Preparation of Novel Cationic Copolymer Microspheres and Evaluation of Their Function by In Vitro and In Vivo tests as Ph-Sensitive Drug Carrier Systems

ABSTRACT

Novel pH-sensitive copolymer microspheres containing methylacrylic acid and styrene cross-linking with divinylbenzene were synthesized by free radical polymerization. The microspheres that were formed were then characterized by Fourier-Transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), size analysis, and X-ray analysis. The copolymer microspheres showed pulsatile swelling behavior whenthe pH of the media changed. The pH-sensitive microspheres were loaded with diltiazem hydrochloride (DH). The release characteristics of the free drug and the drug-loaded microspheres were studied under both simulated gastric conditions and intestinal pH conditions. The in vivo evaluation of the pulsatile preparation was subsequently carried out using beagle dogs as experimental subjects. The results demonstrated that the drug release exhibited a pulsatile character both in vitro and in vivo.     

Evaluation of pH-sensitivity and drug release characteristics of (polyacrylamide-grafted-xanthan)-carboxymethyl cellulose-based pH-sensitive interpenetrating network hydrogel beads

Novel pH-sensitive interpenetrating network hydrogel beads of polyacrylamide-grafted-xanthan (PAAm-g-XG) and sodium carboxymethyl cellulose (NaCMC) loaded with ketoprofen were prepared and evaluated for pH sensitivity and drug release characteristics. The pH-sensitive PAAm-g-XG copolymer was synthesized by free radical polymerization under the nitrogen atmosphere followed by alkaline hydrolysis. The grafting and alkaline hydrolysis reactions were confirmed by Fourier transform infrared spectroscopy. Differential scanning calorimetry and X-ray diffraction studies were carried out to know the crystalline nature of encapsulated drug. Scanning electron microscopic study revealed that the interpenetrating polymer network (IPN) beads possess porous matrix structure in alkaline pH whereas nonporous matrix structure was observed in acidic pH. The swelling of the beads and drug release was significantly increased when pH of the medium was changed from acidic to alkaline. The results of pulsatile swelling study indicated that the IPN beads changed their swelling behavior when pH of the external medium was altered. As pH of the medium was changed from 1.2 to 7.4, a considerable increase in swelling was observed for all the beads. However, swelling process was slower than the deswelling. At higher pH values, the carboxyl functional groups of hydrogels undergo ionization and the osmotic pressure inside the beads increases resulting in higher swelling. Drug release followed case II transport mechanism in acidic medium whereas anomalous/non-Fickian transport mechanism was observed in alkaline medium.     

Evaluation of pH-Sensitivity and Drug Release Characteristics of (Polyacrylamide-Grafted-Xanthan)–Carboxymethyl Cellulose-Based pH-Sensitive Interpenetrating Network Hydrogel Beads

Novel pH-sensitive interpenetrating network hydrogel beads of polyacrylamide-grafted-xanthan (PAAm-g-XG) and sodium carboxymethyl cellulose (NaCMC) loaded with ketoprofen were prepared and evaluated for pH sensitivity and drug release characteristics. The pH-sensitive PAAm-g-XG copolymer was synthesized by free radical polymerization under the nitrogen atmosphere followed by alkaline hydrolysis. The grafting and alkaline hydrolysis reactions were confirmed by Fourier transform infrared spectroscopy. Differential scanning calorimetry and X-ray diffraction studies were carried out to know the crystalline nature of encapsulated drug. Scanning electron microscopic study revealed that the interpenetrating polymer network (IPN) beads possess porous matrix structure in alkaline pH whereas nonporous matrix structure was observed in acidic pH. The swelling of the beads and drug release was significantly increased when pH of the medium was changed from acidic to alkaline. The results of pulsatile swelling study indicated that the IPN beads changed their swelling behavior when pH of the external medium was altered. As pH of the medium was changed from 1.2 to 7.4, a considerable increase in swelling was observed for all the beads. However, swelling process was slower than the deswelling. At higher pH values, the carboxyl functional groups of hydrogels undergo ionization and the osmotic pressure inside the beads increases resulting in higher swelling. Drug release followed case II transport mechanism in acidic medium whereas anomalous/non-Fickian transport mechanism was observed in alkaline medium.     

A pH-sensitive nanocomposite microsphere based on chitosan and montmorillonite with in vitro reduction of the burst release effect

Objective: The aim of this study was to prepare pH-sensitive ofloxacin (OFL)/montmorillonite (MMT)/chitosan (CTS) nanocomposite microspheres that improve the burst release effect of the drug by the solution intercalation technique and emulsification cross-linking techniques. Methods: First, OFL/MMT hybrids were prepared through the solution intercalation technique. Then, OFL/MMT-intercalated OFL/MMT/CTS nanocomposite microspheres were obtained through emulsification cross-linking technology. The intercalated nanocomposite was confirmed by Fourier-transform infrared spectroscopy and X-ray diffraction. Finally, in vitro release of OFL from the microspheres was performed in simulated gastric fluids and simulated intestinal fluids. The effect of MMT content on drug encapsulation efficiency and the drug release of the nanocomposite microspheres were investigated. Results: The results showed that the release rate of OFL from the nanocomposite microspheres at pH 7.4 was higher than that at pH 1.2. Compared with pure CTS microspheres, the incorporation of certain amount of MMT in the nanocomposite microspheres can enhance the drug encapsulation efficiency and reduce the burst release. Conclusion: A sustained release particulate system can be obtained by incorporating MMT into the nanocomposite microspheres and can improve the burst release effect of the drug.     

pH-Sensitive oral insulin delivery systems using Eudragit microspheres

In this paper, we present in vitro and in vivo release data on pH-sensitive microspheres of Eudragit L100, Eudragit RS100 and their blend systems prepared by double emulsion-solvent evaporation technique for oral delivery of insulin. Of the three systems developed, Eudragit L100 was chosen for preclinical studies. Insulin was encapsulated and in vitro experiments performed on insulin-loaded microspheres in pH 1.2 media did not release insulin during the first 2 h, but maximum insulin was released in pH 7.4 buffer media from 4 to 6 h. The microspheres were characterized by scanning electron microscopy to understand particle size, shape and surface morphology. The size of microspheres ranged between 1 and 40 μm. Circular dichroism spectra indicated the structural integrity of insulin during encapsulation as well as after its release in pH 7.4 buffer media. The in vivo release studies on diabetic-induced rat models exhibited maximum inhibition of up to 86%, suggesting absorption of insulin in the intestine.     

Preparation and Biological Evaluation of Ethylcellulose Microspheres Containing Tolmetin

Tolmetin microspheres were prepared by the coacervation process from the ethylcellulose. Microspheres were obtained both in presence and without protecting colloids, such as polyisobutilene (PIB) or ethyl-vinylacetate copolimers (EVA). The effect of these agents on the preparation, drug content, wall thickness, surface morphology, drug dissolution arid release from microspheres, were evaluated. The dissolution rate analysis was carried out also in the presence of a surfactant (Tween 80) at different pH values.

In addition, microspheres containing Tolmetin as a core material were submitted to biological tests, in comparison with the free drug, to evaluate upon experimental models the antipyretic activity and the gastric tolerability.     

Acrylic acid–methyl methacrylate copolymer for oral prolonged drug release

Acrylic acid (AA)–methyl methacrylate (MMA) based copolymers, in different molar ratios (3:7, 4:6, 5:5, 6:4, and 7:3) were synthesized using tetrahydrofuran as solvent and AIBN as free radical initiator. Increase in acrylic acid concentration promoted pH-dependent swelling of copolymer and copolymer AA:MMA (3:7) was selected due to minimum swelling. ATR/FTIR and ¹H NMR spectra of the copolymer showed absence of vinyl bond/protons present in the monomers suggesting successful polymerization. The copolymer was hemocompatible. Flurbiprofen sodium microspheres made with the copolymer, by oil/oil solvent evaporation, were spherical, anionic (zeta potential −59.0 mV) and contained 4.53% drug. ATR spectrum of microspheres showed peaks for aromatic C=C stretching and substituted benzene ring, indicating entrapment of flurbiprofen. XRD analysis revealed crystalline structure of flurbiprofen while copolymer and microspheres were amorphous. DSC thermograms showed a sharp melting endotherm of flurbiprofen sodium at 129.26°C against broad endotherms of copolymer and microspheres having peaks at 82.24 and 86.59°C, respectively. The thermogram of microspheres did not show the melting peak of flurbiprofen. The microspheres exhibited no drug release at pH <6.8 and released 83.4 and 99% drug at pH 6.8 and 7.4 in 3 h. The microspheres did not adhere on gastric mucosa at pH 1.2 but showed mucoadhesion time of 28 min on intestinal mucosa at pH 6.8. Thus, the microspheres on oral administration, would release the drug in distal ileum, suggesting the potential of the hemocompatible copolymer for enteric coating for prolonged drug release.     

Chitosan-Drug Conjugate Microspheres: Preparation and Drug Release Properties of Microspheres Composed of the Conjugate of 2'- or 3'-(4-Carboxy-butyryl)-5- Fluorouridine with Chitosan

The conjugate microspheres (Chi-glu-FUR-m) were prepared by the dry-in-oil method using chitosan-5-fuorouridine conjugate. Chi-glu-FUR-m were characterized by drug content, particle shape and size, swelling property, and drug release. Their characteristics were compared with those of the simple microspheres (Chi/ FUR-m), which were prepared under similar conditions using a mixture of chitosan and 5-fluorouridine. Both microspheres prepared showed a high retention of the drug after preparation and similar particle size and shape. Swelling ratios after incubation in aqueous buflers of pH 7.4 for 6 hr were similar for both microspheres. Chi-glu-FUR-m swelled quickly in aqueous buffers of pH 7.4 and the disintegration was observed to occur gradually from 24 hr afrer the incubation. Chi-glu-FUR-m showed a gradual drug release (50% release time = 61 hr), while Chi/FUR-m released the drug very rapidly, Such characteristics of Chi-glu-FURm as swelling, slow disintegration, and gradual drug release propose its usefulness for localization or chemoembolization therapy.     

Drug Product Development: A Technical Review of Chemistry,Manufacturing, and Controls Information for the Support of Pharmaceutical Compound Licensing Activities

Abstract

Tolmetin microspheres were prepared by the coacervation process from the ethylcellulose. Microspheres were obtained both in presence and without protecting colloids, such as polyisobutilene (PIB) or ethyl-vinylacetate copolimers (EVA). The effect of these agents on the preparation, drug content, wall thickness, surface morphology, drug dissolution arid release from microspheres, were evaluated. The dissolution rate analysis was carried out also in the presence of a surfactant (Tween 80) at different pH values.

In addition, microspheres containing Tolmetin as a core material were submitted to biological tests, in comparison with the free drug, to evaluate upon experimental models the antipyretic activity and the gastric tolerability.     

Polymersome-loaded capsules for controlled release of DNA

The formation of a novel drug-delivery carrier for the controlled release of plasmid DNA that comprises layer-by-layer polymer capsules subcompartmentalized with pH-sensitive nanometer-sized polymersomes is reported. The amphiphilic diblock copolymer poly(oligoethylene glycol methacrylate)-block-poly(2-(diisopropylamino)ethyl methacrylate) forms polymersomes at physiological pH, but transitions to unimeric polymer chains upon acidification to cellular endocytic pH. These polymersomes can thus release an encapsulated payload in response to a change in pH from physiological to endocytic conditions. Multicomponent layer-by-layer capsules are formed by exploiting the ability of tannic acid to act as an efficient hydrogen-bond donor for both the polymersomes and poly(N-vinyl pyrrolidone) at physiological pH. These capsules show release of a plasmid DNA payload encapsulated within the polymersome subcompartments in response to changes in pH between physiological and endocytic conditions.     

Core/shell nanoparticles for pH-sensitive delivery of doxorubicin

Core/shell nanoparticles with lipid core were prepared and characterized as pH-sensitive delivery system of anticancer drug. The lipid core is composed of drug-loaded lecithin and the polymeric shell is composed of Pluronics (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) tri-block copolymer, F-127). Based on the preparation method in the previous report by us, the freeze-drying of drug-loaded lecithin was performed in the F-127 aqueous solution containing trehalose used as a cryoprotectant to form stabilized core/shell nanoparticles. For the application of core/shell nanoparticles as a pH-sensitive drug delivery system for anticancer drug, doxorubicin was loaded into the core/shell nanoparticles and the drug loading amount and drug release behavior in response to pH change were observed.     

Cellulose acetate microspheres as floating depot systems to increase gastric retention of antidiabetic drug: formulation, characterization and in vitro-in vivo evaluation

Gastric emptying is a complex process that is highly variable and makes the in vivo performance of drug delivery systems uncertain. In order to avoid this variability, efforts have been made to increase the retention time of the drug delivery systems for more than 12 hours utilizing floating or hydrodynamically controlled drug delivery systems. The objective of this investigation was to develop a floating, depot-forming drug delivery system for an antidiabetic drug based on microparticulate technology to maintain constant plasma drug concentrations over a prolonged period of time for effective control of blood sugar levels. Formulations were optimized using cellulose acetate as the polymer and evaluated in vitro for physicochemical characteristics and drug release in phosphate buffered saline (pH 7.4), and evaluated in vivo in healthy male albino mice. The shape and the surface morphology of the prepared microspheres were characterized by optical microscopy and scanning electron microscopy. In vitro drug release studies were performed and drug release kinetics were calculated using the linear regression method. Effects of stirring rate during preparation and polymer concentration on the size of microspheres and drug release were observed. The prepared microspheres exhibited prolonged drug release (more than 10 hours) and remained buoyant for over 10 hours. Spherical and smooth-surfaced microspheres with encapsulation efficiency ranging from 73% to 98% were obtained. The release rate decreased and the mean particle size increased at higher polymer concentrations. Stirring speed affected the morphology of the microspheres. This investigation revealed that upon administration, the biocompatible depot-forming polymeric microspheres controlled the drug release and plasma sugar levels more efficiently than plain orally given drug. These formulations, with their reduced frequency of administration and better control over drug disposition, may provide an economic benefit to the user compared with products currently available for diabetes control.     

Acrylic acid–methyl methacrylate (2.5:7.5/2:8) enteric copolymer for colon targeted drug delivery

Enteric copolymers of acrylic acid and methyl methacrylate (2.5:7.5 and 2:8) were prepared using tetrahydrofuran as solvent and AIBN as free radical initiator for colon targeting. FTIR and ¹H NMR spectra of the copolymers showed absence of vinyl bond/protons present in the monomers suggesting successful polymerization. Flurbiprofen sodium microspheres (M1 and M2) made with the copolymers, by oil/oil solvent evaporation, were spherical, anionic (zeta potential –57.8 and –53.7 mV) and contained 5.47 and 5.89% drug. FTIR spectrum of microspheres showed peaks for aromatic C = C stretching and substituted benzene ring, indicating entrapment of flurbiprofen. PXRD revealed crystalline structure of flurbiprofen while copolymer and microspheres were amorphous. DSC thermograms showed a sharp melting endotherm of flurbiprofen sodium at 129.26°C against broad endotherms of copolymers and microspheres. The microspheres released 43 and 36% drug at pH 6.8 in 2 h and 99 and 96% at pH 7.4 in next 3–4 h.The microspheres did not adhere on gastric-mucosa at pH 1.2 but showed mucoadhesion time of 18 min and 9 min on intestinal mucosa at pH 6.8. Thus, the microspheres on oral administration, would release the drug in colon, suggesting the potential of the hemocompatible copolymers for pH dependent colon targeted drug delivery system.     

The release of 5-fluorouracil from microspheres of poly(epsilon-caprolactone-co-ethylene oxide)

The purpose of this study was to evaluate the in vitro release of 5-fluorouracil from microspheres prepared using a novel triblock copolymer of ε-caprolactone and ethylene oxide as the encapsulating material. Microspheres of poly(ε-caprolactone-co-ethylene oxide) were prepared by employing the “hot-melt” method of microencapsulation. Microspheres were sized using sieve analysis and scanning electron microscopy (SEM). Release studies were performed using a custom-made rotating paddle dissolution apparatus. Copolymer microspheres, fabricated by the hot melt method were shown by electron microscopy to have smooth, nonporous surfaces. Drug-loaded microspheres were found to have a broad distribution of sizes, which was thought to be a consequence of the wide range of crystal sizes of the encapsulated unmilled drug. Nonlinear release kinetics were observed from microspheres in the size fraction 75-250 μm, with a pronounced “burst release” associated with the presence of drug at the surface of the microspheres. A specific delineation of the drug release mechanism was not possible due to rapid gelation, swelling, and subsequent dissolution of the microspheres that occurred on hydration. This work describes the preparation of microspheres that swell rapidly and coalesce together on hydration, accompanied by rapid drug release and copolymer dissolution over a 2-hr period.     

Encapsulation and characterization of controlled release flurbiprofen loaded microspheres using beeswax as an encapsulating agent

The aim of the present study was to extend the use of flurbiprofen in clinical settings by avoiding its harmful gastric effects. For this purpose, we designed the controlled release solid lipid flurbiprofen microspheres (SLFM) by emulsion congealing technique. Drug was entrapped into gastro resistant biodegradable beeswax microspheres which were prepared at different drug/beeswax ratios 1:1, 1:2 and 1:3 using gelatin and tween 20 as emulsifying agents. The effect of emulsifiers and the effect drug/beeswax ratios were studied on hydration rate, encapsulating efficiency, micromeritic properties, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (X-RD) analysis and in vitro drug release at pH 1.2 for 2 h and at pH 6.8 for 10 h. SEM revealed that microspheres made with tween 20 were smooth while microspheres made with gelatin showed porous morphology, however, they were all spherical in nature. The practical yield (recovery) showed a dependence on drug-beeswax ratio and it was variable from 53 to 84%. High loading encapsulating efficiency of flurbiprofen from 8 to 94% was achieved. FTIR and DSC analysis confirmed the absence of any drug polymer interaction indicating drug stability during microencapsulation. X-RD of pure flurbiprofen shows sharp peaks, which decreases on encapsulation, indicating decrease in the crystallinity of drug in microspheres. The micromeritic studies confirmed the presence of excellent and good flow properties of microspheres. Entrapment efficiency, morphology, practical yield, hydration rate, flow properties demonstrated their dependence on the HLB value of emulsifiers and emulsifiers with higher HLB were found more appropriate for effective microencapsulation of flurbiprofen. The release kinetics followed zero order mechanism of drug release at pH 6.8. Release pattern depends on the morphology of flurbiprofen microspheres and amount of beeswax used in the microspheres preparation. The microspheres prepared with high HLB values i.e., tween 20 showed effective control of drug release from microspheres. The absence of drug release at pH 1.2 proved the suitability of beeswax for its use as a gastro resistant material.     

Sustained-Release Butorphanol Microparticles

Various butorphanol-loaded microparticles have been prepared with a biodegradable copolymer P(FAD-SA) of erucic acid dimer (FAD) and sebacic acid (SA) and a copolymer P(CPP-SA) of carboxyphenoxypropane (CPP) and SA using a melt compounding and milling method. Drug release was measured in vitro following incubation of drug-loaded microparticles in water for injection at 37°C. It was found that butorphanol was released in a sustained manner, yielding a cumulative drug release of about 100% over a period of 48 hr. Also, drug release was affected by drug loading and the size of the microparticles; however, it was not significantly influenced by the copolymer composition. Scanning electron microscopic (SEM) results showed that most of the particles were irregular in shape with uneven surfaces. The molecular weights of the copolymers were not changed after this fabrication process. In addition, 20% butorphanol-encapsulated microspheres were prepared with copolymer P(FAD-SA) by spray-drying. The SEM micrograph shows that the particle sizes of the microspheres ranged from 2 to 10 μm, and the external surfaces appear smooth. Moreover, rapid drug release was observed for these microspheres, with more than 92% of the encapsulated drug released within the first 2 hr.     

Sustained-release butorphanol microparticles

Various butorphanol-loaded microparticles have been prepared with a biodegradable copolymer P(FAD-SA) of erucic acid dimer (FAD) and sebacic acid (SA) and a copolymer P(CPP-SA) of carboxyphenoxypropane (CPP) and SA using a melt compounding and milling method. Drug release was measured in vitro following incubation of drug-loaded microparticles in water for injection at 37°C. It was found that butorphanol was released in a sustained manner, yielding a cumulative drug release of about 100% over a period of 48 hr. Also, drug release was affected by drug loading and the size of the microparticles; however, it was not significantly influenced by the copolymer composition. Scanning electron microscopic (SEM) results showed that most of the particles were irregular in shape with uneven surfaces. The molecular weights of the copolymers were not changed after this fabrication process. In addition, 20% butorphanol-encapsulated microspheres were prepared with copolymer P(FAD-SA) by spray-drying. The SEM micrograph shows that the particle sizes of the microspheres ranged from 2 to 10 μm, and the external surfaces appear smooth. Moreover, rapid drug release was observed for these microspheres, with more than 92% of the encapsulated drug released within the first 2 hr.     

Multiparticulate drug delivery system of aceclofenac: development and in vitro studies

The aim of this study was to develop an enteric-coated multiunit dosage form containing aceclofenac, a nonsteroidal anti-inflammatory drug. The pellets were prepared by using extrusion/spheronization method, and the core pellets were coated with a pH-sensitive poly(meth) acrylate copolymer (Eudragit L100-55) to achieve site-specific drug release. The formulated pellets were characterized for percentage yield, size distribution, surface morphology studies, drug content, and flow properties. In vitro dissolution test was used for comparison of drug release profiles of various coated pellets. The practical yield was found to be 90-95%. The particle size of enteric-coated pellets was found to be in the range of 0.59-0.71 mm. The pellets were spherical in shape and surfaces of pellets were found to be rough and showing micropores. Enteric-coated pellets showed good flow properties and in vitro dissolution profile. Dissolution tests were carried out in a USP type II dissolution apparatus in media-simulating pH conditions of the gastrointestinal tract. The release of the aceclofenac from formulated pellets was established to be minimum in the pH 1.2 (<5%) for a period of 2 h, and at pH 6.8, it shows the maximum release (85 +/- 5% release within 1 h) which indicates gastric resistance of the formulated pellets. The 20% wt/wt enteric-coated pellets were compared to that of marketed product (tablets), it was observed that pellets showed better release profile. The study concluded that the formulated multiparticulate dosage forms can be used as an ideal drug delivery system for the aceclofenac.     

光热敏感型羧甲基壳聚糖纳米微球的制备及光热性能

羧甲基壳聚糖因其具有良好的水溶性和生物相容性,被广泛应用于生物医学领域。以天然可降解高分子羧甲基壳聚糖为载体,在引发剂过硫酸钾的作用下,通过自由基组合法将N-异丙基丙烯酰胺接枝到羧甲基壳聚糖上,然后在香草醛的交联作用下,采用乳化交联法制备一种负载光敏剂吲哚菁绿(ICG)的新型光热敏感型羧甲基壳聚糖微球,通过傅里叶红外(FT-IR)、核磁(1H-NMR)及扫描电镜(SEM)对共聚物结构及微球形貌进行表征,考察了油水比、转速、香草醛、乳化时间对该纳米微球包载阿霉素载药量的影响,并研究了其光热性能。结果表明,FT-IR和1H-NMR分析证明,N-异丙基丙烯酰胺成功接枝到羧甲基壳聚糖上;SEM分析可知,纳米微球外观呈球状,分布均匀,平均粒径为143 nm。油水比为20∶1,转速为600 r/min,香草醛量为1 mL,乳化时间3 h的微球载药量最高为19.32%。同时,通过改变外界环境条件,纳米微球能缓慢靶向释放药物,具有良好的光热敏感性,该纳米微球在药物控释及药物载体等领域有广泛的应用前景。     

Triple stimulus-responsive polypeptide nanoparticles that enhance intratumoral spatial distribution

To address the limited tumor penetration of nanoparticle drug delivery vehicles, we report the first pH-responsive polypeptide micelle that dissociates at the low extracellular pH of solid tumors. This histidine-rich elastin-like polypeptide block copolymer self-assembles at 37 °C into spherical micelles that are stabilized by Zn(2+) and are disrupted as the pH drops from 7.4 to 6.4. These pH-sensitive micelles demonstrate better in vivo penetration and distribution in tumors than a pH-insensitive control.