Sol-gel processed porous silica carriers for the controlled release of diclofenac diethylamine

Silica xerogels doped with diclofenac diethylamine were prepared by the sol-gel method from a hydrolysed tetraethoxysilane (TEOS) solution containing diclofenac diethylamine. Two different catalysts, drying conditions and levels of water content were used to alter the microstructure of the silica xerogels. The aim of this study was to determine the rate of Diclofenac release from the silica xerogels. This in vitro study showed that the sol-gel method is useful for entrapping Diclofenac in the pores of xerogels. It also showed that, in vitro, Diclofenac is released from the silica xerogel, through the pores, by diffusion. Base-catalysed gels proved to be much more effective than acid-catalyzed gels.     

Preparation and characterization of pH- and temperature-sensitive pullulan microspheres for controlled release of drugs

Most part of pH- and temperature-sensitive microspheres used for the controlled delivery of drugs are not biodegradable. Therefore, the aim of this work is to prepare pH- and temperature-sensitive microspheres from biodegradable and biocompatible natural polymers. Pullulan microspheres were prepared by suspension cross-linking with epichlorohydrin of an aqueous solution of the polymer. In order to confer them temperature sensitivity, poly(N-isopropylacrylamide-co-acrylamide) was grafted onto pullulan microspheres. Then, the pH-sensitive units (-COOH) were introduced by reaction between the remaining -OH groups of the pullulan with succinic anhydride. The grafted pullulan microspheres are more hydrophilic than pullulan microspheres, their swelling degree as well as water regain increase significantly. The thermo-sensitivity of the carboxylated microspheres depends to the number and the ionization form (-COOH/-COO(-)) of carboxylic groups. At a low exchange capacity (0.35 meq/g), microspheres are thermo-sensitive both in the protonated and deprotonated form of -COOH groups. At a higher exchange capacity (2.25 meq/g), microspheres are almost unswellable in the protonated form and swell extensively in the ionized form (up to 28 times than their dried form) loosing in a great extent the thermo-sensitive properties. In isotonic phosphate buffer pH=7.4, both thermo-sensitive and pH/thermo-sensitive microspheres possess a phase transition temperature close to that of the human body temperature. Loading and release profiles of lysozyme, taken as a molecular model system, were investigated.     

Three-month, zero-order piroxicam release from monodispersed double-walled microspheres of controlled shell thickness

Double-walled microspheres represent an increasingly important class of drug delivery devices that provide enhanced control of drug delivery schedules. Clearly, the overall particle size and shell thickness are important parameters in modulating the drug release rates. Precision particle fabrication technology has been used to fabricate double-walled microspheres of predefined uniform diameters of 40-60 microm exhibiting a poly(D,L-lactide-co-glycolide) (PLG) core and poly(L-lactide) (PL) shell of controllable thickness from approximately 2 to 10 microm. The release of a model small-molecule drug, piroxicam, from uniform microspheres of pure PLG and PL is compared to the release from double-walled microspheres exhibiting different PL shell thicknesses. The presence of the PL shell enveloping a PLG core essentially eliminated the initial "burst" of piroxicam that was observed when the drug was released from pure PLG microspheres. In addition, increasing the PL shell thickness shifted the release profile from a biphasic shape for pure PLG microspheres to zero-order piroxicam release over 3 months for the thickest (approximately 10 microm) PL shell.     

Surfactant-assisted controlled release of hydrophobic drugs using anionic surfactant templated mesoporous silica nanoparticles

A series of mesoporous silica nanoparticles (MSNs) were synthesized using the co-structure directing method. A non-cytotoxic anionic surfactant, undec-1-en-11-yltetra(ethylene glycol) phosphate monoester surfactant (PMES), was used as a structure directing agent (SDA) together with aminopropyltrimethoxysilane that functioned as a co-structure directing agent (CSDA). The morphology and mesoporous structure of these materials were tuned by changing the molar ratio of CSDA and SDA. These mesoporous nanomaterials containing PMES inside the pores showed excellent biocompatibility in vitro. The cellular internalization and endosome escape of PMES-MSNs in cervical cancer cells (HeLa) was demonstrated by flow cytometry and confocal microscopy, respectively. The PMES-MSNs were used as drug delivery carriers for resveratrol, a low water solubility drug, by taking advantage of the hydrophobic environment created by the PMES micelle inside the pores. This surfactant-assisted delivery strategy was tested under physiological conditions showing an increase of the drug loading compared to the material without surfactant and steady release of resveratrol. Finally, the therapeutic properties of resveratrol-loaded PMES-MSNs were evaluated in vitro using HeLa and Chinese hamster ovarian cells. We envision that this surfactant-assisted drug delivery method using MSNs as nanovehicles would lead to a new generation of carrier materials for intracellular delivery of a variety of hydrophobic therapeutic agents.     

Immobilization and controlled release of prostaglandin E2 from poly-L-lactide-co-glycolide microspheres

Prostaglandin E(2) (PGE(2)) is an arachidonic acid metabolite involved in physiological homeostasis and numerous pathophysiological conditions. Furthermore, it has been demonstrated that prostaglandins have a stimulating effect not only on angiogenesis in situ and in vitro but also on chondrocyte proliferation in vitro. Thus, PGE(2) represents an interesting signaling molecule for various tissue engineering strategies. However, under physiological conditions, PGE(2) has a half-life time of only 10 min, which limits its use in biomedical applications. In the present study, we investigated if the incorporation of PGE(2) into biodegradable poly-L-lactide-co-glycolide microspheres results in a prolonged release of this molecule in its active form. PGE(2)-modified microspheres were produced by a cosolvent emulsification method using CHCl(3) and HFIP as organic solvents and PVA as emulsifier. Thirteen identical batches were produced; and to each batch 1.0 mL of serum-free medium was added. The medium was removed at defined time points and then analyzed by gas chromatography tandem mass spectrometry (GC/MS/MS) to measure the residual PGE(2) content. In this study we demonstrated the prolonged release of PGE(2), showing a linear increase over the first 12 h, followed by a plateau and a slow decrease. The microspheres were further characterized by scanning electron microscopy.     

Synthesis, characterization, and controlled nitric oxide release from S-nitrosothiol-derivatized fumed silica polymer filler particles

A new type of nitric oxide (NO)-releasing material is described that utilizes S-nitrosothiols anchored to tiny fumed silica (FS) particles as the NO donor system. The synthetic procedures suitable for tethering three different thiol species (cysteine, N-acetylcysteine, and N-acetylpenicillamine) to the surface of FS polymer filler particles are detailed. The thiol-derivatized particles are converted to their corresponding S-nitrosothiols by reaction with t-butylnitrite. The total NO loading on the resulting particles range from 21-138 nmol/mg for the three different thiol-derivatized materials [S-nitrosocysteine-(NO-Cys)-FS, S-nitroso-N-acetylcysteine (SNAC)-FS, and S-nitroso-N-acetylpenicillamine (SNAP)-FS], with SNAP-FS yielding the highest NO loading. NO can be generated from these particles when suspended in solution via the addition of copper(II) ions, ascorbate, or irradiation with visible light. The SNAC-FS and SNAP-FS particles can be blended in polyurethane and silicone rubber matrixes to create films that release NO at controlled rates. Polyurethane films containing SNAC-FS submerged in phosphate-buffered saline (pH 7.4) generate NO surface fluxes approximately 0.1-0.7x10(-10) mol cm-2 min-1 and SNAP-FS films generate NO fluxes of approximately 0-7.5x10(-10) mol cm-2 min-1 upon addition of increasing amounts of copper ions. Silicone rubber films containing SNAC-FS or SNAP-FS do not liberate NO upon exposure to copper ions or ascorbate in phosphate-buffered saline solution. However, such films are shown to release NO at rates proportional to increasing intensities of visible light impinging on the films. Such photoinitiated NO release from these composite materials offers the first NO-releasing hydrophobic polymers with an external on/off trigger to control NO generation.     

Preparation and drug controlled release of porous octyl-dextran microspheres

In this work, porous octyl-dextran microspheres with excellent properties were prepared by two steps. Firstly, dextran microspheres were synthesized by reversed-phase suspension polymerization. Secondly, octyl-dextran microspheres were prepared by the reaction between dextran microspheres and ethylhexyl glycidyl ether and freezing-drying method. Porous structure of microspheres was formed through the interaction between octyl groups and organic solvents. The structure, morphology, dry density, porosity and equilibrium water content of porous octyl-dextran microspheres were systematically investigated. The octyl content affected the properties of microspheres. The results showed that the dry density of microspheres decreased from 2.35 to 1.21 g/ml, porosity increased from 80.68 to 95.05% with the octyl content increasing from 0.49 to 2.28 mmol/g. Meanwhile, the equilibrium water content presented a peak value (90.18%) when the octyl content was 2.25 mmol/g. Octyl-dextran microspheres showed high capacity. Naturally drug carriers play an important role in drug-delivery systems for their biodegradability, wide raw materials sources and nontoxicity. Doxorubicin (DOX) was used as a drug model to examine the drug-loading capacity of porous octyl-dextran microspheres. The drug-loading efficiency increased with the increase in microspheres/drug ratio, while the encapsulation efficiency decreased. When microspheres/drug mass ratio was 4/1, the drug-loading efficiency and encapsulation efficiency were 10.20 and 51.00%, respectively. The release rate of DOX increased as drug content and porosity increased. In conclusion, porous octyl-dextran microspheres were synthesized successfully and have the potential to serve as an effective delivery system in drug controlled release.     

Biodegradable polymer-silica xerogel composite microspheres for controlled release of gentamicin

Single and double layered composite microspheres were prepared by encapsulating gentamicin-loaded silica xerogels with biodegradable PLGA polymers (poly(DL-lactide-co-glycolide)). The in vitro drug release properties of both the composite microspheres were investigated. The single layered composite microspheres showed a high initial burst, followed by two sustained release stages lasting for approximately 6 weeks. The two sustained release stages of the single layered composite microspheres could be attributed to the swelling and bulk erosion of the polymer encapsulations, respectively. In comparison with the single layered composite microspheres, the double layered composite microspheres realized a much reduced initial burst together with three sustained release stages. The whole release period of the double layered composite microspheres could last more than 9 weeks. These distinct behaviors make the double layered composite microspheres promising as a new drug release material for localized drug delivery applications.     

Polymer-coated mesoporous silica nanoparticles for the controlled release of macromolecules

With the goal of achieving constant release of large biological molecules over an extended period of time we focused on hybrid inorganic/organic nanoparticles. We synthesized poly(ethylene glycol) (PEG)-coated mesoporous silica nanoparticles (MSNs) with incorporated trypsin inhibitor (TI), a model protein molecule for growth factors. Due to the goal of incorporating large protein molecules the pore size of the as-synthesized MSNs was expanded by a hydrothermal treatment prior to TI incorporation. In vitro release from the MSNs without the thin polymer film shows an initial burst followed by continuous release. In the case of polymer-coated MSNs the initial burst release was completely suppressed and approximate zero order release was achieved for 4 weeks.     

Biodegradable hollow fibres for the controlled release of drugs

Biodegradable hollow fibres of poly-L-lactic acid (PLLA) filled with a suspension of the contraceptive hormone levonorgestrel in castor oil were implanted subcutaneously in rats to study the rate of drug release, rate of biodegradation and tissue reaction caused by the implant. The in vivo drug release was compared with the release in vitro using different release media. Fibres, disinfected with alcohol showed a zero-order release, both in vitro and in vivo, for over 6 months. Fibres, either gamma-sterilized or disinfected with alcohol were harvested at time intervals ranging from 1 d to 6 months after implantation. Molecular weights of PLLA, tensile strengths, and remaining amounts of drug were determined as a function of time. The tissue reaction can be described as a very moderate foreign body reaction with the initial presence of macrophages, which are gradually replaced by fibroblasts which form a collagen capsule. Molecular weight determinations of PLLA showed a decrease from an initial Mw of 1.59 X 10(5) to 5.5 X 10(4) in 4 months (after alcohol sterilization). A gradual decrease in fibre strength with time was observed which did not significantly impair the release rate of levonorgestrel.     

Controlled release of lysozyme from succinylated gelatin microspheres

Gelatin was anionized to increase the carboxylic acid groups through succinylation. Succinylation of gelatin was performed using varying amounts of succinic anhydride. This gave various percentages of substitution. Lysozyme, a cationic antibacterial enzyme, which has important applications in the reduction of prosthetic valve endocarditis, was chosen as a model protein drug. Microspheres were prepared using unmodified gelatin and succinylated gelatin (SG) and lysozyme was incorporated into them. The percentage loading and release profiles of lysozyme for gelatin and SG microspheres were evaluated and compared. It was found that the SG microspheres exhibited higher loading efficiency for lysozyme (50%) than the unmodified gelatin microspheres. The in vitro release of lysozyme from SG microspheres occurred up to 122 h, compared to 96 h for gelatin microspheres, for the release of most of the lysozyme incorporated. This prolonged release of lysozyme from SG microspheres was attributed to the electrostatic interaction between the cationic lysozyme and the anionic SG microsphere carrier.     

Controlled release of lysozyme from succinylated gelatin microspheres

Gelatin was anionized to increase the carboxylic acid groups through succinylation. Succinylation of gelatin was performed using varying amounts of succinic anhydride. This gave various percentages of substitution. Lysozyme, a cationic antibacterial enzyme, which has important applications in the reduction of prosthetic valve endocarditis, was chosen as a model protein drug. Microspheres were prepared using unmodified gelatin and succinylated gelatin (SG) and lysozyme was incorporated into them. The percentage loading and release profiles of lysozyme for gelatin and SG microspheres were evaluated and compared. It was found that the SG microspheres exhibited higher loading efficiency for lysozyme (50%) than the unmodified gelatin microspheres. The in vitro release of lysozyme from SG microspheres occurred up to 122 h, compared to 96 h for gelatin microspheres, for the release of most of the lysozyme incorporated. This prolonged release of lysozyme from SG microspheres was attributed to the electrostatic interaction between the cationic lysozyme and the anionic SG microsphere carrier.     

Triggered release of small molecules from proteinoid microspheres

Proteinoid microspheres (PM) are formed by the thermal condensation of amino acids. They have been useful to further evolutionary theory, as catalysts for some biochemical reactions, but they have not been overly useful as controlled delivery agents. It is possible however to construct PMs that contain organic small molecules in the interior space. This means that a PM could be used as a delivery agent, if a suitable method could be discovered to cause the release of the internal material. This report describes the formation of a PM that includes a molecular bridging agent that can be removed in a reducing environment. Removal of the bridge opens a hole or window in the PM that allows the interior material to escape. The rate at which the interior material is released from the PM can be controlled by the size of the window or by the reduction potential in the environment. These PMs can be used to temporally treat a variety of complications including wounds (chronic or acute) by delivering a sequestered reagent in a controlled manner and are advantageous in that amino acids are the primary delivery vehicle breakdown product.     

Xanthan gum as a carrier for controlled release of drugs

Systems based on xanthan gum matrix containing 1%, 2% and 5% salicylic acid were prepared and studied as controlled release devices. Swelling of the matrix in distilled water and buffer solutions showed that the ionic strength of the liquid has a strong effect on the sorptive properties of the matrix. From the release experiments, conducted in distilled water at 37 +/- 0.5 degrees C, it was found that the drug delivery process was accomplished within the first 10 hours after immersion and salicylic acid was always released via a non-Fickian transport. The phenomenon can be described by a release exponent (n) in the area of 0.77 independently of the initial concentration of salicylic acid in the xanthan matrix. These results can be interpreted taking into consideration the dimensional and physical changes of the polymeric matrix during swelling.     

Improved collagen bilayer dressing for the controlled release of drugs

A novel bilayer dressing has been developed from bovine succinylated collagen. The dressing contains an antibiotic, Ciprofloxacin, for both immediate and time-regulated release for controlling the infection, as the infected open wounds need special care. The dressing consists of a sponge and a film, both prepared from succinylated bovine collagen. The sponge has a smooth surface on one side; its rough surface on the other side forms the bilayer system with the film. Both sponge and film act as an anionic reservoir to hold the cationic Ciprofloxacin. The drug, after dispersing in poly (N-vinyl-2-pyrrolidione) (PVP) solution is allowed to spread in the bilayer system by diffusion. The drug stays in the bilayer system because of ionic binding, but starts releasing when comes in contact with the wound. Release of the drug is immediate, but it is regulated by ionic binding between the drug and succinylated collagen. The wound exudates, and there is a polarity-controlled release of the drug from the bilayer system. The PVP and bilayer system permits only time-regulated release, and the system lasts up to 5 days with therapeutically sufficient drug availability.     

Poly(methyl methacrylate)-grafted chitosan microspheres for controlled release of ampicillin

Microspheres of 50-500 microm diameter were prepared from a blend of chitosan and chitosan-g-PMMA. Environmental scanning electron microscopic and SEM studies revealed that the microspheres are porous and the pores extend toward the inner core of the microspheres. The microspheres were also found to be hemocompatible and cytocompatible. A model drug ampicillin was used to evaluate the drug loading capacity and the controlled release properties of the microspheres. The system maintained a sustained release of ampicillin for a period of more than 8 days. The drug-loaded chitosan/chitosan-g-PMMA microspheres exhibited higher antibacterial activity for both the gram positive (ATCC 25923 S. aureus) and gram negative (ATCC 25922 E. coli) bacteria than the drug-loaded virgin chitosan microspheres. The percentage release and bioactivity of ampicillin was found to be higher for the chitosan/chitosan-g-PMMA microspheres than the virgin chitosan microspheres. Potential applications such as oral drug delivery, wound dressings, tissue engineering, and so forth, are envisaged from these microspheres.     

The effect of the controlled release of nerve growth factor from collagen gel on the efficiency of neural cell culture

In this study, we tested the hypothesis that the amount of nerve growth factor (NGF) required for pheochromocytoma (PC12) cell culture can be dramatically reduced by controlled release of NGF from a collagen gel coating on the culture surface. Cells were cultured on collagen gels loaded with various amounts of NGF. As a control, PC12 cells were cultured on collagen gels with daily addition of various amounts of NGF to the culture medium. After an initial 12h burst, NGF was steadily released from the gels for 4 days. Apoptotic activity and cell viability were determined using terminal uridine nick end labeling and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, respectively. Neuronal differentiation was determined using immunocytochemistry and Western blot analysis. Compared to 100 ng NGF daily addition (300 ng over 3 days), 1 ng NGF daily addition showed dramatically decreased cell viability and neuronal differentiation and increased apoptotic activity. In contrast, collagen gels loaded with 10 ng NGF yielded cell viability, apoptotic activity, and neuronal differentiation similar to those of culture with 100 ng NGF daily addition. Our method reduced the amount of NGF required for PC12 cell culture to 1/3th of that used in daily addition without affecting cell viability, apoptosis, or differentiation. This method could economize large-scale culture of stem cells by reducing the amount of costly growth factors needed.     

Morphology of and release behavior from porous polyurethane microspheres

A novel biomaterial application of porous microspheres is for sustained delivery of biologically active agents. Recent studies have pointed out the importance of biomaterial porosity in promoting biocompatibility and controlling release rate of active agents. The objective of this research was to investigate the effect of chain-extending agent on the porosity and release behavior of polyurethane (PU) microspheres prepared using a two-step suspension polycondensation method with methylene diphenyl diisocyanate (MDI) as the isocyanate, polyethylene glycol (PEG400) as the diol, and 1,4-butanediol as the chain-extending agent. Chain-extending agent was used to increase the ratio of hard to soft segments of the PU network, and its effect on microsphere morphology was studied with scanning electron microscopy. According to the results, porosity was significantly affected by the amount of chain-extending agent. The pore size decreased as the concentration of chain-extending agent increased from zero to 50 mole%. With further increase of chain-extending agent to 60 and 67%, PU chains became stiffer and formation of pores was inhibited. Therefore, pore morphology was significantly affected by variations in the amount of chain-extending agent. The release behavior of microspheres was investigated with diazinon as the active agent. After an initial burst, corresponding to 3% of the incorporated amount of active agent, the release rate was zero order.     

An intelligent multicompartmental system based on thermo-sensitive starch microspheres for temperature-controlled release of drugs

An original multicompartmental drug delivery system based on encapsulation of “intelligent” starch microspheres was designed and developed. Starch microspheres with thermo-responsive properties and possessing strong anionic functional groups (-SO₃H), capable to bind electrostatically drugs, has been prepared. Firstly, the thermo-responsive units based on copolymer of poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) with a lower critical solution temperature around 36oC, were grafted on preformed starch microspheres. Secondly, the strong anionic groups (-SO₃H) were introduced by sequential grafting of 2-acrylamido-2-methyl-1-propanesulfonic acid on the remaining—OH groups of starch. The thermo-sensitive microspheres with sulfonic groups display a sharp phase transition around the human body temperature. They were complexed with the positively-charged metoclopramide (low molecular weight model drug) and then encapsulated in cellulose acetate butyrate microcapsules by an oil-in-water solvent evaporation method. The swelling and diffusion of encapsulated microspheres to the aqueous continuous phase is avoided because the temperature of aqueous phase is higher than volume phase transition temperature (VPTT) of microspheres. This multicompartmental device could develop the background of “smart” implantable drug delivery system for persons that work in dangerous cold places (builders, climbers). When the temperature of the human body decreases below the normal temperature (the threshold temperature could be tuned), the encapsulated microspheres swell extensively in contact with physiological fluids, break the microcapsules and a large amount of bioactive compounds is released, keeping the activity of the vital organs. In normal physiological conditions (above LCST), the microspheres slightly swell, fill up the microcavities of microcapsules, but do not break them and release the drug in microcompartments. These microcompartments become microreservoirs with bioactive compounds and release it with a very low rate maintaining the necessary concentration for a sustained activity of the body.     

In-vitro osteogenesis of synovium stem cells induced by controlled release of bisphosphate additives from microspherical mesoporous silica composite

In this study, in-vitro osteogenesis was successfully induced in the highly chondrogenic synovium mesenchymal stem cells (SMSCs) by controlled release of a nitrogenous bisphosphonate additive – alendronate (AL) from a mesoporous silica (MS)–hydroxyapatite (HA) composite that was mediated in poly(lactic-co-glycolic acid) (PLGA) microspheres. This microspherical based controlled release system is constructed with three levels of degradable structures: (1) the AL drug was first hybridized with HA nanoparticles; (2) the HA–AL complexes were filled into the mesopores of MS particles by self-assembly in situ; and (3) the HA–AL-laden MS constructs (MSH–AL) were built in the bulk of PLGA microspheres. In comparison with any mono-component construct, the superiority of this multi-component system comes from two aspects of functionalities: (1) significantly greater loading capacity of the extremely hydrophilic drug-AL; and (2) better controlled profile of AL release. Based on this newly developed PLGA/MSH–AL releasing system, as recipients the SMSCs, which usually exhibit exclusively high chondrogenesis, demonstrated a strong osteogenic commitment. The results were verified by alkaline phosphatase (ALP) activity assay, calcium secretion assay, real time PCR and immunohistochemistry analysis. Considering the renewable source and high proliferative profile of SMSCs, the achievement of engineered SMSC osteogenesis with this PLGA/MSH–AL controlled release system would open a new door to major bony reparation and regeneration.