Thermally trainable dual network hydrogels.

Inspired by biological systems, trainable responsive materials have received burgeoning research interests for future adaptive and intelligent material systems. However, the trainable materials to date typically cannot perform active work, and the training allows only one direction of functionality change. Here, we demonstrate thermally trainable hydrogel systems consisting of two thermoresponsive polymers, where the volumetric response of the system upon phase transitions enhances or decreases through a training process above certain threshold temperature. Positive or negative training of the thermally induced deformations can be achieved, depending on the network design. Importantly, softening, stiffening, or toughening of the hydrogel can be achieved by the training process. We demonstrate trainable hydrogel actuators capable of performing increased active work or implementing an initially impossible task. The reported dual network hydrogels provide a new training strategy that can be leveraged for bio-inspired soft systems such as adaptive artificial muscles or soft robotics.

Strain Stiffening and Negative Normal Force of Agarose Hydrogels.

Inspired by the specific strain stiffening and negative normal force phenomena in several biological networks, herein, we show strain stiffening and negative normal force in agarose hydrogels. We use both pre-strain and strain amplitude sweep protocols in dynamic rheological measurements where the gel slip was suppressed by the in situ gelation in the cross-hatched parallel plate rheometer geometry. Within the stiffening region, we show the scaling relation for the differential modulus K ∝ σ1, where σ is stress. The strain at the onset of stiffening is almost constant throughout the concentration range. The gels show negative apparent normal stress difference when sheared as a result of the gel contraction. The pore size of the hydrogel is large enough to allow water to move with respect to the network to balance the pressure difference caused by the hoop stress. The rheological analysis together with scanning electron microscopy suggests that the agarose gels can be described using subisostatic athermal network models where the connectivity dictates the stiffening behavior. Therefore, the simple agarose gels appear to capture several of the viscoelastic properties, which were previously thought to be characteristic to biological protein macromolecules.

A comparison of the laryngeal tube and bag-valve mask ventilation by emergency medical technicians: a feasibility study in anesthetized patients.

Airway management is of major importance in emergency care. The basic technique for all health care providers is bag-valve mask (BVM) ventilation, which requires skill and may be difficult to perform. Endotracheal intubation, which is the advanced method for securing the airway, is a demanding technique that has been shown to be associated with infrequent success, even when used by experienced paramedical personnel. Therefore, alternative airway devices have been sought. The use of the laryngeal tube (LT) by experienced anesthesia personnel had been studied in anesthetized patients and manikins in emergency medical training. We decided to evaluate the ability of inexperienced firefighter-emergency medical technician students (fire-EMT) to insert the LT or perform BVM in anesthetized patients. Thirty fire-EMTs randomly inserted the LT (n = 15) and performed 1 min of ventilation or used the BVM (n = 15). We found that all students successfully (100%) inserted the LT. Those who inserted the LT on the first attempt (73%) required 48.2 +/- 14.7 s for the insertion. Both the LT and BVM provided adequate oxygenation and ventilation. In this study, we found that inexperienced fire-EMT students inserted LT and performed 1-min ventilation with a reasonable success rate and insertion time in anesthetized patients.

Supplemental oxygen does not reduce the incidence of postoperative nausea and vomiting after ambulatory gynecologic laparoscopy.

UNLABELLED: Supplemental 80% oxygen administration halves the incidence of postoperative nausea and vomiting (PONV) in inpatients. Whether it prevents PONV after ambulatory surgery is unknown. We tested the efficacy of supplemental 80% oxygen in decreasing the incidence of PONV after ambulatory gynecologic laparoscopy. One hundred patients were given a standardized sevoflurane anesthetic. They were randomly assigned to two groups: routine oxygen administration with 30% oxygen, balance nitrogen (Group A); and supplemental oxygen with 80% oxygen, balance nitrogen (Group B). Oxygen was administered during surgery and up to 1 h after surgery. The incidence of nausea and vomiting and the need for rescue antiemetics did not differ between the groups in the postanesthesia care unit, in the Phase II unit, or during the 24-h follow-up. The overall incidence of nausea and vomiting during the first postoperative 24 h was 62% in Group A and 55% in Group B (P = 0.486). There were no differences in the recovery profiles and patient satisfaction between the groups. In this study, supplemental oxygen did not prevent PONV in patients undergoing ambulatory gynecologic laparoscopy. IMPLICATIONS: Supplemental 80% oxygen administration during surgery and until 1 h after surgery compared with 30% oxygen administration did not prevent postoperative nausea and vomiting after ambulatory gynecologic laparoscopy.