Engineering a Highly Adhesive and Hemostatic Sealant for Soft Tissues

The existing surgical adhesives and sealants lack strong adherence to the biological tissues in the wet environment. In addition, demonstrating both inherently high adhesion and hemostatic functionalities in one product, is a scarce characteristic of the developed biomaterials. Moreover, to eliminate the physical and mechanical mismatches with native tissues, high tuning ability is desirable but limited in the current products. As a result, the current solutions fail to either close the wound, or maintain a sufficient sealing ability during wound healing. In this work, a novel and efficient synthetic technique was successfully developed to chemically conjugate catechol motifs to the gelatin backbone. The resulting gelatin-catechol compound was then chemically functionalized with methacryloyl groups to form a highly adhesive and photocrosslinkable sealant, named gelatin methacryloyl-catechol (GelMAC). A two-step crosslinking approach was employed to form the double-networked, and highly tunable GelMAC hydrogel system. First, different concentrations of Fe3+ ions (0, 1, 2.5, 5 and 10 �M) were introduced to the 20 %(w/v) GelMAC prepolymer solution. This step was followed by a second crosslinking mechanism utilizing visible light photopolymerization. GelMAC hydrogel with 2.5 �M Fe3+ ion concentration (GelMAC-Fe) was found to have lower elastic and compressive moduli but demonstrated comparable extensibility to Gelatin-methacryloyl (GelMA) hydrogel incorporating the same Fe3+ ion concentration (GelMA-Fe). Moreover, the wound closure test with porcine skin showed a 1.5-fold higher adhesive strength for GelMAC-Fe compared to GelMA-Fe hydrogels. To study the hemostatic efficacy of GelMAC-Fe hydrogel, the time lapse of blood coagulation across experimental groups was studied in vitro. While the negative control group (untreated blood) formed a blood clot after 16 min, GelMAC hydrogels decreased the clotting time significantly to 9 min. These results were also in close agreement with those obtained for the commercially available hemostatic material, SURGICEL�. Finally, the results of the in vivo liver bleeding model showed that GelMAC-Fe hydrogel was able to rapidly crosslink the incision site and stop the bleeding faster compared to other hydrogels. GelMAC-Fe hydrogel exhibited superior adhesion strength while offering significant hemostatic ability owing to the presence of ferric ions (Fe3+) and the dopamine molecule. This novel, highly biocompatible, tunable, adhesive, and hemostatic sealant can therefore be utilized as an effective solution for controlling bleeding and sealing of soft internal organs such as the lung, heart and blood vessels

Engineering a Highly Adhesive and Hemostatic Sealant for Soft Tissues

The existing surgical adhesives and sealants lack strong adherence to the biological tissues in the wet environment. In addition, demonstrating both inherently high adhesion and hemostatic functionalities in one product, is a scarce characteristic of the developed biomaterials. Moreover, to eliminate the physical and mechanical mismatches with native tissues, high tuning ability is desirable but limited in the current products. As a result, the current solutions fail to either close the wound, or maintain a sufficient sealing ability during wound healing. In this work, a novel and efficient synthetic technique was successfully developed to chemically conjugate catechol motifs to the gelatin backbone. The resulting gelatin-catechol compound was then chemically functionalized with methacryloyl groups to form a highly adhesive and photocrosslinkable sealant, named gelatin methacryloyl-catechol (GelMAC). A two-step crosslinking approach was employed to form the double-networked, and highly tunable GelMAC hydrogel system. First, different concentrations of Fe3+ ions (0, 1, 2.5, 5 and 10 �M) were introduced to the 20 %(w/v) GelMAC prepolymer solution. This step was followed by a second crosslinking mechanism utilizing visible light photopolymerization. GelMAC hydrogel with 2.5 �M Fe3+ ion concentration (GelMAC-Fe) was found to have lower elastic and compressive moduli but demonstrated comparable extensibility to Gelatin-methacryloyl (GelMA) hydrogel incorporating the same Fe3+ ion concentration (GelMA-Fe). Moreover, the wound closure test with porcine skin showed a 1.5-fold higher adhesive strength for GelMAC-Fe compared to GelMA-Fe hydrogels. To study the hemostatic efficacy of GelMAC-Fe hydrogel, the time lapse of blood coagulation across experimental groups was studied in vitro. While the negative control group (untreated blood) formed a blood clot after 16 min, GelMAC hydrogels decreased the clotting time significantly to 9 min. These results were also in close agreement with those obtained for the commercially available hemostatic material, SURGICEL�. Finally, the results of the in vivo liver bleeding model showed that GelMAC-Fe hydrogel was able to rapidly crosslink the incision site and stop the bleeding faster compared to other hydrogels. GelMAC-Fe hydrogel exhibited superior adhesion strength while offering significant hemostatic ability owing to the presence of ferric ions (Fe3+) and the dopamine molecule. This novel, highly biocompatible, tunable, adhesive, and hemostatic sealant can therefore be utilized as an effective solution for controlling bleeding and sealing of soft internal organs such as the lung, heart and blood vessels

Engineering a highly elastic bioadhesive for sealing soft and dynamic tissues

Injured tissues often require immediate closure to restore the normal functionality of the organ. In most cases, injuries are associated with trauma or various physical surgeries where different adhesive hydrogel materials are applied to close the wounds. However, these materials are typically toxic, have low elasticity, and lack strong adhesion especially to the wet tissues. In this study, a stretchable composite hydrogel consisting of gelatin methacrylol catechol (GelMAC) with ferric ions, and poly(ethylene glycol) diacrylate (PEGDA) was developed. The engineered material could adhere to the wet tissue surfaces through the chemical conjugation of catechol and methacrylate groups to the gelatin backbone. Moreover, the incorporation of PEGDA enhanced the elasticity of the bioadhesives. Our results showed that the physical properties and adhesion of the hydrogels could be tuned by changing the ratio of GelMAC/PEGDA. In addition, the in vitro toxicity tests confirmed the biocompatibility of the engineered bioadhesives. Finally, using an ex vivo lung incision model, we showed the potential application of the developed bioadhesives for sealing elastic tissues

Engineering elastic sealants based on gelatin and elastin-like polypeptides for endovascular anastomosis.

Cerebrovascular ischemia from intracranial atherosclerosis remains difficult to treat. Although current revascularization procedures, including intraluminal stents and extracranial to intracranial bypass, have shown some benefit, they suffer from perioperative and postoperative morbidity. To address these limitations, here we developed a novel approach that involves gluing of arteries and subsequent transmural anastomosis from the healthy donor into the ischemic recipient. This approach required an elastic vascular sealant with distinct mechanical properties and adhesion to facilitate anastomosis. We engineered two hydrogel-based glues: an elastic composite hydrogel based on methacryloyl elastin-like polypeptide (mELP) combined with gelatin methacryloyl (GelMA) and a stiff glue based on pure GelMA. Two formulations with distinct mechanical characteristics were necessary to achieve stable anastomosis. The elastic GelMA/mELP composite glue attained desirable mechanical properties (elastic modulus: 288 ± 19 kPa, extensibility: 34.5 ± 13.4%) and adhesion (shear strength: 26.7 ± 5.4 kPa) to the blood vessel, while the pure GelMA glue exhibited superior adhesion (shear strength: 49.4 ± 7.0 kPa) at the cost of increased stiffness (elastic modulus: 581 ± 51 kPa) and reduced extensibility (13.6 ± 2.5%). The in vitro biocompatibility tests confirmed that the glues were not cytotoxic and were biodegradable. In addition, an ex vivo porcine anastomosis model showed high arterial burst pressure resistance of 34.0 ± 7.5 kPa, which is well over normal (16 kPa), elevated (17.3 kPa), and hypertensive crisis (24 kPa) systolic blood pressures in humans. Finally, an in vivo swine model was used to assess the feasibility of using the newly developed two-glue system for an endovascular anastomosis. X-ray imaging confirmed that the anastomosis was made successfully without postoperative bleeding complications and the procedure was well tolerated. In the future, more studies are required to evaluate the performance of the developed sealants under various temperature and humidity ranges

Engineering a naturally derived hemostatic sealant for sealing internal organs.

Controlling bleeding from a raptured tissue, especially during the surgeries, is essentially important. Particularly for soft and dynamic internal organs where use of sutures, staples, or wires is limited, treatments with hemostatic adhesives have proven to be beneficial. However, major drawbacks with clinically used hemostats include lack of adhesion to wet tissue and poor mechanics. In view of these, herein, we engineered a double-crosslinked sealant which showed excellent hemostasis (comparable to existing commercial hemostat) without compromising its wet tissue adhesion. Mechanistically, the engineered hydrogel controlled the bleeding through its wound-sealing capability and inherent chemical activity. This mussel-inspired hemostatic adhesive hydrogel, named gelatin methacryloyl-catechol (GelMAC), contained covalently functionalized catechol and methacrylate moieties and showed excellent biocompatibility both in vitro and in vivo. Hemostatic property of GelMAC hydrogel was initially demonstrated with an in vitro blood clotting assay, which showed significantly reduced clotting time compared to the clinically used hemostat, Surgicel®. This was further assessed with an in vivo liver bleeding test in rats where GelMAC hydrogel closed the incision rapidly and initiated blood coagulation even faster than Surgicel®. The engineered GelMAC hydrogel-based seaalant with excellent hemostatic property and tissue adhesion can be utilized for controlling bleeding and sealing of soft internal organs

Improved Humoral Immunity and Protection against Influenza Virus Infection with a 3d Porous Biomaterial Vaccine.

New vaccine platforms that activate humoral immunity and generate neutralizing antibodies are required to combat emerging pathogens, including influenza virus. A slurry of antigen-loaded hydrogel microparticles that anneal to form a porous scaffold with high surface area for antigen uptake by infiltrating immune cells as the biomaterial degrades is demonstrated to enhance humoral immunity. Antigen-loaded-microgels elicited a robust cellular humoral immune response, with increased CD4+ T follicular helper (Tfh) cells and prolonged germinal center (GC) B cells comparable to the commonly used adjuvant, aluminum hydroxide (Alum). Increasing the weight fraction of polymer material led to increased material stiffness and antigen-specific antibody titers superior to Alum. Vaccinating mice with inactivated influenza virus loaded into this more highly cross-linked formulation elicited a strong antibody response and provided protection against a high dose viral challenge. By tuning physical and chemical properties, adjuvanticity can be enhanced leading to humoral immunity and protection against a pathogen, leveraging two different types of antigenic material: individual protein antigen and inactivated virus. The flexibility of the platform may enable design of new vaccines to enhance innate and adaptive immune cell programming to generate and tune high affinity antibodies, a promising approach to generate long-lasting immunity

Improved Humoral Immunity and Protection against Influenza Virus Infection with a 3d Porous Biomaterial Vaccine

Abstract New vaccine platforms that activate humoral immunity and generate neutralizing antibodies are required to combat emerging pathogens, including influenza virus. A slurry of antigen‐loaded hydrogel microparticles that anneal to form a porous scaffold with high surface area for antigen uptake by infiltrating immune cells as the biomaterial degrades is demonstrated to enhance humoral immunity. Antigen‐loaded‐microgels elicited a robust cellular humoral immune response, with increased CD4+ T follicular helper (Tfh) cells and prolonged germinal center (GC) B cells comparable to the commonly used adjuvant, aluminum hydroxide (Alum). Increasing the weight fraction of polymer material led to increased material stiffness and antigen‐specific antibody titers superior to Alum. Vaccinating mice with inactivated influenza virus loaded into this more highly cross‐linked formulation elicited a strong antibody response and provided protection against a high dose viral challenge. By tuning physical and chemical properties, adjuvanticity can be enhanced leading to humoral immunity and protection against a pathogen, leveraging two different types of antigenic material: individual protein antigen and inactivated virus. The flexibility of the platform may enable design of new vaccines to enhance innate and adaptive immune cell programming to generate and tune high affinity antibodies, a promising approach to generate long‐lasting immunity