Alginate (Alg) and bacterial nanocellulose (BNC) have exhibited great potential in biomedical applications, especially wound dressing. Non-toxicity and a moisture-maintaining nature are common ...features making them favorable for functional dressing fabrication. BNC is a natural biopolymer that promotes major advances to the current and future biomedical materials, especially in a flat or tubular membrane form with excellent mechanical strength at hydrated state. The main drawback limiting wide applications of both BNC and Alg is the lack of antibacterial activity, furthermore, the inherent poor mechanical property of Alg leads to the requirement of a secondary dressing in clinical treatment. To fabricate composite dressings with antibacterial activity and better mechanical properties, sodium alginate was efficiently incorporated into the BNC matrix using a time-saving vacuum suction method followed by cross-linking through immersion in separate solutions of six cations (manganese, cobalt, copper, zinc, silver, and cerium). The results showed the fabricated composites had not only pH-responsive antibacterial activities but also improved mechanical properties, which are capable of acting as smart dressings. All composites showed non-toxicity toward fibroblast cells. Rat model evaluation showed the skin wounds covered by the dressings healed faster than by BNC.
•Mercerization successfully controlled the dimensions of native BNC conduits.•Superior mechanical properties of BNC conduits were achieved via mercerization.•Mercerized BNC (MBNC) conduits exhibited ...nice hemocompatibility in absence of bioactive compounds.•MBNC conduits satisfied a long-term patency over 16 weeks in a rat abdominal aorta model.
Bacterial nanocellulose (BNC) is a natural polysaccharide synthesized principally by Komagataeibatacter xylinus which can be formed into tubes and other shapes through the use of special bioreactors. Although tubular BNC has considerable potential as a small-caliber vascular graft (<6 mm), its poor mechanical properties in its hydrogel form, lack of compliance, and its thick walls that do not match natural vessels limit their potential clinical use and long-term patency rate after implantation. Mercerization is an approach in which an alkaline treatment changes the chemistry of BNC products. Following mercerization, tubular BNC grafts exhibited greater mechanical strength combined with thinner walls. Volumetric reduction of the tubular BNC was effective (by nearly 90%) when using a NaOH concentration greater than 10% (w/v), which caused fewer platelets to adhere to the luminal surface. Mercerized tubular BNC (MBNC) promoted the proliferation of endothelial cells in vitro. The MBNC obtained using 20% NaOH was selected for transplantation within a rat abdominal aorta model. Normal blood flow was observed for 16 weeks, indicating that the MBNC conduit maintained long-term patency. The results indicate that mercerization can control the size of tubular BNC and thus the MBNC conduit is a promising candidate for blood vessel replacement.
Bacterial nanocellulose (BNC) is a promising material for small-caliber artificial blood vessels, although promoting its anticoagulant properties with more rapid endothelialization would improve ...long-term patency. Silk fibroin nanoparticles (SFNP) were introduced into the luminal wall surface of BNC conduits both with and without heparin (Hep) through pressurization followed by fixation. Hep was introduced in two ways: (1) embedded within SF nanoparticles to form SF-HepNPs for construction of the BNC-SF-HepNP conduit and (2) chemically grafted onto BNC and BNC-SFNP to form BNC-Hep and BNC-SFNP-Hep conduits. Fourier transform infrared spectroscopy confirmed the formation of SF-HepNPs, although they did not incorporate into the fibrillar network due to their large size. Hep was successfully grafted onto BNC and BNC-SFNP, verified by toluidine blue staining. The hemocompatibility and cytocompatibility of the five samples (BNC, BNC-SFNP, BNC-SF-HepNP, BNC-Hep, and BNC-SFNP-Hep conduits) were compared in vitro. The heparinized BNC-Hep and BNC-SFNP-Hep conduits improved the anticoagulant properties, and BNC-SFNP-Hep promoted human umbilical vein endothelial cell proliferation but also controlled excessive human arterial smooth muscle cell proliferation, assisting rapid endothelialization and improving lumen patency. No significant inflammatory reaction or material degradation was observed after subcutaneous implantation for 4 weeks. Autogenous tissues were observed around the conduits, and cells infiltrated into the edges of all samples, the BNC-SFNP conduit causing the deepest infiltration, providing an appropriate microenvironment for angiogenesis when used in small-caliber blood vessel applications. Few inflammatory cells were found around the BNC-Hep and BNC-SFNP-Hep conduits. Thus, the anticoagulant properties of the BNC-SFNP-Hep conduit and its stimulation of endothelialization suggest that it has great potential in clinical applications as a small-caliber artificial blood vessel.
Therapeutic benefits of small caliber artificial blood vessels to cure cardio and cerebrovascular diseases are mainly limited by their low patency during long-term transplantation. Bacterial ...nanocellulose (BNC), as a natural polysaccharide mainly synthesized by a bacterium Komagataeibatacter xylinus, has shown great potential in small-caliber vascular graft applications due to its shape controllability, and furthermore its physical surface structure can be adjusted with different treatments. However, influences of physical surface structure and properties of BNC conduits on behaviors of vascular cells have not been investigated. In this work, mercerized BNC conduits (MBNC) with different surface roughness and stiffness were constructed by controlled alkali (NaOH) treatment. The changes of surface structures and properties significantly affected the behaviors of vascular cells and gene expression; meanwhile, the cell seeding density also affected the cell responses. After mercerization with NaOH concentration > 10 %, it was observed that the increased stiffness of MBNC decreased several functional gene expressions of human vascular endothelial cells, and the pathological transformation of smooth muscle cells was inhibited. This study demonstrates physical surface structure of MBNC conduits will critically regulate functions and behaviors of vascular cells and it also provides important designing parameters to improve the long-term patency of BNC-based conduits.
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Size and properties of tubular bacterial nanocellulose (BNC) can be regulated by controllable mercerization with thinner tube walls, better mechanical properties, and improved biocompatibility. ...Although mercerized BNC (MBNC) conduits have considerable potential as small-caliber vascular grafts (<6 mm), poor suture retention and lack of compliance that cannot match natural blood vessels increase the difficulty of surgery and limit potential clinical application. Polyvinyl alcohol (PVA) is a kind of hydrophilic polymer with good biocompatibility and elasticity, which can precipitate in alkaline solutions. In this study, novel elastic mercerized BNC/PVA conduits (MBP) are manufactured combining mercerization of BNC tubes with precipitation and phase separation of PVA with thinner tube wall, improved suture retention, better elasticity, good hemocompatibility and great cytocompatibility. The MBP obtained with 12.5 % PVA is selected for transplantation in a rat abdominal aorta model. For 32 weeks, normal blood flow is observed using Doppler sonographic inspection, which demonstrates long-term patency. Immunofluorescence staining results also indicate the formation of endothelium and smooth muscle layers. The results indicate the introduction of PVA, and its phase separation into mercerization of tubular BNC can endow MBP conduits with better compliance and suture retention, making it a promising candidate for blood vessel replacement.
•Mercerized BNC/PVA conduits (MBP) were produced via mercerization of BNC with PVA.•Superior suture retention and compliance were endowed on BNC-based conduits.•MBP conduits exhibited nice hemocompatibility in absence of anticoagulant compound.•MBP conduits satisfied a long-term patency over 32 weeks in rat abdominal aorta.
There is an increasing demand for small-diameter blood vessels. Currently, there is no clinically available small-diameter artificial vessel. Bacterial nanocellulose (BNC) has vast potential for ...applications in artificial blood vessels due to its good biocompatibility. At the same time, medical polyurethane (PU) is a highly elastic polymer material widely used in artificial blood vessels. This study reports a composite small-diameter BNC/PU conduit using a non-solvent-induced phase separation method with the highly hydrophilic BNC tube as the skeleton and the hydrophobic polycarbonate PU as the filling material. The results revealed that the compliance and mechanical matching of BNC/PU tubes were higher than BNC tubes; the axial/radial mechanical strength, burst pressure, and suture strength were significantly improved; the blood compatibility and cell compatibility were also excellent. The molecular and subcutaneous embedding tests showed that the composite tubes had lighter inflammatory reactions. The results of the animal substitution experiments showed that the BNC/PU tubes kept blood flow unobstructed without tissue proliferation after implantation in rats for 9 months. Thus, the BNC/PU small-diameter vascular prosthesis had the potential for long-term patency and acted as an ideal material for small-diameter vessels.
•A BNC/PU small-caliber vascular graft was obtained with a reinforced concrete structure.•Bacterial cellulose network was used as skeleton and elastic polyurethane as reinforcement.•The graft mechanical properties were superior to that of human great saphenous vein.•The vascular graft was unobstructed in vivo for 9 months with rapid in situ endothelialization.•The composite graft significantly decreased the expression of TNF-α, MCP-1 and IL-6.
High moisture permeability, excellent mechanical properties in a wet state, high water-holding capability, and high exudate absorption make bacterial nanocellulose (BNC) a favorable candidate for ...biomedical device production, especially wound dressings. The lack of antibacterial activity and healing-promoting ability are the main drawbacks that limit its wide application. Pullulan (Pul) is a nontoxic polymer that can promote wound healing. Zinc oxide nanoparticles (ZnO-NPs) are well-known as a safe antibacterial agent. In this study, aminoalkylsilane was chemically grafted on a BNC membrane (A-g-BNC) and used as a bridge to combine BNC with Pul-ZnO-NPs hybrid electrospun nanofibers. FTIR results confirmed the successful production of A-g-BNC/Pul-ZnO. The obtained dressing demonstrated blood clotting performance better than that of BNC. The dressing showed an ability to release ZnO, and its antibacterial activity was up to 5 log values higher than that of BNC. The cytotoxicity of the dressing toward L929 fibroblast cells clearly showed safety due to the proliferation of fibroblast cells. The animal test in a rat model indicated faster healing and re-epithelialization, small blood vessel formation, and collagen synthesis in the wounds covered by A-g-BNC/Pul-ZnO. The new functional dressing, fabricated with a cost-effective and easy method, not only showed excellent antibacterial activity but could also accelerate wound healing.
The fluid movement motion has an important influence on the evolution of the pul?sating flow in the hot runner. Using the large eddy simulation numerical method, the instantaneous velocity, wall ...shear stress, boundary-layer thickness, and Nusselt number of hot runner section under different structural parameters at an inlet pressure of 5000 Pa were studied. The research results showed that the backflow vortex can be formed in the hot runner, and the fluid at the axis center of hot runner can form a pulsating flow under the squeezing action of the backflow vortex. The pulsating flow had a strong disturbance effect on the fluid around the axis center and accelerated the heat exchange between the fluid around the axis center and the wall. The disturbance effect of pulsating flow gradually strengthened with the flow of the main flow to the downstream. When d2/d1 was 1-1.8, the wall shear stress first increased and then decreased, and the wall heat transfer efficiency first increased and then decreased. The maximum wall shear stress was 36.4 Pa. When L/D was 0.45-0.65, the boundary-layer thickness first decreased and then increased, and the heat transfer efficiency first increased and then decreased. The minimum boundary-layer thickness was 0.392 mm and the maximum Nusselt number was 138. When d2/d1=1.4 and L/D=0.55, the maximum comprehensive evaluation factor reached 1.241, and the heat transfer efficiency was increased by 24.1%.
There are no small-caliber (<6 mm) vascular prostheses so far commercially available around the globe. Bacterial nanocellulose (BNC) is considered a promising material for small-caliber artificial ...blood vessel applications. Although BNC hydrogel-like (BNC-Gel) materials possess a 3D network structure, facilitating nutrient exchange when used as vascular prostheses, they are difficult to suture during surgery due to their softness. Furthermore, a water content greater than 99% prevents the material from convenient methods of preservation and transport. Air-drying the BNC (BNC-Dry) would solve these problems. The comparative morphology, mechanical properties, hemocompatibility, and cytocompatibility of the BNC-Gel and BNC-Dry conduits of 3 mm in diameter were recorded in the present study, the results indicating that the mechanical properties, hemocompatibility, and cytocompatibility of BNC-Dry conduits were superior to conduits of BNC-Gel. Forty-six days after replacement of the carotid artery in New Zealand white rabbits, the BNC-Dry conduits remained patent. Composite blood vessels composed of cellulose and autologous tissue were harvested for immunohistochemistry and immunofluorescence staining. Sections demonstrated that the outer walls of the conduits were wrapped with autologous tissue. Contractile smooth muscle cells (SMCs) were observed on the outer surface of the conduit, similar to that observed in natural blood vessels. BNC-Dry conduits exhibited excellent performance and possessed properties convenient for surgical applications as small-diameter blood vessels.
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•An air-dried BNC conduit was evaluated as small-caliber vascular prosthesis for the first time.•Greater tensile strength and suture retention were found besides convenience to storage and transportation.•The air-dried conduit possessed excellent anticoagulant properties and cells compatibility.•Patency of at least 46 days was achieved with 2 mm caliber conduits in a rabbit model.
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