Hemocompatibility of polymeric nanostructured surfaces

Blood Clotting Dissolution in the Presence of a Magnetic Field and Preliminary Study with MG63 Osteoblast-like Cells-Further Developments for Guided Bone Regeneration?

BACKGROUND

The influence of a magnetic field on the activation of bone cells and remodelling of alveolar bone is known to incite bone regeneration. Guided Bone Regeneration (GBR) aims to develop biomimetic scaffolds to allow for the functioning of the barrier and the precise succession of wound healing steps, including haemostasis. The effect of a magnetic field on blood clot dissolution has not been studied yet.

METHODS

We conducted a methodological study on the clot stability in the presence of a static magnetic field (SMF). Preformed whole blood (WB) clots were treated with either a broad proteolytic enzyme (trypsin) or a specific fibrinolytic agent, i.e., tissue-type plasminogen activator (t-PA). MG63 osteoblast-like cells were added to preformed WB clots to assess cell proliferation.

RESULTS

After having experienced a number of clotting and dissolution protocols, we obtained clot stability exerted by SMF when tissue factor (for clotting) and t-PA + plasminogen (for fibrinolysis) were used. WB clots allowed osteoblast-like cells to survive and proliferate, however no obvious effects of the magnetic field were noted.

CONCLUSIONS

Paramagnetic properties of erythrocytes may have influenced the reduction in clot dissolution. Future studies are warranted to fully exploit the combination of magnetic forces, WB clot and cells in GBR applied to orthodontics and prosthodontics.

COVID-19 repellent cloth

In this research work, for the first time, we have developed and demonstrated a COVID-19 repellent coating on cotton cloth that not only repels the virus but also most of the human body fluids (superhemophobic). The coating was tested in the BSL3 lab. The controlled experiments revealed no significant increase in the log viral particles on coated fabric compared to the uncoated surface, evidence that the coated fabric resisted the SARS-CoV-2 inoculum. Further, the coated cloth exhibited excellent dust-free nature and stain resistance against body fluids (blood, urine, bovine serum, water, and saliva aerosol). It also shows sufficient robustness for repetitive usage. The fabrication process for the developed COVID-19 repellent cloth is simple and affordable and can be easily scaled up for mass production. Such coating could be applied on various surfaces, including daily clothes, masks, medical clothes, curtains, etc. The present finding could be a mammoth step towards controlling infection spread, including COVID-19.

Functional coatings enable navigation of light-propelled micromotors in blood for effective biodetoxification

Herein we report the coating of visible light-driven polycaprolactone (PCL) based micromotors with an anti-biofouling poly lactic-co-glycolic acid (PLGA) layer for effective navigation and detoxification in blood samples. The micromotors encapsulate CdSe@ZnS quantum dots as photoresponsive materials and a Fe₃O₄ nanoparticle patch to promote electron transfer and reaction with glucose present in the media for diffusiophoretic propulsion in diluted blood. The coating of the micromotor with the PLGA layer prevents red blood cell adhesion and protein adsorption due to the creation of a highly efficient hydration layer. This results in an enhanced speed and efficient operation for enhanced toxin removal as compared with the bare PCL micromotors. Hemolysis and MTT assays along with no platelets aggregation revealed the high biocompatibility of the micromotors with living cells. Effective adsorptive removal of two relevant toxins, sepsis associated Escherichia coli O111:B4 toxin and snake venom α-bungarotoxin from blood is achieved with the PLGA micromotors. The new developments illustrated here represent one step forward in the use of light-driven micromotors for biomedical applications.

Antithrombogenic properties of Tulbaghia violacea aqueous leaf extracts: assessment of platelet activation and whole blood clotting kinetics

Tulbaghia violacea plant extracts have been investigated for their potential therapeutic effects in the management of various ailments, among which are cardiovascular diseases, due to the wide range of phytocompounds that the plant possesses. One of the major challenges in clinical practice is the inability to control platelet activation and clotting caused by cardiovascular disease interventions. Current treatment methods to inhibit platelet aggregation and thromboxane formation have been associated with major undesirable side effects. This has led to increased research studies on the development of newer and more effective antiplatelet agents. In particular, there has been a growing interest on the potential antiplatelet activity of plant-derived extracts. Hence this study methodically evaluates the anticlotting and antiplatelet properties of T. violacea aqueous leaf extracts. The platelet activity of the plant extracts was assessed using total platelet adhesion, platelet morphology and whole blood clotting kinetics. The 0.1 mg ml⁻¹T. violacea extract mixed with blood plasma demonstrated the lowest platelet adhesion and activation and also reduced whole blood clotting kinetics. There was a reduction of about 70% in platelet adhesion for the 0.1 mg ml⁻¹ treatment compared to the control in the first 15 min which was supported by morphological characterization under SEM. These observations suggest that T. violacea may be a potential antiplatelet therapeutic agent to inhibit the initial step of platelet adhesion and ultimately reduce the incidence of cardiovascular events.

Tulbaghia violacea plant extracts have been investigated for their potential therapeutic effects in the management of various ailments, among which are cardiovascular diseases, due to the wide range of phytocompounds that the plant possesses.

Hydrothermally treated titanium surfaces for enhanced osteogenic differentiation of adipose derived stem cells

Implant surface plays a crucial role in improving osseointegration and long-term implant life. When the implant comes in contact with the bone tissue, the bone marrow mesenchymal cells interact with the implant surface and the surface properties such as morphology, wettability, mechanical properties and chemistry influences cell migration, proliferation and differentiation. Different surface modification strategies such as ceramic coatings, surface dealloying, and surface topography modifications for improving osteointegration have been investigated. However, studies have not yet established which of the surface property is more influential. In this study, titanium surfaces were treated hydrothermally with sodium hydroxide and sulfuric acid separately. This treatment led to the development of two unique surface topography at nanoscale. These modified surfaces were characterized for surface morphology, wettability, chemistry, and crystallinity. Cytotoxicity, cell adhesion, proliferation, morphology, and differentiation of adipose derived stem cells on modified surfaces was investigated. The results indicate that wettability does influence initial cell adhesion. However, the surface morphology can play major role in cell spreading, proliferation and differentiation. The results indicate that titanium surfaces treated hydrothermally with sodium hydroxide led to a nanoporous architecture that promoted appropriate cell interaction with the surface promoting osteoblastic lineage.

Improved hemostatic effects by Fe3+ modified biomimetic PLLA cotton-like mat via sodium alginate grafted with dopamine

The development of an excellent, bioabsorbable hemostatic material for deep wound remains a challenge. In this work, a biodegradable cotton-like biomimetic fibrous mat of poly (l-lactic acid) (PLLA) was made by melt spinning. Subsequently, SD composite was prepared by cross-linking sodium alginate (SA) with dopamine (DA). It was immobilized on the fibre surface, which inspired by mussel byssus. Finally, Fe3+ was loaded onto the 0.5SD/PLLA composite by chelation with the carboxyl of alginate and phenolic hydroxy of dopamine. The haemostasis experiment found that the hemostatic time 47 s in vitro. However, the bleeding volume was 0.097 g and hemostatic time was 23 s when 20Fe3+-0.5SD/PLLA was applied in the haemostasis of the rat liver. As a result of its robust hydrophilicity and bouffant cotton-like structure, it could absorb a large water from blood, which could concentrate the component of blood and reduce the clotting time. Furthermore, the addition of Fe3+ in the 0.5SD/PLLA had a significant effect on improve hemostatic property. It also displayed excellent antibacterial property for Escherichia coli and Staphylococcus aureus. Notably, it possesses superior hemocompatibility, cytocompatibility and histocompatibility. Hence, 20Fe3+-0.5SD/PLLA has high potential application in haemostasis for clinical settings due to its outstanding properties.

A Strong Dual-Component Bioadhesive Based on Solventless Thiol-isocyanate Click Chemistry

Isocyanate is an efficient tissue anchor for engineering of strong bioadhesives. However, isocyanate-containing adhesives were seldom manufactured due to their requirement of water-free administration and time-consuming moisture-induced solidification. To address this issue, here, a solventless dual-component bioadhesive based on thiol-isocyanate cross-linking chemistry is reported. This dual-component bioadhesive consists of a hyperbranched polymer with thiol groups (HBPTE) and an isocyanate-modified polyethylene glycol (PEGNCO). HBPTE and PEGNCO are low-viscosity fluids at room temperature and hence could be used directly as adhesive components, in the absence of a catalyst and a solvent. The thiol-isocyanate click chemistry of components provides the HBPTE-PEGNCO mixture with a gelation time of 1.8-3 min, which makes it acceptable for practical applications. The abundance of isocyanate groups in the adhesive molecule provides strong bonding strength through formation of chemical linkages with reactive groups on the tissue. Moreover, in vitro and in vivo evaluations showed excellent biocompatibility of the HBPTE-PEGNCO adhesive. This dual-component bioadhesive based on solventless thiol-isocyanate click chemistry displayed a fast gelation time and excellent bonding performance, providing a pioneering idea for engineering isocyanate-containing bioadhesives.

Improved hemocompatibility and reduced bacterial adhesion on superhydrophobic titania nanoflower surfaces

Thrombosis formation and bacterial infection are key challenges for blood-contacting medical devices. When blood components encounter a device's surface, proteins are adsorbed, followed by the adhesion and activation of platelets as well as an immune response. This culminates in clot formation via the trapping of red blood cells in a fibrin matrix, which can block the device's function and cause severe complications for the patient. In addition, bacteria may adhere to a device's surface. This can lead to the formation of a biofilm, a protective layer for bacteria that significantly increases resistance to antibiotics. Despite years of research, no long-term solutions have been discovered to combat these issues. To impede thrombosis, patients often take antiplatelet drugs for the life of their device, which can cause excess bleeding and other complications. Patients can take antibiotics to fight bacterial infection, but these are often ineffective if biofilms are formed. Superhydrophobic surfaces show promise in reducing both thrombosis and bacterial infection on devices by impeding contact between biological components and the biomaterial. In this study, superhydrophobic titania nanoflower surfaces were successfully fabricated on a titanium alloy Ti-6Al-4V substrate with hydrothermal synthesis and vapor-phase silanization. The surface topography, surface wettability, surface chemistry, and surface crystallography of the surfaces was subsequently characterized. Surface hemocompatibility was investigated through lactate dehydrogenase (LDH) cytotoxicity analysis, blood-plasma protein adsorption, platelet and leukocyte adhesion and activation, and whole blood clotting analysis. Surface bacterial infection was characterized through Gram-positive and Gram-negative bacterial adhesion and biofilm morphology. The results indicated a reduction of protein adsorption, platelet and leukocyte adhesion and activation, bacterial adhesion, and biofilm formation as well as improved contact angle stability compared to control surfaces.

Superhemophobic and Antivirofouling Coating for Mechanically Durable and Wash-Stable Medical Textiles

Medical textiles have a need for repellency to body fluids such as blood, urine, or sweat that may contain infectious vectors that contaminate surfaces and spread to other individuals. Similarly, viral repellency has yet to be demonstrated and long-term mechanical durability is a major challenge. In this work, we demonstrate a simple, durable, and scalable coating on nonwoven polypropylene textile that is both superhemophobic and antivirofouling. The treatment consists of polytetrafluoroethylene (PTFE) nanoparticles in a solvent thermally sintered to polypropylene (PP) microfibers, which creates a robust, low-surface-energy, multilayer, and multilength scale rough surface. The treated textiles demonstrate a static contact angle of 158.3 ± 2.6° and hysteresis of 4.7 ± 1.7° for fetal bovine serum and reduce serum protein adhesion by 89.7 ± 7.3% (0.99 log). The coated textiles reduce the attachment of adenovirus type 4 and 7a virions by 99.2 ± 0.2% and 97.6 ± 0.1% (2.10 and 1.62 log), respectively, compared to noncoated controls. The treated textiles provide these repellencies by maintaining a Cassie-Baxter state of wetting where the surface area in contact with liquids is reduced by an estimated 350 times (2.54 log) compared to control textiles. Moreover, the treated textiles exhibit unprecedented mechanical durability, maintaining their liquid, protein, and viral repellency after extensive and harsh abrasion and washing. The multilayer, multilength scale roughness provides for mechanical durability through self-similarity, and the samples have high-pressure stability with a breakthrough pressure of about 255 kPa. These properties highlight the potential of durable, repellent coatings for medical gowning, scrubs, or other hygiene textile applications.

In Vitro Investigation of Hemocompatibility of Hydrothermally Treated Titanium and Titanium Alloy Surfaces

For decades, titanium and its alloys have been established as a biocompatible material for cardiovascular medical devices such as heart valves, stents, vascular grafts, catheters, etc. However, thrombosis is one of the reasons for implant failure, where blood clot forms on the implant surface, thus obstructing the flow of the blood and that leads to some serious complications. Various surface modification techniques such as heparin modification, albumin coating, surface anodization, plasma etching, and hydrothermal treatments have been explored to improve the hemocompatibility of titanium-based materials. However, there are several limitations related to the robustness of the surfaces and long-term efficacy in vivo. In this study, titanium and its alloy Ti-6Al-4V were hydrothermally treated to form nanostructured surfaces with the aim to enhance their hemocompatibility. These modified surfaces were characterized for their wettability, surface morphology, surface chemistry, and crystallinity. The hemocompatibility of these surfaces was characterized by evaluating blood plasma protein adsorption, platelet adhesion and activation, platelet-leukocyte complex formation, and whole blood clotting. The results indicate lower fibrinogen adsorption, cell adhesion, platelet activation, and whole blood clotting on hydrothermally treated surfaces. Thus, these surfaces may be a promising approach to prevent thrombosis for several titanium blood-contacting medical devices.

Antithrombogenic properties of Tulbaghia violacea–loaded polycaprolactone nanofibers

A broad range of polymers have been utilized for the development of blood-contacting implantable medical devices; however, their rate of failure has raised the need for developing more hemocompatible biomaterial surfaces. In this study, a novel scaffold based on polycaprolactone incorporated with 10% and 15% (w/w) Tulbaghia violacea plant extracts were fabricated using electrospinning technique. The fabricated scaffolds were then treated with T. violacea aqueous plant extracts (100 and 1000 µg/mL) to investigate their use as interfaces for blood-contacting implants. The 10% Tvio scaffold produced the lowest mean fibre diameter (193 ± 30 nm), whereas the 15% Tvio scaffold produces the highest mean fibre diameter (538 ± 236 nm) when compared with the control polycaprolactone (275 ± 61 nm) scaffold. The number of adhered platelets was directly linked to fibre diameter and concentration of plant extract in such a way that the lowest fibre diameter scaffold (10% Tvio) inhibited platelet adhesion, whereas more platelets adhered to the scaffold with the highest fibre diameter (15% Tvio scaffolds). There was also an increase in platelet adhesion as the concentration of T. violacea was increased from 100 to 1000 µg/mL for all designed scaffolds. The improved blood compatibility demonstrated by the 10% Tvio scaffold suggests that the plant possesses antithrombogenic properties, particularly at lower concentrations.

Evaluating Whole Blood Clotting in vitro on Biomaterial Surfaces

Biomaterial-associated thrombosis is still a major concern for blood-contacting implants. After the medical device is implanted and comes in contact with blood, several complex reactions occur, which may lead to thrombus formation and failure of the device. Therefore, it is essential to evaluate the biomaterial interaction with the whole blood. Several studies have been reported in the literature that evaluate different steps in the coagulation cascade, such as protein adsorption, plasma activation, and platelet adhesion in vitro, however, evaluation of whole blood clotting on biomaterial surfaces is not widely reported. Here, a protocol to evaluate whole blood clotting in vitro on 2D biomaterials surfaces via a simple and fast hemolysis assay is presented. Whole human blood is placed onto the biomaterial surfaces and is allowed to clot for different time periods. After the specific time intervals, the surfaces are transferred into deionized (DI) water to release the free hemoglobin and the absorbance of this solution is measured. The absorbance value is proportional to the free hemoglobin concentration in the DI water due to lysis of red blood cells and gives an indirect correlation to the extent of blood clotting on the biomaterial surfaces. This protocol provides a fast, facile and effective method to measure the anti-thrombogenic properties of biomaterials.

Nanofiber membranes as biomimetic and mechanically stable surface coatings

Elastomers have been extensively exploited to study cell physiology in fields such as mechanobiology, however, their intrinsic high hydrophobicity renders their surfaces incompatible for prolonged cell adhesion and proliferation. Electrospun fiber networks on the other side provide a promising environment for enhanced cell adhesion and growth due to their architecture closely mimicking the structure of the extracellular matrix present within tissues of the human body. Here, we explored the stable integration of electrospun fibers onto the surfaces of elastomeric materials to promote cytocompatibility of these composites. Elastomers based on room temperature vulcanizing silicone (RTV), polydimethylsiloxane (PDMS) as well as functionalized PDMS-based materials were chosen as wafer substrates for attachment of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDFhfp) fibers, a well-known antithrombotic polymer. Electrospinning the fibers onto uncured interfaces acted as bonding agents on the wafers, enabling penetration and formation of a stable bond between the fibers surfaces and the elastomers after curing the interface. Dimensional analysis revealed a relationship between peeling force, intrusion depth and the elastic modulus of the wafers. A design parameter Π_α was extrapolated to be used as a predictive tool of the peeling force when intrusion depth of PVDFhfp fibers and elastic modulus of the wafers are known. Cultivating fibroblasts on these hybrid membranes showed cell attachment and growth over 7 days regardless of the composition of the substrate, confirming high cytocompatibility for all composite materials. The presented approach opens avenues to establish nanofiber morphologies as a novel, stable surface texturing tool for tissue engineering, cell biology, medical devices and textiles.

Interaction of blood plasma proteins with superhemophobic titania nanotube surfaces

The need to improve blood biocompatibility of medical devices is urgent. As soon as blood encounters a biomaterial implant, proteins adsorb on its surfaces, often leading to several complications such as thrombosis and failure of the device. Therefore, controlling protein adsorption plays a major role in developing hemocompatible materials. In this study, the interaction of key blood plasma proteins with superhemophobic titania nanotube substrates and the blood clotting responses was investigated. The substrate stability was evaluated and fibrinogen adsorption and thrombin formation from plasma were assessed using ELISA. Whole blood clotting kinetics was also investigated, and Factor XII activation on the substrates was characterized by an in vitro plasma coagulation time assay. The results show that superhemophobic titania nanotubes are stable and considerably decrease surface protein adsorption/Factor XII activation as well as delay the whole blood clotting, and thus can be a promising approach for designing blood contacting medical devices.

Effect of crystalline phases of titania nanotube arrays on adipose derived stem cell adhesion and proliferation

The aim of this work was to evaluate the cellular response to titanium nanotube arrays with variable crystalline structure. Cytotoxicity, viability and the ability of the titania nanotube arrays to stimulate adhesion and proliferation of adipose derived stem cells (ADSCs) was evaluated. Titania nanotube arrays were fabricated by electrochemical anodization of titanium in diethyleneglycol/hydrofluoric acid electrolyte at 60 V for 6 h, then annealed at 300, 530 and 630 °C for 5 h. The nanotube arrays were characterized using scanning electron microscopy (SEM), contact angle goniometry, x-ray diffraction (XRD) and protein adsorption. ADSCs were cultured on titania nanotube arrays at a density of 1 × 10⁴ cells/ml. The cells were allowed to adhere and to proliferate for 1, 4 and 7 days. Cell viability was characterized by the CellTiter-Blue® Cell Viability Assay; and cell morphology was characterized by SEM. Cell adhesion, proliferation and morphology were characterized using fluorescence microscopy by staining the cells with DAPI and rhodamine/phalloidin. The results from this study showed that the annealing at 300 and 530 °C formed anatase phase, and annealing at 630 °C formed anatase/rutile phase. The results indicated that the modification of the crystalline structure (i.e. anatase/rutile phase) of titania nanotube arrays influenced the ADSC adhesion and proliferation. Future studies are now directed towards evaluating differentiation of this cellular model in osteoblasts.

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.

Surface topography of polylactic acid nanofibrous mats: influence on blood compatibility

Fabricating nanofibrous scaffolds with robust blood compatibility remains an unmet challenge for cardiovascular applications since anti-thrombogenic surface coatings did not withstand physiological shear force. Hence, the present study envisages the influence of smooth and porous topographies of poly(lactic acid) (PLA) nanofibers on hemocompatibility as it could offer time-independent blood compatibility. Further, recent studies have evolved to integrate various contrasting agents for augmenting the prognostic properties of tissue engineered scaffolds; an attempt was also made to synthesize Curcumin-superparamagnetic iron oxide nanoparticle complex (Cur-SPION) as a contrasting agent and impregnated into PLA nanofibers for evaluating the blood compatibility. Herein, electrospun nanofibers of PLA with different topographies (smooth and porous) were fabricated and characterized for surface morphology, zeta potential, fluorescence, and crystallinity. The scaffolds with smooth, porous and rough surface topographies were thoroughly investigated for its hemocompatibility by evaluating hemolysis percentage, platelet adhesion, in vitro kinetic clotting time, serum protein adsorption, plasma recalcification time (PRT), capture and release of erythrocytes. Although the nanofibers of all three groups showed acceptable hemolytic percentage (HP < 5%), the adhered RBCs on Cur-SPION based fibers undergo morphological transformation from biconcave discocytes to echinocytes with cube-like protrusions. On the contrary, no morphological changes were observed in RBCs cultured on smooth and porous nanofibers. Porous fibers exhibited excellent anti-thrombogenic property and adhered lesser platelets and maintained the discoidal morphology of native platelets. Cur-SPION integrated PLA nanofibers showed inactivated platelets with anti-thrombogenic activity compared to smooth nanofibers. In conclusion, PLA nanofibers porous topography did not affect the RBC membrane integrity and maintained discoidal morphology of platelets with superior anti-thrombogenic activity. However, smooth and Cur-SPION integrated PLA nanofibers were found to activate the platelets and deform the RBC membrane integrity, respectively. Hence, the nanofibers with porous structures provide an ideal topography for time-independent hemocompatibility.

Hyaluronan enhancement of expanded polytetrafluoroethylene cardiovascular grafts

Heart disease continues to be the leading cause of death in the United States. The demand for cardiovascular bypass procedures increases annually. Expanded polytetrafluoroethylene is a popular material for replacement implants, but it does have drawbacks such as high thrombogenicity and low patency, particularly in small diameter grafts. Hyaluronan, a naturally occurring polysaccharide in the human body, is known for its wound healing and anticoagulant properties. In this work, we demonstrate that treating the luminal surface of expanded polytetrafluoroethylene grafts with hyaluronan improves hemocompatibility without notably changing its mechanical properties and without significant cytotoxic effects. Surface characterization such as ATR-FTIR and contact angle goniometry demonstrates that hyaluronan treatment successfully changes the surface chemistry and increases hydrophilicity. Tensile properties such as elastic modulus, tensile strength, yield stress and ultimate strain are unchanged by hyaluronan enhancement. Durability data from flow loop studies demonstrate that hyaluronan is durable on the expanded polytetrafluoroethylene inner lumen. Hemocompatibility tests reveal that hyaluronan-treated expanded polytetrafluoroethylene reduces blood clotting and platelet activation. Together our results indicate that hyaluronan-enhanced expanded polytetrafluoroethylene is a promising candidate material for cardiovascular grafts.

Comprehensive assessment of electrospun scaffolds hemocompatibility

Biodegradable polyesters, namely polycaprolactone (PCL) and copolymer of polylactide and polycaprolactone (PLCL) were electrospun into various fibrous structures and their hemocompatibility was evaluated in vitro. Firstly, hemolytic effect was evaluated upon incubation with diluted whole blood. The results showed that the degree of hemolysis depended on chemical composition and fibrous morphology. Electrospun polycaprolactone induced slight degree of hemolysis depending on its molecular weight and fibrous morphology; copolymer PLCL did not cause detectable hemolysis. The influence of coagulation pathways was examined by measurement of coagulation times. It was showed that intrinsic coagulation pathway assessed by activated partial thromboplastin time (APTT) was moderately accelerated after incubation with PCL and prolonged after incubation with copolymer PLCL. Extrinsic activation of coagulation tested by prothrombin time (PT) was slightly accelerated after incubation with all tested electrospun samples. Thrombogenicity assessment of fibrous samples revealed high thrombogenic properties of fibrous materials that was comparable to high degree of collagen thrombogenicity. The level of platelet activation was dependent on chemical composition and surface morphology of tested materials.

Hemocompatibility of Superhemophobic Titania Surfaces

The hemocompatibility of superhemophobic surfaces is investigated and compared with that of hemophobic surfaces and hemophilic surfaces. This analysis indicates that only those superhemophobic surfaces with a robust Cassie-Baxter state display significantly lower platelet adhesion and activation. It is envisioned that the understanding gained through this work will lead to the fabrication of improved hemocompatible, superhemophobic medical implants.

Glycocalyx-Inspired Nitric Oxide-Releasing Surfaces Reduce Platelet Adhesion and Activation on Titanium

The endothelial glycocalyx lining the inside surfaces of blood vessels has multiple features that prevent inflammation, blood clot formation, and infection. This surface represents the highest standard in blood compatibility for long-term contact with blood under physiological flow rates. Engineering materials used in blood-contacting biomedical devices, including metals and polymers, have undesirable interactions with blood that lead to failure modes associated with inflammation, blood clotting, and infection. Platelet adhesion and activation are key events governing these undesirable interactions. In this work, we propose a new surface modification to titanium with three features inspired by the endothelial glcyocalyx: First, titanium surfaces are anodized to produce titania nanotubes with high surface area. Second, the nanostructured surfaces are coated with heparin-chitosan polyelectrolyte multilayers to provide glycosaminoglycan functionalization. Third, chitosan is modified with a nitric oxide-donor chemistry to provide an important antithrombotic small-molecule signal. We show that these surfaces are nontoxic with respect to platelets and leukocytes. The combination of glycocalyx-inspired features results in a dramatic reduction of platelet and leukocyte adhesion and platelet activation.

Physical Characterization and Platelet Interactions under Shear Flows of a Novel Thermoset Polyisobutylene-based Co-polymer

Over the years, several polymers have been developed for use in prosthetic heart valves as alternatives to xenografts. However, most of these materials are beset with a variety of issues, including low material strength, biodegradation, high dynamic creep, calcification, and poor hemocompatibility. We studied the mechanical, surface, and flow-mediated thrombogenic response of poly(styrene-coblock-4-vinylbenzocyclobutene)-polyisobutylene-poly(styrene-coblock-4-vinylbenzocylcobutene) (xSIBS), a thermoset version of the thermoplastic elastomeric polyolefin poly(styrene-block-isobutylene-block-styrene) (SIBS), which has been shown to be resistant to in vivo hydrolysis, oxidation, and enzymolysis. Uniaxial tensile testing yielded an ultimate tensile strength of 35 MPa, 24.5 times greater than that of SIBS. Surface analysis yielded a mean contact angle of 82.05° and surface roughness of 144 nm, which was greater than for poly(ε-caprolactone) (PCL) and poly(methyl methacrylate) (PMMA). However, the change in platelet activation state, a predictor of thrombogenicity, was not significantly different from PCL and PMMA after fluid exposure to 1 dyn/cm(2) and 20 dyn/cm(2). In addition, the number of adherent platelets after 10 dyn/cm(2) flow exposure was on the same order of magnitude as PCL and PMMA. The mechanical strength and low thrombogenicity of xSIBS therefore suggest it as a viable polymeric substrate for fabrication of prosthetic heart valves and other cardiovascular devices.

Controlled Release of Salicylic Acid from Biodegradable Cross-Linked Polyesters

The purpose of this work was to develop a family of cross-linked poly(xylitol adipate salicylate)s with a wide range of tunable release properties for delivering pharmacologically active salicylic acid. The synthesis parameters and release conditions were varied to modulate polyester properties and to understand the mechanism of release. Varying release rates were obtained upon longer curing (35% in the noncured polymer to 10% in the cured polymer in 7 days). Differential salicylic acid loading led to the synthesis of polymers with variable cross-linking and the release could be tuned (100% release for the lowest loading to 30% in the highest loading). Controlled release was monitored by changing various factors, and the release profiles were dependent on the stoichiometric composition, pH, curing time, and presence of enzyme. The polymer released a combination of salicylic acid and disalicylic acid, and the released products were found to be nontoxic. Minimal hemolysis and platelet activation indicated good blood compatibility. These polymers qualify as "bioactive" and "resorbable" and can, therefore, find applications as immunomodulatory resorbable biomaterials with tunable release properties.

Antithrombogenic Properties of Amphiphilic Block Copolymer Coatings: Evaluation of Hemocompatibility Using Whole Blood

Antithrombogenicity is one of the most critical properties required for materials used in biomedical devices, particularly in devices that contact blood. The antithrombogenicity of surfaces coated with amphiphilic block copolymers composed of hydrophobic poly(2-methoxyethyl acrylate) (M) and hydrophilic poly(N,N-dimethylacrylamide) (D) segments was investigated using plasma protein and whole blood with regard to protein adsorption, thrombus formation, platelet activation, and clotting kinetics. Three types of block copolymers and a random copolymer were synthesized using one-pot reversible addition-fragmentation chain-transfer (RAFT) polymerization under conditions of high yield and high molecular weight. Triblock and 4-arm block copolymers with MDM and (MD)₄ architecture, respectively, showed good adhesion to both organic and inorganic substrates, including polyvinyl chloride (PVC) tubes, and the resulting coated surfaces showed superior protein repellency and hemocompatibility compared to the diblock or random copolymer coatings and noncoated control. In a Chandler-loop method with whole blood, PVC tubes coated with MDM and (MD)₄ showed improved thromboresistance and adsorption resistance to blood-derived proteins. This high hemocompatibility was also confirmed with human whole blood by thrombelastography (suppression of blood-clotting behavior in both intrinsic and extrinsic coagulation pathways) and platelet function analyses (significant reductions in the aggregation activity of platelets under two types of stimulation). The antithrombogenicity has been discussed based on the structural analyses of the MDM-coated surface. The results of this study will enable the development of more effective biomedical and analytical devices with excellent antithrombogenic characteristics by using a simple and environmentally friendly approach.

Improved in vitro blood compatibility of polycaprolactone nanowire surfaces

There are a multitude of polymeric materials currently utilized to prepare a variety of blood-contacting implantable medical devices. These devices include tissue grafts, coronary artery and vascular stents, and orthopedic implants. The thrombogenic nature of such materials can cause serious complications in patients, and ultimately lead to functional failure. To date, there is no truly hemocompatible biomaterial surface. Nanostructured surfaces improve cellular interactions but there is a limited amount of information regarding their blood compatibility. In this study, the in vitro blood compatibility of four different surfaces (control, PCL; nanowire, NW; collagen immobilized control, cPCL; collagen immobilized nanowire, cNW) were investigated for their use as interfaces for blood-contacting implants. The results presented here indicate enhanced in vitro blood compatibility of nanowire surfaces compared control surfaces. Although there were no significant differences in leukocyte adhesion, there was a decrease in platelet adhesion on NW surfaces. Scanning electron microscopy images showed a decrease in platelet/leukocyte complexes on cNW surfaces and no apparent complexes were formed on NW surfaces compared to PCL and cPCL surfaces. The increase in these complexes likely contributed to a higher expression of specific markers for platelet and leukocyte activation on PCL and cPCL surfaces. No significant differences were found in contact and complement activation on any surface. Further, thrombin antithrombin complexes were significantly reduced on NW surfaces. A significant increase in hemolysis and fibrinogen adsorption was identified on PCL surfaces likely caused by its hydrophobic surface. This work shows the improved blood-compatibility of nanostructured surfaces, identifying this specific nanoarchitecture as a potential interface for promoting the long-term success of blood-contacting biomaterials.

Nanostructured biomaterials from electrospun demineralized bone matrix: a survey of processing and crosslinking strategies

In the design of scaffolds for tissue engineering biochemical function and nanoscale features are of particular interest. Natural polymers provide a wealth of biochemical function, but do not have the processability of synthetic polymers, limiting their ability to mimic the hierarchy of structures in the natural extracellular matrix. Thus, they are often combined with synthetic carrier polymers to enable processing. Demineralized bone matrix (DBM), a natural polymer, is allograft bone with inorganic material removed. DBM contains the protein components of bone, which includes adhesion ligands and osteoinductive signals, such as important growth factors. Herein we describe a novel method for tuning the nanostructure of DBM through electrospinning without the use of a carrier polymer. This work surveys solvents and solvent blends for electrospinning DBM. Blends of hexafluoroisopropanol and trifluoroacetic acid are studied in detail. The effects of DBM concentration and dissolution time on solution viscosity are also reported and correlated to observed differences in electrospun fiber morphology. We also present a survey of techniques to stabilize the resultant fibers with respect to aqueous environments. Glutaraldehyde vapor treatment is successful at maintaining both macroscopic and microscopic structure of the electrospun DBM fibers. Finally, we report results from tensile testing of stabilized DBM nanofiber mats, and preliminary evaluation of their cytocompatibility. The DBM nanofiber mats exhibit good cytocompatibility toward human dermal fibroblasts (HDF) in a 4-day culture; neither the electrospun solvents nor the cross-linking results in any measurable residual cytotoxicity toward HDF.

The effect of protein corona composition on the interaction of carbon nanotubes with human blood platelets

Carbon nanotubes (CNT) are one of the most promising nanomaterials for use in medicine. The blood biocompatibility of CNT is a critical safety issue. In the bloodstream, proteins bind to CNT through non-covalent interactions to form a protein corona, thereby largely defining the biological properties of the CNT. Here, we characterize the interactions of carboxylated-multiwalled carbon nanotubes (CNTCOOH) with common human proteins and investigate the effect of the different protein coronas on the interaction of CNTCOOH with human blood platelets (PLT). Molecular modeling and different photophysical techniques were employed to characterize the binding of albumin (HSA), fibrinogen (FBG), γ-globulins (IgG) and histone H1 (H1) on CNTCOOH. We found that the identity of protein forming the corona greatly affects the outcome of CNTCOOH's interaction with blood PLT. Bare CNTCOOH-induced PLT aggregation and the release of platelet membrane microparticles (PMP). HSA corona attenuated the PLT aggregating activity of CNTCOOH, while FBG caused the agglomeration of CNTCOOH nanomaterial, thereby diminishing the effect of CNTCOOH on PLT. In contrast, the IgG corona caused PLT fragmentation, and the H1 corona induced a strong PLT aggregation, thus potentiating the release of PMP.

Smooth muscle cell functionality on collagen immobilized polycaprolactone nanowire surfaces

Inhibition of smooth muscle cell (SMC) proliferation and preservation of a differentiated state are important aspects in the management, avoidance and progression of vascular diseases. An understanding of the interaction between SMCs and the biomaterial involved is essential for a successful implant. In this study, we have developed collagen immobilized nanostructured surfaces with controlled arrays of high aspect ratio nanowires for the growth and maintenance of human aortic SMCs. The nanowire surfaces were fabricated from polycaprolactone and were immobilized with collagen. The objective of this study is to reveal how SMCs interact with collagen immobilized nanostructures. The results indicate significantly higher cellular adhesion on nanostructured and collagen immobilized surfaces; however, SMCs on nanostructured surfaces exhibit a more elongated phenotype. The reduction of MTT was significantly lower on nanowire (NW) and collagen immobilized NW (colNW) surfaces, suggesting that SMCs on nanostructured surfaces may be differentiated and slowly dividing. Scanning electron microscopy results reveal that SMCs on nanostructured surfaces are more elongated and that cells are interacting with the nano-features on the surface. After providing differentiation cues, heavy chain myosin and calponin, specific to a contractile SMC phenotype, are upregulated on collagen immobilized surfaces. These results suggest that nanotopography affects cell adhesion, proliferation, as well as cell elongation, while collagen immobilized surfaces greatly affect cell differentiation.

Direct co-culture of endothelial and smooth muscle cells on poly(ε-caprolactone) nanowire surfaces

In this study, we have investigated co-cultures of ECs and SMCs on nanostructured poly(ε-caprolactone) surfaces. The results presented here indicate that nanostructured surfaces may be good interfaces for use in cardiovascular applications and warrants further investigation.

Anti-thrombogenic properties of a nitric oxide-releasing dextran derivative: evaluation of platelet activation and whole blood clotting kinetics

Controlling platelet activation and clotting initiated by cardiovascular interventions remains a major challenge in clinical practice. In this work, the anti-thrombotic properties of a polysaccharide-based nitric oxide (NO)-releasing dextran derivative are presented. Total platelet adhesion, platelet morphology and whole blood clotting kinetics were used as indicators to evaluate the anti-clotting properties of this material. With a total NO delivery of 0.203±0.003 μmol, the NO-releasing dextran derivative (Dex-SNO) mixed with blood plasma demonstrated a significantly lower amount of platelet adhesion and activation onto a surface and reduced whole blood clotting kinetics. Nearly 75% reduction in platelet adhesion and a significant retention of platelet morphology were observed with blood plasma treated with Dex-SNO, suggesting this to be a potential anti-platelet therapeutic agent for preventing thrombosis that does not have an adverse effect on circulating platelets.