Novel injectable progesterone-loaded nanoparticles embedded in SAIB-PLGA in situ depot system for sustained drug release

Poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) have attracted considerable interest in the medical community as a sustained-release drug delivery system for localized treatment. However, it is currently a grand challenge to simultaneously achieve low-dose drugs, stable and prolonged drug release, and long-term retention circumventing uptake by macrophages. Here, we construct a solvent-exchange in-situ depot system by incorporating progesterone (PRG) loaded PLGA NPs into a sucrose acetate isobutyrate (SAIB) and PLGA matrix for the long term treatment of Assisted Reproductive Technology (ART). The results showed that different solvent and PLGA contents could affect the drug release rate of PRG NPs-SAIB-PLGA in-situ depot system (PSPIDS). When DMSO was used as solvent with the addition of 8% PLGA to the depot, PSPIDS could achieve a constant drug release with no burst for 2 weeks in vitro. After a single intramuscular injection, such PSPIDS showed higher drug concentration and AUC (6773.0 ± 348.8 μg/L·h) over the entire 7-day testing period compared with the commercial multiple-day-dosing intramuscular PRG-oil solution (1914.5 ± 180.7 μg/L·h) in vivo. Importantly, PSPIDS could be administered at a dose of 3.65 mg/kg, which was one fourth of dose required for PRG-oil solution. The results demonstrate that PRG NPs could successfully achieve both reduced administered dosage and burst release, and therefore that PSPIDS is a promising long-acting composite system for hydrophobic drugs.

Supercritical Impregnation of Ketoprofen into Polylactic Acid for Biomedical Application: Analysis and Modeling of the Release Kinetic

Ketoprofen (KET) is an anti-inflammatory drug often used in medicine due to its analgesic and antipyretic effects. If it is administered in a controlled form by means of different dosing devices, it acts throughout the patient’s recovery period improving its efficacy. This study intends to support the use of supercritical solvent impregnation (SSI) as an efficient technique to develop polylactic acid (PLA) functionalized with ketoprofen, for use as controlled drug release devices. For this purpose, firstly, the influence of different SSI variables on the desirable swelling of the polymer structure, while avoiding their foaming, were evaluated. Then, the resulting ketoprofen loading was evaluated under different pressure/temperature conditions. It was generally found that as pressure and temperature are higher, the drug impregnation loads also increase. The maximum impregnation loads (at about 9% KET/PLA) were obtained at 200 bar and 75 °C. In vitro drug release tests of the impregnated compound were also carried out, and it was found that drug release profiles were also dependent on the specific pressure and temperature conditions used for the impregnation of each polymer filament.

Solvent-Free Processing of Drug-Loaded Poly(ε-Caprolactone) Scaffolds with Tunable Macroporosity by Combination of Supercritical Foaming and Thermal Porogen Leaching

Demand of scaffolds for hard tissue repair increases due to a higher incidence of fractures related to accidents and bone-diseases that are linked to the ageing of the population. Namely, scaffolds loaded with bioactive agents can facilitate the bone repair by favoring the bone integration and avoiding post-grafting complications. Supercritical (sc-)foaming technology emerges as a unique solvent-free approach for the processing of drug-loadenu7d scaffolds at high incorporation yields. In this work, medicated poly(ε-caprolactone) (PCL) scaffolds were prepared by sc-foaming coupled with a leaching process to overcome problems of pore size tuning of the sc-foaming technique. The removal of the solid porogen (BA, ammonium bicarbonate) was carried out by a thermal leaching taking place at 37 °C and in the absence of solvents for the first time. Macroporous scaffolds with dual porosity (50-100 µm and 200-400 µm ranges) were obtained and with a porous structure directly dependent on the porogen content used. The processing of ketoprofen-loaded scaffolds using BA porogen resulted in drug loading yields close to 100% and influenced its release profile from the PCL matrix to a relevant clinical scenario. A novel solvent-free strategy has been set to integrate the incorporation of solid porogens in the sc-foaming of medicated scaffolds.

Injectable hydrogel derived from chitosan with tunable mechanical properties via hybrid-crosslinking system

Thermo-sensitive injectable hydrogels that spontaneously react to physiological temperature have been widely studied to be used in biomedical fields. However, several challenges on their unstable structures with large-sized pores and low mechanical strength under physiological conditions must be addressed to enable their practical applications. We synthesized the hydroxybutyl methacrylated chitosan (HBC-MA) hydrogel that possesses both thermo-sensitive and photo-crosslinkable properties. The HBC-MA showed effective sol-gel transition under physiological temperature as well as a sensitive photo-crosslinkable property with visible light capable of skin penetration. The co-nonsolvency property and thermo-sensitivity of HBC-MA prevented unintended loss of the hydrogel graft after being subcutaneously injected in mice. Subsequently applied visible light on the skin beneath which the hydrogel was injected significantly improved the mechanical strength and stability of the graft. The injectable HBC-MA hydrogel developed in this study can be applicable to a wide range of biomedical fields such as drug delivery system and tissue engineering.

Thermoresponsive functional polymers based on 2,6-diaminopyridine motif with tunable UCST behaviour in water/alcohol mixtures

Two thermoresponsive polyacrylamides based on the 2,6-diaminopyridine motif were synthesized and their UCST-type reversible thermoresponsive behaviour was studied in water/alcohol mixtures.

Synthesis of aspirin-loaded polymer-silica composites and their release characteristics

This study describes a novel approach to the synthesis of polymer-drug-silica nanocomposites via encapsulation/isolation of drug molecules, introduced into the polymer matrix by the silica gel. For the first time, tetraethoxysilane (TEOS) gelation in the vapor phase of the acidic catalyst is presented as an efficient method to enter the silica gel nanoparticles into the polymer-aspirin conjugate. The conducted studies reveal that the internal structure of the polymer carrier is significantly reorganized after the embedding of aspirin molecules and the silica gel. The total porosity of the polymer-drug-silica nanocomposites and the molecular structure of the silica gel embedded in the system strongly depend on the conditions of the silica source transformation. Additionally, the release of the drug was fine-tuned by adapting the conditions of hydrolysis and condensation of the silica gel precursor. Finally, to prove the usefulness of the proposed synthesis, the controlled release of aspirin from the polymer-drug-silica nanocomposites is demonstrated.

Synthesis and characterization of biocompatible poly(organophosphazenes) aiming for local delivery of protein drugs

Biocompatible and thermosensitive poly(organophosphazenes) with a lower critical solution temperature (LCST) below body temperature have been designed with the aim for the local delivery of peptide and protein drugs. These polymers could be synthesized by introducing short chain tri- or tetraethylene glycol as a hydrophilic group and a dipeptide, GlyGluEt2 as a hydrophobic group into the polyphosphazene backbone. The local tolerance tests using rabbits have shown that our polymers are biocompatible. Using the amphiphilic properties of these polymers, in vitro studies were performed for loading and releasing of a human growth hormone (hGH) as a model drug. The entrapment efficiency (%) of hGH by the polymer decreased as its polymer concentration increased, but exhibited high efficiency of more than 95% even at 20% hGH concentration in the polymer. The entrapped hGH has shown to be controlled releasing for 3-4 days.

Preparation of thermoresponsive core–shell copolymer latex with potential use in drug targeting

A core-shell copolymer latex with thermal-responsive properties was prepared and its potential application as a vehicle for drug targeting was investigated in this work, where the crosslinked copolymer of N-isopropylacrylamide (NIPAAm) and chitosan was prepared as the core and the copolymer of methacrylic acid (MAA) and methyl methacrylate (MMA) was prepared as the shell. By using soapless dispersion polymerization, the poly(NIPAAm-chitosan) crosslinked copolymer latex was synthesized first. Then the monomers of MAA and MMA were added to continue the reaction to obtain the core-shell copolymer latex. The weight ratio of MAA/MMA and the concentration of shell monomers (MAA and MMA) in the feed of the reaction mixture had been changed to investigate their effects on the particle size, reaction rate, zeta-potential, specific surface area, and surface functional groups of the latex particles. The swelling and thermoresponsive behavior of the film made from these core-shell latices were also studied under different pH values of buffer solution. The model drug (caffeine) could be merged inside the copolymer particles and protected from releasing through the transport process effectively. And the thermoresponsive property of these copolymer particles significantly enhances the ligand (protein) conjugation that shows the potential of the latex being applied on the targeting drug carrier.

On-off transport through a thermoresponsive hydrogel composite membrane

A novel thermoresponsive composite membrane is described through which the permeation of molecules is dependent on the temperature of the milieu. The thermoresponsive composite membranes utilise a thermosensitive crosslinked polymeric hydrogel, which possesses a volume phase transition temperature (VPTT). The hydrogel was polymerised in situ within the pores of a sintered glass filter, through which significant permeation of molecules only occurred at temperatures above the VPTT of the hydrogel. It was found that the permeation of molecules through the thermoresponsive composite membranes could be modulated by changing the environmental temperature.

On the importance and mechanisms of burst release in matrix-controlled drug delivery systems

Although the significance of burst release in controlled delivery systems has not been entirely ignored, no successful theories have been put forth to fully describe the phenomenon. Despite the fact that the fast release of drug in a burst stage is utilized in certain drug administration strategies, the negative effects brought about by burst can be pharmacologically dangerous and economically inefficient. Therefore a thorough understanding of the burst effect in controlled release systems is undoubtedly necessary. In this article, we review experimental observations of burst release in monolithic polymer controlled drug delivery systems, theories of the physical mechanisms causing burst, some of the unique ideas used to prevent burst, and the treatment of burst release in controlled release models.

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)/poly(epsilon-caprolactone) (PCL) amphiphilic block copolymeric nanospheres. II. Thermo-responsive drug release behaviors

Amphiphilic block copolymers composed of relatively hydrophilic PEO-PPO-PEO block copolymer (Pluronic) and poly (epsilon-caprolactone) with hydrophobic character were synthesized by ring-opening polymerization of epsilon-caprolactone in the presence of PEO-PPO-PEO block copolymer using stannous octoate as a catalyst. Pluronic/PCL block copolymeric nanospheres with core-shell structure were prepared by dialysis method. They showed the average diameter of 116-196 nm depending on the type of copolymer. All the nanosphere samples exhibited a narrow size distribution. The critical micelle concentrations of Pluronic/PCL amphiphilic block copolymers determined by fluorescence spectroscopy were lower than that of the common low molecular weight surfactant. Their core-shell structure was confirmed by 1H NMR spectroscopy. Pluronic/PCL block copolymeric nanospheres exhibited the reversible change of size depending on the temperature. Release behaviors of indomethacin from Pluronic/PCL block copolymeric nanospheres also showed temperature dependence and a sustained release pattern. In addition, cytotoxicity test using an MTT assay method revealed that these indomethacin-loaded Pluronic/PCL nanospheres could remarkably reduce the cell damage compared with the unloaded free indomethacin.

Temperature- and pH-sensitive terpolymers for modulated delivery of streptokinase

Controlled release devices were designed which respond to changes in pH and temperature by reversibly swelling and deswelling to control release of streptokinase. Copolymer hydrogels composed of N-isopropylacrylamide (NIPAAm) and methacrylic acid (MAA) as well as terpolymer hydrogels containing NIPAAm, acrylic acid (AA), and 2-hydroxyethyl methacrylate (HEMA) were synthesized. Hydrogels containing NIPAAm display a change in swelling behavior across the lower critical solubility temperature of PNIPAAm, whereas hydrogels with MAA and AA swelled only at high pH values due to the ionization of carboxylic pendant groups. HEMA was chosen as a third component to add mechanical strength and integrity to the hydrogel. Pulsatile pH- and temperature-dependent swelling studies were performed to determine the extent and rate at which the hydrogels swell in response to changing conditions. Results showed that increasing the NIPAAm concentration in the copolymers or terpolymers resulted in a higher degree of temperature-sensitive swelling. Synthesis of a terpolymer in which segments rich in NIPAAm were distributed within P(AA-co-HEMA) chains led to hydrogels displaying increased temperature sensitivity. Streptokinase was incorporated into the hydrogels, and its release was observed under the combined effects of temperature and pH. The streptokinase release pattern followed the swelling state of the hydrogel, with drug release occurring at a significantly higher rate from the most swollen hydrogels.

Electrophoresis of DNA in novel thermoreversible matrices

We demonstrate the feasibility of temperature-sensitive polymers as novel matrices for capillary and slab electrophoresis of DNA. These matrices combine the case-of-use of agarose with resolution properties of polyacrylamide. Two classes of matrices are used: (i) aqueous suspensions of gel microspheres and (ii) solutions containing uncross-linked temperature-sensitive polymers. When heated, the viscosity of these solutions drops dramatically because of the phase transition behavior of these polymers, and therefore these formulations are easy to pour or load. Results are presented for separation of double-stranded DNA fragments (< 2000 bp) in capillary, tube, and slab electrophoresis. Preliminary results are also presented for separation of single-stranded sequencing fragments by capillary electrophoresis. In the tube format, good resolution was obtained for phi X174/HaeIII fragments. In the slab format, excellent resolution of double-stranded DNA was obtained, including simultaneous separation of a 10 bp ladder up to 150 base pairs. In the capillary format, pBR322/MspI fragments were completely resolved, and single-base resolution of sequencing fragments was obtained up to 150 bases. We believe that temperature-sensitive polymers represent a new and promising class of electrophoretic media.

Biomaterials with permanent hydrophilic surfaces and low protein adsorption properties

Low protein adsorbing polymer films have been prepared with which to fabricate intravenous containers, designed for compatibility with low concentrations of protein drugs. The material is economically manufactured utilizing physical melt blending of water-soluble surface-modifying polymers (PEO, PEOX, PVA, and PNVP) with a base polymer (EVA, PP, PETG, PMMA, SB, and nylon). Permanency of the hydrophilic surfaces so generated was confirmed by surface contact angle experiments and total organic carbon leachables analysis of the aqueous contacting solutions. Binding of IgG, albumin and insulin was studied. A sixfold reduction of protein adsorption was obtained by adding 5% PVA13K to EVA, for IgG at a bulk concentration of 2.5 ppm. Surface bound protein measured by micro-BCA colorimetry, agreed with the solution protein lost, as determined by the Fluoraldehyde procedure. Imaging of the protein exposed plastic surfaces by silver enhanced protein conjugated gold staining agreed with the quantitative assay determinations.

Surface-modulated skin layers of thermal responsive hydrogels as on-off switches: II. Drug permeation

'On-off' regulation of drug permeation through membranes in response to external temperature change has already been achieved using thermosensitive copolymers of N-isopropyl acrylamide (IPAAm) with butyl methacrylate (BMA). Increasing temperature induced formation of a dehydrated polymeric surface skin layer that stopped drug permeation. In this study, to control 'on-off' permeability of a drug, the polymer surface shrinking process was regulated by changing the length of alkyl side chain of the copolymer methacrylate component. Permeation experiments with indomethacin were performed in response to stepwise temperature changes between 20 and 30 degrees C with copolymers of IPAAm with BMA, hexyl methacrylate (HMA), and lauryl methacrylate (LMA). Burst permeation was found at the initial stage of the second 'on' period for both poly(IPAAm-co-HMA) and poly(IPAAm-co-LMA). These results suggest that drug diffuses during 'off' periods to change the concentration profile in the polymer gel. Polymer surface skin formation maintains a localized high water content inside the polymer gel even if drug permeation stops. The length of the alkyl side chain is an important parameter to control 'on-off' permeability of drug.

Surface-modulated skin layers of thermal responsive hydrogels as on-off switches: I. Drug release

Thermosensitive co-polymers of isopropyl acrylamide (IPAAm) with butyl methacrylate (BMA) are capable of 'on-off' regulation of drug release in response to external temperature changes due to skin formation with increasing temperature. To clarify the role of the surface-modulated skin and controlled pulsatile drug release patterns, the surface shrinking process was regulated by changing the length of the methacrylate alkyl side-chain. Release of indomethacin in response to stepwise temperature changes between 20 and 30 degrees C from co-polymers of IPAAm with BMA, hexyl methacrylate (HMA), and lauryl methacrylate (LMA) was studied. The drug release rate during the 'on' state (20 degrees C) remained constant before and after the 'off' state (30 degrees C) when the period of the 'off' state was increased. These results suggest that the drug in the polymeric matrices diffused from the inside to the surface during the 'off' state even when no drug release was seen. The length of alkyl side-chain was found to be an important parameter in controlling the thickness and density of the surface skin layer.