Formulation - Properties effects of novel dual composite hydrogels for use as medical sealants

Cellulose fibres enhance the function of hemostatic composite medical sealants

Tissue adhesives and sealants offer promising alternatives to traditional wound closure methods, but the existing trade-off between biocompatibility and strength is still a challenge. The current study explores the potential of a gelatin-alginate-based hydrogel, cross-linked with a carbodiimide, and loaded with two functional fillers, the hemostatic agent kaolin and cellulose fibres, to improve the hydrogel's mechanical strength and hemostatic properties for use as a sealant. The effect of the formulation parameters on the mechanical and physical properties was studied, as well as the biocompatibility and microstructure. The incorporation of the two functional fillers resulted in a dual micro-composite structure, with uniform dispersion of both fillers within the hydrogel, and excellent adhesion between the fillers and the hydrogel matrix. This enabled to strongly increase the sealing ability and the tensile strength and modulus of the hydrogel. The fibres' contribution to the enhanced mechanical properties is more dominant than that of kaolin. A combined synergistic effect of both fillers resulted in enhanced sealing ability (247%), tensile strength (400%), and Young's modulus (437%), compared to the unloaded hydrogel formulation. While the incorporation of kaolin almost did not affect the physical properties of the hydrogel, the incorporation of the fibres strongly increased the viscosity and decreased the gelation time and swelling degree. The cytotoxicity tests indicated that all studied formulations exhibited high cell viability. Hence, the studied new dual micro-composite hydrogels may be suitable for medical sealing applications, especially when it is needed to get a high sealing effect within a short time. The desired hemostatic effect is obtained due to kaolin incorporation without affecting the physical properties of the sealant. Understanding the effects of the formulation parameters on the hydrogel's properties enables the fitting of optimal formulations for various medical sealing applications.

Recent advances in the application of clay-containing hydrogels for hemostasis and wound healing

INTRODUCTION

Immediate control of bleeding and anti-infection play important roles in wound management. Multiple organ dysfunction syndrome and death may occur if persistent bleeding, hemodynamic instability, and hypoxemia are not addressed. The combination of clay and hydrogel provides a new outlet for wound hemostasis. In this review, the current research progress of hydrogel/clay composite hemostatic agents was reviewed.

AREAS COVERED

This paper summarizes the characteristics of several kinds of clay including kaolinite, montmorillonite, laponite, sepiolite, and palygorskite. The advantages and disadvantages of its application in hemostasis were also summarized. Future directions for the application of hydrogel/clay composite hemostatic agents are presented.

EXPERT OPINION

Clay can activate the endogenous hemostatic pathway by increasing blood cell concentration and promoting plasma absorption to accelerate the hemostasis. Clay is antimicrobial due to the slow release of metal ions and has a rich surface charge with a high affinity for proteins and cells to promote tissue repair. Hydrogels have some properties such as good biocompatibility, strong adhesion, high stretchability, and good self-healing. Despite promising advances, hydrogel/clay composite hemostasis remains a limitation. Therefore, more evidence is needed to further elucidate the risk factors and therapeutic effects of hydrogel/clay in hemostasis and wound healing.

Progress and future prospects of hemostatic materials based on nanostructured clay minerals

The occurrence of uncontrolled hemorrhage is a significant threat to human life and health. Although hemostatic materials have made remarkable advances in the biomaterials field, it remains a challenge to develop safe and effective hemostatic materials for global medical use. Natural clay minerals (CMs) have long been used as traditional inorganic hemostatic agents due to their good hemostatic capability, biocompatibility and easy availability. With the advancement of science, technology and ideology, CM-based hemostatic materials have undergone continuous innovations by integrating new inspirations with conventional concepts. This review systematically summarizes the hemostatic mechanisms of different natural CMs based on their nanostructures. Moreover, it also comprehensively reviews the latest research progress for CM-based hemostatic hybrid and nanocomposite materials, and discusses the challenges and developments in this field.

Closure of Long Surgical Incisions with Hemostatic Tissue Adhesive in a Porcine Skin Model

OBJECTIVE

Skin adhesives offer many advantages over traditional wound-closure devices. Recently, the current research group reported on tissue adhesives composed of natural polymers (gelatin and alginate), which are biocompatible with mechanical properties suitable for tissue adhesion. The objective of the present study was to conduct clinical and histologic assessment of this hemostatic bioadhesive in the healing of long skin incisions (≥4 cm) in comparison with traditional and commercially available methods.

METHODS

Researchers created 24 long incisions on the ventral side of two domestic pigs to compare four different treatment modalities: two topical bioadhesives based on gelatin and alginate combined with the hemostatic agent kaolin, nylon sutures, and commercial tissue adhesive N-butyl-2-cyanoacrylate. The bioadhesive compounds were spread on the incision surface and then mixed either manually or with a double-headed syringe. After 14 days, clinical and histologic measurements were performed to evaluate the healing phase of the wounds.

RESULTS

The bioadhesive formulation that contained a relatively low crosslinker concentration demonstrated superior results to the formulation that contained a standard crosslinker concentration. However, no significant statistical differences were observed compared with the control incisions (sutures and commercial adhesive N-butyl-2-cyanoacrylate). This was verified by immunohistochemical analysis for epithelial integrity and scar formation as well as by clinical assessment.

CONCLUSIONS

This newly developed bioadhesive demonstrated suitable properties for the closure of long incisions in a porcine skin model.

Bacteria-Polymer Composite Material for Glycerol Valorization

Bacterial immobilization is regarded as an enabling technology to improve the stability and reusability of biocatalysts. Natural polymers are often used as immobilization matrices but present certain drawbacks, such as biocatalyst leakage and loss of physical integrity upon utilization in bioprocesses. Herein, we prepared a hybrid polymeric matrix that included silica nanoparticles for the unprecedented immobilization of the industrially relevant Gluconobacter frateurii (Gfr). This biocatalyst can valorize glycerol, an abundant by-product of the biodiesel industry, into glyceric acid (GA) and dihydroxyacetone (DHA). Different concentrations of siliceous nanosized materials, such as biomimetic Si nanoparticles (SiNps) and montmorillonite (MT), were added to alginate. These hybrid materials were significantly more resistant by texture analysis and presented a more compact structure as seen by scanning electron microscopy. The preparation including 4% alginate with 4% SiNps proved to be the most resistant material, with a homogeneous distribution of the biocatalyst in the beads as seen by confocal microscopy using a fluorescent mutant of Gfr. It produced the highest amounts of GA and DHA and could be reused for up to eight consecutive 24 h reactions with no loss of physical integrity and negligible bacterial leakage. Overall, our results indicate a new approach to generating biocatalysts using hybrid biopolymer supports.

Injectable metronidazole-eluting gelatin-alginate hydrogels for local treatment of periodontitis

Infection of the periodontal pocket presents two major challenges for drug delivery: administration into the periodontal pocket and a high fluid clearance rate in the pocket. The current study aimed to develop and study a novel hydrogel system for delivery of the antibiotic drug metronidazole directly into the periodontal pocket via injection followed by in situ gelation. The natural polymers gelatin and alginate served as basic materials, and their crosslinking using a carbodiimide resulted in a dual hydrogel network. The study focused on the effects of the hydrogel's formulation parameters on the drug release profile and the hydrogel's physical and mechanical properties. A cell viability test was conducted on human fibroblasts. The metronidazole-loaded hydrogels demonstrated a decreasing release rate with time, where most of the drug eluted within 24 h. These hydrogels exhibited fibroblast viability of at least 75% after 24 and 48 h, indicating that they are highly biocompatible. Although the alginate concentration used in this study was relatively low, it had a strong effect on the physical as well as the mechanical properties of the hydrogel. An increase in the alginate concentration increased the crosslinking rate and enabled enhanced entanglement of the 3D structure, resulting in a decrease in the gelation time (less than 10 s) and swelling degree, which are both desired for the studied periodontal application. Increasing the gelatin concentration without changing the crosslinker concentration resulted in significant changes in the physical properties and slight changes in the mechanical properties. Metronidazole incorporation slightly decreased the hydrophilicity of the hydrogel and therefore also its viscosity, and affected the sealing ability and the tensile and compression moduli. The developed hydrogels exhibited controllable mechanical and physical properties, can target a wide range of conditions, and are therefore of high significance in the field of periodontal treatment.

Cell viability of novel composite hydrogels loaded with hydroxyapatite for oral and maxillofacial bone regeneration

The development of hydrogels for maxillofacial bone regeneration holds vast potential. However, some challenges need to be addressed to further their application in clinical settings. One challenge is optimizing cell viability. To improve mechanical strength, various materials have been investigated; however, incorporation of these materials within the hydrogel network may affect cell viability. The purpose of this study was to evaluate the cell viability of novel gelatin-alginate composite hydrogels loaded with hydroxyapatite (HA) and nano-hydroxyapatite (n-HA) for maxillofacial bone regeneration. Nine different hydrogels were prepared: three loaded with 0.5%, 1%, and 3% w/v HA; three loaded with 0.25%, 0.5%, and 1% w/v n-HA; one not loaded as a control and two HA and n-HA hydrogels with a lower concentration of the EDC crosslinker. Cell viability of human osteoblasts exposed to the hydrogels as affected by the HA type, size, and concentration, as well as to the crosslinker concentration, was investigated. An Alamar Blue assay was used to evaluate cell viability in the presence of hydrogel extracts and in aqueous solutions (without the hydrogel). A qualitative model was developed for explaining cell viability and growth. Higher percentages of cell viability were observed in the hydrogels loaded with hydroxyapatite as compared with the control. The effect of HA-related parameters, i.e., particle size and concentration, was found to increase the cytotoxic effect, as expressed in lower cell viability. The most favorable composites were the n-HA hydrogels. The incorporation of n-HA in the hydrogel to form a composite seems to be a very promising approach for maxillofacial bone regeneration applications.