Exploiting Nonlinear Elasticity for Anomalous Magnetoresponsive Stiffening.

A paradigm for enhanced magnetorheological elastic materials is introduced and experimentally established. We show that a nonlinearly stiffening polymer matrix can be exploited to achieve anomalous magneto-elastomer stiffening exceeding standard magneto-elastomer theory and experiment in terms of percentage stiffness change and sensitivity to applied magnetic flux. Using a model system of a semiflexible fibrin network embedded with micron sized carbonyl iron particles, we demonstrate that even at a modest particle volume fraction (0.5-4%), a coupling between the magnetically interacting dipoles and a strain-stiffening polymer mesh provides previously unexplored opportunities for material design. Our experiments indicate that confined particles within the fibrin network internally tension and stiffen the polymer mesh when an external field is applied, resulting in a field-dependent stiffening response from the polymer mesh that superposes with the magnetic interparticle interactions.

Stapedotomy using a 4 mm endoscope: any advantage over a microscope?

OBJECTIVES: To ascertain the feasibility of endoscopic (4 mm) stapedotomy, and compare intra- and post-operative variations with microscopic stapedotomies. METHODS: Forty otosclerosis patients were scheduled for microscopic or endoscopic stapedotomy. Intra-operative variables compared were: incision, canalplasty, canal wall curettage for ossicular assessment, chorda tympani manipulation, ability to perform stapes footplate perforation before its supra-structure removal, and operative time. Post-operative variables compared were ear pain and hearing improvement. RESULTS: Of the 20 microscopy patients, 4 required endaural incision and canalplasty because of canal overhangs, and 7 required canal wall curettage for ossicular assessment. None of the 20 endoscopy patients required these procedures. Chorda tympani was manipulated in 13 and 6 patients in the microscopy and endoscopy groups respectively, while the stapes footplate could be perforated in 5 and 11 patients respectively. Mean operative time was 50.25 and 76.05 minutes in the microscopy and endoscopy groups respectively. In the endoscopy group, mean air-bone gap was 37.12 and 10.73 dB pre- and post-operation respectively; in the microscopy group, these values were 35.95 and 13.81 dB. CONCLUSION: Endoscopic stapedotomy has comparable hearing outcomes. Sinonasal endoscope serves as a better tool for: minimal incision, canalplasty avoidance, less chorda tympani mobilisation, and stapes footplate perforation ability.

Integration of colloids into a semi-flexible network of fibrin.

Typical colloid-polymer composites have particle diameters much larger than the polymer mesh size, but successful integration of smaller colloids into a large-mesh network could allow for the realization of new colloidal states of spatial organization and faster colloid motion which can allow the possibility of switchable re-configuration of colloids or more dramatic stimuli-responsive property changes. Experimental realization of such composites requires solving non-trivial materials selection and fabrication challenges; key questions include composition regime maps of successful composites, the resulting structure and colloidal contact network, and the mechanical properties, in particular the ability to form a network and retain strain stiffening in the presence of colloids. Here, we study these fundamental questions by formulating composites with fluorescent (though not stimuli-responsive) carboxylate modified polystyrene/latex (CML) colloidal particles (diameters 200 nm and 1000 nm) in bovine fibrin networks (a semi-flexible biopolymer network with mesh size 1-5 µm). We describe and characterize two methods of composite preparation: adding colloids before fibrinogen polymerization (Method I), and electrophoretically driving colloids into a network already formed by fibrinogen polymerization (Method II). We directly image the morphology of colloidal and fibrous components with two-color fluorescent confocal microscopy under wet conditions and SEM of fixed dry samples. Mechanical properties are studied with shear and extensional rheology. Both fabrication methods are successful, though with trade-offs. Method I retains the nonlinear strain-stiffening and extensibility of the native fibrin network, but some colloid clustering is observed and fibrin network integrity is lost above a critical colloid concentration that depends on fibrinogen and thrombin concentration. Larger colloids can be included at higher volume fractions before massive aggregation occurs, indicating surface interactions as a limiting factor. Method II results in a loss of measurable strain-stiffening, but colloids are well dispersed and template along the fibrous scaffold. The results here, with insight into both structure and rheology, form a foundational understanding for the integration of other colloids, e.g. with stimuli-responsive functionalities, into semi-flexible networks.

Temporal Modulation of Stem Cell Activity Using Magnetoactive Hydrogels.

Cell activity is coordinated by dynamic interactions with the extracellular matrix, often through stimuli-mediated spatiotemporal stiffening and softening. Dynamic changes in mechanics occur in vivo through enzymatic or chemical means, processes which are challenging to reconstruct in cell culture materials. Here a magnetoactive hydrogel material formed by embedding magnetic particles in a hydrogel matrix is presented whereby elasticity can be modulated reversibly by attenuation of a magnetic field. Orders of magnitude change in elasticity using low magnetic fields are shown and reversibility of stiffening with simple permanent magnets is demonstrated. The broad applicability of this technique is demonstrated with two therapeutically relevant bioactivities in mesenchymal stem cells: secretion of proangiogenic molecules, and dynamic control of osteogenesis. The ability to reversibly stiffen cell culture materials across the full spectrum of soft tissue mechanics, using simple materials and commercially available permanent magnets, makes this approach viable for a broad range of laboratory environments.

Morphometry and variations of the human suprascapular notch.

AIM: The present study proposes a simple method to study variations in shape and dimensions of suprascapular notch, to classify different types and subtypes of notch and to measure the thickness of superior transverse scapular bar (ossified superior transverse ligament of scapula). MATERIAL AND METHODS: Seven hundred and twenty-eight dried scapulae were observed, examined and studied in detail. Scapulae with suprascapular notch, with suprascapular foramen having varying degree of ossification in the form of transverse scapular bar were included in the present study. Measurements of suprascapular notch and superior transverse scapular bar were taken with the help of digital vernier calliper and recorded in millimetres. The superior transverse diameter, inferior transverse diameter, depth, maximum thickness of suprascapular notch and thickness at lateral and medial end of transverse scapular bar, mean thickness of superior transverse scapular bar were recorded. The data was analyzed statistically. OBSERVATIONS AND RESULTS: We observed five types of notch in scapulae, type I: without a discrete notch (ill defined), 25 (3.43%); type II: a "V" shaped notch, 192 (26.37%); type III: "U" shaped notch, 383 (52.60%); type IV: inverted "V" shaped notch, 28 (3.84%); type V with absent suprascapular notch: 6 (0.82%). Type II and type III were again subclassified into subtypes (a, b, c and d) on the basis of depth of notch. Scapulae with superior transverse scapular bar (n=94, 12.91%) were classified according to variation in mean thickness of transverse scapular bar (MTSB). CONCLUSION: This study will help clinicians to correlate suprascapular nerve entrapment with a specific type of suprascapular notch and notch with ossified transverse scapular ligament.

Role of tracheostomy in the management of foreign body airway obstruction in children.

INTRODUCTION: Foreign body aspiration in the airway of children is a life-threatening clinical situation. Endoscopic retrieval alone is successful in the majority of patients. Occasionally, open surgical intervention in the form of tracheostomy, thoracotomy and bronchotomy and/or pulmonary resection is needed. We analysed the specific indications for tracheostomy during the removal of airway foreign bodies in our study. METHODS: The records of four patients who needed tracheostomy, out of 342 cases of foreign body airway obstruction managed by the senior author, were analysed. These patients underwent an additional tracheostomy for open removal of the foreign body and/or to secure the airway to facilitate the foreign body removal. RESULTS: Rigid bronchoscopy was successful in retrieving the foreign bodies in 338 (98.8 percent) cases, while four (1.2 percent) cases required additional tracheostomy, either to protect the airway during the procedure or to assist in removing the foreign body. The indications for tracheostomy were subglottic foreign bodies of long duration, sharp subglottic foreign bodies and foreign bodies that were larger than the glottic chink. There was no mortality or long-term complication because of the tracheostomies. CONCLUSION: Tracheostomy is occasionally indicated in foreign body extraction, when they are subglottic in location and impacted, or are large foreign bodies that get obstructed at the glottic chink during removal.

Phrenic nerve palsy in severe tetanus.

Unilateral or bilateral raised hemidiaphragms were observed on chest X-ray in three patients with severe tetanus. Diaphragmatic movement was absent on ultrasonography and fluoroscopy. Nerve conduction study confirmed phrenic nerve palsy. Bilateral involvement caused delayed weaning from the ventilator, whereas unilateral involvement was asymptomatic. There was complete recovery from phrenic nerve palsy in all patients.

ICU management of blunt chest trauma: our experience.

Blunt chest tramma is a major cause of mortality and morbidity following road side accident. An understanding of the factors affecting the mortality and morbidity will help in formulating better management strategies. The records of 40 consecutive patients presenting with blunt chest trauma (BCT) requiring ICU care from 1994-1996 were reviewed. Flail chest was the most common chest injury seen in 35 patients (87.5%). Isolated flail chest was seen in 22 patients, isolated pulmonary contusion in 2 patients and a combined injury in 13 patients. Ventilatory assistance was required in 34 patients (85%) for an average duration of 16 days (range 2-43 days). All patients with anterior flail required assisted ventilation in contrast to 75% and 88% of patients with unilateral and bilateral flail respectively. Presence of pulmonary contusion with or without flail was also associated with a high incidence of ventilatory support requirement. Chest infection (pneumonia) was the most common complication seen (65%). Adverse outcome occurred in 12 patients (30%). The main contributing factors for increased morbidity and mortality were: associated pulmonary contusion, associated extrathoracic injuries and preexisting medical illness. Statistical significance was observed only with pulmonary contusion.