stress in the implant at safe levels. The in vitro mechanical testing of the prototype resulted in similar axial mobility predicted by the analysis and as that of a typical natural tooth. The abutment screw did not loosen under repeated loading and there was no static or fatigue failure.

Impact of fibular torsion and rotation on chronic ankle instability.

BACKGROUND: The fibula is known not to involve in transmission of weight but known simply as an ankle stabilizer. However, its main function in stabilizing the ankle remains obscure. Since the fibula has an impact on torsion and rotation of the ankle, its effect on lateral ankle instability should be investigated. MATERIALS AND METHODS: Twenty patients with lateral ankle instability (Group 1) and 19 healthy volunteers (Group 2) were included in the study. The tibiofibular and talofibular relationships were evaluated using MRI images. Fibular torsion and rotation angles were calculated using a new method. Range of motion of the ankle joint was investigated while the knee was at flexion (90°) and extension (0°). The comparisons performed between the 2 groups and independent from the groups were statistically evaluated and, the p value of <0.05 was considered as statistically significant. RESULTS: A significant difference was found between the two groups for age (p<0.05). There were no statistically significant differences between the right and left sides for all measurements in the group 1 and 2 (p>0.05). There was a statistically significant difference between the two groups in dorsal flexion when the knee is at flexion (90°) and extension (0°) position. There was also a statistically significant difference between the two groups in plantar flexion which was measured while the knee was at extension (0°) position. No statistically significant difference was found between both groups in terms of fibular torsion and rotation. However, independent from the groups when the patients were divided into 2 groups according to whether the fibula localized posteriorly or not, in patients with posteriorly localized fibula it was demonstrated that the fibular torsion and rotation was increased significantly. CONCLUSION: We did not detect any relationship between fibular torsion and rotation and ankle instability. However, independent from the groups when the patients were divided into 2 groups according to whether the fibula localized posteriorly or not, we realized that in patients with posteriorly localized fibula, fibular torsion and rotation significantly increased. This finding did not explain the cause of instability. However, it may gain significance with new further studies regarding ankle instability.

Non-integer viscoelastic constitutive law to model soft biological tissues to in-vivo indentation.

PURPOSE: During the last decades, derivatives and integrals of non-integer orders are being more commonly used for the description of constitutive behavior of various viscoelastic materials including soft biological tissues. Compared to integer order constitutive relations, non-integer order viscoelastic material models of soft biological tissues are capable of capturing a wider range of viscoelastic behavior obtained from experiments. Although integer order models may yield comparably accurate results, non-integer order material models have less number of parameters to be identified in addition to description of an intermediate material that can monotonically and continuously be adjusted in between an ideal elastic solid and an ideal viscous fluid. METHODS: In this work, starting with some preliminaries on non-integer (fractional) calculus, the "spring-pot", (intermediate mechanical element between a solid and a fluid), non-integer order three element (Zener) solid model, finally a user-defined large strain non-integer order viscoelastic constitutive model was constructed to be used in finite element simulations. Using the constitutive equation developed, by utilizing inverse finite element method and in vivo indentation experiments, soft tissue material identification was performed. RESULTS: The results indicate that material coefficients obtained from relaxation experiments, when optimized with creep experimental data could simulate relaxation, creep and cyclic loading and unloading experiments accurately. CONCLUSIONS: Non-integer calculus viscoelastic constitutive models, having physical interpretation and modeling experimental data accurately is a good alternative to classical phenomenological viscoelastic constitutive equations.

Predicting bone remodeling around tissue- and bone-level dental implants used in reduced bone width.

The objective of this study was to predict time-dependent bone remodeling around tissue- and bone-level dental implants used in patients with reduced bone width. The remodeling of bone around titanium tissue-level, and titanium and titanium-zirconium alloy bone-level implants was studied under 100 N oblique load for one month by implementing the Stanford theory into three-dimensional finite element models. Maximum principal stress, minimum principal stress, and strain energy density in peri-implant bone and displacement in x- and y- axes of the implant were evaluated. Maximum and minimum principal stresses around tissue-level implant were higher than bone-level implants and both bone-level implants experienced comparable stresses. Total strain energy density in bone around titanium implants slightly decreased during the first two weeks of loading followed by a recovery, and the titanium-zirconium implant showed minor changes in the axial plane. Total strain energy density changes in the loading and contralateral sides were higher in tissue-level implant than other implants in the cortical bone at the horizontal plane. The displacement values of the implants were almost constant over time. Tissue-level implants were associated with higher stresses than bone-level implants. The time-dependent biomechanical outcome of titanium-zirconium alloy bone-level implant was comparable to the titanium implant.

Effects of custom-made insole on gait pattern of patients with unilateral displaced intra-articular calcaneal fracture: evaluation with computerized gait analysis.

OBJECTIVE: The aim of this study was to investigate whether use of custom-fabricated insoles improves the gait pattern in patients with displaced intra-articular calcaneal fractures. METHODS: Fourteen patients (7 female, 7 male; mean age: 39 ± 12 years) and 11 healthy individuals (mean age: 42 ± 13 years) were included in the study. Treatment protocol included conservative treatment involving immobilization, with or without closed reduction, active exercises, wear of a custom-fabricated insole and prospective follow-up. All patients were evaluated by physical examination, axial and lateral radiographs, computerized tomography, and computerized gait analysis. RESULTS: The use of custom-made insoles significantly improved step and stride lengths and the peak values of fore-aft component in the involved foot and tended to increase plantar flexor moment and total ankle power. The majority of patients (71%) continued to have substantial mechanical abnormalities by computerized gait analysis. Plantar flexion moment, total ankle power, vertical component of ground reaction forces (GRFs), and total sagittal plane excursion were significantly decreased in the involved foot when compared to the uninvolved foot. Plantar flexion moment, total ankle power, vertical, fore-aft and mediolateral components of GRFs were significantly decreased in the involved foot when compared to the healthy control group. CONCLUSION: Use of a custom-made insole improves advancement of limb and weight-bearing in patients with a displaced intra-articular calcaneal fracture. Nevertheless, mechanical abnormalities persist in the affected limb, which does not appear to recover a gait pattern similar to that of normal walking.

Ankle clonus and its relationship with the medium-latency reflex response of the soleus by peroneal nerve stimulation.

Ankle clonus and soleus medium-latency reflex are stretch-induced responses. Clonus is traditionally considered to be the result of oscillation in the group Ia mediated spinal stretch reflex but the soleus medium-latency reflex response originates mainly from the activation of group II afferents. The medium latency reflex response (MLR) was recorded in soleus muscle by peroneal nerve stimulation and clonus beats were recorded in soleus muscle using EMG in 19 spastic patients. The dorsiflexion (DF) and plantarflexion (PF) times of clonus and the half-period were calculated based on accelerometric measurements in 11 patients. The MLR of the soleus was 73.63 ± 8.9 ms. The half-period of the clonus was 79.34 ± 12.31 ms. The difference between the MLR and half-period was significant. The PF was 71.75 ± 6.73 ms, and the DF was 88.63 ± 10.83 ms. The difference between the soleus MLR and PF part of the clonus beat was not significant. The PF part of the clonus beat is due to soleus muscle contraction and controlled by the neural part of the oscillation. There may be relationship between the soleus MLR and the PF part of the clonus. Clonus is considered to be the result of oscillations in the group Ia spinal stretch reflex, but there is sufficient time for group II afferents to be involved.

Predicting time-dependent remodeling of bone around immediately loaded dental implants with different designs.

The purpose of this study was to predict time-dependent biomechanics of bone around cylindrical screw dental implants with different macrogeometric designs under simulated immediate loading condition. The remodeling of bone around a parallel-sided and a tapered dental implant of same length was studied under 100N oblique load by implementing the Stanford theory into three-dimensional finite element models. The results of the analyses were examined in five time intervals consisting loading immediately after implant placement, and after 1, 2, 3 and 4 weeks following implantation. Maximum principal stress, minimum principal stress, and strain energy density in peri-implant bone and displacement in x-(implant lateral direction with a projection of the oblique force) and y-(implant longitudinal direction) axes of the implant were evaluated. The highest value of the maximum and minimum principal stresses around both implants increased in cortical bone and decreased in trabecular bone. The maximum and minimum principal stresses in cortical bone were higher around the tapered cylindrical implant, but stresses in the trabecular bone were higher around the parallel-sided cylindrical implant. Strain energy density around both implants increased in cortical bone, slightly decreased in trabecular bone, and higher values were obtained for the parallel-sided cylindrical implant. Displacement values slightly decreased in time in x-axis, and an initial decrease followed by a slight increase was observed in the y-axis. Bone responded differently in remodeling for the two implant designs under immediate loading, where the cortical bone carried the highest load. Application of oblique loading resulted in increase of stiffness in the peri-implant bone.

Numeric simulation of time-dependent remodeling of bone around loaded oral implants.

PURPOSE: The objective of this study was to investigate the time-dependent biomechanics of marginal bone around osseointegrated dental implants within physiologic loading conditions. MATERIALS AND METHODS: The remodeling of marginal bone around a 4.1-mm-diameter, 10-mm-long implant was studied by implementing the Stanford theory into axisymmetric mathematical models simulating different bone support at the implant neck: 1-mm-thick cortical bone (model 1), 0.5-mm-thick cortical bone (model 2), absence of cortical bone (model 3), and absence of cortical bone with 0.5 mm of resorption of marginal trabecular bone (model 4). The results were examined separately for all models at five time intervals: the first loading after osseointegration and 3, 6, 9, and 12 months after osseointegration. Minimum principal stress, maximum principal stress, strain energy, total equivalent strain, displacement, average elastic modulus, and bone density were evaluated. RESULTS: In models 1 and 2, the magnitude of the stresses increased during the 1-year period. The distributions of stresses in models 3 and 4 were less variable and lower than models with cortical bone. The region of high stresses enlarged during the first 3 months and then decreased over time. There was a time-dependent increase in strain energy density around the neck of the implant in models 1 and 2. The time-dependent displacement values of implants were almost constant over time (maximum 1 Mum change). The lowest implant displacement values were observed in model 1. There was a slight increase in the elastic modulus of cortical bone and a decrease in trabecular bone (maximum 1% change). CONCLUSION: The time-dependent increase in stresses in the marginal zone of the implants with cortical bone support was higher than that of the implants supported solely by trabecular bone in the first year of function. Higher strain energy density around the implants with cortical bone support might indicate apposition and increase in interface stiffness, whereas lower strain energy density around implants supported solely by trabecular bone could be associated with skeletal tissue loss.

Axial rotation and mediolateral translation of the fibula during passive plantarflexion.

BACKGROUND: Since the fibula is linked to the ankle as well as the knee joint, its importance for knee and ankle disabilities should be investigated. This study evaluates its movement during range of motion of the ankle. MATERIALS AND METHODS: An instrument, together with the experimental protocol, was devised to determine the relative motion of the fibula in reference to the tibia with motion of the ankle joint on 20 paired lower extremity cadaver specimens. RESULTS: It was demonstrated in all specimens that the fibula had a relative rotation around its longitudinal axis and mediolateral translation with reference to the tibia with ankle motion. The distal end of the fibula rotates more compared to the proximal end. The mediolateral translation of the proximal end of the fibula is rather close to that of the distal end. Although there was no consistent pattern for rotation, dorsiflexion caused lateral translation and plantarflexion caused medial displacement for most of the specimens. CONCLUSION: A novel, invasive but relatively simple test setup was devised. Movement of the fibula which is important for the kinematics and kinetics of the knee and ankle joints was evaluated by this new device. CLINICAL RELEVANCE: Evaluation of the fibula movement in normal lower extremities may lead to better understanding of its dynamic function which could have treatment implications for pathological conditions.

Numerical study of the aerodynamic effects of septoplasty and partial lateral turbinectomy.

OBJECTIVES: To investigate, first, the effects of septal deviation and concha bullosa on nasal airflow, and second, the aerodynamic changes induced by septoplasty and partial lateral turbinectomy, using computational fluid dynamics (CFD). METHODS: A three-dimensional model of a nasal cavity was generated using paranasal sinus computed tomography images of a cadaver with concha bullosa and septal deviation. Virtual septoplasty and partial lateral turbinectomy were performed on this model to generate a second model representing the postoperative anatomy. Aerodynamics of the nasal cavity in the presence of concha bullosa and septal deviation as well as postoperative changes due to the virtual surgery were analyzed by performing CFD simulations on both models. Inspiratory airflow with a constant flow rate of 500 mL/second was used throughout the analyses. RESULTS: In the preoperative model, the airflow mostly pass through a narrow area close to the base of the nasal cavity. Following the virtual operation, a general drop in the maximum intranasal air speed is observed with a significant increase of the airflow through right middle meatus. While in the preoperative model the greatest reduction in pressure is found to be in the localization of anterior septal deviation on the right side and confined to a very short segment, for the postoperative model, it is observed to be in the nasal valve region in both nasal cavities. Following septoplasty and partial lateral turbinectomy, total nasal resistance is reduced significantly. CONCLUSIONS: CFD simulations promise to make great contributions to understand the airflow characteristics of healthy and pathologic noses. Before surgery, planning for any specific intervention using CFD techniques on the nasal cavity model of the patient may help foreseeing the aerodynamic effects of the operation and might increase the success rate of the surgical treatment.

Dynamic function of the fibula. Gait analysis evaluation of three different parts of the shank after fibulectomy: proximal, middle and distal.

The purpose of this case study was to investigate the dynamic features of fibular movement to gait pattern by analyzing the gait of individuals with three different parts of the fibula resected. Gait analyses revealed that proximal fibula resection impaired knee stability, whereas distal fibula resection disturbed ankle kinematics significantly. Except a mild secondary quadriceps weakness, middle fibula resection did not cause a significant biomechanical disturbance on gait.

The annular ligament: an anatomical study.

BACKGROUND: Despite documentations of ligamentous structures of the elbow, the anatomy and clinical and functional importance of the annular ligament has not been comprehensively defined in the orthopaedic literature. HYPOTHESIS: The annular ligament is an important component of both the proximal radioulnar and humeroradial joints, as well as an important component of the neighboring muscles and ligaments. STUDY DESIGN: Descriptive laboratory study. MATERIALS AND METHODS: To investigate the annular ligament and its relationship with neighboring structures, macroscopic and microscopic dissections were performed on both upper extremities of 30 cadavers (12 female and 18 male) fixed in 10% formaldehyde and on 1 upper extremity of a fresh cadaver (male). RESULTS: The distal ulnar insertion of discrete fibers on the supinator crest was defined as the inferior oblique band of the annular ligament, and the proximal insertion of the annular ligament was defined as the superior oblique band of the annular ligament. These patterns were noted in all specimens. It was difficult to distinguish the fibers of the supinator muscle in every specimen because they were intimately fused with the fibers of the annular ligament. CONCLUSIONS: The superior and inferior oblique bands of the annular ligament attached proximally and distally onto the ulna, thus helping to secure the annular ligament in place.

Functional evaluation of intraarticular severely comminuted fractures of the calcaneus with gait analysis.

Twenty-one patients (23 feet) treated nonsurgically for severely comminuted intraarticular fractures of the calcaneus were evaluated prospectively with a clinical scoring scale and computerized gait analysis. All patients had Sanders type III and type IV fractures. The treatment protocol consisted of no closed reduction, immobilization in removable splint, physiotherapy after edema subsided, and weightbearing after 8 weeks. All patients had a minimum follow-up of 2 years (mean, 38 months). Clinical results were good in 2 patients, fair in 3 patients, and poor in 16 patients. Gait analysis showed that patients were at high risk of gastrocnemius weakness and ankle and knee instability. These results may be useful for comparison with the results of other methods, such as open reduction and internal fixation, nonsurgical closed reduction, and arthrodesis.

Accuracy of a manual torque application device for morse-taper implants: a technical note.

PURPOSE: The objective of this study was to compare torques applied by new and used manual torque devices for Morse-taper implants. MATERIAL AND METHODS: Fifteen ITI manual torque devices were tested. Those in group 1 (n = 5) were new (ie, never used), those in group 2 (n = 5) had been used 50 to 200 times, and those in group 3 (n = 5) had been used 500 to 1,000 times. The torques applied by each device were measured for 35 Ncm and 15 Ncm targets in an experimental setup by a custom-made wrench with strain gauges connected to a data acquisition system. The strain-gauge signals were simultaneously delivered to a computer at a sample rate of 10,000 Hz and converted to torque units. RESULTS: New devices applied higher torques than used devices for the 35-Ncm torque target (P < .05). The torques applied by group 3 devices were approximately 1.5 Ncm lower than those of other groups for the 35-Ncm target and approximately 1 Ncm lower for the 15-Ncm target. DISCUSSION AND CONCLUSION: ITI manual torque devices deliver consistent torque output, although a slight decrease occurs as a consequence of clinical use.

Nonlinear viscoelastic material property estimation of lower extremity residual limb tissues.

Axisymmetric nonlinear finite-element analysis was used to simulate force-relaxation and creep data obtained during in vivo indentation of the residual limb soft tissues of six individuals with trans-tibial amputation [1]. The finite-element models facilitated estimation of an appropriate set of nonlinear viscoelastic material coefficients of extended James-Green-Simpson material formulation for bulk soft tissue at discrete, clinically relevant test locations. The results indicate that over 90% of the experimental data can be simulated using the two-term viscoelastic Prony series extension of James-Green-Simpson material formulation. This phenomenological material formulation could not, however, predict the creep response from relaxation experiments, nor the relaxation response from creep experiments [2-5]. The estimated material coefficients varied with test location and subject indicating that these coefficients cannot be readily extrapolated to other sites or individuals.