Morphing in nature and beyond: a review of natural and synthetic shape-changing materials and mechanisms

Shape-changing materials open an entirely new solution space for a wide range of disciplines: from architecture that responds to the environment and medical devices that unpack inside the body, to passive sensors and novel robotic actuators. While synthetic shape-changing materials are still in their infancy, studies of biological morphing materials have revealed key paradigms and features which underlie efficient natural shape-change. Here, we review some of these insights and how they have been, or may be, translated to artificial solutions. We focus on soft matter due to its prevalence in nature, compatibility with users and potential for novel design. Initially, we review examples of natural shape-changing materials—skeletal muscle, tendons and plant tissues—and compare with synthetic examples with similar methods of operation. Stimuli to motion are outlined in general principle, with examples of their use and potential in manufactured systems. Anisotropy is identified as a crucial element in directing shape-change to fulfil designed tasks, and some manufacturing routes to its achievement are highlighted. We conclude with potential directions for future work, including the simultaneous development of materials and manufacturing techniques and the hierarchical combination of effects at multiple length scales.</p

Patient-controlled epidural analgesia after thoracotomy: A comparison of meperidine with and without bupivacaine

The purpose of this study was to compare meperidine to meperidine with bupivacaine when used for patient-controlled epidural analgesia (PCEA) after thoracotomy. For 3 days after thoracotomy patients received thoracic PCEA with meperidine 0.1% plain or with added bupivacaine 0.1% or 0.01%. No background infusion was used. All patients received indomethacin postoperatively for the duration of the study. Patients were assessed with respect to meperidine consumption, analgesia, and side effects. Sixty-six patients participated. Patients in all three groups obtained effective analgesia with median meperidine consumption of 5-6 mg/h. There were no significant differences between groups in meperidine consumption or pain scores at rest or with coughing. The addition of bupivacaine 0.1% reduced the incidence of pruritus (P = 0.036), but 5 of 23 patients in this group were withdrawn from the study because of significant hypotension, oliguria, and/or motor or sensory block (P = 0.006). We conclude that the addition of bupivacaine 0.1% or 0.01% to thoracic PCEA meperidine 0.1% does not affect meperidine requirements or analgesia after thoracotomy. The addition of bupivacaine 0.1% may reduce pruritus, but is associated with signs of excessive sensory, motor, or autonomic blockade in a significant number of patients

Continuous epidural ropivacaine 0.2% for analgesia after lower abdominal surgery

The purpose of this study was to determine whether a lumbar epidural infusion of ropivacaine 0.2% would provide effective analgesia with an acceptably low incidence of motor blockade and side effects after lower abdominal surgery. After combined general and epidural anesthesia and surgery, 125 patients were randomly assigned to receive either saline or ropivacaine 0.2% at a rate 6, 8, 10, 12, or 14 mL/h (Groups R6, R8, R10, R12, and R14, respectively) for 21 h. Supplemental analgesia, if required, was provided with intravenous patient-controlled analgesia with morphine. Data were collected at 4, 8, and 21 h, and included morphine consumption, pain scores at rest and with coughing, motor and sensory block, and adverse events. Cumulative morphine consumption was less in Groups R10, R12, and R14 compared with the saline group. At 4 h analgesia was better among patients receiving ropivacaine, but at 21 h pain scores were identical. Sensory blockade at 8 and 21 h was greater in the ropivacaine groups compared with the saline group. Approximately 30% of R8, R10, and R12 patients, and 63% of R14 patients had demonstrable motor block of the lower limbs at 21 hours. We conclude that lumbar epidural ropivacaine 0.2% reduces parenteral morphine requirements but has little effect on pain scores and may be associated with motor blockade