Novel Guidewire Design and Coating for Continuous Delivery of Adenosine During Interventional Procedures.

Background The "no-reflow phenomenon" compromises percutaneous coronary intervention outcomes. There is an unmet need for a device that prevents no-reflow phenomenon. Our goal was to develop a guidewire platform comprising a nondisruptive hydrophilic coating that allows continuous delivery of adenosine throughout a percutaneous coronary intervention. Methods and Results We developed a guidewire with spaced coils to increase surface area for drug loading. Guidewires were plasma treated to attach hydroxyl groups to metal surfaces, and a methoxy-polyethylene glycol-silanol primer layer was covalently linked to hydroxyl groups. Using polyvinyl alcohol, polyvinyl pyrrolidone, and polyvinyl acetate, a drug layer containing jet-milled adenosine was hydrogen-bonded to the polyethylene glycol-silanol layer and coated with an outer diffusive barrier layer. Coatings were processed with a freeze/thaw curing method. In vitro release studies were conducted followed by in vivo evaluation in pigs. Coating quality, performance, and stability with sterilization were also evaluated. Antiplatelet properties of the guidewire were also determined. Elution studies with adenosine-containing guidewires showed curvilinear and complete release of adenosine over 60 minutes. Porcine studies demonstrated that upon insertion into a coronary artery, adenosine-releasing guidewires induced immediate and robust increases (2.6-fold) in coronary blood flow velocity, which were sustained for ≈30 minutes without systemic hemodynamic effects or arrhythmias. Adenosine-loaded wires prevented and reversed coronary vasoconstriction induced by acetylcholine. The wires significantly inhibited platelet aggregation by >80% in vitro. Guidewires passed bench testing for lubricity, adherence, integrity, and tracking. Conclusions Our novel drug-releasing guidewire platform represents a unique approach to prevent/treat no-reflow phenomenon during percutaneous coronary intervention.

Interfacial optimization of fiber-reinforced hydrogel composites for soft fibrous tissue applications.

Meniscal tears are the most common orthopedic injuries to the human body, yet the current treatment of choice is a partial meniscectomy, which is known to lead to joint degeneration and osteoarthritis. As a result, there is a significant clinical need to develop materials capable of restoring function to the meniscus following an injury. Fiber-reinforced hydrogel composites are particularly suited for replicating the mechanical function of native fibrous tissues due to their ability to mimic the native anisotropic property distribution present. A critical issue with these materials, however, is the potential for the fiber-matrix interfacial properties to severely limit composite performance. In this work, the interfacial properties of an ultra-high-molecular-weight polyethylene (UHMWPE) fiber-reinforced poly(vinyl alcohol) (PVA) hydrogel are studied. A novel chemical grafting technique, confirmed using X-ray photoelectron spectroscopy, is used to improve UHMWPE-PVA interfacial adhesion. Interfacial shear strength is quantified using fiber pull-out tests. Results indicate significantly improved fiber-hydrogel interfacial adhesion after chemical grafting, where chemically grafted samples have an interfacial shear strength of 256.4±64.3kPa compared to 11.5±2.9kPa for untreated samples. Additionally, scanning electron microscopy of fiber surfaces after fiber pull-out reveal cohesive failure within the hydrogel matrix for treated fiber samples, indicating that the UHMWPE-PVA interface has been successfully optimized. Lastly, inter-fiber spacing is observed to have a significant effect on interfacial adhesion. Fibers spaced further apart have significantly higher interfacial shear strengths, which is critical to consider when optimizing composite design. The results in this study are applicable in developing similar chemical grafting techniques and optimizing fiber-matrix interfacial properties for other hydrogel-based composite systems.

Assessing the transport of receptor-mediated drug-delivery devices across cellular monolayers.

Receptor-mediated endocytosis (RME) has been extensively studied as a method for augmenting the transport of therapeutic devices across monolayers. These devices range from simple ligand-therapeutic conjugates to complex ligand-nanocarrier systems. However, characterizing the uptake of these carriers typically relies on their comparisons to the native therapeutic, which provides no understanding of the ligand or cellular performance. To better understand the potential of the RME pathway, a model for monolayer transport was designed based on the endocytosis cycle of transferrin, a ligand often used in RME drug-delivery devices. This model established the correlation between apical receptor concentration and transport capability. Experimental studies confirmed this relationship, demonstrating an upper transport limit independent of the applied dose. This contrasts with the dose-proportional pathways that native therapeutics rely on for transport. Thus, the direct comparison of these two transport mechanisms can produce misleading results that change with arbitrarily chosen doses. Furthermore, transport potential was hindered by repeated use of the RME cycle. Future studies should base the success of this technology not on the performance of the therapeutic itself, but on the capabilities of the cell. Using receptor-binding studies, we were able to demonstrate how these capabilities can be predicted and potentially adopted for high-throughput screening methods.

Aging behavior of PVA hydrogels for soft tissue applications after in vitro swelling using osmotic pressure solutions.

The osmotic pressure of the medium used for in vitro swelling evaluation has been shown to have a significant effect on the swelling behavior of a material. In this study, the effect of osmotic pressure during swelling on poly(vinyl alcohol) hydrogel material properties was evaluated in vitro. Osmotic pressure solutions are necessary in order to mimic the swelling pressure observed in vivo for soft tissues present in load-bearing joints. Hydrogels were characterized after swelling by mechanical testing, X-ray diffraction and optical microscopy in the hydrated state. Results indicated that hydrogel mechanical properties remained tailorable with respect to initial processing parameters; however, significant aging occurred in osmotic solution. This was observed when evaluating the mechanical properties of the hydrogels, which, before swelling, ranged from 0.04 to 0.78 MPa but, after swelling in vitro using osmotic pressure solution, ranged from 0.32 to 0.93 MPa. Significant aging was also noted when evaluating crystallinity, with the relative crystallinity ranging between 0.4 and 5.0% before swelling and between 6.5 nd 8.0% after swelling. When compared to swelling in a non-osmotic pressure solution or in phosphate-buffered saline solution, the mechanical properties were more dependent upon the final swelling content. Furthermore, increases in crystallinity were not as significant after swelling. These results highlight the importance of choosing the appropriate swelling medium for in vitro characterization based on the desired application.

A novel method for the direct fabrication of growth factor-loaded microspheres within porous nondegradable hydrogels: controlled release for cartilage tissue engineering.

Because of similar mechanical properties to native cartilage, synthetic hydrogels based on poly(vinyl alcohol) (PVA) have been proposed for replacement of damaged articular cartilage, but they suffer from a complete lack of integration with surrounding tissue. In this study, insulin-like growth factor-1 (IGF-1), an important growth factor in cartilage regeneration, was encapsulated in degradable poly(lactic-co-glycolic acid) (PLGA) microparticles embedded in the PVA hydrogels in a single step based on a double emulsion. The release of IGF-1 from these hydrogels was sustained over 6 weeks in vitro. Poly(glycolic acid) (PGA) fiber scaffolds were wrapped around the hydrogels, seeded with chondrocytes, and implanted subcutaneously in athymic mice. The release of IGF-1 enhanced cartilage formation in the layers surrounding the hydrogels, in terms of the content of extracellular matrix components and mechanical properties, and increased integration between the cartilage layers and the hydrogels, according to gross observation of the cross-sections and histology. The compressive modulus of the cartilage-hydrogel constructs without IGF-1 was 0.07±0.02MPa, compared to 0.17-0.2MPa for hydrogels that contained IGF-1. The biochemical and mechanical markers of cartilage formation were not different between the low and high concentrations of IGF-1, despite an order of magnitude difference in concentration. This study shows that the sustained release of IGF-1 can enhance tissue formation and points to a possible strategy for effecting integration with surrounding tissue.

Design of semi-degradable hydrogels based on poly(vinyl alcohol) and poly(lactic-co-glycolic acid) for cartilage tissue engineering.

Articular cartilage damage is a persistent challenge in biomaterials and tissue engineering. Poly(vinyl alcohol) (PVA) hydrogels have shown promise as implants, but their lack of integration with surrounding cartilage prevents their utility. We sought to combine the advantages of PVA hydrogels with poly(lactic-co-glycolic acid) (PLGA) scaffolds, which have been successful in facilitating the integration of neocartilage with surrounding tissue. Through a novel double-emulsion technique, PLGA microparticles and a high level of porosity were simultaneously incorporated into PVA hydrogels. The porosity, average pore size and swelling properties of the hydrogels were controlled by varying initial processing parameters, such as the relative amounts of PLGA and solvent. Average pore sizes were in the ranged 50-100 µm. The PLGA microparticles degraded within the hydrogels over time in aqueous conditions, resulting in increases in porosity and pore size. After 4 weeks in cell culture, immature cartilage tissue filled many of the pores of the hydrogels that initially contained PLGA, and proteoglycan production was proportional to the amount of PLGA. In contrast, there was little cell attachment and no proteoglycan production in control hydrogels without PLGA. The compressive moduli of the hydrogels were similar to that of healthy cartilage and increased over time from 0.05-0.1 to 0.3-0.7 MPa. The generation of a hybrid cartilage-hydrogel construct using this technique may finally allow the integration of PVA hydrogels with surrounding cartilage.

Hydrogels for the repair of articular cartilage defects.

The repair of articular cartilage defects remains a significant challenge in orthopedic medicine. Hydrogels, three-dimensional polymer networks swollen in water, offer a unique opportunity to generate a functional cartilage substitute. Hydrogels can exhibit similar mechanical, swelling, and lubricating behavior to articular cartilage, and promote the chondrogenic phenotype by encapsulated cells. Hydrogels have been prepared from naturally derived and synthetic polymers, as cell-free implants and as tissue engineering scaffolds, and with controlled degradation profiles and release of stimulatory growth factors. Using hydrogels, cartilage tissue has been engineered in vitro that has similar mechanical properties to native cartilage. This review summarizes the advancements that have been made in determining the potential of hydrogels to replace damaged cartilage or support new tissue formation as a function of specific design parameters, such as the type of polymer, degradation profile, mechanical properties and loading regimen, source of cells, cell-seeding density, controlled release of growth factors, and strategies to cause integration with surrounding tissue. Some key challenges for clinical translation remain, including limited information on the mechanical properties of hydrogel implants or engineered tissue that are necessary to restore joint function, and the lack of emphasis on the ability of an implant to integrate in a stable way with the surrounding tissue. Future studies should address the factors that affect these issues, while using clinically relevant cell sources and rigorous models of repair.

Analysis of the in vitro swelling behavior of poly(vinyl alcohol) hydrogels in osmotic pressure solution for soft tissue replacement.

An osmotic solution was used to evaluate poly(vinyl alcohol) (PVA) hydrogels as potential non-degradable soft tissue replacements in vitro. Osmotic solutions are necessary in order to mimic the swelling pressure observed in vivo for soft tissues present in load-bearing joints. In vitro studies indicated that PVA hydrogels experience minimal changes in swelling with a polymer concentration of 20 wt.% PVA in phosphate-buffered saline solution (0 atm) and between 30 and 35 wt.% PVA in osmotic solution with a pressure of 0.95 atm. Swelling in osmotic pressure solutions caused decreases in the equilibrium hydrogel hydration. An investigation of hydrogel compressive modulus indicated that PVA hydrogels are within the range of articular cartilage, meniscal tissue, and the temporomandibular joint disk. Furthermore, it is possible to tailor PVA hydrogels through careful modification of the polymer concentration and freeze-thaw cycles during hydrogel preparation to match both a desired swelling ratio and a desired compressive modulus or porosity. The microstructure of the PVA hydrogels was also evaluated as a function of freeze-thaw cycles and polymer concentration to give an insight into the processes occurring during synthesis and swelling in osmotic solutions.

Mechanical evaluation of poly(vinyl alcohol)-based fibrous composites as biomaterials for meniscal tissue replacement.

In this study, poly(vinyl alcohol) (PVA) hydrogels were reinforced with ultrahigh molecular weight polyethylene (UHMWPE) and PP fibers and evaluated as potential nondegradable meniscal replacements. An investigation of hydrogel and composite mechanical properties indicates that fiber-reinforced PVA hydrogels could replicate the unique anisotropic modulus distribution present in the native meniscus; the most commonly damaged orthopedic tissue. More specifically, fibrous reinforcement successfully increased the tensile modulus of the biomaterial from 0.23±0.02MPa without any reinforcement to 258.1±40.1MPa at 29vol.% UHMWPE. Additionally, the molecular weight between cross-links, bound water and the microstructure of the PVA hydrogels were evaluated as a function of freeze-thaw cycles and polymer concentration to lend insight into the processes occurring during synthesis. These results suggest the presence of multiple mechanisms as causes for increasing hydrogel modulus with freeze-thaw cycling, including hydrogen bonding between amorphous and/or crystalline regions, and the formation of highly concentrated regions of mostly amorphous PVA chains. It is possible that the formation of regions with highly concentrated amounts of PVA increases the load-bearing ability of the hydrogels.

Synthesis and recovery characteristics of branched and grafted PNIPAAm-PEG hydrogels for the development of an injectable load-bearing nucleus pulposus replacement.

A family of injectable poly(N-isopropyl acrylamide) (PNIPAAm) copolymer hydrogels has been fabricated in order to tune mechanical properties to support load-bearing function and dimensional recovery for possible use as load-bearing medical devices, such as a nucleus pulposus replacement for the intervertebral disc. PNIPAAm-polyethylene glycol (PEG) copolymers were synthesized with varying hydrophilic PEG concentrations as grafted or branched structures to enhance dimensional recovery of the materials. Polymerizations were confirmed with attenuated total reflectance-Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy studies. Incorporation of PEG was effective in raising water content of pure PNIPAAm hydrogels (29.3% water for pure PNIPAAm vs. 47.7% for PEG branches and 39.5% for PEG grafts). PNIPAAm with 7% grafted as well as 7% branched PEG had significantly reduced compressive modulus compared to that of pure PNIPAAm. Initially recovered compressive strain was significantly increased for 7% PEG branches after pre-testing immersion in PBS for up to 33 days, while 7% PEG grafts decreased this value. Sample height recovery for pure PNIPAAm was limited to 31.6%, while PNIPAAm with 7% branches was increased to 71.3%. When mechanically tested samples were allowed to recover without load over 30 min, each composition was able to significantly recover height, indicating that the time to recovery is slower than the unloading rates typically used in testing. While the incorporation of hydrophilic PEG was expected to alter the mechanical behavior of the hydrogels, only the branched form was able to significantly enhance dimensional recovery.

Characterization of the behavior of porous hydrogels in model osmotically-conditioned articular cartilage systems.

The evaluation of hydrogel swelling behavior is a vital step in development of new materials for biomedical applications. Phosphate-buffered saline (PBS) is the most commonly chosen swelling medium to model hydrogel behavior in articular cartilage (AC). However, the use of PBS does not fully elucidate the osmotic pressure hydrogels will face in many tissues in vivo. Thus, there is a critical need to assess the performance of hydrogels in a model system that can better reflect the native tissues for a specified application. The aim of this study was to evaluate the mechanical properties, porosity, and swelling behavior of poly(vinyl alcohol) hydrogels with a degradable poly(lactic-co-glycolic acid) (PLGA) phase in synthetic models and in ex vivo AC model systems. The controlled degradation of the PLGA phase reflected the dynamic nature of native tissues and allowed for the assessment of hydrogel swelling characteristics under fluctuating osmotic pressures. When hydrogels were implanted ex vivo into bovine AC, their swelling ratios and water contents significantly decreased. This response was matched by hydrogels immersed in a solution of PEG having an osmotic pressure matching AC. The hydrogels were further characterized over 6 weeks in PEG and in PBS, with each system having unique affects on the hydrogel swelling behavior and material properties. The results show that a PEG solution conditioned to an osmotic pressure of AC is a strong model for the effects of the osmotic environment on hydrogels and that PBS is an ineffective predictor of swelling changes in vivo.

Synthesis, characterization and in vivo efficacy of PEGylated insulin for oral delivery with complexation hydrogels.

PURPOSE: This work evaluated the feasibility of combining insulin PEGylation with pH responsive hydrogels for oral insulin delivery. METHODS: A mono-substituted PEG-insulin conjugate was synthesized and purified. The site of conjugation was determined by MALDI-TOF MS. Uptake and release of PEGylated insulin was performed in complexation hydrogels to simulate oral dosing. The bioactivity of the conjugate and PK/PD profile was measured in vivo in rats. RESULTS: PEGylation was confirmed to be specifically located at the amino terminus of the B-chain of insulin. Higher loading efficiency was achieved with PEGylated insulin than regular human insulin in pH responsive hydrogels. The release of PEGylated insulin was lower than that of human insulin at all pH levels considered. Full retention of bioactivity of the PEG-insulin conjugate was confirmed by intravenous dosing while subcutaneous dosing exhibited a relative hypoglycemic effect 127.8% that of human insulin. CONCLUSIONS: Polyethylene glycol conjugated specifically to the amino terminus of the B-chain of insulin maintained the bioactivity of the protein and significantly extended the duration of the hypoglycemic effect. Used in combination with pH responsive hydrogels, PEGylated insulin has significant potential for oral delivery.

Key functions in polymer carriers for intestinal absorption of insulin.

This work aimed to clarify the relationship between polymer function and insulin absorption, and to evaluate the optimized preparative formulation predicted from this relationship. Insulin-loaded polymer (ILP) carrier systems were prepared following a two-factor composite second-order spherical experimental design. To investigate the polymer function, we evaluated its insulin release, bioadhesiveness, and protective effect. Each ILP was administered intestinally, and glucose reduction was monitored as the pharmacological effect. Based on these data, an optimized formulation was predicted and how the polymer function affects insulin absorption was clarified by multivariate spline (MVS) interpolation. A greater pharmacological effect was apparent in ILPs with a smaller particle size and loaded with more insulin. The pharmacological effect predicted by MVS after the administration of ILP made under optimized preparative conditions was almost identical to the observed effect. Moreover, MVS clarified the relationship between the polymer function and the pharmacological effect. These results supported that MVS can be an effective tool with which to approximate the relationship between the function of a dosage form and its absorption, and to explore the optimized preparative conditions.

Superporous hydrogels for cartilage repair: Evaluation of the morphological and mechanical properties.

Despite extensive research in the design of biomaterials for articular cartilage repair, there remains a need for the development of materials with the mechanical compliance to function synergistically with healthy cartilage, but porous enough to allow for tissue integration. In this study, superporous hydrogels of poly(vinyl alcohol) and poly(vinyl pyrrolidone) were prepared using a novel technique consisting of a double emulsion process. The hydrogel emulsions were physically cross-linked by freeze-thaw cycling. The hydrogels had a high degree of porosity, determined using environmental scanning electron microscopy, a technique superior to any method that involves dehydrating the samples. Increasing the volume of organic solvent increased porosity, due to cross-linking of the hydrogel solution around the droplets in the emulsion, leaving pores where the organic solvent was present. Poly(lactic-co-glyclic acid) microparticles formed and were embedded in the matrix. The mechanical properties, measured in confined creep and in unconfined, uniaxial compression, were similar to native articular cartilage. The permeability of the samples was unaffected by changing solvent content, despite changes in porosity. These materials are good candidates for tissue engineering of cartilage because they can mimic mature cartilage mechanically while providing a porous matrix through which cells can migrate and proliferate.

Evaluation of in vitro release and in vivo efficacy of mPEG-PLA-haloperidol conjugate micelle-like structures.

Polymeric prodrugs of mPEG-PLA-haloperidol (methoxy poly(ethylene glycol)-b-poly (lactic acid)), self-assemble into nanoscale micelle-like structures in aqueous solutions. The micelles range in size from 28 to 52 nm in diameter and have been shown to be spherical in shape using cryogenic transmission electron microscopy. In this current work there is evidence shown that suggests these micelle-like structures do not dissociate below their critical micelle concentration (CMC) when the PEG weight percent is at least 68, releasing physically entrapped drug from intact micelles over a 3-day period. However, 55 wt % PEG micelles dissociate below their CMC, and release their physically entrapped drug within 8 h. Conjugate polymer micelles most closely approach a linear release profile over a 5-day period. Conjugate micelles with free drug incorporated, known as combination micelle-like structures, release drug over 4 days. However, these combination micelles have the fastest burst release indicating that free drug was potentially dominating the first 8 h of release, after which hydrolysis of covalently linked drug took over. In vivo behavioral studies can assess haloperidol bioactivity from drug loaded micelle-like structures on ketamine induced hyperlocomotion. Results are consistent with in vitro release data, showing that conjugate and combination micelles continue to release haloperidol 4 days post injection, attenuating the effects of the ketamine induced hyperlocomotion. Furthermore, results indicate that the sedative side effects of haloperidol were reduced with the micelle delivery systems as compared to the acute haloperidol injection.

Pharmacokinetic and behavioral characterization of a long-term antipsychotic delivery system in rodents and rabbits.

RATIONALE: Non-adherence with medication remains the major correctable cause of poor outcome in schizophrenia. However, few treatments have addressed this major determinant of outcome with novel long-term delivery systems. OBJECTIVES: The aim of this study was to provide biological proof of concept for a long-term implantable antipsychotic delivery system in rodents and rabbits. MATERIALS AND METHODS: Implantable formulations of haloperidol were created using biodegradable polymers. Implants were characterized for in vitro release and in vivo behavior using prepulse inhibition of startle in rats and mice, as well as pharmacokinetics in rabbits. RESULTS: Behavioral measures demonstrate the effectiveness of haloperidol implants delivering 1 mg/kg in mice and 0.6 mg/kg in rats to block amphetamine (10 mg/kg) in mice or apomorphine (0.5 mg/kg) in rats. Additionally, we demonstrate the pattern of release from single polymer implants for 1 year in rabbits. CONCLUSIONS: The current study suggests that implantable formulations are a viable approach to providing long-term delivery of antipsychotic medications in vivo using animal models of behavior and pharmacokinetics. In contrast to depot formulations, implantable formulations could last 6 months or longer. Additionally, implants can be removed throughout the delivery interval, offering a degree of reversibility not available with depot formulations.

Quantitation of humalog insulin by reversed-phase high-performance liquid chromatography.

INTRODUCTION: The methodology for in vitro testing of insulin delivery systems for long-term infusion of lispro insulin requires insulin flow studies over time, with the measurement of lispro concentrations in wells or other laboratory fluid collection systems. We postulated that the efficiency of the insulin assay could be improved if the insulin collected in the wells could be measured without having to perform dilutions of insulin samples. The manufacturer's method for the identification of Humalog(R) insulin by high-performance liquid chromatography (HPLC) does not provide a detailed method for the quantitation of the clinical formulation. No reports could be found in the literature describing a method to quantitate lispro insulin's entire concentration range, nor could we find detailed information on pH effects. The purpose of this study was to investigate the use of a reversed-phase HPLC method to quantitate Humalog insulin at three levels of pH. METHODS: Serial dilutions of Humalog insulin stock solution were prepared at pH levels of 2.6 and 7.4 (concentrations 0.20-100 IU/ml) to construct calibration curves. Samples were also prepared at lower concentrations (0.23-15.0 IU/ml) at pH levels of 4.0 and 7.4. Areas under curve data were plotted against known concentrations, and the limit of quantitation and precision of the assay were determined. RESULTS: Calibration curves for the 0.20-100 IU/ml concentration (pH 7.4 and 2.6) revealed no significant differences (p < 0.01) between those curves. pH and concentration did not have an effect on the overall precision of the method. Linearity was not conserved past the 15-IU/ml concentration. Coefficient of variation (CV) values were generally <15% except at the lower concentrations where the largest CVs were observed. Mean known concentrations plotted on a logarithmic scale demonstrated linearity from 12.5 to 100 IU/ml. CONCLUSIONS: Humalog insulin clinical formulation can be quantitated over the entire concentration range by a reversed-phase HPLC method using nonlinear regression analysis. The method is reproducible at lower (<15 IU/ml) and higher insulin concentrations. Linear regression analysis may be used when the concentrations of interest are in the 0- to 15-IU range. Preparation of insulin solutions at pH 2.6, 4.0, and 7.4 did not significantly affect the reproducibility of the assay.

Novel oral insulin delivery systems based on complexation polymer hydrogels: single and multiple administration studies in type 1 and 2 diabetic rats.

Insulin-loaded polymer microparticles (ILP) composed of crosslinked poly(methacrylic acid) and poly(ethylene glycol) are multi-functional carriers showing high insulin incorporation efficiency, a rapid insulin release in the intestine based on their pH-dependent complexation properties, enzyme-inhibiting effects and mucoadhesive characteristics. Thus, they are potential carriers for insulin delivery via an oral route. Recent studies suggest that the polymer composition and particle size of ILP strongly influenced insulin bioavailability. Therefore, the present study aimed at finding an optimal formulation and designing carriers for oral insulin delivery using in vivo experiments. Various types of ILPs were prepared and administered orally to healthy and type 1 and 2 diabetic rats. The most promising formulation was subsequently used for in vivo multiple oral administration studies using diabetic rats. The microparticles of diameters of <53 microm (SS-ILP) composed of a 1:1 molar ratio of methacrylic acid/ethylene glycol units showed the most pronounced hypoglycaemic effects following oral administration to healthy rats, achieving a 9.5% pharmacological availability compared to subcutaneous insulin injection. Their usefulness was also confirmed with both type 1 and 2 diabetic rat groups. In a multiple administration study, SS-ILP significantly suppressed the postprandial rise in blood glucose and showed continuous hypoglycaemic effects following 3 times/day oral administration to both diabetic rat groups in the presence of foods. These results indicate that the blood glucose levels of diabetic rats can be effectively controlled by oral SS-ILP administration, and thus SS-ILP would be a promising delivery carrier of insulin via the oral route.

Mucosal insulin delivery systems based on complexation polymer hydrogels: effect of particle size on insulin enteral absorption.

Insulin-loaded polymer (ILP) microparticles composed of poly(methacrylic acid) and poly(ethylene glycol), which have pH-dependent complexation and mucoadhesive properties have been thought to be potential carriers for insulin via an oral route. Nevertheless, further optimization of the polymer delivery system is required to improve clinical application. Therefore, the effect of particle size of the ILP (L-ILP: 180-230 microm, S-ILP: 43-89 microm, SS-ILP: <43 microm) on insulin absorption was studied in the in situ loop system, hypothesizing smaller particle sizes of ILP could induce bigger hypoglycemic effects due to increase mucoadhesive capacity. To verify the hypothesis, the adhesive capacities of differently sized ILPs to the mucosal tissues were evaluated. Additionally, the intestinal site-specificity of ILP for insulin absorption was investigated. Intra- and inter-cellular integrity and/or damage were also examined by lactate dehydrogenase leakage and membrane electrical resistance change to ensure the safety of ILP as a carrier for oral route. As hypothesized, the smaller sized microparticles (SS-ILP) showed a rapid burst-type insulin release and higher insulin absorption compared with the microparticles having larger sizes, resulting in greater hypoglycemic effects without detectable mucosal damage. In fact, SS-ILP demonstrated higher mucoadhesive capacity to the jejunum and the ileum than those of L-ILP. Moreover, SS-ILP's enhancement effect of insulin mucosal absorption showed a site-specificity, demonstrating maximum effect at the ileal segment. These results imply that the particle size and delivery site are very important factors for ILP with respect to increasing the bioavailability of insulin following oral administration.

Oral insulin delivery using P(MAA-g-EG) hydrogels: effects of network morphology on insulin delivery characteristics.

Hydrogels of poly(methacrylic acid-g-ethylene glycol) were prepared using different reaction water contents in order to vary the network mesh size, swelling behavior and insulin loading/release kinetics. Gels prepared with greater reaction solvent contents swelled to a greater degree and had a larger network mesh size. All of the hydrogels were able to incorporate insulin and protected it from release in acidic media. At higher pH (7.4), the release rates increased with reaction solvent content. Using a closed loop animal model, all of the insulin loaded formulations produced significant insulin absorption in the upper small intestine combined with hypoglycemic effects. In these studies, bioavailabilities ranged from 4.6% to 7.2% and were dependent on reaction solvent content.