Along with an increased incidence of cardiovascular diseases, there is a strong need for small-diameter vascular grafts. Silk has been investigated as a biomaterial to develop such grafts thanks to different processing options. Endothelialization was shown to be extremely important to ensure graft patency and there is ongoing research on the development and behavior of endothelial cells on vascular tissue-engineered scaffolds. This article reviews the endothelialization of silk-based scaffolds processed throughout the years as silk non-woven nets, films, gel spun, electrospun, or woven scaffolds. Encouraging results were reported with these scaffolds both in vitro and in vivo when implanted in small- to middle-sized animals. The use of coatings and heparin or sulfur to enhance, respectively, cell adhesion and scaffold hemocompatibility is further presented. Bioreactors also showed their interest to improve cell adhesion and thus promoting in vitro pre-endothelialization of grafts even though they are still not systematically used. Finally, the importance of the animal models used to study the right mechanism of endothelialization is discussed.
MathersCDLoncarD. Projections of global mortality and burden of disease from 2002 to 2030. PLoS Med2006; 3(11): e442.
3.
MathersCFatDMBoermaJT, et al. (eds). The global burden of disease: 2004 update. Geneva: World Health Organization, 2008.
4.
GoldmanSZadinaKMoritzT, et al. Long-term patency of saphenous vein and left internal mammary artery grafts after coronary artery bypass surgery. J Am Coll Cardiol2004; 44(11): 2149–2156.
5.
RajendranS. Implantable materials: an overview. In: AnandSCKennedyJFMiraftabM, et al. (eds) Medical and healthcare textiles. Amsterdam: Elsevier, 2010, pp. 329–333.
6.
DeanEWUdelsmanBBreuerCK. Current advances in the translation of vascular tissue engineering to the treatment of pediatric congenital heart disease. Yale J Biol Med2012; 85(2): 229–238.
7.
DeutschMMeinhartJFischleinT, et al. Clinical autologous in vitro endothelialization of infrainguinal ePTFE grafts in 100 patients: a 9-year experience. Surgery1999; 126(5): 847–855.
8.
VepariCKaplanDL. Silk as a biomaterial. Prog Polym Sci2007; 32: 991–1007.
9.
AltmanGHDiazFJakubaC, et al. Silk-based biomaterials. Biomaterials2003; 24: 401–416.
10.
HeslotH. Artificial fibrous proteins: a review. Biochimie1998; 80(1): 19–31.
11.
WinklerSKaplanDL. Molecular biology of spider silk. J Biotechnol2000; 74(2): 85–93.
12.
GarelJ-P. The silkworm, a model for molecular and cellular biologists. Trends Biochem Sci1982; 7: 105–108.
13.
KaplanDAdamsWWFarmerB, et al. Silk: biology, structure, properties, and genetics. In: KaplanDAdamsWWFarmerB, et al. (eds) Silk polymers. Washington, DC: American Chemical Society, 1993, pp. 2–16.
14.
ZhouC-Z. Fine organization of Bombyx mori fibroin heavy chain gene. Nucleic Acids Res2000; 28(12): 2413–2419.
15.
TanakaKInoueSMizunoS. Hydrophobic interaction of P25, containing Asn-linked oligosaccharide chains, with the H-L complex of silk fibroin produced byBombyx mori. Insect Biochem Mol Biol1999; 29(3): 269–276.
16.
ThurberAEOmenettoFGKaplanDL. In vivo bioresponses to silk proteins. Biomaterials2015; 71: 145–157.
17.
WangDLiuHFanY. Silk fibroin for vascular regeneration: silk fibroin for vascular regeneration. Microsc Res Tech2017; 80: 280–290.
18.
WangYRudymDDWalshA, et al. In vivo degradation of three-dimensional silk fibroin scaffolds. Biomaterials2008; 29(24–25): 3415–3428.
19.
AraiTFreddiGInnocentiR, et al. Biodegradation of Bombyx mori silk fibroin fibers and films. J Appl Polym Sci2004; 91: 2383–2390.
20.
OmenettoFGKaplanDL. New opportunities for an ancient material. Science2010; 329(5991): 528–531.
21.
ShaoZVollrathF. Surprising strength of silkworm silk. Nature2002; 418(6899): 741.
22.
KunduBRajkhowaRKunduSC, et al. Silk fibroin biomaterials for tissue regenerations. Adv Drug Deliv Rev2013; 65(4): 457–470.
23.
IivanainenEKähäriV-MHeinoJ, et al. Endothelial cell–matrix interactions. Microsc Res Tech2003; 60: 13–22.
24.
RatcliffeA. Tissue engineering of vascular grafts. Matrix Biol2000; 19: 353–357.
25.
Zorc-PleskovicRPleskovicAVraspir-PorentaO, et al. Immune cells and vasa vasorum in the tunica media of atherosclerotic coronary arteries. Bosn J Basic Med Sci2018; 18(3): 240–245.
26.
ClarkJMGlagovS. Transmural organization of the arterial media. The lamellar unit revisited. Arteriosclerosis1985; 5(1): 19–34.
GimbroneMAJrGarcia-CardenaG. Endothelial cell dysfunction and the pathobiology of atherosclerosis. Circ Res2016; 118(4): 620–636.
29.
RadkeDJiaWSharmaD, et al. Tissue engineering at the blood-contacting surface: a review of challenges and strategies in vascular graft development. Adv Healthc Mater2018; 7(15): e1701461.
CinesDBPollakESBuckCA, et al. Endothelial cells in physiology and in the pathophysiology of vascular disorders. Blood1998; 91(10): 3527–3561.
32.
SarkarSSalesKMHamiltonG, et al. Addressing thrombogenicity in vascular graft construction. J Biomed Mater Res B Appl Biomater2007; 82(1): 100–108.
33.
JaffeEAHoyerLWNachmanRL. Synthesis of von Willebrand factor by cultured human endothelial cells. Proc Natl Acad Sci1974; 71: 1906–1909.
34.
McGuiganAPSeftonMV. The influence of biomaterials on endothelial cell thrombogenicity. Biomaterials2007; 28(16): 2547–2571.
35.
AndrewsRKBerndtMC. Platelet physiology and thrombosis. Thromb Res2004; 114: 447–453.
36.
GongXLiuHDingX, et al. Physiological pulsatile flow culture conditions to generate functional endothelium on a sulfated silk fibroin nanofibrous scaffold. Biomaterials2014; 35(17): 4782–4791.
37.
TaylorCAHumphreyJD. Open problems in computational vascular biomechanics: hemodynamics and arterial wall mechanics. Comput Methods Appl Mech Eng2009; 198(45–46): 3514–3523.
38.
DaviesPF. Hemodynamic shear stress and the endothelium in cardiovascular pathophysiology. Nat Clin Pract Cardiovasc Med2009; 6(1): 16–26.
39.
GrevenJPfeiferRZhiQ, et al. Update on the role of endothelial cells in trauma. Eur J Trauma Emerg Surg2018; 44(5): 667–677.
40.
QuillonAFromyBDebretR. Endothelium microenvironment sensing leading to nitric oxide mediated vasodilation: a review of nervous and biomechanical signals. Nitric Oxide2015; 45: 20–26.
41.
UngerREKrump-KonvalinkovaVPetersK, et al. In vitro expression of the endothelial phenotype: comparative study of primary isolated cells and cell lines, including the novel cell line HPMEC-ST1.6R. Microvasc Res2002; 64(3): 384–397.
42.
TresoldiCPellegataAFManteroS. Cells and stimuli in small-caliber blood vessel tissue engineering. Regen Med2015; 10(4): 505–527.
43.
FuchsSHermannsMIKirkpatrickCJ. Retention of a differentiated endothelial phenotype by outgrowth endothelial cells isolated from human peripheral blood and expanded in long-term cultures. Cell Tissue Res2006; 326(1): 79–92.
44.
FuchsSMottaAMigliaresiC, et al. Outgrowth endothelial cells isolated and expanded from human peripheral blood progenitor cells as a potential source of autologous cells for endothelialization of silk fibroin biomaterials. Biomaterials2006; 27(31): 5399–5408.
45.
ClowesAWKirkmanTRReidyMA. Mechanisms of arterial graft healing. Rapid transmural capillary ingrowth provides a source of intimal endothelium and smooth muscle in porous PTFE prostheses. Am J Pathol1986; 123: 220–230.
46.
SánchezPFBreyEMBricenoJC. Endothelialization mechanisms in vascular grafts. J Tissue Eng Regen Med2018; 12(11): 2164–2178.
47.
PiterinaACloonanAMeaneyC, et al. ECM-based materials in cardiovascular applications: inherent healing potential and augmentation of native regenerative processes. Int J Mol Sci2009; 10(10): 4375–4417.
48.
WilliamsDF. Biocompatibility pathways. In: WilliamsD (ed.) Essential biomaterials science. Cambridge: Cambridge University Press, 2014, pp. 220–221.
49.
BaguneidMSSeifalianAMSalacinskiHJ, et al. Tissue engineering of blood vessels. Br J Surg2006; 93: 282–290.
50.
ZillaPBezuidenhoutDHumanP. Prosthetic vascular grafts: wrong models, wrong questions and no healing. Biomaterials2007; 28(34): 5009–5027.
51.
FloreyHWGreerSJKiserJ, et al. The development of the pseudointima lining fabric grafts of the aorta. Br J Exp Pathol1962; 43: 655–660.
WangYKimH-JVunjak-NovakovicG, et al. Stem cell-based tissue engineering with silk biomaterials. Biomaterials2006; 27(36): 6064–6082.
54.
UngerR. Growth of human cells on a non-woven silk fibroin net: a potential for use in tissue engineering. Biomaterials2004; 25(6): 1069–1075.
55.
UngerREPetersKWolfM, et al. Endothelialization of a non-woven silk fibroin net for use in tissue engineering: growth and gene regulation of human endothelial cells. Biomaterials2004; 25(21): 5137–5146.
56.
DuXWangYYuanL, et al. Guiding the behaviors of human umbilical vein endothelial cells with patterned silk fibroin films. Colloids Surf B Biointerfaces2014; 122: 79–84.
57.
HuangFSunLZhengJ. In vitro and in vivo characterization of a silk fibroin-coated polyester vascular prosthesis. Artif Organs2008; 32(12): 932–941.
58.
LiuHLiXNiuX, et al. Improved hemocompatibility and endothelialization of vascular grafts by covalent immobilization of sulfated silk fibroin on poly(lactic-co-glycolic acid) scaffolds. Biomacromolecules2011; 12(8): 2914–2924.
59.
ZhangWWrayLSRnjak-KovacinaJ, et al. Vascularization of hollow channel-modified porous silk scaffolds with endothelial cells for tissue regeneration. Biomaterials2015; 56: 68–77.
60.
WrayLSRnjak-KovacinaJMandalBB, et al. A silk-based scaffold platform with tunable architecture for engineering critically-sized tissue constructs. Biomaterials2012; 33(36): 9214–9224.
61.
ZhuMWangKMeiJ, et al. Fabrication of highly interconnected porous silk fibroin scaffolds for potential use as vascular grafts. Acta Biomater2014; 10(5): 2014–2023.
62.
TaoHMarelliBYangM, et al. Inkjet printing of regenerated silk fibroin: from printable forms to printable functions. Adv Mater2015; 27(29): 4273–4279.
63.
ShiWSunMHuX, et al. Structurally and functionally optimized silk-fibroin–gelatin scaffold using 3D printing to repair cartilage injury in vitro and in vivo. Adv Mater2017; 29(29): 1701089.
64.
SchachtKJungstTSchweinlinM, et al. Biofabrication of cell-loaded 3D spider silk constructs. Angew Chem Int Ed Engl2015; 54(9): 2816–2820.
65.
WeiLWuSKussM, et al. 3D printing of silk fibroin-based hybrid scaffold treated with platelet rich plasma for bone tissue engineering. Bioact Mater2019; 4: 256–260.
66.
MelkeJMidhaSGhoshS, et al. Silk fibroin as biomaterial for bone tissue engineering. Acta Biomater2016; 31: 1–16.
67.
SommerMRSchaffnerMCarnelliD, et al. 3D printing of hierarchical silk fibroin structures. ACS Appl Mater Interfaces2016; 8(50): 34677–34685.
68.
LovettMLCannizzaroCMVunjak-NovakovicG, et al. Gel spinning of silk tubes for tissue engineering. Biomaterials2008; 29(35): 4650–4657.
69.
LovettMEngGKlugeJ, et al. Tubular silk scaffolds for small diameter vascular grafts. Organogenesis2010; 6(4): 217–224.
70.
BosioVEBrownJRodriguezMJ, et al. Biodegradable porous silk microtubes for tissue vascularization. J Mater Chem B2017; 5(6): 1227–1235.
71.
RodriguezMKlugeJASmootD, et al. Fabricating mechanically improved silk-based vascular grafts by solution control of the gel-spinning process. Biomaterials2019; 230: 119567.
72.
SofferLWangXZhangX, et al. Silk-based electrospun tubular scaffolds for tissue-engineered vascular grafts. J Biomater Sci Polym Ed2008; 19(5): 653–664.
73.
ZhangXBaughmanCBKaplanDL. In vitro evaluation of electrospun silk fibroin scaffolds for vascular cell growth. Biomaterials2008; 29(14): 2217–2227.
74.
CattaneoIFigliuzziMAzzolliniN, et al. In vivo regeneration of elastic lamina on fibroin biodegradable vascular scaffold. Int J Artif Organs2013; 36(3): 166–174.
75.
FilipeECSantosMHungJ, et al. Rapid endothelialization of off-the-shelf small diameter silk vascular grafts. JACC Basic Transl Sci2018; 3(1): 38–53.
76.
WangSZhangYWangH, et al. Preparation, characterization and biocompatibility of electrospinning heparin-modified silk fibroin nanofibers. Int J Biol Macromol2011; 48(2): 345–353.
77.
ZhangXWangXKeshavV, et al. Dynamic culture conditions to generate silk-based tissue-engineered vascular grafts. Biomaterials2009; 30(19): 3213–3223.
78.
AlessandrinoAChiariniABiagiottiM, et al. Three-layered silk fibroin tubular scaffold for the repair and regeneration of small caliber blood vessels: from design to in vivo pilot tests. Front Bioeng Biotechnol2019; 7: 356.
79.
EnomotoSSumiMKajimotoK, et al. Long-term patency of small-diameter vascular graft made from fibroin, a silk-based biodegradable material. J Vasc Surg2010; 51(1): 155–164.
80.
YagiTSatoMNakazawaY, et al. Preparation of double-raschel knitted silk vascular grafts and evaluation of short-term function in a rat abdominal aorta. J Artif Organs2011; 14(2): 89–99.
81.
WangJWeiYYiH, et al. Cytocompatibility of a silk fibroin tubular scaffold. Mater Sci Eng C Mater Biol Appl2014; 34: 429–436.
82.
AytemizDSakiyamaWSuzukiY, et al. Small-diameter silk vascular grafts (3 mm diameter) with a double-raschel knitted silk tube coated with silk fibroin sponge. Adv Healthc Mater2013; 2(2): 361–368.
83.
FukayamaTOzaiYShimokawadokoH, et al. Effect of fibroin sponge coating on in vivo performance of knitted silk small diameter vascular grafts. Organogenesis2015; 11(3): 137–151.
84.
LiHWangYSunX, et al. Steady-state behavior and endothelialization of a silk-based small-caliber scaffold in vivo transplantation. Polymers2019; 11: 1303.
85.
NakazawaYSatoMTakahashiR, et al. Development of small-diameter vascular grafts based on silk fibroin fibers from Bombyx mori for vascular regeneration. J Biomater Sci Polym Ed2011; 22(1–3): 195–206.
86.
FukayamaTOzaiYShimokawatokoH, et al. Evaluation of endothelialization in the center part of graft using 3 cm vascular grafts implanted in the abdominal aortae of the rat. J Artif Organs2017; 20(3): 221–229.
87.
ZamaniMKhafajiMNajiM, et al. A biomimetic heparinized composite silk-based vascular scaffold with sustained antithrombogenicity. Sci Rep2017; 7: 4455.
88.
WangQTuFLiuY, et al. The effect of hirudin modification of silk fibroin on cell growth and antithrombogenicity. Mater Sci Eng C Mater Biol Appl2017; 75: 237–246.
89.
TuFLiuYLiH, et al. Vascular cell co-culture on silk fibroin matrix. Polymers2018; 10: 39.
90.
DastagirKDastagirNLimbourgA, et al. In vitro construction of artificial blood vessels using spider silk as a supporting matrix. J Mech Behav Biomed Mater2020; 101: 103436.
91.
HagaMYamamotoSOkamotoH, et al. Histological reactions and the in vivo patency rates of small silk vascular grafts in a canine model. Ann Vasc Dis2017; 10(2): 132–138.
92.
LovettMCannizzaroCDaheronL, et al. Silk fibroin microtubes for blood vessel engineering. Biomaterials2007; 28(35): 5271–5279.
YuEZhangJThomsonJA, et al. Fabrication and characterization of electrospun thermoplastic polyurethane/fibroin small-diameter vascular grafts for vascular tissue engineering. Int Polym Process2016; 31(5): 638–646.
95.
YuEMiH-YZhangJ, et al. Development of biomimetic thermoplastic polyurethane/fibroin small-diameter vascular grafts via a novel electrospinning approach. J Biomed Mater Res A2018; 106(4): 985–996.
96.
BaiLZhaoJLiQ, et al. Biofunctionalized electrospun PCL-PIBMD/SF vascular grafts with PEG and cell-adhesive peptides for endothelialization. Macromol Biosci2019; 19(2): e1800386.
97.
MiH-YJiangYJingX, et al. Fabrication of triple-layered vascular grafts composed of silk fibers, polyacrylamide hydrogel, and polyurethane nanofibers with biomimetic mechanical properties. Mater Sci Eng C Mater Biol Appl2019; 98: 241–249.
98.
JinDHuJXiaD, et al. Evaluation of a simple off-the-shelf bi-layered vascular scaffold based on poly(L-lactide-co-ε-caprolactone)/silk fibroin in vitro and in vivo. Int J Nanomedicine2019; 14: 4261–4276.
99.
BondarBFuchsSMottaA, et al. Functionality of endothelial cells on silk fibroin nets: comparative study of micro- and nanometric fibre size. Biomaterials2008; 29(5): 561–572.
100.
PengGYaoDNiuY, et al. Surface modification of multiple bioactive peptides to improve endothelialization of vascular grafts. Macromol Biosci2019; 19(5): e1800368.
101.
SeibFPHerklotzMBurkeKA, et al. Multifunctional silk–heparin biomaterials for vascular tissue engineering applications. Biomaterials2014; 35(1): 83–91.
102.
MaXCaoCZhuH. The biocompatibility of silk fibroin films containing sulfonated silk fibroin. J Biomed Mater Res B Appl Biomater2006; 78(1): 89–96.
103.
LiuHDingXBiY, et al. In vitro evaluation of combined sulfated silk fibroin scaffolds for vascular cell growth. Macromol Biosci2013; 13: 755–766.
104.
LiuHLiXZhouG, et al. Electrospun sulfated silk fibroin nanofibrous scaffolds for vascular tissue engineering. Biomaterials2011; 32(15): 3784–3793.
105.
LinhardtRJ. 2003Claude S. Hudson award address in carbohydrate chemistry. Heparin: structure and activity. J Med Chem2003; 46(13): 2551–2564.
106.
ZhangYLiXSGuexAG, et al. A compliant and biomimetic three-layered vascular graft for small blood vessels. Biofabrication2017; 9(2): 025010.
107.
ManteroSSadrNRiboldiSA, et al. A new electro-mechanical bioreactor for soft tissue engineering. J Appl Biomater Biomech2007; 5(2): 107–116.
108.
AsnaghiMACandianiGFareS, et al. Trends in biomedical engineering: focus on Regenerative Medicine. J Appl Biomater Biomech2011; 9(2): 73–86.
109.
WendtDRiboldiSACioffiM, et al. Bioreactors in tissue engineering: scientific challenges and clinical perspectives. Berlin; Heidelberg: Springer.
110.
ByromMJBannonPGWhiteGH, et al. Animal models for the assessment of novel vascular conduits. J Vasc Surg2010; 52(1): 176–195.
111.
FukayamaTTakagiKTanakaR, et al. Biological reaction to small-diameter vascular grafts made of silk fibroin implanted in the abdominal aortae of rats. Ann Vasc Surg2015; 29(2): 341–352.
Supplementary Material
Please find the following supplemental material available below.
For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.
For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.
