A Mechanical Analysis of Chemically Stimulated Linear Shape Memory Polymer Actuation.

In the present work, we study the role of programming strain (50% and 100%), end loads (0, 0.5, 1.0, and 1.5 MPa), and chemical environments (acetone, ethanol, and water) on the exploitable stroke of linear shape memory polymer (SMP) actuators made from ESTANE ETE 75DT3 (SMP­E). Dynamic mechanical thermal analysis (DMTA) shows how the uptake of solvents results in a decrease in the glass temperature of the molecular switch component of SMP-E. A novel in situ technique allows chemically studying triggered shape recovery as a function of time. It is found that the velocity of actuation decreases in the order acetone > ethanol > water, while the exploitable strokes shows the inverse tendency and increases in the order water > ethanol > acetone. The results are interpreted on the basis of the underlying chemical (how solvents affect thermophysical properties) and micromechanical processes (the phenomenological spring dashpot model of Lethersich type rationalizes the behavior). The study provides initial data which can be used for micromechanical modeling of chemically triggered actuation of SMPs. The results are discussed in the light of underlying chemical and mechanical elementary processes, and areas in need of further work are highlighted.

An In Vitro Comparison Study of the Use of a Drill or a Saw in the Hunsuck-Dal Pont Modification of the Obwegeser Sagittal Split Osteotomy in Pig Mandibles.

PURPOSE: Fracture lines in unfavorable locations are referred to as "bad splits" in a mandibular sagittal split osteotomy (SSO). Several modifications of the technique by Obwegeser have been introduced to minimize this risk. This in vitro study was performed to determine whether the shape of the osteotomy cut affects the torque and the fracture pattern of an SSO in pig mandibles. MATERIALS AND METHODS: In a split-mouth model, 16 mandibles were split according to the Hunsuck-Dal Pont modification of the Obwegeser technique. Using an oscillating saw, sharp-edged osteotomies were created on one side of the mandible and round-edged osteotomies were created on the contralateral side using a Lindemann bur. Torque forces were measured during the splitting, and the lingual fracture pattern of each split was classified. RESULTS: Torque forces were significantly (P < .05 by paired t test) decreased by 0.77 N-m (15.6%) when a saw was used for the osteotomy. In the 2 groups, fractures were produced along the mandibular canal. The mandible was more often completely fractured, including the lower mandibular border, when the fracture was created with an oscillating saw (P = .06 by Pearson χ2 test). No correlation was found between the torque used and the fracture pattern. CONCLUSION: Compared with round-edged osteotomies, sharp-edged osteotomies in pig mandibles facilitated the Hunsuck-Dal Pont modification of the Obwegeser sagittal splitting procedure and produced predictable results with decreased torque.

In vitro comparison of the sagittal split osteotomy with and without inferior border osteotomy.

PURPOSE: By adding an osteotomy of the inferior border of the mandibular body to the classic sagittal split osteotomy, the authors expected to prevent unfavorable splits and damage to the inferior alveolar nerve. MATERIALS AND METHODS: Thirty-five human mandibles were used to perform 70 sagittal split osteotomies as an in vitro study. Conducted as a split-mouth model, each mandible was split at the midline. One side of the mandible was split using the traditional Obwegeser-Dal Pont technique, and the other side was split in the same manner with an additional osteotomy of the inferior mandible border. The torque used to split the mandible was measured, and the fracture line of the mandible was recorded. RESULTS: The average torque associated with the original technique was 1.38 Nm (standard deviation, 0.60 Nm), with a fracture line along the mandibular canal. The average torque required to split the hemimandible with the modified technique was 1.02 Nm (standard deviation, 0.50 Nm), a significant (P < .001) difference, with a fracture line parallel to the posterior ramus of the mandible. The fracture pattern depended significantly on the technique used (P < .001), but not on the applied torque force. CONCLUSION: By adding an osteotomy of the inferior mandibular border to the sagittal split osteotomy, less torque was needed to split the mandible. The fracture line was more predictable, even when all the surgical manipulations were performed at a safe distance from the inferior alveolar nerve.

Comparison of laparoscopic aortic clamps in a pulsatile circulation model.

PURPOSE: This study was designed to evaluate the fatigue characteristics and the safety and effectiveness of laparoscopic aortic clamps in a pulsatile circulation model. METHODS: A heart-lung machine was used to create a pulsatile circulation model with bovine aortas resembling the vessels being cross-clamped. Four different models (A-D) of laparoscopic aortic clamps were investigated, and three identical probes of each model underwent testing. Preliminary examinations were conducted to define the size and thickness of the bovine aortas that would allow effective cross-clamping and to detect gross material or functional deficits of the clamps. Then, the instruments were placed in the circulation model, which was set at a frequency of 82/min and a pressure of 200/120 mm Hg. Each clamp was subjected to these conditions for 120 hours and was opened and closed 40 times to stimulate real-life conditions. Clamping failures and mechanical defects were recorded, and the clamp parts were afterward examined with an electron microscope. RESULTS: Two clamp models had to be eliminated from the study after the preliminary examinations. All three probes of model B displayed mechanical defects after a few applications. All probes of model D were excluded because none effectively occluded the aortas. All probes of model A and one probe of model C provided effective cross-clamping during the 120-hour test phase and showed no signs of mechanical failure. Two probes of model C broke after 51 and 57 hours of testing, respectively. Both times, the defect occurred during application of the clamps. The detailed analysis of all instruments after the testing, including electron microscope imaging, revealed that several construction deficits and weak points were responsible for the mechanical failures. CONCLUSION: A surprisingly high incidence of clamping failures and mechanical deficits were encountered during the testing. Of the four clamps tested, only one (model A) seemed to be safe and effective enough for routine clinical use. These disappointing results demonstrate the need for further cooperation between vascular surgeons and instrument manufacturers to develop safe and effective laparoscopic vascular clamps.