Impact of NaOH based perfusion-decellularization protocol on mechanical resistance of structural bone allografts.

INTRODUCTION: To mitigate the post-operative complication rates associated with massive bone allografts, tissue engineering techniques have been employed to decellularize entire bones through perfusion with a sequence of solvents. Mechanical assessment was performed in order to compare conventional massive bone allografts and perfusion/decellularized massive bone allografts. MATERIAL AND METHODS: Ten porcine femurs were included. Five were decellularized by perfusion. The remaining 5 were left untreated as the "control" group. Biomechanical testing was conducted on each bone, encompassing five different assessments: screw pull-out, 3-points bending, torsion, compression and Vickers indentation. RESULTS: Under the experimental conditions of this study, all five destructive tested variables (maximum force until screw pull-out, maximum elongation until screw pull-out, energy to pull out the screw, fracture resistance in flexion and maximum constrain of compression) were statistically significantly superior in the control group. All seven nondestructive variables (Young's modulus in flexion, Young's modulus in shear stress, Young's modulus in compression, Elastic conventional limit in compression, lengthening to rupture in compression, resilience in compression and Vickers Hardness) showed no significant difference. DISCUSSION: Descriptive statistical results suggest a tendency for the biomechanical characteristics of decellularized bone to decrease compared with the control group. However, statistical inferences demonstrated a slight significant superiority of the control group with destructive mechanical stresses. Nondestructive mechanical tests (within the elastic phase of Young's modulus) were not significantly different.

Mechanical assessment of novel compliant mechanisms for underactuated prosthetic hands.

This paper proposes novel compliant mechanisms for constructing hand prostheses based on soft robotics. Two models of prosthetic hands are developed in this work. Three mechanical evaluations are performed to determine the suitability of the two designs for carrying out activities of daily living (ADLs). The first test measures the grip force that the prosthesis can generate on objects. The second determines the energy required and dissipated from the prosthesis to operate. The third test identifies the maximum traction force that the prosthesis can support. The tests showed that the PrHand1 prosthesis has a maximum grip force of 23.38 ± 1.5 N, the required energy is 0.76 ± 0.13 J, and the dissipated energy is 0.21 ± 0.17 J. It supports a traction force of 173.31 ± 5.7 N. The PrHand2 prosthesis has a maximum grip force of 36.13 ± 2.3 N, the required energy is 1.28 ± 0.13 J, the dissipated energy is 0.96 ± 0.12 J, and it supports a traction force of 78.48 ± 0 N. In conclusion, the PrHand1 prosthesis has a better performance in terms of energy and tensile force supported. The difference between the energy and traction force results is related to two design features of the PrHand2: fully silicone-coated fingers and a unifying mechanism that requires more force on the tendons to close the prosthesis. The grip force of the PrHand2 prosthesis was more robust than the PrHand1 due to its silicone coating, which allowed for an improved grip.

Mechanical Performance Assessment of Physician Modified Aortic Stent Graft.

OBJECTIVE: This study aimed to compare various fenestration configurations of physician modified aortic stent grafts in order to identify which design parameters have a significant influence on the mechanical behaviour of the fenestration. METHODS: the fenestration configurations were considered according to different manufacturing parameters: cutting technique, fenestration reinforcement, suture material, reinforcement loop design, and number of suture points. The performance of the graft/bridging stent assembly was assessed at various levels: (1) branch pull out force; (2) fenestration enlargement and rupture strength; (3) balloon angioplasty resistance; and (4) behaviour under cyclic fatigue. RESULTS: Sixty manual fenestrations were created. The tests performed on the fenestrations had several main findings. First, reinforcement increased the radial force on the branch, which increased the pull out force; this may limit migration of the bridging stent in vivo. The phenomenon was amplified with a snare reinforced fenestration, which seemed to be the most efficient. Moreover, increasing the number of suture passes also appeared to increase the branch extraction force securing the assembly. The enlargement tests showed that non-reinforced fenestrations had the weakest radial strength. This was confirmed with the balloon angioplasty test, which showed that these latter specimens undergo the most significant textile degradation. After fatigue tests, all fenestrations were larger, showing that elastic recoil was incomplete in all samples. The largest recoil was observed in the non-reinforced ophthalmological cautery (OC) fenestrations (40%). Regarding the behaviour of the samples up to rupture, all samples behaved in a similar way; however, the double loop fenestration strength level was the highest. CONCLUSION: This study demonstrated that the snare double loop reinforcement has an advantage regarding durability of the graft branch assembly. Moreover, non-reinforced fenestrations show signs of weakness and lack of stability, which questions the in situ or laser fenestration procedures.

An AFM study of the nanostructural response of New Zealand white rabbit Achilles tendons to cyclic loading.

The nanostructural response of New Zealand white rabbit Achilles tendons to a fatigue damage model was assessed quantitatively and qualitatively using the endpoint of dose assessments of each tendon from our previous study. The change in mechanical properties was assessed concurrently with nanostructural change in the same non-viable intact tendon. Atomic force microscopy was used to study the elongation of D-periodicities, and the changes were compared both within the same fibril bundle and between fibril bundles. D-periodicities increased due to both increased strain and increasing numbers of fatigue cycles. Although no significant difference in D-periodicity lengthening was found between fibril bundles, the lengthening of D-periodicity correlated strongly with the overall tendon mechanical changes. The accurate quantification of fibril elongation in response to macroscopic applied strain assisted in assessing the complex structure-function relationship in Achilles tendons.

A multiscale study of morphological changes in tendons following repeated cyclic loading.

The response of white New Zealand rabbit Achilles tendons to load was assessed using mechanical measures and confocal arthroscopy (CA). The progression of fatigue-loading-induced damage of the macro- (tenocyte morphology, fiber anisotropy and waviness), as well as the mechanical profile, were assessed within the same non-viable intact tendon in response to prolonged cyclic and static loading (up to four hours) at different strain levels (3%, 6% and 9%). Strain-mediated repeated loading induced a significant decline in mechanical function (p < 0.05) with increased strain and cycles. Mechanical and structural resilience was lost with repeated loading (p < 0.05) at macroscales. The lengthening of D-periodicity correlated strongly with the overall tendon mechanical changes and loss of spindle shape in tenocytes. This is the first study to provide a clear concurrent assessment of form (morphology) and function (mechanics) of tendons undergoing different strain-mediated repeated loading at multiple-scale assessments. This study identifies a variety of multiscale properties that may contribute to the understanding of mechanisms of tendon pathology.

Production and characterization of bovine hoof membranes as standardized in vitro model for nail studies.

Several studies can be found using bovine hoof membranes as a nail in vitro model. Most of them are actually permeability studies, while it is very hard to find reference in literature related to the use of those membranes to evaluate safety and efficacy of products. In facts, some effects, both desirable or not, are not strongly related to the penetration of the products thru all of the nail plate keratin layers. There are morphological characteristics and properties such as mechanical ones which could be affected even by a product acting on the surface of the nail. Moreover, hoof membranes production is not a standardized procedure, as well as membranes characterization which is a critical step to deal with when we are looking for a specific in vitro model. In this work, hoof membranes production is described in detail, along with the characterization techniques and parameters chosen for studying the model, such as contact angle measurement and mechanical properties assessment. The production method developed in this work has shown to be effective, making it possible to obtain membranes with desirable thickness, homogenous morphology and suitable mechanical properties. Mechanical properties were the most challenging to be assessed, also for the poor coverage of the topic by scientific literature. In particular the mechanical assessment has never been used before with this specific aim thus this research could be considered as a feasibility protocol in order to obtain a suitable nail model for further studies concerning drug permeability or safety and efficacy of final products .

Transmission efficiency of Ilizarov external fixator orthopedic force based on coordinate transformation theory / 中国组织工程研究

BACKGROUND: The study on the mechanism of force conduction of Ilizarov bone external fixator is of great significance for clinical orthodontics of the knee varus, the knee valgus and the tibial fracture. OBJECTIVE: To explore the force conduction mechanism of Ilizarov bone external fixator and the force changes of each orthopedic force in the process of tibia correction, and to objectively evaluate the overall use effect of the external fixator. METHODS: According to the structure of the external fixator, the coordinate transformation matrix relations were established, and the mathematical transformation relationship between the holding force and the pulling tension was obtained. A special laboratory bench was set. The experiment of tibia correction was conducted. The load on the external fixator and the variation of the orthotic force were measured. The theoretical value of the tension at the broken bone is calculated and compared with the actual value of the tension measured by the six-dimensional force sensor. The curve of efficiency of force transmission during correction was obtained. RESULTS AND CONCLUSION: (1) During the correction, the structure of the Ilizarov bone external fixator resulted in the interaction and restriction of its adjustment rod and support rod. When one adjustment force increased, the other adjustment force would decrease. (2) The efficiency of force transmission was increased greatly in the early stage, and then stabilized at about 50%. The experimental results could evaluate the overall correction effect of the external fixator. (3) Theoretical calculation and experiment of the tension at the broken bone due to the loss during the force transmission process were different in the result curves, but from the experimental results, it could be indicated that the overall force change trend of the adjustment force, supporting force, the theoretical value of the tension and the actual value of the tension was basically the same, indicating the validity of the theoretical calculations and experimental results. The evaluation results can provide a reference for the optimal design of Ilizarov’s external fixation architecture and the precise control of tibial orthopedic surgery.

Mechanical Safety of Embedded Electronics for In-body Wearables: A Smart Mouthguard Study.

The growing popularity of contact sports drives the requirement for better design of protective equipment, such as mouthguards. Smart mouthguards with embedded electronics provide a multitude of new ways to provide increased safety and protection to users. Characterisation of how electronic components embedded in typical mouthguard material, ethylene vinyl acetate (EVA), behave under typical sports impacts is crucial for future designs. A novel pendulum impact rig using a hockey ball disc impactor was developed to investigate impact forces and component failure. Two sets of dental models (aluminium and plastic padding chemical metal) were used to manufacture post-thermoformed mouthguards. Seven embedding conditions with varying thickness of EVA (1.5 and 3 mm) and locations of electrical components were tested. Component failures were observed in four out of seven test conditions, and the experimental failure forces at which the electrical component had a 50% chance of failure were reported for those cases. The experimental results showed that an EVA thickness of 3 mm surrounding the electrical component gives the most comprehensive protection even under extreme surface conformity. Computational models on surface conformity of EVA showed that a block of EVA with a minimum thickness of 1.5 mm was better at reducing stress concentration than a shell with an overall thickness of 1.5 mm. This study demonstrated that the thickness of a mouthguard is important when protecting electrical components from extreme dental surface conformity, furthermore the surface geometry should not be overlooked when considering electrical component safety for in-body wearables that are impact prone.

Mechanical assessment of tripled hamstring tendon graft when using suspensory fixation for cruciate ligament reconstruction.

BACKGROUND: Tripling semitendinosus tendon for ACL graft preparation facilitates creation of longer and thicker grafts. Our objective was to evaluate the mechanical difference between tripled tendon grafts, prepared by three methods, by comparing with quadrupled tendon graft. METHODS: Bovine hind-foot hoof extensors were allocated to four groups. Group I had quadrupled graft construct. Tripled graft constructs were prepared by passing the tendon to the Endobutton CL loop and stitching the third strand to (i) the loop (in Group II) or (ii) to one strand(in Group III) or (iii)to loop and both tendon strands (in Group IV). The constructs were preloaded from 10 to 50 N at 0.1 Hz for 10 cycles, followed by 1000 cycles of sinusoidal loading between 50 and 250 N at a frequency of 0.5 Hz. The specimens were then subjected to load to failure test at the rate of 50 mm/min. Displacement with cyclic loading, load at failure and the mode of failure were noted. RESULTS: The load at failure was 957 ± 23.30 N (Mean ± Standard Deviation) in Group I, 590.8 ± 24.40 N in Group II, 682.6 ± 59.28 N in Group III and 963.4 ± 21.72 N in Group IV. The displacement with cyclic loading was 1.13 ± 0.11 mm in Group I, 4.908 ± 0.55 mm in Group II, 1.822 ± 0.55 mm in Group III and 1. 126 ± .018 mm in Group IV. There was no significant difference between the Groups I and IV with respect to the load at failure and displacement (p > 0.05). The values were significantly different in Group II and Group III (p < 0.01), when compared to groups I and IV. CONCLUSIONS: Tripled grafts have mechanical properties equivalent to quadrupled grafts only when the three strands are sutured together. Caution may be warranted when using suspensory fixation device with tripled tendons and the third strand must be securely attached to the loop of fixation device and to the other two strands.