Tissue-Adhesive Paint of Silk Microparticles for Articular Surface Cartilage Regeneration

Current biomaterials and tissue engineering techniques have shown a promising efficacy on full-thickness articular cartilage defect repair in clinical practice. However, due to the difficulty of implanting biomaterials or tissue engineering constructs into a partial-thickness cartilage defect, it remains a challenge to provide a satisfactory cure in joint surface regeneration in the early and middle stages of osteoarthritis. In this study, we focused on a ready-to-use tissue-adhesive joint surface paint (JS-Paint) capable of promoting and enhancing articular surface cartilage regeneration. The JS-Paint is mainly composed of N-(2-aminoethyl)-4-(4-(hydroxymethyl)-2-methoxy-5-nitrosophenoxy) butanamide (NB)-coated silk fibroin microparticles and possess optimal cell adhesion, migration, and proliferation properties. NB-modified silk fibroin microparticles can directly adhere to the cartilage and form a smooth layer on the surface via the photogenerated aldehyde group of NB reacting with the -NH₂ groups of the cartilage tissue. JS-Paint treatment showed a significant promotion of cartilage regeneration and restored the smooth joint surface at 6 weeks postsurgery in a rabbit model of a partial-thickness cartilage defect. These findings revealed that silk fibroin can be utilized to bring about a tissue-adhesive paint. Thus, the JS-Paint strategy has some great potential to enhance joint surface regeneration and revolutionize future therapeutics of early and middle stages of osteoarthritis joint ailments.

Temperature/near-infrared light-responsive conductive hydrogels for controlled drug release and real-time monitoring

Stimuli-responsive hydrogels with adaptable physical properties show great potential in the biomedical field. In particular, the collection of electrical signals is essential for precision medicine. Here, a simple strategy is demonstrated for achieving controlled drug release and real-time monitoring using an interpenetrating binary network consisting of a graphene aerogel and a poly(N-isopropylacrylamide) hydrogel with incorporated polydopamine nanoparticles (PDA-NPs). Owing to the good physical properties of graphene and the embedded PDA-NPs, the hybrid hydrogel shows enhanced mechanical properties and good electrical conductivity. In addition, the hybrid hydrogel also shows dual thermo- and near-infrared light responsiveness, as revealed by the controlled release of a model drug. In addition, as the hydrogel exhibits detectable changes in resistance during drug release, the drug-release behavior of the hydrogel can be monitored in real time using electrical signals. Moreover, owing to the abundance of catechol groups on the PDA-NPs, the hybrid hydrogel shows good tissue adhesiveness, as demonstrated using in vivo experiments. Thus, the developed hybrid hydrogel exhibits considerable practical applicability for drug delivery and precision medicine.

In situ polymerizable polyethyleneglycol containing polyesterpolyol acrylates for tissue sealant applications

Polyesterpolyol macromers were prepared with succinic acid and polyethylene glycols (PEG) of different molecular weights. The resulting polyols were acrylated to render them photo-cross-linkable. They could be very rapidly cross-linked into non-tacky films with long-wavelength UV radiation. The resulting products were characterized by gel content, water equilibrium swell, cross-link density, Tg , tensile strength, degradation and in vitro burst strengths. Though all of them formed transparent contact lens like films, increasing the PEG molecular weight has resulted in polymers with higher hydrophilicity resulting in higher swelling, faster degradation, higher tensile strength, elongation at break and burst strength. Addition of vinyl pyrrolidinone as a reactive diluent has increased the mechanical as well as burst strength of the polymer. In vitro release of sulfamethoxazole entrapped in these cross-linked matrices was also studied.

Novel visible-light-induced photocurable tissue adhesive composed of multiply styrene-derivatized gelatin and poly(ethylene glycol) diacrylate

A novel photocurable tissue adhesive glue, which is composed of styrene-derivatized (styrenated) gelatin, poly(ethylene glycol) diacrylate (PEGDA), and carboxylated camphorquinone in phosphate-buffered saline (PBS), was prepared. The prototype formulation suitable for arterial repair was determined based on the gel yield, degree of swelling, tissue adhesive strength, and breaking (or burst) strength in vitro. The formulated photocurable tissue adhesive glue with an appropriate viscosity was converted to a water-swollen gel within 1 min of visible light irradiation. The tissue adhesive glue, which was coated on a rat abdominal aorta incised with a pair of scissors, was immediately converted to a swollen gel upon subsequent irradiation with visible light, and concomitantly hemostasis was completed. Histological examination showed that the produced gel was tightly adhered to the artery shortly after photoirradiation. The gel gradually degraded with time and was completely absorbed within 4 weeks after treatment. These results indicate that the photocurable glue developed here may serve as a tissue adhesive glue applicable to vascular surgery.

Absorption properties of alternative chromophores for use in laser tissue soldering applications

The feasibility of using alternative chromophores in laser tissue soldering applications was explored. Two commonly used chromophores, indocyanine green (ICG), and methylene blue (MB) were investigated, as well as three different food colorings: red #40 (RFC), blue #1 (BFC), and green consisting of yellow #5 and blue #1 (GFC). Three experimental studies were conducted: (i) The absorption profiles of the five chromophores, when diluted in deionized water and when bound to protein, were recorded; (ii) the effect of accumulated thermal dosages on the absorption profile of the chromophores was evaluated; and (iii) the stability of the absorption profiles of the chromophore-doped solutions when exposed to ambient light for extended time periods was measured. The peak absorption wavelengths of ICG, MB, RFC, and BFC, were found to be 805 nm, 665 nm, 503 nm, and 630 nm respectively in protein solder. The GFC had two absorption peaks at 426 nm and 630 nm, corresponding to the two dye components comprising this color. The peak absorption wavelength of ICG and MB was dependent on the choice of solvent (deionized water or protein). In contrast, the peak absorption wavelengths of the three chromophores were not dependent on the choice of solvent. ICG and MB showed a significant decrease in absorbance units with increased time and temperature when heated to temperature up to 100 degrees C. A significant decrease in the absorption peak occurred in the ICG and MB samples when exposed to ambient light for a period of 7 days. Negligible change in absorption with accumulated thermal dose up to 100 degrees C or light dose (over a period of 84 days) was observed for any of the three food colorings investigated.

Effect of varying chromophores used in light-activated protein solders on tensile strength and thermal damage profile of repairs

Clinical adoption of laser tissue welding (LTW) techniques has been beleaguered by problems associated with thermal damage of tissue and insufficient strength of the resulting tissue bond. The magnitude of these problems has been significantly reduced with the incorporation of indocyanine green (ICG)-doped protein solders into the LTW procedure to form a new technique known as laser tissue soldering (LTS). With the addition of ICG, a secondary concern has arisen relating to the potential harmful effects of the degradation products of the chromophore upon thermal denaturation of the protein solder with a laser. In this study, two different food colorings were investigated, including blue #1 and green consisting of yellow #5 and blue #1, as alternative chromophores for use in LTS techniques. Food coloring has been found to have a suitable stability and safety profile for enteral use when heated to temperatures above 200 degrees C; thus, it is a promising candidate chromophore for LTS which typically requires temperatures between 50 degrees C and 100 degrees C. Experimental investigations were conducted to test the tensile strength of ex vivo repairs formed using solders doped with these alternative chromophores in a bovine model. Two commonly used chromophores, ICG and methylene blue (MB), were investigated as a reference. In addition, the temperature rise, depth of thermal coagulation in the protein solder, and the extent of thermal damage in the surrounding tissue were measured. Temperature rise at the solder/tissue interface, and consequently the degree of solder coagulation and collateral tissue thermal damage, was directly related to the penetration depth of laser light in the protein solder. Variation of the chromophore concentration such that the laser light penetrated to a depth approximately equal to half the thickness of the solder resulted in uniform results between each group of chromophores investigated. Optimal tensile strength of repairs was achieved by optimizing laser and solder parameters to obtain a temperature of approximately 65 degrees C at the solder/tissue interface. The two alternative chromophores tested in this study show considerable promise for application in LTS techniques, with equivalent tensile strength to solders doped with ICG or MB, and the potential advantage of eliminating the risks associated with harmful byproducts.

Optimal parameters for arterial repair using light-activated surgical adhesives

The clinical acceptance of laser-tissue repair techniques is dependent on the reproducibility of viable repairs. Reproducibility is dependent on two factors: (i) the choice of materials to be used as the adhesive; and (ii) obtaining temperatures high enough to cause protein denaturation at the vital tissue interface without causing excessive thermal damage to the surrounding tissue. The use of a polymer scaffold as a carrier for the protein solder provides for uniform application of the solder to the tissue, thus allowing for pre-selection of optimal laser parameters. The scaffold also facilitates precise tissue alignment and ease of clinical application. In addition, the scaffold can be doped with various pharmaceuticals such as hemostatic and thrombogenic agents to aid wound healing. An ex vivo study was performed to correlate solder and tissue temperature with the tensile strength of arterial repairs formed using scaffold-enhanced light-activated surgical adhesives. Previous studies by our group using solid protein solder without the scaffold indicate that a solder/tissue, interface temperature of 65 degrees C is optimal. Using this parameter as a benchmark, laser irradiance was varied and temperatures were recorded at the surface and at the tissue interface of scaffold-enhanced protein solder using an infrared temperature monitoring system, designed by the researchers, and a type-K thermocouple, respectively.

The study of a light-activated albumin protein solder to bond layers of porcine small intestinal submucosa

This study investigated the feasibility of bonding layers of porcine small intestinal submucosa (SIS, Cook Biotech, Inc.) with a light-activated protein solder. SIS is an acellular, collagen-based extracellular matrix material that is approximately 100 microns thick. The solder consists of bovine serum albumin and indocyanine green dye (ICG) in deionized water. The solder is activated by an 808 nm diode laser, which denatures the albumin, causing the albumin to bond with the collagen of the tissue. The predictable absorption and thermal energy diffusion rates of ICG increase the chances of reproducible results. To determine the optimal condition for laser soldering SIS, the following parameters were varied: albumin concentration (from 30-45% (w/v) in increments of 5%), the concentration of ICG (from 0.5-2.0 mg/ml H2O) and the irradiance of the laser (10-64 W/cm2). While many of the solder compositions and laser irradiance combinations resulted in no bonding, a solder composition of 45% albumin, ICG concentration of 0.5 mg/ml H2O, and a laser irradiance of 21 W/cm2 did produce a bond between two pieces of SIS. The average shear strength of this bond was 29.5 +/- 17.1 kPa (n = 14). This compares favorably to our previous work using fibrin glue as an adhesive, in which the average shear strength was 27 +/- 15.8 kPa (n = 40).

Improved vascular tissue fusion using new light-activated surgical adhesive on a canine model

Newly developed light-activated surgical adhesives have been investigated as a substitute to traditional protein solders for vascular tissue fusion without the need for sutures. Canine femoral arteries (n = 14), femoral veins (n = 14), and carotid arteries (n = 10) were exposed, and a 0.3-0.6 cm longitudinal incision was made in the vessel walls. The surgical adhesive, composed of a poly(L-lactic-co-glycolic acid) scaffold doped with the traditional protein solder mix of bovine serum albumin and indocyanine green dye, was used to close the incisions in conjunction with an 805 nm diode laser. Blood flow was restored to the vessels immediately after the procedure and the incision sites were checked for patency. The new adhesives were flexible enough to be wrapped around the vessels while their solid nature avoided the problems associated with "runaway" of the less viscous liquid protein solders widely used by researchers. Assessment parameters included measurement of the ex vivo intraluminal bursting pressure 1-2 h after surgery, as well as histology. The acute intraluminal bursting pressures were significantly higher in the laser-solder group (>300 mmHg) compared to the suture control group (<150 mmHg) where four evenly spaced sutures were used to repair the vessel (n = 4). Histological analysis showed negligible evidence of collateral thermal damage to the underlying tissue in the laser-solder repair group. These initial results indicated that laser-assisted vascular repair using the new adhesives is safe, easy to perform, and contrary to conventional suturing, provides an immediate leak-free closure. In addition, the flexible and moldable nature of the new adhesives should allow them to be tailored to a wide range of tissue geometries, thus greatly improving the clinical applicability of laser-assisted tissue repair.

Solubility study of albumin solders for laser tissue-welding

BACKGROUND/OBJECTIVE

Current albumin solders for tissue-welding are soluble in physiological fluids, prior to laser irradiation. These solders are therefore subjected to mechanical alterations, which can weaken the solder-tissue repair. In this study, an albumin solder (laser activated) was developed with low solubility and with the ability to retain (partially) its mechanical characteristics in saline solution.

STUDY DESIGN/MATERIALS AND METHODS

Gauged protein samples of solder were immersed into 0.5 ml saline solution for fixed intervals of time. The solder samples contained four bovine serum albumin (BSA) concentrations: 56%, 66%, 70%, and 75% (by weight). A Bradford protein assay measured the BSA solubility of the solders. The 70% and 75% BSA solders were also used to weld in vitro Wistar rat intestine sections with a diode laser (lambda = 810 nm, power = 270 mW).

RESULTS

The solubility of the 75% BSA solder was significantly decreased with respect to the other solders (Anova, P < 0.05). This solder also showed comparable weld strength (13 gm) to the 70% BSA solder.

CONCLUSION

The 75% BSA solder strongly reduced the albumin solubility in saline solution, without affecting its tissue-welding properties.

Photocurable surgical tissue adhesive glues composed of photoreactive gelatin and poly(ethylene glycol) diacrylate

This article presents a novel photochemically driven surgical tissue adhesive technology using photoreactive gelatins and a water-soluble difunctional macromer (poly(ethylene glycol) diacrylate: PEGDA).The gelatins were partially derivatized with photoreactive groups, such as ultraviolet light (UV)-reactive benzophenone and visible light-reactive xanthene dye (e.g., fluorescein sodium salt, eosin Y, and rose bengal). A series of the prepared photocurable tissue adhesive glues, consisting of the photoreactive gelatin, PEGDA, and a saline solution with or without ascorbic acid as a reducing agent, were viscous solutions under warming, and their effectiveness was evaluated as hemostasis- and anastomosis-aid in cardiovascular surgery. Regardless of the type of photoreactive groups, the irradiation of the photocurable tissue adhesive glues by UV or visible light within 1 min produced water-swollen gels, which had a high adhesive strength to wet collagen film. These were due to the synergistic action of photoreactive group-initiated photo-cross-linking and photograft polymerization. An increase in the irradiation time resulted in increased gel yield and reduced water swellability. A decrease in the molecular weight of PEGDA and an increase in concentration of both gelatin and PEGDA resulted in reduced water swellability and increased tensile and burst strengths of the resultant gels. In rats whose livers were injured with a trephine in laparotomy, the bleeding spots were coated with the photocurable adhesive glue and irradiated through an optical fiber. The coated solution was immediately converted to a swollen gel. The gel was tightly adhered to the liver tissue presumably by interpenetration, and concomitantly hemostasis was completed. The anastomosis treatment with the photocurable glue in the canine abdominal or thoracic aortas incised with a knife resulted in little bleeding under pulsatile flow after declamping. Histological examination showed that the glues photocured on rat liver surfaces were gradually degraded with time in vivo with infiltration of inflammatory cells and connective tissues without necrotic sign in surrounding tissue. In addition, in the laparoscopic surgery, percutaneous delivery of the glue and its in situ photogelation on rat liver surfaces were demonstrated using a specially designed fiberscope. These results indicate that the photocurable glues developed here may serve as a biodegradable tissue adhesive glue usable in cardiovascular surgery and endoscopic surgery.

Newly designed hemostatic technology based on photocurable gelatin

In this article, the authors present a novel photochemically driven hemostatic technology using photocurable gelatins partially derivatized with photoreactive xanthene dyes (fluorescein, eosin, and rose bengal) and a hydrophilic difunctional macromer. The developed hemostatic glue consisted of dye derivatized gelatin (20 wt%), poly(ethylene glycol) diacrylate (10 wt%), and ascorbid acid (0.3 wt%), all of which were dissolved in a saline solution. Irradiation of the hemostatic glue by visible light produced a swollen gel within a few tenths of a second due to dye sensitized photo-crosslinking and photograft polymerization. An increase in irradiation time resulted in an increased gel yield and reduced water swellability. A rat liver injured on laparotomy was coated with the hemostatic glue. Upon visible light irradiation through an optical fiber, the coated viscous solution was immediately converted to a swollen gel and, concomitantly, hemostasis was completed. Histologic examination showed that, at 7 days after surgery, little gelatin remained in the injured region, scarring with little necrosis occurred, and inflammatory cells infiltrated from the surrounding tissue and tissue regeneration proceeded well. During laparoscopic surgery, in situ gelation of the hemostatic glue on the liver surface was demonstrated using a specially designed fiberscope.