Polymer grafting onto starch nanocrystals

Monocrystalline starch nanoparticles were successfully grafted with poly(tetrahydrofuran), poly(caprolactone), and poly(ethylene glycol) monobutyl ether chains using toluene 2,4-diisocyanate as a linking agent. Surface grafting was confirmed using Fourier transform infrared and X-ray photoelectron spectroscopies, differential scanning calorimetry, elemental analysis, and contact angle measurements. Transmission electron microscopy observations of modified starch nanocrystals showed either the individualization of nanoparticles or the formation of a film, depending on the polymer used. It was shown that grafting efficiency decreased with the length of the polymeric chains, as expected. The resulting modified nanoparticles can find applications in the field of co-continuous nanocomposite materials.     

Graft copolymers of starch and its application in textiles

The graft copolymerization of styrene (ST), methyl methacrylate (MMA)/butyl acrylate (BA) with starch was carried chemically using ferrous ion-peroxide redox system. The grafting was performed at 60 °C and the monomer ratios of ST/MMA and ST/BA was varied with their % composition as 80/20, 50/50 and 20/80 parts by weight. The effect of initiator concentration, starch concentration and the monomer ratio on the grafting efficiency was studied. The grafted starch granules (GSG) were further analyzed for their particle size, bulk density and by sizing on cotton yarn for its physico-mechanical properties such as tensile strength, elongation at break, etc. The rheological properties of the resulting granular product in water as well as the starch graft copolymer emulsion were studied.     

Enhanced intracellular delivery of quantum dot and adenovirus nanoparticles triggered by acidic pH via surface charge reversal

Quantum dot (QD) and adenovirus (ADV) nanoparticles were surface-modified with graft copolymers that exhibited a charge reversal behavior under acidic condition. Poly(L-lysine) (PLL) was grafted with multiple biotin-PEG chains (biotin-PEG-PLL graft copolymer), and the remaining primary amine groups in the PLL backbone were postmodified using citraconic anhydride, a pH-sensitive primary amine blocker, to generate carboxylate groups. The surfaces of streptavidin-conjugated QDs were modified with citraconylated biotin-PEG-PLL copolymer, producing net negatively charged QD nanoparticles. Under acidic conditions, citraconylated amide linkages were cleaved, resulting in the recovery of positively charged amine groups with subsequent alteration of surface charge values. Intracellular delivery of QD nanoparticles was greatly enhanced in an acidic pH condition due to the surface charge reversal. The surface of avidin-conjugated adenovirus (ADV-Avi) encoding an exogenous green fluorescent protein (GFP) gene was also modified in the same fashion. The expression extent of GFP was significantly increased at more acidic pH than pH 7.4. This study demonstrates that various nanosized drug carriers, imaging agents, and viruses could be surface-engineered to enhance their cellular uptake specifically at a low pH microenvironment like solid tumor tissue.     

Effects of amylose/amylopectin ratio on starch-based superabsorbent polymers

Biodegradable superabsorbent polymers (SAPs) were prepared by grafting acrylamide onto starches then crosslinking with N,N′-methylene-bisacrylamide. This work focused on the effects of the amylose/amylopectin ratio of starches from the same source (corn) on the grafting reactions and performance of the resultant starch-based SAPs. To characterise each SAP, the acrylamide groups grafted onto the starch were detected by FTIR; grafting ratio and grafting efficiency were evaluated by a gravimetric method; and graft position and the length of the grafted segment were investigated by NMR. The relationships between the microstructures of the starches, and the graft reactions and performance of the SAPs were studied based on the amylose content in the starches. It was found that under the same reaction conditions, the grafting ratio and efficiency increased with increasing amylose content, which corresponds with water absorption ratio. NMR results indicated that the acrylamide group mainly grafted onto C6, and that the length of the grafted segment decreased with increasing amylopectin content in general, and in particular for waxy starch. The high molecular weight and branched structure of amylopectin reduced the mobility of the polymer chains and increased viscosity, which could explain the graft reactions and performance of the starch-based SAPs.     

Biodegradation of poly(epsilon-caprolactone)/starch blends and composites in composting and culture environments: the effect of compatibilization on the inherent biodegradability of the host polymer

The biodegradability of poly(epsilon-caprolactone) (PCL) was studied in blends and composites of modified and granular starch. Four types of PCL-starch compositions were prepared: (i) PCL-granular starch blends; (ii) hydrophobic coating of starch particles by n-butylisocyanate (C(4) starch) and octadecyltrichlorosilane (C(18) starch), followed by melt blending with PCL; (iii) PCL-starch blends compatibilized by PCL-g-dextran grafted copolymer (PGD); and (iv) PCL-grafted starch particles (PGS) as obtained by in situ ring-opening polymerization of caprolactone (CL) initiated directly from hydroxyl functions at the granular starch surface. Biodegradability of these materials was measured by monitoring the percentage of weight loss in composting and the rate of fungal colonization when samples were used as a sole carbon source for fungus (A. niger). Intrinsic viscosity [eta] of host PCL chains was measured after extraction of composted samples in boiled chloroform. SEM was used to study the surface morphology after compost incubation of the samples. The inherent biodegradability of host polymer was enhanced with surface compatibilization during composting for longer incubation. It was observed that the weight loss during composting increased with the decrease in interfacial tension between filler and polymer. In general, it was concluded that inherent biodegradability does not depend very significantly on the concentration of starch in the polyester matrix, but on the compatibilization efficiency. The effect of the PCL fraction in the graft copolymer, when used as compatibilizer, was also studied on the biodegradability of the host polymer.     

Syntheses and characterisation of graft copolymers of maize starch and methacrylonitrile

Grafting of methacrylonitrile (MAN) onto dried maize starch using ceric ammonium nitrate (CAN) as an initiator has been studied gravimetrically under nitrogen atmosphere in aqueous medium. The percentage grafting is favoured by increasing monomer concentration and reaction time but is affected by higher concentration of initiator and high temperature. No grafting was observed beyond 45°C. The optimum conditions established for grafting were: [CAN]=0.002 mol/l which was added in molar nitric acid; [MAN]=0.755 mol/l; reaction time, 180 min; and temperature, 35°C. The graft copolymers were analyzed by infrared spectroscopy and acid hydrolysis. The grafting of methacrylonitrile onto starch does not alter the thermal stability of starch. The crystalline region of starch was also involved in grafting. Scanning electron microscopy showed a thick polymer coating of grafted PMAN on the starch surface.     

新型人工红细胞的制备

目的:接枝淀粉包裹血红蛋白制备新型人造红细胞的代替品。方法:利用油酸接枝淀粉,在超声条件下下自组装,包裹天然牛血红蛋白,并鉴定其物理化学及生物学性能。测定包封率、红外光谱分析(FTIR)、电镜观察形态学及粒径,测定P50和Hill系数。结果:人工红细胞呈圆球形,平均粒径250nm,包封率高,具有良好的携氧、释氧能力。结论:成功制备了人工纳米红细胞,为进一步临床应用提供了基础。     

Synthesis of poly-(ε)-caprolactone grafted starch co-polymers by ring-opening polymerisation using silylated starch precursors

Poly-(ε)-caprolactone grafted corn starch co-polymers were synthesized using a hydrophobised silylated starch precursor. The silylation reaction was performed using hexamethyl disilazane (HMDS) as the reagent in DMSO at 70 °C. Silylated starch with a degree of substitution (DS) between 0.45 and 0.7 was obtained. ε-Caprolactone is grafted to silylated starch by a ring-opening polymerisation catalysed by Al(OiPr)₃ in THF at 50 °C. The grafting efficiency varies between 28% and 58%, the remainder being homopolymers of ε-caprolactone. The DS of the polycaprolactone graft is between 0.21 and 0.72. The poly-(ε)-caprolactone side chains consist of 40–55 monomer units and is a function of the reagent intakes. Experiments with native starch under similar conditions do not result in the desired poly-(ε)-caprolactone grafted corn starch co-polymers and unreacted starch was recovered after work-up. Removal of the silyl groups of the poly-(ε)-caprolactone grafted starch co-polymers is possible using a mild acid treatment with diluted hydrochloric acid in THF at room temperature.     

Synthesis of superabsorbent from carbohydrate waste

A mixture of acrylamide (AM) and acrylic acid (AA) monomers were grafted on germinated gelatinized wheat starch using potassium persulfate (KPS) as an initiator to yield superabsorbent. The effects of different parameters such as time, temperature, monomer feed (AM:AA), starch: monomers ratio and initiator concentration on graft add-on were studied, and the optimized values were found to be 2 h, 60 °C, 1:1 (w/w), 1:1(w/w) & 1% (with respect to starch powder), respectively. The product so formed was saponified with 0.1N NaOH, dried and finely powdered sample was characterized using FT-IR, TGA. Product showed maximum absorbency of 150 g/g.     

Synthesis and in vitro evaluation of carboxymethyl starch-chitosan nanoparticles as drug delivery system to the colon

The purpose of this study was to examine chitosan (CS)-carboxymethyl starch (CMS) nanoparticles as drug delivery system to the colon. The 5-aminosalicylic acid (5-ASA) was chosen as model drug molecule. CS-CMS nanoparticles were formulated by a complex coacervation process under mild conditions. The influence of process variables, including the two ionic polymers, on particle size, and nanoparticles entrapment of 5-ASA was studied. In vitro release of 5-ASA was also evaluated, and the integrity of 5-ASA in the release fraction was assessed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The release of 5-ASA from nanoparticle was based on the ion-exchange mechanism. The CS-CMS nanoparticles developed based on the modulation of ratio show promise as a system for controlled delivery of drug to the colon.     

Synthesis of partly debranched starch-g-poly(2-acryloyloxyethyl trimethyl ammonium chloride) catalyzed by horseradish peroxidase and the effect on adhesion to polyester/cotton yarn

We performed a dual-modification of starch via debranching and graft copolymerization to improve its adhesion to fibers. We synthesized the partly debranched starch-g-poly(2-acryloyloxyethyl trimethyl ammonium chloride) (PDS-g-PATAC) using horseradish peroxidase in the presence of hydrogen peroxide and acetylacetone. PDSs of different molecular structures were prepared by debranching waxy cornstarch for different periods of time. With increasing debranching time, the degree of hydrolysis of PDS increased from 0.85 % (10 min) to 1.13 % (30 min), while the degree of branching decreased from 8.37 % to 7.99 %. Fourier transform infrared analysis confirmed that ATAC units had been successfully grafted onto the starch (debranched or not debranched). The degree of substitution (DS) and grafting ratio (GR) of the PDS-g-PATACs were characterized by ¹H nuclear magnetic resonance. The DS and GR of grafted starches positively related with debranching time. Thermogravimetry-differential thermogravimetry analysis showed that grafted starch had lower thermal stability than ungrafted starch. The adhesion of PDS-g-PATAC to polyester/cotton yarns was evaluated. The PATAC chains grafted onto the starch enhanced the adhesion of starch to polyester/cotton yarn. The grafted starch produced from the copolymerization of PDS (after debranching for 10 min), exhibited the strongest adhesion to polyester/cotton yarn with a resulting tensile strength of 98.20 N.     

Preparation of cassava starch grafted with polystyrene by suspension polymerization

Cassava starch grafted with polystyrene (PS-g-starch) copolymer was synthesized via free-radical polymerization of styrene by using suspension polymerization technique. Potassium persulfate (PPS) was used as an initiator and water was used as a medium. The graft copolymer was characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis, X-ray diffraction and scanning electron microscopy. The sub-micron spherical beads of PS were observed on the surface of starch granules. SEM micrographs showed porous patches of PS adhering on the starch granules after Soxhlet extraction. FTIR spectra also indicated the presence of PS-g-starch copolymer. XRD analysis exhibited insignificant changes in crystalline structure and degree of crystallinity. The effects of starch:styrene weight ratio, amount of PPS, reaction time and reaction temperature on the percentage of grafting – G (%), were investigated. G (%) increased with increasing starch content. Other variables showed their own individual optimal values. The optimum condition yielding 31.47% of G (%) was derived when the component ratio was 1:3 and reaction temperature and time were 50 °C and 2 h, respectively. Graft copolymerization did not change granular shape and crystallinity of starch. This study demonstrated the capability of polymerization of styrene monomer on the granular starch without emulsifier and the synthesis of graft copolymer without gelatinization of starch.     

Synthesis and characterization of superparamagnetic nanoparticles coated with carboxymethyl starch (CMS) for magnetic resonance imaging technique

Magnetic nanoparticles have been proposed for use as biomedical purposes to a large extent for several years. The development of techniques that could selectively deliver drug molecules to the diseased site, without a concurrent increase in its level in healthy tissues, is currently one of the most active areas of cancer research. The conjugate carboxymethyl starch (CMS)/SPIO nanoparticles were prepared by chemical reaction. Several parameters including the drug/polymer ratios in range of 1:14 were examined to optimize formulation. The size distribution and morphology of nanoparticles and in vitro release profile in phosphate buffer medium (pH 7.4) during 12 h were then investigated. The magnetic NPs prepared in this study were spherical with a relatively mono-dispersed size distribution. The conjugate carboxymethyl starch (CMS)/SPIO nanoparticles were exhaustively studied as controlled-release systems for parenteral administration of a model drug 5-aminosalicyclic acid (mesalamine) and analyzed using various release kinetic studies.     

Investigation of polymer and nanoparticle properties with nicotinic acid and p-aminobenzoic acid grafted on poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) via click chemistry

In this study, the grafting of nicotinic acid and p-aminobenzoic acid (PABA) onto poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) was performed by Huisgen's 1,3-dipolar cycloaddition, also known as click chemistry. Concentrations used for grafting were 0.10, 0.20, and 0.30 molar ratios with respect to caproyl units. The grafted copolymers were successfully obtained at all ratios as confirmed by NMR, GPC, and FT-IR. According to the DSC results, the polymorphisms of these grafted copolymers were mostly changed from semicrystalline to amorphous depending on the type and the amount of grafting compounds. TGA thermograms showed different thermal stabilities of the grafted copolymers compared to the original copolymers. Cytotoxicity results from HUVEC models suggested that the toxicity of grafted nanoparticles increased with the molar ratios of grafting units. Due to differences in molecular structure between nicotinic acid and PABA, physicochemical properties (particle size and surface charge) of grafted copolymer nanoparticles were substantially different. With increasing molar ratio of the grafting units, the particle size of blank nanoparticles tended to increase, resulting from an increase in the hydrophobic fragments of the grafted copolymer. Ibuprofen was chosen as a model drug to evaluate the interaction between grafted copolymers and loaded drug. After ibuprofen loading, the particle size of the loaded nanoparticles of both grafted copolymers increased compared to that of the blank nanoparticles. Significant differences in loading capacity between nicotinic acid and PABA grafted copolymer nanoparticles were clearly shown. This is most likely a result of different compatibility between each grafting compound and ibuprofen, including hydrogen bond interaction, π-π stacking interaction, and steric hindrance.     

Darunavir-Loaded Lipid Nanoparticles for Targeting to HIV Reservoirs

Darunavir has a low oral bioavailability (37%) due to its lipophilic nature, metabolism by cytochrome P450 enzymes and P-gp efflux. Lipid nanoparticles were prepared in order to overcome its low bioavailability and to increase the binding efficacy of delivery system to the lymphoid system. Darunavir-loaded lipid nanoparticles were prepared using high-pressure homogenization technique. Hydrogenated castor oil was used as lipid. Peptide, having affinity for CD4 receptors, was grafted onto the surface of nanoparticles. The nanoparticles were evaluated for various parameters. The nanoparticles showed size of less than 200 nm, zeta potential of ? 35.45 mV, and a high drug entrapment efficiency (90%). 73.12% peptide was found conjugated to nanoparticles as studied using standard BSA calibration plot. Permeability of nanoparticles in Caco-2 cells was increased by 4-fold in comparison to plain drug suspension. Confocal microscopic study revealed that the nanoparticles showed higher uptake in HIV host cells (Molt-4 cells were taken as model containing CD4 receptors) as compared to non-CD4 receptor bearing Caco-2 cells. In vivo pharmacokinetic in rats showed 569% relative increase in bioavailability of darunavir as compared to plain drug suspension. The biodistribution study revealed that peptide-grafted nanoparticles showed higher uptake in various organs (also in HIV reservoir organs namely the spleen and brain) except the liver compared to non-peptide-grafted nanoparticles. The prepared nanoparticles resulted in increased binding with the HIV host cells and thus could be promising carrier in active targeting of the drugs to the HIV reservoir.     

Surface interaction forces of cellulose nanocrystals grafted with thermoresponsive polymer brushes

The colloidal stability and thermoresponsive behavior of poly(N-isopropylacrylamide) brushes grafted from cellulose nanocrystals (CNCs) of varying graft densities and molecular weights was investigated. Indication of the grafted polymer brushes was obtained after AFM imaging of CNCs adsorbed on silica. Also, aggregation of the nanoparticles carrying grafts of high degree of polymerization was observed. The responsiveness of grafted CNCs in aqueous dispersions and as an ultrathin film was evaluated by using light scattering, viscosimetry, and colloidal probe microscopy (CPM). Light transmittance measurements showed temperature-dependent aggregation originating from the different graft densities and molecular weights. The lower critical solution temperature (LCST) of grafted poly(NiPAAm) brushes was found to decrease with the ionic strength, as is the case for free poly(NiPAAm) in aqueous solution. Thermal responsive behavior of grafted CNCs in aqueous dispersions was observed by a sharp increase in dispersion viscosity as the temperature approached the LCST. CPM in liquid media for asymmetric systems consisting of ultrathin films of CNCs and a colloidal silica probe showed the distinctive effects of the grafted polymer brushes on interaction and adhesive forces. The origin of such forces was found to be mainly electrostatic and steric in the case of bare and grafted CNCs, respectively. A decrease in the onset of attractive and adhesion forces of grafted CNCs films were observed with the ionic strength of the aqueous solution. The decreased mobility of polymer brushes upon partial collapse and decreased availability of hydrogen bonding sites with higher electrolyte concentration were hypothesized as the main reasons for the less prominent polymer bridging between interacting surfaces.     

A chitosan-based flocculant prepared with gamma-irradiation-induced grafting

A natural polymer, chitosan, was modified to prepare an efficient flocculant using grafting method initiated by gamma ray in acid-water solution. A vinyl monomer, acrylamide, was used as the grafted monomer. The graft copolymer obtained was characterized using Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis. Effects of acetic acid concentration, total irradiation dose, dose rate and monomer concentration on the grafting percentage were investigated. Flocculation experiment results demonstrated that the graft copolymer produced was significantly superior to chitosan and polyacrylamide (PAM).     

Usefulness of raw bagasse for oil absorption: A comparison of raw and acylated bagasse and their components

Raw bagasse or sugar cane cellulosic residues were modified using acylation grafting with fatty acid. The capability of the grafted bagasse to absorb oil from aqueous solution was studied and compared with the raw bagasse. It was found that the grafted material was significantly more hydrophobic than the raw bagasse. This grafted bagasse had little affinity for water and good affinity for oil. It was also found that bleaching of raw bagasse did not enhance its oil absorptivity. The grafted raw bagasse would be most suitable for applications where oil is to be removed from an aqueous environment. For oil absorbing applications in the absence of water, the raw bagasse was an excellent material.     

Isocyanate crosslinked reactive starch nanoparticles for thermo-responsive conducting applications

Hydrophobic nanoparticles and nanocomposite films of 1,4-hexamethylene diisocyanate (HMDI)-modified starch nanoparticles (SNPs) have been synthesized at ambient temperatures. The platelet-like starch nanocrystals become pseudospherical after modification with HMDI and the size increases or decreases depending on diisocyanate concentration compared to the ungrafted particles as revealed by transmission electron microscopy (TEM) results. The obtained nanocrystals were characterized by means of the FT-IR and X-ray diffraction (XRD) techniques. When compared with the hydrophobic performance of the unmodified starch nanocrystals, that of crosslinked starch nanocrystals significantly increased. X-ray diffraction reveals that the crystalline structure of modified starch nanocrystals was preserved. The resulting hydrophobic starch nanoparticles are versatile precursors to the development of nanocomposites. The polyether-polyurethane crosslinked with SNPs nanocomposite film exhibited thermo-responsive electrical conductivity.     

Highly filled bionanocomposites from functionalized polysaccharide nanocrystals

Cellulose and starch nanocrystals obtained from the acid hydrolysis of ramie fibers and waxy maize starch granules, respectively, were subjected to isocyanate-mediated reaction to graft polycaprolactone (PCL) chains with various molecular weights on their surface. Grafted nanoparticles were characterized by X-ray diffraction analysis and contact angle measurements. We observed that the nanoparticles kept their initial morphological integrity and native crystallinity. Nanocomposite films were processed from both unmodified and PCL-grafted nanoparticles and PCL as matrix using a casting/evaporation technique. We showed that mechanical properties of resulting films were notably different. Compared to unmodified nanoparticles, the grafting of PCL chains on the surface results in lower modulus values but significantly higher strain at break. This unusual behavior clearly reflects the originality of the reinforcing phenomenon of polysaccharide nanocrystals resulting from the formation of a percolating network thanks to chain entanglements and cocrystallization.