Development of a new surgical sheet containing both silk fibroin and thermoplastic polyurethane for cardiovascular surgery.

PURPOSE: The surgical sheets that are currently used for congenital cardiovascular surgery have several drawbacks, including material deterioration, calcification, and pseudo-intimal proliferation resulting in hemodynamic disturbance. The aim of this study was to evaluate a newly developed sheet made from a combination of silk fibroin (SF) and a synthetic polymer, thermoplastic polyurethane (TPU), for surgical use. METHODS: The hybrid SF/TPU sheet was a non-woven fabric with nanofibers that was made using the electrospinning method. The mechanical properties of the SF/TPU sheet were characterized. To determine its biocompatibility, part of the wall of the canine descending aorta was replaced with a SF/TPU sheet as a patch. The patches were removed after 3 months and a histological examination was performed. RESULTS: The flexibility, water permeability, and suture retention strength of the SF/TPU sheet were excellent and equivalent to those of existing sheets. The SF/TPU sheet had excellent handling properties and fit well into the vascular wall without needle hole bleeding. The histological examination revealed that the intimal tissue was restored well over the intraluminal surface of the explanted SF/TPU sheet, the absence of calcium deposition, and minimal inflammatory reaction, without signs of degradation. CONCLUSION: The SF/TPU sheet had excellent mechanical properties and tissue biocompatibility. These favorable features and possible biodegradability of the SF portion warrant a long-term follow-up study.

Silk fibroin-Pellethane® cardiovascular patches: Effect of silk fibroin concentration on vascular remodeling in rat model.

Life-threatening cardiovascular anomalies require surgery for structural repair with cardiovascular patches. The biomaterial patch, derived from Bombyx mori silk fibroin (SF), is used as an alternative material due to its excellent tissue affinity and biocompatibility. However, SF lacks the elastomeric characteristics required for a cardiovascular patch. In order to overcome this shortcoming, we combined the thermoplastic polyurethane, Pellethane® (PU) with SF to develop an elastic biocompatible patch. Therefore, the purpose of this study was to investigate the feasibility of the blended SF/PU patch in a vascular model. Additionally, we focused on the effects of different SF concentrations in the SF/PU patch on its biological and physical properties. Three patches of different compositions (SF, SF7PU3 and SF4PU6) were created using an electrospinning method. Each patch type (n = 18) was implanted into rat abdominal aorta and histopathology was assessed at 1, 3, and 6 months post-implantation. The results showed that with increasing SF content the tensile strength and elasticity decreased. Histological evaluation revealed that inflammation gradually decreased in the SF7PU3 and SF patches throughout the study period. At 6 months post-implantation, the SF7PU3 patch demonstrated progressive remodeling, including significantly higher tissue infiltration, elastogenesis and endothelialization compared with SF4PU6. In conclusion, an increase of SF concentration in the SF/PU patch had effects on vascular remodeling and physical properties. Moreover, our blended patch might be an attractive alternative material that could induce the growth of a neo-artery composed of tissue present in native artery.

Biological reaction to small-diameter vascular grafts made of silk fibroin implanted in the abdominal aortae of rats.

BACKGROUND: Bombyx mori silk fibroin (SF) is biocompatible and degradable and has been proposed as a new material for small-diameter vascular grafts. We compared biological reactions to vascular grafts made of SF and polyethylene terephthalate (PET) to reveal the potential ability of SF as a base and/or coating materials for vascular prostheses. METHODS: SF was combined with PET or gelatin (G) to make 4 types of vascular grafts (SF/SF, SF/G, PET/SF, and PET/G, shown as "base/coating material," respectively), which are 1.5 mm in diameter and 10 mm in length. The 4 types of grafts (n = 6, respectively) were implanted into rat abdominal aortae and explanted 2 weeks or 3 months later. RESULTS: Two weeks after implantation, there are no significant differences among the 4 kinds of grafts in biological reactions evaluated by histopathologic examination. However, a remarkable difference was observed after 3 months. The area of tissue infiltration into the inside of the graft wall was approximately 2.5 times larger in SF/SF than that in PET/G. The endothelialization was achieved almost 100% in SF/SF, despite only 50% was achieved in PET/G. CONCLUSIONS: Results show that SF has a higher potential as a base of vascular grafts than the commercially available PET/G graft. The larger tissue infiltration area in PET/SF compared with that in PET/G also indicates the potential of SF as a coating material. In the present study, SF delivered promising results as base and coating materials for small-diameter vascular prostheses.

Effect of experimental periodontitis on cardiac functions: a comprehensive study using echocardiography, hemodynamic analysis, and histopathological evaluation in a rat model.

Introduction: Periodontitis is a prevalent and severe dental condition characterized by the gradual degradation of the bone surrounding the teeth. Over the past two decades, numerous epidemiological investigations have suggested a potential link between periodontitis and cardiovascular disease. However, the complex mechanistic relationship between oral health issues and cardiovascular disorders remains unclear. Aim: This study aimed to explore comprehensively the cardiac function through various methods, including conventional echocardiography, intraventricular pressure gradient (IVPG) analysis, speckle tracking echocardiography (STE), and hemodynamics analysis. Methods: Ligature-induced periodontitis was established in a group of rats while the second group served as sham. The successful establishment of the periodontitis model was confirmed through staining and radiographic examination of the affected mandibles. Results: X-ray films and methylene blue staining revealed alveolar bone resorption in the affected first molar in the model rats, confirming the successful induction of periodontitis. The rats with periodontitis displayed a decrease in ejection fraction compared to the sham group, accompanied by a decrease in mid-to-apical IVPG and mid IVPG. Lower values of strain rate were recorded in the apical segment of the septum, the middle segment of the septum, and the basal segment of the lateral free wall in the periodontitis group, which was associated with histopathological examination showing some degree of myocardial tissue damage. Conversely, rats with periodontitis showed an increase in heart rate, end-systolic volume, and arterial elastance when compared to the sham rats. However, they also exhibited a decrease in stroke work, stroke volume, cardiac output, and end-systolic pressure. Conclusion: This study suggests that experimental periodontitis may lead to cardiac dysfunction especially compromised systolic function and myocardial relaxation, potentially indicating an increased risk of cardiovascular events in clinical periodontitis cases. The comprehensive assessment of cardiac function, hemodynamics, and histopathological evaluation underscores the profound impact of periodontitis on heart functions within this specific experimental model.

A novel gradient and multilayered sheet with a silk fibroin/polyvinyl alcohol core-shell structure for bioabsorbable arterial grafts.

Bioabsorbable arterial grafts can potentially improve patency and neovessel formation; however, their application in clinical settings has not been realized. In this study, we developed bioabsorbable gradient sheets based on silk fibroin (SF) and polyvinyl alcohol (PVA) with a core-shell nanofibrous structure. This gradient sheet was expected to promote vascular remodeling while we maintained its physical properties and a gradual degrading process from the luminal surface. ESP was conducted at various flow rates for SF and PVA to achieve the multilayer gradient structure. Furthermore, the elasticity of the gradient sheet could be increased by increasing the PVA flow rate; however, this reduced the tensile strength of the core-shell fibers. Notably, the physical properties of the gradient sheet did not degrade even after 7 days of immersion in a phosphate buffer saline solution, which indicates that the structure could maintain its structural integrity while resisting arterial pressure. In vitro experiments revealed that the number of endothelial cells attached to the SF/PVA sheet was notably higher than that on the cell-culture dish. The gradient sheets were implanted in rat abdominal aortas and explanted after 14 days to confirm acute-phase patency and vascular remodeling. The gradient sheets constructed with SF composed of polyurethane and PVA improved the ease of handling of the material, and these sheets resulted in a favorable vascular remodeling outcome. Our results strongly suggest that the SF/PVA-based gradient sheets described in this study can serve as a novel design for bioabsorbable arterial grafts upon further modifications.

The Pivotal Role of Stem Cells in Veterinary Regenerative Medicine and Tissue Engineering.

The introduction of new regenerative therapeutic modalities in the veterinary practice has recently picked up a lot of interest. Stem cells are undifferentiated cells with a high capacity to self-renew and develop into tissue cells with specific roles. Hence, they are an effective therapeutic option to ameliorate the ability of the body to repair and engineer damaged tissues. Currently, based on their facile isolation and culture procedures and the absence of ethical concerns with their use, mesenchymal stem cells (MSCs) are the most promising stem cell type for therapeutic applications. They are becoming more and more well-known in veterinary medicine because of their exceptional immunomodulatory capabilities. However, their implementation on the clinical scale is still challenging. These limitations to their use in diverse affections in different animals drive the advancement of these therapies. In the present article, we discuss the ability of MSCs as a potent therapeutic modality for the engineering of different animals' tissues including the heart, skin, digestive system (mouth, teeth, gastrointestinal tract, and liver), musculoskeletal system (tendons, ligaments, joints, muscles, and nerves), kidneys, respiratory system, and eyes based on the existing knowledge. Moreover, we highlighted the promises of the implementation of MSCs in clinical use in veterinary practice.

Silk fibroin-based vascular repairing sheet with angiogenic-promoting activity of SVVYGLR peptide regenerated the damaged vascular in rats.

Medical sheets are useful in surgically repair vascular disease. To avoid long-term side effects, they are to be replaced with regenerated tissue after implantation. Silk fibroin is a fibrous protein secreted by silkworm. The advantage of silk fibroin is its biocompatibility and has been used as regenerative artificial materials. The problem of its biodegradability is that the effect is time consuming. In this study, SVVYGLR peptide was used to expect promoting cell migration and accelerating the biodegradation of silk fibroin. Silk fibroin and polyurethane-based medical sheets with or without SVVYGLR peptide were implanted in rat abdominal aorta (silk fibroin/polyurethane/SVVYGLR peptide versus silk fibroin/polyurethane). The result of histological evaluation indicated that the new cell layer created under both sheets was composed of endothelial cells, smooth muscle, and fibroin in both sheets and similar to a native vessel. Both sheets did not show any excessive inflammation or calcification, and moderate biodegradability was observed. The decrease of silk fibroin indicated the biodegradability of all sheets. Silk fibroin/polyurethane/SVVYGLR peptide had many small vessels in the regenerated tissue than silk fibroin/polyurethane. This appearance indicated that SVVYGLR peptide promoted the angiogenesis in the regenerative tissue. This study suggested that SVVYGLR peptide could give the angiogenic-promoting activity to silk fibroin-based vascular repairing sheet.

Silk fibroin/polyurethane patch implantation in hyperglycemic rat model.

PURPOSE: To understand the complication and histopathological characteristics between the Silk Fibroin/Polyurethanes (SF/PU) and the host response, and to unveil the compatibility of the patch in diabetes individuals. METHODS: Rats were divided into DM and control (CT) groups, and the DM group was induced with streptozotocin. All groups underwent the SF/PU patch implantation in the abdominal aorta, and the implanted patches were evaluated at one, two, three, and four weeks after implantation. RESULTS: DM group had more fibrosis formation and a delayed endothelialization compared to the CT group. There was no evidence of chronic inflammation in both DM and CT groups. CONCLUSIONS: Fibrosis in hyperglycemic individuals could promote the formation of new vascular structures in the implanted patch such as endothelial and vascular smooth muscle cells. In summary, the SF/PU patch was no serious complications when implanted under hyperglycemia, and the patch was suitable to implant in diabetes mellitus.

Intrathoracic retention of insoluble hyaluronic acid and its absorption process in rats.

BACKGROUND: Post-thoracotomy adhesions are frequent postoperative complications. It has been reported that insoluble hyaluronic acid may prevent adhesions. MATERIALS AND METHODS: This study had two objectives: first, to determine the in vivo degradation and absorption process, as well as the intrathoracic retention, of solid insoluble hyaluronic acid membrane; and second, to elucidate the association between postoperative intrathoracic retention and the morphological changes of insoluble hyaluronic acid in 12 Wistar rats. Insoluble hyaluronic acid membranes were cut into 2.0 cm × 1.0 cm rectangles in a dry state. After weighing, the test membranes were soaked and washed with saline to be implanted after pericardiotomy via thoracotomy. At Days 4, 7, 10, 14, and 28 after implantation, the rats were euthanized, the chest was opened, and the condition and implantation site of the inserted test membrane were examined. RESULTS: Although approximately 10 days were required for the test membrane to decrease to half in the thoracic cavity, the intrathoracic remnant decreased to a mean of ~2% just 4 days later. CONCLUSION: This study clarified the time-dependent degradation process and remnants of insoluble hyaluronic acid in the thoracic cavity. A close relationship between the intrathoracic remnant of insoluble hyaluronic acid and its morphological change associated with degradation was demonstrated.

Basic study on improvement of plastic drape adhesion for surgery: effect of adhesive layer thickness on drape detachment from wound edge.

BACKGROUND: Plastic drapes are used in surgery for a wide range of purposes, but currently marketed drapes often become detached from the wound edge during surgery. The purpose of this study was to determine the appropriate adhesive layer thickness for optimal peel and shear strength and the smallest peeled area to improve surgical drape wound adhesion. METHODS: Thirty-two rats were randomly assigned to four groups of different adhesive layer thickness (50, 100, 300 and 800-1000 µm). The rats were anaesthetized, and drapes were applied to the dorsal chest. After incision, the peeled area was visualized by dropping ink in the wound site to measure the peeled area over time. RESULTS: All drapes peeled off from the wound edge, and the peeled area increased over time. The peeled area decreased in the order of 50 µm > 100 µm > 800-1000 µm > 300 µm. CONCLUSIONS: It is possible to control the peeling of plastic drapes during surgery by limiting the peeled area at the time of cutting. Three-hundred micrometres is the suitable adhesive layer thickness to minimize the peeled area at cutting.

The effect of a silk Fibroin/Polyurethane blend patch on rat Vessels.

Patch grafts are widely used in various kind of vascular surgeries such as detect repair or dilation of vascular stenosis. Expanded polytetrafluoroethylene (ePTFE) patches are flexible and handle well, but have shown problems with calcification as they are non-bioabsorbable and therefore permanently remain in the body. It is important to develop an alternative biocompatible patch. Silk fibroin (SF) was developed as a biocompatible material, but it lacks of the elasticity required for surgery as a patch. Polyurethane (PU) is also a well-known elastomer so this study focused on the SF and the PU blend materials with a weight ratio of 5:5 (SF/PU). To evaluate the SF/PU patch, the patches were implanted into the abdominal aortas of rats, using the ePTFE patch in the control group. Because it was more flexible the SF/PU patch was easier to implant than the ePTFE patch. At 1 week after implantation, the SF/PU patch had been infiltrated with cells and collagen fiber. The ePTFE control patch did not accumulate collagen fiber until 3 months and calcification occurred at 4 weeks. The SF/PU patch did not present any signs of calcification for 3 months. This study addressed the problems associated with using SF in isolation and showed that the SF/PU patch can be considered as a useful alternative to the ePTFE to overcome the problem of calcification.

An experimental study of apico-aortic valved conduit (AAVC) for surgical treatment of aortic stenosis in dogs.

A new valved conduit was developed using a canine aortic valve. The bioprosthetic valve was fixed with glutaraldehyde and epoxy compound (Denacol-EX313/810). A vascular graft composed of ultra-fine polyester fiber (10 mm in diameter, 200 mm in length) was used. Four dogs underwent apico-aortic valved conduit (AAVC) implantation and aortic banding (bypass group, BG), while another 4 dogs underwent aortic banding without AAVC implantation (control group, CG). Cardiac catheterization and angiocardiography were performed for assessment of hemodynamics 2 weeks and 6 months after surgery. Left ventricular systolic pressure, left ventricular end-diastolic pressure and the left ventricular-aortic pressure gradient differed significantly (P<0.01) between the BG and CG dogs. Left ventricular angiocardiography showed patency of the valved conduit in all the BG dogs. Echocardiography was performed before and 2, 4 and 6 months after surgery, and showed that while pressure overload caused concentric myocardial hypertrophy in the CG dogs, the left ventricle dilated eccentrically in the BG dogs. Furthermore, relief of left ventricular pressure overload by AAVC was maintained.

Effect of fibroin sponge coating on in vivo performance of knitted silk small diameter vascular grafts.

Vascular grafts under 5 mm or less in diameter are not developed due to a problem caused by early thrombus formation, neointimal hyperplasia, etc. Bombyx mori silk fibroin (SF) which has biodegradability and tissue infiltration is focused as tube and coating material of vascular grafts. Coating is an important factor to maintain the strength of the anastomotic region of vascular grafts, and to prevent the blood leak from the vascular grafts after implantation. Therefore, in this research, we focused on the SF concentration of the coating solution, and tissue infiltration and remodeling were compared among each SF concentration. Silk poly (-ethylene) glycol diglycidyl ether (PGDE) coating with concentrations of 1.0%, 2.5%, 5.0%, and 7.5% SF were applied for the double-raschel knitted small-sized vessel with 1.5 mm diameter and 1cm in length. The grafts were implanted in the rat abdominal aorta and removed after 3 weeks or 3 months. Vascular grafts patency was monitored by ultrasound, and morphological evaluation was performed by histopathological examination. SF concentration had no significant effects on the patency rate. However, tissue infiltration was significantly higher in the sample of 2.5% SF in 3 weeks, and 1.0% and 2.5% SF in 3 months. Also, in comparison of length inside of the graft, stenosis were not found in 3 weeks, however, found with 5.0% and 7.5% in 3 months. From these results, it is clear that 2.5% SF coating is the most suitable concentration, based on the characteristics of less stenosis, early tissue infiltration, and less neointimal hyperplasia.

A long term comparison between Denacol EX-313-treated bovine jugular vein graft and ultrafine polyester fiber graft for reconstruction of tight ventricular outflow tract in dogs.

A Denacol EX-313 (Denacol)-treated bovine venous graft and an ultrafine polyester fiber (UFPF) graft were transplanted as patch graft into the right ventricular outflow tract under extracorporeal circulation in six dogs each experimentally. Hemodynamics in right heart and histological findings around the graft were compared between both groups over a period of one year after grafting. Pressure measurements and angiocardiography were performed through a cardiac catheter. Right ventricular pressure, pulmonary artery pessure, and right ventricle to pulmonary artery gradient were within normal limits in both groups at 1, 2, 3, 4, 6, and 12 months or more after grafting. No difference were seen between the values for the Denacol and the UFPF group. Histologically, the medial surface at the site of grafting was covered with vascular endothelial cells at one month after grafting in both groups. The density of the vascular endothelial cells increased with time after grafting, showing no clear difference between the two groups. Subendothelial layers comprised of collagen fibers, elastic fibers, and inflammatory cells decreased with time in both groups, but there was less cell infiltration in the Denacol group than in the UFPF group at all time points after grafting. In addition, the central cut thickness value of the graft tended to be thinner in the Denacol group than in the UFPF group at all observation time points after grafting. In the Denacol group, very slight metaplasia of cartilage was noted in a portion of the graft margin at six months or more after grafting, but no other abnormalities were observed. These results suggest that the Denacol-treated bovine venous graft has better grafting characteristics than the UFPF graft with easier intra-operative handlings and less tissue reactions after grafting.

Small-diameter silk vascular grafts (3 mm diameter) with a double-raschel knitted silk tube coated with silk fibroin sponge.

Small-diameter (less than 6 mm in diameter) vascular grafts are highly desirable due to the large demand for surgical revascularization; however, there are no available artificial grafts. Vascular grafts of 1.5 mm diameter prepared by our group with silk fibroin fiber have been proved to be excellent grafts with remarkably high patency and remodeling, based on rat implantation experiment (Enomoto et al., 2010). In this study, a silk fibroin vascular graft with 3 mm diameter which can be used for the coronary arteries or lower extremity arteries is prepared with a double-raschel knitted Bombyx mori silk fiber tube coated with B. mori silk fibroin sponge. Here the silk sponge is prepared from an aqueous solution of the silk fibroin and poly(ethylene) glycol diglycidyl ether as porogen. Sufficient strength, proper elasticity, and protection from loose ends in the implantation process are obtained for the silk fibroin graft; low water permeability and relatively large compliance are also attained. These excellent physical properties make silk fibroin grafts suitable to be implanted in a canine model.