A series of N-isopropylacrylamide (NIPAAm) copolymer gels with different hydrophilicities were prepared from NIPAAm, hydrophilic acrylamide
(AAm) and hydrophobic butyl methacrylate (BMA). The swelling and thermo-responsive properties of PNIPAAm P (NIPAm-co-BMA)
and P(NIPAm-co-AAm) copolymer hydrogels were investigated. The drug loading and releasing behaviors for two kinds of model drug with different
hydrophilicities were studied. The result shows that the copolymer gels present negative thermo-sensitivities. The lower critical
solution temperature (LCST), equilibrium swelling degree and the initial swelling rate increase as the hydrophilicity of gels
increases when the temperature is below the LCST. With increasing gel hydrophilicity the loading ratio for sodium salicylate
increases, while for salicylic acid, the reverse is observed. The initial drug releasing rate of sodium salicylate and salicylic
acid also increase with increasing gel hydrophilicity. The initial drug releasing rate of sodium salicylate is significantly
higher than that of salicylic acid. For salicylic acid which is less hydrophilic, the equilibrium releasing ratio at high
temperature is lower than that at low temperature while for sodium salicylate which is more hydrophilic, the equilibrium releasing
ratio at high temperature is almost the same as that at low temperature. Equilibrium releasing ratios of the three gels are
significantly different from each other for salicylic acid when the temperature is below LCST while the equilibrium releasing
ratios of the three gels are all 100% for sodium salicylate.
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Translated from Journal of Central South University (Science and Technology), 2007, 38(5): 906–911 [译自: 中南大学学报(自然科学版)] 相似文献
We investigated the rapid and precise molecular release from hydrogels in response to dual stimuli. To achieve precise on/off drug release using thermoresponsive poly(N-isopropylacrylamide) hydrogels, we prepared nano-structured semi-IPNs, which consisted of thermosensitive PNIPAAm networks penetrated by pH-responsive poly(acrylic acid) (PAAc) linear chains and perforated to create nano-tracts as a molecular pathway. The present nano-tracted semi-IPNs show a rapid deswelling response to both temperature and pH. Model drug releases were investigated when simultaneous changes in temperature and pH were applied. We observed that the cationic drug was rapidly released and then abruptly discontinued from the nano-tracted semi-IPNs in response to the dual stimuli, and clear release and stopping cycles were repeatedly observed on successive steps. Moreover, the release rates and amount of drug released were controllable by the deswelling speed of the gels and the PAAc content inside the gels. This novel release system using the nano-tracted semi-IPNs may be useful for the high performance, pulsed release of molecules. 相似文献
Shell cross-linked (SCL) thermoresponsive hybrid micelles consisting of a cross-linked thermoresponsive hybrid hydrophilic shell and a hydrophobic core domain were synthesized from poly(N-isopropylacrylamide-co-3- (trimethoxysilyl)propyl methacrylate)-b-polymethyl methacrylate (P(NIPAAm-co-MPMA)-b-PMMA) amphiphilic block copolymers. Transmission electron microscopy (TEM) images showed that the SCL micelles formed regularly globular nanoparticles. The SCL micelles showed reversible dispersion/aggregation in response to temperature cycles through an outer polymer shell lower critical solution temperature (LCST) for PNIPAAm at around 33 degrees C, observed by turbidity measurements and dynamic light scattering (DLS). The drug loading and in vitro drug release properties of the SCL micelles bearing a silica-reinforced PNIPAAm shell were further studied, which showed that the SCL micelles exhibited a much improved entrapment efficiency (EE) as well as a slower release rate which allowed the entrapped molecules to be slowly released over a much longer period of time as compared with pure PNIPAAm-b-PMMA micelles. 相似文献
Gamma radiation was used in every step of the synthesis of a sequential interpenetrating polymer network made of two “smart” polymers: poly(acrylic acid) (PAAc) and poly (N-isopropylacrylamide) (PNIPAAm), the latter grafted onto polypropylene (PP) films (PP-g-PNIPAAm) with the aim of developing medicated coatings for medical devices. Three steps were followed for obtaining net-PP-g-PNIPAAm-inter-net-PAAc: graft copolymerization of PNIPAAm onto PP films by gamma pre-irradiation oxidative method, cross-linking of PP-g-PNIPAAm by gamma irradiation in water to form the first network, with or without N,N′-methylenebis(acrylamide) (MBAAm), and finally the formation of the second network through the polymerization and cross-linking of AAc inside cross-linked PP-g-PNIPAAm by a low gamma radiation dose of 2.5 kGy. The films were characterized regarding the amount of grafted polymers and their composition (FTIR-ATR), thermal behavior (DSC), temperature- and pH-responsive swelling and contact angle (critical pH 6 and lower critical solution temperature ∼33 °C), and loading and release rate of vancomycin. Drug loading was driven by specific interactions between vancomycin and PAAc. Drug-loaded films sustained the delivery for several hours at pH 7.4 and provided release rate values adequate for killing bacteria attempting to adhere the surface of the films. 相似文献
Environmentally sensitive poly(N-isopropylacrylamide) (PNIPAAm) nanofibrous scaffolds loaded with a hydrophilic drug were fabricated via an electrospinning process. First, thermally crosslinkable poly(NIPAAm-co-N-methylolacrylamide) (PNN) was synthesized by redox polymerization below the phase transition temperature of PNIPAAm. The phase transition temperature of the PNN copolymer could be altered from 34 to 40 °C by changing the ratio of N-methylolacrylamide (NMA) to NIPAAm. Subsequently, PNN/chitosan nanofibers were electrospun using ethanol/acetic acid/water as a cosolvent. The PNN/chitosan nanofibers were sensitive to both pH and temperature. The fibrous structure of the soaked PNN/chitosan nanofibers was successfully preserved by the crosslinking of NMA. Furthermore, the chitosan-based nanoparticles (NPs) were introduced into the PNN nanofibers (PNN/NPs) to achieve prolonged drug release. The nanoparticles were observed in the PNN nanofibers by transmission electron microscopy. All of the scaffolds examined had high tensile strengths (1.45 MPa or above) and exhibited no significant cytotoxicity toward human fetal skin fibroblasts. Finally, doxycycline hyclate was used as a model drug. The results illustrated that PNN/NPs nanofibrous scaffolds exhibited continuous drug release behavior for up to 1 week, depending on the pH and temperature. 相似文献
Controlled delivery systems would be more beneficial and ideal if the drug could be delivered with respond to external environmental change. It could be used to overcome the shortcomings of conventional dosage forms. Therefore, the correct amount of drug would be released upon the stimulation of such a temperature and concentration change. The purpose of study is to investigate the influence of temperature and drug concentration from poly(2-hydroxyethyl methacrylate and N-isopropylacrylamide)/poly(HEMA-NIPAAm). The macroporous structure 5HEMA15NIPAAm was showed the most rapid responsiveness in swelling ratio, polymer volume fraction, swelling and deswelling kinetics. The high drug loading capacity was achieved at or below ambient temperature, whilst the release profile was revealed sustain release of conventional anti-inflammatory drug; prednisolone 21 hemisuccinate sodium salt. In general, drug loading capacity and drug diffusion kinetics are influence by the porosity of hydrogels, temperature, and drug concentration. 相似文献
Crosslinked chitosan/silk fibroin blend films were prepared by a solution casting technique using glutaraldehyde as crosslinking agent. Drug release characteristics of the blend films with various blend compositions were investigated. Theophylline, diclofenac sodium, amoxicillin trihydrate, and salicylic acid were used as model drugs. The release studies were performed at 37 °C in buffer solutions at pH 2.0, 5.5, and 7.2. It was found that the blend films with 80% chitosan content showed the maximum amount of model drug release at pH 2.0 for all the drugs studied here. This result corresponded to the swelling ability of the blend films. From a swelling study, the maximum degrees of swelling of the drug‐loaded blend films were obtained at this pH and blend composition. The amount of drugs released from the films with 80% chitosan content, from the highest to the lowest values, occurred in the following sequence: salicylic acid > theophylline > diclofenac sodium > amoxicillin.
Comparison of the amounts of drug released from chitosan and the blend film with 80% chitosan content at pH 2.0: (filled) chitosan film, and (blank) blend film with 80% chitosan content (SAL = salicylic acid, THEO = theophylline, DFS = diclofenac sodium, AMX = amoxicillin). 相似文献
Poly(β-aminoester) dendrimers have been prepared. These systems represent the first degradable dual pH- and temperature-responsive dendrimers displaying photoluminescence. The pH/temperature sensitivities are interrelated; the lower critical solution temperature of the dendrimer decreases as the pH of the solution is increased. The sensitivities are mainly due to phase changes of the surface groups with changes in pH or temperature. These dual-responsive dendrimers are very useful in drug delivery. They may be loaded with a hydrophobic drug at low temperature without using organic solvents. The loaded drug is released very slowly and steadily at 37 °C and physiological pH, but can be quickly released at acidic pH, for example the lysosomal pH (pH 4-5), for intracellular drug release. These dendrimers also display strong photoluminescence, which can be exploited for monitoring drug loading and release. Thus, poly(β-aminoester) dendrimers constitute ideal drug carriers since their thermal sensitivity allows the loading of drugs without using organic solvents, their pH sensitivity permits fast intracellular drug release, and their photoluminescence provides a means of monitoring drug loading and release. 相似文献