Porous Silk Research Articles

Porous Silk Fibroin Microspheres Sustainably Releasing Bioactive Basic Fibroblast Growth Factor.

Basic fibroblast growth factor (bFGF) plays a significant role in stimulating cell proliferation. It remains a challenge in the field of biomaterials to develop a carrier with the capacity of continuously releasing bioactive bFGF. In this study, porous bFGF-loaded silk fibroin (SF) microspheres, with inside-out channels, were fabricated by high-voltage electrostatic differentiation, and followed by lyophilization. The embedded bFGF exhibited a slow release mode for over 13 days without suffering burst release. SEM observations showed that incubated L929 cells could fully spread and produce collagen-like fibrous matrix on the surface of SF microspheres. CLSM observations and the results of cell viability assay indicated that bFGF-loaded microspheres could significantly promote cell proliferation during five to nine days of culture, compared to bFGF-unloaded microspheres. This reveals that the bFGF released from SF microspheres retained obvious bioactivity to stimulate cell growth. Such microspheres sustainably releasing bioactive bFGF might be applied to massive cell culture and tissue engineering as a matrix directly, or after being combined with three-dimensional scaffolds.

Facile incorporation of REDV into porous silk fibroin scaffolds for enhancing vascularization of thick tissues

Rapid neovascularization within scaffolds is critical for the regeneration of thick complex tissues. The surface immobilization of peptides and other active molecules have been explored to improve the vascularization capacity of implants. However, the rapid degradation of these molecules, the reaction conditions and cross-linking usually result in decreased vascularization capability. Here, we introduced a temperate, all-aqueous process to achieve bulk porous silk fibroin (SF) scaffolds. A temperature controlled process was used to induce the water stable structure by SF self-assembly. Arg-Glu-Asp-Val (REDV) peptides were added into SF solution and fixed within SF scaffolds during the self-assembly process. The results showed that the functionalized scaffolds markedly promoted the adhesion of endothelial cells in vitro. Moreover, the in vivo studies indicated enhanced cell infiltration in the bulk functionalized SF scaffolds and impressive vascularization at 4 weeks post-implantation. The functionalized scaffolds demonstrated excellent vascularization capability, providing an exciting biomaterial option for thick tissue regeneration.

Synthesis, characterization and biocompatible properties of novel silk fibroin/graphene oxide nanocomposite scaffolds for bone tissue engineering application

Novel three-dimensional porous silk fibroin/graphene oxide (SF/GO) nanocomposite scaffolds with different graphene oxide (GO) concentrations were prepared by using the freeze-drying technique. The obtained SF/GO scaffolds were characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, Brunauer–Emmett–Teller isotherm and Fourier transform infrared spectroscopy techniques. The water absorption, compressive properties, porosity, degradation, biomineralization capability, cell attachment and cell viability of the composite scaffolds were studied as well. Cytocompatibility of the scaffolds was studied in vitro by employing the methylthiazoletetrazolium assay. The results showed that the presence of graphene oxide nanoparticles throughout the fibroin matrix led to an increase in water uptake and mechanical properties; at the same time, the porosity of the scaffolds was decreased. The cell adhesion results also indicated that human osteoblast cells (MG-63) could adhere to the surface of SF/GO nanocomposites and develop on them. These suggest that SF/GO nanocomposite scaffolds may be a good candidate for bone tissue engineering applications.

Repair of urethral defects by an adipose mesenchymal stem cell‑porous silk fibroin material.

The aim of the present study was to determine whether it was possible to repair urethral defects with a material of adipose mesenchymal stem cells (ADMSCs)-porous silk fibroin (SF). A total of 39 male New Zealand white rabbits were randomly divided into a control group, an SF group and a bromodeoxyuridine (BrdU)-labeled ADMSCs-SF group (SSF group; n=13/group). Defects were made by resecting the posterior urethral wall. The defects in the SF and SSF groups were repaired using SF and BrdU-labeled ADMSCs-SF materials respectively. Then the anterior wall was sutured, and the urethral catheter was retained for 3 weeks following surgery. The catheter was rinsed with nitrofurazone once a day. The cells with positive expressions of factor VIII related antigen (FVIII-RAg), α-smooth muscle actin (α-SMA) and pan-cytokeratin (AE1/AE3) were detected by immunohistochemical assay, and the distributions of BrdU positive cells and macrophages were observed. Urethrography was performed prior to and following surgery. All rabbits had normal urethral morphologies prior to surgery. The incidence rates of postoperative complications in the control, SF and SSF groups were 76.92 (7/13), 23.07 (3/13) and 15.38% (2/13), respectively (P<0.05). The number of positive macrophages in the SSF group was significantly lower than that of the SF group 4 weeks following surgery (P<0.05). In the SSF group, BrdU positive cells were scattered within the SF material following surgery, primarily at the intersection between the SF material and the urethra. The number of FVIII-RAg positive cells in the SSF and SF groups were significantly different (P<0.05), which were also significantly higher than that of control group (P<0.01). The number of α-SMA positive cells in the SSF and SF groups were significantly different (P<0.05), and these values also significantly exceeded those exhibited by the control group (P<0.01). In addition, the SSF and SF groups had positive staining of AE1/AE3. Similar to normal urethral mucosa, the cytoplasm was stained brownish yellow (P<0.05). It is thus feasible to repair urethral defects using ADMSCs-SF material.

Combinatory approach for developing silk fibroin scaffolds for cartilage regeneration

Several processing technologies and engineering strategies have been combined to create scaffolds with superior performance for efficient tissue regeneration. Cartilage tissue is a good example of that, presenting limited self-healing capacity together with a high elasticity and load-bearing properties. In this work, novel porous silk fibroin (SF) scaffolds derived from horseradish peroxidase (HRP)-mediated crosslinking of highly concentrated aqueous SF solution (16 wt%) in combination with salt-leaching and freeze-drying methodologies were developed for articular cartilage tissue engineering (TE) applications. The HRP-crosslinked SF scaffolds presented high porosity (89.3 ± 0.6%), wide pore distribution and high interconnectivity (95.9 ± 0.8%). Moreover, a large swelling capacity and favorable degradation rate were observed up to 30 days, maintaining the porous-like structure and β-sheet conformational integrity obtained with salt-leaching and freeze-drying processing. The in vitro studies supported human adipose-derived stem cells (hASCs) adhesion, proliferation, and high glycosaminoglycans (GAGs) synthesis under chondrogenic culture conditions. Furthermore, the chondrogenic differentiation of hASCs was assessed by the expression of chondrogenic-related markers (collagen type II, Sox-9 and Aggrecan) and deposition of cartilage-specific extracellular matrix for up to 28 days. The cartilage engineered constructs also presented structural integrity as their mechanical properties were improved after chondrogenic culturing. Subcutaneous implantation of the scaffolds in CD-1 mice demonstrated no necrosis or calcification, and deeply tissue ingrowth. Collectively, the structural properties and biological performance of these porous HRP-crosslinked SF scaffolds make them promising candidates for cartilage regeneration. Statement of SignificanceIn cartilage tissue engineering (TE), several processing technologies have been combined to create scaffolds for efficient tissue repair. In our study, we propose novel silk fibroin (SF) scaffolds derived from enzymatically crosslinked SF hydrogels processed by salt-leaching and freeze-drying technologies, for articular cartilage applications. Though these scaffolds, we were able to combine the elastic properties of hydrogel-based systems, with the stability, resilience and controlled porosity of scaffolds processed via salt-leaching and freeze-drying technologies. SF protein has been extensively explored for TE applications, as a result of its mechanical strength, elasticity, biocompatibility, and biodegradability. Thus, the structural, mechanical and biological performance of the proposed scaffolds potentiates their use as three-dimensional matrices for cartilage regeneration.

Functional, RF-Trilayer Sensors for Tooth-Mounted, Wireless Monitoring of the Oral Cavity and Food Consumption.

Wearable devices have emerged as powerful tools for personalized healthcare in spite of some challenges that limit their widespread applicability as continuous monitors of physiological information. Here, a materials-based strategy to add utility to traditional dielectric sensors by developing a conformal radiofrequency (RF) construct composed of an active layer encapsulated between two reverse-facing split ring resonators is applied. These small (down to 2 mm × 2 mm) passive dielectric sensors possess enhanced sensitivity and can be further augmented by functionalization of this interlayer material. Demonstrator devices are shown where the interlayer is: (i) a porous silk film, and (ii) a modified PNIPAM hydrogel that swells with pH or temperature. In vivo use is demonstrated by adhesion of the device on tooth enamel to detect foods during human ingestion. Such sensors can be easily multiplexed and yield data-rich temporal information during the diffusion of analytes within the trilayer structure. This format could be extended to a suite of interlayer materials for sensing devices of added use and specificity.

Silk Fibroin Acts as a Self-Emulsifier to Prepare Hierarchically Porous Silk Fibroin Scaffolds through Emulsion-Ice Dual Templates.

Silk fibroin (SF) has shown enormous potentials in various fields; however, application of SF in emulsion technology is quite limited. Here, we use SF as a self-emulsifier to form an oil-in-water (O/W) emulsion by emulsifying 1-butanol in SF aqueous solution. This showed that SF possessed strong surface activity to stabilize the O/W emulsion without the need for any other surface-active agent until its solidification because of 1-butanol-induced conformational transition of SF to β-sheet. After freezing the preformed emulsions at −20 °C, robust three-dimensional porous SF scaffolds were prepared without the need for any further post-treatment. The evolution from the O/W emulsion to porous scaffold formation under freezing was tracked, and an emulsion–ice dual template mechanism was proposed for scaffold formation, based on which SF scaffolds with controllable hierarchically porous structures were achieved by tuning the dispersed droplet volume fraction. Furthermore, SF scaffolds with hierarchical porosity showed significantly higher bioactivity toward L929 fibroblasts than that of SF scaffolds with mono macroporosity, highlighting the great asset of this hierarchically porous SF scaffold for broad applications in tissue engineering. Therefore, the strong surface-active characteristic of SF presented here, in addition to its distinct advantages, sheds a bright light on the application of SF in the vast range of emulsion technologies, especially in cosmetic-, food-, and biomedical-related areas.

Repair of rabbit radial bone defects using bone morphogenetic protein-2 combined with 3D porous silk fibroin/β-tricalcium phosphate hybrid scaffolds

Our study aimed to investigate the effect of bone morphogenetic protein-2 (BMP-2) bound to silk fibroin and β-tricalcium phosphate (SF/β-TCP) hybrid on the healing of critical-size radial defects in rabbits. A 15-mm critical-size defect was induced at mid-diaphysis in the left radius of 20 New Zealand white rabbits (average age, 3.5 months; weight, 2.5–3.0 kg). The animals were randomized into Group 1 (SF/β-TCP combined with BMP-2), Group 2 (SF/β-TCP alone), and Group 3 (nothing implanted). Radiographs were obtained every 2 weeks and euthanasia was performed after 8 weeks for visual, radiological, micro-computed tomography (micro-CT), and histological studies. Eight weeks after implantation (SF/β-TCP combined with BMP-2), radiographs showed that new bone formed on the surface of the implant and had bridged the defect in Group 1. Micro-CT imaging also confirmed the formation of new bone around the implant, and the newly formed bone was quantified. Histological examination revealed newly formed bone in the implanted area. Meanwhile, there was no formation of new bone in Group 3. Among the groups, most active formation of new bones was found in Group 1, while there was no difference between Group 2 and Group 3. Based on these results, we concluded that BMP-2-SF/β-TCP showed significant improvement in healing of critical-size defects. Therefore, the combination of BMP-2 and SF/β-TCP would be useful in the field of bone tissue engineering.

A novel method for developing three dimensional (3D) silk–PVA microenvironments for bone tissue engineering—an in vitro study

Three dimensional (3D) porous scaffold based bone tissue engineering can possibly serve as an alternative approach to repairing severe bone injuries. The present study was carried out to evaluate the impact of 3D porous silk fibroin (SF)–polyvinyl alcohol (PVA) based scaffolds on human osteoblast-like (MG63) cell attachment and proliferation in vitro. SF and PVA blended porous scaffolds (3:1 ratio) with tunable porosity and mechanical properties were prepared by a freeze drying method in a solvent-free system. Citric acid plays a dual role of cross-linking and a gas foaming reaction with sodium bicarbonate (NaHCO3). Porosity was induced by gas foaming using different weight fractions (0.5%, 1.0%, 1.5% and 2.0% w/v) of NaHCO3. The developed scaffolds were characterized for porosity, swelling ratio, compressive and biodegradation properties. The scaffolds were proved to be non-toxic to the osteoblast-like cells in MTT assay. The DNA content of the cells attached to the scaffolds was also estimated. The cell attachment and proliferation onto the scaffolds were studied using SEM. The study highlights the potential of such 3D scaffolds with controlled porosity as an effective biomaterial for bone regeneration.

Strong and biocompatible three-dimensional porous silk fibroin/graphene oxide scaffold prepared by phase separation

Silk fibroin (SF) is blended with graphene oxide (GO) to prepare the strong and biocompatible three dimensional porous SF/GO blended scaffold via phase separation. GO could be well dispersed in SF solution and GO could also be well distributed in the SF scaffold. Furthermore, the introduction of GO can lead to structural change in the bended scaffold. Higher concentration of GO resulted in more compact structure and smaller pore size of the composite scaffolds without decreasing their porosity. Scanning electron microscopy and energy dispersive spectrometry results also reveal that SF and GO are homogeneous blended together. Analysis of chemical structures of the scaffold shows that addition of GO do not affect the crystalline structure of SF and it is evenly blended with SF. The blended scaffold has significantly higher breaking strength than the pure SF scaffold. In vitro study indicates that both pure SF scaffold and SF/GO composite scaffold support growth and proliferation of MC3T3-E1 osteoprogenitor cells. However, the addition of GO contribute to the proliferation of MC3T3-E1 osteoprogenitor. The testing results show that the blended scaffold is an appropriate candidate for tissue engineering.

Multifunctional Bioreactor System for Human Intestine Tissues.

The three-dimensional (3D) cultivation of intestinal cells and tissues in dynamic bioreactor systems to represent in vivo intestinal microenvironments is essential for developing regenerative medicine treatments for intestinal diseases. We have previously developed in vitro human intestinal tissue systems using a 3D porous silk scaffold system with intestinal architectures and topographical features for the adhesion, growth, and differentiation of intestinal cells under static culture conditions. In this study, we designed and fabricated a multifunctional bioreactor system that incorporates pre-epithelialized 3D silk scaffolds in a dynamic culture environment for in vitro engineering of human intestine tissues. The bioreactor system allows for control of oxygen levels in perfusion fluids (aerobic simulated intestinal fluid (SIF), microaerobic SIF, and anaerobic SIF), while ensuring control over the mechanical and chemical microenvironments present in native human intestines. The bioreactor system also enables 3D cell culture with spatial separation and cultivation of cocultured epithelial and stromal cells. Preliminary functional analysis of tissues housed in the bioreactor demonstrated that the 3D tissue constructs survived and maintained typical phenotypes of intestinal epithelium, including epithelial tight junction formation, intestinal biomarker expression, microvilli formation, and mucus secretion. The unique combination of a dynamic bioreactor and 3D intestinal constructs offers utility for engineering human intestinal tissues for the study of intestinal diseases and discovery options for new treatments.

Functional hepatocyte clusters on bioactive blend silk matrices towards generating bioartificial liver constructs.

An end stage liver disease called cirrhosis perturbs the self-healing ability and physiological functions of liver. Due to the scarcity of healthy donors, a functional in vitro hepatic construct retaining the liver-specific functions is in great demand for its prospects in bioartificial liver (BAL) and cell-based tissue engineering. Physicochemical attributes of a matrix influence the behavior of cultured hepatocytes in terms of attachment, morphology and functionality. Mulberry and non-mulberry silk fibroin presents unique amino acid sequence with difference in hydrophobicity and crystallinity. Considering this, the present study focuses on the development of a suitable three-dimensional (3D) bioactive matrix incorporating both mulberry silk fibroin and cell adhesion motif (RGD) rich non-mulberry silk fibroin. Porous silk blend scaffolds facilitated the formation of hepatocyte clusters with enhanced liver-specific functions emphasizing both cell-cell and cell-matrix interactions. Hemocompatibility and integral property of blend scaffolds offers a biological niche for seeding functional liver cells that would have future prospects in biohybrid devices.

A Preliminary Study of the &lt;i&gt;In Vitro&lt;/i&gt; Biocompatibility Testing of Silk Fibroin/Alpha Tricalcium Phosphate Composite Scaffolds for Bone Tissue Engineering

Silk fibroin is a natural biodegradable polymer that has been demonstrated for use as scaffolds for bone tissue engineering. To improve the osteoconductivity and the osteoinductivity of silk fibroin scaffolds, ceramics were added. α-tricalcium phosphate (α-TCP) is the expected ceramic that useful for scaffolds for bone tissue engineering either alone or blended with silk fibroin. From the previous study, we evaluated the mechanical properties of three-dimensional porous silk fibroin/ α-TCP scaffolds and concluded that the scaffolds containing 8% (w/w) α-TCP exhibited the highest compressive modulus. The objective of this study was to evaluate the biological properties of three-dimensional porous silk fibroin/α-TCP scaffolds. The scaffolds were constructed using a solvent casting and salt leaching technique. The hybrid strain of degummed Thai silk fibroin, Nangnoi Srisaket 1 x Mor, was dissolved in hexafluoroisopropanol at 16% (w/v). α-TCP was incorporated to produce 4, 8, 12, and 16 wt% solution. Sucrose (particle size 250-450 μm; sucrose/silk fibroin = 8.5/1 w/w) was used as a porogen. Human gingival fibroblasts (passage 5) were cultured in these scaffolds. After 72 h, the biocompatibility of seeded scaffolds was evaluated under the inverted phase contrast microscopy. Cell proliferation was determined by DNA assays and scanning electron microscopy. The images from inverted phase contrast microscopy revealed the human gingival fibroblasts can be attached at the surface of scaffolds in all groups. The results from the DNA assays showed that the number of human gingival fibroblasts was increased as the culture period was prolonged but was not as the increasing of α-TCP. At 120 h, the scaffolds containing 8% (w/w) α-TCP exhibited the highest cell number. The scanning electron microscope images at 24, 72, and 120 h after cell culturing presented human gingival fibroblasts can be expanded well and exhibited the normal morphology. The results suggested that the scaffolds containing 8% (w/w) α-TCP may be a potential candidate for bone tissue engineering applications.

Accelerated Vascularization of Silk Fibroin Scaffolds Through Immobilized Basic Fibroblast Growth Factor (bFGF)

Angiogenesis of an implanted tissue is one of the most important issues in skin repairment. Porous bFGF-immobilized silk fibroin (bSF) scaffolds was fabricated by freeze drying using EDC agent crosslinking bFGF and SF with an aim of controlling bFGF delivery for the revascularization improvement. The bSF scaffolds retained a porous structure with 200～300 μm diameter and 85～91% porosity. The seeded L929 cells had notably improved growth and proliferation on bSF scaffolds, suggesting bFGF sustained release from SF scaffolds and remained bioactivity. After implantation into the skin defect of sprague-dawley (SD) rat dorsum, the bSF scaffolds revealed significantly higher wound recovery rate with complete reepithelialization and regeneration of skin appendages compared with SF scaffolds. The new vessels density and collagen deposition were also higher in bSF scaffolds after 4-week treatment, which provided the therapeutic potentials of the SF scaffolds in the regeneration of wounded tissue.

Fractal characteristics of the microvascular network: A useful index to assess vascularization level of porous silk fibroin biomaterial.

The neovascularization of biomaterials for tissue engineering is not only related to growth of capillaries but also involves appropriate hierarchy distribution of the microvessels. In this study, we proposed hierarchy distribution contrast method which can assess vascular transport capacity, in order to examine the hierarchy distribution of the neovessels during vascularization of the porous silk fibroin biomaterials implanted into rats and its evolution. The results showed that the fractal characteristics appeared toward the end of the vascularization stages, and the structure of the microvascular network after 3weeks of implantation was similar to the fractal microvascular tree with bifurcation exponent x=3 and fractal dimension D=1.46, which became a sign of maturation of the regenerative vasculature. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2276-2290, 2017.

Modified porous scaffolds of silk fibroin with mimicked microenvironment based on decellularized pulp/fibronectin for designed performance biomaterials in maxillofacial bone defect.

Maxillofacial bone defect is a critical problem for many patients. In severe cases, the patients need an operation using a biomaterial replacement. Therefore, to design performance biomaterials is a challenge for materials scientists and maxillofacial surgeons. In this research, porous silk fibroin scaffolds with mimicked microenvironment based on decellularized pulp and fibronectin were created as for bone regeneration. Silk fibroin scaffolds were fabricated by freeze-drying before modification with three different components: decellularized pulp, fibronectin, and decellularized pulp/fibronectin. The morphologies of the modified scaffolds were observed by scanning electron microscopy. Existence of the modifying components in the scaffolds was proved by the increase in weights and from the pore size measurements of the scaffolds. The modified scaffolds were seeded with MG-63 osteoblasts and cultured. Testing of the biofunctionalities included cell viability, cell proliferation, calcium content, alkaline phosphatase activity (ALP), mineralization and histological analysis. The results demonstrated that the modifying components organized themselves into aggregations of a globular structure. They were arranged themselves into clusters of aggregations with a fibril structure in the porous walls of the scaffolds. The results showed that modified scaffolds with a mimicked microenvironment of decellularized pulp/fibronectin were suitable for cell viability since the cells could attach and spread into most of the pores of the scaffold. Furthermore, the scaffolds could induce calcium synthesis, mineralization, and ALP activity. The results indicated that modified silk fibroin scaffolds with a mimicked microenvironment of decellularized pulp/fibronectin hold promise for use in tissue engineering in maxillofacial bone defects. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1624-1636, 2017.

Development Model of Micro vascular Network in Porous Silk Fibroin Film

Development Model of Micro vascular Network in Porous Silk Fibroin Film

Tympanic membrane organ culture using cell culture well inserts engrafted with tympanic membrane tissue explants.

Tissue engineering approaches using growth factors and various materials for repairing chronic perforations of the tympanic membrane are being developed, but there are surprisingly few relevant tissue culture models available to test new treatments. Here, we present a simple three-dimensional model system based on micro-dissecting the rat tympanic membrane umbo and grafting it into the membrane of a cell culture well insert. Cell outgrowth from the graft produced sufficient cells to populate a membrane of similar surface area to the human tympanic membrane within 2 weeks. Tissue grafts from the annulus region also showed cell outgrowth but were not as productive. The umbo organoid supported substantial cell proliferation and migration under the influence of keratinocyte growth medium. Cells from umbo grafts were enzymatically harvested from the polyethylene terephthalate (PET) membrane for expansion in routine culture and cells could be harvested consecutively from the same graft over multiple cycles. We used harvested cells to test cell migration properties and to engraft a porous silk scaffold material as proof-of-principle for tissue engineering applications. This model is simple enough to be widely adopted for tympanic membrane regeneration studies and has promise as a tissue-equivalent model alternative to animal testing.

3D Functional Corneal Stromal Tissue Equivalent Based on Corneal Stromal Stem Cells and Multi-Layered Silk Film Architecture.

The worldwide need for human cornea equivalents continues to grow. Few clinical options are limited to allogenic and synthetic material replacements. We hypothesized that tissue engineered human cornea systems based on mechanically robust, patterned, porous, thin, optically clear silk protein films, in combination with human corneal stromal stem cells (hCSSCs), would generate 3D functional corneal stroma tissue equivalents, in comparison to previously developed 2D approaches. Silk film contact guidance was used to control the alignment and distribution of hCSSCs on RGD-treated single porous silk films, which were then stacked in an orthogonally, multi-layered architecture and cultured for 9 weeks. These systems were compared similar systems generated with human corneal fibroblasts (hCFs). Both cell types were viable and preferentially aligned along the biomaterial patterns for up to 9 weeks in culture. H&E histological sections showed that the systems seeded with the hCSSCs displayed ECM production throughout the entire thickness of the constructs. In addition, the ECM proteins tested positive for keratocyte-specific tissue markers, including keratan sulfate, lumican, and keratocan. The quantification of hCSSC gene expression of keratocyte-tissue markers, including keratocan, lumican, human aldehyde dehydrogenase 3A1 (ALDH3A1), prostaglandin D2 synthase (PTDGS), and pyruvate dehydrogenase kinase, isozyme 4 (PDK4), within the 3D tissue systems demonstrated upregulation when compared to 2D single silk films and to the systems generated with the hCFs. Furthermore, the production of ECM from the hCSSC seeded systems and subsequent remodeling of the initial matrix significantly improved cohesiveness and mechanical performance of the constructs, while maintaining transparency after 9 weeks.

Biodegradable Porous Silk Microtubes for Tissue Vascularization.

Cardiovascular diseases are the leading cause of mortality around the globe, and microvasculature replacements to help stem these diseases are not available. Additionally, some vascular surgeries needing small diameter vascular grafts present different performance requirements. In this work silk fibroin scaffolds based on silk/polyethylene oxide blends were developed as microtubes for vasculature needs and for different tissue regeneration times, mechanical properties and structural designs. Systems with 13, 14 and 15% silk alone or blended with 1 or 2% of polyethylene oxide (PEO) were used to generate porous microtubes using gel-spinning. Microtubes with inner diameters (ID) of 150-300 μm and 100 μm wall thickness were fabricated. The systems were assessed for porosity, mechanical properties, enzymatic degradability, and in vitro vascular endothelial cell attachment and metabolic activity. After 14 days all tubes supported the proliferation of cells and cell attachment increased with porosity. The silk tubes with PEO had similar crystallinity but higher elastic modulus compared with the systems without PEO. The silk (13%)/PEO (1%) system showed the highest porosity (20 μm pore diameters on average), highest cell attachment and fastest degradation profile. There was a good correlation between these parameters with silk concentration and the presence of PEO. The results demonstrate the ability to generate versatile and tunable tubular biomaterials based on silk-PEO-blends with potential for microvascular grafts.