Knitted Silk Research Articles

Fabrication of green composite hand knitted silk mesh reinforced with silk hydrogel

Soft tissue defects like hernia and post-surgical fistula formation can be resolved with modern biomaterials in the form of meshes without post-operative complications. In the present study hand knitted silk meshes were surface coated with regenerated silk fibroin hydrogel and pure natural extracts. Two phytochemicals (Licorice extract (LE) and Bearberry extract (BE)) and the two honeybee products (royal jelly (RJ) and honey (HE)) were incorporated separately to induce antibacterial, anti-inflammatory, and wound healing ability to the silk hydrogel coated knitted silk meshes. Meshes were dip coated with a blend of 4 % silk hydrogel (w/v) and 5 % extracts. Dried modified meshes were characterized using SEM, DMA, GC–MS and FTIR. Antimicrobial testing, in-vitro cytotoxicity, in-vitro wound healing and Q-RT-PCR were also performed.SEM analysis concluded that presence of coating reduced the pore size up to 47.7 % whereas, fiber diameter was increased up to 17.9 % as compared to the control. The presence of coating on the mesh improved the mechanical strength/Young's modulus by 1602.8 %, UTS by 451.7 % and reduced the % strain by 51.12 %. Sustained release of extracts from MHRJ (62.9 % up to 72 h) confirmed that it can induce antibacterial activity against surgical infections. Cytocompatibility testing and gene expression results suggest that out of four variables MHRJ presented best cell viability, % wound closure and expression of wound healing marker genes. In-vivo analyses in rat hernia model were carried out using only MHRJ variant, which also confirmed the non- toxic nature and wound healing characteristics of the modified mesh. The improved cell proliferation and activated wound healing in vitro and in vivo suggested that MHRJ could be a valuable candidate to promote cell infiltration and activate soft tissue and hernia repair as a biomedical implant.

A clinical comparison of pure knitted silk and a complex synthetic skin substitute for the treatment of partial thickness burns.

Currently, many dressings are commercially available for the treatment of burn wounds. Some of these wound dressings remain on the wound, prevent painful dressing changes, and reduce tissue scarring. Nevertheless, still a wound dressing that is cost‐effective, produces good wound healing properties, and has a high patient satisfaction is needed. Standard care of superficial burn wounds differs between burn centres. This study aimed to determine a dressing with easy appliance, accurate pain control, favourable outcome, and cost‐effectiveness. Therefore, we compared the widely used but expensive Suprathel with the rather new but much cheaper Dressilk in the clinical setting. In a prospective clinical study, the healing of partial thickness burn wounds after simultaneous treatment with Suprathel and Dressilk was examined in 20 patients intra‐individually. During wound healing, pain, infection, exudation, and bleeding were evaluated. A subjective scar evaluation was performed using the Patient and Observer Scar Scale. Both dressings were easy to apply, remained on the wound in place, and were gradually cut back as reepithelisation proceeded and showed similar times to wound closure. Dressing changes were not necessary, and neither infections nor bleeding was detected. Overall exudation and pain were highest in the beginning but declined during the wound‐healing phase without significant differences. In the follow‐up scar evaluation after 12 months, patients reported overall high satisfaction. Overall, the modern dressings Suprathel and Dressilk (solely made out of pure silk) led to safe wound healing without infection and rapidly reduced pain. There was no need for dressing changes, and they had similar clinical outcomes in scar evaluation. Therefore, both dressings seem to be ideal for the treatment of superficial burns. Because acquisition costs remain one of the main factors in the treatment of burns, Dressilk, which is ~20 times cheaper than Suprathel, remains a good option for the treatment of partial thickness burns.

Evaluation of physical, mechanical and biological properties of poly 3-hydroxybutyrate-chitosan-multiwalled carbon nanotube/silk nano-micro composite scaffold for cartilage tissue engineering applications.

Nano-micro scaffolds are developed for long-term healing tissue engineering like cartilage. The poly 3-hydroxybutyrate (P3HB)-chitosan/silk and P3HB-chitosan-1 wt% multi-walled carbon nanotubes functionalized by COOH (MWNTs)/silk nano-micro scaffolds are fabricated through electrospinning the solution on a knitted silk which is saturated (S) or unsaturated (U) with P3HB as a mediator to enhance the interaction at nano/microinterface. Consuming MWNTs lead to a decrease in fiber diameter, while an increase in specific surface area, tensile strength and bioactivity properties. The saturation condition as well as MWNTs leads to intensification in the hydrophilicity properties. The nanolayer in all scaffolds lead to an increase in tensile strength in comparison with the pure knitted silk. The scaffold containing MWNTs showed slower degradation rate. MWNTs beside the chitosan and silk provide an appropriate environment for attachment and growth of chondrocytes. The P3HB-chitosan-MWNTs/silk (S) nano-microscaffold can be appropriate for a long-term tissue engineering application like cartilage.

Assessing the physical and mechanical properties of poly 3‐hydroxybutyrate‐chitosan‐multi‐walled carbon nanotube/silk nano–micro composite scaffold for long‐term healing tissue engineering applications

The new nano–micro hybrid scaffolds were fabricated through electrospinning the poly 3-hydroxibutyrate-chitosan-multi-walled carbon nanotube (MWNT) nanofibres on the silky knitted microfibers, orderly and randomly. The scaffolds were prepared by varying the concentration of MWNT. The samples were compared as to their alignment and MWNT concentration. The morphological and physical properties were assessed through scanning electron microscopy, Fourier transform infra-red (FT-IR) spectroscopy and water contact angle test. Mechanical properties were determined through tensile strength test run on optimal samples chosen according to the results obtained from above-mentioned tests. The morphological view of the scaffolds showed that an increase in the amount of MWNT up to 1 wt% led to a better fibres diameter distribution and alignment in comparison with other samples. The porosity percentage of all scaffolds were >80% which is appropriate for tissue engineering applications. The FT-IR spectra indicated that the nanofibrous coat on knitted silk did not have any effect on crystallinity structures of silk fibroin. There existed a direct relation between hydrophilicity of scaffolds and MWNT concentration according to water contact angle. The presence of nanofibrous coat on knitted silk had no effect on tensile strength increment in comparison with pure knitted silk. The poly 3-hydroxybutyrate-Chitosan-1 wt% MWNT/Silk scaffolds could be an appropriate biomimetic for extracellular matrix of long-term healing tissues in order to their tissue engineering applications.

Knitted Silk Fibroin‐Reinforced Bead‐on‐String Electrospun Fibers for Sustained Drug Delivery Against Colon Cancer

AbstractBead‐on‐string electrospun fibers containing camptothecin (CPT) are fabricated on the surface of knitted silk fibroin (SF) meshes. Microscopic characterization reveals that the bead‐on‐string structure is prepared successfully and CPT is mainly located within the beaded structure. Interestingly, the CPT‐loaded beaded SF mesh (CPT‐SF mesh) has excellent mechanical properties. More importantly, it is able to perform a sustained CPT release without burst release. In vitro cytotoxicity tests further indicate that the CPT‐SF mesh shows much stronger anticolon cancer activity in comparison with SF meshes and beaded SF meshes. Hence, the CPT‐SF mesh has great potential as a promising local drug delivery system for colon cancer treatment.

Comparison of the knitted silk vascular grafts coated with fibroin sponges prepared using glycerin, poly(ethylene glycol diglycidyl ether) and poly(ethylene glycol) as porogens

Development of a small-diameter artificial vascular graft is urgent because existing materials often occlude within a short time. We have shown that small-diameter vascular graft using Bombyx mori silk fibroin is a potential candidate. Silk fibroin grafts are fabricated by coating silk fibroin on the knit tube prepared from silk fibroin fibers. However, there is a serious problem that the coated silk fibroin portion hardens when alcohol is used for insolubilization of the coated silk fibroin. This hardening prevents the desired biodegradation of the coated silk fibroin. In this study, we improved the silk fibroin coating method of the knit silk fibroin tube. Namely, the silk fibroin sponge coating was performed using glycerin, poly(ethylene glycol diglycidyl ether) or poly(ethylene glycol). In addition, silk fibroin grafts were prepared avoiding dryness during the coating process and were kept in the hydrated state until implantation into the abdominal aorta was complete. After implantation of the hydrated silk fibroin grafts, grafts were taken out at two weeks or three months, and histopathological examination was performed. The grafts coated with three types of silk fibroin sponges had a higher tissue infiltration rate than alcohol-treated grafts and were superior in the formation of smooth muscle cell and vascular endothelial cell remodeling. Biodegradations of the silk fibroin grafts prepared using the three types of silk fibroin sponge coatings and alcohol-treated silk fibroin grafts were also examined with protease XIV in vitro, and the grafts were observed by scanning electron microscopy before and 24 h after biodegradation. Faster biodegradations were observed for grafts coated with the three types of silk fibroin sponges. 13C solid-state nuclear magnetic resonance studies showed that the conformation of the silk fibroin sponge prepared using porogen was a random coil with high mobility in the hydrated state. We believe that small-diameter silk fibroin vascular grafts coated with quick biodegradable silk fibroin sponges can be developed based on these findings.

Characterization of Silk/Poly 3-Hydroxybutyrate-chitosan-multi-walled Carbon Nanotube Micro-nano Scaffold: A New Hybrid Scaffold for Tissue Engineering Applications

Long-term healing tissue engineering scaffolds must hold its full mechanical strength at least for 12 weeks. Nano-micro scaffolds consist of electrospinning nanofibers and textile microfibers to support cell behavior and mechanical strength, respectively. The new nano-micro hybrid scaffold was fabricated by electrospinning poly 3-hydroxybutyrate-chitosan-multi-walled carbon nanotube (MWNT functionalized by COOH) solution on knitted silk in a random manner with different amounts of MWNT. The physical, mechanical, and biodegradation properties were assessed through scanning electron microscopy, Fourier-transform infrared (FTIR) spectroscopy, water contact angle test, tensile strength test, and weight loss test. The scaffold without MWNT was chosen as control sample. An increase in the amount of MWNT up to 1 wt% leads to better fiber diameter distribution, more hydrophilicity, biodegradation rate, and higher tensile strength in comparison with other samples. The porosity percentage of all scaffolds is more than 80%. According to FTIR spectra, the nanofibrous coat on knitted silk did not have any effect on silk fibroin crystallinity structures, and according to tensile strength test, the coat had a significant effect on tensile strength in comparison with pure knitted silk (P ≤ 0.05). The average fiber diameter decreased due to an increase in electrical conductivity of the solution and fiber stretch in electrical field due to MWNTs. The scaffold containing 1 wt% MWNT was more hydrophilic due to the presence of many COOH groups of functionalized MWNT, thus an increase in the hydrolysis and degradation rate of this sample. High intrinsic tensile strength of MWNTs and improvement of nano-micro interface connection lead to an increase in tensile strength in scaffolds containing MWNT.

Preparation of collagen/polyurethane/knitted silk as a composite scaffold for tendon tissue engineering.

The main objective of this study was to prepare a hybrid three-dimensional scaffold that mimics natural tendon tissues. It has been found that a knitted silk shows good mechanical strength; however, cell growth on the bare silk is not desirable. Hence, electrospun collagen/polyurethane combination was used to cover knitted silk. A series of collagen and polyurethane solutions (4%-7% w/v) in aqueous acetic acid were prepared and electrospun. According to obtained scanning electron microscopy images from pure collagen and polyurethane nanofibers, concentration was set constant at 5% (w/v) for blend solutions of collagen/polyurethane. Afterward, blend solutions with the weight ratios of 75/25, 50/50 and 25/75 were electrospun. Scanning electron microscopy images demonstrated the smooth and uniform morphology for the optimized nanofibers. The least fibers diameter among three weight ratios was found for collagen/polyurethane (25/75) which was 100.86 ± 40 nm and therefore was selected to be electrospun on the knitted silk. Attenuated total reflectance-Fourier transform infrared spectra confirmed the chemical composition of obtained electrospun nanofibers on the knitted silk. Tensile test of the specimens including blend nanofiber, knitted silk and commercial tendon substitute examined and indicated that collagen/polyurethane-coated knitted silk has appropriate mechanical properties as a scaffold for tendon tissue engineering. Then, Alamar Blue assay of the L929 fibroblast cell line seeded on the prepared scaffolds demonstrated appropriate viability of the cells with a significant proliferation on the scaffold containing more collagen content. The results illustrate that the designed structure would be promising for being used as a temporary substitute for tendon repair.

Alignment of collagen fiber in knitted silk scaffold for functional massive rotator cuff repair.

Massive rotator cuff tear is one of the most common shoulder injuries, and poses a formidable clinical challenge to the orthopedic surgeon. Tissue engineering of tendon can potentially overcome the problem. However, more efficacious scaffolds with good biocompatibility, appropriate pore size, favorable inductivity and sufficient mechanical strength for repairing massive rotator cuff tendon injuries need to be developed. In this study, we developed a novel macroporous 3D aligned collagen/silk scaffold, and demonstrated that this novel scaffold enhanced the efficacy of rotator cuff tendon regeneration by inducing aligned supracellular structures similar to natural tendon, which in turn enhanced cellular infiltration and tenogenic differentiation of stem/progenitor cells from both the tendon itself and surrounding tissues. Hence, it can potentially be a clinically useful application for tendon tissue engineering.

Optimizing the mechanical properties of a bi-layered knitted/nanofibrous esophageal prosthesis using artificial intelligence

AbstractThe esophagus is a tubular multi-layer organ that carries the food bolus and liquids from the mouth to the stomach. Esophageal prostheses and scaffolds should have the appropriate mechanical and strain properties in the longitudinal and circumferential directions. A novel bi-layered esophageal prosthesis was produced using knitted tubular silk fabric and a coating of polyurethane (PU) nanofibers. The optimization process was performed in two steps. First, 12 different tubular structures of knitted silk fabrics were produced and mechanical properties were measured in both directions. The mechanical properties were optimized using an artificial neural network (ANN) and a genetic algorithm (GA) and the optimum knitted structure was produced as a substrate for coating with PU nanofibers. In second step, 20 different samples were produced by electrospinning the PU nanofibers at different process conditions (collector speed, feeding rate) on the optimized structure of the knitted fabric. Finally, the elastic properties of the bi-layered tubular structures were measured and optimized by the ANN and GA methods. Results presented show that the optimized structure of the esophageal prosthesis had proper mechanical properties similar to the esophagus. Such a structure can be used as a substitute in esophageal disorders.

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

ABSTRACTVascular 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.

Anterior cruciate ligament reconstruction in a rabbit model using silk-collagen scaffold and comparison with autograft.

The objective of the present study was to perform an in vivo assessment of a novel silk-collagen scaffold for anterior cruciate ligament (ACL) reconstruction. First, a silk-collagen scaffold was fabricated by combining sericin-extracted knitted silk fibroin mesh and type I collagen to mimic the components of the ligament. Scaffolds were electron-beam sterilized and rolled up to replace the ACL in 20 rabbits in the scaffold group, and autologous semitendinosus tendons were used to reconstruct the ACL in the autograft control group. At 4 and 16 weeks after surgery, grafts were retrieved and analyzed for neoligament regeneration and tendon-bone healing. To evaluate neoligament regeneration, H&E and immunohistochemical staining was performed, and to assess tendon-bone healing, micro-CT, biomechanical test, H&E and Russell-Movat pentachrome staining were performed. Cell infiltration increased over time in the scaffold group, and abundant fibroblast-like cells were found in the core of the scaffold graft at 16 weeks postoperatively. Tenascin-C was strongly positive in newly regenerated tissue at 4 and 16 weeks postoperatively in the scaffold group, similar to observations in the autograft group. Compared with the autograft group, tendon-bone healing was better in the scaffold group with trabecular bone growth into the scaffold. The results indicate that the silk-collagen scaffold has considerable potential for clinical application.

Influence of different surface modification treatments on silk biotextiles for tissue engineering applications.

Biotextile structures from silk fibroin have demonstrated to be particularly interesting for tissue engineering (TE) applications due to their high mechanical strength, interconnectivity, porosity, and ability to degrade under physiological conditions. In this work, we described several surface treatments of knitted silk fibroin (SF) scaffolds, namely sodium hydroxide (NaOH) solution, ultraviolet radiation exposure in an ozone atmosphere (UV/O3) and oxygen (O2) plasma treatment followed by acrylic acid (AAc), vinyl phosphonic acid (VPA), and vinyl sulfonic acid (VSA) immersion. The effect of these treatments on the mechanical properties of the textile constructs was evaluated by tensile tests in dry and hydrated states. Surface properties such as morphology, topography, wettability and elemental composition were also affected by the applied treatments. The in vitro biological behavior of L929 fibroblasts revealed that cells were able to adhere and spread both on the untreated and surface-modified textile constructs. The applied treatments had different effects on the scaffolds' surface properties, confirming that these modifications can be considered as useful techniques to modulate the surface of biomaterials according to the targeted application.

Long-term effects of knitted silk–collagen sponge scaffold on anterior cruciate ligament reconstruction and osteoarthritis prevention

Anterior cruciate ligament (ACL) is difficult to heal after injury due to the dynamic fluid environment of joint. Previously, we have achieved satisfactory regeneration of subcutaneous tendon/ligament with knitted silk–collagen sponge scaffold due to its specific “internal-space-preservation” property. This study aims to investigate the long-term effects of knitted silk–collagen sponge scaffold on ACL regeneration and osteoarthritis prevention. The knitted silk–collagen sponge scaffold was fabricated and implanted into a rabbit ACL injury model. The knitted silk–collagen sponge scaffold was found to enhance migration and adhesion of spindle-shaped cells into the scaffold at 2 months post-surgery. After 6 months, ACL treated with the knitted silk–collagen sponge scaffold exhibited increased expression of ligament genes and better microstructural morphology. After 18 months, the knitted silk–collagen sponge scaffold-treated group had more mature ligament structure and direct ligament-to-bone healing. Implanted knitted silk–collagen sponge scaffolds degraded much more slowly compared to subcutaneous implantation. Furthermore, the knitted silk–collagen sponge scaffold effectively protected joint surface cartilage and preserved joint space for up to 18 months post-surgery. These findings thus demonstrated that the knitted silk–collagen sponge scaffold can regenerate functional ACL and prevent osteoarthritis in the long-term, suggesting its clinical use as a functional bioscaffold for ACL reconstruction.

Characterization of silk sponge in the wet state using13C solid state NMR for development of a porous silk vascular graft with small diameter

The 13C solid state NMR spectra of the sponge prepared from Bombyx mori silk fibroin with different 13C labeling sites, [3-13C]Ser, [3-13C]Tyr and [3-13C]Ala were observed in dry and wet states. Here the silk fibroin sponge was prepared using poly(ethylene) glycol diglycidyl ether (PGDE) as porogen. Two broad peaks assigned to β-sheet and random coil were observed for each 13C-labeled site in the dry state. Moreover, in the wet state, one additional sharp peak assigned to random coil with high mobility due to the presence of water was observed. When the silk fibroin aqueous solution and PGDE was mixed in the sponge preparation process, the slow structural change from random coil to β-sheet structure occurs together with decrease in the motion of the silk fibroin backbone chain. The silk fibroin graft with small diameter was prepared with a knitted silk fiber tube coated with this silk fibroin sponge. The high porosity and suture retention strength which are comparable to an ePTFE vascular graft were attained. The excellent results, high patency and high tissue ingrowth, were obtained with the porous silk fibroin graft with small diameter by a rat abdominal aorta implantation experiment.

Konverents "Traditsioonilised kampsunid Läänemeremaades"

The International Crafts Conference ‘Traditional Knitted Sweaters around the Baltic Sea’ was held on the initiative of the Department of Estonian Native Crafts of the University of Tartu Viljandi Culture Academy from 16-18 May 2013. During its three days, the conference focussed on the kinds of sweaters that have historically been knitted around the Baltic Sea and how they reflect our common history. Almost all craft researchers who delivered presentations came to the same conclusion: the tradition of our knitted sweaters started from the knitted silk night sweaters exported from England in the 16th century, which people in the Nordic countries started copying using local materials. The function of the sweater changed from nightwear to an everyday piece of clothing.
 The conference was attended by around a hundred foreign guests from the Shetland Islands, Denmark, Sweden, Finland, Norway, Latvia, Germany and the United States, plus more than a hundred guests from Estonia. The heads of the national central folk art and craft unions of Finland and Sweden also attended, as Estonia handed the status of the lead state of the Nordic Folk Art and Craft Association over to Finland at the conference.
 Approximately 450 people attended the Omamood 2013 fashion show, which took place on the first day of the conference. The second international competition in knitting whilst walking, ‘Walk & Knit’, was also held within the scope of the conference. The success of the conference is a good reason to start planning new international events. This model – where the same event includes looking back at historical items, while considering the implementation of this knowledge in contemporary creations – fulfils the mission of the Department of Estonian Native Crafts and will help to inspire our crafts circles.
 Keywords: sweaters, knitting, Nordic Folk Art and Craft Association

In Vitro Evaluation of Combined Sulfated Silk Fibroin Scaffolds for Vascular Cell Growth

A combined sulfated silk fibroin scaffold is fabricated by modifying a knitted silk scaffold with sulfated silk fibroin sponges. In vitro hemocompatibility evaluation reveals that the combined sulfated silk fibroin scaffolds reduce platelet adhesion and activation, and prolong the activated partial thromboplastin time (APTT), thrombin time (TT), and prothrombin time (PT). The response of porcine endothelial cells (ECs) and smooth muscle cells (SMCs) on the scaffolds is studied to evaluate the cytocompatibility of the scaffolds. Vascular cells are seeded on the scaffolds and cultured for 2 weeks. The scaffolds demonstrate enhanced EC adhesion, proliferation, and maintenance of cellular functions. Moreover, the scaffolds inhibit SMC proliferation and induce expression of contractile SMC marker genes.

Enhanced osteoinductivity and osteoconductivity through hydroxyapatite coating of silk‐based tissue‐engineered ligament scaffold

Hybrid silk scaffolds combining knitted silk fibers and silk sponge have been recently developed for use as ligament-alone grafts. Incorporating an osteoinductive phase into the ends of a ligament scaffold may potentially generate an integrated "bone-ligament-bone" graft and improve graft osteointegration with host bone. To explore the possible application of hydroxyapatite (HA) coating in the fabrication of osteoinductive ends of silk-based scaffold, HA was coated on the hybrid silk scaffold and the effects to the bone-related cells were evaluated. HA could be coated in a uniform and controlled manner on the silk sponge, using an alternate soaking technology, with the amount deposited being dependent on the number of soaking cycles. HA coating also progressively reduced the hydrophobicity of silk surface (decreasing water contact angle from 87° to 42-76°, after 1-3 soaking cycles), making the HA-coated silk scaffold less favorable for initial cell attachments; but the attached cells showed viability and sustained proliferation on the HA-coated scaffold. As demonstrated by real-time polymerase chain reaction and alkaline phosphatase assay, the osteoinductivity of HA-coated silk scaffolds resulted in the osteogenic differentiation of bone marrow mesenchymal stem cells, and the osteoconductivity of HA-coated silk scaffolds supported osteoblasts growth and maintained the properties of mature osteoblasts. These properties of HA-coating demonstrated its possible application in fabricating osteoinductive ends of the silk-based ligament graft to potentially enhance graft-to-host bone integration.

Allogenous Tendon Stem/Progenitor Cells in Silk Scaffold for Functional Shoulder Repair

Tendon stem/progenitor cells (TSPCs) were recently identified within tendon tissues. The aim of this study was to investigate TSPC-seeded knitted silk-collagen sponge scaffold for functional shoulder repair. The multidifferentiation potential, proliferation, and immune properties of TSPCs were investigated in vitro, while the efficacy of TSPC-seeded knitted silk-collagen sponge scaffolds in promoting rotator cuff regeneration was evaluated in vivo within a rabbit model. TSPCs, which exhibited universal stem cell characteristics (i.e., clonogenicity, high proliferative capacity, and multidifferentiation potential), nonimmunogenicity, and immunosuppression, proliferated well on our scaffold in vitro. Implantation of allogenous TSPC-seeded scaffolds within a rabbit rotator cuff injury model did not elicit an immunological reaction, but instead increased fibroblastic cell ingrowth and reduced infiltration of lymphocytes within the implantation sites at 4 and 8 weeks postsurgery. After 12 weeks, the allogenous TSPC-treated group exhibited increased collagen deposition and had better structural and biomechanical properties compared to the control group. This study thus demonstrated that the allogenous TSPC-seeded knitted silk-collagen sponge scaffold enhanced the efficacy of rotator cuff tendon regeneration by differentiating into tenocytes, and by secreting anti-inflammatory cytokines that prevent immunological rejection. Hence, allogenous TSPC-seeded knitted silk-collagen sponge scaffolds can be a clinically useful application for tendon tissue engineering.

A Hybrid Silk/RADA-Based Fibrous Scaffold with Triple Hierarchy for Ligament Regeneration

While silk-based microfibrous scaffolds possess excellent mechanical properties and have been used for ligament tissue-engineering applications, the microenvironment in these scaffolds is not biomimetic. We hypothesized that coating a hybrid silk scaffold with an extracellular matrix (ECM)-like network of self-assembling peptide nanofibers would provide a biomimetic three-dimensional nanofibrous microenvironment and enhance ligament tissue regeneration after bone marrow-derived mesenchymal stem cell (BMSC)-seeding. A novel scaffold possessing a triple structural hierarchy comprising macrofibrous knitted silk fibers, a silk microsponge, and a peptide nanofiber mesh was developed by coating self-assembled RADA16 peptide nanofibers on a silk microfiber-reinforced-sponge scaffold. Compared with the uncoated control, RADA-coated scaffolds showed enhanced BMSC proliferation, metabolism, and fibroblastic differentiation during the 3 weeks of culture. BMSC-seeded RADA-coated scaffolds showed an increasing temporal expression of key fibroblastic ECM proteins (collagen type I and III, tenascin-C), with a significantly higher tenascin-C expression compared with the controls. BMSC-seeded RADA-coated scaffolds also showed a temporal increase in total collagen and glycosaminoglycan production (the amount produced being higher than in control scaffolds) during 3 weeks of culture, and possessed 7% higher maximum tensile load compared with the BMSC-seeded control scaffolds. The results indicate that the BMSC-seeded RADA-coated hybrid silk scaffold system has the potential for use in ligament tissue-engineering applications.