Hemocompatibility of Poly(vinyl alcohol)-Gelatin Core-Shell Electrospun Nanofibers: A Scaffold for Modulating Platelet Deposition and Activation

Recent Advances in the Fabrication and Performance Optimization of Polyvinyl Alcohol Based Vascular Grafts

Cardiovascular disease is one of the diseases with the highest morbidity and mortality rates worldwide, and coronary artery bypass grafting (CABG) is a fast and effective treatment. More researchers are investigating in artificial blood vessels due to the limitations of autologous blood vessels. Despite the availability of large-diameter vascular grafts (Ø > 6 mm) for clinical use, small-diameter vascular grafts (Ø < 6 mm) have been a challenge for researchers to overcome in recent years. Vascular grafts made of polyvinyl alcohol (PVA) and PVA-based composites have excellent biocompatibility and mechanical characteristics. In order to gain a clearer and more specific understanding of the progress in PVA vascular graft research, particularly regarding the preparation methods, principles, and functionality of PVA vascular graft, this article discusses the mechanical properties, biocompatibility, blood compatibility, and other properties of PVA vascular graft prepared or enhanced with different blends using various techniques that mimic natural blood vessels. The findings reveal the feasibility and promising potential of PVA or PVA-based composite materials as vascular grafts.

Engineered biomimetic micro/nano-materials for tissue regeneration

The incidence of tissue and organ damage caused by various diseases is increasing worldwide. Tissue engineering is a promising strategy of tackling this problem because of its potential to regenerate or replace damaged tissues and organs. The biochemical and biophysical cues of biomaterials can stimulate and induce biological activities such as cell adhesion, proliferation and differentiation, and ultimately achieve tissue repair and regeneration. Micro/nano materials are a special type of biomaterial that can mimic the microstructure of tissues on a microscopic scale due to its precise construction, further providing scaffolds with specific three-dimensional structures to guide the activities of cells. The study and application of biomimetic micro/nano-materials have greatly promoted the development of tissue engineering. This review aims to provide an overview of the different types of micro/nanomaterials, their preparation methods and their application in tissue regeneration.

Comprehensive hemocompatibility analysis on the application of diamond-like carbon to ePTFE artificial vascular prosthesis

The aim of this study was to obtain comprehensive data regarding the hemocompatibility of diamond-like carbon (DLC)-coated expanded polytetrafluoroethylene (ePTFE). DLC increased the hydrophilicity and smoothened the surface and fibrillar structure, respectively, of the ePTFE. DLC-coated ePTFE had more albumin and fibrinogen adsorption and less platelet adhesion than uncoated ePTFE. There were scarce red cell attachments in in vitro human and in vivo animal (rat and swine) whole blood contact tests in both DLC-coated and uncoated ePTFE. DLC-coated ePTFE had a similar but marginally thicker band movement than uncoated-ePTFE with SDS-PAGE after human whole blood contact test. In addition, survival studies of aortic graft replacement in rats (1.5 mm graft) and arteriovenous shunt in goats (4 mm graft) were performed to compare the patency and clot formation between DLC-coated and uncoated ePTFE grafts. Comparable patency was observed in both animal models. However, clots were observed in the luminal surface of the patent 1.5 mm DLC-coated ePTFE grafts, but not in that of uncoated ePTFE grafts. In conclusions, hemocompatibility of DLC-coated ePTFE was high and comparable to that of uncoated ePTFE. However, it failed to improve the hemocompatibility of 1.5 mm ePTFE graft probably because increased fibrinogen adsorption canceled the other beneficial effects of DLC.

An overview of substrate stiffness guided cellular response and its applications in tissue regeneration

Cell-matrix interactions play a critical role in tissue repair and regeneration. With gradual uncovering of substrate mechanical characteristics that can affect cell-matrix interactions, much progress has been made to unravel substrate stiffness-mediated cellular response as well as its underlying mechanisms. Yet, as a part of cell-matrix interaction biology, this field remains in its infancy, and the detailed molecular mechanisms are still elusive regarding scaffold-modulated tissue regeneration. This review provides an overview of recent progress in the area of the substrate stiffness-mediated cellular responses, including 1) the physical determination of substrate stiffness on cell fate and tissue development; 2) the current exploited approaches to manipulate the stiffness of scaffolds; 3) the progress of recent researches to reveal the role of substrate stiffness in cellular responses in some representative tissue-engineered regeneration varying from stiff tissue to soft tissue. This article aims to provide an up-to-date overview of cell mechanobiology research in substrate stiffness mediated cellular response and tissue regeneration with insightful information to facilitate interdisciplinary knowledge transfer and enable the establishment of prognostic markers for the design of suitable biomaterials.

•

Substrate stiffness physically determines cell fate and tissue development.

•

Rational design of scaffolds requires the understanding of cell-matrix interactions.

•

Substrate stiffness depends on scaffold molecular-constituent-structure interaction.

•

Substrate stiffness-mediated cellular responses vary in different tissues.

Metronidazole Topically Immobilized Electrospun Nanofibrous Scaffold: Novel Secondary Intention Wound Healing Accelerator

The process of secondary intention wound healing includes long repair and healing time. Electrospun nanofibrous scaffolds have shown potential for wound dressing. Biopolymers have gained much attention due to their remarkable characteristics such as biodegradability, biocompatibility, non-immunogenicity and nontoxicity. This study anticipated to develop a new composite metronidazole (MTZ) immobilized nanofibrous scaffold based on poly (3-hydroxy butyrate) (PHB) and Gelatin (Gel) to be utilized as a novel secondary intention wound healing accelerator. Herein, PHB and Gel were mixed together at different weight ratios to prepare polymer solutions with final concentration of (7%), loaded with two different concentrations 5% (Z₁) and 10% (Z₂) of MTZ. Nanofibrous scaffolds were obtained by manipulating electrospinning technique. The properties of MTZ immobilized PHB/Gel nanofibrous scaffold were evaluated (SEM, FTIR, TGA, water uptake, contact angle, porosity, mechanical properties and antibacterial activity). Additionally, in vitro cytocompatibility of the obtained nanofibrous scaffolds were assessed by using the cell counting kit-8 (CCK-8 assay). Moreover, in vivo wound healing experiments revealed that the prepared nanofibrous scaffold highly augmented the transforming growth factor (TGF-β) signaling pathway, moderately suppressed the pro-inflammatory cytokine (IL-6). These results indicate that MTZ immobilized PHB/Gel nanofibrous scaffold significantly boost accelerating secondary intention wound healing.

Enhanced blood coagulation and antibacterial activities of carboxymethyl-kappa-carrageenan-containing nanofibers

Ideal wound dressings should be biocompatible, exhibit high antibacterial activity, and promote blood coagulation. To impart these imperative functions, carboxymethyl-kappa-carrageenan was incorporated into poly(vinyl alcohol) nanofibers (PVA-CMKC). The antibacterial activity of the nanofibers was evaluated. Adsorption of two important blood proteins, fibrinogen and albumin, was also assessed. The adhesion and activation of platelets, and the clotting of whole blood were evaluated to characterize the ability of the nanofibers to promote hemostasis. Adhesion and morphology of both Staphylococcus aureus and Pseudomonas aeruginosa were evaluated using fluorescence microscopy and scanning electron microscopy. CMKC-containing nanofibers demonstrated significant increases in platelet adhesion and activation, percentage of coagulation in whole blood clotting test and fibrinogen adsorption, compared to PVA nanofibers, showing blood coagulation activity. Incorporating CMKC also reduces adhesion and viability of S. aureus and P. aeruginosa bacteria after 24 h of incubation. PVA-CMKC nanofibers show potential application as dressings for wound healing applications.

The strategy of modulation blood responses by surface modification with different functional groups on polyester film

A main problem in the design of blood-contacting biomaterials has been the deficiency of a systematic understanding of blood-biomaterial interactions and the strategy to modulate blood responses. In this work, different functional groups including carboxyl (COOH), hydroxyl (OH) and zwitterionic sulfobetaine group (⊕N((CH₃ )₂ )(CH₂ )₃ SO_3-○- , SMDB) were grafted on the poly (butylene terephthalate) (PBT) film to study how the functional groups modulate blood responses and in terms of interaction with the coagulation system, the complement system, and platelets. The results showed protein absorption and platelet adhesion was stronger on the PBT bearing COOH group than PBT films bearing OH and zwitterionic sulfobetaine groups (total protein (μg/cm² ): 32.92 ± 5.89 vs. 22.02 ± 1.44 vs. 19.09 ± 1.59; platelet adhesion (/mm² ): 1,626.7 ± 120.1 vs. 1,395.6 ± 363.3 vs. 1,102.2 ± 373.7), which had a rougher and negatively charged surface, and the coagulation system was inhibited by binding fibrinogen (Fg) and coagulation factors. Meanwhile, PBT-PSMDB showed anticoagulant property and induced platelet activation. As a result, complement formation on these two films were less than PBT bearing OH groups by inhibiting the coagulation system (C3a (ng/ml): 3,745.4 ± 143.9 vs. 3,290.9 ± 249.7 vs. 4,887.9 ± 88.9; C5a (ng/ml): 22.1 ± 2.6 vs. 22.3 ± 1.8 vs. 27.9 ± 2.0). On the other hand, PBT bearing OH groups did not facilitate remarkable platelet adhesion and activation, and had no influence on platelet aggregation, hypotonic shock response, and coagulation system. The above results showed that the blood responses were highly interlinked, and could be modulated by grafting with different functional groups on the biomaterial surfaces. These findings may help identify a strategy to design materials with better hemocompatibility for blood contact, filtration, and purification applications.

Surface engineering at the nanoscale: A way forward to improve coronary stent efficacy

Coronary in-stent restenosis and late stent thrombosis are the two major inadequacies of vascular stents that limit its long-term efficacy. Although restenosis has been successfully inhibited through the use of the current clinical drug-eluting stent which releases antiproliferative drugs, problems of late-stent thrombosis remain a concern due to polymer hypersensitivity and delayed re-endothelialization. Thus, the field of coronary stenting demands devices having enhanced compatibility and effectiveness to endothelial cells. Nanotechnology allows for efficient modulation of surface roughness, chemistry, feature size, and drug/biologics loading, to attain the desired biological response. Hence, surface topographical modification at the nanoscale is a plausible strategy to improve stent performance by utilizing novel design schemes that incorporate nanofeatures via the use of nanostructures, particles, or fibers, with or without the use of drugs/biologics. The main intent of this review is to deliberate on the impact of nanotechnology approaches for stent design and development and the recent advancements in this field on vascular stent performance.

Challenges and strategies for in situ endothelialization and long-term lumen patency of vascular grafts

Vascular diseases are the most prevalent cause of ischemic necrosis of tissue and organ, which even result in dysfunction and death. Vascular regeneration or artificial vascular graft, as the conventional treatment modality, has received keen attentions. However, small-diameter (diameter < 4 mm) vascular grafts have a high risk of thrombosis and intimal hyperplasia (IH), which makes long-term lumen patency challengeable. Endothelial cells (ECs) form the inner endothelium layer, and are crucial for anti-coagulation and thrombogenesis. Thus, promoting in situ endothelialization in vascular graft remodeling takes top priority, which requires recruitment of endothelia progenitor cells (EPCs), migration, adhesion, proliferation and activation of EPCs and ECs. Chemotaxis aimed at ligands on EPC surface can be utilized for EPC homing, while nanofibrous structure, biocompatible surface and cell-capturing molecules on graft surface can be applied for cell adhesion. Moreover, cell orientation can be regulated by topography of scaffold, and cell bioactivity can be modulated by growth factors and therapeutic genes. Additionally, surface modification can also reduce thrombogenesis, and some drug release can inhibit IH. Considering the influence of macrophages on ECs and smooth muscle cells (SMCs), scaffolds loaded with drugs that can promote M2 polarization are alternative strategies. In conclusion, the advanced strategies for enhanced long-term lumen patency of vascular grafts are summarized in this review. Strategies for recruitment of EPCs, adhesion, proliferation and activation of EPCs and ECs, anti-thrombogenesis, anti-IH, and immunomodulation are discussed. Ideal vascular grafts with appropriate surface modification, loading and fabrication strategies are required in further studies.

Syntheses and characterization of anti-thrombotic and anti-oxidative Gastrodin-modified polyurethane for vascular tissue engineering

Vascular grafts must avoid negative inflammatory responses and thrombogenesis to prohibit fibrotic deposition immediately upon implantation and promote the regeneration of small diameter blood vessels (<6 mm inner diameter). Here, polyurethane (PU) elastomers incorporating anti-coagulative and anti-inflammatory Gastrodin were fabricated. The films had inter-connected pores with porosities equal to or greater than 86% and pore sizes ranging from 250 to 400 μm. Incorporation of Gastrodin into PU films resulted in desirable mechanical properties, hydrophilicity, swelling ratios and degradation rates without collapse. The released Gastrodin maintained bioactivity over 21 days as assessed by its anti-oxidative capability. The Gastrodin/PU had better anti-coagulation response (less observable BSA, fibrinogen and platelet adhesion/activation and suppressed clotting in whole blood). Red blood cell compatibility, measured by hemolysis, was greatly improved with 2Gastrodin/PU compared to other Gastrodin/PU groups. Notably, Gastrodin/PU upregulated anti-oxidant factors Nrf2 and HO-1 expression in H2O2 treated HUVECs, correlated with decreasing pro-inflammatory cytokines TNF-α and IL-1β in RAW 264.7 cells. Upon implantation in a subcutaneous pocket, PU was encapsulated by an obvious fibrous capsule, concurrent with a large amount of inflammatory cell infiltration, while Gastrodin/PU induced a thinner fibrous capsule, especially 2Gastrodin/PU. Further, enhanced adhesion and proliferation of HUVECs seeded onto films in vitro demonstrated that 2Gastrodin/PU could help cell recruitment, as evidenced by rapid host cell infiltration and substantial blood vessel formation in vivo. These results indicate that 2Gastrodin/PU has the potential to facilitate blood vessel regeneration, thus providing new insight into the development of clinically effective vascular grafts.

S-Nitrosoglutathione-Based Nitric Oxide-Releasing Nanofibers Exhibit Dual Antimicrobial and Antithrombotic Activity for Biomedical Applications

The novel use of nanofibers as a physical barrier between blood and medical devices has allowed for modifiable, innovative surface coatings on devices ordinarily plagued by thrombosis, delayed healing, and chronic infection. In this study, the nitric oxide (NO) donor S-nitrosoglutathione (GSNO) is blended with the biodegradable polymers polyhydroxybutyrate (PHB) and polylactic acid (PLA) for the fabrication of hemocompatible, antibacterial nanofibers tailored for blood-contacting applications. Stress/strain behavior of different concentrations of PHB and PLA is recorded to optimize the mechanical properties of the nanofibers. Nanofibers incorporated with different concentrations of GSNO (10, 15, 20 wt%) are evaluated based on their NO-releasing kinetics. PLA/PHB + 20 wt% GSNO nanofibers display the greatest NO release over 72 h (0.4-1.5 × 10-10  mol mg-1 min-1 ). NO-releasing fibers successfully reduce viable adhered bacterial counts by ≈80% after 24 h of exposure to Staphylococcus aureus. NO-releasing nanofibers exposed to porcine plasma reduce platelet adhesion by 64.6% compared to control nanofibers. The nanofibers are found noncytotoxic (>95% viability) toward NIH/3T3 mouse fibroblasts, and 4',6-diamidino-2-phenylindole and phalloidin staining shows that fibroblasts cultured on NO-releasing fibers have improved cellular adhesion and functionality. Therefore, these novel NO-releasing nanofibers provide a safe antimicrobial and hemocompatible coating for blood-contacting medical devices.

Antibacterial properties and cytocompatibility of biobased nanofibers of fish scale gelatine, modified polylactide, and freshwater clam shell

We report herein new nanofibers prepared from fish scale gelatine (FSG), modified polylactide (MPLA), and a natural antibacterial agent of freshwater clam (Corbicula fluminea Estefanía) shell powder (FCSP). A preparation of FSG from Mullet scales is also described. To improve the biocompatibility and antibacterial activity of the non-woven nanofibers, MPLA/FCSP was added to enhance their antibacterial properties. FSG was then combined with MPLA/FCSP using an electrospinning technique to improve the biocompatibility of the as-fabricated 100-500-nm-diameter non-woven MPLA/FCSP/FSG nanofibers. The resulting tensile properties and morphological characteristics indicated enhanced adhesion among FSG, FCSP, and MPLA in the MPLA/FCSP/FSG nanofibers, as well as improved water resistance and tensile strength, compared with the PLA/FSG nanofibers. MTT assay, cell-cycle, and apoptosis analyses showed that both PLA/FSG and MPLA/FCSP/FSG nanofibers had good biocompatibility. Increasing the FSG content in PLA/FSG and MPLA/FCSP/FSG nanofibers enhanced cell proliferation and free-radical scavenging ability, but did not affect cell viability. Quantitative analysis of bacteria inhibition revealed that FCSP imparts antibacterial activity.

Gelatin: sources, preparation and application in food and biomedicine

Gelatin is a proteinaceous substance composed of all the essential amino acids (except tryptophan) and derived from collagen using a hydrolysis technique. Hydrogels and modified composites based on gelatin are widely used in the food industry, biomedicine, pharmaceutical industry and food packaging materials due to their biocompatibility, biodegradability, nonimmunogenicity and ability to stimulate cell adhesion and proliferation. Gelatin can absorb 5-10 times its weight of water and is the main ingredient of hard and soft capsules in pharmaceutical industry. It melts above 30°C and easily releases biologically active compounds, nutrients and drugs in human gastrointestinal tract. In addition, gelatin contains arginine-glycine-asparagine RGD-sequences in the polymer structure and contributes to various functions such as antioxidant, anti-hypertensive, anti-microbial, tissue regeneration, wound healing, enhances bone formation and anti-cancer therapy. This article reports a brief overview of gelatin sources, gelatin preparation processes and its physico-chemical properties, as well as advances in the preparation of gelatin-based composite materials and hydrogels for tissue engineering, drug delivery, wound dressings, active packaging using various cross-linking techniques.

One-Pot Covalent Grafting of Gelatin on Poly(Vinyl Alcohol) Hydrogel to Enhance Endothelialization and Hemocompatibility for Synthetic Vascular Graft Applications

Cardiovascular diseases remain the leading cause of death worldwide. Patency rates of clinically-utilized small diameter synthetic vascular grafts such as Dacron® and expanded polytetrafluoroethylene (ePTFE) to treat cardiovascular disease are inadequate due to lack of endothelialization. Sodium trimetaphosphate (STMP) crosslinked PVA could be potentially employed as blood-compatible small diameter vascular graft for the treatment of cardiovascular disease. However, PVA severely lacks cell adhesion properties, and the efforts to endothelialize STMP-PVA have been insufficient to produce a functioning endothelium. To this end, we developed a one-pot method to conjugate cell-adhesive protein via hydroxyl-to-amine coupling using carbonyldiimidazole by targeting residual hydroxyl groups on crosslinked STMP-PVA hydrogel. Primary human umbilical vascular endothelial cells (HUVECs) demonstrated significantly improved cells adhesion, viability and spreading on modified PVA. Cells formed a confluent endothelial monolayer, and expressed vinculin focal adhesions, cell-cell junction protein zonula occludens 1 (ZO1), and vascular endothelial cadherin (VE-Cadherin). Extensive characterization of the blood-compatibility was performed on modified PVA hydrogel by examining platelet activation, platelet microparticle formation, platelet CD61 and CD62P expression, and thrombin generation, which showed that the modified PVA was blood-compatible. Additionally, grafts were tested under whole, flowing blood without any anticoagulants in a non-human primate, arteriovenous shunt model. No differences were seen in platelet or fibrin accumulation between the modified-PVA, unmodified PVA or clinical, ePTFE controls. This study presents a significant step in the modification of PVA for the development of next generation in situ endothelialized synthetic vascular grafts.

Soft-sheath, stiff-core microfiber hydrogel for coating vascular implants

Vascular implants remain clinically challenged due to often-occurring thrombosis and stenosis. Critical to addressing these complications is the design of implant material surfaces to inhibit the activities of platelets, smooth muscle cells (SMCs) and inflammatory cells. Recent mechanobiology studies accentuate the significance of material elasticity to cells and tissues. We thus developed and characterized an implant coating composed of hybrid, viscoelastic microfibers with coaxial core-sheath nanostructure. The coating over metallic stent material was formed by first depositing coaxially-electrospun fibers of poly(L-lactic acid) core and polyethylene glycol dimethacrylate sheath, and then polymerizing fibers with various UV times. Material characterizations were performed to evaluate the coating structure, mechanical property and biocompatibility. Results showed that coaxial microfibers exhibited arterial-like mechanics. The soft surface, high water content and swelling ratio of the coaxial fibers resemble hydrogels, while they are mechanically strong with an elastic modulus of 172-729 kPa. The coating strength and surface elasticity were tunable with the photopolymerization time. Further, the elastic fibers, as conformal coating on stent metal, strongly reduced SMC overgrowth and discouraged platelet adhesion and activation, compared to bare metals. Importantly, after 7-day subcutaneous implantation, coaxial fiber-coated implants showed more favorable in vivo responses with reduced tissue encapsulation, compared to bare stent metals or those coated with a two-layered fiber mixture composed of fibers from individual polymers. The excellent biocompatibility aroused from nanostructural interfaces of hybrid fibers offering hydrated, soft, nonfouling microenvironments. Such integrated fiber system may allow creation of advanced vascular implants that possess physico-mechanical properties of native arteries.

Clopidogrel eluting electrospun polyurethane/polyethylene glycol thromboresistant, hemocompatible nanofibrous scaffolds

Biomaterials used as blood-contacting material must be hemocompatible and exhibit lower thrombotic potential while maintaining hemostasis and angiogenesis. With the aim of developing thromboresistant, hemocompatible nanofibrous scaffolds, polyurethane/polyethylene glycol scaffolds incorporated with 1, 5, and 10 wt% Clopidogrel were fabricated and evaluated for their physiochemical properties, biocompatibility, hemocompatibility, and antithrombotic potential. The results of physicochemical characterization revealed the fabrication of nanometer-sized scaffolds with smooth surfaces. The incorporation of both polyethylene glycol and Clopidogrel to polyurethane enhanced the hydrophilicity and water uptake potential of polyurethane/polyethylene glycol/Clopidogrel scaffolds. The dynamic mechanical analysis revealed the enhancement in mechanical strength of the polyurethane/polyethylene glycol scaffolds on incorporation of Clopidogrel. The polyurethane/polyethylene glycol/Clopidogrel scaffolds showed a tri-phasic drug release pattern. The results of hemocompatibility assessment demonstrated the excellent blood compatibility of the polyurethane/polyethylene glycol/Clopidogrel scaffolds, with the developed scaffolds exhibiting lower hemolysis, increased albumin and plasma protein adsorption while reduction in fibrinogen adsorption. Further, the platelet adhesion was highly suppressed and significant increase in coagulation period was observed for Clopidogrel incorporated scaffolds. The results of cell adhesion and cell viability substantiate the biocompatibility of the developed nanofibrous scaffolds with the HUVEC cell viability on polyurethane/polyethylene glycol, polyurethane/polyethylene glycol/Clopidogrel-1, 5, and 10% at day 7 found to be 12.35, 13.36, 14.85, and 4.18% higher as compared to polyurethane scaffolds, and the NIH/3T3 cell viability found to be 35.27, 70.82, 36.60, and 7.95% higher as compared to polyurethane scaffolds, respectively. Altogether the results of the study advocate the incorporation of Clopidogrel to the polyurethane/polyethylene glycol blend in order to fabricate scaffolds with appropriate antithrombotic property, hemocompatibility, and cell proliferation capacity and thus, might be successfully used as antithrombotic material for biomedical application.

Surface Modification of Electrospun Scaffolds for Endothelialization of Tissue-Engineered Vascular Grafts Using Human Cord Blood-Derived Endothelial Cells

Tissue engineering has gained attention as an alternative approach for developing small diameter tissue-engineered vascular grafts intended for bypass surgery, as an option to treat coronary heart disease. To promote the formation of a healthy endothelial cell monolayer in the lumen of the graft, polycaprolactone/gelatin/fibrinogen scaffolds were developed, and the surface was modified using thermoforming and coating with collagen IV and fibronectin. Human cord blood-derived endothelial cells (hCB-ECs) were seeded onto the scaffolds and the important characteristics of a healthy endothelial cell layer were evaluated under static conditions using human umbilical vein endothelial cells as a control. We found that polycaprolactone/gelatin/fibrinogen scaffolds that were thermoformed and coated are the most suitable for endothelial cell growth. hCB-ECs can proliferate, produce endothelial nitric oxide synthase, respond to interleukin 1 beta, and reduce platelet deposition.

Blood interactions with nano- and microfibers: Recent advances, challenges and applications in nano- and microfibrous hemostatic agents

Nanofibrous materials find a wide range of applications, such as vascular grafts, tissue-engineered scaffolds, or drug delivery systems. This phenomenon can be attributed to almost arbitrary biomaterial modification opportunities created by a multitude of polymers used to form nanofibers, as well as by surface functionalization methods. Among these applications, the hemostatic activity of nanofibrous materials is gaining more and more interest in biomedical research. It is therefore crucial to find both materials and nanofiber structural properties that affect organism responses. The present review critically analyzes the response of blood elements to natural and synthetic polymers, and their blends and composites. Also assessed in this review is the incorporation of pro-coagulative substances or drugs that can decrease bleeding time. The review also discusses the main animal models that were used to assess hemostatic agent safety and effectiveness. STATEMENT OF SIGNIFICANCE: The paper contains an in-depth review of the most representative studies recently published in the topic of nanofibrous hemostatic agents. The topic evolved from analysis of pristine polymeric nanofibers to multifunctional biomaterials. Furthermore, this study is important because it helps clarify the use of specific blood-biomaterial analysis techniques with emphasis on protein adsorption, thrombogenicity and blood coagulation. The paper should be of interest to the readers of Acta biomaterialia who are curious about the strategies and materials used for the development of multifunctional polymer nanofibers for novel blood-contacting applications.

PEGylated stereocomplex polylactide coating of stent for upregulated biocompatibility and drug storage

Treatment of coronary heart disease by percutaneous coronary intervention (PCT) is usually limited to the high restenosis rate after implantation of bare-metal stent. To solve the problem, the coating of PEGylated stereocomplex poly(l-lactide) (PEG-cPLA) was utilized on the surface modification of stainless steel (SS) sheet. Specifically, the 3-aminopropyltriethoxysilane (APTES)-modified methoxy-poly(ethylene glycol)-poly(d-lactide) (mPEG-PDLA) was grafted onto the surface of hydroxylated SS sheet through coupling reaction, and poly(l-lactide)-poly(ethylene glycol)-poly(l-lactide) (PLLA-PEG-PLLA) was coated onto the surface through stereocomplex interaction between DLA and LLA units. The increase of contact angle firstly confirmed the changes of surface composition and hydrophilicity for the PEG-scPLA-modified SS sheet. The decreased fibrinogen adsorption, down-regulated platelet activation, and improved adhesion of human umbilical vein endothelial cells (HUVECs) indicated the excellent biocompatibility of PEG-scPLA-modified SS sheet. In addition, the drug loading capability of SS sheet was greatly upregulated through the formation of scPLA coating on the surface, where fluorescein (FLU) was chosen as a model molecule. Overall, the surface modification of SS sheet with PEG-scPLA could enhance the comprehensive performances, such as biocompatibility and drug loading capability, demonstrating that PEG-scPLA is a promising coating of coronary stent for PCT.

Coaxial electrospun PCL/Gelatin-MA fibers as scaffolds for vascular tissue engineering

Coaxial electrospinning is a technique that allows the production of nanofibers with a core-shell structure. Such fibers present several advantages as materials for the preparation of scaffolds, namely due to the possibility of combining a core with the desired mechanical properties with a shell prepared from biocompatible materials that will establish proper interactions with the host. Herein, core-shell fibrous meshes, composed of a polycaprolactone (PCL) core and a functionalized gelatin shell, were prepared by coaxial electrospinning and then photocrosslinked under UV light aiming to be used in vascular tissue regeneration. The suitability of the meshes for the pretended biomedical application was evaluated by assessing their chemical/physical properties as well as their haemo and biocompatibility in vitro. The obtained results revealed that meshes' shell prepared with a higher content of gelatin showed fibers with diameters presenting a unimodal distribution and a mean value of 600nm. Moreover, those fibers with higher content of gelatin also displayed lower water contact angles, and therefore higher hydrophilicities. Such features are crucial for the good biologic performance displayed by these meshes, when in contact with blood and with Normal Human Dermal Fibroblasts cells.

Synthesis and Fabrication of Collagen-Coated Ostholamide Electrospun Nanofiber Scaffold for Wound Healing

A novel scaffold for effective wound healing treatment was developed utilizing natural product bearing collagen-based biocompatible electrospun nanofibers. Initially, ostholamide (OSA) was synthesized from osthole (a natural coumarin), characterized by ¹H, ¹³C, DEPT-135 NMR, ESI-MS, and FT-IR spectroscopy analysis. OSA was incorporated into polyhydroxybutyrate (PHB) and gelatin (GEL), which serve as templates for electrospun nanofibers. The coating of OSA-PHB-GEL nanofibers with collagen resulted in PHB-GEL-OSA-COL nanofibrous scaffold which mimics extracellular matrix and serves as an effective biomaterial for tissue engineering applications, especially for wound healing. PHB-GEL-OSA-COL, along with PHB-GEL-OSA and collagen film (COLF), was characterized in vitro and in vivo to determine its efficacy. The developed PHB-GEL-OSA-COL nanofibers posed an impressive mechanical stability, an essential requirement for wound healing. The presence of OSA had contributed to antimicrobial efficacy. These scaffolds exhibited efficient antibacterial activity against common wound pathogens, Pseudomonas aeruginosa (P. aeruginosa) and Staphylococcus aureus (S. aureus). The zones of inhibition were observed to be 14 ± 22 and 10 ± 2 mm, respectively. It was observed that nanofibrous scaffold had the ability to release OSA in a controlled manner, and hence, OSA would be present at the site of application and exhibit bioactivity in a sustained manner. PHB-GEL-OSA-COL nanofiber was determined to be stable against enzymatic degradation, which is the most important parameter for promoting proliferation of cells contributing to repair and remodeling of tissues during wound healing applications. As hypothesized, PHB-GEL-OSA-COL was observed to imbibe excellent cytocompatibility, which was determined using NIH 3T3 fibroblast cell proliferation studies. PHB-GEL-OSA-COL exhibited excellent wound healing efficacy which was confirmed using full thickness excision wound model in Wistar rats. The rats treated with PHB-GEL-OSA-COL nanofibrous scaffold displayed enhanced healing when compared to untreated control. Both in vitro and in vivo analysis of PHB-GEL-OSA-COL presents a strong case of therapeutic biomaterial suiting wound repair and regeneration.

A bio-inspired high strength three-layer nanofiber vascular graft with structure guided cell growth

A bio-inspired three-layer vascular graft with strong mechanical properties and good cell biocompatibility was fabricated by electrospinning. It will play an important role in vessel remodeling and regeneration.

A Novel Platelet-Repellent Polyphenolic Surface and Its Micropattern for Platelet Adhesion Detection

Surface patterning provides a powerful tool to the diagnosis of platelet adhesion. However, the current methodologies of constructing platelet-patterned surfaces require laborious and complicated steps. Herein, a novel and simple platelet-repellent surface was reported by metal (Fe³⁺ ions)-polyphenol (tannic acid, TA) coordination interaction. The platelet-repellent effect was significantly better than that of poly(ethylene glycol) (PEG) in a long-term. Moreover, the platelet-repellent behavior could extend to other polyphenols-functionalized surfaces. On the basis of these observations, a TA-based micropattern was fabricated in situ by one-step microcontact printing for well-defined platelet adhesion, which can effectively avoid the traditional introduction of inert hydrophilic polymers and bioactive ligands. Afterward, the TA-based micropattern was applied to monitor the adhesion of defective platelets treated with an antiplatelet drug (tirofiban). This work provided a facile, versatile, and environmentally friendly strategy to construct platelet-repellent polyphenolic surfaces and their micropattern. We expect that this simple micropattern could act as a low-cost and label-free platform for biomaterials and biosensors, and could be widely used in the clinical diagnoses of platelet adhesive functions and the evaluation of antiplatelet therapies.

Polynaphthoxazine-based 1D carbon nano-materials: electrospun fabrication, characterization and electrochemical properties

Polynaphthoxazine-based 1D carbon nano-materials were fabricated by a single-nozzle electrospinning process in a mixed polymer solution followed by curing and carbonization.

Core-shell PVA/gelatin electrospun nanofibers promote human umbilical vein endothelial cell and smooth muscle cell proliferation and migration

Cardiovascular disease is the leading cause of death in the world. In this study, coaxial electrospinning is employed to fabricate fibers in a core-shell structure with polyvinyl alcohol (PVA) in the core and gelatin in the shell for evaluation as a potential vascular tissue engineering construct. PVA, a synthetic polymer, provides mechanical strength to the biocompatible and weak gelatin sheath. The HUVEC (human umbilical vein endothelial cells) and rSMC (rat smooth muscle cells) demonstrated a flattened morphology with multiple attachment sites on the gelatin and coaxial scaffolds, with an increase in cell spreading seen as mechanical stiffness of the scaffold increased. Additionally, HUVEC had an increase in migration on the coaxial scaffolds, which was attributed to the increase in stiffness; however, this increase in migration was not seen with the rSMC, which had the highest outward migration on the flat surfaces (tissue culture polystyrene and gelatin film). Overall, these scaffolds are appealing substrates for vascular tissue engineering applications.

STATEMENT OF SIGNIFICANCE

The worldwide burden of cardiovascular disease presents an ongoing need and opportunity for creating a variety of vascular prostheses. Fabrication of novel scaffolds and constructs for these are needed, providing strength and biological properties facilitating endothelial (EC) and smooth muscle (SMC) cell attachment, migration, and integration. Using electrospinning we formed 3D core:shell nanofibers and examined their effectiveness as substrates for EC and SMC attachment and growth, compared to a 2D (flat) substrate. We found that ECs attached and grew best on 3D core:shell fibers, whereas SMCs favored 2D gelatin surfaces. Interestingly, we found that EC attachment, migration and growth correlated and improved with increasing fiber stiffness. These materials and insights may foster novel vascular prostheses development.

Surface modification and endothelialization of biomaterials as potential scaffolds for vascular tissue engineering applications

This review highlights the recent developments of surface modification and endothelialization of biomaterials in vascular tissue engineering applications.