Diffusional release of solutes from polymer matrices undergoing structural changes has been analysed by incorporating the
dependence of solute diffusivity on time. The functional dependence of diffusivity with time has been experimentally verified
and its utility and limitations are discussed. Criteria for predicting release characteristics have been arrived at based
on two model parameters,K and β. HereK represents the reciprocal of the time required for the structural change and β is the ratio of the solute diffusivity prior
to the onset and after the completion of the structural change. The criteria, which are independent of the mechanistic details
of the structural change, have been validated by analysing solute release from polymeric matrices undergoing diverse structural
changes. The approach should be useful in predicting the relase characteristics of solutes on the basis of the physicochemical
characteristics of the polymer-solute systems. It should also help in tailoring the polymers to obtain the desired release
kinetics. 相似文献
Hydrophobically modified alginate hydrogels have great potential in drug delivery as they are biologically compatible and cost efficient. While previous works have shown successful protein, and hydrophobic and hydrophilic drug delivery, little information regarding the relationship between crosslinker density and drug release rate is known. This paper investigates the impact of crosslinker density and hydrophobic degree of substitution within modified alginate gels and solutions on the release kinetics using model hydrophobic drug, sulindac. Near zero‐order release was obtained for an extended period of 5 days. Drug release rates decreased as the crosslinker density within both modified alginate hydrogels and solutions increased. Release data fit well to a simplified Fickian relationship, suggesting that the release mechanism is diffusion‐limited. These release characteristics also correlate with bulk rheological measurements, indicating a strong interrelationship between the mechanical properties and the drug release characteristics of the hydrogels. 相似文献
Thin composite layers of silica with incorporated bioactive organic compounds (BOC) can be prepared by mixing metal oxide
sols with dissolved BOC and coating with a conventional film coating machine. The release of antibacterial benzoic acid from
the silica layers into a surrounding aqueous medium can be controlled by the mass ratio of silica to benzoic acid, by modification
of the silica matrix and by addition of soluble or swelling penetration agents, respectively. Therefore, such composite materials
are applicable for controlled release sytems in medicine and biology with excellent long-time effects. 相似文献
This study deals with flexible films incorporating nisin for antibacterial active packaging purposes. A novel approach was used to gain control over nisin release profile from a thermoplastic film in order to enhance its antibacterial efficiency. This approach involves polymer blends of ethylene vinyl acetate copolymer and co‐polyamide at various ratios. It was shown that the release profile of an antibacterial substance from active packaging to foodstuff is a key factor concerning the antibacterial efficiency. Samples of 400[μm] were produced by using a laboratory twin screw compounder and a laboratory hot press. Samples were characterized for their migration kinetics, molecular interactions, mechanical properties, and water swelling properties. Antibacterial activity tests show that nisin incorporated films reduced bacterial count by different extents. Listeria ATCC 33090 was used as target bacteria (data not shown). Nisin migration profile to water medium was determined by Lowry's protocol. Scanning electron microscopy images and thermal analysis indicated that no significant molecular interactions occurred. Furthermore, droplet and co‐continues like morphology were seen at different polymer blend ratios. Osmotic pressure driven release mechanism appears to be the dominant migration mechanism, and diffusion kinetics was dominant. Results show that morphology of the polymer blend matrix alters the diffusion coefficient. In addition, water swelling characterization of different samples was done in order to reveal the relations with the diffusion coefficient. It seems that there is an inverse resemblance between water swelling and the diffusion coefficient trends. 相似文献
The intelligent controlled drug delivery systems (DDS) are a series of the preparations including microcapsules or nanocapsules composed of intelligent polymers and medication. The properties of preparations can change with the external stimuli, such as pH value, temperature,chemical substance, light, electricity and magnetism etc. According to this properties, the DDS can be intelligently controlled. This paper has reviemed research on syntheses and applications of intelligent controlled DDS of polymer carriers.Drug delivery system with pH stimuliThe volume of polymer hydrogel can change with the pH value of external environment. The sensitive polymer hydrogels to pH are often as carriers. The polymer hydrogel carrying medicine is especially suitable for taking orally. In order to protect medicine from losing activation, we enwrapped medicine into polymer hydrogel with acidic group. In the acidic environment of stomach,the volume of polymer hydrogel contracts because of the hydrogen bond. The medicine in the polymer hydrogel cannot disperse out. When it goes to the intestine of basic environment, the hydrogen bond will be broken, and the medicine can release.Drug delivery system with temperatureTemperature sensitive polymer hydrogel can change its volume with changing of environmental temperature. This kind of polymer hydrogel can be also used as a carrier of medicine. At a low temperature, the polymer chains form hydrogen bond with water to swell to let medicine disperse out from the hydrogel. On the other hand, the hydrogen bond will be broken and polymer chain will lose water to contract with temperature's increasing. And the medicine will not disperse out. For example,the poly(N-isopropylacrylamide)(PNIPAAm) is the hydrogel that is swelled at lower temperature and contracted at higher temperature. PNIPAAm has the lower critical solution temperature(LCST).We can adjust its LCST to control PNIPAAm hydrogel's swelling or contraction to let medicine release or not.Drug delivery system with other stimuliThe polymer carrier drug delivery system can be intelligently controlled with the stimuli of pH value and temperature. In addition, there are still some other stimuli for DDS. For example, DDS with light; DDS with electricity(or electric field); DDS with magnetism(magnetic field); DDS with chemical substance; etc. The characteristic of intelligent polymer carrier is based on P.J.Flory's gel-swelling theory. Intelligent polymer carrier DDS will be widely used in biological and medical fields. 相似文献
Agricultural production is influenced by the water content in the soil and availability of fertilizers. Thus, superabsorbent hydrogels, based on polyacrylamide, natural cashew tree gum (CG) and potassium hydrogen phosphate (PHP), as fertilizer and water releaser were developed. The structure, morphology, thermal stability and chemical composition of samples of polyacrylamide and cashew tree gum hydrogels with the presence of fertilizer (HCGP) and without fertilizer (HCG) were investigated, using X-ray diffractometry (XRD), Fourier Transformed Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA/DTG) and Energy Dispersive Spectroscopy (EDS). Swelling/reswelling tests, textural analysis, effect of pH, release of nutrients and kinetics were determined; the ecotoxicity of the hydrogels was investigated by the Artemia salina test. The results showed that PHP incorporation in the hydrogel favored the crosslinking of chains. This increased the thermal stability in HCGP but decreased the hardness and adhesion properties. The HCGP demonstrated good swelling capacity (~15,000 times) and an excellent potential for reuse after fifty-five consecutive cycles. The swelling was favored in an alkaline pH due to the ionization of hydrophilic groups. The sustained release of phosphorus in HCGP was described by the Korsmeyer–Peppas model, and Fickian diffusion is the main fertilizer release mechanism. Finally, the hydrogels do not demonstrate toxicity, and HCGP has potential for application in agriculture. 相似文献
A solution to Fick's equation is presented which accurately predicts the transfer of mass out of a polymeric rod or sheet undergoing relaxation by a solvent permeating it by Case II transport. There is a critical length. Before the solvent permeates to this length the diffusible material can diffuse away from the moving boundary faster than it is becoming available at the boundary. Afterward the reverse is true. Five sets of experimental data from three different sources have been used to test the model. The agreement is excellent. 相似文献
In this series of papers, a new model has been presented for symmetrical, planar, three-layer (ABA) matrix-controlled release (MCR) devices, wherein all the advanced features of a previous monolithic MCR model have been incorporated. An extensive parametric study was performed to explore the possibilities afforded by the ABA configuration to alleviate, or even practically eliminate the undesirable features of initially very high, and subsequently continuously declining, release rates which normally characterize diffusion-limited monolithic devices. ABA matrices with uniform material properties (UMP) and layers A and B carrying different solute loads were examined in Part I. The results presented here refer to the more general case, where A and B may also represent non-uniformity in sorption and transport properties (non-UMP ABA devices). It is shown that judicious choice of two different polymeric materials for layers A and B may further improve the favorable results previously obtained for ABA–UMP matrices to the point where demands of very narrow limits for dose rate uniformity in conjunction with very high efficiency, can be met. The applicability and utility of the ABA, non-UMP model was demonstrated in a real experimental situation concerning surface-modified PVA matrices. Parameterization of the model on the basis of the experimental information provided and on literature data, resulted in successful interpretation of the effect of two different degrees of surface crosslinking on the relative rates of water uptake and proxyphylline release. 相似文献
A procedure to obtain a controlled-release microencapsulated anti-inflammatory drug based on a solvent evaporation method
is described. The present method makes use of ethylcellulose as the polymer and methylene chloride as solvent. The evaporation
of solvent is controlled by means of an air stream. Variations in the preparative procedure and their effects on capsule dimensions
and permeabilities were studied. The release behavior of the drug is determined, and two different diffusion constants are
also determined: 7.0×10−10 cm2/s and 1.2×10−10 cm2/s, corresponding to low and high release time. Based on these results it is proposed that these microcapsules have a nonhomogeneous
polymeric wall, and are more porous in the outer surface. This model might be applicable to the microcapsules obtained by
means of the solvent evaporation method. 相似文献
A telomerase‐responsive DNA icosahedron was designed to precisely release caged platinum nanodrugs into cisplatin‐resistance tumor cells for effective therapy. This DNA icosahedron was constructed from two pyramidal DNA cages connected with telomerase primers and telomeric repeats, and platinum nanodrugs were then encapsulated into the DNA structure. In the presence of telomerase, the primers are extended, leading to inner‐chain substitution of the DNA icosahedron and subsequent release of the caged nanodrugs. This DNA icosahedron can precisely release caged nanodrugs in response to telomerase in tumor cells, giving enhanced anticancer efficacy in drug‐resistant carcinoma and with reduced toxicity to normal tissues. We speculate that this precisely designed, well controlled DNA cage could be generalized to diverse anticancer drugs. 相似文献
Molecularly imprinted polymer (MIP) has gained wide interest among researchers due to its unique molecular recognition of the template that is suitable as a drug carrier. Therefore, the preparation and formulation of the MIP are significant to suit the needs of the intended use. Due to its significance in drug delivery, this review aims to highlight various methods in the preparation of MIP, the composition for both controlled and stimuli-responsive drug delivery systems, and the release mechanism of the drugs. In drug delivery systems, MIP should have a sustained release performance as well as flexibility in surface modification for targeted delivery via a range of stimuli-responses, including external stimuli (magnetic, light) and internal stimuli (pH, temperature, redox, biological). The properties of sustained release and targeted delivery of the MIP can improve the drug's therapeutic efficacy as well as the breakthrough for the tumor targeting application. 相似文献
Summary: A novel thermosensitive amphiphilic copolymer (PCL‐g‐P(NIPAAm‐co‐HEMA)) comprised of hydrophobic PCL segments and hydrophilic P(NIPAAm‐co‐HEMA) segments was designed and synthesized. The structure of the copolymer was characterized by FT‐IR, 1H NMR and GPC analysis. The copolymer may self‐assemble into micelles in water and the resulting micelles demonstrated temperature sensitivity with a lower critical solution temperature (LCST) of 33 °C. The critical micellar concentration (CMC) obtained from surface tension measurements and the fluorescence method was around 30 mg · L−1. Transmission electron microscopy (TEM) showed that the micelles exhibit a nanospheric morphology within a narrow size range of 150–160 nm. A cytotoxicity study showed that the PCL‐g‐P(NIPAAm‐co‐HEMA) copolymer exhibits good biocompatibility. The controlled drug release of the resulting micelles was investigated and it was found that micelles loaded with prednisone acetate showed improved drug release behavior due to the special micellar structure.
Self‐assembly of the PCL‐g‐P(NIPAAm‐co‐HEMA) copolymers. 相似文献
Chitosan‐based molecular imprinted polymer (CS‐MIP) nanogel is prepared in the presence of morphine template, fully characterized and used as a new vehicle to extend duration of morphine analgesic effect in Naval Medical Research Institute mice. The CS‐MIP nanogel with ≈25 nm size range exhibits 98% loading efficiency, and in vitro release studies show an initial burst followed by an extended slow release of morphine. In order to study the feasibility of CS‐MIP nanogel as morphine carrier, 20 mice are divided into two groups randomly and received subcutaneous injection of morphine‐loaded CS‐MIP and morphine (10 mg kg?1) dissolved in physiologic saline. Those received injection of morphine‐loaded CS‐MIP show slower and long lasting release of morphine with 193 min effective time of 50% (ET50) analgesia compared to 120 min ET50 in mice received morphine dissolved in physiologic saline. These results suggest that CS‐MIP nanogel can be a possible strategy as morphine carrier for controlled release and extension of its analgesic efficacy.
Polyphenolic compounds are used for treating various diseases due to their antioxidant and anticancer properties. However, utilization of hydrophobic compounds is limited due to their low bioavailability. In order to achieve a greater application of hydrophobic bioactive compounds, hydrogel beads based on biopolymers can be used as carriers for their enhanced incorporation and controlled delivery. In this study, beads based on the biopolymers-κ-carrageenan, sodium alginate and poloxamer 407 were prepared for encapsulation of curcumin. The prepared beads were characterized using IR, SEM, TGA and DSC. The curcumin encapsulation efficiency in the developed beads was 95.74 ± 2.24%. The release kinetics of the curcumin was monitored in systems that simulate the oral delivery (pH 1.2 and 7.4) of curcumin. The drug release profiles of the prepared beads with curcumin indicated that the curcumin release was significantly increased compared with the dissolution of curcumin itself. The cumulative release of curcumin from the beads was achieved within 24 h, with a final release rate of 12.07% (gastric fluid) as well as 81.93% (intestinal fluid). Both the in vitro and in vivo studies showed that new hydrogel beads based on carbohydrates and poloxamer improved curcumin’s bioavailability, and they can be used as powerful carriers for the oral delivery of different hydrophobic nutraceuticals. 相似文献