Silk Vascular Grafts with Optimized Mechanical Properties for the Repair and Regeneration of Small Caliber Blood Vessels

As the incidence of cardiovascular diseases has been growing in recent years, the need for small-diameter vascular grafts is increasing. Considering the limited success of synthetic grafts, vascular tissue engineering/repair/regeneration aim to find novel solutions. Silk fibroin (SF) has been widely investigated for the development of vascular grafts, due to its good biocompatibility, tailorable biodegradability, excellent mechanical properties, and minimal inflammatory reactions. In this study, a new generation of three-layered SF vascular scaffolds has been produced and optimized. Four designs of the SILKGraft vascular prosthesis have been developed with the aim of improving kink resistance and mechanical strength, without compromising the compliance with native vessels and the proven biocompatibility. A more compact arrangement of the textile layer allowed for the increase in the mechanical properties along the longitudinal and circumferential directions and the improvement of the compliance value, which approached that reported for the saphenous and umbilical veins. The higher braid density slightly affected the grafts' morphology, increasing surface roughness, but the novel design mimicked the corrugation approach used for synthetic grafts, causing significant improvements in kink resistance

In-vivo evaluation of silk fibroin small-diameter vascular grafts: state of art of preclinical studies and animal models

Autologous vein and artery remains the first choice for vascular grafting procedures in small-diameter vessels such as coronary and lower limb districts. Unfortunately, these vessels are often found to be unsuitable in atherosclerotic patients due to the presence of calcifications or to insufficient size. Synthetic grafts composed of materials such as expanded polytetrafluoroethylene (ePTFE) are frequently employed as second choice, because of their widespread availability and success in the reconstruction of larger arteries. However, ePTFE grafts with small diameter are plagued by poor patency rates due to surface thrombogenicity and intimal hyperplasia, caused by the bioinertness of the synthetic material and aggravated by low flow conditions. Several bioresorbable and biodegradable polymers have been developed and tested to exploit such issues for their potential stimulation to endothelialization and cell infiltration. Among these, silk fibroin (SF) has shown promising pre-clinical results as material for small-diameter vascular grafts (SDVGs) because of its favorable mechanical and biological properties. A putative advantage in graft infection in comparison with synthetic materials is plausible, although it remains to be demonstrated. Our literature review will focus on the performance of SF-SDVGs in vivo, as evaluated by studies performing vascular anastomosis and interposition procedures, within small and large animal models and different arterial districts. Efficiency under conditions that more accurately mime the human body will provide encouraging evidence towards future clinical application

Silk Fibroin Vascular Graft: From Design to In Vitro and In Vivo Test

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Electrospun Silk Fibroin Scaffolds for Tissue Regeneration: Chemical, Structural, and Toxicological Implications of the Formic Acid-Silk Fibroin Interaction

The dissolution of Bombyx mori silk !broin (SF) !lms in formic acid (FA) for the preparation of electrospinning dopes is widely exploited to produce electrospun SF scaffolds. The SilkBridge® nerve conduit is an example of medical device having in its wall structure an electrospun component produced from an FA spinning dope. Though highly volatile, residual FA remains trapped into the bulk of the SF nano!bers. The purpose of this work is to investigate the type and strength of the interaction between FA and SF in electrospun mats, to quantify its amount and to evaluate its possible toxicological impact on human health. The presence of residual FA in SF mats was detected by FTIR and Raman spectroscopy (new carbonyl peak at about 1,725 cm!1) and by solid state NMR, which revealed a new carbonyl signal at about 164.3 ppm, attributed to FA by isotopic 13C substitution. Changes occurred also in the spectral ranges of hydroxylated amino acids (Ser and Thr), demonstrating that FA interacted with SF by forming formyl esters. The total amount of FA was determined by HS-GC/MS analysis and accounted for 247 ± 20 !mol/g. The greatest part was present as formyl ester, a small part (about 3%) as free FA. Approximately 17% of the 1,500 !mol/g of hydroxy amino acids (Ser and Thr) theoretically available were involved in the formation of formyl esters. Treatment with alkali (Na2CO3) succeeded to remove the greatest part of FA, but not all. Alkali-treated electrospun SF mats underwent morphological, physical, and mechanical changes. The average diameter of the !bers increased from about 440 nm to about 480 nm, the mat shrunk, became stiffer (the modulus increased from about 5.5 MPa to about 7 MPa), and lost elasticity (the strain decreased from about 1 mm/mm to about 0.8 mm/mm). Biocompatibility studies with human adult dermal !broblasts did not show signi!cant difference in cell proliferation (313 ± 18 and 309 ± 23 cells/ mm2 for untreated and alkali-treated SF mat, respectively) and metabolic activity. An in-depth evaluation of the possible toxicological impact of residual FA was made using the SilkBridge® nerve conduit as case study, following the provisions of the ISO 10993-1 standard. The Potential Patient Daily Intake, calculated from the total amount of FA determined by HS-GC/MS, was 2.4 mg/day and the Tolerable Exposure level was set to 35.4 mg/day

Three-Layered Silk Fibroin Tubular Scaffold for the Repair and Regeneration of Small Caliber Blood Vessels: From Design to in vivo Pilot Tests

Silk fibroin (SF) is an eligible biomaterial for the development of small caliber vascular grafts for substitution, repair, and regeneration of blood vessels. This study presents the properties of a newly designed multi-layered SF tubular scaffold for vascular grafting (SilkGraf). The wall architecture consists of two electrospun layers (inner and outer) and an intermediate textile layer. The latter was designed to confer high mechanical performance and resistance on the device, while electrospun layers allow enhancing its biomimicry properties and host\u2019s tissues integration. In vitro cell interaction studies performed with adult Human Coronary Artery Endothelial Cells (HCAECs), Human Aortic Smooth Muscle Cells (HASMCs), and Human Aortic Adventitial Fibroblasts (HAAFs) demonstrated that the electrospun layers favor cell adhesion, survival, and growth. Once cultured in vitro on the SF scaffold the three cell types showed an active metabolism (consumption of glucose and glutamine, release of lactate), and proliferation for up to 20 days. HAAF cells grown on SF showed a significantly lower synthesis of type I procollagen than on polystyrene, meaning a lower fibrotic effect of the SF substrate. The cytokine and chemokine expression patterns were investigated to evaluate the cells\u2019 proliferative and pro-inflammatory attitude. Interestingly, no significant amounts of truly pro-inflammatory cytokines were secreted by any of the three cell types which exhibited a clearly proliferative profile. Good hemocompatibility was observed by complement activation, hemolysis, and hematology assays. Finally, the results of an in vivo preliminary pilot trial on minipig and sheep to assess the functional behavior of implanted SF-based vascular graft identified the sheep as the more apt animal model for next medium-to-long term preclinical trials

Decellularized silk fibroin scaffold primed with adipose mesenchymal stromal cells improves wound healing in diabetic mice

Introduction: Silk fibroin (SF) scaffolds have been shown to be a suitable substrate for tissue engineering and to improve tissue regeneration when cellularized with mesenchymal stromal cells (MSCs). We here demonstrate, for the first time, that electrospun nanofibrous SF patches, cellularized with human adipose-derived MSCs (Ad-MSCs-SF) or decellularized (D-Ad- MSCs-SF) are effective in the treatment of skin wounds, improving skin regeneration in db/db diabetic mice. Methods: The conformational and structural analyses of SF and D-Ad-MSCs-SF patches were performed by scanning electron microscopy, confocal microscopy, Fourier transform infrared spectroscopy and differential scanning calorimetry. Wounds were performed by a 5mm punch biopsy tool on the mouse\u2019s back. Ad-MSCs-SF and D-Ad-MSCs-SF patches were transplanted and the efficacy of treatments was assessed by measuring the wound closure area, by histological examination and by gene expression profile. We further investigated the in vitro angiogenic properties of Ad-MSCs-SF and D-Ad-MSCs-SF patches by affecting migration of human umbilical vein endothelial cells (HUVECs), keratinocytes (KCs) and dermal fibroblasts (DFs), through the aortic ring assay and, finally, by evaluating the release of angiogenic factors. Results: We found that Ad-MSCs adhere and grow on SF, maintaining their phenotypic mesenchymal profile and differentiation capacity. Conformational and structural analyses on SF and D-Ad- MSCs-SF samples, showed that sterilization, decellularization, freezing and storing did not affect the SF structure. When grafted in wounds of diabetic mice, both Ad-MSCs-SF and DAd- MSCs-SF significantly improved tissue regeneration, reducing the wound area respectively by 40% and 35%, within three days, completing the process in around 10 days compared to 15-17 days of controls. RT2 gene profile analysis of the wounds treated with Ad- MSCs-SF and D-Ad-MSCs-SF showed an increment of genes involved in angiogenesis and matrix remodelling. Finally, Ad-MSCs-SF and D-Ad-MSCs-SF co-cultured with HUVECs, DFs and KCs, preferentially enhanced the HUVECs\u2019 migration and the release of angiogenic factors stimulating microvessel outgrowth in the aortic ring assay. Conclusions: Our results highlight for the first time that D-Ad-MSCs-SF patches are almost as effective as Ad-MSCs-SF patches in the treatment of diabetic wounds, acting through a complex mechanism that involves stimulation of angiogenesis. Our data suggest a potential use of DAd- MSCs-SF patches in chronic diabetic ulcers in humans

Electrospun silk fibroin mats for tissue engineering

Processing Silk Fibroin (SF) with electrospinning (ES) offers a very attractive opportunity for producing a variety of 2D and 3D matrices with great potential for tissue regeneration and repair due to the superior biocompatibility and mechanical properties of SF. Different combinations of ES parameters were explored to investigate the best experimental set-up related to the dimension and uniformity of the fibers in the electrospun silk fibroin (ES-SF) mats. Using SEM it was found that the ES-SF mats contain uniform fibers with a diameter in the nanometric range obtained by electrospinning a 7.5% w/v SF solution in formic acid, with an electric field of 2.4 kV/cm and a spinneret-collector distance of 10 cm. FT-IR and DSC analyses were performed to investigate the structure of the ES-SF mats before and after immersion in methanol for different times (5, 10, and 15 min). The methanol treatment was able to promote the crystallization of SF by conformational transition of random coil and other poorly ordered conformations (turns and bends) to the b-sheet structure. The degree of crystallinity was enhanced as shown by the trend of both the FT-IR crystallinity index and the melting/decomposition peak temperature (from DSC). To study the cytocompatibility of ES-SF mats, tests with L929 murine fibroblasts were carried out. Samples were seeded with the cells and incubated for 1, 3, and 7 days at 37 °C. At each time point, SEM investigations and Alamar blue tests were performed. The SEM images showed cell adhesion and proliferation just after 1 day and cell confluence at 7 days. Alamar blue test demonstrated that there were very low differences between cell viability on ES-SF mats and the tissue culture plastic control

L'informazione sportiva: dagli anni '60 al Codice Media e Sport

Il volume raccoglie una serie di contributi che approfondiscono gli aspetti storici, sociali e istituzionali che hanno condotto all’elaborazione del Codice Media Sport per l’autoregolamentazione dell’informazione sportiva (2007). La necessità di tale codice nasce dalla rilevazione del continuo manifestarsi di episodi di violenza nel corso degli eventi sportivi. Tali episodi non sono sempre adeguatamente stigmatizzati dal circuito informativo e in taluni casi i molteplici messaggi trasmessi dai vari soggetti coinvolti nella produzione e distribuzione di informazioni legate ad eventi e pratiche sportive hanno contribuito a fomentare atteggiamenti di intolleranza e comportamenti violenti. D’altro canto il circuito mass-mediatico, proprio in virtù dell’influenza che è in grado di esercitare, può fornire invece un fondamentale contributo alla crescita culturale e civile dei soggetti che partecipano, a vario titolo, agli eventi sportivi, facendosi artefice della promozione dei valori sportivi