Anuj Singh Chauhan - Academia.edu (original) (raw)

Papers by Anuj Singh Chauhan

International Journal of Cosmetic Science, 2016

Sunscreens are commonly used to protect the body from damage caused by UV light. Some components ... more Sunscreens are commonly used to protect the body from damage caused by UV light. Some components of organic sunscreens have been shown to pass through the skin during wear which could raise toxicity concerns for these compounds. This study explores the potential for oils and fruit and vegetable juices to be substitutes for these compounds. METHODS: The absorptivity of various oils (canola oil, citronella oil, coconut oil, olive oil, soya bean oil, vitamin E, as well as aloe vera) and fruit and vegetable juices (acerola, beet, grape, orange carrot, purple carrot and raspberry) was measured in vitro. The mean absorptivity was compared with FDA-approved UV absorbers to gauge the potential of the natural products. The most promising candidates were incorporated into formulations, and the UV transmittance of a 20-lm-thick film of the formulation was measured. The formulations were also imaged by light microscopy and scanning electron microscopy. RESULTS: The absorptivity of oils was at least two orders of magnitude lower compared to the commercial UV blockers. The fruit juice powders were more effective at UV blocking but still showed an order of magnitude lower absorptivity compared to commercial UV blockers. CONCLUSION: The UV blocking from most natural oils is insufficient to obtain a significant UV protection. Formulations containing 50wt% purple carrot showed good UV-blocking capabilities and represent a promising ingredient for sunscreen and cosmetic applications. queurs d'UV commerciaux. CONCLUSION: Le blocage UV de la plupart des huiles naturelles est insuffisante pour obtenir une protection significative UV. Les formulations contenant 50% en poids de carotte violette ont montr e une bonne capacit e de blocage UV et repr esentent un ingr edient prometteur pour la cr eme solaire et des applications cosm etiques.

International Journal of Pharmaceutics, 2015

Ultraviolet (UV) light has the potential to cause many adverse effects on the body including caus... more Ultraviolet (UV) light has the potential to cause many adverse effects on the body including causing the cancers melanoma and squamous cell carcinoma. The use of sunscreens to protect against these harmful effects has become common practice. However, many of the sunscreens currently being used have the ability to cross the skin barrier and enter the body. These components can produce reactive oxygen species inside the body which can cause damage to cells. We have developed a sunscreen product that contains organic particles that are too large to diffuse into the skin. These particles are formed from four FDA approved UV blocking molecules that are solids at room temperature. The components are first mixed together, melted, and then emulsified in water and allowed to cool. Once cooled, the particles slowly crystallize in the solution forming sphere to rod-like particles about one micron wide and one to tens of microns in length. SPF measurements of the samples showed comparable results to two commercially available sunscreens with SPFs of 50. The particles were shown to maintain their excellent UV blocking properties after exposure to UV light and show great promise as possible sunscreens.

IOSR Journal of Engineering, 2011

In this paper, we present a delay based routing algorithm for ad hoc wireless networks. In an ad ... more In this paper, we present a delay based routing algorithm for ad hoc wireless networks. In an ad hoc environment there is no wired infrastructure and the mobile hosts work as a router to maintain the status about the connectivity. A mobile ad hoc network is an autonomous collection of mobile users (nodes) that communicates over relatively bandwidthconstrained wireless links. Each node is equipped with wireless receivers and transmitters using antennas that may be omnidirectional, highly directional, or possibly steer able. Due to nodal mobility, the network topology may change rapidly and unpredictably over time. The network is decentralized, where network organization and message delivery must be executed by the nodes themselves, i.e., routing functionally will be incorporated into mobile nodes. The design of the network protocols for mobile ad hoc network is a complex issue. These networks need efficient distributed algorithm to determine network organization (connectivity), link scheduling, and routing. But, the existing routing algorithms designed for ad hoc wireless networks have slow response, excessive overhead and become unsuitable under the above considerations. The full approach, for referring the internal state of the network relies on Round Trip Time (RTT) measurements only. We consider the RTT mean and RTT variance as fuzzy input variables and delay as a fuzzy output variable. Under such condition the performance of the proposed algorithm is tested. It is shown that under these conditions the algorithm gives better results. The proposed routing algorithm is simulated in MATLAB 6.5.

Journal of Colloid and Interface Science, 2015

Dryness and discomfort are the main reasons for dropouts in contact lens wearers. Incorporating s... more Dryness and discomfort are the main reasons for dropouts in contact lens wearers. Incorporating surfactants in lens formulations could improve wettability and lubricity, which can improve comfort. We have focused on incorporating polymerizable surfactants in hydroxyethyl methacrylate lenses to improve comfort, while minimizing the potential for surfactant release into the tears. The surfactants were added to the polymerization mixture, followed by UV curing and extraction of leachables in hot water. Wettability and lubricity were characterized by measuring the contact angle and coefficient of friction. Lenses were also characterized by measuring transmittance, loss and storage moduli and ion permeability. Incorporation of surfactants significantly reduced contact angle from 90° for p-HEMA gels to about 10° for 2.43% (w/w) surfactant loading in hydrated gel. The coefficient of friction also decreased from about 0.16 for HEMA gels to 0.05 for the gels with 2.43% surfactant loading. There was a good correlation between the contact angle and coefficient of friction suggesting that both effects can be related to the stretching of the surfactant tails near the surface into the aqueous phase. The water content was also correlated with the surfactant loading but the contact angle was more sensitive suggesting that the observed improvements in wettability and lubricity arise from the protrusion of the surfactant tails in into the liquid, and not purely from the increase in the water content. The gels were clear and certain compositions also have the capability to block UVC and UVB radiation. The results suggest that incorporation of polymerizable surfactants could be useful in improving surface properties without significantly impacting any bulk property.

Rheologica Acta, 1996

This paper examines the linear hydrodynamic stability of an inviscid compound jet. We perform the... more This paper examines the linear hydrodynamic stability of an inviscid compound jet. We perform the temporal and the spatial analyses in a unified framework in terms of transforms. The two analyses agree in the limit of large jet velocity. The dispersion equation is explicit in the growth rate, affording an analytical solution. In the temporal analysis, there are two growing modes, stretching and squeezing. Thin film asymptotic expressions provide insight into the instability mechanism. The spatial analysis shows that the compound jet is absolutely unstable for small jet velocities and admits a convec-tively growing instability for larger velocities. We study the effect of the system parameters on the temporal growth rate and that of the jet velocity on the spatial growth rate. Predictions of both the temporal and the spatial theories compare well with experiment.

Optometry and Vision Science, 2008

Purpose. An increase in residence time of dry eye medications including artificial tears will lik... more Purpose. An increase in residence time of dry eye medications including artificial tears will likely enhance therapeutic benefits. The drainage rates and the residence time of eye drops depend on the viscosity of the instilled fluids. However, a quantitative understanding of the dependence of drainage rates and the residence time on viscosity is lacking. The current study aims to develop a mathematical model for the drainage of Newtonian fluids and also for power-law non-Newtonian fluids of different viscosities. Methods. This study is an extension of our previous study on the mathematical model of tear drainage. The tear drainage model is modified to describe the drainage of Newtonian fluids with viscosities higher than the tear viscosity and power-law non-Newtonian fluids with rheological parameters obtained from fitting experimental data in literature. The drainage rate through canaliculi was derived from the modified drainage model and was incorporated into a tear mass balance to calculate the transients of total solute quantity in ocular fluids and the bioavailability of instilled drugs. Results. For Newtonian fluids, increasing the viscosity does not affect the drainage rate unless the viscosity exceeds a critical value of about 4.4 cp. The viscosity has a maximum impact on drainage rate around a value of about 100 cp. The trends are similar for shear thinning power law fluids. The transients of total solute quantity, and the residence time agrees at least qualitatively with experimental studies. Conclusions. A mathematical model has been developed for the drainage of Newtonian fluids and power-law fluids through canaliculi. The model can quantitatively explain different experimental observations on the effect of viscosity on the residence of instilled fluids on the ocular surface. The current study is helpful for understanding the mechanism of fluid drainage from the ocular surface and for improving the design of dry eye treatments.

Langmuir, 2012

Transport of surface active anesthetic drugs through silicone hydrogel contact lenses containing ... more Transport of surface active anesthetic drugs through silicone hydrogel contact lenses containing nanosized vitamin E aggregates is explored for achieving extended anesthetics delivery. Commercial silicone hydrogel contact lenses release most ophthalmic drugs including local anesthetics for only a few hours, which is not adequate. Here we focus on creating dispersion of highly hydrophobic vitamin E aggregates in the lenses as barriers for drug diffusion for increasing the release durations. This approach has been shown previously to be successful in extending the release durations for some common hydrophilic ophthalmic drugs. The topical anesthetic drugs considered here (lidocaine, bupivacaine, and tetracaine) are hydrophilic at physiologic pH due to the charge, and so these cannot partition into the vitamin E barriers. However, these surface active drug molecules adsorb on the surface of the vitamin E barriers and diffuse along the surface, leading to only a small decrease in the effective diffusivity compared to non-surface-active hydrophilic drugs. The drug adsorption can be described by the Langmuir isotherm, and measurements of surface coverage of the drugs on the vitamin E provide an estimate of the available surface area of vitamin E, which can then be utilized to estimate the size of the aggregates. A diffusion controlled transport model that includes surface diffusion along the vitamin E aggregates and diffusion in the gel fit the transport data well. In conclusion, the vitamin E loaded silicone contact lens can provide continuous anesthetics release for about 1−7 days, depending on the method of drug loading in the lenses, and thus could be very useful for postoperative pain control after corneal surgery such as the photorefractive keratectomy (PRK) procedure for vision correction.

Journal of Ocular Pharmacology and Therapeutics, 2013

We have developed a cylindrical insert that can be inserted in the fornix for extended release of... more We have developed a cylindrical insert that can be inserted in the fornix for extended release of glaucoma drug timolol. The insert is prepared by incorporating timolol-loaded nanoparticles into a poly hydroxyl ethyl methacrylate (p-HEMA) matrix. A 1-mm diameter, 7.5-mm long insert with 25% (w/w) particles can release timolol for about 10 days at an average rate of about 15 mg/day, which may be therapeutically effective. The increase in particle fraction increases drug loading, but also increases the release duration. The net effect of increasing the particle fraction is a significant increase in release duration, but a decrease in daily drug release rates, in the first few weeks. The release duration increases to about 1 and 3 months on increasing the particle fraction to 50% and 75%, respectively. The average daily release rates in the first 3 weeks are 15, 9, and 3 mg/day for the inserts with 50%, 75%, and 100% (w/w) particles, respectively. The mechanism of release is hydrolysis of the ester bond that links timolol to the propoxylated glyceryl triacrylate matrix, and thus the release profiles fit a first order reaction model. The water content of the inserts decreases from 31% to almost zero on increasing the particle loading from 25% to 100%. The rate constant for the hydrolysis decreases with an increase in particle loading in the insert most likely due to the reduction in the water content. The inserts can be packaged in wet conditions and stored in a refrigerator, but the inserts will exhibit a burst release caused by release of the drug from the particles into the p-HEMA matrix during the shelf life. Also, the magnitude of drug release after the initial burst is reduced due to the storage. The burst effect could potentially be avoided by packaging the inserts in a dry state, with hydration before insertion.

Journal of Membrane Science, 2012

Abstract Transport of ions through contact lenses is essential to maintain lens movement on the e... more Abstract Transport of ions through contact lenses is essential to maintain lens movement on the eye. We measure the effective diffusivity and partition coefficient of sodium chloride through silicone hydrogels by measuring kinetics of salt release and permeation in a diffusion cell. The results obtained from both approaches are compared and mechanisms related to linearity of transport and dominant transport mechanisms are explored. Also, transport parameters are measured from silicone hydrogels of several compositions to explore the dependency of ion transport on composition. Transport parameters are also correlated with the water fraction in the gel in the context of the free volume theory. Results show that the transport is linear in concentration and satisfies diffusive scaling suggesting that the transport of sodium and chloride ions can be lumped into an effective diffusion model. The permeation approach which is typically used for determining only the permeability can be utilized to yield both effective salt diffusivity and the partition coefficients if the short time transient data is fitted to a diffusion model. The values of diffusivity and partition coefficient obtained from both kinetic and permeation approach are comparable. The partition coefficient changes smoothly with variations in composition but there are discontinuities observed in diffusivity values likely due to changes in microstructure from dispersed to bicontinuous. The diffusivity cannot be related to the water content through the classical free volume theory because of the variations in the microstructure of the gels.

Journal of Fluid Mechanics, 2006

Operational notes on the inversion integrals in (29) Since in the present setting the integrand i... more Operational notes on the inversion integrals in (29) Since in the present setting the integrand is explicit in s, it is convenient to consider the alternate, equivalent view of the s-integral as the inner one. The resulting k-integrand is a sum of s-plane residues whose values and character depend on k. This integrand has a number of branch points/cuts, including along the real k-axis, which complicate the process of carrying out the kintegral as a contour integration. In addition, the inner square root in the s-solution has branch points symmetrically placed in each of the four k-plane quadrants, and these branch points are the sources of branch cuts that would render integral closure in the upper half k-plane as branch cut integrations. Instead we opt to handle part of the k-integration directly-for |k r |>k rc a cutoff value for s-plane residue i, we calculate the long time limit of this part of the integral as zero using the Riemann-Lebesgue lemma (Rudin 1987). Owing to the symmetries of the integrand discussed below, we consider only the portion of the integral k rc ≥k r ≥0 and carry it out as a contour integration with a contour in the fourth quadrant that avoids the branch cut just described in that quadrant, i.e., closer to the origin than the branch point, when possible. This additional contour Γ begins asymptotically close to the origin (also a branch point) and ends asymptotically close to k rc. If the system contains a source point at s=±iω 0 and if this contour encloses a point k: s r (k)=0, then this point would allow for a change in character of the s-plane residue by virtue of the merging of a pole of |A| with a source pole. As such, if in addition k i <0, it generates a pole in the k-plane that gives rise to a convective instability.

Journal of Fluid Mechanics, 2000

Compound threads and jets consist of a core liquid surrounded by an annulus of a second immiscibl... more Compound threads and jets consist of a core liquid surrounded by an annulus of a second immiscible liquid. Capillary forces derived from axisymmetric disturbances in the circumferential curvatures of the two interfaces destabilize cylindrical base states of compound threads and jets (with inner and outer radii R1 and aR1 respectively). The capillary instability causes breakup into drops; the presence of the annular phase allows both the annular- and core-phase properties to influence the drop size. Of technological interest is breakup where the core snaps first, and then the annulus. This results in compound drops. With jets, this pattern can form composite particles, or if the annular fluid is evaporatively removed, single drops whose size is modulated by both fluids.This paper is a study of the linear temporal instability of compound threads and jets to understand how annular fluid properties control drop size in jet breakup, and to determine conditions which favour compound drop ...

Journal of Controlled Release, 2013

Glaucoma is the second major cause of blindness in the world after cataract. Glaucoma management ... more Glaucoma is the second major cause of blindness in the world after cataract. Glaucoma management through eye drops that reduce the intraocular pressure (IOP) has major deficiencies including low patient compliance and low bioavailability. Extended wear contact lenses that deliver glaucoma drugs for extended periods could increase patient compliance, while also increasing the bioavailability. To develop extended wear contact lenses that can also provide extended glaucoma therapy, we disperse nanoparticles of PGT (propoxylated glyceryl triacylate) that contain a glaucoma drug timolol. The particles can also be loaded into prefabricated lenses by soaking the lenses in a solution of particles in ethanol. The particle loaded gels can release timolol in phosphate buffered saline (PBS) for about a month at room temperature. The most likely rate controlling mechanism is hydrolysis of the ester bond that links timolol to the PGT matrix, but other mechanisms such as water and drug diffusion, drug dissolution, drug-polymer chain cleavage, time-dependent drug permeability within the polymeric matrix, etc. may also be important. Nanoparticle incorporation in the silicone hydrogels results in reduction in ion and oxygen permeabilities, and an increase in modulus, and the impact on each of these properties is proportional to the particle loading. A gel with 5% particle loading can deliver timolol at therapeutic doses for about a month at room temperature, with a minimal impact on critical lens properties. Preliminary animal studies in Beagle dogs conducted with lenses in which particles are loaded by soaking the lenses in ethanol show a reduction in IOP.

Journal of Controlled Release, 2010

Ophthalmic drug delivery by contact lenses is expected to be more efficient due to continuous ext... more Ophthalmic drug delivery by contact lenses is expected to be more efficient due to continuous extended release of drug and increased residence time in the tear film. However, commercial contact lenses release ophthalmic drugs for a short period of about an hour and are thus not suitable for extended delivery use. Here we explore a novel approach of increasing the release duration of dexamethasone (DX) from commercial contact lenses by loading Vitamin E into the lenses. The Vitamin E was loaded into the lenses by soaking the lenses in Vitamin E-ethanol solution followed by ethanol removal through evaporation. The results show that with about 30% of Vitamin E loading in the contact lens, the DX release time can be increased to 7 to 9 days for ACUVUE(®) OASYS™, NIGHT&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;DAY™, and O(2)OPTIX™, which is a 9 to 16 fold increase compared to the DX release duration by pure contact lens without Vitamin E loading. The DX delivery by contact lens can be viewed as a one-dimensional transport by a flat thin film, and a mathematical model based on the drug diffusivity difference between Vitamin E and silicone hydrogel was also proposed to explain the DX release time increase by Vitamin E loaded contact lens.

Journal of Controlled Release, 2012

We combine laboratory-based timolol release studies and in vivo pharmacodynamics studies in beagl... more We combine laboratory-based timolol release studies and in vivo pharmacodynamics studies in beagle dogs to evaluate the efficacy of glaucoma therapy through extended wear contact lenses. Commercial contact lenses cannot provide extended delivery of ophthalmic drugs and so the studies here focused on increasing the release duration of timolol from ACUVUE® TruEye™ contact lenses by incorporating vitamin E diffusion barriers. The efficacy of timolol delivered via extended wear contact lenses was then compared to eye drops in beagle dogs that suffer from spontaneous glaucoma. The lenses were either replaced every 24 h or continuously worn for 4 days, and the pharmacodynamics effect of changes in the intraocular pressure (IOP) of timolol from the ACUVUE® TruEye™ contact lenses can be significantly increased by incorporation of vitamin E. The in vivo studies showed that IOP reduction from baseline by pure contact lens on daily basis was comparable with that by eye drops but with only 20% of drug dose, which suggested higher drug bioavailability for contact lenses. In addition, by inclusion of vitamin E into the lenses, the IOP was reduced significantly during the 4-day treatment with continuous wear of lens.

Journal of Controlled Release, 2011

Cyclosporine A (CyA) is effective in treating chronic dry eyes and contact lens mediated dry eyes... more Cyclosporine A (CyA) is effective in treating chronic dry eyes and contact lens mediated dry eyes. CyA is delivered through eye drops of an oil-in-water emulsion, which has a small residence time in the eyes, leading to low bioavailability. Here we explore delivery of CyA from contact lenses to provide controlled and extended drug delivery with an increased bioavailability due to enhanced ocular residence time. Loading and release profiles of CyA from commercial contact lenses are presented to show that 1-DAY ACUVUE® releases CyA for about a day and extended wear silicone hydrogel (SiH) lenses release CyA for about 2-weeks. The longer duration from SiH lenses compared to the 1-DAY ACUVUE®lens is due to larger partition coefficients in the gel. A novel approach is presented for increasing release duration from the SiH lenses to the desired 1-month through incorporation of Vitamin E. The results show that Vitamin E loaded lenses can provide CyA release within the therapeutic window for a period of about a month. This pilot study demonstrates the promising potential of delivering CyA from contact lens for treatment of chromic dry eyes and contact lens mediated dry eyes.

Journal of Colloid and Interface Science, 2012

Protein binding in hydrogels adversely affects their performance and can interfere with their usa... more Protein binding in hydrogels adversely affects their performance and can interfere with their usage in several biomedical applications including contact lenses. In this study we focus on understanding and modeling the mechanisms of protein transport in hydrogels, specifically focusing on the effect of protein concentration and gel crosslinking on transport. Specifically, we focus on lysozyme, the most abundant protein in tear fluid, and hydrogels of poly-hydroxyethyl methacrylate (p-HEMA), a common contact lens material. Protein uptake experiments with gels of different thicknesses showed a time scale increase as the square of the thickness suggesting diffusion controlled transport. Partition coefficient was found to be dependent on the equilibrium concentration of lysozyme, and also on the degree of crosslinking. Since transport is related to mesh size, gel modulus was obtained for various crosslinkings and utilized to estimate the mesh size. The transport data were fitted to a diffusion model and the fitted diffusivity was compared to diffusivity predicted from a model based on hydrogel mesh size. Both protein absorption and desorption data fitted the diffusion model with the same value of diffusivity, but the experimentally measured diffusivities were significantly smaller than those estimated on the basis of the gel mesh size. Models were modified to take into account protein binding to the polymer but the modified predictions were still larger than the measured values. The results of this study could assist in the development of contact lens materials that exhibit minimal protein binding, in designing cleaning regimens for protein removal from contact lenses, and in applications related to protein binding in several other biomaterials.

Journal of Colloid and Interface Science, 2013

Surfactant loaded polymeric hydrogels find applications in several technological areas including ... more Surfactant loaded polymeric hydrogels find applications in several technological areas including drug delivery. Drug transport can be attenuated in surfactant loaded gels through partitioning of the drug in the surfactant aggregates. The drug transport depends on the type of the aggregates and also on the surfactant transport because diffusion of the surfactant leads to dissolution of the aggregates. The drug and the surfactant transport can be characterized by the surfactant monomer diffusivity Ds. and the critical aggregation concentration C(*). Here we focus on the transport in hydroxyethyl methacrylate (HEMA) hydrogels loaded with three different types of Brij surfactants. We measure transport of a hydrophobic drug cyclosporine and the surfactant for surfactant loadings ranging from 0.1% to 8%, and utilize the data to predict the values of Ds. and C(*). We show that the predictions based on surfactant transport are significantly different from those based on modeling the drug transport. The differences are attributed to the assumption of just one type of aggregate in the gel irrespective of the total concentration. The transport data suggests existence of multiple types of aggregates and this hypothesis is validated for Brij 98 by imaging of the microstructure with free fracture SEM.