Biomedical subjects

H B Bohidar

Publications and source records attributed to H B Bohidar.

At least 19 recordsLinked to original sources

PubMed2006

Free-energy landscape of alcohol driven coacervation transition in aqueous gelatin solutions.

Liquid-liquid phase separation of a homogeneous polyampholyte (gelatin) solution into a dense polymer-rich coacervate and the dilute supernatant phase is discussed through free-energy landscape formalism. We have evaluated the free energy and entropy of the system as it undergoes the phenomenon of simple coacervation, driven by the addition of a nonsolvent. Electrophoretic mobility (mu) and turbidity measurements were performed on 0.01% and 0.05% (w/v) aqueous gelatin solutions that were driven towards coacervation by the addition of ethanol. The mobility of the polyampholyte molecules, which was typically mu approximately 0.38+/-0.02 microm/s cm/V in water, gradually reduced for the soluble intermolecular complexes to a plateau value of mu approximately 0.11+/-0.01 microm/s cm/V as the ethanol volume fraction equaled phi(ns) approximately 0.47+/-0.03, which coincided with the first appearance of coacervate droplets (coacervation transition) observed from turbidity measurements, a behavior found to be invariant of gelatin concentration. These results were used as input to the theoretical model to explicitly construct the free-energy landscape for a single gelatin chain and the global system comprising the polymer-rich coacervate and the dilute supernatant phase.

Journal Article↗

PubMed2006

Effect of temperature on alpha olefin sulfonate induced softening of gelatin hydrogels.

Dynamic light scattering (DLS) and oscillatory rheology experiments were performed to study temperature dependence (T=10-25 degrees C) of the interactions in hydrogels of gelatin with AOS (alpha olefin sulfonate, anionic surfactant) for surfactant concentrations in the range 25-100 mM, chosen larger than cmc (approximately 8mM). The network mesh size (xi) values deduced from fastmode diffusivity (D(f)) data obtained from dynamic structure factor measurements, S(q, t) approximately exp(-D(f)q(2)t) (for t<or=1 ms and q being the scattering wave vector), of micelle-bound gelatin gels was analyzed within the framework of Flory-Rhener theory of cross-linking, which revealed a temperature dependence, xi approximately (0.5-chi)(1/5)exp(-DeltaG(Total)/RT) where chi is the Flory-Huggins interaction parameter, the free-energy of the gel-surfactant complex is DeltaG(Total) and R is universal gas constant. The low-frequency isochronal storage, G' and loss, G'' modulii revealed a transition from the rigid to a softened gel state occurring at surfactant concentration close to 55 mM, independent of temperature. The free-energy of interaction between gel and surfactant deduced from Arrhenius plots obtained from temperature dependent rheology, and light scattering data support this observation.

Alkenes↗

PubMed2006

Swelling and de-swelling kinetics of gelatin hydrogels in ethanol-water marginal solvent.

Controlled osmotic swelling and de-swelling measurements have been performed on gelatin, a polyampholyte, hydrogels suspended in water-ethanol marginal solvent at room temperature (20 degrees C) where the alcohol concentration was changed from 0 to 100% (v/v). The change in gel mass was monitored as function of time until osmotic equilibrium was established with the surrounding solvent. It was observed that osmotic pressure of polymer-solvent mixing, pi(m)<<pi(el) (pi(el) being the osmotic pressure due to network elasticity). The osmotic pressure arising from ionic contributions, pi(ion) was found to play a significant role in controlling volume phase transitions. For gelatin hydrogels, total swelling pressure of gel, pi(tot) could be related to gelatin volume fraction phi(2), relaxed volume of network V(0), and crosslink density v(e) as: pi(tot)/RT approximately -(v(e)/V(0))[phi(2)(1/3)-phi(2)/2]+(rho(0)exp(phi(2)/2)) independent of gel pH and swelling time (rho(0) is the reference gelatin charge density at phi(2)=0.01). The entire experimental data generated collapsed onto a single master plot. Asymmetric volume transition was observed about iso-electric pH. Results are compared with those obtained for strong bio-polyelectrolyte gels, and chemically crosslinked gelatin gels.

Anions↗

PubMed2005

Effect of molecular weight heterogeneity on drug encapsulation efficiency of gelatin nano-particles.

Influence of molecular weight heterogeneity and drug solubility, drug loading and hydrodynamic conditions on drug release kinetics from gelatin nanoparticles were investigated. Also to assess the ability of gelatin nanoparticles as a potential intravascular probe for diagnostic purposes and in improving the biodelivery of cycloheximide (CHX), which is being used as a representative drug. Comparative characterization of 75 Bloom (type B, bovine), 175 and 300 Bloom (type A, porcine) gelatin nanoparticles was done to understand the phase behavior and hydrodynamic properties of gelatin chains and its nanoparticles. Gelatin nanoparticles were prepared by two-step desolvation method. Dynamic light scattering studies were performed to estimate hydrodynamic radii as well as intermolecular interaction. Effects of parameters like pH, temperature and molecular weight on the size and stability of the nanoparticles were studied. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) measurements were done for size and stability analysis. Enhanced visco-elastic properties of nanoparticles were observed as compared to normal solutions of gelatin.

Gelatin↗

PubMed2005

Kinetics of phase separation in systems exhibiting simple coacervation.

The kinetics of phase separation of a homogeneous polyelectrolytic solution into a dense polymer-rich coacervate and the dilute supernatant phase is discussed through statistical thermodynamics. It has been shown that the coacervate phase is associated with higher internal pressure, consequently giving rise to syneresis. Physical conditions for phase separations has been deduced explicitly which reveals that sigma(2)/qrt[I] > or = constant (where sigma is polyelectrolyte charge density and I is solution ionic strength), consistent with experimental observations. In the lattice model, r is the number of sites occupied by the polymer having a volume critical fraction psi(2c), it was found that phase separation would ensue when sigma(3)r > or = (64/9 alpha(2)) [psi(2c)/(1 - omega(2c))(2)], which reduces to (sigma(3)r/psi(2c)) > or = (64/9 alpha(2)) approximately 0.45 at 20 degrees C for psi(2c) < 1. The separation kinetics mimics a spinodal decomposition process. Rate of release of supernatant due to syneresis was found to be independent of the initial coacervate mass. Syneresis results are discussed in the context of temporal evolution of self-organization in polymer melts through Avrami model.

Journal Article↗

PubMed2005

Characterization of polyanion-protein complexes by frontal analysis continuous capillary electrophoresis and small angle neutron scattering: effect of polyanion flexibility.

The binding constant (K(obs)) for the beta-lactoglobulin-poly(vinylsulfate) (BLG-PVS) complex was measured by frontal analysis continuous capillary electrophoresis at pH values above the isoelectric point of BLG, and the persistence length (L(p)) of PVS was measured by small angle neutron scattering, to examine the effect of polyelectrolyte chain stiffness on its binding efficiency to proteins. The values of K(obs) and L(p) were compared with those of BLG-PSS and BLG-PAMPS (poly(2-acrylamido-2-methylpropanesulfonate)) reported previously. The relationship between K(obs) and L(p) was reciprocal, indicating that protein binding is enhanced by the flexibility of the polyanion, at least in the case where the net protein charge is negative. In addition, at a fixed pH, the polymer systems displayed a similar ionic strength dependence of K(obs). This similarity was consistent with the proposal that the binding properties of PVS and PAMPS polyanions are governed purely by electrostatic interactions and are independent of their molecular structure.

Electrophoresis, Capillary↗

PubMed2005

Effect of cationic size on gelation temperature and properties of gelatin hydrogels.

Effect of Na+, K+ and Ca2+ on gel transition temperature (Tg) of gelatin hydrogels (5%, w/v) has been studied by oscillatory rheology in the salt concentration range I = 0.01-0.1 M, which showed increase in Tg with salt concentration with the trend for Tg showing Ca2+ > K+ > Na+. The dynamic light scattering (DLS) measurements in the sol state (T>Tg) showed two distinct relaxation modes whereas only a gel mode was observed in the gel state in all the samples which contained significant amount of heterodyne contribution. Low frequency (1.5 rad/s) isochronal storage modulus data revealed the formation of strong gel in presence of CaCl2 compared to that of NaCl and KCl situations. The slow mode relaxation and heterodyne parameter obtained from DLS data indicate the presence of larger clusters in Ca2+ gels.

Biocompatible Materials↗

PubMed2005

Microscopic structure of gelatin coacervates.

Microscopic structure of simple coacervates of gelatin having concentration approximately 130 g/l were studied at 25 degrees C by atomic force microscopy (AFM), rheology, small angle neutron scattering (SANS), UV absorption and circular dichroism (CD) techniques. The behavior of viscoelastic exponents Delta' and Delta'' of storage and loss modulii (G'(omega) approximately omega Delta', G''(omega) approximately omega Delta") revealed that, Delta' = 0.25+/-0.01 and Delta'' = 0.78+/-0.1 for coacervates. The mass fractal dimension 'd(f)' for coacervate was found to be 2.27, which attributed a compact heterogeneous network structure to the coacervates. This is supported by AFM pictures. The CD and UV absorption data indicated presence of helical structures inside the coacervates phase. SANS results showed the existence of a single length scale associated with this system identified as gelatin persistence length, zeta = 27+/-2 A. These studies indicate that the coacervate phase is a low dimensional dense heterogeneous material comprised of strongly interconnected triple helices which imparts a large storage modulus to this material.

Circular Dichroism↗

PubMed2005

Release kinetics from bio-polymeric nanoparticles encapsulating protein synthesis inhibitor- cycloheximide, for possible therapeutic applications.

Cycloheximide, a protein synthesis inhibitor, was encapsulated in cross-linked gelatin nanoparticles (Type B, Bovine skin, 75 Bloom) of 168 nm diameter with 26% entrapment efficiency. In-vitro release kinetics of the drug from the nanoparticles was done in phosphate buffer saline (PBS) at pH 7.4 and pH 5.8. The release kinetics showed a bi-phasic curve. Interestingly, the release of drug is approx 90% in acidic pH as compared to 50% release in neutral pH. The particle size was determined by Dynamic Light Scattering (DLS) technique, and size distribution spectra at different pH were observed to vary inversely with increase in pH. These drug loaded nanoparticles were found to be stable in whole blood showing negligible haemolysis. Cytotoxicity in HBL-100 and MCF-7, breast cancer cell lines was done in a 24-72 hrs assay, showing increased anti-tumour activity over a period of time indicating slow release. Dose dependent cytotoxicity was observed after 24 hours upto 72 hours of incubation of nanoparticles while the drug per se (<4 microg) showed 93% toxicity within 24 hours. Phase contrast microscopy of nanoparticle-cell interaction, clearly indicated aggregation along the lipid cell-membrane. Electron Microscopy (TEM, SEM) studies revealed its size and spherical shape. The stability of the particle, the slow and controlled release of drug from the gelatin nanoparticles indicate that it is a good candidate to deliver bio-pharmaceuticals. These behave as "intelligent" carriers for drug delivery, and can be exploited to empty their drug load in acidic medium. The paper focuses on the release kinetics of the gelatin nanoparticles that can be successfully exploited to treat solid tumors.

Antineoplastic Agents↗

PubMed2004

Anomalous self-assembly of gelatin in ethanol-water marginal solvent.

Light scattering, rheology, and atomic force microscope (AFM) studies have been performed on solutions of a polyampholyte (gelatin) prepared in water-ethanol marginal solvent. At ethanol concentration approximately 45+/-2% v/v anomalous aggregation led to formation of fractal (on hydrophilic substrates; glass, quartz and silicon) aggregate of polypeptide molecules having fractal dimension d(f) in 2D=1.60+/-0.08. The time evolution morphology of these self-assembled and self-organized structures formed on hydrophilic substrates was driven by selective ethanol evaporation and was observed by an AFM. These fractal aggregates eventually transformed into near-spherical clusters with fractal corona having same fractal dimension (d(f)=1.58+/-0.05) and finally, the corona separated and regular aggregates were formed. The kinetics of aggregation on substrates could be modeled through random sequential adsorption of particles with continuum power-law size distribution. The temporal growth of aggregate hydrodynamic radius R(h)(t) and scattered intensity I(s)(t) measured in the bulk were observed to exhibit; R(h)-t(z) and I(s)-t(z)-with z=1/d(f), giving a fractal dimension d(f) in 3D approximately equal to 2.6+/-0.2, which is discussed within the framework of Smoluchowski aggregation kinetics. This growth in R(h) is accompanied by narrowing down of the particle size distribution. Solution rheology at this ethanol concentration revealed minimum thixotropy and maximum infinite shear viscosity features.

Journal Article↗

PubMed2004

Gelatin-alpha olefin sulfonate interactions studied by dynamic light scattering.

Dynamic light scattering (DLS) measurements were performed to study the binding of anionic surfactant alpha olefin sulfonate (AOS) to gelatin chains at various NaCl concentrations at 30 degrees C in aqueous sodium phosphate buffer (pH = 6.8) solutions. The surfactant concentration was varied from 0 to 80 mM and the NaCl concentrations chosen were 0.025, 0.05, and 0.1 M. AOS exhibited electrostatic binding to the positively charged sites of the polypeptide chain resulting in considerable reduction in its hydrodynamic radius up to critical micellar concentration (cmc = 8 mM for no salt, 0.01 and 0.025 M, and 5 mM for 0.05 M and 2 mM for 0.1 M solutions). The correlation function revealed the presence of two types of structures above cmc; namely the micelles of AOS and gelatin-AOS micelle complexes. The micellar radii (Rm), the effective gelatin-surfactant complex radii (Rc), have been determined as a function of salt concentration. No critical aggregation concentration (cac) was observed. The inter-gelatin-surfactant complex (kD1) and inter-micellar interactions (kD2), were determined by fitting the concentration dependence of Rm and Rc to a virial expansion in reduced concentration (c - cmc), which are compared. While kD1 showed strong ionic strength dependence, kD2 remained invariant of the same. The protein to surfactant binding ratio was found to be smaller than normal. Results have been discussed within the framework of the necklace-bead model of polymer-surfactant interactions.

Alkanesulfonates↗

PubMed2003

Potential of laser immunoassay for detection of HIV in human blood serum and urine.

The potential of Light Scattering Immunoassay (LIA) for detection of HIV in human blood serum has been explored by monitoring the agglutination of antigen coated polystyrene particles by dynamic light scattering. ELISA tested human sera having HIV, TB, Filaria along with normal sera have been analyzed using two specific synthetic peptide antigen (SP1, SP2) and one nonspecific peptide antigen (NSP). Few paired human sera and urine samples and nonspecific (of nonHIV diseases) urine samples have also been tested using the same antigens to check the possibility of replacement of sera by urine.

Antibody Specificity↗

PubMed2000

Anomalous colloidal stability of protein coated polystyrene latex beads studied by small angle light scattering.

Results of small angle laser light scattering experiments carried out on polystyrene latex beads coated with lysate of Plasmodium falciparum (Pf) antigen (Ag) and human seropositive sera (10:1 ratio) are reported for various NaCl concentrations (0-300 mM). The protein coated beads showed time-dependent coagulation. The normalised intensity of scattered light I(s)(t)/I(0) showed I(s)(t)/I(0)=1+(Gammat)(delta) behaviour with the coagulation rate, Gamma and exponent, delta showing anomalous dependence on NaCl concentration. The coagulation rate exhibited strong increase up to NaCl concentration of 50 mM, above this and up to 300 mM the coagulation rate was found to remain independent of NaCl concentration yielding non-DLVO behaviour. The same was true for delta which increased from 1.04+/-0.06 to 6.94+/-0.07 as NaCl concentration was raised from 0 to 50 mM. Above 50 mM it remained constant with delta=6.94+/-0.07. Results are discussed through Smoluchowski aggregation kinetics and theoretical construction of interparticle interaction potentials relevant to our problem.

Animals↗

PubMed2000

pH-induced coacervation in complexes of bovine serum albumin and cationic polyelectrolytes.

Turbidity and light scattering measurements, along with phase contrast microscopy, were used to follow the processes leading to coacervation when aqueous solutions of bovine serum albumin (BSA) and poly-(dimethyldiallylammonium chloride) (PDADMAC) were brought from pH = 4 to 10. The state of macromolecular assembly of complexes formed between BSA and PDADMAC prior to and during the pH-induced coacervation could be characterized by specific pH values at which recognizable transitions took place. In addition to the two characteristic pH values (pHcrit and pH phi) previously identified through turbidimetry, other transitions were explicitly established. On the basis of the pH-induced evolution of scattering intensity measurements, we concluded that the formation of soluble primary protein-polymer complexes is initiated at pHcrit and proceeds until "pH'crit". A subsequent increase in scattering intensity at "pHpre" may arise from the assembly of quasi-neutralized primary complexes as their net positive charge decreases with increase in pH. Subsequently, a maximum in scattering intensity at pH phi is observed coincident with the appearance of turbidity and also corresponding to the first microscopic observation of coacervate droplets. The temperature independence of pHcrit and pH phi suggests that hydrophobic contributions are negligible for the initial BSA-PDADMAC interactions and the subsequent coacervation process. The pH dependence of scattering intensity profiles allowed the identification of two other transitions beyond pH phi. Spherical microcoacervate droplets first observed around pH phi subsequently displayed morphological changes at "pHmorph", followed by the transformation to solid or flocculant substances at pHprecip.

Animals↗

PubMed1999

Laser light scattering immunoassay for malaria.

Laser light scattering immunoassay (LIA) was proposed as a prospective diagnostic method for the detection of antibody (or antigen) by monitoring the agglutination of antigen (or antibody) coated carrier particles using dynamic light scattering (DLS) as probe. LIA is a very sensitive assay as it can detect microscopic immune complexes even when antibody (or antigen) level is low. A sizeable number of human sera collected from malaria endemic areas and hospitals have been analysed by ELISA using Pf parasite lysate or a RESA derived synthetic peptide as antigen parallel to LIA using Pf antigen coated polystyrene latex beads. Comparative analysis of data suggests LIA to be as good as ELISA and possibly better in terms of sensitivity and simplicity. LIA can be a simple and inexpensive immunoassay suitable for field use and mass application.

Antigens, Protozoan↗

PubMed1998

Laser light scattering immunoassay: an improved data analysis by CONTIN method.

Laser light scattering immunoassay (LIA) is a diagnostic method for the detection of antibody by monitoring the agglutination of antigen carrier particles mediated by antibody, using dynamic light scattering (DLS) as probe. We have used this method for the detection of antibody to P. falciparum that cause malaria. The data were analysed using CONTIN method and the superiority of the distribution analysis over the conventional interpretation of the data in terms of mean diffusion coefficient or hydrodynamic radius is discussed in detail.

Agglutination↗

PubMed1998

Light scattering and viscosity study of heat aggregation of insulin.

Aggregation behavior and hydrodynamic parameters of insulin have been determined from static and dynamic light scattering experiments and intrinsic viscosity measurements carried out at pH 4.0, 7.5, and 9.0 in the temperature range 20-40 degrees C in aqueous solutions. The protein aggregated extensively at elevated temperatures in the acidic solutions. Intermolecular interactions were found to be attractive and to increase with temperature. The measured intrinsic viscosity [eta], diffusion coefficient D0, molecular weight M, and radius of gyration Rg exhibited the universal behavior: M[eta] = (2.4 +/- 02) x 10(-27) (Re, eta/Re, D)3(D0 eta 0/T)-3 and (D0 square root of n)-1 approximately equal to (square root of pi eta 0 xi beta/kBT) [1 + 0.201)(v/beta 3) square root of n], where n is the number of segments in the polypeptide. The effective hydrodynamic radii deduced from [eta], (Re, eta) and the same deduced from D0, (Re, D) showed a constant ratio, (Re, eta/Re, D = 1.1 +/- 0.1). Re, D/Rg = xi was found to be (0.76 +/- 0.07). From the known solvent viscosity eta 0, the segment length beta was deduced to be (10 +/- 1) A. The excluded volume was deduced to be (5 A)3 regardless of pH. The Flory-Huggins interaction parameter was found to be chi = 0.45 +/- 0.04, independent of pH and temperature.

Chemical Phenomena↗

PubMed1998

Hydrodynamic properties of gelatin in dilute solutions.

Aggregation properties of Gelatin chains in neutral aqueous solutions, are reported in the temperature range T = 35-60 degrees C, from the measured intrinsic viscosity [eta], diffusion coefficient, D(o), molecular weight Mw, and radius of gyration (Rg) data. Gelatin chains doubled their size as the solution was cooled to 35 degrees C from 60 degrees C. The intermolecular interaction was found to be repulsive which showed significant decrease as the temperature was reduced. The data provides excellent fitting to the scaling relations Mw[eta] = (1.96 +/- 0.06) x 10(-26)(Re,eta/Re,D)3(D(o) eta o/T)-3 and (D(o)n1/2)-1 approximately equal to (6 1/2 pie eta o chi beta/kB/T)[1 + 0.201(v/beta 3)n1/2] where n is the number of segments in the chain. The ratio of the hydrodynamic radius (Re,D) (deduced from D(o)) and Rg, (Re,D/Rg = zeta) was found to be 0.555. From the known solvent viscosity eta o, the segment length beta, was deduced to be (15 +/- 2) A. The deduced excluded volume was v approximately equal to (4.1 A)3. The Flory-Huggins interaction parameter (zeta) did not show observable temperature dependence.

Biopolymers↗