David C. Lin

Mechanical Properties of a Reversible, DNA-Crosslinked Polyacrylamide Hydrogel

Mechanical properties of a polyacrylamide gel with reversible DNA crosslinks are presented. In this system, three DNA strands replace traditional chemical crosslinkers. In contrast to thermoset chemically crosslinked polyacrylamide, the new hydrogel is thermoreversible; crosslink dissociation without the addition of heat is also feasible by introducing a specific removal DNA strand. This hydrogel is characterized by a critical crosslink concentration at which gelation occurs. Below the critical point, a characteristic temperature exists at which a transition in viscosity is observed. Both temperature-dependent viscosity and elastic modulus of the material are functions of crosslink density.

Association between severity of asthma and degree of chronic rhinosinusitis.

Background There is a clinical association between asthma and chronic rhinosinusitis (CRS). This study was designed to determine whether severity of coexistent asthma affects the clinical presentation of CRS. Methods Cross-sectional analysis was performed of prospectively collected data in 187 patients with CRS who were evaluated in a large, tertiary academic nasal and sinus center. Patients were stratified into three groups based on asthma status using National Institutes of Health criteria: (1) nonasthmatic, (2) intermittent/mild asthma, (3) or moderate/severe asthma. Results Mean Lund-Mackay scores were 9.7, 11.6, and 15.6, respectively. ANOVA testing with post-hoc Tukey analysis revealed that Lund-MacKay scores were significantly greater in group 3 than either group 1 (p < 0.05) or group 2 (p < 0.01). The prevalence of allergic sensitization was 72.4, 82.8, and 100% in groups 1, 2, and 3, respectively (p = 0.03). The prevalence of nasal polyposis was 31.4% in group 1, 48.3% in group 2, and 94.4% in group 3 (p < 0.0001). No differences were observed regarding demographic factors or the incidence of the triad of aspirin sensitivity, asthma, and nasal polyposis among those with different severities of asthma. Conclusion Increasing severity of asthma is associated with advancing radiological severity of CRS and a greater prevalence of allergic sensitization and nasal polyposis. This large adult series shows that asthma severity may have a significant correlation with the presentation of CRS. This study adds to the growing support for the unified airway theory.

A quantitative analysis of pendular motion of the lower leg in spastic human subjects

Gravity-induced oscillations of the lower leg in normal and spastic subjects were examined with a view towards evaluating a clinical test of spasticity called the pendulum test. For passive limb motion (in which no reflex excitation occurred), a second-order linear model did not provide an adequate description of the motion for either spastic or normal legs. System equations including nonlinear mechanical properties simulating asymmetries in the swing and amplitude dependent variations in stiffness and damping provided a more accurate description. For spastic limb motion (in which reflex excitation did occur) accurate simulation required components accounting for abnormal reflex activation, coinciding with the time course of EMG activation. These included increased stiffness and damping with their gains related to reflex EMG magnitude, and changes in the rest length of the stiffness. Comparison of numerical with experimental data showed that the nonlinear model simulated the motion accurately, with the variance accounted for usually exceeding 90%.<<ETX>>

Reduced expression of antimicrobial PLUNC proteins in nasal polyp tissues of patients with chronic rhinosinusitis

Chronic rhinosinusitis (CRS) is a disease characterized by inflammation of the nasal mucosa and paranasal sinuses. This inflammation may result in part from decreased epithelial barrier and innate immune responses, leading to frequent bacterial and fungal colonization. The objectives of this study were to investigate the expression of innate immune proteins of the palate lung and nasal epithelium clone (PLUNC) family in patients with CRS.

Atopic profile of patients failing medical therapy for chronic rhinosinusitis.

Chronic rhinosinusitis (CRS) is an inflammatory condition of the nasal airway and paranasal sinuses that can broadly be classified into CRS with nasal polyps (CRSwNP) and CRS without nasal polyps (CRSsNP). The relationship between CRS and atopy to inhalant allergens remains unclear. We sought to examine the presence of atopy in patients failing medical therapy for both types of CRS. The objective of this research was to analyze the frequency and distribution of allergen sensitivity in patients failing medical therapy for CRSwNP and CRSsNP in comparison to rhinitis patients without CRS and the general population.

Minimal Seasonal Alterations in the Skeletal Muscle of Captive Brown Bears

Previous studies on wild black bears (Ursus americanus) have shown that skeletal muscle morphology, composition, and overall force‐generating capacity do not differ drastically between seasons despite prolonged inactivity during hibernation. However, the amount and characteristics of the seasonal variations were not consistent in these studies. The goals of this study were to compare the amount of muscle atrophy in captive brown bears (Ursus arctos) with that observed in wild black bears and measure seasonal differences in twitch characteristics. Samples from the biceps femoris muscle were collected during the summer and winter. Protein concentration, fiber‐type composition, and fiber cross‐sectional area were measured along with twitch characteristics. The protein concentration of the winter samples was 8.2% lower than that of the summer samples; fiber cross‐sectional area and the relative proportion of fast and slow fibers remained unchanged between seasons. Myosin heavy chain isoforms I, IIa, and IIx were identified by immunoblotting and electrophoresis, and the proportions did not change between seasons. The half‐rise time in the twitch contractions increased in winter relative to summer samples, which is unexpected under disuse conditions. These results agreed with a study that showed minimal skeletal muscle atrophy between seasons in wild black bears.

Gravitational demand on the neck musculature during tablet computer use

Tablet computer use requires substantial head and neck flexion, which is a risk factor for neck pain. The goal of this study was to evaluate the biomechanics of the head–neck system during seated tablet computer use under a variety of conditions. A physiologically relevant variable, gravitational demand (the ratio of gravitational moment due to the weight of the head to maximal muscle moment capacity), was estimated using a musculoskeletal model incorporating subject-specific size and intervertebral postures from radiographs. Gravitational demand in postures adopted during tablet computer use was 3–5 times that of the neutral posture, with the lowest demand when the tablet was in a high propped position. Moreover, the estimated gravitational demand could be correlated to head and neck postural measures (0.48 < R 2 < 0.64, p < 0.001). These findings provide quantitative data about mechanical requirements on the neck musculature during tablet computer use and are important for developing ergonomics guidelines. Practitioner Summary: Flexed head and neck postures occur during tablet computer use and are implicated in neck pain. The mechanical demand on the neck muscles was estimated to increase 3–5 times during seated tablet computer use versus seated neutral posture, with the lowest demand in a high propped tablet position but few differences in other conditions.

Defining and evaluating wrapping surfaces for MRI-derived spinal muscle paths.

Muscle paths can be approximated in biomechanical models by wrapping the path around geometric objects; however, the process for selecting and evaluating wrapping surface parameters is not well defined, especially for spinal muscles. In this study, we defined objective methods to select the shape, orientation, size and location of wrapping surfaces and evaluated the wrapping surfaces using an error metric based on the distance between the modeled muscle path and the centroid path from magnetic resonance imaging (MRI). We applied these methods and the error metric to a model of the neck musculature, where our specific goals were (1) to optimize the vertebral level at which to place a single wrapping surface per muscle; and (2) to define wrapping surface parameters in the neutral posture and evaluate them in other postures. Detailed results are provided for the sternocleidomastoid and the semispinalis capitis muscles. For the sternocleidomastoid, the level where the wrapping surface was placed did not significantly affect the error between the modeled path and the centroid path; use of wrapping surfaces defined from the neutral posture improved the representation of the muscle path compared to a straight line in all postures except contralateral rotation. For the semispinalis capitis, wrapping surfaces placed at C3 or C4 resulted in lower error compared to other levels; and the use of wrapping surfaces significantly improved the muscle path representation in all postures. These methods will be used to improve the estimates of muscle length, moment arm and moment-generating capacity in biomechanical models.

Chronic rhinosinusitis in the setting of other chronic inflammatory diseases

OBJECTIVES The objectives of the study were to determine the prevalence of chronic rhinosinusitis (CRS) overall and its 2 phenotypic variants, CRS with and without polyposis (NP), in patients with chronic inflammatory comorbidities including autoimmune disorders, inflammatory bowel disease, and atopic dermatitis. These findings were compared with data in patients with asthma. Patients with hypertension were also used as a reference group to estimate the incidence of CRS in a group with regular medical follow-up. STUDY DESIGN A retrospective, cross-sectional query of a large tertiary care electronic medical record database was performed. RESULTS Electronic medical record database prevalence of CRS in patients with hypertension was 4.4%. The prevalence of CRS was 18% in asthma (P < .0001), 7% in atopic dermatitis, 3.5% in inflammatory bowel disease, and ranged from 1.4% to 5.9% in autoimmune disorders. The frequency of CRS patients exhibiting the NP phenotype was similarly low in patients with autoimmune disease and hypertension, but was significantly greater in patients with asthma (P < .0001), inflammatory bowel disease (P = .033), and atopic dermatitis (P = .049), CONCLUSIONS These findings suggest similar prevalence of overall CRS in patients with autoimmune disease and inflammatory bowel disease, and background rates as estimated by observations in hypertension patients. Inflammatory bowel disease and atopic dermatitis patients with CRS exhibit some skewing toward the NP phenotype, as do asthmatics, where this association is well known.

Use of Rigid Spherical Inclusions in Young’s Moduli Determination: Application to DNA-Crosslinked Gels

Current techniques for measuring the bulk shear or elastic (E) modulus of small samples of soft materials are usually limited by materials handling issues. This paper describes a nondestructive testing method based on embedded spherical inclusions. The technique simplifies materials preparation and handling requirements and is capable of continuously monitoring changes in stiffness. Exact closed form derivations of E as functions of the inclusion force-displacement relationship are presented. Analytical and numerical analyses showed that size effects are significant for medium dimensions up to several times those of the inclusion. Application of the method to DNA-crosslinked gels showed good agreement with direct compression tests.