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.

Complexation Hydrogels as Oral Delivery Vehicles of Therapeutic Antibodies: An in Vitro and ex Vivo Evaluation of Antibody Stability and Bioactivity.

Oral administration of monoclonal antibodies (mAbs) may enable the localized treatment of infections or other conditions in the gastrointestinal tract (GI) as well as systemic diseases. As with the development of oral protein biotherapeutics, one of the most challenging tasks in antibody therapies is the loss of biological activity due to physical and chemical instabilities. New families of complexation hydrogels with pH-responsive properties have demonstrated to be excellent transmucosal delivery vehicles. This contribution focuses on the design and evaluation of hydrogel carriers that will minimize the degradation and maximize the in vivo activity of anti-TNF-α, a mAb used for the treatment of inflammatory bowel disease (IBD) in the GI tract and systemically for the treatment of rheumatoid arthritis. P(MAA-g-EG) and P(MAA-co-NVP) hydrogels systems were optimized to achieve adequate swelling behavior, which translated into improved protein loading and release at neutral pH simulating the small intestine conditions. Additionally, these hydrogel systems preserve antibody bioactivity upon release resulting in the systemic circulation of an antibody capable of effectively performing its biological function. The compatibility if these hydrogels for mAb bioactivity preservation and release makes them candidates for use as oral delivery systems for therapeutic antibodies.

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.

Implications of poly(N-isopropylacrylamide)-g-poly(ethylene glycol) with codissolved brain-derived neurotrophic factor injectable scaffold on motor function recovery rate following cervical dorsolateral funiculotomy in the rat.

OBJECT: In a follow-up study to their prior work, the authors evaluated a novel delivery system for a previously established treatment for spinal cord injury (SCI), based on a poly(N-isopropylacrylamide) (PNIPAAm), lightly cross-linked with a polyethylene glycol (PEG) injectable scaffold. The primary aim of this work was to assess the recovery of both spontaneous and skilled forelimb function following a cervical dorsolateral funiculotomy in the rat. This injury ablates the rubrospinal tract (RST) but spares the dorsal and ventral corticospinal tract and can severely impair reaching and grasping abilities. METHODS: Animals received an implant of either PNIPAAm-g-PEG or PNIPAAm-g-PEG + brain-derived neurotrophic factor (BDNF). The single-pellet reach-to-grasp task and the staircase-reaching task were used to assess skilled motor function associated with reaching and grasping abilities, and the cylinder task was used to assess spontaneous motor function, both before and after injury. RESULTS: Because BDNF can stimulate regenerating RST axons, the authors showed that animals receiving an implant of PNIPAAm-g-PEG with codissolved BDNF had an increased recovery rate of fine motor function when compared with a control group (PNIPAAm-g-PEG only) on both a staircase-reaching task at 4 and 8 weeks post-SCI and on a single-pellet reach-to-grasp task at 5 weeks post-SCI. In addition, spontaneous motor function, as measured in the cylinder test, recovered to preinjury values in animals receiving PNIPAAm-g-PEG + BDNF. Fluorescence immunochemistry indicated the presence of both regenerating axons and BDA-labeled fibers growing up to or within the host-graft interface in animals receiving PNIPAAm-g-PEG + BDNF. CONCLUSIONS: Based on their results, the authors suggest that BDNF delivered by the scaffold promoted the growth of RST axons into the lesion, which may have contributed in part to the increased recovery rate.

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.

Biodegradable nanoparticles for protein delivery: analysis of preparation conditions on particle morphology and protein loading, activity and sustained release properties.

PLGA particles have been extensively used as a sustained drug-delivery system, but there are multiple drawbacks when delivering proteins. The focus of this work is to address the most significant disadvantages to the W/O/W double emulsion procedure and demonstrate that simple changes to this procedure can have significant changes to particle size and dispersity and considerable improvements to protein loading, activity and sustained active protein release. A systematic approach was taken to analyze the effects of the following variables: solvent miscibility (dichloromethane (DCM), ethyl acetate, acetone), homogenization speed (10 000-25 000 rpm), PLGA concentration (10-30 mg/ml) and additives in both the organic (sucrose acetate isobutyrate (SAIB)) and aqueous (bovine serum albumin (BSA)) phases. Increasing solvent miscibility decreased particle size, dispersity and protein denaturation, while maintaining adequate protein loading. Increasing solvent miscibility also lowered the impact of homogenization on particle size and dispersity and protein activity. Changes to PLGA concentration demonstrated a minimum impact on particle size and dispersity, but showed an inverse relationship between protein encapsulation efficiency and particle protein weight percent. Most particles tested provided sustained release of active protein over 60 days. Increasing solvent miscibility resulted in increases in the percent of active protein released. When subjected to synthesis conditions with DCM as the solvent, BSA as a stabilizer resulted in the maximum stabilization of protein at a concentration of 100 mg/ml. At this concentration, BSA allowed for increases in the total amount of active protein delivered for all three solvents. The benefit of SAIB was primarily increased protein loading.

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.

A pilot study of poly(N-isopropylacrylamide)-g-polyethylene glycol and poly(N-isopropylacrylamide)-g-methylcellulose branched copolymers as injectable scaffolds for local delivery of neurotrophins and cellular transplants into the injured spinal cord.

OBJECT: The authors investigated the feasibility of using injectable hydrogels, based on poly(N-isopropylacrylamide) (PNIPAAm), lightly cross-linked with polyethylene glycol (PEG) or methylcellulose (MC), to serve as injectable scaffolds for local delivery of neurotrophins and cellular transplants into the injured spinal cord. The primary aims of this work were to assess the biocompatibility of the scaffolds by evaluating graft cell survival and the host tissue immune response. The scaffolds were also evaluated for their ability to promote axonal growth through the action of released brain-derived neurotrophic factor (BDNF). METHODS: The in vivo performance of PNIPAAm-g-PEG and PNIPAAm-g-MC was evaluated using a rodent model of spinal cord injury (SCI). The hydrogels were injected as viscous liquids into the injury site and formed space-filling hydrogels. The host immune response and biocompatibility of the scaffolds were evaluated at 2 weeks by histological and fluorescent immunohistochemical analysis. Commercially available matrices were used as a control and examined for comparison. RESULTS: Experiments showed that the scaffolds did not contribute to an injury-related inflammatory response. PNIPAAm-g-PEG was also shown to be an effective vehicle for delivery of cellular transplants and supported graft survival. Additionally, PNIPAAm-g-PEG and PNIPAAm-g-MC are permissive to axonal growth and can serve as injectable scaffolds for local delivery of BDNF. CONCLUSIONS: Based on the results, the authors suggest that these copolymers are feasible injectable scaffolds for cell grafting into the injured spinal cord and for delivery of therapeutic factors.

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.

Enhanced mucoadhesive capacity of novel co-polymers for oral protein delivery.

Graft co-polymer networks have shown promise as devices for oral delivery of proteins. By increasing adhesion of these networks at the delivery site of the upper small intestine by utilizing small covalent chemical linkages caused by the addition of an aldehyde functional group we can make them more viable. These aldehydes bind covalently by way of a condensation reaction with the amines of the amino acids found in the glycoprotein network of the mucus layer of the small intestine to form imines. To investigate the effectiveness of this linkage the co-polymers are prepared in three different percentages of poly(ethylene glycol) (PEG) and aldehyde-modified PEG, and characterized through swelling, release and adhesion testing. The percentages of aldehyde-modified PEG used are 0.06, 0.6 and 3.3%. The swelling results indicate that the formulations with the aldehyde-modified PEG maintained the same pH sensitivity and transition around a pH of 5.8 as those formulations without the aldehyde moiety. Release results indicate that the release of insulin of the most promising 3.3% aldehyde formulation was successful with a release of about 80% after 3 h, which compares favorably with the similar release of the controls done in previous work. Adhesion testing was carried out through the use of a mechanical testing apparatus. Data have been gathered and plotted to give a detachment force (N) versus displacement (m) curve, of which the work of adhesion (µJ) was found by taking the area underneath the curve. Adhesion results indicate an increase to the already present adhesion of the co-polymers due to increased percentages of the aldehyde-modified PEG tethers where the 3.3% formulation showed an increase of 10-30 µJ over both control formulations.

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.

In vitro analysis of PNIPAAm-PEG, a novel, injectable scaffold for spinal cord repair.

Nervous tissue engineering in combination with other therapeutic strategies is an emerging trend for the treatment of different CNS disorders and injuries. We propose to use poly(N-isopropylacrylamide)-co-poly(ethylene glycol) (PNIPAAm-PEG) as a minimally invasive, injectable scaffold platform for the repair of spinal cord injury (SCI). The scaffold allows cell attachment, and provides mechanical support and a sustained release of neurotrophins. In order to use PNIPAAm-PEG as an injectable scaffold for treatment of SCI, it must maintain its mass and volume over time in physiological conditions. To provide mechanical support at the injury site, it is also critical that the engineered scaffold matches the compressive modulus of the native neuronal tissue. This study focused on studying the ability of the scaffold to release bioactive neurotrophins and matching the material properties to those of the native neuronal tissue. We found that the release of both BDNF and NT-3 was sustained for up to 4 weeks, with a minimal burst exhibited for both neurotrophins. The bioactivity of the released NT-3 and BDNF was confirmed after 4 weeks. In addition, our results show that the PNIPAAm-PEG scaffold can be designed to match the desired mechanical properties of the native neuronal tissue, with a compressive modulus in the 3-5 kPa range. The scaffold was also compatible with bone marrow stromal cells, allowing their survival and attachment for up to 31 days. These results indicate that PNIPAAm-PEG is a promising multifunctional scaffold for the treatment of SCI.

Semi-degradable scaffold for articular cartilage replacement.

Existing technologies have not met the challenge of designing a construct for the repair of focal cartilage defects such that it mimics the mechanical properties of and can integrate with native cartilage. Herein we describe a novel construct consisting of a non-degradable poly-vinyl alcohol (PVA) scaffold to provide long-term mechanical stability, interconnected pores to allow for the infiltration of chondrocytes, and poly-lactic glycolic acid (PLGA) microspheres for the incorporation of growth factors to enhance cellular migration. The objective of this study was to characterize the morphological features and mechanical properties of our porous PVA-PLGA construct as a function of PLGA content. Varying the PLGA content was found to have a significant effect on the morphological features of the construct. As PLGA content increased from 10% to 75%, samples exhibited a 6-fold increase in average percentage porosity, an increase in average microsphere diameter from 8 to 34 microm and an increase in average pore diameter from 29 to 111 microm. The effect of PLGA content on aggregate modulus and permeability was less profound. Our findings suggest that that morphology of the construct can be tailored to optimize cellular infiltration and the dynamic mechanical response. The experiments herein presented were conducted at the Hospital for Special Surgery.

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.