Starch urea formaldehyde matrix encapsulation of solid agrochemicals. I. Matrix synthesis and characterizations

A starch urea formaldehyde (starch-UF) matrix has been studied for application to the encapsulation of a solid insecticide. The pertinent parameters relating to the matrix synthesis have been identified and the influences of these parameters on release of the insecticide from the starch UF matrix have been investigated. The key parameter controlling the rate of release is the urea to starch ratio. It is shown that the release process can be described in terms of the generalized equation M_t/M_∞ = ktⁿ where k and n vary with system variables.     

扩散控制型混合药膜包膜体系缓释的数学模型

A release model for diffusion-controlled monolithic matrix coated with outer membrane system is proposed and solved by using the refined double integral method. The calculated results are in satisfactory agreement with the experimental release data. The present model can be well used to describe the release process for all Cd/Cs.values. In addition, the release effects of the monolithic matrix coated with outer membrane system are discussed theoretically.     

低相对分子质量聚乳酸及其与壳聚糖的共混为载体的药物控释研究

以两种低黏均相对分子质量(Mη=3 595和10 306)聚乳酸及其与壳聚糖按5∶1,10∶1,20∶1,40∶1质量比共混为载体,用熔融法制备了吡虫啉控释制剂;用体外实验测定了制剂中吡虫啉的释放动力学;通过测定释放过程中释放介质水的pH,初步考察了基体的降解性能;通过测定释放实验结束时制剂残留质量,考察了基体的溶蚀性能,初步探讨了释放机理。结果表明,低相对分子质量聚乳酸及其与壳聚糖共混材料为载体,可以用于吡虫啉的控制释放,呈现扩散和溶蚀共同控制的缓慢释放,和溶蚀控制的快速释放两阶段释放规律。提高聚乳酸的相对分子质量可以减缓吡虫啉的释放,使释放特征发生从初期的快速释放和后期的缓慢释放,到初期缓慢释放和随后的快速持续释放的转变。降低聚乳酸相对分子质量或在基体中加入壳聚糖,可加大基体的溶蚀,使溶蚀控制的吡虫啉快速释放阶段提前。在Mη=10 306的聚乳酸中加入不同质量比的壳聚糖,可使释放介质水的pH约为中性,在117-336 h内调节快速释放开始时间,在228-445 h内调节释药中值时间。这种聚乳酸/壳聚糖共混载体可望在多功能型种子处理控释制剂上获得应用。     

Silylated montmorillonite based molecularly imprinted polymer for the selective binding and controlled release of thiamine hydrochloride

In the present study, specific binding and controlled release of thiamine hydrochloride (THC) to and from a novel molecularly imprinted polymer (MIP) matrix namely, THC-templated-silylated montmorillonite-itaconic acid polymer was investigated. The polymer matrix was characterized by means of XRD, FTIR and SEM analyses. Optimization of various imprinting components and binding characteristics of THC by the novel MIP were examined in detail. The binding affinity of THC for MIP was found to be greater than that for non-imprinted polymer (NIP). The maximum binding was found to be at solution pH of 4.5. The Sips isotherm model was found to describe well the equilibrium binding data with maximum binding capacity of 100 mg/g for MIP. The kinetic study revealed that the binding of THC onto MIP follows pseudo-second-order kinetic model with correlation coefficient 0.999. The swelling study of MIP in distilled water showed that the maximum swelling capacity is 329.0 g/g at about 8 h. In vitro release experiments showed that MIP releases drug in intestinal fluid with a controlled manner. The release kinetics of drug from MIP was analyzed using Ritger–Peppas model. The binding specificity of MIP for THC was tested using different substrates having structural analogue to the template, THC.     

Sustained Release of Metoprolol Tartarate from Radiation-Grafted pH-Responsive Hydrogels

pH-responsive hydrogels composed of methacrylic acid (MAA) grafted on poly(ethylene oxide)-poly(vinylpyrrolidone)(PEO-PVP) network were made by electron beam irradiation technique. The grafting was carried out at various concentrations of MAA with different irradiation doses. The gels were characterized by IR, DSC and SEM techniques. The swelling behavior of the gels was studied under different pH conditions. The swelling parameters were evaluated. The mode of water diffusion into the gels was found to be structure-dependent. The pH responsiveness of the gels was evident from the enhanced swelling of the gels with increasing pH of the medium. The suitability of these gels as matrix materials for stimuli-responsive sustained-release drug formulations was studied. The in vitro release profile of an antihypertensive drug, metoprolol tartarate, from these gels was studied at pH 1.2 and 7.4. The extent of drug release is found to be pH-dependent. The data were analyzed to understand the mechanism of drug release from the gels. The gels exhibited diffusion-controlled release behavior. Drug release kinetic analysis indicated “first order” release where the amount of drug released is dependent on the matrix drug load and the value of the diffusion coefficient indicated anomalous diffusion.     

氯苯酚在活性炭纤维上吸附平衡的研究

研究了水溶液中氯苯酚在活性炭纤维上的吸附平衡,实验探讨了反应温度、溶液pH值对活性炭纤维吸附平衡的影响。实验结果表明,平衡吸附量随着温度降低而升高;当pH值<7时,平衡吸附量几乎不随溶液的pH值而变化,而当pH值>7时,氯苯酚在活性炭纤维上的平衡吸附量随着pH值的增加而减小,pH值愈大,平衡吸附量减小的愈快。分别采用Langmuir模型和Freundlich模型描述吸附平衡等温线,在实验范围内Langmuir模型与实验数据吻合较好。     

Real time monitoring of the drug release of rhodamine B on graphene oxide

A real time method for monitoring the drug load and release on graphene oxide (GO) in a cuvette is reported using rhodamine B (RB) as a model for a drug. The mechanisms of the release of RB at different pH were investigated, by monitoring the time dependency of the accumulative drug release. In vitro real time experimental results indicated that RB could be loaded on GO with a capacity of 0.5 mg/mg. The drug release of RB was pH sensitive as observed at pH 7.4 and pH 4.5 PBS solutions. The higher pH values lead to weaker hydrophobic force and hydrogen bonds, and thus higher release rate. The ionic strength also influenced the release of RB, as shown from the different release rates between PBS solutions and double distilled water. These results indicated a case II transport process at pH 7.4 and an anomalous diffusion process at pH 4.5 and in water. The method described here allows real time detection of the drug release rate, in contrast to common dialysis analysis. This method also points to other real time detections in biomedical investigations.     

Description of Release Process of Doxorubicin from Modified Carbon Nanotubes

The article discusses the release process of doxorubicin hydrochloride (DOX) from multi-wall carbon nanotubes (MWCNTs). The studies described a probable mechanism of release and actions between the surface of functionalized MWCNTs and anticancer drugs. The surface of carbon nanotubes (CNTs) has been modified via treatment in nitric acid to optimize the adsorption and release process. The modification efficiency and physicochemical properties of the MWCNTs+DOX system were analyzed by using SEM, TEM, EDS, FTIR, Raman Spectroscopy and UV-Vis methods. Based on computer simulations at pH 7.4 and the experiment at pH 5.4, the kinetics and the mechanism of DOX release from MWNT were discussed. It has been experimentally observed that the acidic pH (5.4) is appropriate for the efficient release of the drug from CNTs. It was noted that under acidic pH conditions, which is typical for the tumour microenvironment almost 90% of the drug was released in a relatively short time. The kinetics models based on different mathematical functions were used to describe the release mechanism of drugs from MWCNTs. Our studies indicated that the best fit of experimental kinetic curves of release has been observed for the Power-law model and the fitted parameters suggest that the drug release mechanism of DOX from MWCNTs is controlled by Fickian diffusion. Molecular dynamics simulations, on the other hand, have shown that in a neutral pH solution, which is close to the blood pH, the release process does not occur keeping the aggregation level constant. The presented studies have shown that MWCNTs are promising carriers of anticancer drugs that, depending on the surface modification, can exhibit different adsorption mechanisms and release.     

Properties of pH‐dependent tertiary amine‐based gels as potential drug delivery matrices

The rheological and morphological properties and in vitro theophylline release of tertiary amine‐based microgels were evaluated. The testing of such a formulation through in vitro diffusion experiments revealed that the release of theophylline from the microgels was pH‐dependent and differs significantly with respect to a nonresponsive gel like scleroglucan (Scl). The microgels were obtained from 2‐(diethyl amino) ethylmethacrylate (DEA) in the presence of a bifunctional crosslinker at pH 8–9. As the resulting microgels are pH‐responsive and an increase in viscosity from high to low pH range is exhibited, the in vitro release of theophylline as model drug was studied at different pHs of both the matrix and the receptor medium. The release behaviors of PDEA‐based microgels were compared to nonresponsive natural gel Scl, studied previously. For microgels, diverse release patterns were found at different acidity conditions. This observation seems to be related to complex diffusion phenomena and the different gel structure obtained for samples prepared at dissimilar pH. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4035–4040, 2007     

Gelatin based pH‐sensitive hydrogels for colon‐specific oral drug delivery: Synthesis,characterization, and in vitro release study

Based on gelatin (Gltn) and acrylic acid (AAc), biodegradable pH‐sensitive hydrogel was prepared using gamma radiation as super clean source for polymerization and crosslinking. Incorporation of PAAc in the prepared hydrogel was confirmed by Fourier transform infrared spectroscopy (FTIR). The effect of PAAc content on the morphological structure of the prepared hydrogel swollen at pH 1, 5, and 7 was examined using scanning electron microscopy (SEM). The results showed the dependence of the porous structure of the prepared hydrogels on AAc content and the pH of the swelling medium. Swelling properties of gelatin/acrylic acid copolymer hydrogels with different AAc contents were investigated at different pH values. Swelling data showed that the prepared hydrogels possessed pronounced pH sensitivity. In vitro release studies were performed to evaluate the hydrogel potential as drug carrier using ketoprofen as a model drug. Experimental data showed that the release profile depends on both hydrogel composition and pH of the releasing medium. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Control release of some pesticides from starch/(ethylene glycol‐co‐methacrylic acid) copolymers prepared by γ‐irradiation

Starch/(Ethylene glycol‐co‐Methacrylic acid) [Starch/(EG‐co‐MAA)] hydrogels were designed for controlled delivery of pesticides, such as Fluometuron (FH); Thiophanate Methyl (TF) and Trifluralin (TI) which are use in the agricultural field. The delivery device was prepared by using γ‐irradiation and was characterized by FTIR, DSC, and SEM. The swelling behavior of hydrogels as a function of copolymer composition and irradiation dose was detected. This article discusses the swelling kinetics of polymer matrix and release dynamics of Trifluralin from hydrogels for the evaluation of the diffusion mechanism and diffusion coefficients. The values of the diffusion exponent ‘n’ for both the swelling of hydrogels and the release of Trifluralin from the hydrogels have been observed between 0.56 and 0.86 when the MAA content in the polymers was varied from 20 to 80 wt %, respectively. It is inferred from the values of the ‘n’ that non‐Fickian diffusion mechanism has occurred for different EG/MAA compositions. The release rate from matrices prepared under different conditions was studied to determine which factors have the most affect and control over the hydrogel matrix release property. The preparation conditions such as EG/MAA hydrogel composition, pesticide concentration, type of pesticide and irradiation dose greatly affect the pesticide release rate, which also influenced by the pH and temperature of the matrix‐surrounding medium. The pesticide release rate decreased as the irradiation dose and pH increased, but it increased as the MAA content, pesticide concentration and temperature increased. The release rate of Trifluralin is the highest one, whereas the Fluometuron is the lowest. The properties of the prepared hydrogels may make them acceptable for practical use as bioactive controlled release matrices. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Drug‐release behavior of chitosan‐g‐poly(vinyl alcohol) copolymer matrix

Chitosan‐g‐poly(vinyl alcohol) (PVA) copolymers with different grafting percent were prepared by grafting water‐soluble PVA onto chitosan. The drug‐release behavior was studied using the chitosan‐g‐PVA copolymer matrix containing prednisolone in a drug‐delivery system under various conditions. The relationship between the amount of the released drug and the square root of time was linear. From this result, the drug‐release behavior through the chitosan‐g‐PVA copolymer matrix is shown to be consistent with Higuchi's diffusion model. The drug‐release apparent constant (K_H) was slightly decreased at pH 1.2, but increased at pH 7.4 and 10 according to the increasing PVA grafting percent. Also, K_H was decreased by heat treatment and crosslinking. The drug release behavior of the chitosan‐g‐PVA copolymer matrix was able to be controlled by the PVA grafting percent, heat treatment, or crosslinking and was also less affected by the pH values than was the chitosan matrix. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 458–464, 1999     

Chitosan–Polyelectrolyte complexation for the preparation of gel beads and controlled release of anticancer drug. I. Effect of phosphorous polyelectrolyte complex and enzymatic hydrolysis of polymer

Enzymic hydrolyzed chitosan was employed to prepare chitosan–tripolyphosphate and chitosan–polyphosphoric acid gel beads using a polyelectrolyte complexation method for the sustained‐release of anticancer agent, 6‐mercaptopurine (6‐MP). pH responsive swelling ability, drug‐release characteristics, and morphology of the chitosan gel bead depends on polyelectrolyte complexation mechanism and molecular weight of the enzymic hydrolyzed chitosan. The complexation mechanism of chitosan beads gelled in pentasodium tripolyphosphate or polyphosphoric acid solution was ionotropic crosslinking or interpolymer complex, respectively. The drug‐release patterns of all chitosan gel beads in pH 6.8 seemed to be diffusional based, which might be in accordance with the Higuchi model, whereas release profiles of the chitosan–tripolyphosphate gel beads in pH 1.2 medium seemed to be non‐Fickian diffusion controlled due to the swelling or matrix erosion of the beads. The rate of 6‐MP releasing from chitosan–tripolyphosphate or chitosan–polyphosphoric acid gel matrix were significantly increased with the decreased molecular weight of enzymic hydrolyzed chitosan. However, the dissolution rates of 6‐MP entraped in chitosan–tripolyphosphate and chitosan–polyphosphoric acid gel matrix were significantly slower than the dissolution rate of the original drug. These results indicate that the chitosan–polyphosphoric acid gel bead is a better polymer carrier for the sustained release of anticancer drugs in simulated intestinal and gastric juice medium than the chitosan–tripolyphosphate gel beads. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1868–1879, 1999     

Controlled drug release of 5-amino salicylic acid by poly(2-hydroxyethylmethacrylate) grafted agar

The utilization of poly (2-hydroxyethylmethacrylate) grafted agar (Ag-g-P(HEMA)) as a matrix for the controlled release of 5-aminosalicylic acid was investigated. Grafted copolymers of 2-hydroxyethylmethacrylate (HEMA) monomers on agar were synthesized by microwave assisted method. In vitro drug release studies were performed at pH values of 2 and 7 in order to investigate the possibility of pH triggered release for colon targeted drug delivery. Further, the percent grafting vs. t₅₀ (the time taken for release of 50% of the enclosed drug) value was studied and the results indicate that it may be possible to develop a programmable drug release matrix based on grafted polysaccharide. Ag-g-P(HEMA) appears to be a useful matrix for controlled release.     

Inter-polymer complex microspheres of chitosan and cellulose acetate phthalate for oral delivery of 5-fluorouracil

Inter-polymer complexes (IPCs) of chitosan (CS) and cellulose acetate phthalate (CAP) have been prepared to develop spherical microspheres by a novel emulsion-solvent evaporation technique. The microspheres were used for the oral delivery of 5-fluorouracil (5-FU), an antimetabolite and antineoplastic agent, whose release time was extended up to 12 h. Formulations were prepared by varying the concentrations of CS, CAP and 5-FU. FTIR confirmed the formation of IPC, indicating no chemical interactions of 5-FU with the polymer matrix. Scanning electron microscopy suggested spherical shape of the microspheres with smooth surfaces. Average particle size measured by optical microscopy varied between 2.7 and 5.5 μm. Differential scanning calorimetry showed amorphous dispersion of 5-FU particles into the IPC matrix. Encapsulation efficiency as estimated by UV was dependent on polymer composition with the highest value of 96 %. Water uptake by the IPC microspheres was higher at higher concentration of CS in the matrix. In vitro drug release performed in pH 1.2 and pH 7.4 buffer media showed a dependence on compositions of CS, CAP and drug loading. Molar mass between cross-links (M _c) and cross-link density (d _x ) values of the polymer matrix calculated from swelling data indicated the formation of a dense matrix between CS and CAP; the matrix was able to control the release of 5-FU. The in vitro release data have been fitted to empirical equations to understand the nature of drug release mechanism.     

Preparation of 2,4-dichlorophenoxyacetic acid loaded on cysteamine-modified polydopamine and its release behaviors

With dopamine as the monomer, the model pesticide 2,4-dichlorophenoxyacetic acid (2,4D) was loaded on cysteamine (NHSH)-modified polydopamine (PDA) nanospheres [2,4-dichlorophenoxyacetic acid bound to cysteamine-modified polydopamine (2,4D–PDA–NHSH)] via the construction of amide bonds. We investigated the materials’ structure, adhesive capability, and release behaviors, especially the mechanism of the release processes. The results demonstrate that the materials were spherical in appearance and adhesive. 2,4D loaded on the PDA vehicle was amorphous in structure. The amide bond between PDA and 2,4D generated by NHSH not only enhanced the loading amount of PDA from 296.28 to 692.56 mg/g but also decreased the thermal stability from 291 to 230 °C. The 2,4D–PDA–NHSH showed no pH responsiveness, whereas the PDA system without NHSH modification exhibited pH sensitivity. A mechanism for the observed behaviors was suggested. First-order, logistic, Weibull, and Korsmeyer–Peppas models were applied to describe the release behaviors at different pH values. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47469.     

Simplified point defect model for growth of anodic passive films on iron

We present a simplified point defect model to describe the growth of the primary passive oxide film on the surface of iron. The model postulates a reduced set of elementary interfacial reactions to describe the formation and dissolution of the oxide film. By casting the model in dimensionless form, we obtain a relatively small set of parameters that must be assigned values. Parameter values are set by matching the film thickness predicted by the model with one experimental data point. The model is then used to predict variations in film thickness with time, temperature, and applied potential, yielding reasonable agreement with experimental data. The model also gives the correct qualitative trend in the dependence of film thickness on electrolyte pH. Although the model parameters used in our comparisons are probably not unique, they suggest that physical picture embodied in the model provides a suitable starting point for modeling the growth of passive films on Fe.     

Synthesis and characterization of chitosan‐polycaprolactone blended with organoclay for control release of doxycycline

In the present research program, chitosan has been mixed with polycaprolactone (PCL) (80 : 20) for using them for control delivery of doxycycline. Organoclay, Cloisite 30B of different concentrations 1, 2.5, and 5% has been blended with the composite. Chitosan is a natural biodegradable polymer where as polycaprolactone is a synthetic biopolymer. The blending of the two polymers has been carried out varying the proportion of nanoclay so that the composite can be a better drug carrier. The blends were characterized by Fourier Transmission Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), X‐ray Diffraction (XRD) analysis. From the FTIR spectra, the various groups present in chitosan and PCL blend were monitored. The homogeneity, morphology, and crystallinity of the blends were ascertained from SEM and XRD data, respectively. The swelling studies have been carried out at different drug loading. Swelling study is an important parameter to predict the diffusion of the drugs from the matrix. The kinetics of the drug delivery system has been systematically studied. Drug release kinetics was analyzed by plotting the cumulative release data versus time by fitting to an exponential equation which indicated the non‐Fickian type of kinetics. The drug release was investigated at different pH medium, and it was found that the drug release depends upon the pH medium as well as the nature of matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A facile synthesis of PLGA encapsulated cerium oxide nanoparticles: release kinetics and biological activity

In the present article a facile synthesis of cerium oxide nanoparticles (CNPs) encapsulated in PLGA microparticles is reported. The release kinetics of the CNPs from the PLGA matrix was investigated under acidic, basic and near-neutral pH. A diffusion model was applied to determine the diffusivity of the CNPs from the PLGA matrix. The morphology of the degraded PLGA particles was characterized by high resolution SEM. Superoxide dismutase (SOD) mimetic activity was retained in released CNPs for a longer period of time (～90 days) under different pH. PLGA encapsulated CNP showed excellent biocompatibility. This study demonstrates a potential strategy to deliver CNPs using biodegradable PLGA that ensures a slow release of the CNPs over a long period of time. Thus, the synthesized PLGA encapsulated CNPs could find potential applications in tissue engineering like bone remodelling and regeneration, and protection from disorders caused by neurodegeneration.     

Control release of some pesticides from Starch/(Ethylene glycol-co-Methacrylic acid) copolymers prepared by γ-irradiation

Starch/(Ethylene glycol-co-Methacrylic acid) [Starch/(EG-co-MAA)] hydrogels were designed for controlled delivery of pesticides, such as Fluometuron (FH); Thiophanate Methyl (TF) and Trifluralin (TI) which are use in the agricultural field. The delivery device was prepared by using γ-irradiation and was characterized by FTIR, DSC, and SEM. The swelling studies as a function of copolymer composition and irradiation dose were identified. This article discusses the swelling kinetics of polymer matrix and release dynamics of Trifluralin from hydrogels for the evaluation of the diffusion mechanism and diffusion coefficients. The values of the diffusion exponent ‘n’ for both the swelling of hydrogels and the release of Trifluralin from the hydrogels have been observed between 0.56 and 0.86 when the MAA content in the polymers was varied from 20 to 80 wt%, respectively. It is inferred from the values of the ‘n’ that non-Fickian diffusion mechanism has occurred for different EG/MAA compositions. The release rate from matrices prepared under different conditions was studied to determine which factors have the most affect and control over the hydrogel matrix release property. The preparation conditions such as EG/MAA hydrogel composition, pesticide concentration, type of pesticide and irradiation dose greatly affect the pesticide release rate which also influenced by the pH and temperature of the matrix-surrounding medium. The pesticide release rate decreased as the irradiation dose and pH increased, but it increased as the MAA content, pesticide concentration and temperature increased. The release rate of Trifluralin is the highest one while the Fluometuron is the lowest. The properties of the prepared hydrogels may make them acceptable for practical use as bioactive controlled release matrices.