Shear-thinning Gel Research Articles

Development of hydrogels from cell wall of Aspergillus oryzae containing chitin-glucan and wet spinning to monofilaments

Fungal mycelium is emerging as a source for sustainable bio-based materials. Fungal biomass of Aspergillus oryzae was prepared by cultivation on bread waste hydrolysate to valorize this abundant food waste. Chitin-glucan-rich alkali-insoluble material (AIM) was isolated from fungal biomass, formed into hydrogels, and wet spun into monofilaments. AIM in the form of fungal microfibers containing 0.09 g polymer of glucosamine (GlcN)/g AIM was subjected to freeze–thaw and deacetylation treatments to increase the amount of GlcN. The GlcN fraction was 0.19 and 0.34 g polymer of GlcN/g AIM, for AIM subjected to deacetylation (AIM-DAC) and freeze–thaw cycles and deacetylation (AIM-FRTH-DAC), respectively. The increased GlcN fraction enabled the formation of hydrogels via the protonation of amino groups after the addition of lactic acid. Morphological differences in the hydrogels included aggregation of the fungal microfibers in the AIM-DAC hydrogel, whereas the microfibers in the AIM-FRTH-DAC hydrogel had a porous and interconnected network. Rheological assessment revealed shear thinning behavior and gel properties of the produced hydrogels. Wet spinning of the hydrogels resulted in monofilaments with tensile strengths of up to 70 MPa and 12 % elongation at break. This demonstrates promising avenues for biomaterial development from fungal cell walls containing chitin-glucan via food waste valorization.

Chitosan-nanoclay embolic material for catheter-directed arterial embolization.

Minimally invasive transcatheter embolization is a common nonsurgical procedure in interventional radiology. It is used for the deliberate occlusion of blood vessels for the treatment of disease or injured vasculature, including vascular malformation and malignant/benign tumors. Here, we introduce a gel embolic agent comprising chitosan nanofibers and nanoclay with excellent catheter injectability and tunable mechanical properties for embolization. The properties of the gel were optimized by varying the ratio between each individual component and also adjusting the total solid content. The rheological studies confirm the shear thinning property and gel nature of the developed gel as well as their recoverability. Injection force was measured to record the force required to pass the embolic gel through a clinically relevant catheter, evaluating for practicality of hand-injection. Theoretical predicted injection force was calculated to reduce the development time and to enhance the physician's experience. The stability of occlusion was also tested in vitro by monitoring the pressure required to displace the gel. The engineered gels exhibited sterility, hemocompatibility and cell biocompatibility, highlighting their potential for transcatheter embolization.

Abstract 11376: Catheter-Injectable Hydrogel for the Delivery of a Minicircle Encoding SDF-la as Therapy for Myocardial Infarction

Myocardial infarction ( MI ) is a leading cause of cardiovascular disease in the U.S. and abroad. Transient delivery of stromal cell-derived factor 1 ( SDF-1 α ) either through the delivery of protein-encoding genes or the protein itself has demonstrated improved cardiac function in preclinical models. However, the delivery of the therapy suffers from two limitations: (1) poor retention when injected into the contracting myocardium, and (2) rapid degradation of the protein, which requires prolonged activity to be therapeutically effective. To mitigate these limitations, we developed a catheter-injectable gel to deliver SDF-1 α encoding minicircles ( MC ). Design of gels for injection into the myocardium is historically challenging since traditional chemical strategies result in gels that are either too stiff and not catheter injectable or too weak and quickly ejected out of the contracting heart muscle. To address this challenge, our approach is to use dynamic covalent chemical (DCC) bonds, which are mechanically strong yet reversible, resulting in a shear-thinning gel (hence catheter injectable) and self-healing (hence retained in the contracting heart muscle). This biocompatible gel is chemically defined for future FDA approval and is synthesized from completely biodegradable polymers: recombinant elastin-like protein and hyaluronic acid. Rheological characterization identified several gel formulations that were easily extruded through a catheter (2 m long and .25 mm internal diameter) and rapidly reformed into a gel within 5 seconds after extrusion. To demonstrate the potential for clinical translatability, we evaluated the injectability and retention of the gel within the contracting rat myocardium. Our gel significantly improved the retention of a microparticle cargo by 200% compared to delivery in Matrigel. Current work is focused on evaluating the therapeutic efficacy of the gel in a rat myocardial infarct model when delivering a therapeutic cargo of SDF-1a-encoding MC. This biocompatible, catheter-injectable gel has great potential to significantly improve the delivery and retention of therapeutic cargo within mechanically active tissues, significantly improving the prolonged efficacy of MI therapies.

Fucose-containing Abroma augusta mucilage hydrogel as a potential probiotic carrier with prebiotic function

The mucilaginous polysaccharide from Abroma augusta stem was examined for its physicochemical, thermal, and functional behavior and explored as a carrier for probiotic bacteria. Composed of glucose, galactose, rhamnose, galactouronic acid and fucose, Abroma augusta mucilage (AAM) exhibited shear thinning behavior (following power law equation) and gel like characteristic (showing higher G′ value than G″ value). AAM promoted the growth of probiotic strains with positive prebiotic scores of 0.5 ± 0.06 and 0.51 ± 0.05 for Lactobacillus acidophilus and Lactobacillus casei, respectively. Further, probiotic strains were embedded in the AAM matrix followed by freeze-drying with embedding efficiency of >95%. Viscoelastic properties were retained substantially in the rehydrated probiotic-embedded matrix. AAM could protect probiotic bacteria in simulated gastrointestinal conditions, at elevated (80 °C, 20 min) and at low (4 °C, 4 months) temperatures ensuring higher viabilities of embedded probiotic cells. Our findings established potential carrier capabilities of AAM polysaccharides for probiotic bacteria with thickening and prebiotic activity.

Versatile carbon-loaded shellac ink for disposable printed electronics

Emerging technologies such as smart packaging are shifting the requirements on electronic components, notably regarding service life, which counts in days instead of years. As a result, standard materials are often not adapted due to economic, environmental or manufacturing considerations. For instance, the use of metal conductive tracks in disposable electronics is a waste of valuable resources and their accumulation in landfills is an environmental concern. In this work, we report a conductive ink made of carbon particles dispersed in a solution of shellac. This natural and water-insoluble resin works as a binder, favourably replacing petroleum-derived polymers. The carbon particles provide electrical conductivity and act as a rheology modifier, creating a printable shear-thinning gel. The ink’s conductivity and sheet resistance are 1000 S m−1 and 15 Ω sq−1, respectively, and remain stable towards moisture. We show that the ink is compatible with several industry-relevant patterning methods such as screen-printing and robocasting, and demonstrate a minimum feature size of 200 μm. As a proof-of-concept, a resistor and a capacitor are printed and used as deformation and proximity sensors, respectively.

P.122: Development of an Oxygen Durability Model to Overcome Hypoxia in Encapsulated Islets Within a Functionalized Oxygenated Biomaterial

Introduction: Post-transplantation islet survival is inherently limited by the lack of suitable support matrix and insufficient oxygen supply (hypoxia), which is aggravated in macroencapsulation devices.Graft failure can be overcome by cell encapsulation in highly oxygenated functionalized biomaterials able to provide oxygen and extracellular matrix (ECM) support. An estimation of the oxygen durability in these encapsulation matrices is critical to define the cell density and implant size for optimal graft survival, especially until the macroencapsulation device is sufficiently re-vascularized. The aim of this study was to develop a predictive mathematical model that could estimate the oxygen lifetime of an oxygenated biomaterial (Oxygel) encapsulating different diabetes-relevant cell lines. Methods: Oxygel was formulated by the shear mixing of a physically crosslinked native Hyaluronic acid hydrogel and a Perfluocarbon/lipoid nanoemulsion. Oxygel was oxygenated by flushing oxygen using a customized static Y-mixer while the gel was infused with a syringe pump or using a designed scaled-up oxygenator. Post-oxygenation O2 levels of Oxygel and controls were monitored by microinvasive fibre optic needle-type oxygen microsensors (n=3). Oxygen diffusion coefficient (Dv) was estimated by the experimental fitting of the oxygen release profiles to a diffusion model governed by Fick’s second law. Oxygen durability predictions were performed using a non-diffusion-controlled model considering: (i) recorded initial oxygen tension, (ii) gel concentration and Ostwald oxygen solubility constants of different gel components, (iii) cell density and (iv) oxygen consumption rate (OCR) of the studied cell line. Different diabetes-relevant cell lines (INS-1E, iPS derived B-cells, rat islets, human islets) were modelled using experimental (Agilent Seahorse analyzer) and/or bibliographic OCR values. Summary of results: A self-stable and shear-thinning gel was successfully formulated and oxygenated. A high initial oxygen tension was achieved (650–700 torr, 87–94 % O2 saturation), that was diminished after the cell encapsulation/dilution step (520–550 torr, 70–74 % O2 saturation, Fig 1). Acellular oxygel released oxygen for 100 h until stabilization at atmospheric levels, presenting a 14-times smaller Dv in Oxygel than in PBS. The impact of the model parameters in cell lines with different OCR values was investigated, showing shorter oxygen lifetime in islets (or IEQ) compared to single cell analogues.Conclusion: A highly oxygenated encapsulation matrix for enhanced islet survival was developed and their properties as oxygen carrier evaluated, showing a high oxygen payload and prolonged sustained release properties. Model predictions shows the importance of islet O2 metabolism in the design of macroencapsulation devices and supporting ECM. G.P.D. and D.A.D.-L. acknowledge the DELIVER project that received funding from the European Union’s Horizon 2020 Marie Skłodowska-Curie Actions programme under grant agreement number 812865. G.P.D. acknowledges funding from Science Foundation Ireland under grant SFI/12/RC/2278, Advanced Materials and Bioengineering Research (AMBER) Centre and financial support from the College of Medicine, Nursing and Health Sciences, National University of Ireland Galway.

Therapeutic Efficacy of Cryopreserved, Allogeneic Extracellular Vesicles for Treatment of Acute Myocardial Infarction.

Extracellular vesicles (EV) that are derived from endothelial progenitor cells (EPC) have been determined to be a novel therapy for acute myocardial infarction, with a promise for immediate "off-the-shelf" delivery. Early experience suggests delivery of EVs from allogeneic sources is safe. Yet, clinical translation of this therapy requires assurances of both EV stability following cryopreservation and absence of an adverse immunologic response to EVs from allogeneic donors. Thus, more bioactivity studies on allogeneic EVs after cold storage are necessary to establish quality standards for its widespread clinical use. Thus, in this study, we aimed to demonstrate the safety and efficacy in delivering cryopreserved EVs in allogeneic recipients as a therapy for acute myocardial infarction.In this present study, we have analyzed the cardioprotective effects of allogeneic EPC-derived EVs after storage at -80°C for 2 months, using a shear-thinning gel (STG) as an in vivo delivery vehicle. EV size, proteome, and nucleic acid cargo were observed to remain steady through extended cryopreservation via nanoparticle tracking analysis, mass spectrometry, and nanodrop analysis, respectively. Fresh and previously frozen EVs in STG were delivered intramyocardially in a rat model of myocardial infarction (MI), with both showing improvements in contractility, angiogenesis, and scar thickness in comparison to phosphate-buffered saline (PBS) and STG controls at 4 weeks post-MI. Pathologic analyses and flow cytometry revealed minimal inflammatory and immune upregulation upon exposure of tissue to EVs pooled from allogeneic donor cells.Allogeneic EPC-EVs have been known to elicit minimal immune activity and retain therapeutic efficacy after at least 2 months of cryopreservation in a post-MI model.

Intravascular Embolization: Nanocomposite Hydrogel with Tantalum Microparticles for Rapid Endovascular Hemostasis (Adv. Sci. 1/2021)

Endovascular embolization is performed to treat various vascular diseases including hemorrhage, aneurysms, and vascular malformations. In article number 2003327, Rahmi Oklu, Ali Khademhosseini, and co-workers report a tantalum microparticle-loaded shear-thinning gel embolic material (Ta-GEM) that can be rapidly delivered into diseased arteries using clinical catheters to achieve rapid hemostasis. The cover image shows the swine pelvic vasculature, with both iliac arteries demonstrating vascular hemorrhage. The left side is successfully occluded using the gel embolic material (GEM), whereas the right side received coil embolization (the standard treatment today) where blood continues to bleed through the coils.

Injection of Zerovalent Iron Gels for Aquifer Nanoremediation: Lab Experiments and Modeling

One of the main technical problems faced during field-scale injections of iron microparticles (mZVI) for groundwater nanoremediation is related to their poor colloidal stability and mobility in porous media. In this study, a shear-thinning gel, composed of a mixture of two environmentally friendly biopolymers, i.e., guar gum and xanthan gum, was employed to overcome these limitations. The slurry rheology and particle mobility were characterized by column transport tests. Then, a radial transport experiment was performed to mimic the particle delivery in more realistic conditions. The gel, even at a low polymeric content (1.75 g/L), proved effective in enhancing the mobility of high concentrated mZVI suspensions (20 g/L) in field-like conditions. The high radius of influence (73 cm) and homogeneous iron distribution were achieved by maintaining a low injection overpressure (<0.4 bar). Based only on the information derived from column tests, the MNMs 2018 software (Micro- and Nanoparticle transport, filtration, and clogging Model-Suite) was able to predict the particle distribution and pressure build-up measured in the radial domain. Experimental and simulated results showed good agreement, thus proving that a simplified experimental-modeling procedure based on 1D column tests could be used to effectively upscale the slurry behavior to more representative scales, e.g., radial domains.

Physico-chemical characteristics of the sulfated polysaccharides of the red microalgae Dixoniella grisea and Porphyridium aerugineum

The sulfated polysaccharides of red microalgae have attracted increasing attention in recent years due to their unique rheological and bioactivities. Todate, most studies are devoted to the polysaccharide of the marine species Porphyridium sp., with limited information about that of the brackish water- Dixoniella grisea and the freshwater- Porphyridium aerugineum. We therefore conducted a comparative study of the two less explored sulfated polysaccharides, emphasizing their similarities and differences in composition, physical properties and biocompatibility. Both polysaccharides were found to be composed of 6–8 monosaccharides, predominantly xylose. Sulfur content was 0.8% for P. aerugineum and 1.6% for D. grisea. Solutions of both polysaccharides were highly viscous and exhibited shear thinning and weak gel behavior. Both were found to be stable in an alkaline environment, whereas in an acidic environment the viscosity of the polysaccharide of the brackish water species increased while that of the freshwater species decreased. Both exhibited a similar morphology, having a porous fibrous structure with a rough amorphous surface. By complementing previous studies on the Porphyridium sp. polysaccharide, we have established a sound basis for elucidating the structure/function relationships that in turn, will promote the development of innovative applications for the biotech industries for pharmaceutics, food and drug-delivery.

Delayed delivery of endothelial progenitor cell-derived extracellular vesicles via shear thinning gel improves postinfarct hemodynamics

BackgroundExtracellular vesicles (EVs) are promising therapeutics for cardiovascular disease, but poorly-timed delivery might hinder efficacy. We characterized the time-dependent response to endothelial progenitor cell (EPC)-EVs within an injectable shear-thinning hydrogel (STG+EV) post-myocardial infarction (MI) to identify when an optimal response is achieved. MethodsThe angiogenic effects of prolonged hypoxia on cell response to EPC-EV therapy and EV uptake affinity were tested in vitro. A rat model of acute MI via left anterior descending artery ligation was created and STG+EV was delivered via intramyocardial injections into the infarct border zone at time points corresponding to phases of post-MI inflammation: 0 hours (immediate), 3 hours (acute inflammation), 4 days (proliferative), and 2 weeks (fibrosis). Hemodynamics 4 weeks post-treatment were compared across treatment and control groups (phosphate buffered saline [PBS], shear-thinning gel). Scar thickness and ventricular diameter were assessed histologically. The primary hemodynamic end point was end systolic elastance. The secondary end point was scar thickness. ResultsEPC-EVs incubated with chronically versus acutely hypoxic human umbilical vein endothelial cells resulted in a 2.56 ± 0.53 versus 1.65 ± 0.15-fold increase (P = .05) in a number of vascular meshes and higher uptake of EVs over 14 hours. End systolic elastance improved with STG+EV therapy at 4 days (0.54 ± 0.08) versus PBS or shear-thinning gel (0.26 ± 0.03 [P = .02]; 0.23 ± 0.02 [P = .01]). Preservation of ventricular diameter (6.20 ± 0.73 mm vs 8.58 ± 0.38 mm [P = .04]; 9.13 ± 0.25 mm [P = .01]) and scar thickness (0.89 ± 0.05 mm vs 0.62 ± 0.03 mm [P < .0001] and 0.58 ± 0.05 mm [P < .0001]) was significantly greater at 4 days, compared wit PBS and shear-thinning gel controls. ConclusionsDelivery of STG+EV 4 days post-MI improved left ventricular contractility and preserved global ventricular geometry, compared with controls and immediate therapy post-MI. These findings suggest other cell-derived therapies can be optimized by strategic timing of therapeutic intervention.

A gellan-based fluid gel carrier to enhance topical spray delivery

Autologous cell transplantation was introduced to clinical practice nearly four decades ago to enhance burn wound re-epithelialisation. Autologous cultured or uncultured cells are often delivered to the surface in saline-like suspensions. This delivery method is limited because droplets of the sprayed suspension form upon deposition and run across the wound bed, leading to uneven coverage and cell loss. One way to circumvent this problem would be to use a gel-based material to enhance surface retention. Fibrin systems have been explored as co-delivery system with keratinocytes or as adjunct to ‘seal’ the cells following spray delivery, but the high costs and need for autologous blood has impeded its widespread use. Aside from fibrin gel, which can exhibit variable properties, it has not been possible to develop a gel-based carrier that solidifies on the skin surface. This is because it is challenging to develop a material that is sprayable but gels on contact with the skin surface. The manuscript reports the use of an engineered carrier device to deliver cells via spraying, to enhance retention upon a wound. The device involves shear-structuring of a gelling biopolymer, gellan, during the gelation process; forming a yield-stress fluid with shear-sensitive behaviours, known as a fluid gel. In this study, a formulation of gellan gum fluid gels are reported, formed with from 0.75 or 0.9% (w/v) polymer and varying the salt concentrations. The rheological properties and the propensity of the material to wet a surface were determined for polymer modified and non-polymer modified cell suspensions. The gellan fluid gels had a significantly higher viscosity and contact angle when compared to the non-polymer carrier. Viability of cells was not impeded by encapsulation in the gellan fluid gel or spraying. The shear thinning property of the material enabled it to be applied using an airbrush and spray angle, distance and air pressure were optimised for coverage and viability. Statement of significanceSpray delivery of skin cells has successfully translated to clinical practice. However, it has not yet been widely accepted due to limited retention and disputable cell viability in the wound. Here, we report a method for delivering cells onto wound surfaces using a gellan-based shear-thinning gel system. The viscoelastic properties allow the material to liquefy upon spraying and restructure rapidly on the surface. Our results demonstrate reduced run-off from the surface compared to currently used low-viscosity cell carriers. Moreover, encapsulated cells remain viable throughout the process. Although this paper studies the encapsulation of one cell type, a similar approach could potentially be adopted for other cell types. Our data supports further studies to confirm these results in in vivo models.

Direct Ink Writing of Cement Structures Modified with Nanoscale Additive

Synthetic structures built with cement benefit from high compressive strength, but their brittleness limits their fracture toughness under conditions where repeated, unnegotiable strains are imparted. This could be somewhat alleviated, if complex structures with tunable geometries is created, for example, via direct ink writing (DIW)‐based 3D printing. However, the nature of the slurries used in the DIW printing of cement must be modified with proper rheology to be effectively and programmatically printed with distinct mechanical properties intended for specific applications. Here, the authors have developed a nano‐clay modified cement‐based direct ink that enables high‐resolution 3D printing of complex architected structures of tunable geometries. The developed ink has a significant shear thinning and rapid gel strength properties which facilitate extrusion from a micro‐nozzle (≈400 μm) under ambient conditions conserving the filamentary shape with holding the load of the subsequent printed layer above. A series of architected structures have revealed how nanoscale additive, fabrication process, and architecture of the structures can influence both the stiffness and toughness in the cementitious materials. Understanding these construction principles based on architectures, materials, and processing can change the brittle cement‐based structure to a tough one for structural and functional applications.

3496 Mesenchymal Stem Cell Extracellular Vesicle Delivery in a Shear-Thinning Hydrogel For Therapy in an Acute Myocardial Infarction Model: A Comparative Analysis

OBJECTIVES/SPECIFIC AIMS: The primary aim is to assess differences in therapeutic effect between MSC and EPC EVs on acute ischemic rat hearts through delivery in a biocompatible and shear-thinning hydrogel. Primary outcomes for therapeutic assessment include an in-vitro angiogenesis assay and in-vivo hemodynamic analysis, mainly identifying differences in ejection fraction and contractility. Secondary hemodynamic outcomes include cardiac output, stroke volume, and end-diastolic pressure volume relationship (EDPVR). Secondary structural outcomes include post-mortem scar analysis and immunohistochemistry (IHC) staining for angiomyogenesis. METHODS/STUDY POPULATION: MSCs and EPCs will be cultured according to previously published protocols. EVs will be isolated from cultured cell lines through precipitation methods with polyethylene glycol. EVs will be qualitatively analyzed with nanoparticle tracking analysis (NTA) and flow cytometry. The shear thinning hydrogel (STG) will be constructed using a hyaluronic backbone conjugated to adamantane or beta-cyclodextrin, ultimately facilitating guest-host interactions with shear thinning properties. Controls and treatment groups mixed with the hydrogel will be injected into the border zone of infarcted Wistar rat hearts immediately following a left anterior descending artery ligation. Hemodynamic assessment will be performed at four weeks through left ventricular catheter based pressure-volume recordings. Ex-vivo analysis will include scar thickness assessment using Masson collagen staining and IHC stain for vessel (anti-vonWillebrand factor; anti-Isolectin) and myocyte formation (anti-cardiac Troponin I). RESULTS/ANTICIPATED RESULTS: We hypothesize that, in-vitro, MSC-EVs will demonstrate non-inferior angiogenic potential as compared to EPC-EVs. We posit that MSC-EVs will demonstrate superior therapeutic effect to EPC-EVs in-vivo as measured by functional hemodynamics and structural assessment. We have successfully isolated MSC and EPC EVs and have validated uniformity across EV populations (Figure 1). Preliminary data from the angiogenesis assay (n=3) demonstrated that MSC-EV and EPC-EV produce non-significantly different angiogenic potential as measured by number of vascular meshing extremes (p=0.144) and length of master vascular segment (p=0.193), with significant differences compared to either positive or negative controls. DISCUSSION/SIGNIFICANCE OF IMPACT: Novel regenerative therapies are needed for patients with a history of AMI given current limitations to therapy and sequelae of ischemic heart disease. Delivery of extracellular vesicles through a shear-thinning gel is a novel “off-the-shelf” translational approach to address the current clinical need.

Structural characterization and rheological properties of dextran produced by native strains isolated of Agave salmiana

The genus Leuconostoc belongs to a group of lactic acid bacteria usually isolated from fermented vegetables, which includes species involved in the production of exopolysaccharides (EPS) with commercial potential. This study was aimed to produce and characterize exopolysaccharides of four strains of Leuconostoc mesenteroides, which were isolated from aguamiel of Agave salmiana. The EPS were obtained with sucrose, pH 6, without agitation and incubation at 30 °C for 24 h. The EPS were precipitated as gummy masses by the addition of ethanol and characterized as the important long chain glucose polymer known as dextran (Strain SF3 with 20 g/L yield). The chemical and rheological properties of the produced EPS were investigated. Dextrans produced by these strains have a backbone chain of α (1 → 6) linkages with α (1 → 3) branching. The rheological behavior of dextran solutions exhibited typical shear thinning and weak gel properties.

Smart Shear-Thinning Hydrogels as Injectable Drug Delivery Systems.

In this study, we fabricated and characterized a smart shear-thinning hydrogel composed of gelatin and laponite for localized drug delivery. We added chitosan (Chi) and poly N-isopropylacrylamide-co-Acrylic acid (PNIPAM) particles to the shear-thinning gel to render it pH-responsive. The effects of total solid weight and the percentage of laponite in a solid mass on the rheological behavior and mechanical properties were investigated to obtain the optimum formulation. The nanocomposite gel and particles were characterized using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), zeta potential, and dynamic light scattering techniques. Finally, release related experiment including degradability, swelling and Rhodamine B (Rd) release at various pH were performed. The results suggest that incorporation of silicate nanoplatelets in the gelatin led to the formation of the tunable porous composite, with a microstructure that was affected by introducing particles. Besides, the optimum formulation possessed shear-thinning properties with modified rheological and mechanical properties which preserved its mechanical properties while incubated in physiological conditions. The release related experiments showed that the shear-thinning materials offer pH-sensitive behavior so that the highest swelling ratio, degradation rate, and Rd release were obtained at pH 9.18. Therefore, this nanocomposite gel can be potentially used to develop pH-sensitive systems.

Linear and non-linear flow behavior of welan gum solutions

Rheological and microstructural properties of welan gum aqueous solutions were studied as a function of polymer concentration in the 0.2–0.6% (m/m) range at fixed temperature 20 °C. Welan gum is an exopolysaccharide produced by Sphingomonas sp. All the systems exhibited a shear thinning and weak gel–like behavior whose parameters were well adjusted to a power law with the concentration. Furthermore, time-concentration superposition methods were carried out to obtain two master curves, one from the flow curves and the other from the mechanical spectra, which made it possible to extend the accessible experimental range. The non-linear viscoelastic properties were also studied by means of parallel superposition tests. The superimposed shear stress induced a change from weak gel to entangled solution behavior. This latter flow behavior is characterized by a frequency crossover that has been shown to have a linear dependence on the superimposed steady-state shear rate. Finally, Cryo-SEM images revealed a network with numerous junction zones between polymer chains.

Delivery of progenitor cells with injectable shear-thinning hydrogel maintains geometry and normalizes strain to stabilize cardiac function after ischemia

ObjectivesThe ventricle undergoes adverse remodeling after myocardial infarction, resulting in abnormal biomechanics and decreased function. We hypothesize that tissue-engineered therapy could minimize postischemic remodeling through mechanical stress reduction and retention of tensile myocardial properties due to improved endothelial progenitor cell retention and intrinsic biomechanical properties of the hyaluronic acid shear-thinning gel. MethodsEndothelial progenitor cells were harvested from adult Wistar rats and resuspended in shear-thinning gel. The constructs were injected at the border zone of ischemic rat myocardium in an acute model of myocardial infarction. Myocardial remodeling, tensile properties, and hemodynamic function were analyzed: control (phosphate-buffered saline), endothelial progenitor cells, shear-thinning gel, and shear-thinning gel + endothelial progenitor cells. Novel high-resolution, high-sensitivity ultrasound with speckle tracking allowed for global strain analysis. Uniaxial testing assessed tensile biomechanical properties. ResultsShear-thinning gel + endothelial progenitor cell injection significantly increased engraftment and retention of the endothelial progenitor cells within the myocardium compared with endothelial progenitor cells alone. With the use of strain echocardiography, a significant improvement in left ventricular ejection fraction was noted in the shear-thinning gel + endothelial progenitor cell cohort compared with control (69.5% ± 10.8% vs 40.1% ± 4.6%, P = .04). A significant normalization of myocardial longitudinal displacement with subsequent stabilization of myocardial velocity with shear-thinning gel + endothelial progenitor cell therapy compared with control was also evident (0.84 + 0.3 cm/s vs 0.11 ± 0.01 cm/s, P = .03). A significantly positive and higher myocardial strain was observed in shear-thinning gel + endothelial progenitor cell (4.5% ± 0.45%) compared with shear-thinning gel (3.7% ± 0.24%), endothelial progenitor cell (3.5% ± 0.97%), and control (8.6% ± 0.3%, P = .05). A resultant reduction in dynamic stiffness was noted in the shear-thinning gel + endothelial progenitor cell cohort. ConclusionsThis novel injectable shear-thinning hyaluronic acid hydrogel demonstrates stabilization of border zone myocardium with reduction in adverse myocardial remodeling and preservation of myocardial biomechanics. The cellular construct provides a normalization of strain measurements and reduces left ventricular dilatation, thus resulting in improvement of left ventricular function.

Abstract 16818: Frozen in Time: Endothelial Progenitor Cell-Derived Extracellular Vesicles Maintain Therapeutic Efficacy for Clinically Translatable Treatment of Acute Myocardial Infarction After Long Term Storage

Introduction: Extracellular vesicles (EV) derived from progenitor cells are a novel therapy for ischemic cardiomyopathy, with promise for “off-the-shelf” delivery. Clinical translation and timely delivery post-myocardial infarction (MI) requires assurance of EV stability after storage. Bioactivity studies of EVs after freezing are currently lacking and are necessary to establish quality standards for widespread clinical use of EVs. Hypothesis: We hypothesize that endothelial progenitor cell-derived EVs (EPC-EVs) can be frozen at -80 °C for at least 2 months without decrement of therapeutic effect when delivered intramyocardially to ischemic tissue. Methods: EVs were isolated from male Wistar rat bone marrow EPCs. Fresh preparations of EVs isolated from 700,000 EPCs were compared to frozen EVs stored in dPBS for 2-4 months at -80 °C. Particle size of EVs was analyzed via nanoparticle tracking analysis. In vitro angiogenesis was measured with Matrigel assay. A rat model of MI via left anterior descending artery ligation was used to assess EPC-EV function. Hemodynamics, scar thickness and vasculogenesis were assessed 4 weeks post-intramyocardial injection of EPC-EV within a shear-thinning gel (STG). Results: After 4 months’ storage at -80 °C, frozen EVs had stable mean particle diameter. In vivo analysis demonstrated equivalent hemodynamic outcomes between fresh and 2-month frozen EVs (p=1.0), both of which had statistically significantly improved measures of contractility over PBS as measured by Ees (p=0.0001; p=0.0008) and dp/dt (p=0.01; p=0.03, respectively). Scar thickness was increased in fresh, but not frozen EVs vs PBS (0.68, 0.64 v 0.50; p=0.031, p=0.22). On IHC, fresh and frozen EVs had significantly increased vascular density vs PBS (Δ665.5, Δ907.5; p=0.05). Conclusions: EPC-EVs retain adequate functionality after 2 months of freezing to produce hemodynamic benefits equivalent to freshly prepared EPC-EVs when delivered in STG to ischemic myocardium.

Production and Characterization of Nanoparticle Based Hyaluronate Gel Containing Retinyl Palmitate for Wound Healing.

Wound healing is a biological process that can get in a state of pathologic inflammation, requiring the use of specific medications able to promote proper tissue repair. The study describes the production and characterization of nanoparticle based gel for wound healing treatment designed to deliver hyaluronic acid and retinyl palmitate onto the skin. Tristearin solid lipid nanoparticles and nanostructured lipid carriers based on a tristearin and caprylic/capric triglyceride mixture were produced and characterized. Gel spreadability and viscosity were investigated. Drug diffusion and "in vitro" wound healing were assessed by Franz cell and scratch wound assay in keratinocytes. Cryogenic transmission electron microscopy evidenced flat discoid nanoparticles. Photon correlation spectroscopy analysis indicated homogeneous dimensional distribution and mean diameter 132±46 nm. X-ray evidenced a lamellar inner structure of lipid nanoparticles. Nanostructured lipid carriers, being based on a heterogeneous solid/ liquid lipid mixture, could better solubilize retinyl palmitate and control its stability. The hyaluronic acid directly added into nanoparticles' dispersion enabled to obtain a shear-thinning gel suitable for cutaneous administration. Retynil palmitate diffusion was slower from the nanoparticulate gel with respect to the plain nanoparticle dispersion. The "wound healing" effect of nanoparticulate gel containing retinyl palmitate and hyaluronic acid, analyzed in HaCaT cells, showed significant differences in wounded areas between treated and control cells during the first 24 h postwounding suggesting a synergic effect of retinyl palmitate and hyaluronic acid in "in vitro" wound healing. This study suggests that a nanoparticle based hyaluronate gel containing retinyl palmitate can be efficiently used for wound healing.