Polydispersity Values Research Articles

Response surface method for polyhydroxybutyrate (PHB) bioplastic accumulation in Bacillus drentensis BP17 using pineapple peel.

Polyhydroxybutyrate (PHB) is a biodegradable biopolymer which is useful for various applications including packing, medical and coating materials. An endospore-forming bacterium (strain BP17) was isolated from composted soil and evaluated for PHB production. Strain BP17, taxonomically identified as Bacillus drentensis, showed enhanced PHB accumulation and was selected for further studies. To achieve maximum PHB production, the culture conditions for B. drentensis BP17 were optimized through response surface methodology (RSM) employing central composite rotatable design (CCRD). The final optimum fermentation conditions included: pineapple peel solution, 11.5% (v/v); tryptic soy broth (TSB), 60 g/L; pH, 6.0; inoculum size, 10% (v/v) and temperature, 28°C for 36 h. This optimization yielded 5.55 g/L of PHB compared to the non-optimized condition (0.17 g/L). PHB accumulated by B. drentensis BP17 had a polydispersity value of 1.59 and an average molecular weight of 1.15x105 Da. Thermal analyses revealed that PHB existed as a thermally stable semi-crystalline polymer, exhibiting a thermal degradation temperature of 228°C, a melting temperature of 172°C and an apparent melting enthalpy of fusion of 83.69 J/g. It is evident that B. drentensis strain BP17 is a promising bacterium candidate for PHB production using agricultural waste, such as pineapple peel as a low-cost alternative carbon source for PHB production.

Hybrid polymers bearing oligo-l-lysine(carboxybenzyl)s: synthesis and investigations of secondary structure.

Hybrid polymers of peptides resembling (partially) folded protein structures are promising materials in biomedicine, especially in view of folding-interactions between different segments. In this study polymers bearing repetitive peptidic folding elements, composed of N-terminus functionalized bis-ω-ene-functional oligo-l-lysine(carboxybenzyl(Z))s (Lysn) with repeating units (n) of 3, 6, 12, 24 and 30 were successfully synthesized to study their secondary structure introduced by conformational interactions between their chains. The pre-polymers of ADMET, narrowly dispersed Lysns, were obtained by ring opening polymerization (ROP) of N-carboxyanhydride (NCA) initiated with 11-amino-undecene, following N-terminus functionalization with 10-undecenoyl chloride. The resulting Lysns were subsequently polymerized via ADMET polymerization by using Grubbs’ first generation (G1) catalyst in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) generating the ADMET polymers (A-[Lysn]m) (m = 2–12) with molecular weights ranging from 3 to 28 kDa, displaying polydispersity (Đ) values in the range of 1.5–3.2. After chemical analyses of Lysns and A-[Lysn]ms by 1H-NMR, GPC and MALDI-ToF MS, secondary structural investigations were probed by CD spectroscopy and IR spectroscopy in 2,2,2-trifluoroethanol (TFE). In order to study A-[Lysn]ms with defined molecular weights and low polydispersity values (Đ = 1.03–1.48), the ADMET polymers A-[Lysn=3]m=3 and A-[Lysn=24]m=4 were fractionated by preparative GPC, and subsequently analysed by 1H-NMR, analytical GPC, MALDI-ToF MS and CD spectroscopy. We can demonstrate the influence of chain length of the generated polymers on the formation of secondary structures by comparing Lysns with varying n values to the ADMET-polymers with the help of spectroscopic techniques such as CD and FTIR-spectroscopy in a helicogenic solvent.

Influence of Dextransucrase of Weissella Cibaria Nitcsk4 on Low Molecular Weight Dextran Yield: a Statistical Approach using Mixed Level Taguchi Design and Artificial Neural Network

In the present study, the influence of dextransucrase of Weissella cibaria NITCSK4 (DSWc4), sucrose concentration, and reaction temperature on the yield of low molecular weight dextran (LMWD-DexWc4) was investigated using mixed level Taguchi design and back propagation neural network (BPNN). BPNN model with three neurons in a hidden layer generated a low mean squared error (MSE). The determination coefficients (R2 -value) for ANN and Taguchi models were 0.991 and 0.998, respectively. Considering absolute average deviation (AAD) and MSE, Taguchi model is more adequate. Among three factors, the percentage yield of low molecular weight of dextran is invariably dependent on the sucrose concentration. The study suggested that a low sucrose concentration (3% w/v), DSWc4 (0.25 IU/ml) and slightly high temperature (35°C) ultimately favored the production of LMWD-DexWc4 (91.639%). LMW-DexWc4 produced by DSWc4 at optimized conditions was analyzed. The weight average molecular weight of LMW-DexWc4 was calculated using M-H expression, found to be 85775 (≈90 kDa). The relative percentage error between the number and weight average molecular weight was found to be less (4.42%). The polydispersity (PD) index of the LMW-DexWc4 was found to be 0.9576 and the value is close to 1. The PD value depicted that the molecular weight distribution of dextran was narrowly dispersed.

Order to Disorder Transition in a Coarsening Two-Dimensional Foam.

We quantify the spatiotemporal transformation of a monodisperse and well-ordered monolayer of bubbles, as they undergo Ostwald ripening, by tracking the size polydispersity of the bubbles and local ordering of the foam. After nuclei of disorder appear at random locations, the transition takes place through two successive phases: first, the disordered regions grow while the value of polydispersity increases slowly, then the polydispersity grows rapidly once the disordered zones begin to merge together. The transition is captured by a modified logistic model.

The effect of water/ethanol ratio and monomer concentration on the size and morphology of polyacrylamide nanogels in a surfactant-free synthesis

In this contribution, we propose a polyacrylamide surfactant-free nanogel synthesis technique in a water/ethanol system using N,N'-methylenebisacrylamide (MBAm) as a crosslinker agent. The polymerization reactions were carried out using the potassium persulfate (KPS) and N,N,N′,N′-tetramethylethylenediamine (TEMED) redox pair. The main contribution of this paper is a two-dimensional study of the particle size, polydispersity, and morphology as a function of the solvent water/ethanol wt. ratio and wt. % of monomer (acrylamide, AM) during the particle synthesis. The results show that the obtained particles have a similar morphology compared to those prepared using surfactants. The particle size was measured using Quasi-Elastic Light Scattering (QELS) of the redispersed nanogel, obtaining particle sizes from 41 to 1050 nm, with polydispersity values between 0.31 and 1. In all cases, we found three particle sizes with different abundance distributions, each having a prevailing abundancy ranging from 65% to 95%. Finally, the nanogel morphology was analyzed with Field Emission Scanning Electron Microscopy (FE-SEM) and Transmission Electron Microscopy (TEM).

Pursuit of optimal synthetic conditions for obtaining colloidal zero-valent iron nanoparticles by scanning pulsed laser ablation in liquids

Liquid-Assisted Pulsed Laser Ablation (LA-PLA) is a promising top-down method to directly synthesize colloidal dispersions of nanoparticles in a eco-friendly manner. However, the role of LA-PLA synthesis parameters is not yet fully agreed. This work seeks to optimize the production of nanoscale zero-valent iron (nZVI) particles suitable for biomedical or environmental applications using nanosecond LA-PLA on iron targets with different ablation media, laser and target scanning parameters. The use of alcohols as solvents produces iron-iron oxide core-shell nanoparticles with amorphous cores, except for a small crystalline fraction corresponding to the biggest core sizes. Decreasing carbon chain length and complexity leads to a thinning of the carbonaceous material coatings and an increase of the colloidal stability and the nanoparticle productivity. Moreover, a decrease of solvent density and surface tension allows obtaining reduced sizes and polydispersity values. Among, laser and scanning parameters, the pulse accumulation per spot displayed a clear effect in boosting size and productivity. As main outcome, aqueous dispersions with suitable colloidal properties are obtained, either by transferring to water of optimized nZVI particles produced in ethanol, or by direct formation of nZVI particles and in situ coating with hydrophilic molecules in aqueous solutions of these molecules.

A Novel Approach of Drug Localization through Development of Polymeric Micellar System Containing Azelastine HCl for Ocular Delivery.

Background: Development of polymeric micelles for the management of allergic conjunctivitis to overcome the limitations of topical installation, such as poor patient compliance, poor stromal permeability, and significant adverse effects, increase precorneal residence time and efficacy, and also control the release of drug at the target site.Objective: The investigation was aimed at developing a polymeric micellar system of Azelastine HCl for Ocular Delivery.Methods: Drug loaded micelles of tri-block copolymers Pf 127 were prepared by Thin Film hydration method. The polymeric micelles formulations (F1 to F9) were assessed for entrapment efficiency, micelle size, in vitro permeation, ex vivo transcorneal permeation, in vivo Ocular Irritation, and Histology.Results: Optimized micelles formulation (F3), with the lowest micelle size of 92 nm, least polydispersity value of 0.135, highest entrapment efficiency of 95.30 ± 0.17%, and a cumulative drug permeation of 84.12 ± 1.26% in 8h, was selected to develop pH-sensitive micelles loaded carbopol in situ gel. The optimized in situ gel (G4) proved to be superior in its ex vivo transcorneal permeation when compared with Market Preparation and pure drug suspension, exhibiting 43.35 ± 1.48% Permeation with zero-order kinetics (r2 = 0.9944) across goat cornea. Transmission Electron microscopy revealed spherical polymeric micelles trapped in the gel matrix. A series of experiments showed hydration capability, non-irritancy, and histologically safe gel formulation that had appropriate handling characteristics.Conclusion: A controlled release pH-sensitive ocular formulation capable of carrying the drug to the anterior section of the eye via topical delivery was successfully developed for the treatment of allergic conjunctivitis.

PEMBUATAN NANOPARTIKEL-PERAK EKSTRAK DAUN UBI JALAR ORANGE (Ipomoea batatas L.) DENGAN METODE BIOREDUKSI DAN UJI AKTIVITAS TERHADAP JUMLAH TROMBOSIT Mus musculus

This study aims to make silver nanoparticles (NPP) of orange Sweet potato extract (Ipomoea batatas L.) using bioreduction method and test the effect of giving silver nanoparticles - leaf extract of Ipomoea batatas L. orange (Ipomoea batatas L.) to the number of thrombocyte from male of Mus musculus induced by aspirin. The precursor used is 1 mM AgNO3 solution and as bioreductor is an antioxidant compound in orange sweet potato extract (Ipomoea batatas L.). The ratio of AgNO3 1 mM solution volume and orange sweet potato leaf extract is 9: 1 with 2 hours time. The characteristic test again obtained NPP is done using FTIR and Particle Size Analyzer (PSA) using Dynamyc Light Scattering method (DLS). The results showed that from the PSA analysis is known the average size of NPP – I. Batatas, L leaf extract is an average of 86.0 nm with a polydispersity value (PDI) of 0.17 < 1 that indicates that the NPP-leaf extract particle size distribution It is less homogeneous and are less stable.The results show that the administration of silver nanoparticles - orange sweet potato extract (Ipomoea batatas L.) can increase the platelet count of male mice significantly Dose of 0.014 g / Kgbb of 259,600 / mm3.

Design of β-lactoglobulin micro- and nanostructures by controlling gelation through physical variables

β-lactoglobulin (β-Lg) is the major protein fraction of bovine whey serum and its principal gelling agent. Its gelation capacity enables conformational changes associated with protein-protein interactions that allow the design of structures with different properties and morphologies. Thus, the aim of this work was to successfully use β-Lg, purified from a commercial whey protein isolate, to develop food-grade micro- (with diameters between 200 and 300 nm) and nano- (with diameters ≤ 100 nm) structures. For this purpose, the phenomena involved in β-Lg gelation were studied under combined effects of concentrations (from 5 to 15 mg mL−1), heating temperature (from 60 to 80 °C) and heating time (from 5 to 25 min) for pH values of 3, 4, 6 and 7. The effects of such conditions on β-Lg structures were evaluated and the protein was fully characterized in terms of size, polydispersity index (PDI) and surface charge (by dynamic light scattering – DLS), morphology (by transmission electron microscopy - TEM) and conformational structure (circular dichroism, intrinsic and extrinsic fluorescence). Results have shown that β-Lg nanostructures were formed at pH 3 (with diameters between 12.1 and 22.3 nm) and at 7 (with diameters between 8.9 and 35.3 nm). At pH 4 structures were obtained at macroscale (i.e., ≥ 6 μm) for all β-Lg concentrations when heated at 70 and 80 °C, independent of the time of heating. For pH 6, it was possible to obtain β-Lg structures either at micro- (245.0 – 266.4 nm) or nanoscale (≤ 100 nm) with the lowest polydispersity (PDI) values (≤ 0.25), in accordance with TEM analyses, for heating at 80 °C for 15 min. Intrinsic and extrinsic fluorescence data and far-UV circular dichroism spectra measurements revealed conformational changes on β-Lg structure that support these evidences. A strict control of the physical and environmental conditions is crucial for developing β-Lg structures with the desired characteristics, thus calling for the understanding of the mechanisms of protein aggregation and intermolecular interaction when designing β-Lg structures with novel functionalities.

Branched poly(biphenylene‐co‐sulfone)ether ion exchange membranes containing perfluorocyclobutane groups for fuel cell applications

ABSTRACTA series of branched poly(biphenylene‐co‐sulfone) ion exchange membranes containing perfluorocyclobutane groups were prepared for fuel cells. Two bifunctional trifluorovinyloxy‐terminated monomers (sulfonable 4,4′‐bis(trifluorovinyloxy)biphenyl and insulfonable 4,4′‐sulfonyl‐bis(trifluorovinyloxy)biphenyl) and a trifunctional trifluorovinyloxy‐terminated branching agent (1,1,1‐tris(4′‐trifluorovinyloxyphenyl)ethane) were synthesized and terpolymerized via thermal [2π + 2π] cyclodimerization to obtain partially fluorinated and branched polymers containing 0–5 mol% of the branching agent. They were then postsulfonated by chlorosulfonic acid at room temperature, cast as membranes, and characterized to evaluate their electrochemical properties for fuel cell applications. As the branching agent content was increased, their polydispersity values highly increased, indicating they became highly branched. It was confirmed that higher branching agent content also increased the ion exchange capacity, water uptake, and proton conductivity of the branched ion exchange membranes containing perfluorocyclobutane groups. This indicates that their electrochemical properties can be easily controlled by the degree of branching. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48373.

Molecular weight determination of heparosan- and chondroitin-like capsular polysaccharides: figuring out differences between wild -type and engineered Escherichia coli strains

Heparin and chondroitin sulfate are used as anti-thrombic and anti-osteoarthritis drugs, respectively, but their pharmacological actions depend on their structural characteristics such as their sulfation grade and their molecular weight. In the last years, new fermentation-based biotechnological approaches have tried to obtain heparin and chondroitin sulfate starting from the heparosan and chondroitin-like capsular polysaccharides produced by Escherichia coli K5 and K4. The study of the microbial capsular polysaccharide molecular weight is critical to obtain nature-like or structural tailor cut glycosaminoglycan homologues. However, so far, it has been scarcely investigated. In this paper, for the first time, a new protocol was set up to determine the molecular weights of the capsular polysaccharides of three wild-type and three engineered E. coli K5 and K4 strains. The protocol includes a small-scale downstream train to purify the intact polysaccharides, directly from the fermentation broth supernatants, by using ultrafiltration membranes and anion exchange chromatography, and it couples size exclusion chromatography analyses with triple detector array. In the purification high recovery (> 85.0%) and the removal of the main contaminant, the lipopolysaccharide, were obtained. The averaged molecular weights of the wild-type capsular polysaccharides ranged from 51.3 to 90.9kDa, while the engineered strains produced polysaccharides with higher molecular weights, ranging from 68.4 to 130.6kDa, but with similar polydispersity values between 1.1 and 1.5.

Experimental study on the microscopic characteristics of foams stabilized by viscoelastic surfactant and nanoparticles

Viscoelastic surfactant and nanoparticles have gained significant attention in the development of foamed fracturing fluid. In this article, the microscopic characteristics of foams stabilized by viscoelastic surfactant (EAPB) and nanoparticles (SiO2) at different temperature were investigated. By analyzing the bubble images taken from optical microscope, it is concluded that there was synergistic effect between elongated wormlike micelles and nanoparticles to stabilize foams which was indicated by large bubble number, small average bubble diameter and spherical shape of bubbles over time. Results showed that although temperature played a vital role on the acceleration of drainage rate and Ostwald ripening rate, this acceleration would be weakened by applying viscoelastic surfactant and nanoparticles together. Two calculation methods that are polydispersity based on statistic data and fractal theory based on box counting method were proposed to investigate the bubble size distribution and bubble structure. The small value of polydispersity and fractal dimension of the foams stabilized by 3% EAPB and 1% SiO2 demonstrated the relatively uniform bubble size distribution and regular bubble structure. Lastly, cryo-SEM was applied to observe the bubble morphology at microscopic scale, which showed the intense and compact bubble structure due to the formation of particle-micelle network. This study provides the workflow for the analysis of foams at microscopic scale and broadens the application of foamed fracturing fluid in the development of unconventional resources.

Stabilized Production of Lipid Nanoparticles of Tunable Size in Taylor Flow Glass Devices with High-Surface-Quality 3D Microchannels.

Nanoparticles as an application platform for active ingredients offer the advantage of efficient absorption and rapid dissolution in the organism, even in cases of poor water solubility. Active substances can either be presented directly as nanoparticles or can be integrated in a colloidal carrier system (e.g., lipid nanoparticles). For bottom-up nanoparticle production minimizing particle contamination, precipitation processes provide an adequate approach. Microfluidic systems ensure a precise control of mixing for the precipitation, which enables a tunable particle size definition. In this work, a gas/liquid Taylor flow micromixer made of chemically inert glass is presented, in which the organic phases are injected through a symmetric inlet structure. The 3D structuring of the glass was performed by femtosecond laser ablation. Rough microchannel walls are typically obtained by laser ablation but were smoothed by a subsequent annealing process resulting in lower hydrophilicity and even rounder channel cross-sections. Only with such smooth channel walls can a substantial reduction of fouling be obtained, allowing for stable operation over longer periods. The ultrafast mixing of the solutions could be adjusted by simply changing the gas volume flow rate. Narrow particle size distributions are obtained for smaller gas bubbles with a low backflow and when the rate of liquid volume flow has a small influence on particle precipitation. Therefore, nanoparticles with adjustable sizes of down to 70 nm could be reliably produced in continuous mode. Particle size distributions could be narrowed to a polydispersity value of 0.12.

Amphiphilic Modified Galactomannan as a Novel Potential Carrier for Hydrophobic Compounds

The present work aims at developing and characterizing a modified galactomannan for the production of nano-sized micelles through the solvent diffusion method and its evaluation as a new carrier for hydrophobic compounds. Guar gum galactomannan was acetylated and a new polymer with different degrees of acetylation was obtained. The acetylation and substitution degree of the polymer was determined and characterized by means of Fourier transform infrared spectroscopy and thermogravimetric analysis. Galactomannan acetate (GA) was evaluated for development of micelles through the solvent diffusion method. Critical micellar concentration (CMC) was evaluated through dynamic light scattering where the effect of a wide range of GA concentrations in the micelle formation was studied. Results showed that CMC is around 0.2 mg mL-1 and an increase of GA concentration leads to the formation of monodisperse micelles with low values of polydispersity. The influence of the degree of acetylation was evaluated in terms of size average, polydispersity (PdI) and zeta potential. Transmission electron microscopy was used to evaluate micelles’ morphology. It was shown that GA can be used to form micelles for the encapsulation of curcumin (used as model compound) with an encapsulation efficiency higher than 99 % and a loading capacity ranging from 5.5 to 7.7 %. Results showed that the degree of acetylation can be used to control particle size: micelles produced from GA with the lowest degree of acetylation have a diameter which is around 25 % smaller than that of micelles produced from GA with the highest degree of acetylation. This study provides information concerning the preparation of polymeric micelles based on a modified natural galactomannan for application in the food and pharmaceutical industry. To our knowledge, it is the first work dealing with galactomannans’ modification.

The novel calix[4]resorcinarene-PEG conjugate: Synthesis, self-association and encapsulation properties

The synthesis and study of self-association and encapsulation ability of new low toxic conjugate of tetraphenyleneoxypentylcalix[4]resorcinarene and methoxy-poly(ethylene glycole) (C5OPh-mPEG) were described. The conjugate is characterized by 1H, 13C NMR, FT-IR, MS, SLS methods. In an aqueous solution the conjugate form multimicellar nanoparticles with low polydispersity value (0.1, DLS method). The self-association of the conjugate was studied by DLS, fluorescence, fluorescence anisotropy method, TEM, and SAXS methods. The SAXS data were detailed analyzed, and the conjugate associates structure as ellipsoidal core-shell particles was proposed. The encapsulation efficiency is a result of the affinity of the conjugate low rim substituents to substrates and reaches of 39.8, 26.7, and 28.9% toward naproxen, ibuprofen and doxorubicin drugs, respectively.

Experimental characterization of a micro cross-junction as generator of Newtonian and non-Newtonian droplets in silicone oil flow at low Capillary numbers

In this paper the generation of Newtonian and non-Newtonian droplets in a continuous silicone oil flow through a micro cross-junction has been studied experimentally. The results obtained by using, as dispersed phase, pure water, water with Tween 20 and different concentrations of Xanthan gum aqueous solutions with the addition of Tween 20 are presented and discussed with the aim to put spotlight on the effect of properties of the involved immiscible liquids on the droplet regimes. A commercial micro cross-junction based on two glass microchannels having a stadium-shaped cross-section and inner hydrophobic walls has been employed. A wide range of volumetric flow rates of the continuous and dispersed phase has been imposed at the inlets of the micro cross-junction by two independent syringe pumps. The main droplet regimes have been correlated to the Capillary number linked to the continuous phase (Cac) and the volumetric flow rate ratio (α). The role of the viscosity ratio (λ) and of the shear-thinning nature of Xanthan gum aqueous solutions on the droplet regime is discussed. The results evidence that the tested micro cross-junction is able to generate very uniform monodispersed droplets with low polydispersity values (P < 6%) at low Capillary numbers (Cac < 0.02) in presence of both Newtonian and non-Newtonian dispersed phases.

Desolvation Conditions for Production of Sulfasalazine Based Albumin Nanoparticles: Physical Properties

Background: Albumin-based nanoparticles have been used as drug carriers to improve therapeutic effect. This study aimed to produce sulfasalazine (SSZ)-loaded bovine serum albumin (BSA) nanoparticles by desolvation technique and characterize their physical properties. Drug loading effect was also investigated. Methods: SSZ albumin nanoparticles were batch produced by desolvation technique and lyophilized. Physical characteristics of nanoparticles including size distribution, zeta potential and entrapment efficiency were studied. Results: Nanoparticles were spherical and typically 200–400 nm with low polydispersity (PDI). The zeta potentials of nanoparticles ranged from −21 to −41 mV, which were attributed to BSA and SSZ. The highest actual drug loading was close to 0.5%w/w. The addition of 2% sucrose during lyophilization was essential to avoid cake collapse and the particle sizes increased slightly where their PDI values were low. Although the presence of sucrose led to a slight reduction in zeta potential, it had limited effect on zeta potential of the nanoparticles. The interactions between SSZ and formulation excipients were also confirmed with FTIR and DSC analyses. Conclusion: Desolvation technique produced stable sulfasalazine-loaded nanoparticles that can be administered parenterally.

Astaxanthin-Loaded Nanostructured Lipid Carriers for Preservation of Antioxidant Activity.

Astaxanthin is a xanthophyll carotenoid showing efficient scavenging ability and represents an interesting candidate in the development of new therapies for preventing and treating oxidative stress-related pathologies. However, its high lipophilicity and thermolability often limits its antioxidant efficacy in human applications. Here, we developed a formulation of lipid carriers to protect astaxanthin’s antioxidant activity. The synthesis of natural astaxanthin-loaded nanostructured lipid carriers using a green process with sunflower oil as liquid lipid is presented. Their antioxidant activity was measured by α-Tocopherol Equivalent Antioxidant Capacity assay and was compared to those of both natural astaxanthin and α-tocopherol. Characterizations by dynamic light scattering, atomic force microscopy, and scattering electron microscopy techniques were carried out and showed spherical and surface negative charged particles with z-average and polydispersity values of ~60 nm and ~0.3, respectively. Astaxanthin loading was also investigated showing an astaxanthin recovery of more than 90% after synthesis of nanostructured lipid carriers. These results demonstrate the capability of the formulation to stabilize astaxanthin molecule and preserve and enhance the antioxidant activity.

Electron Paramagnetic Resonance and Small-Angle X-ray Scattering Characterization of Solid Lipid Nanoparticles and Nanostructured Lipid Carriers for Dibucaine Encapsulation.

Dibucaine (DBC) is one of the most potent long-acting local anesthetics, but it also has significant toxic side effects and low water solubility. Solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) have been proposed as drug-delivery systems to increase the bioavailability of local anesthetics. The purpose of the present study was to characterize SLNs and NLCs composed of cetyl palmitate or myristyl myristate, a mixture of capric and caprylic acids (for NLCs only) plus Pluronic F68 prepared for the encapsulation of DBC. We intended to provide a careful structural characterization of the nanoparticles to identify the relevant architectural parameters that lead to the desirable biological response. Initially, SLNs and NLCs were assessed in terms of their size distribution, morphology, surface charge, and drug loading. Spectroscopic techniques (infrared spectroscopy and electron paramagnetic resonance, EPR) plus small-angle X-ray scattering (SAXS) provided information on the interactions between nanoparticle components and their structural organization. The sizes of nanoparticles were in the 180 nm range with low polydispersity and negative zeta values (-25 to -46 mV). The partition coefficient of DBC between nanoparticles and water at pH 8.2 was very high (>104). EPR (with doxyl-stearate spin labels) data revealed the existence of lamellar arrangements inside the lipid nanoparticles, which was also confirmed by SAXS experiments. Moreover, the addition of DBC increased the molecular packing of both SLN and NLC lipids, indicative of DBC insertion between the lipids, in the milieu assessed by spin labels. Such structural information brings insights into understanding the molecular organization of these versatile drug-delivery systems which have already demonstrated their potential for therapeutic applications in pain control.

THE INHIBITION OF HUMAN PLATELET AGGREGATION BY A LOW-MOLECULAR WEIGHT CHITOSAN

Chitosan derivatives were obtained by chemical (MW of 6 kDa, DD 99% - Ch6/99; MW13 kDa, DD 98% - Ch13/98) and enzymatic (MW of 5 kDa, DD 85% - Ch5/85; MW of 10 kDa, DD 85% - Ch10/85) depolymeri-sation of chitosan with a MW of 334 and 1000 kDa. Chitosan derivatives (almost identical MW pairs and different DD) possessed insignificant an-ticoagulant activity, did not promote human platelet aggregation and re-duced ADP or collagen-induced platelet aggregation. The studied sam-ples at a concentration of 2 mg/ml reduced the aggregation of platelets more than twice induced in 2x10-6M and 1x10-5M concentrations; at weak activation in 2x10-6M, the Ch10/85 sample was the most effective. The Ch6/99 and Ch13/98 samples were 20 times more effective at the inhibi-tion of collagen-induced platelet aggregation than the Ch10/85 sample. The latter can be explained by the greater value of positive charge (DD) and polydispersity (Mw/Mn) of chitosan samples obtained by chemical de-polymerisation.