Pure elongation flow of an electrorheological fluid: insights on wall slip from electrorheology.

In this work we study the pure elongation flow behavior of an electrorheological (ER) fluid as a model soft-jammed system, wherein the extent of jamming is controlled by an externally applied electric-field. More specifically, a pure elongation flow has been achieved by facilitating significant slip at the contact between the material and rheometer-plate while pulling it with constant pulling velocity under a constant external electric-field. The normal force exerted by the top plate on the material was measured as a function of gap during the flow for various combinations of electric-field strength and pulling velocity. For any force-gap curve, at first force increases to the maximum (region-I), then it decreases with gap (region-II). In region-II, the normal force-gap curve shifts to higher gaps with increasing electric-field strength for any given pulling velocity. Interestingly, these curves (region-II) demonstrate gap-electric field-velocity superposition, manifesting the self-similar nature of the flow. Finally, we have modeled the flow curves using a slip-layer model, which rendered a remarkable prediction of flow curves and also led to estimation of slip-layer thickness. We observed that slip-layer thickness decreases with increasing magnitude of electric field for a given pulling velocity, which suggests that the extent of jamming plays a crucial role in slip dynamics.

Thermoresponsive keratin-methylcellulose self-healing injectable hydrogel accelerating full-thickness wound healing by promoting rapid epithelialization.

Chronic wounds suffer from impaired healing due to microbial attack and poor vascular growth. Thermoresponsive hydrogels gained attention in wound dressing owing to their gelation at physiological temperature enabling them to take the shape of asymmetric wounds. The present study delineates the development of thermoresponsive hydrogel (MCK), from hair-derived keratin (K) and methylcellulose (MC) in the presence of sodium sulfate. The gelation temperature (Tg) of this hydrogel is in the range of 30 °C to 33 °C. Protein-polymer interaction leading to thermoreversible sol-gel transition involved in MCK blends has been analyzed and confirmed by FTIR, XRD, and thermal studies. Keratin, has introduced antioxidant properties to the hydrogel imparted cytocompatibility towards human dermal fibroblasts (HDFs) as evidenced by both MTT and live dead assays. In vitro wound healing assessment has been shown by enhanced migration of HDFs in the presence of MCK hydrogel compared to the control. Also, CAM assay and CD31 expression by the Wistar rat model has shown increased blood vessel branching after the implantation of MCK hydrogel. Further, in vivo study, demonstrated MCK efficacy of hydrogel in accelerating full-thickness wounds with minimal scarring in Wistar rats, re-epithelialization, and reinstatement of the epidermal-dermal junction thereby exhibiting clinical relevance for chronic wounds.

Bioactive self-assembling silk fibroin-sericin films for skin tissue engineering.

The quest for an ideal wound dressing material has been a strong motivation for researchers to explore novel biomaterials for this purpose. Such explorations have led to the extensive use of silk fibroin (SF) as a suitable polymer for several applications over the years. Unfortunately, another major silk protein-sericin has not received its due attention yet in spite of having favorable biological properties. In this study, we report an approach of blending SF and silk sericin (SS) without the usage of chemical crosslinkers is made possible by the usage of formic acid which evaporates to induceß-sheets formation to form cytocompatible films. Raman spectroscopy confirms the presence of SF/SS components in blend and formation ofß-sheet in films.In situ, gelation kinetics studies were conducted to understand the change in gelation properties with addition of sericin into SF. Methyl thiazolyl tetrazolium and live/dead assays were performed to study cellular attachment, viability and proliferation on SF/SS films. The antibacterial properties of SF/SS films were tested using Gram-negative and Gram-positive bacteria. The re-structured SF/SS films were stable, transparent, show good mechanical properties, antibacterial activity and cytocompatibility, therefore can serve as suitable biomaterial candidates for skin regeneration applications.

Prediction of viscoelastic properties of peanut-based 3D printable food ink.

Viscoelastic properties of 3D printable peanut-based food ink were investigated using frequency sweep and relaxation test. The incorporation of xanthan gum (XG) improved the shear thinning behavior (n value ranging from 0.139 to 0.261) and lowered the η*, G', and G'' values, thus making food ink 3D printable. The addition of XG also caused a downward shift in the relaxation curve. This study evaluates the possibility of an artificial neural network (ANN) approach as a substitute for the Maxwell three-element and Peleg model for predicting the viscoelastic behavior of food ink. The results revealed that all three models accurately predicted the decay forces. The inclusion of XG decreased the hardness and enhanced the cohesiveness, so enabling the 3D printing of food ink. The hardness was highly positively correlated with Maxwell model parameters Fe , F1 , F2 , F3, and Peleg constant k2 (0.57) and negatively correlated with k1 (-0.76).

Printable Carbon Nanotube-Liquid Elastomer-Based Multifunctional Adhesive Sensors for Monitoring Physiological Parameters.

Developing a printed elastomeric wearable sensor with good conformity and proper adhesion to skin, coupled with the capability of monitoring various physiological parameters, is very crucial for the development of point-of-care sensing devices with high precision and sensitivity. While there have been previous reports on the fabrication of elastomeric multifunctional sensors, research on the printable elastomeric multifunctional adhesive sensor is not very well explored. Herein, we report the development of a stencil printable multifunctional adhesive sensor fabricated in a solvent-free condition, which demonstrated the capability of having good contact with skin and its ability to function as a temperature and strain sensor. Functionalized liquid isoprene rubber was selected as the matrix while carboxylated multiwalled carbon nanotubes (c-CNTs) were used as the nanofiller. The selection of the above model compounds facilitated the printability and also helped the same composition to demonstrate stretchability and adhesiveness. A realistic three-dimensional microstructure (representative volume element model) was generated through a computational framework for the current c-CNT-liquid elastomer. Further computational simulations were performed to test and validate the correlation between electrical responses to that of experimental studies. Various physiological parameters like motion sensing, pulse, respiratory rate, and phonetics detection were detected by leveraging the electrically resistive nature of the sensor. This development route can be extended toward developing different innovative adhesives for point-of-care sensing applications.

Microfluidic thin film pressure balance for the study of complex thin films.

Investigations of free-standing liquid films enjoy an increasing popularity due to their relevance for many fundamental and applied scientific problems. They constitute soap bubbles and foams, serve as membranes for gas transport or as model membranes in biophysics. More generally, they provide a convenient tool for the investigation of numerous fundamental questions related to interface- and confinement-driven effects in soft matter science. Several approaches and devices have been developed in the past to characterise reliably the thinning and stability of such films, which were commonly created from low-viscosity, aqueous solutions/dispersions. With an increasing interest in the investigation of films made from strongly viscoelastic and complex fluids that may also solidify, the development of a new generation of devices is required to manage reliably the constraints imposed by these formulations. We therefore propose here a microfluidic chip design which allows for the reliable creation, control and characterisation of free-standing films of complex fluids. We provide all technical details and we demonstrate the device functioning for a larger range of systems via a selection of illustrative examples, including films of polymer melts and gelling hydrogels.

Signatures of Overaging in an Aqueous Dispersion of Carbopol.

In this work, we study the effect of the deformation field on the physical aging behavior of an aqueous Carbopol dispersion. It is composed of soft swollen particles of gel that get deformed and acquire a polygonal shape, with flat interfaces rendering the dispersion a soft solid-like consistency as filled volume fraction approaches unity. It has been proposed that owing to release of stored elastic energy in the deformed particles, Carbopol dispersion undergoes microstructural evolution that is reminiscent of physical aging in soft glassy materials. We observe that application of moderate magnitude of oscillatory strain to Carbopol dispersion slows down its relaxation dynamics, thereby showing characteristics of overaging. On the other hand, the sufficiently high magnitude of strain makes the relaxation dynamics faster, causing rejuvenation. We also solve the soft glassy rheology model, which, when subjected to the same flow field, corroborates with experimental observations on the Carbopol dispersion. This behavior, therefore, suggests that in a system of jammed soft particles of Carbopol, the particles occupying shallow energy wells upon application of moderate strain field adjust themselves in such a manner that they predominantly occupy the deeper energy wells leading to observe the overaging dynamics.

Biomimetic silk fibroin and xanthan gum blended hydrogels for connective tissue regeneration.

Combination of naturally occurring materials instead of chemically synthesized products has always been an attractive proposition in the field of tissue engineering. In this study, silk fibroin (SF) and xanthan gum(XG) were physically crosslinked to form biocompatible hydrogels. SF/XG hydrogels were prepared using ultrasonication, which induces ß-sheets from random coils in SF solution and allows entrapment of heated XG chains homogeneously in the SF network. It is a novel way of blending SF and XG polymers which avoids the usage of chemical crosslinkers. SF/XG blended solutions were used at different ratios for the hydrogel formation. Scanning electron microscopy (SEM) and micro-computed tomography (MCT) were used for morphological analysis of the interconnected network and porosity of the scaffolds, respectively. Rheological studies were performed to understand the changes in mechanical properties due to the incorporation of XG into SF hydrogels. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of SF and XG moieties in the blend scaffolds. Additionally, thermal Analysis (TGA & DSC) established the homogenous mixture and presence of XG in the SF network without any phase separation. Furthermore, the MTT assay demonstrates the cytocompatibility of scaffolds using L929 fibroblast cells. Thus, fabricated SF/XG scaffolds could mimic natural cartilage ECM by exhibiting enhanced water swelling capacity and suitable porosity along with its cytocompatible studies, indicating its potential application in soft tissue engineering.

Tailorable hydrogel of gelatin with silk fibroin and its activation/crosslinking for enhanced proliferation of fibroblast cells.

Gelatin based hydrogel (Gel) possess remarkable cytocompatibility profile rendering it appropriate for tissue engineering applications. Herein, the questionable mechanical property of Gel was tuned by tailoring with different loading concentrations of silk fibroin (SF). The as tailored matrix was reconnoitred for its physico-mechanical, chemical and biological properties in order to investigate the effect of SF loading. Ethanol treatment lead to enhance ß-sheet formation of silk and subsequently, carbodiimide coupling was deployed to covalently crosslink the matrix. Substantial increase in cohesive energy with amplifying concentration of SF in the Gel matrix. As evidenced by Raman spectroscopy, right shift of the Amide I peak and stretching of COO- confirms activation of fibroin moiety along with crosslinking of gelatin, respectively. Moreover, with addition of SF, surface properties were tuned to attain maximum cell adhesion and proliferation. Further, MTT assay corroborated the same with definite increase in mitochondrial activities of L929 fibroblast cells for SF containing matrix as compared to its bare counterfeit while enhanced proliferation was confirmed by Rhodamine-DAPI staining. The alteration in mechanical and textural tribology of SF tailored Gel matrix certainly portrayed improved stability along with excellent cytocompatibility thus making it a plausible alternative in regenerative medicine.

Three-dimensional yielding in anisotropic materials: validation of Hill's criterion.

Yielding transition in isotropic soft materials under the superposition of orthogonal deformation fields is known to follow von Mises' criterion. However, in anisotropic soft materials, von Mises' criterion fails owing to the preferred directions associated with the system. In this work we study a model anisotropic yield stress system: electrorheological (ER) fluids which show structural formation in the direction of an electric field. We subject the ER fluids to the superposition of orthogonal stress fields which leads to different yield stress values. We obtain a yielding state diagram by plotting the normalized rotational shear stress against the normalized radial shear stress corresponding to a yield point for a given electric field. Remarkably, the state diagram validates the Hill yielding criterion, which is a general yielding criterion for materials with anisotropy along three orthogonal directions, originally developed for metallic systems. Validation of Hill's criterion suggests the universality of its application in anisotropic systems including conventional anisotropic soft materials having yield stress.

Passive microrheology in the effective time domain: analyzing time dependent colloidal dispersions.

We studied the aging dynamics of an aqueous suspension of LAPONITE®, a model time dependent soft glassy material, using a passive microrheology technique. This system is known to undergo physical aging during which its microstructure evolves progressively to explore lower free energy states. Optical microscopy is used to monitor the motion of micron-sized tracer probes embedded in a sample kept between two glass plates. The mean square displacements (MSD) obtained from the motion of the tracer particles show a systematic change from a purely diffusive behavior at short aging times to a subdiffusive behavior as the material ages. Interestingly, the MSDs at all the aging times as well as different LAPONITE® concentrations superpose remarkably to show a time-aging time master curve when the system is transformed from the real time domain to the effective time domain, which is obtained by rescaling the material clock to account for the age dependent relaxation time. The transformation of the master curve from the effective time domain to the real time domain leads to the prediction of the MSD in real time over a span of 5 decades when the measured data at individual aging times are only over 2 decades. Since the MSD obtained from microrheology is proportional to the creep compliance of a material, by using the Boltzmann superposition principle along with the convolution relation in the effective time domain, we predict the stress relaxation behavior of the system in real time. This work shows that the effective time approach applied to microrheology facilitates the prediction of long time creep and relaxation dynamics of a time dependent soft material by carrying out short time experiments at different aging times.

Analyzing aging under oscillatory strain field through the soft glassy rheology model.

In this work, we solve the Soft Glassy Rheology (SGR) model under application of oscillatory deformation field with varying magnitudes of strain as well as frequency for different noise temperatures. In the glassy domain, the SGR model undergoes time evolution of elastic modulus. Increase in strain magnitude beyond the linear regime is observed to enhance the rate of aging as manifested by a faster evolution of elastic modulus with increase in strain amplitude due to overaging. However at higher strain magnitudes, the rejuvenation effect starts dominating over the aging, thereby reducing the rate at which elastic modulus evolves. We also plot the aging phase diagram describing an occurrence of the linear, the overaging, and the rejuvenation regimes as a function of strain and frequency for different noise temperatures. The aging phase diagram suggests that while the linear regime remains unaffected by the changes in frequency and noise temperature, the width of the overaging regime increases with increase in frequency and noise temperature. We also study the time evolution of the shapes of relaxation time spectra as a function of strain amplitude, which renders further insight into the overaging and the rejuvenation behavior. While the phenomenon of overaging is observed to be an inherent character of the SGR model, experimentally not all the materials demonstrate overaging. Such a discrepancy suggests that the energy well depths before and after a yielding event may not be completely uncorrelated as assumed in the SGR formalism.

Linear viscoelasticity of soft glassy materials.

Owing to lack of time translational invariance, aging soft glassy materials do not obey fundamental principles of linear viscoelasticity. We show that by transforming the linear viscoelastic framework from a real time domain into an effective time domain, wherein the material clock is readjusted to account for evolution of relaxation time, the soft glassy materials obey effective time translational invariance. Consequently, we demonstrate successful validation of principles of linear viscoelasticity (the Boltzmann superposition principle and a convolution relation for creep compliance and stress relaxation modulus) for different types of soft glassy materials in the effective time domain.

Tailoring relaxation time spectrum in soft glassy materials.

Physical properties of out of equilibrium soft materials depend on time as well as deformation history. In this work we propose to transform this major shortcoming into gain by applying controlled deformation field to tailor the rheological properties. We take advantage of the fact that deformation field of a certain magnitude can prevent particles in an aging soft glassy material from occupying energy wells up to a certain depth, thereby populating only the deeper wells. We employ two soft glassy materials with dissimilar microstructures and demonstrate that increase in strength of deformation field while aging leads to narrowing of spectrum of relaxation times. We believe that, in principle, this philosophy can be universally applied to different kinds of glassy materials by changing nature and strength of impetus.

Extra vestibular schwannoma: a two year experience.

We present series of head, neck extracranial non-vestibular schwannomas treated during 2-year period. All patients with head and neck schwannomas treated at our department from April 2007 to July 2009 were reviewed. There was female predominance (72%). The mean age at diagnosis was 38 years. All (100%) presented with a neck mass. Most common nerves of origin were the vagus and the cervical sympathetic chain. Treatment for all cases was complete excision with nerve preservation. Among all schwannoma patients, postoperative neural deficit occurred in four with partial to complete resolution in three. The follow-up period was 24 months. Non-vestibular extracranial head and neck schwannomas most frequently present as an innocuous longstanding unilateral parapharyngeal neck mass. Preoperative diagnosis may be aided by fine-needle cytology and magnetic resonance imaging or computed tomographic imaging. The mainstay of treatment is complete intracapsular excision preserving the nerve of origin.

Primary hyperparathyroidism: retrospective 10-year study of 32 cases.

BACKGROUND: Parathyroid glands are endocrine glands that regulate calcium metabolism. Usually four in number, they lie mostly on the posterior aspect of thyroid glands. Primary hyper-parathyroidism (PHPT) refers to a condition wherein they secrete an excess of parathyroid hormone leading to signs and symptoms of hypercalcemia. PATIENTS AND METHODS: Thirty-two patients of primary hyper-parathyroidism were seen by us in the ten years. Majority of patients were below 40 years of age (88%). Male: female ratio was 1:4. The diagnosis was made incidentally in patients who reported for various signs and symptoms not responding to treatment. High serum calcium pointed to the diagnosis of primary parathyroid hyperplasia. It was confirmed by high level of serum parathyroid hormone and localization of enlarged parathyroid glands by USG / MRI and / or Tc-99 Technetium scan. Of the 32 patients examined, 43 parathyroid glands were excised, five cases had two glands excised; out of these 4 cases underwent parathyroid reimplantation in neck/forearm muscles. One unusual case underwent operation for giant-cell tumor of the head of humerus. This patient presented with excessive vomiting not responding standard medical management in post-operative period. RESULTS: During investigations serum calcium was found to be very high, the diagnosis was confirmed by finding high parathyroid hormone and corroborated by T(99) Technetium scan. Parathyroidectomy was done in all cases, of which 59% (18 cases) developed mild to severe tetany due to hypocalcaemia. CONCLUSION: Primary hyperplasia of thyroid gland is the most important cause of hypercalcemia. Hypercalcemia is found in all cases of PHPT in our series with high parathyroid hormone levels. Majority of our cases have one gland involvement and hypocalcaemia in our series is unusually high following excision of involved gland.

Microsatellite instability and its correlation with clinicopathological features in a series of thyroid tumors prevalent in iodine deficient areas.

Thyroid tumors display diverse spectrum of histopathological groups with geographic variation in its prevalence. Influence of iodine deficiency (a major causative factor) in its etiology, prevalence, or aggressiveness is debatable which reflects the existence of various genetic events in pathogenesis. The present study was undertaken to study the role of Microsatellite instability (MSI) or LOH (loss of heterozygosity), an indicator of defective mismatch repair system as a genetic change and to explore it as a prognostic marker in thyroid tumors. Tumor tissues from total thyroidectomy surgical specimens and blood (matched control) of 36 patients from iodine deficient areas (10 benign; 26 malignant) were obtained after their consent. Urinary iodine analysis was done by alkali ash method for which 10 ml of urine was collected from 18 patients before surgery. Genomic DNA, isolated from tumor tissue and blood was amplified by polymerase chain reaction (PCR) using mono and dinucleotide markers - BAT-26, BAT-40, TGF(RII, IGFIIR, hMSH3, BAX, D2S123, D9S283, D9S851 and D18S58. PCR products were analysed on 8% denaturing polyacrylamide gel followed by autoradiography. Of total, 66.6% of tumors [70% (7/10) benign and 65.4% malignant cases (17/26)] showed MSI/LOH. Strong association of MSI/LOH with low iodine (P = 0.01) and with AMES risk groups i.e. age (P = 0.02), tumor size (P = 0.04) and metastases (P = 0.002) in thyroid tumors was observed. This may help in predicting the biological behaviour and strengthening the hypothesis that iodine deficiency has influence on MSI in thyroid tumors. Our results further substantiate the risk group classification and help in deciding the treatment modality in particular patient.

Management of enterocutaneous fistulas.

Despite advances in antimicrobial chemotherapy, nutritional support, and perioperative critical care, the development of an enterocutaneous fistula continues to represent a major therapeutic challenge, with appreciable morbidity and mortality. Specific problems that must be addressed for the successful management of patients with enterocutaneous fistulas are the control of sepsis, maintenance of adequate fluid and electrolyte balance, provision of adequate and complication-free nutritional support, and skin-stoma care. In addition, many patients with postoperative intestinal fistulation suffer from significant psychological morbidity, which must be addressed during often prolonged periods of rehabilitation. The complex nature of the care required for successful management of patients with enterocutaneous fistulas mandates a multidisciplinary team approach, with specialist nurses, dieticians, pharmacists, radiologists, physicians, and surgeons all having important roles to play.