Physico-chemical characterization of aspirated and simulated human gastric fluids to study their influence on the intrinsic dissolution rate of cinnarizine.

To elucidate the critical parameters affecting drug dissolution in the human stomach, the intrinsic dissolution rate (IDR) of cinnarizine was determined in aspirated and simulated human gastric fluids (HGF). Fasted aspirated HGF (aspHGF) was collected from 23 healthy volunteers during a gastroscopic examination. Hydrochloric acid (HCl) pH 1.2, fasted state simulated gastric fluid (FaSSGF), and simulated human gastric fluid (simHGF) developed to have rheological, and physico-chemical properties similar to aspHGF, were used as simulated HGFs. The IDR of cinnarizine was significantly higher in HCl pH 1.2 (952 ± 27 µg/(cm2·min)) than in FaSSGF pH 1.6 (444 ± 7 µg/(cm2·min)), and simHGF pH 2.5 (49 ± 5 µg/(cm2·min)) due to the pH dependent drug solubility and viscosity differences of the three simulated HGFs. The shear thinning behavior of aspHGF had a significant impact on the IDR of cinnarizine, indicating that the use of FaSSGF, with viscosity similar to water, to evaluate gastric drug dissolution, might overestimate the IDR by a factor of 100-10.000, compared to the non-Newtonian, more viscous, fluids in the human stomach. The developed simHGF simulated the viscosity of the gastric fluids, as well as the IDR of the model drug, making it a very promising medium to study gastric drug dissolution in vitro.

Exploring the Complexity of Processing-Induced Dehydration during Hot Melt Extrusion Using In-Line Raman Spectroscopy.

The specific aim in this study was to understand the effect of critical process parameters on the solid form composition of model drug compounds during hot melt extrusion using in-line Raman spectroscopy combined with Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) modeling for semi-quantitative kinetic profiling. It was observed that the hydrate and anhydrate solid forms of two model drugs in the melts of nitrofurantoin (NF):polyethylene oxide (PEO) and piroxicam (PRX):PEO could be resolved from a MCR-ALS model without an external calibration dataset. Based on this model, the influence of two critical process parameters (shear and temperature) on the solid form composition could be evaluated in a real-time mode and the kinetics of complex transformation pathways could be explored. Additionally, the dehydration pathways of NF monohydrate and PRX monohydrate in molten PEO could be derived. It can be concluded that dehydration of both hydrates in PEO occurs via competing mechanisms-a solution-mediated transformation pathway and a solid-solid transformation, and that the balance between these mechanisms is determined by the combined effect of both temperature and shear. Another important observation was that the water released from these hydrate compounds has a detectable effect on the rheological characteristics of this mixture.

In vivo evaluation of solid lipid microparticles and hybrid polymer-lipid microparticles for sustained delivery of leuprolide.

This study aims to investigate the potential of solid lipid microparticles (MP) and hybrid polymer-lipid MPs for sustained delivery of a peptide drug, leuprolide. A peptide-phospholipid complex was prepared to increase the compatibility of the peptide with triglyceride (TG) and poly (lactide-co-glycolide) (PLGA). Peptide loaded solid lipid MPs, PLGA MPs, and hybrid MPs were prepared using a spray drying method and characterized in terms of particle size, morphology and encapsulation efficiency. The pharmacokinetics and pharmacodynamics of leuprolide after subcutaneous injection of spray-dried MPs were evaluated in rats. Spray-dried MPs were spherical ranging in size from 4 µm to 10 µm, which are suitable for injection. After subcutaneous administration of reconstituted MPs, leuprolide could be detected in plasma samples of rats for one to two months, depending on the formulation and dose. Sustained release of leuprolide from PLGA MPs and glyceryl tristearate (TG18) MPs was observed over one month, with a chemical castration effect of 25 and 30 days, respectively. The bioavailability of leuprolide from PLGA-TG18 hybrid MPs was approximately four times higher than that from TG18 MP and PLGA MP alone using the same dose of leuprolide (6 mg/kg). Chemical castration in rats was observed over 30 and 60 days after injection of the PLGA-TG18 hybrid MP with a dose of 3 mg/kg and 6 mg/kg leuprolide, respectively. Additionally, a much lower Cmax was observed for the hybrid MP group. In conclusion, spray-dried PLGA-triglyceride hybrid MPs can be used as better carriers than other MPs for subcutaneous delivery of peptide drugs due to the synergetic effect of lipids and PLGA for sustained drug release from the spray-dried MP.

Qualitative and quantitative analysis of the biophysical interaction of inhaled nanoparticles with pulmonary surfactant by using quartz crystal microbalance with dissipation monitoring.

Understanding the interaction between inhaled nanoparticles and pulmonary surfactant is a prerequisite for predicting the fate of inhaled nanoparticles. Here, we introduce a quartz crystal microbalance with dissipation monitoring (QCM-D)-based methodology to reveal the extent and nature of the biophysical interactions of polymer- and lipid-based nanoparticles with pulmonary surfactant. By fitting the QCM-D data to the Langmuir adsorption equation, we determined the kinetics and equilibrium parameters [i.e., maximal adsorption (Δmmax), equilibrium constant (Ka), adsorption rate constant (ka) and desorption rate constant (kd)] of polymeric nanoparticles adsorption onto the pulmonary surfactant (e.g., an artificial lipid mixture and an extract of porcine lung surfactant). Furthermore, our results revealed that the nature of the interactions between lipid-based nanoparticles (e.g., liposomes) and pulmonary surfactant was governed by the liposomal composition, i.e., incorporation of cholesterol and PEGylated phospholipid (DSPE-PEG2000) into DOPC-based liposomes led to the adsorption of intact liposomes onto the pulmonary surfactant layer and the mass exchange between the liposomes and pulmonary surfactant layer, respectively. In conclusion, we demonstrate the applicability of the QCM-D technique for qualitative and quantitative analysis of the biophysical interaction of inhaled nanoparticles with pulmonary surfactant, which is vital for rational design and optimization of inhalable nanomedicines.

On-line rheological characterization of semi-solid formulations.

The rheological profile of a semi-solid product is a critical quality attribute. To monitor changes of this attribute during manufacturing, it would be beneficial to measure the rheological parameters in an on-line or in-line mode and implement this as a part of a control strategy for manufacturing of semi-solids. None of the process analytical technology (PAT) tools for measuring the rheological parameters have yet been widely accepted in the pharmaceutical area, as most of the equipment can only measure viscosity. Therefore, an automated system based on the measurement of pressure difference across both a topology optimized channel and a tube geometry (capillary viscometer) was investigated. The Pressure Difference Apparatus (PDA) can sample from the bulk intermediate/product stream and press the sample through the apparatus at different flow rates to yield a frequency sweep (G' and G″) and a flow curve (viscosity). A calibration model was successfully prepared and verified with hydroxyethyl cellulose gels with polymer content varying from 1.0 to 1.5% (w/w) resulting in gels of different viscosities. The calibration model was used on-line during manufacturing of a gel and manufacturing changes related to dilution of the product were clearly reflected in the batch evolution profiles. The measurements with the PDA reflected the shear rate and frequency ranges relevant for manufacturing and thereby complemented the rheology measurements obtained with a standard rheometer with real time data.

Effect of excipients on encapsulation and release of insulin from spray-dried solid lipid microparticles.

The study aimed at investigating the potential of spray drying method for encapsulation of protein drugs into solid lipid microparticles (MP) and evaluating effects of excipients on encapsulation and release of protein from MP. After transformation of model protein insulin to insulin-phospholipid complex, it was dissolved together with lipid excipients in organic solvent, which was spray-dried to form solid lipid MP. Polymeric MP with D, L-lactic-co-glycolic acid (PLGA) were prepared similarly. Around 90% of insulin was encapsulated in glycerol monostearate MP and glycerol distearate MP, whereas the encapsulation efficiency was 60% and 35% for tristearate (TG18) MP and tribehenate (TG22) MP, respectively. The secondary structure of insulin in the spray-dried MP was substantially similar to that of the insulin control solution, suggesting that only minor alterations occurred during the spray drying process. Sustained release of insulin was observed from both TG18 MP and TG22 MP. The burst release of insulin from TG18 MP and TG22 MP was around 30% and 10%, respectively, which was significantly lower than that from PLGA MP (40%). In conclusion, spray drying a solution containing both lipids and protein-phospholipid complex is a promising method for encapsulating protein into solid lipid MP, which can be used for sustained delivery of protein drugs.

Lipid Shell-Enveloped Polymeric Nanoparticles with High Integrity of Lipid Shells Improve Mucus Penetration and Interaction with Cystic Fibrosis-Related Bacterial Biofilms.

Nanoparticle (NP) mediated drug delivery into viscous biomatrices, e.g., mucus and bacterial biofilms, is challenging. Lipid shell-enveloped polymeric NPs (Lipid@NPs), composed of a polymeric NP core coated with a lipid shell, represent a promising alternative to the current delivery systems. Here, we describe the facile methods to prepare Lipid@NPs with high integrity of lipid shells and demonstrate the potential of Lipid@NPs in an effective mucus penetration and interaction with cystic fibrosis-related bacterial biofilms. Lipid shell-enveloped polystyrene NPs with high integrity of lipid shells ( cLipid@PSNPs) were prepared by using an electrostatically mediated layer-by-layer approach, where the model polystyrene NPs (PSNPs) were first modified with positively charged poly-l-lysine (PLL) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), followed by subsequent fusion with zwitterionic, PEGylated small unilamellar vesicles (SUVs). The interaction of the PSNPs with SUVs was significantly enhanced by modifying the PSNPs with PLL and DOTAP, which eventually resulted in the formation of cLipid@PSNPs, i.e., Lipid@PLL-PSNPs and Lipid@DOTAP-PSNPs. Improved mucus-penetrating property of cLipid@PSNPs was demonstrated by quartz crystal microbalance with dissipation monitoring measurements. Furthermore, fluorescence resonance energy transfer measurements showed that the interaction of the cLipid@PSNPs with bacterial biofilms was significantly promoted. In conclusion, we prepared cLipid@PSNPs via an electrostatically mediated layer-by-layer approach. Our results suggest that the integrity of the lipid envelopes is crucial for enabling the diffusion of Lipid@PSNPs into the mucus layer and promoting the interaction of Lipid@PSNPs with a bacterial biofilm.

Bladder wall biomechanics: A comprehensive study on fresh porcine urinary bladder.

Regenerative medicine for reconstructive urogenital surgery has been widely studied during the last two decades. One of the key factors affecting the quality of bladder regeneration is the mechanical properties of the bladder scaffold. Insight into the biomechanics of this organ is expected to assist researchers with functional regeneration of the bladder wall. Due to extensive similarities between human bladder and porcine bladder, and with regard to lack of comprehensive biomechanical data from the porcine bladder wall (BW), our main goal here was to provide a thorough evaluation on viscoelastic properties of fresh porcine urinary BW. Three testing modes including Uniaxial tensile, ball-burst (BB) and Dynamic Mechanical Analysis (DMA) were applied in parallel. Uniaxial tests were applied to study how different circumferential and longitudinal cut-outs of lateral region of BW behave under load. DMA was used to measure the viscoelastic properties of the bladder tissue (storage and loss modulus) in a frequency range of 0.1-3Hz. BB was selected as a different technique, replicating normal physiological conditions where the BW is studied in whole. According to uniaxial tests, the anisotropic behavior of bladder is evident at strain loads higher than 200%. According to DMA, storage modulus is consistently higher than loss modulus in both directions, revealing the elasticity of the BW. The stress-strain curves of both uniaxial and BB tests showed similar trends. However, the ultimate stress measured from BB was found to be around 5 times of the relevant stress from uniaxial loading. The ultimate strain in BB (389.9 ± 59.8) was interestingly an approximate average of rupture strains in longitudinal (358 ± 21) and circumferential (435 ± 69) directions. Considering that each testing mode applied here reveals distinct information, outcomes from the combination of the three can be considered as a helpful data-base to refer to for researchers aiming to regenerate the bladder.

The effect of HPMC and MC as pore formers on the rheology of the implant microenvironment and the drug release in vitro.

Porous implants or implantable scaffolds used for tissue regeneration can encourage tissue growth inside the implant and provide extended drug release. Water-soluble polymers incorporated into a biodegradable or inert implant matrix may leach out upon contact with biological fluids and thereby gradually increasing the porosity of the implant and simultaneously release drug from the implant matrix. Different molecular weight grades of methylcellulose (MC) and hydroxypropyl methylcellulose (HPMC) were mixed with polylactide and extruded into model implants containing nitrofurantoin as a model drug. The effect of the leached pore formers on the implant porosity and the rheology of the implant microenvironment in vitro was investigated and it was shown that HPMC pore formers had the greatest effect on the surrounding viscosity, with higher drug release and pore forming ability as compared to the MC pore formers. The highest molecular weight HPMC led to the most significant increase in viscosity of the implant microenvironment, while the highest drug release was achieved with the lowest molecular weight HPMC. The data suggested that the microenvironmental rheology of the implant, both in the formed pores and in biological fluids in the immediate vicinity of the implant could be an important factor affecting the diffusion of the drug and other molecules in the implantation site.

Melt Extrusion of High-Dose Co-Amorphous Drug-Drug Combinations : Theme: Formulation and Manufacturing of Solid Dosage Forms Guest Editors: Tony Zhou and Tonglei Li.

PURPOSE: Many future drug products will be based on innovative manufacturing solutions, which will increase the need for a thorough understanding of the interplay between drug material properties and processability. In this study, hot melt extrusion of a drug-drug mixture with minimal amount of polymeric excipient was investigated. METHODS: Using indomethacin-cimetidine as a model drug-drug system, processability of physical mixtures with and without 5% (w/w) of polyethylene oxide (PEO) were studied using Differential Scanning Calorimetry (DSC) and Small Amplitude Oscillatory Shear (SAOS) rheometry. Extrudates containing a co-amorphous glass solution were produced and the solid-state composition of these was studied with DSC. RESULTS: Rheological analysis indicated that the studied systems display viscosities higher than expected for small molecule melts and addition of PEO decreased the viscosity of the melt. Extrudates of indomethacin-cimetidine alone displayed amorphous-amorphous phase separation after 4 weeks of storage, whereas no phase separation was observed during the 16 week storage of the indomethacin-cimetidine extrudates containing 5% (w/w) PEO. CONCLUSIONS: Melt extrusion of co-amorphous extrudates with low amounts of polymer was found to be a feasible manufacturing technique. Addition of 5% (w/w) polymer reduced melt viscosity and prevented phase separation.

Molecular weight-dependent degradation and drug release of surface-eroding poly(ethylene carbonate).

Poly(ethylene carbonate) (PEC) is a unique biomaterial showing significant potential for controlled drug delivery applications. The current study investigated the impact of the molecular weight on the biological performance of drug-loaded PEC films. Following the preparation and thorough physicochemical characterization of diverse PEC (molecular weights: 85, 110, 133, 174 and 196kDa), the degradation and drug release behavior of rifampicin- and bovine serum albumin-loaded PEC films was investigated in vitro (in the presence and absence of cholesterol esterase), in cell culture (RAW264.7 macrophages) and in vivo (subcutaneous implantation in rats). All investigated samples degraded by means of surface erosion (mass loss, but constant molecular weight), which was accompanied by a predictable, erosion-controlled drug release pattern. Accordingly, the obtained in vitro degradation half-lives correlated well with the observed in vitro half-times of drug delivery (R2=0.96). Here, the PEC of the highest molecular weight resulted in the fastest degradation/drug release. When incubated with macrophages or implanted in animals, the degradation rate of PEC films superimposed the results of in vitro incubations with cholesterol esterase. Interestingly, SEM analysis indicated a distinct surface erosion process for enzyme-, macrophage- and in vivo-treated polymer films in a molecular weight-dependent manner. Overall, the molecular weight of surface-eroding PEC was identified as an essential parameter to control the spatial and temporal on-demand degradation and drug release from the employed delivery system.

Electrospinnability of Poly Lactic-co-glycolic Acid (PLGA): the Role of Solvent Type and Solvent Composition.

PURPOSE: In this study, the electrospinnability of poly(lactic-co-glycolic acid) (PLGA) solutions was investigated, with a focus on understanding the influence of molecular weight of PLGA, solvent type and solvent composition on the physical properties of electrospun nanofibers. METHOD: Various solvents were tested to dissolve two PLGA grades (50 KDa-RG755, 100 KDa-RG750). The viscoelasticity, surface tension, and evaporation rate of the PLGA solutions were characterized prior to the electrospinning process. The resulting electrospun nanofibers were characterized with respect to the morphology and mechanical properties. RESULTS: Two pairs of solvent mixtures, i.e. dimethylformamide (DMF)-tetrahydrofuran (THF) and DMF-chloroform (CHL), were identified to provide a stable cone-jet. Within the polymer concentration range studied (10-30%, w/v), RG750 solutions could be electrospun into uniform fibers at 30% (w/v) or at 20% (w/v) when modifying the solvent composition. In comparison to DMF-THF solution, fibers had larger diameter, higher stiffness and tensile strength when electrospun from DMF-CHL solution. CONCLUSION: The high molecular weight polymer could ensure sufficient intermolecular interaction to generate uniform fibers. The solvent could influence the morphology and mechanical properties of the electrospun fibers by altering the properties of PLGA solution, and drying rate of fibers in the electrospinning process.

The evaluation of physical properties of injection molded systems based on poly(ethylene oxide) (PEO).

The effect of product design parameters on the formation and properties of an injection molded solid dosage form consisting of poly(ethylene oxide)s (PEO) and two different active pharmaceutical ingredients (APIs) was studied. The product design parameters explored were melting temperature and the duration of melting, API loading degree and the molecular weight (Mw) of PEO. The solid form composition of the model APIs, theophylline and carbamazepine, was of specific interest, and its possible impact on the in vitro drug release behavior. Mw of PEO had the greatest impact on the release rate of both APIs. High Mw resulted in slower API release rate. Process temperature had two-fold effect with PEO 300,000g/mol. Firstly, higher process temperature transformed the crystalline part of the polymer into metastable folded form (more folded crystalline regions) and less into the more stable extended form (more extended crystalline regions), which lead to enhanced theophylline release rate. Secondly, the higher process temperature seemed to induce carbamazepine polymorphic transformation from p-monoclinic form III (carbamazepine (M)) into trigonal form II (carbamazepine (T)). The results indicated that the actual content of carbamazepine (T) affected drug release behavior more than the magnitude of transformation.

Oscillatory Shear Rheology in Examining the Drug-Polymer Interactions Relevant in Hot Melt Extrusion.

The flow properties of drug-polymer mixtures have a significant influence on their processability when using techniques such as hot melt extrusion (HME). Suitable extrusion temperature and screw speed to be used in laboratory scale HME were evaluated for mixtures containing 30% of paracetamol (PRC), ibuprofen (IBU), or indomethacin (IND), and 70% of polyethylene oxide, by using small amplitude oscillatory shear rheology. The initial evaluation of the drug:polyethylene oxide solubility was estimated by differential scanning calorimetry of the physical mixtures containing a wide range of weight fractions of the drug substances. Consecutively, the mixtures were extruded, and the maximum plasticizing weight fraction of each drug was determined by means of rheological measurements. IBU was found to have an efficient plasticizing functionality, decreasing the viscosity of the mixtures even above its apparent saturation solubility, whereas IND and PRC initially lowered the viscosity of the mixture slightly but increased it significantly with increasing drug load. The main reason for the enhanced plasticization effect seems to be the lower melting temperature of IBU, which is closer to the used HME temperature, compared to PRC and IND. This study highlights the importance of rheological investigation in understanding the drug-polymer interactions in melt processing.

Role of Electrostatic Interactions on the Transport of Druglike Molecules in Hydrogel-Based Articular Cartilage Mimics: Implications for Drug Delivery.

In the field of drug delivery to the articular cartilage, it is advantageous to apply artificial tissue models as surrogates of cartilage for investigating drug transport and release properties. In this study, artificial cartilage models consisting of 0.5% (w/v) agarose gel containing 0.5% (w/v) chondroitin sulfate or 0.5% (w/v) hyaluronic acid were developed, and their rheological and morphological properties were characterized. UV imaging was utilized to quantify the transport properties of the following four model compounds in the agarose gel and in the developed artificial cartilage models: H-Ala-ß-naphthylamide, H-Lys-Lys-ß-naphthylamide, lysozyme, and α-lactalbumin. The obtained results showed that the incorporation of the polyelectrolytes chondroitin sulfate or hyaluronic acid into agarose gel induced a significant reduction in the apparent diffusivities of the cationic model compounds as compared to the pure agarose gel. The decrease in apparent diffusivity of the cationic compounds was not caused by a change in the gel structure since a similar reduction in apparent diffusivity was not observed for the net negatively charged protein α-lactalbumin. The apparent diffusivity of the cationic compounds in the negatively charged hydrogels was highly dependent on the ionic strength, pointing out the importance of electrostatic interactions between the diffusant and the polyelectrolytes. Solution based affinity studies between the model compounds and the two investigated polyelectrolytes further confirmed the electrostatic nature of their interactions. The results obtained from the UV imaging diffusion studies are important for understanding the effect of drug physicochemical properties on the transport in articular cartilage. The extracted information may be useful in the development of hydrogels for in vitro release testing having features resembling the articular cartilage.

Rheology as a tool for evaluation of melt processability of innovative dosage forms.

Future manufacturing of pharmaceuticals will involve innovative use of polymeric excipients. Hot melt extrusion (HME) is an already established manufacturing technique and several products based on HME are on the market. Additionally, processing based on, e.g., HME or three dimensional (3D) printing, will have an increasingly important role when designing products for flexible dosing, since dosage forms based on compacting of a given powder mixture do not enable manufacturing of optimal pharmaceutical products for personalized treatments. The melt processability of polymers and API-polymer mixtures is highly dependent on the rheological properties of these systems, and rheological measurements should be considered as a more central part of the material characterization tool box when selecting suitable candidates for melt processing by, e.g., HME or 3D printing. The polymer processing industry offers established platforms, methods, and models for rheological characterization, and they can often be readily applied in the field of pharmaceutical manufacturing. Thoroughly measured and calculated rheological parameters together with thermal and mechanical material data are needed for the process simulations which are also becoming increasingly important. The authors aim to give an overview to the basics of rheology and summarize examples of the studies where rheology has been utilized in setting up or evaluating extrusion processes. Furthermore, examples of different experimental set-ups available for rheological measurements are presented, discussing each of their typical application area, advantages and limitations.

Simple measurements for prediction of drug release from polymer matrices - Solubility parameters and intrinsic viscosity.

PURPOSE: This study describes how protein release from polymer matrices correlate with simple measurements on the intrinsic viscosity of the polymer solutions used for casting the matrices and calculations of the solubility parameters of polymers and solvents used. METHOD: Matrices of poly(dl-lactide-co-glycolide) (PLGA) were cast with bovine serum albumin (BSA) as a model drug using different solvents (acetone, dichloromethane, ethanol and water). The amount of released protein from the different matrices was correlated with the Hildebrand and Hansen solubility parameters of the solvents, and the intrinsic viscosity of the polymer solutions. Matrix microstructure was investigated by transmission and scanning electron microscopy (TEM and SEM). Polycaprolactone (PCL) matrices were used in a similar way to support the results for PLGA matrices. RESULTS: The maximum amount of BSA released and the release profile from PLGA matrices varied depending on the solvent used for casting. The maximum amount of released BSA decreased with higher intrinsic viscosity, and increased with solubility parameter difference between the solvent and polymer used. The solvent used also had an effect on the matrix microstructure as determined by TEM and SEM. Similar results were obtained for the PCL polymer systems. CONCLUSIONS: The smaller the difference in the solubility parameter between the polymer and the solvent used for casting a polymer matrix, the lower will be the maximum protein release. This is because of the presence of smaller pore sizes in the cast matrix if a solvent with a solubility parameter close to the one of the polymer is used. Likewise, the intrinsic viscosity of the polymer solution increases as solubility parameter differences decrease, thus, simple measurements of intrinsic viscosity and solubility parameter difference, allow the prediction of protein release profiles.

Pharmaceutical microparticle engineering with electrospraying: the role of mixed solvent systems in particle formation and characteristics.

Microparticles of Celecoxib, dispersed in a matrix of poly(lactic-co-glycolic acid) (PLGA), were prepared by electrospraying using different solvent mixtures to investigate the influence upon particle formation and the resulting particle characteristics. Mixtures consisting of a good solvent, acetone, and an anti-solvent, methanol, for PLGA were studied in different ratios. Properties of the spraying solutions were examined and the resulting microparticles were characterized with regard to size, morphology, porosity, solid state form, surface chemistry and drug release. Particle formation was strongly influenced by the polymer molecular conformation during droplet formation and by the anti-solvent concentration during droplet drying. A strong correlation was found between particle morphology and the solubility of the polymer in the solvent mixtures. The lack of chain entanglements in droplets containing anti-solvent resulted in compact polymer conformation and grain-like particle morphology. Further, the early precipitation of polymer and low chain interaction with increasing content of anti-solvent resulted in surface enrichment of drug (from 10 and 20% up to 41 and 57% respectively), also demonstrated by the increasingly higher drug release rates. The results demonstrate the importance of solvent composition in particle preparation and indicate potential for exploiting this dependence to improve pharmaceutical particle design and performance.

Modified thermoresponsive Poloxamer 407 and chitosan sol-gels as potential sustained-release vaccine delivery systems.

Thermoresponsive, particle-loaded, Poloxamer 407 (P407)-Pluronic-R® (25R4) or chitosan-methyl cellulose (MC) formulations were developed as single-dose, sustained release vaccines. The sol-gels, loaded either with a particulate vaccine (cubosomes) or soluble antigen (ovalbumin) and adjuvants (Quil A and monophosphoryl lipid A), were free-flowing liquids at room temperature and formed stable gels at physiological temperatures. Rheological results showed that both systems meet the criteria of being thermoresponsive gels. The P407-25R4 sol-gels did not significantly sustain the release of antigen in vivo while the chitosan-MC sol-gels sustained the release of antigen up to at least 14 days after administration. The chitosan-MC sol-gels stimulated both cellular and humoral responses. The inclusion of cubosomes in the sol-gels did not provide a definitive beneficial effect. Further analysis of the formulations with small-angle X-ray scattering (SAXS) revealed that while cubosomes were stable in chitosan-MC gels they were not stable in P407-25R4 formulations. The reason for the mixed response to cubosome-loaded vehicles requires more investigation, however it appears that the cubosomes did not facilitate synchronous vaccine release and may in fact retard release, reducing efficacy in some cases. From these results, chitosan-MC sol-gels show potential as sustained release vaccine delivery systems, as compared to the P407-25R4 system that had a limited ability to sustain antigen release.

Design and processing of nanogels as delivery systems for peptides and proteins.

Nanogels, cross-linked networks of >1 µm in size, are attractive drug-delivery systems, as they not only possess the potential advantages of nanoscale formulations, but also the attractive abilities of a hydrogel; high hydrophilicity, high loading capacity and the potential for biocompatibility and controlled release. The focus of this review is to provide an overview of the recent developments within the nanogel field, and how the chemical design of the nanogel polymer has been found to influence the properties of the nanogel system. Novel nanogel systems are discussed with respect to their type of cross-linkage and their suitability as therapeutic delivery systems, as well as their ability to stabilize the protein/peptide drug.