Structure and properties of nitrocellulose: approaching 200 years of research.

This review brings together almost 200 years of fragmented research on the structure of nitrocellulose to give an overview that covers production to application in composite materials. As a mouldable plastic, energetic rocket propellant and biomolecular binding membrane, nitrocellulose still finds widespread practical application today despite the inception of synthetic plastics. The influence of different cellulose source materials affects the structure and properties of nitrocellulose in ways that are not fully understood, and so this review brings together relatively recent developments in the understanding of cellulose nanostructures to highlight where the gaps in understanding now reside. The influence of nitration conditions on the material properties of nitrocellulose is described, together with the proposed mechanisms and equilibria associated with these synthetic routes. The reported crystal structures of nitrocellulose are also reviewed, and the confirmed structural features are separated from those yet to be proven. We also consider how nitrocellulose interacts with other compounds, to help explain the distinct properties of its composite materials. This review points to further work that is required to obtain well founded structural models of nitrocellulose, while highlighting opportunities to control and direct its structure to improve its material properties.

High power, low frequency ultrasound: meniscal tissue interaction and ablation characteristics.

This study evaluates high power low frequency ultrasound transmitted via a flat vibrating probe tip as an alternative technology for meniscal debridement in the bovine knee. An experimental force controlled testing rig was constructed using a 20 kHz ultrasonic probe suspended vertically from a load cell. Effect of variation in amplitude of distal tip displacement (242-494 µm peak-peak) settings and force (2.5-4.5 N) on tissue removal rate (TRR) and penetration rate (PR) for 52 bovine meniscus samples was analyzed. Temperature elevation in residual meniscus was measured by embedded thermocouples and histologic analysis. As amplitude or force increases, there is a linear increase in TRR (Mean: 0.9 to 11.2 mg/s) and PR (Mean: 0.08 to 0.73 mm/s). Maximum mean temperatures of 84.6°C and 52.3°C were recorded in residual tissue at 2 mm and 4 mm from the ultrasound probe-tissue interface. There is an inverse relationship between both amplitude and force, and temperature elevation, with higher settings resulting in less thermal damage.

Extubation of the surgically resected airway--a role for remifentanil and propofol infusions.

PURPOSE: To report the use of propofol and remifentanil infusions to facilitate smooth extubation of a surgically resected airway. CLINICAL FEATURES: A 19-yr-old man weighing 85 kg was scheduled for tracheal resection surgery following postintubation tracheal stenosis. He had a relatively long segment (4 cm) of his trachea resected and anastomosed. Postoperatively, he was sedated and electively ventilated for four days in a chin to chest position by stay sutures. In order to reduce any risk of traumatic disruption to the tracheal anastomosis, we planned to extubate his trachea under light general anesthesia. Attempts to extubate his trachea using propofol and alfentanil infusions failed. We used propofol and remifentanil infusions to achieve a state of sedate cooperation and extubated his trachea with fibreoptic bronchoscope guidance. CONCLUSION: Propofol and remifentanil infusions in combination can facilitate successful extubation of the surgically resected airway with high risk of disruption.