Enhanced Sealing by Hydrophobic Modification of Alaska Pollock-Derived Gelatin-Based Surgical Sealants for the Treatment of Pulmonary Air Leaks

Effect of Alaska pollock-gelatin sheet on repair strength and regeneration of nerve

The aim of the study was to investigate the repair strength and the biocompatibility of Alaska pollock-derived gelatin (ApGltn) sheet for nerve repair. Cadaveric digital nerves were repaired with double suture, single suture + ApGltn sheet, single suture + fibrin glue, single suture, ApGltn sheet and fibrin. Maximum failure loads were measured (20 nerves each). Rat sciatic nerves were repaired with double suture, single suture + ApGltn sheet, single suture, ApGltn sheet, fibrin glue and resection (10 nerves each). Macroscopic appearance, muscle weight and histopathological findings were examined 8 weeks postoperatively. The mean failure load of ApGltn sheet (0.39 N) was significantly higher than that of a fibrin (0.05 N), and that of single suture + ApGltn sheet (1.32 N) was significantly higher than that of a single suture alone (0.97 N). Functional and histological assessments showed similar nerve recovery among the suture, ApGltn and fibrin groups. ApGltn sheet has potential for clinical application as an alternative to fibrin.

Improved hydration property of tissue adhesive/hemostatic microparticle based on hydrophobically-modified Alaska pollock gelatin

The management of bleeding is an important aspect of endoscopic surgery to avoid excessive blood loss and minimize pain. In clinical settings, sprayable hemostatic particles are used for their easy delivery, adaptability to irregular shapes, and rapid hydration. However, conventional hemostatic particles present challenges associated with tissue adhesion. In a previous study, we reported tissue adhesive microparticles (C10-sa-MPs) derived from Alaska pollock gelatin modified with decyl groups (C10-sa-ApGltn) using secondary amines as linkages. The C10-sa-MPs adhere to soft tissues through a hydration mechanism. However, their application as a hemostatic agent was limited by their long hydration times, attributed to their high hydrophobicity. In this study, we present a new type microparticle, C10-am-MPs, synthesized by incorporating decanoyl group modifications into ApGltn (C10-am-ApGltn), using amide bonds as linkages. C10-am-MPs exhibited enhanced hydration characteristics compared to C10-sa-MPs, attributed to superior water absorption facilitated by amide bonds rather than secondary amines. Furthermore, C10-am-MPs demonstrated comparable tissue adhesion properties and underwater adhesion stability to C10-sa-MPs. Notably, C10-am-MPs exhibited accelerated blood coagulation in vitro compared to C10-sa-MPs. The application of C10-am-MPs in an in vivo rat liver hemorrhage model resulted in a hemostatic effect comparable to a commercially available hemostatic particle. These findings highlight the potential utility of C10-am-MPs as an effective hemostatic agent for endoscopic procedures and surgical interventions.

Natural Polymer-Polyphenol Bioadhesive Coacervate with Stable Wet Adhesion, Antibacterial Activity, and On-Demand Detachment

Medical adhesives are emerging as an important clinical tool as adjuvants for sutures and staples in wound closure and healing and in the achievement of hemostasis. However, clinical adhesives combining cytocompatibility, as well as strong and stable adhesion in physiological conditions, are still in demand. Herein, a mussel-inspired strategy is explored to produce adhesive coacervates using tannic acid (TA) and methacrylate pullulan (PUL-MA). TA|PUL-MA coacervates mainly comprise van der Waals forces and hydrophobic interactions. The methacrylic groups in the PUL backbone increase the number of interactions in the adhesives matrix, resulting in enhanced cohesion and adhesion strength (72.7 Jm-2), compared to the non-methacrylated coacervate. The adhesive properties are kept in physiologic-mimetic solutions (72.8 Jm-2) for 72 h. The photopolymerization of TA|PUL-MA enables the on-demand detachment of the adhesive. The poor cytocompatibility associated with the use of phenolic groups is here circumvented by mixing reactive oxygen species-degrading enzyme in the adhesive coacervate. This addition does not hamper the adhesive character of the materials, nor their anti-microbial or hemostatic properties. This affordable and straightforward methodology, together with the tailorable adhesivity even in wet environments, high cytocompatibility, and anti-bacterial activity, enables foresee TA|PUL-MA as a promising ready-to-use bioadhesive for biomedical applications.

Sprayable tissue adhesive microparticle-magnetic nanoparticle composites for local cancer hyperthermia

Incomplete removal of early-stage gastrointestinal cancers by endoscopic treatments often leads to recurrence induced by residual cancer cells. To completely remove or kill cancer tissues and cells and prevent recurrence, chemotherapy, radiotherapy, and hyperthermia using biomaterials with drugs or nanomaterials are usually administered following endoscopic treatments. However, there are few biomaterials that can be applied using endoscopic devices to locally kill cancer tissues and cells. We previously reported that decyl group-modified Alaska pollock gelatin-based microparticles (denoted C10MPs) can adhere to gastrointestinal tissues under wet conditions through the formation of a colloidal gel driven by hydrophobic interactions. In this study, we combined C10MPs with superparamagnetic iron oxide nanoparticles (SPIONs) to develop a sprayable heat-generating nanomaterial (denoted SP/C10MP) for local hyperthermia of gastrointestinal cancers. The rheological property, tissue adhesion strength, burst strength, and underwater stability of SP/C10MP were improved through decyl group modification and SPION addition. Moreover, SP/C10MP that adhered to gastrointestinal tissues formed a colloidal gel, which locally generated heat in response to an alternating magnetic field. SP/C10MP successfully killed cancer tissues and cells in colon cancer-bearing mouse models in vitro and in vivo. Therefore, SP/C10MP has the potential to locally kill residual cancer tissues and cells after endoscopic treatments.

Robust aortic media adhesion using hydrophobically modified Alaska pollock gelatin-based adhesive for aortic dissections

Type-A aortic dissection is an acute injury involving the delamination of the aorta at the parts of the aortic media. Aldehyde crosslinker-containing glues have been used to adhere to the media of the dissected aorta before joining an artificial graft. These glues effectively adhere to the aortic media; however, they show low biocompatibility due to the release of aldehyde compounds. In this study, we report innovative adhesives based on hydrophobically modified Alaska pollock gelatin (hm-ApGltn) with different alkyl or cholesteryl (Chol) groups that adhere to the media of the dissected aorta by combining hm-ApGltns with a biocompatible crosslinker, pentaerythritol poly(ethylene glycol) ether tetrasuccinimidyl glutarate. The modification of alkyl or Chol groups contributed to enhanced adhesion strength between porcine aortic media. The adhesion strength increased with increasing modification ratios of alkyl groups from propanoyl to dodecanoyl groups and then decreased at a modification ratio of ~20 mol %. Porcine aortic media adhered using 7.5Chol-ApGltn adhesive showed stretchability even when expanded and shrunk vertically by 25% at least five times. Hm-ApGltn adhesives subcutaneously injected into the backs of mice showed no severe inflammation and were degraded during the implantation period. These results indicated that hm-ApGltn adhesives have potential applications in type-A aortic dissection.

Improved Swelling Property of Tissue Adhesive Hydrogels Based on α-Cyclodextrin/Decyl Group-Modified Alaska Pollock Gelatin Inclusion Complexes

Adhesives/sealants are used after suturing to prevent leakage of cerebrospinal fluid from an anastomotic site. Commercial adhesives/sealants have been used to close the cerebral dura. However, swelling of the cured adhesives/sealants induces increased intracranial pressure and decreases the strength of the seal. In the present study, tissue adhesive hydrogels with improved swelling property using inclusion complex composed of α-cyclodextrin (αCD) and decyl group (C10)-modified Alaska pollock-derived gelatin (C10-ApGltn) with a high degree of substitution (DS) (>20 mol%) are developed. Viscosity of C10-ApGltn with a high DS solution remarkably decreased by the addition of αCD. The resulting αCD/C10-ApGltn adhesive hydrogel composed of αCD/C10-ApGltn inclusion complexes and poly(ethylene glycol) (PEG)-based crosslinker showed improved swelling property after immersion in saline. Also, the resulting adhesive has a significantly higher burst strength than fibrin-based adhesives and is as strong as a PEG-based adhesive. Quantitative analysis of αCD revealed that the improved swelling property of the resulting adhesive hydrogels is induced by the release of αCD from cured adhesive, and the subsequent assembly of decyl groups in the saline. These results suggest that adhesives developed using the αCD/C10-ApGltn inclusion complex can be useful for closing the cerebral dura mater.

Progress of tissue adhesives based on proteins and synthetic polymers

In recent years, polymer-based tissue adhesives (TAs) have been developed as an alternative to sutures to close and seal incisions or wounds owing to their ease of use, rapid application time, low cost, and minimal tissue damage. Although significant research is being conducted to develop new TAs with improved performances using different strategies, the applications of TAs are limited by several factors, such as weak adhesion strength and poor mechanical properties. Therefore, the next-generation advanced TAs with biomimetic and multifunctional properties should be developed. Herein, we review the requirements, adhesive performances, characteristics, adhesive mechanisms, applications, commercial products, and advantages and disadvantages of proteins- and synthetic polymer-based TAs. Furthermore, future perspectives in the field of TA-based research have been discussed.

Multifunctional Dual Cross-Linked Bioadhesive Patch with Low Immunogenic Response and Wet Tissues Adhesion

The development of bioadhesives is an important, yet challenging task as seemingly mutually exclusive properties need to be combined in one material, that is, strong adhesion, water resistance, and high biocompatibility. Here, a biocompatible and biodegradable protein-based bioadhesive patch (PBP) with high adhesion strength and low immunogenic response is reported. PBP exists as a strong adhesion for biological surfaces, which is higher than some conventional bioadhesives (i.e., polyethylene glycol and fibrin). Robust adhesion and strength are realized through the removal of interfacial water and fast formation of multiple supramolecular interactions induced by metal ions. The PBP's high biocompatibility is evaluated and immunogenic response in vitro and in vivo is neglected. The strong adhesion on soft biological tissues qualifies the PBP as biomedical glue outperforming some commercial products for applications in hemostasis performance, accelerated wound healing, and sealing of defected organs, anticipating to be useful as a tissue adhesive and sealant.

Cohesion mechanisms for bioadhesives

Due to the nature of non-invasive wound closure, the ability to close different forms of leaks, and the potential to immobilize various devices, bioadhesives are altering clinical practices. As one of the vital factors, bioadhesives' strength is determined by adhesion and cohesion mechanisms. As well as being essential for adhesion strength, the cohesion mechanism also influences their bulk functions and the way the adhesives can be applied. Although there are many published reports on various adhesion mechanisms, cohesion mechanisms have rarely been addressed. In this review, we have summarized the most used cohesion mechanisms. Furthermore, the relationship of cohesion strategies and adhesion strategies has been discussed, including employing the same functional groups harnessed for adhesion, using combinational approaches, and exploiting different strategies for cohesion mechanism. By providing a comprehensive insight into cohesion strategies, the paper has been integrated to offer a roadmap to facilitate the commercialization of bioadhesives.

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Bioadhesive are altering clinical practices.

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Bioadhesives for medical applications needs different cohesion strategies.

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Better understanding of cohesion mechanism can design suitable bioadhesives.

Prevention of postoperative adhesion with a colloidal gel based on decyl group-modified Alaska pollock gelatin microparticles

Postoperative adhesion, bonding of the abdominal wall to damaged organs, causes severe complications after abdominal surgery. Despite the availability of physical barriers (i.e., solutions, films, and hydrogels), adhesion prevention materials that are a single-substance system with stability in wet tissue and ease of use have not been reported. Here, we report a microparticle based, sprayable adhesion prevention material comprising decyl group modified Alaska pollock gelatin (C10-ApGltn). C10-ApGltn microparticles (C10-MPs) were prepared by a coacervation method, freeze drying, and thermal crosslinking. The C10-MPs adhered to and formed a colloidal gel layer on intestinal serosal tissue by hydration without any crosslinking agents. After hydration of the C10-MPs, the resulting colloidal gel layer did not adhere to other tissues. Additionally, the C10-MP colloidal gel layer formed on the stomach serosal tissue showed stability when submersed in saline for 2 days. The colloidal gel layer also showed tissue followability. An in vivo rat adhesion model revealed that C10-MP colloidal gel layer on the cecum and abdominal wall defects effectively reduced postoperative adhesion and induced tissue remodeling, including re-mesothelialization. Therefore, C10-MPs are a potential anti-adhesion material for preventing postoperative adhesion. STATEMENT OF SIGNIFICANCE: We evaluated the postoperative adhesion prevention ability of a colloidal gel based on decyl group modified Alaska pollock gelatin (ApGltn) microparticles (C10-MPs). These microparticles are sprayable and form a colloidal gel with only hydration on the gastrointestinal tissue. We revealed that the modification of the decyl group into ApGltn improved the stability of C10-MP colloidal gel on the tissue by hydrophobic interaction in the in-vitro experiments. The gel prevented postoperative adhesion by being a physical barrier in the in-vivo rat adhesion model.

The Topical Hemostatic Materials for Coagulopathy

Medical sciences have witnessed significant progresses in hemostatic materials which have saved lives by supporting natural hemostatic ability. However, for the treatment of coagulopathy, where natural hemostatic ability is dysfunctional,...

Comparative study of hydrophobically modified gelatin-based sealant with commercially available sealants

Air leakage is one of the major complications related to pulmonary surgeries. To reduce this complication, we developed a decyl group (C10)-modified Alaska pollock gelatin (ApGltn) (C10-ApGltn) sealant and evaluated its practical performance against commercially available sealants, Beriplast® and DuraSeal®. C10-ApGltn was synthesized by reductive amination of the amino groups in ApGltn with decanal. C10-ApGltn was crosslinked with a poly(ethylene glycol)-based crosslinker to form a tissue sealant. The crosslinking time of the C10-ApGltn sealant was fast enough for curing on tissue and application as a spray system. Although the percent swelling of C10-ApGltn and DuraSeal was significantly greater than Beriplast, C10-ApGltn and DuraSeal exhibited excellent tissue sealing properties on pleura tissue under a long-term moist condition. Additionally, C10-ApGltn and DuraSeal did not cause severe inflammatory responses in a rat subcutaneous example. Therefore, C10-ApGltn sealant had comparable tissue sealing properties to DuraSeal under a moist condition, indicating the potential of C10-ApGltn sealant for pulmonary surgeries.

A Novel Alaska Pollock Gelatin Sealant Shows Higher Bonding Strength and Nerve Regeneration Comparable to That of Fibrin Sealant in a Cadaveric Model and a Rat Model

BACKGROUND

A novel biocompatible sealant composed of Alaska pollock-derived gelatin (ApGltn) has recently shown good burst strength and biocompatibility in a porcine aorta. The purpose of this study was to investigate the bonding strength and biocompatibility of the ApGltn sealant in transected digital nerves of fresh frozen cadavers and in the sciatic nerves of a rat model.

METHODS

Eighty human digital nerves of fresh frozen cadavers were transected for biomechanical traction testing. They were treated with four surgical interventions: (1) suture plus ApGltn sealant; (2) suture; (3) ApGltn sealant; and (4) fibrin sealant. Forty-three sciatic nerves of male Wistar rats were used for functional and histopathologic evaluation. They were treated with six surgical interventions: (1) suture plus ApGltn sealant; (2) suture; (3) ApGltn sealant; (4) fibrin sealant; (5) resection with a 5-mm gap (10 rats per group); and (6) sham operation (three rats). Macroscopic confirmation, muscle weight measurement, and histopathologic findings including G-ratio were examined 8 weeks after the procedure.

RESULTS

The maximum failure load of the ApGltn sealant was significantly higher than that of a fibrin sealant (0.22 ± 0.05 N versus 0.06 ± 0.04 N). The maximum failure load of the ApGltn sealant was significantly lower that of suture plus ApGltn sealant (1.37 N) and suture (1.27 N). Functional evaluation and histologic examination showed that sciatic nerves repaired with ApGltn sealant showed similar nerve recovery compared to repair with the suture and fibrin sealant.

CONCLUSION

The ApGltn sealant showed higher bonding strength and equal effect of nerve regeneration when compared with the fibrin sealant.

Fish Gelatin-Based Absorbable Dural Sealant with Anti-inflammatory Properties

Cerebrospinal fluid (CSF) leakage from the dura mater during craniotomy is a common complication, which is associated with infection, meningitis, pneumocephalus, and delayed wound healing. In the present study, we developed an absorbable fish gelatin-based anti-inflammatory sealant for dura mater sealing to prevent CSF leakage. Gelatin derived from Alaska pollock (ApGltn) was modified with α-linolenic acid (ALA), an omega-3 fatty acid that exhibits anti-inflammatory properties, and cross-linked with a poly(ethylene glycol)-based cross-linker to develop ALA-ApGltn sealant (ALA-Seal). ALA-Seal demonstrated a higher storage modulus and tangent delta (tan δ) compared with those of the original ApGltn sealant (Org-Seal). The swelling ratio of ALA-Seal was markedly lower than that of DuraSeal, a commercially available dural sealant. Ex vivo burst strength measurements using porcine dura mater indicated that there was no significant difference between DuraSeal and ALA-Seal, despite ALA-Seal having an order of magnitude lower storage modulus. The anti-inflammatory properties of ALA-Seal, evaluated using brain microglial cells, were considerably higher than those of DuraSeal and Org-Seal, with a minimal adverse effect on cell viability. Therefore, compared to DuraSeal, ALA-Seal is a potential dural sealant with a lower swelling ratio, similar burst strength, and higher anti-inflammatory properties, which may prevent CSF leakage.

Enhanced skin adhesive property of α-cyclodextrin/nonanyl group-modified poly(vinyl alcohol) inclusion complex film

For skin contact medical devices, realizing a strong contact with skin is essential to precisely detect human biological information and enable human-machine interaction. In this study, we aimed to fabricate and characterize an inclusion complex film (ICF) for skin adhesion using α-cyclodextrin (α-CD) and nonanyl group-modified PVA (C9-PVA) under wet conditions. Based on the water insolubility of C9-PVA and the inclusion ability of α-CD for alkyl groups, α-CD/C9-PVA ICF was prepared. Among the prepared ICFs, α-CD/2.5C9-PVA (w/w = 0.5) ICF showed the highest bonding strength and T-peeling strength to porcine skin. Furthermore, α-CD/2.5C9-PVA (w/w = 0.5) ICF had better water vapor transmission rate than that of commercial tapes. In addition, the ion permeability test revealed that α-CD/2.5C9-PVA (w/w = 0.5) ICF exhibited excellent Na and Cl ion permeability. These results demonstrated that the multi-functional α-CD/2.5C9-PVA (w/w = 0.5) ICF can be a promising adhesive for skin contact medical devices.

Efficacy of Alaska pollock gelatin sealant for pulmonary air leakage in porcine models

BACKGROUND

Postoperative prolonged air leakage is a frequent complication following lung resection. We have developed a new sealant based on a hydrophobically modified Alaska pollock-derived gelatin (ApGltn) sealant. The purpose of this study was to evaluate the adhesive strength of the ApGltn sealant in comparison with a fibrin sealant using a new spray system in ex vivo and in vivo models.

METHODS

Pleural defects in ex vivo and in vivo porcine models were created, to which the ApGltn sealant or the fibrin sealant was applied. The pressure resistance was assessed with a stepwise increase in airway pressure to confirm air leakage from the sealing site. Tissue samples covered with each sealant were obtained for histologic assessment.

RESULTS

In the ex vivo experiment, the leak pressures of the ApGltn sealant were significantly greater than those of the fibrin sealant (102.94 ± 15.6 cmH₂O and 28.37 ± 5.1 cmH₂O, respectively) (p < 0.01). In the in vivo experiment, the leak pressures of the ApGltn sealant were also significantly greater than those of the fibrin sealant (68.82 ± 18.04 cmH₂O and 43.33 ± 7.13 cmH₂O, respectively) (p = 0.043). The histologic examination confirmed that the ApGltn sealant adhered tightly to both the pleura and the surface of the pleural defect.

CONCLUSIONS

The ApGltn sealant has sufficiently high adhesive quality in ex vivo and in vivo porcine lungs, which could be considered suitable and effective for use in the prevention of air leakage from the lungs.

Bonding a titanium plate and soft tissue interface by using an adhesive bone paste composed of α-tricalcium phosphate and α-cyclodextrin/nonanyl group-modified poly(vinyl alcohol) inclusion complex

Adhesive bone pastes for dental implants and soft tissue interfaces were developed using α-tricalcium phosphate (α-TCP) and α-cyclodextrin (α-CD)/nonanyl group-modified poly(vinyl alcohol) (C9-PVA) inclusion complex solution (ICS). The thixotropic solution of α-CD/C9-PVA ICS was prepared by mixing α-CD and C9-PVA in deionized water. The α-CD/C9-PVA bone paste led to the highest bonding and shear adhesion between commercial pure titanium plates and soft tissue like collagen casing. Moreover, the compressive strength of these pastes reached 14.1 ± 3.8 MPa within 24 h incubation. Young's modulus of the α-CD/C9-PVA bone paste was lower than that of commercial calcium phosphate paste. Furthermore, the surface of α-CD/C9-PVA bone paste demonstrated excellent cell adhesion for cultured L929 fibroblast cells. Overall, the α-CD/C9-PVA bone paste can likely be effectively used to adhere dental implant abutments and soft tissue interfaces.

Robust closure of post-endoscopic submucosal dissection perforation by microparticle-based wound dressing

Endoscopic submucosal dissection (ESD) has been used as a minimally invasive cancer treatment for early-stage gastrointestinal cancer. However, cancer dissection in thin tissues, such as the duodenum and large intestine, often cause post-ESD and delayed perforation, which elicit severe complications. In this study, we report a microparticle-based wound dressing with hydrophobically-modified gelatin that can close the perforation after ESD. Hydrophobized microparticles were prepared using a coacervation method in a water/ethanol mixed solvent. The optimized alkyl chain length and degree of substitution of hydrophobic groups improved the mechanical strength of the hydrogel formed by hydration and fusion of the microparticles. The hydrogels formed on tissue defects revealed higher burst strength in ex vitro perforation models using duodenum, large intestine, and stomach under wet conditions compared with hydrogels without hydrophobic modification. The particle fusion was determined to be a crucial step to yield a high burst strength. An in vivo degradability evaluation showed that microparticle hydrogels subcutaneously implanted in rats degraded within 14 days. The microparticle wound dressing is expected to be applicable to post-ESD perforation and prevent delayed perforation.

Enhanced skin adhesive property of electrospun α-cyclodextrin/nonanyl group-modified poly(vinyl alcohol) inclusion complex fiber sheet

Many medical tapes on the market lack sufficient adhesive strength and breathability. Owing to its high biocompatibility, poly(vinyl alcohol) (PVA), a synthetic polymer, has attracted attention in the medical field. In this study, we aimed to prepare an inclusion complex fiber (ICFiber) using α-cyclodextrin (α-CD) and nonanyl-group-modified PVA (C9-PVA) for skin adhesion with improved performance. By changing the concentration of α-CD, six microfiber sheets were fabricated by electrospinning the α-CD/2.3C9-PVA inclusion complex solutions. The bonding strength and energy of the ICFiber sheets on the porcine skin were evaluated. Among the tested ICFiber sheets, the ICFiber-3 (molar ratio of α-CD/C9 groups was 0.612) sheet showed high tensile strength and break strain. The bonding strength and energy of ICFiber-3 sheet on porcine skin were 1.10 ± 0.11 N and 5.07 ± 0.94 J m-2, respectively, in the presence of water. In addition, ICFiber-3 sheet showed a better water vapor transmission rate (0.95 ± 0.02 mL per day) than commercial tapes. These results demonstrate that the α-CD/2.3C9-PVA ICFiber sheet is a promising adhesive for wearable medical devices.

Prevention of pulmonary air leaks using a biodegradable tissue-adhesive fiber sheet based on Alaska pollock gelatin modified with decanyl groups

Tissue adhesives have been widely used in surgery to treat pulmonary air leaks. However, conventional adhesives have poor interfacial strength under wet conditions. To overcome this clinical problem, we modified Alaska pollock-derived gelatin to include decanyl (C10) groups (C10-ApGltn) and used electrospinning to create a tissue-adhesive fiber sheet (AdFS). C10-AdFS showed higher burst strength when adhering to porcine pleura compared with a sheet of original ApGltn (Org-ApGltn). Hematoxylin-eosin-stained sections after burst experiments reveal that a dense C10-AdFS layer remained on the surface of the porcine pleura. The effect of the degree of C10 modification of ApGltn on the burst strength was evaluated. ApGltn with a C10 modification ratio of 13 mol% amino groups (13C10-AdFS) exhibited the highest burst strength. Furthermore, from ex vivo experiments with extracted rat lung, 13C10-AdFS exhibited a higher burst strength (41 cm H₂O) than Org-AdFS. The decanyl groups in 13C10-AdFS interacted with the hydrophobic proteins and the lipid bilayers of the cells, resulting in the high interfacial strength between 13C10-AdFS and the pleura. Moreover, 13C10-AdFS samples implanted subcutaneously in the backs of rats were completely degraded within 21 days without any severe inflammation. These results show that 13C10-AdFS is a promising adhesive material for the treatment of pulmonary air leaks.

Evaluation of an octyl group-modified Alaska pollock gelatin-based surgical sealant for prevention of postoperative adhesion

Postoperative adhesion can lead to an increase in the number of surgeries required, longer operation times, and high medical costs, resulting in the quality of life of the patient being lowered. To address these clinical problems, we developed a surgical sealant with anti-adhesion properties for the prevention of postoperative adhesion following application to the large intestine surface. The developed sealant was composed of octyl (C8) group-modified Alaska pollock-derived gelatin (C8-ApGltn) and a poly(ethylene)glycol-based 4-armed crosslinker (4S-PEG) (C8-ApGltn/4S-PEG sealant). Hydrophobic modification of the ApGltn molecule with C8 groups effectively enhanced both the burst strength on the large intestine surface and the bulk modulus. An in vitro anti-adhesion test indicated that cured C8-ApGltn/4S-PEG sealant adhered to the large intestine surface showed low adhesive strength compared with commercial anti-adhesion film. Besides, cured C8-ApGltn/4S-PEG sealant effectively inhibited albumin permeation and penetration of L929 fibroblasts. In vivo experiments using a rat peritoneal anti-adhesion model showed that C8-ApGltn/4S-PEG sealant acted as a sealing barrier on the target cecum surface and also provided an anti-adhesion barrier to prevent postoperative adhesion between the peritoneum and cecum. C8-ApGltn/4S-PEG sealant showed sufficient cytocompatibility and biodegradability and therefore has potential for use in gastroenterological surgery.

Improved tissue adhesion property of a hydrophobically modified Alaska pollock derived gelatin sheet by UV treatment

Tissue adhesives have been developed for sealing tissue damaged in surgery. Among these, sheet-type adhesives require a relatively long time to adhere to biological tissue under wet conditions. To address this clinical problem, we fabricated a tissue-adhesive fiber sheet (AdFS) based on decanyl group (C10) modified Alaska pollock-derived gelatin (C10-ApGltn) using electrospinning. Ultraviolet (UV) irradiation of the AdFS was performed to increase the affinity between the AdFS and wet biological tissue by introducing hydrophilic functional groups. The UV irradiated AdFS (UV-C10-AdFS) strongly adhered to porcine pleura within 2 min under wet conditions and showed higher burst strength compared with the original ApGltn (Org-ApGltn) sheet. Hematoxylin-eosin stained sections revealed that a dense UV-C10-AdFS layer remained on the surface of the porcine pleura even after burst strength measurement. Moreover, UV-C10-AdFS has excellent cytocompatibility and efficiently supports the growth of L929 cells. UV-C10-AdFS is a promising adhesive material for sealing wet biological tissue.

Anti-Inflammatory and Tissue Adhesion Properties of an α-Linolenic Acid-Modified Gelatin-Based In Situ Hydrogel

Poly unsaturated fatty acids (PUFAs)-natural chemicals derived from fish and nuts-have anti-inflammatory and antioxidative properties that are attributed to the inhibition of inflammatory pathways and the radical scavenging activity of their double bonds. In this study, Alaska pollock-derived gelatin (ApGltn), which has a low sol-gel transition temperature, was modified with α-linolenic acid (ALA) to obtain ALA-ApGltn, which was subsequently cross-linked to give a hydrogel (ALA-gel). Although the elastic modulus of ALA-gel and nonmodified ApGltn gel (Org-gel) was almost the same, ALA-gel exhibited a higher tan δ as well as a lower swelling ratio and enzymatic degradation rate than Org-gel. Moreover, ALA-gel showed enhanced tissue adhesive strength compared with a commercial fibrin adhesive. The concentration of a tumor necrosis factor (TNF)-α secreted from macrophage-like cells and the intracellular mitochondrial activity indicated that ALA-ApGltn exerted anti-inflammatory effects and maintained cell viability compared with the higher toxicity nonconjugated ALA. In addition, ALA-gel demonstrated suppressed formation of lamellipodia and secretion of TNF-α. ALA-gel therefore has potential as an adhesive biomaterial for wound sealing and treating burn injuries.

The recent progress of tissue adhesives in design strategies, adhesive mechanism and applications

Tissue adhesives have emerged as an effective method for wound closure and hemostasis in recent decades, due to their ability to bond tissues together, preventing separation from one tissue to another. However, existing tissue adhesives still have several limitations. Tremendous efforts have been invested into developing new tissue adhesives by improving upon existing adhesives through different strategies. Therefore, highlighting and analyzing these design strategies are essential for developing the next generation of advanced adhesives. To this end, we reviewed the available strategies for modifying traditional adhesives (including cyanoacrylate glues, fibrin sealants and BioGlue), as well as design of emerging adhesives (including gelatin sealants, methacrylated sealants and bioinspired adhesives), focusing on their structures, adhesive mechanisms, advantages, limitations, and current applications. The bioinspired adhesives have numerous advantages over traditional adhesives, which will be a wise direction for achieving tissue adhesives with superior properties.

Enhanced Skin Adhesive Property of Hydrophobically Modified Poly(vinyl alcohol) Films

Hydrophobically modified poly(vinyl alcohol) (hm-PVA) films with various alkyl chain lengths were prepared. Their surface/mechanical properties, cytocompatibility, and porcine skin adhesion strength were evaluated. hm-PVAs had 10 °C higher glass transition temperature than poly(vinyl alcohol) (PVA) (33.4 ± 2.5 °C). The water contact angle of the hm-PVA films increased with alkyl chain length and/or hydrophobic group modification ratio. The tensile strength of the hm-PVA films decreased with increasing alkyl chain length and/or hydrophobic group modification ratio. hm-PVA with short chain lengths (4 mol % propanal-modified PVA; 4C3-PVA) had low cytotoxicity compared with long alkyl chain length hm-PVAs (4 mol % hexanal and nonanal-modified PVA; 4C6-PVA and 4C9-PVA). The 4C3-PVA film had the highest porcine skin adhesion strength. Thus, the 4C3-PVA film is promising as an adhesive for wearable medical devices.

Underwater-adhesive microparticle dressing composed of hydrophobically-modified Alaska pollock gelatin for gastrointestinal tract wound healing

Despite the success of minimally-invasive endoscopic submucosal dissection (ESD) for the treatment of early gastrointestinal cancer, additional symptoms after ESD, including contracture, perforation, bleeding, and esophageal stricture remain. Conventional wound dressings were ineffective in preventing stricture because of poor stability of underwater-adhesives on living tissues. Here, we present a microparticle-based wound dressing with underwater adhesive stability for the treatment of gastrointestinal tract wound healing after ESD. Monodisperse microparticles composed of hydrophobically-modified Alaska pollock gelatin were prepared by self-assembly of gelatin in water-ethanol mixed solvents and thermal crosslinking. Hydrophobic modification of gelatin with aliphatic aldehydes increased adhesion strength to gastric and esophageal submucosal tissues through hydrophobic interaction with living tissues and cohesion force. Optimal hydrophobic modification drastically improved underwater stability of microparticles compared to that of non-modified gelatin and formed a thick, integrated hydrogel layer on tissues. Histological observation of rat skin wound healing models showed that hydrophobically-modified gelatin microparticles decreased the expression levels of α-smooth muscle actin in the dermis layer and could suppress fibrosis and inflammation after ESD. The microparticle wound dressing with high underwater-adhesive stability has enormous therapeutic potential to promote wound healing in the gastrointestinal tract and prevent additional symptoms after ESD. STATEMENT OF SIGNIFICANCE: The goal of this study was to develop wound dressing with strong tissue-adhesive property to living tissues for promoting wound healing after ESD treatment. Monodisperse microparticles composed of hydrophobically-modified Alaska pollock gelatin were prepared by self-assembly of gelatin in water-ethanol mixed solvents and thermal crosslinking. Hydrophobic modification of gelatin with aliphatic aldehydes enhanced adhesion strength to gastric and esophageal submucosal tissues through hydrophobic interaction with living tissues and cohesion force. Optimal hydrophobic modification drastically improved underwater stability of microparticles. The in vivo studies were performed to evaluate the ability of this colloidal wound dressing to suppress fibrosis. This new biomaterial has enormous potential to promote wound healing after ESD.

Multifunctional Hydrophobized Microparticles for Accelerated Wound Healing after Endoscopic Submucosal Dissection

Endoscopic submucosal dissection (ESD) provides strong therapeutic benefits for early gastrointestinal cancer as a minimally invasive treatment. However, there is currently no reliable treatment to prevent scar contracture resulting from ESD which may lead to cicatricial stricture. Herein, a multifunctional colloidal wound dressing to promote tissue regeneration after ESD is demonstrated. This sprayable wound dressing, composed of hydrophobized microparticles, exhibits the multifunctionality necessary for wound healing including tissue adhesiveness, blood coagulation, re-epithelialization, angiogenesis, and controlled inflammation based on hydrophobic interaction with biological systems. An in vivo feasibility study using swine gastric ESD models reveals that this colloidal wound dressing suppresses fibrosis and accelerates wound healing. Multifunctional colloidal and sprayable wound dressings have an enormous therapeutic potential for use in a wide range of biomedical applications including accelerated wound healing after ESD, prevention of perforation, and the treatment of inflammatory diseases.

Hemostatic properties of in situ gels composed of hydrophobically modified biopolymers

Hemorrhaging often occurs during cardiac surgery, and postoperative bleeding is associated with medical complications or even death. Medical complications resulting from hemorrhaging can lead to longer hospital stays, thus increasing costs. Hemostatic agents are the main treatment for bleeding. In the present study, hemostatic agents composed of aldehyde groups and hydrophobically modified with hyaluronic acid (ald-hm-HyA) and hydrophobically modified gelatin (hm-ApGltn) were developed and their hemostatic effects were evaluated. These modified hemostatic agents formed more stable blood clots compared with the nonhydrophobically modified HyA-based hemostatic agent. The bulk strength of the whole blood clot using the aldehyde and stearoyl group-modified hyaluronic acid (ald-C18-HyA)/hm-ApGltn-based hemostatic agent was higher than that of the aldehyde group only modified HyA (ald-HyA)/hm-ApGltn-based hemostatic agent. Rheological experiments using α-cyclodextrin showed that hydrophobic modification of HyA with C18 groups effectively enhanced anchoring to the red blood cell surface. Therefore, the ald-hm-HyA/hm-ApGltn-based hemostatic agent has potential applications in cardiac surgery.

Cross-Linking of a Hydrophilic, Antimicrobial Polycation toward a Fast-Swelling, Antimicrobial Superabsorber and Interpenetrating Hydrogel Networks with Long Lasting Antimicrobial Properties

A hemocompatible, antimicrobial 3,4en-ionene (PBI) derived by polyaddition of trans-1,4-dibromo-2-butene and N,N,N',N'-tetramethyl-1,3-propanediamine was cross-linked via its bromine end groups using tris(2-aminoethyl)amine (TREN) to form a fast-swelling, antimicrobial superabsorber. This superabsorber is taking up the 30-fold of its weight in 60 s and the granulated material is taking up 96-fold of its weight forming a hydrogel. It fully prevents growth of the bacterium Staphylococcus aureus. The PBI network was swollen with 2-hydroxyethyl acrylate and glycerol dimethacrylate followed by photopolymerization to form an interpenetrating hydrogel (IPH) with varying PBI content in the range of 2.0 to 7.8 wt %. The nanophasic structure of the IPH was confirmed by atomic force microscopy and transmission electron microscopy. The bacterial cells of the nosocomial strains Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa are killed on the IPH even at the lowest PBI concentration. The antimicrobial activity was retained after washing the hydrogels for up to 4 weeks. The IPHs show minor leaching of PBI far below its antimicrobial active concentration using a new quantitative test for PBI detection in solution. This leaching was shown to be insufficient to form an inhibition zone and killing bacterial cells in the surroundings of the IPH.

Enhanced sealing strength of a hydrophobically-modified Alaska pollock gelatin-based sealant

A novel tissue sealant composed of hydrophobically-modified Alaska pollock gelatin and polyethylene glycol-based crosslinker showed higher sealing effect than commercially available tissue sealant.