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At least 19 recordsLinked to original sources
PubMed2006

Delivery of hydrophobised 5-fluorouracil derivative to brain tissue through intravenous route using surface modified nanogels.

Random copolymeric micelles composed of N-isopropylacrylamide (NIPAAM) and N-vinylpyrrolidone (VP) cross-linked with N,N'-methylenebisacrylamide (MBA) have been used as nanogel carriers to encapsulate N-hexylcarbamoyl-5-fluorouracil (HCFU), a prodrug of 5-FU, and have been targeted to brain tissue across blood-brain barrier (BBB) after coating with polysorbate 80. Accumulation of nanogel particles in the brain and other tissues of "strain A" mice had been monitored by radiolabeling of nanogels with (99m)Tc. Gamma Scintigraphic technique was also performed to see the distribution of (99m)Tc labeled nanogels in the brain. The retention time in blood appeared to be slightly longer for coated nanogels than that of uncoated nanogels though the accumulation of coated nanogels in the RES was more or less same as that of uncoated nanogels. The blood however had almost double accumulation of polysorbate 80 coated nanogels in the initial 5 min compared to that shown by uncoated nanogels. We speculate that coating of nanogels with polysorbate 80 alters the surface properties of nanogels, which results in relatively higher uptake in the brain tissue. The studies revealed that a large portion of (99m)Tc labeled HCFU loaded nanogels are accumulated in the RES (lung, liver and spleen). The accumulation of the labeled nanogels in the brain, however, is much less compared to RES and it has been found that while an amount of uncoated labeled nanogels was found to be 0.18% of the injected dose, it increased to 0.52% on coating with polysorbate 80. The optimal amount of polysorbate 80 added to nanogels for the maximum delivery of particles to brain was found to be 1% w/w. These results were further supported by the gamma scintigrams of New Zealand rabbits. Thus, the present nanogel system has opened a new avenue for poorly soluble drugs to be targeted to brain by coating the particles with polysorbate 80.

Animals↗
PubMed2004

Sparsely cross-linked "nanogel" matrixes as fluid, mechanically stabilized polymer networks for high-throughput microchannel DNA sequencing.

We have developed sparsely cross-linked "nanogels", subcolloidal polymer structures composed of covalently linked, linear polyacrylamide chains, as novel replaceable DNA sequencing matrixes for capillary and microchip electrophoresis. Nanogels were synthesized via inverse emulsion (water-in-oil) copolymerization of acrylamide and a low percentage (approximately 10(-4) mol %) of N,N-methylene bisacrylamide (Bis). Nanogels and nanogel networks were characterized by multiangle laser light scattering and rheometry, respectively, and tested for DNA sequencing in both capillaries and chips with four-color LIF detection. Typical nanogels have an average radius of approximately 230 nm, with approximately 75% of chains incorporating a Bis cross-linker. The properties and performance of nanogel matrixes are compared here to those of a linear polyacrylamide (LPA) network, matched for both polymer weight-average molar mass (M(w)) and the extent of interchain entanglements (c/c). At sequencing concentrations, the two matrixes have similar flow characteristics, important for capillary and microchip loading. However, because of the physical network stability provided by the internally cross-linked structure of the nanogels, substantially longer average read lengths are obtained under standard conditions with the nanogel matrix at a 98.5% accuracy of base-calling (for CE: 680 bases, an 18.7% improvement over LPA, with the best reads as long as 726 bases, compared to 568 bases for the LPA matrix). We further investigated the use of the nanogel matrixes in a high-throughput microfabricated DNA sequencing device consists of 96 separation channels densely fabricated on a 6-in. glass wafer. Again, preliminary DNA sequencing results show that the nanogel matrixes are capable of delivering significantly longer average read length, compared to an LPA matrix of comparable properties. Moreover, nanogel matrixes require 30% less polymer per unit volume than LPA. The addition of a small amount of low molar mass LPA or ultrahigh molar mass LPA to the optimized nanogel sequencing matrix further improves read length as well as the reproducibility of read length (RSD < 1.6%). This is the first report of a replaceable DNA sequencing matrix that provides better performance than LPA, in a side-by-side comparison of polymer matrixes appropriately matched for molar mass and the extent of interchain entanglements. These results could have significant implications for the improvement of microchip-based DNA sequencing technology.

Acrylic Resins↗
PubMed2006

Comparison of nanogel drug carriers and their formulations with nucleoside 5'-triphosphates.

PURPOSE: The aim of the study is to synthesize and characterize nanogel carriers composed of amphiphilic polymers and cationic polyethylenimine for encapsulation and delivery of cytotoxic nucleoside analogs 5'-triphosphates (NTPs) into cancer cells. METHODS: Nanogels were synthesized by a novel micellar approach and compared with carriers prepared by the emulsification/evaporation method. Complexes of nanogels with NTP were prepared; particle size and in vitro drug release were characterized. Resistance of the nanogel-encapsulated NTP to enzymatic hydrolysis was analyzed by ion-pair high-performance liquid chromatography. Binding to isolated cellular membranes, cellular accumulation and cytotoxicity were compared using breast carcinoma cell lines CL-66, MCF-7, and MDA-MB-231. In vivo biodistribution of the 3H-labeled NTP encapsulated in different types of nanogels was evaluated in comparison to the injected NTP alone. RESULTS: Nanogels with a particle size of 100-300 nm in the unloaded form and less than 140 nm in the NTP-loaded form were prepared. An in vitro release of NTP was >50% during the first 24 h. Nanogel formulations ensured increased NTP drug stability against enzymatic hydrolysis as compared to the drug alone. Pluronic-based nanogels NG(F68), NG(F127), NG(P85), and NGM(P123) demonstrated 2-2.5 times enhanced interaction with cellular membranes and association with various cancer cells compared to NG(PEG). Among them, NG(F68) and NG(F127) exhibited the lowest cytotoxicity. Injection of nanogel-formulated NTP significantly modulated the drug accumulation in different mouse organs. CONCLUSIONS: Nanogels composed of Pluronic F68 and P123 were shown to display certain advanced properties compared to NG(PEG) as a drug delivery system for NTP analogs. Formulations of nucleoside analogs in active NTP form with these nanogels will improve the delivery of these cytotoxic drugs to cancer cells and the therapeutic potential of this anticancer chemotherapy.

Animals↗
PubMed2005

Polyplex Nanogel formulations for drug delivery of cytotoxic nucleoside analogs.

Hydrophilic nanosized particles consisting of the cross-linked cationic polymer network (Nanogels) are suggested as a drug delivery system for nucleoside analog 5'-triphosphates, an active form of cytotoxic anticancer drugs. Preparation, properties, and cellular effects of several polyplex Nanogel formulations with the 5'-triphosphate of cytotoxic 5-fluoroadenine arabinoside (fludarabine) (FATP) were examined and discussed here. The polyplexes have formed spontaneously by mixing solutions of FATP and Nanogels because of ionic interactions between protonated polyethylenimine (PEI) chains in Nanogel network with polyphosphate groups of the drug. Subsequent compaction of the flexible Nanogel network has resulted in an encapsulation of the FATP/PEI complex in a dense core surrounded by hydrophilic poly(ethylene glycol) (PEG) envelope. This structure has provided a sustained release of the drug, as well as an efficient protection of FATP against enzymatic degradation. The drug loading could reach up to 33% by weight of the drug-Nanogel formulation. In vitro 35% of loaded drug has released from Nanogel formulations during the first 24 h, and a slower additional release was observed during the next 2 days. Nanogels have protected 90% of the encapsulated FATP from enzymatic dephosphorylation during the first 60 min of incubation in vitro. The drug-Nanogel formulation compared to the drug has demonstrated a significantly enhanced cytotoxicity in cultured cancer cells. Cancer cell-targeting molecules, such as folate, could be easily attached to Nanogels and this modification has resulted in a strong 10-fold increase of the carrier's internalization in human breast carcinoma MCF-7 cells. Moreover, transcellular transport of the folate-Nanogel polyplexes was found to be 4 times more effective compared to the drug alone using Caco-2 cell monolayers as an in vitro intestinal model. The data demonstrate that this carrier-based approach to delivery of cytotoxic drugs may enhance tumor specificity and significantly reduce side effects related to systemic toxicity usually observed during cancer chemotherapy.

Breast Neoplasms↗
PubMedDate not supplied

Cross-linked polymeric nanogel formulations of 5'-triphosphates of nucleoside analogues: role of the cellular membrane in drug release.

Activation of cytotoxic nucleoside analogues in vivo depends primarily on their cell-specific phosphorylation. Anticancer chemotherapy using nucleoside analogues may be significantly enhanced by intracellular administration of active phosphorylated drugs. However, the cellular transport of anionic compounds is very ineffective and restricted by many drug efflux transporters. Recently developed cationic nanogel carriers can encapsulate large amounts of nucleoside 5'-triphosphates that form polyionic complexes with protonated amino groups on the polyethylenimine backbone of the nanogels. In this paper, the 5'-triphosphate of an antiviral nucleoside analogue, 3'-azido-2',3'-dideoxythymidine (AZT), was efficiently synthesized and its complexes with nanogels were obtained and evaluated as potential cytotoxic drug formulations for treatment of human breast carcinoma cells. A selective phosphorylating reagent, tris-imidazolylphosphate, was used to convert AZT into the nucleoside analogue 5'-triphosphate using a one-pot procedure. The corresponding 3'-azido-2',3'-dideoxythymidine 5'-triphosphate (AZTTP) was isolated with high yield (75%). Nanogels encapsulated up to 30% of AZTTP by weight by mixing solutions of the carrier and the drug. The AZTTP/nanogel formulation showed enhanced cytotoxicity in two breast cancer cell lines, MCF-7 and MDA-MB-231, demonstrating IC50 values 130-200 times lower than those values for AZT alone. The exact mechanism of drug release from nanogels remains unclear. One mechanism could involve interaction with negatively charged counterions. A high affinity of nanogels to isolated cellular membranes has been observed, especially for nanogels made of amphiphilic block copolymer, Pluronic P85. Cellular trafficking of nanogel particles, contrasted by polyethylenimine-coordinated copper(II) ions, was studied by transmission electron microscopy (TEM), which revealed membranotropic properties of nanogels. A substantial release of encapsulated drug was observed following interactions of drug-loaded nanogels with cellular membranes. A drug release mechanism triggered by interaction of the drug-loaded nanogels with phospholipid bilayer is proposed. The results illustrate therapeutic potential of the phosphorylated nucleoside analogues formulated in nanosized cross-linked polymeric carriers for cancer chemotherapy.

Anti-HIV Agents↗
PubMed2003

Sparsely cross-linked "nanogels" for microchannel DNA sequencing.

We have developed sparsely cross-linked "nanogels", sub-colloidal polymer structures composed of covalently linked, linear polyacrylamide chains, as novel DNA sequencing matrices for capillary electrophoresis. The presence of covalent cross-links affords nanogel matrices with enhanced network stability relative to standard, linear polyacrylamide (LPA), improving the separation of large DNA fragments. Nanogels were synthesized via inverse emulsion (water-in-oil) copolymerization of acrylamide and N,N-methylenebisacrylamide (Bis). In order to retain the fluidity necessary in a replaceable polymer matrix for capillary array electrophoresis (CAE), a low percentage of the Bis cross-linker (< 10(-4) mol%) was used. Nanogels were characterized by multiangle laser light scattering and rheometry, and were tested for DNA sequencing by CAE with four-color laser-induced fluorescence (LIF) detection. The properties and performance of nanogel matrices were compared to those of a commercially available LPA network, which was matched for both weight-average molar mass (Mw) and extent of interchain entanglements (c/c*). Nanogels presented in this work have an average radius of gyration of 226 nm and a weight-average molar mass of 8.8 x 10(6) g/mol. At concentrations above the overlap threshold, nanogels form a clear, viscous solution, similar to the LPA matrix (Mw approximately 8.9 x 10(6) g/mol). The two matrices have similar flow and viscosity characteristics. However, because of the physical network stability provided by the internally cross-linked structure of the nanogels, a substantially longer read length ( approximately 63 bases, a 10.4% improvement) is obtained with the nanogel matrix at 98.5% accuracy of base-calling. The nanogel network provides higher-selectivity separation of ssDNA sequencing fragments longer than 375 bases. Moreover, nanogel matrices require 30% less polymer per unit volume than LPA. This is the first report of a sequencing matrix that provides better performance than LPA, in a side-by-side comparison of polymer matrices matched for Mw and extent of interchain entanglements.

Acrylic Resins↗
PubMed2005

Hybrid nanogels with physical and chemical cross-linking structures as nanocarriers.

Polymerizable nanogels were prepared by self-assembly of cholesteryl group-bearing pullulan (CHP) with methacryloyl groups (CHPMA). The CHPMA nanogel was polymerized with 2-methacryloyloxyethyl phosphorylcholine (MPC) by radical polymerization in dilute aqueous solution. The solution properties of the polymers in water were investigated by TEM, SEC-MALS, and fluorescence quenching technique. Monodispersed hybrid nanogels of CHPMA-MPC (CM nanogels) (25-30 nm in radius of gyration) were obtained by using CHPMA nanogel as a seed-nanogel. CM nanogels have a dual cross-linking structure that is physically cross-linked with the cholesteryl groups and chemically cross-linked with the MPC polymer chains. CM nanogels trap heat-denatured carbonic anhydrase B (CAB) and prevent their aggregations. The nanogels maintained the ability of trapping and releasing enzymes by host-guest interaction of cholesteryl group and cyclodextrin.

Cholesterol↗
PubMedDate not supplied

Design of hybrid hydrogels with self-assembled nanogels as cross-linkers: interaction with proteins and chaperone-like activity.

New hybrid hydrogels with nanogel domains were obtained by using polymerizable self-assembled nanogels as cross-linkers. Methacryloyl groups were introduced to cholesteryl group-bearing pullulan (CHP). The methacryloyl group-bearing CHPs (CHPMAs) formed nanogels by their self-association in water (R(g) = 14-17 nm). CHPMA nanogels were polymerized with 2-methacryloyloxyethyl phosphorylcholine (MPC) by radical polymerization in a semidilute aqueous solution. CHPMA nanogels acted as effective cross-linkers for gelation. TEM observation showed that the nanogel structure was retained after gelation and that the nanogels were well dispersed in the macrogel. The hybrid hydrogels showed two well-defined networks such as a nanogel intranetwork structure of less than 10 nm (physically cross-linking) and an internetwork structure of several hundred nanometers (chemically cross-linking). The immobilized nanogels retained their ability to trap and release protein (insulin was used as a model protein) by host-guest interaction of the cholesteryl group and cyclodextrin and also showed high chaperone-like activity for refolding of chemically denatured protein.

Cross-Linking Reagents↗
PubMed2006

Amphiphilic poly(D,L-lactic acid)/poly(ethylene glycol)/poly(D,L-lactic acid) nanogels for controlled release of hydrophobic drugs.

Photocrosslinked nanogels with a hydrophobic core and hydrophilic shell are successfully fabricated with the goal of obtaining a biocompatible and biodegradable drug carrier for hydrophobic anticancer drugs. These nanogels are composed of amphiphilic triblock copolymers, poly(D,L-lactic acid)/poly(ethylene glycol)/poly(D,L-lactic acid) (PLA-PEG-PLA), with acrylated groups at the end of the PLA segments. The copolymers are synthesized by ring-opening polymerization and possess a low CMC (49.6 mg x L(-1)), which easily helps to form micelles by self-assembly. The acrylated end groups allow the micelles to be photocrosslinked by ultraviolet irradiation, which turn the micelles into nanogels. These nanogels exhibit excellent stability as a suspension in aqueous media at ambient temperature as compared to the micelles. Moreover, the size of the nanogels is easily manipulated in a range of 150 to 250 nm by changing the concentration of crosslinkers, e.g., ethylene glycol dimethacrylate, and ultraviolet light irradiation time. The nanogels achieve a high encapsulation efficiency and offer a steady and long-term release mechanism for the hydrophobic anticancer drug, CPT. It shows that these nanogels are useful for a hydrophobic anticancer drug-carrier system. [pictures: see text] Formation of the PLA-PEG-PLA nanogels.

Biocompatible Materials↗
PubMed2007

Polymeric nanogel formulations of nucleoside analogs.

Nanogels are colloidal microgel carriers that have been recently introduced as a prospective drug delivery system for nucleotide therapeutics. The crosslinked protonated polymer network of nanogels binds oppositely charged drug molecules, encapsulating them into submicron particles with a core-shell structure. The nanogel network also provides a suitable template for chemical engineering, surface modification and vectorisation. This review reveals recent attempts to develop novel drug formulations of nanogels with antiviral and antiproliferative nucleoside analogs in the active form of 5'-triphosphates, discusses structural approaches to the optimisation of nanogel properties, and discusses the development of targeted nanogel drug formulations for systemic administration. Notably, nanogels can improve the CNS penetration of nucleoside analogs that are otherwise restricted from passing across the blood-brain barrier. The latest findings reviewed here demonstrate an efficient intracellular release of nucleoside analogs, encouraging further applications of nanogel carriers for targeted drug delivery.

Animals↗
PubMed2006

Nanogels prepared by self-assembly of oppositely charged globular proteins.

Ovalbumin and lysozyme are two main proteins in hen egg white with the isoelectric points of 4.8 and 11, respectively. Herein we report the manufacture of stable, narrowly distributed nanogels (hydrodynamic radius about 100 nm) using a novel and convenient method: ovalbumin and lysozyme solutions were mixed at pH 5.3, the mixture solution was adjusted to pH 10.3, then subsequently stirred and heated. The nanogels were characterized using a combination of techniques. The nanogels have spherical shape and core-shell structure. The core is mainly composed of lysozyme and the shell is mainly composed of ovalbumin. The proteins in the nanogels are in denatured states and they are bound by intermolecular hydrophobic interactions, hydrogen bonds, and disulfide bonds. The charges of the nanogels can be modulated by the pH of the medium. The electrostatic repulsion of ovalbumin molecules on the nanogel surface stabilizes the nanogels in aqueous solution. The formation mechanism of the nanogels is discussed.

Hot Temperature↗
PubMedDate not supplied

Nanogels for oligonucleotide delivery to the brain.

Systemic delivery of oligonucleotides (ODN) to the central nervous system is needed for development of therapeutic and diagnostic modalities for treatment of neurodegenerative disorders. Macromolecules injected in blood are poorly transported across the blood-brain barrier (BBB) and rapidly cleared from circulation. In this work we propose a novel system for ODN delivery to the brain based on nanoscale network of cross-linked poly(ethylene glycol) and polyethylenimine ("nanogel"). The methods of synthesis of nanogel and its modification with specific targeting molecules are described. Nanogels can bind and encapsulate spontaneously negatively charged ODN, resulting in formation of stable aqueous dispersion of polyelectrolyte complex with particle sizes less than 100 nm. Using polarized monolayers of bovine brain microvessel endothelial cells as an in vitro model this study demonstrates that ODN incorporated in nanogel formulations can be effectively transported across the BBB. The transport efficacy is further increased when the surface of the nanogel is modified with transferrin or insulin. Importantly the ODN is transported across the brain microvessel cells through the transcellular pathway; after transport, ODN remains mostly incorporated in the nanogel and ODN displays little degradation compared to the free ODN. Using mouse model for biodistribution studies in vivo, this work demonstrated that as a result of incorporation into nanogel 1 h after intravenous injection the accumulation of a phosphorothioate ODN in the brain increases by over 15 fold while in liver and spleen decreases by 2-fold compared to the free ODN. Overall, this study suggests that nanogel is a promising system for delivery of ODN to the brain.

Animals↗
PubMed2002

Polymeric nanogels produced via inverse microemulsion polymerization as potential gene and antisense delivery agents.

Polymeric nanogel vectors were developed for cellular gene and antisense delivery. Inverse microemulsion polymerization was utilized to synthesize biocompatible nanogels with controlled size, morphology, and composition. The chemical composition, size, polydispersity, stability, and swelling behavior of the nanogels were investigated by NMR, light scattering, transmission electron microscopy, and atomic force microscopy. The cell viability, uptake, and physical stability of nanogel-DNA complexes were evaluated under physiological conditions. Monodisperse nonionic and cationic nanogels were produced with controllable sizes ranging from 40 to 200 nm in diameter. The nanogels demonstrated extended stability in aqueous media and exhibited low toxicity in cell culture. Cationic nanogels formed monodisperse complexes with oligonucleotides and showed enhanced oligonucleotide uptake in cell culture. The nanogels synthesized in this study demonstrate potential utility as carriers of oligonucleotides and DNA for antisense and gene delivery.

Acrylates↗
PubMed2007

Botryoidal assembly of cholesteryl-pullulan/poly(N-isopropylacrylamide) nanogels.

Hybrid nanogels consisting of cholesteryl-modified pullulan (CHP) and poly(N-isopropylacrylamide) (PNIPAM) were synthesized by graft free-radical copolymerization of N-isopropylacrylamide (NIPAM) onto methacryloyl-substituted CHP nanogels (CHPMA) in water at 50 degrees C in the presence of a water-soluble free radical initiator. Depending on the initial NIPAM/CHPMA ratio, CHP-PNIPAM (CN) nanogels containing 30.8-84.8 wt % PNIPAM were obtained in the form of self-assembled nanoparticles with a hydrodynamic radius (Rh) of 69.0-116.0 nm in water kept at 20 degrees C. Hybrid nanogels of sufficiently high NIPAM content, such as the sample CN90, which contains 79.6 wt % NIPAM, exhibited a two-step response to changes in solution (3 mg/mL) temperature: a decrease in Rh from 93 to 57 nm as the temperature increased from 20 to 35 degrees C, followed by a sharp increase in Rh from 57 nm to 90 nm at 55 degrees C. Both steps in this temperature response were reversible. The multistep response to temperature of the CN nanogels was attributed to the morphology of the nanogels, which are seen as consisting of grape-like (botryoidal) clusters of associated native nanogels held together via cholesteryl cross-linking points and held together by the grafted PNIPAM chains.

Acrylic Resins↗
PubMed2006

Inhibition of the formation of amyloid beta-protein fibrils using biocompatible nanogels as artificial chaperones.

The formation of fibrils by amyloid beta-protein (Abeta) is considered as a key step in the pathology of Alzheimer's disease (AD). Inhibiting the aggregation of Abeta is a promising approach for AD therapy. In this study, we used biocompatible nanogels composed of a polysaccharide pullulan backbone with hydrophobic cholesterol moieties (cholesterol-bearing pullulan, CHP) as artificial chaperones to inhibit the formation of Abeta-(1-42) fibrils with marked amyloidgenic activity and cytotoxicity. The CHP-nanogels incorporated up to 6-8 Abeta-(1-42) molecules per particle and induced a change in the conformation of Abeta from a random coil to alpha-helix- or beta-sheet-rich structure. This structure was stable even after a 24-h incubation at 37 degrees C and the aggregation of Abeta-(1-42) was suppressed. Furthermore, the dissociation of the nanogels caused by the addition of methyl-beta-cyclodextrin released monomeric Abeta molecules. Nanogels composed of amino-group-modified CHP (CHPNH(2)) with positive charges under physiological conditions had a greater inhibitory effect than CHP-nanogels, suggesting the importance of electrostatic interactions between CHPNH(2) and Abeta for inhibiting the formation of fibrils. In addition, CHPNH(2) nanogels protected PC12 cells from Abeta toxicity.

Amyloid beta-Peptides↗
PubMed2003

Protein refolding assisted by self-assembled nanogels as novel artificial molecular chaperone.

Molecular chaperone-like activity for protein refolding was investigated using nanogels of self-assembly of cholesterol-bearing pullulan. Nanogels effectively prevented protein aggregation (i.e. carbonic anhydrase and citrate synthase) during protein refolding from GdmCl denaturation. Enzyme activity recovered in high yields upon dissociation of the gel structure in which the proteins were trapped, by the addition of cyclodextrins. The nanogels assisted protein refolding in a manner similar to the mechanism of molecular chaperones, namely by catching and releasing proteins. The nanogels acted as a host for the trapping of refolded intermediate proteins. Cyclodextrin is an effector molecule that controls the binding ability of these host nanogels to proteins. The present nanogel system was also effective at the renaturation of inclusion body of a recombinant protein of the serine protease family.

Animals↗
PubMed2005

Formation of intra- and interparticle polyelectrolyte complexes between cationic nanogel and strong polyanion.

Polyelectrolyte complex formation of a strong polyanion, potassium poly(vinyl alcohol) sulfate (KPVS), with positively charged nanogels was studied at 25 degrees C in aqueous solutions with different KCl concentrations (C(s)) as a function of the polyion-nanogel mixing ratio based on moles of anions versus cations. Used as the gel sample was a polyampholytic nanogel consisting of lightly cross-linked terpolymer chains of N-isopropylacrylamide, acrylic acid, and 1-vinylimidazole; thus, the complexation was performed at pH 3 at which the imidazole groups are fully protonated to generate positive charges. Turbidimetric titration was employed to vary the mixing ratio. Also employed for studies of the resulting complexes at different stages of the titration were dynamic light scattering (DLS) and static light scattering (SLS) techniques. It was found from the titration as well as DLS and SLS that there is a critical mixing ratio (cmr) at which both the size and molar mass of the complexed gel particles abruptly increase. The value of the cmr at C(s) = 0 or 0.01 M (mol/L) was observed at approximately 1:1 mixing ratio of anions versus cations but at lower mixing ratios than the 1:1 ratio under conditions of C(s) = 0.05 and 0.1 M. At the mixing ratios less than the cmr, the molar mass of the complex agrees with that of one gel particle with the calculated amount of the bound KPVS ions, indicating the formation of an "intraparticle" KPVS-nanogel complex, by the aggregation of which an "interparticle" complex is formed at the cmr. During the process of the intraparticle complex formation, both the hydrodynamic radius by DLS and the radius gyration by SLS decreased with increasing mixing ratio, demonstrating the gel collapse due to the complexation. At C(s) = 0 or 0.01 M and under conditions where the amount of KPVS bindings was less than half of the nanogel cations, however, the decrease of the hydrodynamic radius was very small, while the radius gyration fell monotonically. These results were discussed in connection with a collapse of dangling chains attached to the nanogel surface by the binding of KPVS.

Journal Article↗
PubMed2006

Stable and pH-sensitive nanogels prepared by self-assembly of chitosan and ovalbumin.

Two natural macromolecules, chitosan and ovalbumin, were used to produce nanogels by a new, green, and convenient method. Chitosan and ovalbumin solutions were mixed; the pH of the resulting solution was adjusted; and the solution was successively stirred and heated. After that, ovalbumin gelled forming nanospheres. The chitosan chains are supposed to be partly trapped in the nanogel core upon heating because of the electrostatic attractions between chitosan and ovalbumin, while the rest of the chitosan chains should form the shell of the nanogels. The nanogels did not change the size distribution after long-time storage and did not dissociate in the pH range of 2-10.5. The dispersibility, size, and hydrophobicity/hydrophilicity of the nanogels are pH-dependent. The nanogels are good candidates for cosmetic and pharmaceutical applications.

Chitosan↗