Blood compatible materials: state of the art

Reduction of thrombotic and inflammatory complications of polystyrene-block-polyisoprene-block-polystyrene (SIS) with one-step electrospinning

Polystyrene-block-polyisoprene-block-polystyrene (SIS) has been used as biomaterials due to its soft and stable properties under physiological conditions. However, the thrombotic and inflammatory complications caused by SIS restrain its application as blood-contacting implant. To overcome this problem, the hydrophilic core-shell structured SIS-based microfiber with antioxidant encapsulation is fabricated with one-step reactive electrospinning. We demonstrate that the phase separation of SIS and acylated Pluronic F127 (F127-DA) components and crosslinking during electrospinning renders the microfiber blood compatible and stable under physiological condition; the encapsulation of 2-O-d-glucopyranosyl-l-ascorbic acid (AA-2G) in microfiber and subsequent release of AA-2G detoxifies the excess reactive oxygen species (ROS). The microfibers are nontoxic to cells and promote the fast growth and proliferation of human umbilical vein endothelial cells (HUVECs) in the presence of ROS; the thrombotic and inflammatory complications are effectively reduced with implant evaluation in vivo. Therefore, our work paves a new way to improve the biocompatibility of SIS, making it a promising candidate for blood contact materials.

The effect of Substance P/Heparin conjugated PLCL polymer coating of bioinert ePTFE vascular grafts on the recruitment of both ECs and SMCs for accelerated regeneration

Artificial vascular grafts consisting of ePTFE have been mainly used in clinics for the treatment of cardiovascular disease. However, artificial grafts can become clogged after a long time due to thrombosis, as graft maturation by endothelialization is limited. The strategy introduced in this study is to induce graft remodeling through interaction between the bioinert graft and the body. The Substance P (SP) and heparin were covalently conjugated with PLCL, an elastic biocompatible copolymer and the Substance P-conjugated PLCL (SP-PLCL) and/or heparin-conjugated PLCL (Hep-PLCL) were vacuum-coated onto ePTFE vascular grafts. To assess the effectiveness of the coating, coated samples were evaluated by implanting them subcutaneously into SD-Rats. Coatings allow grafts to be remodeled by creating a microenvironment where cells can grow by infiltrating into the grafts while also greatly enhancing angiogenesis. In particular, a double coating of Hep-PLCL and SP-PLCL (Hep/SP-PLCL) at four weeks showed markedly improved vascular remodeling through the recruitment of mesenchymal stem cells (MSCs), vascular cells (ECs, SMCs) and M2 macrophages. Based on these results, it is expected that when the Hep/SP-PLCL-coated ePTFE vascular grafts are implanted in situ, long-term patency will be assured due to the appropriate formation of an endothelial layer and smooth muscle cells in the grafts like native vessels.

In Vitro Thrombogenicity Testing of Biomaterials

The short- and long-term thrombogenicity of implant materials is still unpredictable, which is a significant challenge for the treatment of cardiovascular diseases. A knowledge-based approach for implementing biofunctions in materials requires a detailed understanding of the medical device in the biological system. In particular, the interplay between material and blood components/cells as well as standardized and commonly acknowledged in vitro test methods allowing a reproducible categorization of the material thrombogenicity requires further attention. Here, the status of in vitro thrombogenicity testing methods for biomaterials is reviewed, particularly taking in view the preparation of test materials and references, the selection and characterization of donors and blood samples, the prerequisites for reproducible approaches and applied test systems. Recent joint approaches in finding common standards for a reproducible testing are summarized and perspectives for a more disease oriented in vitro thrombogenicity testing are discussed.

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.

The blood compatibility challenge. Part 2: Protein adsorption phenomena governing blood reactivity

The adsorption of proteins is the initiating event in the processes occurring when blood contacts a "foreign" surface in a medical device, leading inevitably to thrombus formation. Knowledge of protein adsorption in this context has accumulated over many years but remains fragmentary and incomplete. Moreover, the significance and relevance of the information for blood compatibility are not entirely agreed upon in the biomaterials research community. In this review, protein adsorption from blood is discussed under the headings "agreed upon" and "not agreed upon or not known" with respect to: protein layer composition, effects on coagulation and complement activation, effects on platelet adhesion and activation, protein conformational change and denaturation, prevention of nonspecific protein adsorption, and controlling/tailoring the protein layer composition. STATEMENT OF SIGNIFICANCE: This paper is part 2 of a series of 4 reviews discussing the problem of biomaterial associated thrombogenicity. The objective was to highlight features of broad agreement and provide commentary on those aspects of the problem that were subject to dispute. We hope that future investigators will update these reviews as new scholarship resolves the uncertainties of today.

The blood compatibility challenge. Part 4: Surface modification for hemocompatible materials: Passive and active approaches to guide blood-material interactions

Biomedical devices in the blood flow disturb the fine-tuned balance of pro- and anti-coagulant factors in blood and vessel wall. Numerous technologies have been suggested to reduce coagulant and inflammatory responses of the body towards the device material, ranging from camouflage effects to permanent activity and further to a responsive interaction with the host systems. However, not all types of modification are suitable for all types of medical products. This review has a focus on application-oriented considerations of hemocompatible surface fittings. Thus, passive versus bioactive modifications are discussed along with the control of protein adsorption, stability of the immobilization, and the type of bioactive substance, biological or synthetic. Further considerations are related to the target system, whether enzymes or cells should be addressed in arterial or venous system, or whether the blood vessel wall is addressed. Recent developments like feedback controlled or self-renewing systems for drug release or addressing cellular regulation pathways of blood platelets and endothelial cells are paradigms for a generation of blood contacting devices, which are hemocompatible by cooperation with the host system. STATEMENT OF SIGNIFICANCE: This paper is part 4 of a series of 4 reviews discussing the problem of biomaterial associated thrombogenicity. The objective was to highlight features of broad agreement and provide commentary on those aspects of the problem that were subject to dispute. We hope that future investigators will update these reviews as new scholarship resolves the uncertainties of today.

Controlling the Hydration Structure with a Small Amount of Fluorine To Produce Blood Compatible Fluorinated Poly(2-methoxyethyl acrylate)

Poly(2-methoxyethyl acrylate) (PMEA) shows excellent blood compatibility because of the existence of intermediate water. Various modifications of PMEA by changing its main or side chain's chemical structure allowed tuning of the water content and the blood compatibility of numerous novel polymers. Here, we exploit a possibility of manipulating the surface hydration structure of PMEA by incorporation of small amounts of hydrophobic fluorine groups in MEA polymers using atom-transfer radical polymerization and the (macro) initiator concept. Two kinds of fluorinated MEA polymers with similar molecular weights and the same 5.5 mol % of fluorine content were synthesized using the bromoester of 2,2,3,3,4,4,5,5,6,6,7,7,8,8-pentadecafluoro-1-octanol (F15) and poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) as (macro) initiators, appearing liquid and solid at room temperature, respectively. The fibrinogen adsorption of the two varieties of fluorinated MEA polymers was different, which could not be explained only by the bulk hydration structure. Both polymers show a nanostructured morphology in the hydrated state with different sizes of the features. The measured elastic modulus of the domains appearing in atomic force microscopy and the intermediate water content shed light on the distinct mechanism of blood compatibility. Contact angle measurements reveal the surface hydration dynamics-while in the hydrated state, F15- b-PMEA reorients easily to the surface exposing its PMEA part to the water, the small solid PTFEMA block with high glass-transition temperature suppresses the movement of PTFEMA- b-PMEA and its reconstruction on the surface. These findings illustrate that in order to make a better blood compatible polymer, the chains containing sufficient intermediate water need to be mobile and efficiently oriented to the water surface.

An Albumin Biopassive Polyallylamine Film with Improved Blood Compatibility for Metal Devices

Nowadays, a variety of materials are employed to make numerous medical devices, including metals, polymers, ceramics, and others. Blood-contact devices are one of the major classes of these medical devices, and they have been widely applied in clinical settings. Blood-contact devices usually need to have good mechanical properties to maintain clinical performance. Metal materials are one desirable candidate to fabricate blood-contact devices due to their excellent mechanical properties and machinability, although the blood compatibility of existing blood-contact devices is better than other medical devices, such as artificial joints and artificial crystals. However, blood coagulation still occurs when these devices are used in clinical settings. Therefore, it is necessary to develop a new generation of blood-contact devices with fewer complications, and the key factor is to develop novel biomaterials with good blood compatibility. In this work, one albumin biopassive polyallylamine film was successfully established onto the 316L stainless steel (SS) surface. The polyallylamine film was prepared by plasma polymerization in the vacuum chamber, and then polyallylamine film was annealed at 150 °C for 1 h. The chemical compositions of the plasma polymerized polyallylamine film (PPAa) and the annealed polyallylamine film (HT-PPAa) were characterized by Fourier transform infrared spectrum (FTIR). Then, the wettability, surface topography, and thickness of the PPAa and HT-PPAa were also evaluated. HT-PPAa showed increased stability when compared with PPAa film. The major amino groups remained on the surface of HT-PPAa after annealing, indicating that this could be a good platform for numerous molecules' immobilization. Subsequently, the bovine serum albumin (BSA) was immobilized onto the HT-PPAa surface. The successful introduction of the BSA was confirmed by the FTIR and XPS detections. The blood compatibility of these modified films was evaluated by platelets adhesion and activation assays. The number of the platelets that adhered on BSA-modified HT-PPAa film was significantly decreased, and the activation degree of the adhered platelets was also decreased. These data revealed that the blood compatibility of the polyallylamine film was improved after BSA immobilized. This work provides a facile and effective approach to develop novel surface treatment for new-generation blood-contact devices with improved hemocompatibility.

Modifying the Band Gap of Semiconducting Two-Dimensional Materials by Polymer Assembly into Different Structures

Polyethylene glycol (PEG) assembled on the surface of two-dimensional tungsten disulfide (WS₂) into a limited number of nanoislands (NIs), nanoshells (NSs), and granular nanoparticulates (GNPs) depending on its chain length. NI assemblies showed a nonmeasurable shift of photoluminescence (PL) and the A and B absorption peaks of WS₂. This confirmed that the electronic doping by thiol is not effective. The PEG NS assembly displayed a smaller red shift of the PL and a slight decrease of the energy difference between the A and B absorption peaks of WS₂. However, increasing the dielectric function on the surface of WS₂ has a small influence on their optical properties. The PEG NP assembly on WS₂ exhibited a significant red shift of the PL spectrum and a large decrease of the energy difference between A and B absorption peaks. Deforming the WS₂ sheet by the PEG NP assembly decreased the orbital coupling and lowered the electronic direct band gap significantly. Raman bands of WS₂ are shifted to a higher frequency on improving its mechanical strength after the PEG assembly.

BloodSurf 2017: News from the blood-biomaterial frontier

From stents and large-diameter vascular grafts, to mechanical heart valves and blood pumps, blood-contacting devices are enjoying significant clinical success owing to the application of systemic antiplatelet and anticoagulation therapies. On the contrary, research into material and device hemocompatibility aimed at alleviating the need for systemic therapies has suffered a decline. This research area is undergoing a renaissance fueled by recent fundamental insights into coagulation and inflammation that are offering new avenues of investigation, the growing recognition of the limitations facing existing therapeutic approaches, and the severity of the cardiovascular disorders epidemic. This Opinion article discusses clinical needs for hemocompatible materials and the emerging research directions for fulfilling those needs. Based on the 2017 BloodSurf conference that brought together clinicians, scientists, and engineers from academia, industry, and regulatory bodies, its purpose is to draw the attention of the wider clinical and scientific community to stimulate further growth. STATEMENT OF SIGNIFICANCE: The article highlights recent fundamental insights into coagulation, inflammation, and blood-biomaterial interactions that are fueling a renaissance in the field of material hemocompatibility. It will be useful for clinicians, scientists, engineers, representatives of industry and regulatory bodies working on the problem of developing hemocompatible materials and devices for treating cardiovascular disorders.

Blood coagulation response and bacterial adhesion to biomimetic polyurethane biomaterials prepared with surface texturing and nitric oxide release

A dual functional polyurethane (PU) film that mimics aspects of blood vessel inner surfaces by combining surface texturing and nitric oxide (NO) release was fabricated through a soft lithography two-stage replication process. The fabrication of submicron textures on the polymer surface was followed by solvent impregnation with the NO donor, S-nitroso-N-acetylpenicillamine (SNAP). An in vitro plasma coagulation assay showed that the biomimetic surface significantly increased the plasma coagulation time and also exhibited reduced platelet adhesion and activation, thereby reducing the risk of blood coagulation and thrombosis. A contact activation assay for coagulation factor XII (FXII) demonstrated that both NO release and surface texturing also reduced FXII contact activation, which contributes to the inhibition of plasma coagulation. The biomimetic surface was also evaluated for bacterial adhesion in plasma and results demonstrate that this combined strategy enables a synergistic effect to reduce bacterial adhesion of Staphylococcus epidermidis, Staphylococcus aureus, and Pseudomonas aeruginosa microorganisms. The results strongly suggest that the biomimetic modification with surface texturing and NO release provides an effective approach to improve the biocompatibility of polymeric materials in combating thrombosis and microbial infection. STATEMENT OF SIGNIFICANCE: (1) Developed a dual functional polyurethane (PU) film that mimics blood vessel inner surface by combining surface texturing and nitric oxide (NO) release for combatting biomaterial associated thrombosis and microbial infection. (2) Studied the blood coagulation response and bacterial adhesion to such biomimetic PU surfaces, and demonstrated that the combination of surface texturing and NO release synergistically reduced the platelet adhesion and bacterial adhesion in plasma, providing an effective approach to improve the biocompatibility of biomaterials used in blood-contacting medical devices. (3) The NO releasing surface significantly inhibits the plasma coagulation via the reduction of contact activation of FXII, indicating the multifunctional roles of NO in improving the biocompatibility of biomaterials in blood-contacting medical devices.

Engineering modifiers bearing benzophenone with enhanced reactivity to construct surface microstructures

A novel strategy is proposed to construct a patterned surface with controllable thickness by designing the chain backbone of BP-capped modifiers.

A negative correlation between water content and protein adsorption on polymer brushes

A negative correlation between the water content inside polymer brushes and protein adsorption.

Low-fouling, mixed-charge poly-l-lysine polymers with anionic oligopeptide side-chains

Biosensors and biomedical devices require antifouling surfaces to prevent the non-specific adhesion of proteins or cells, for example, when aiming to detect circulating cancer biomarkers in complex natural media (e.g., in blood plasma or serum). A mixed-charge polymer was prepared by the coupling of a cationic polyelectrolyte and an anionic oligopeptide through a modified "grafting-to" method. The poly-l-lysine (PLL) backbone was modified with different percentages (y%) of maleimide-NHS ester chains (PLL-mal(y%), from 13% to 26%), to produce cationic polymers with specific grafting densities, obtaining a mixed-charge polymer. The anionic oligopeptide structure (CEEEEE) included one cysteine (C) and five glutamic acid (E) units, which were attached to the PLL-mal(y%) polymers, preadsorbed on gold substrates, through the thiol-maleimide Michael-type addition. Contact angle and PM-IRRAS data confirmed monolayer formation of the modified PLLs. Antifouling properties of peptide-PLL surfaces were assessed in adsorption studies using quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance imaging (SPRI) techniques. PLL-mal(26%)-CEEEEE showed the best antifouling performance in single-protein solutions, and the nonspecific adsorption of proteins was 46 ng cm^-2 using diluted human plasma samples. The new PLL-mal(26%)-CEEEEE polymer offers a prominent low-fouling activity in complex media, with rapid and simple procedures for the synthesis and functionalization of the surface compared to conventional non-fouling materials.

Thermo-triggered ultrafast self-healing of microporous coating for on-demand encapsulation of biomacromolecules

Medical coatings cooperated with biomacromolecules can regulate biological events and tissue responses, thus increasing medical implant longevity and providing improved and/or new therapeutic functions. In particular, medical coatings, which can load the correct species and doses of biomacromolecules according to individual diagnoses, will significantly optimize treatment effects and satisfy the rising clinical need of "precision medicine". Herein, we report on a dynamic microporous coating with an ultrafast self-healing property to fulfill the "load-and-play" concept for "precision medicine". A structure-switchable coating based on poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) triblock copolymer network is constructed. The coating can be switched to microporous morphology via a water swelling and freeze-drying process. Then, through a mild thermo-trigger as low as 40 °C, this spongy coating can undergo self-healing to switch back to a pore-free structure within minutes to even 5 s. Based on this dynamic coating, we suggest a simple and versatile method to encapsulate biomacromolecules for surface-mediated delivery. The ultrafast self-healing of the microporous structure enables uniform incorporation of biomacromolecules with an easily achieved high loading of albumin of 16.3 μg/cm² within 1 min. More importantly, controllable encapsulation can be realized by simple control of the concentration of the loading solution. We further demonstrate that the encapsulated biomacromolecules retained their bioactivity. This work may benefit clinicians with flexibility to provide personalized medical coatings for individual patients during treatment.

Fabrication of Supramolecular Bioactive Surfaces via β-Cyclodextrin-Based Host-Guest Interactions

Supramolecular host-guest interactions provide a facile and versatile basis for the construction of sophisticated structures and functional assemblies through specific molecular recognition of host and guest molecules to form inclusion complexes. In recent years, these interactions have been exploited as a means of attaching bioactive molecules and polymers to solid substrates for the fabrication of bioactive surfaces. Using a common host molecule, β-cyclodextrin (β-CD), and various guest molecules as molecular building blocks, we fabricated several types of bioactive surfaces with multifunctionality and/or function switchability via host-guest interactions. Other groups have also taken this approach, and several intelligent designs have been developed. The results of these investigations indicate that, compared to the more common covalent bonding-based methods for attachment of bioactive ligands, host-guest based methods are simple, more broadly ("universally") applicable, and allow convenient renewal of bioactivity. In this Spotlight on Applications, we review and summarize recent developments in the fabrication of supramolecular bioactive surfaces via β-CD-based host-guest interactions. The main focus is on the work from our laboratory, but highlights on work from other groups are included. Applications of the materials are also emphasized. These surfaces can be categorized into three types based on: (i) self-assembled monolayers, (ii) polymer brushes, and (iii) multilayered films. The host-guest strategy can be extended from material surfaces to living cell surfaces, and work along these lines is also reviewed. Finally, a brief perspective on the developments of supramolecular bioactive surfaces in the future is presented.

Nanostructured Surfaces That Mimic the Vascular Endothelial Glycocalyx Reduce Blood Protein Adsorption and Prevent Fibrin Network Formation

Blood-contacting materials are critical in many applications where long-term performance is desired. However, there are currently no engineered materials used in cardiovascular implants and devices that completely prevent clotting when in long-term contact with whole blood. The most common approach to developing next-generation blood-compatible materials is to design surface chemistries and structures that reduce or eliminate protein adsorption to prevent blood clotting. This work proposes a new paradigm for controlling protein-surface interactions by strategically mimicking key features of the glycocalyx lining the interior surfaces of blood vessels: negatively charged glycosaminoglycans organized into a polymer brush with nanoscale domains. The interactions of two important proteins from blood (albumin and fibrinogen) with these new glycocalyx mimics are revealed in detail using surface plasmon resonance and single-molecule microscopy. Surface plasmon resonance shows that these blood proteins interact reversibly with the glycocalyx mimics, but have no irreversible adsorption above the limit of detection. Single-molecule microscopy is used to compare albumin and fibrinogen interactions on surfaces with and without glycocalyx-mimetic nanostructures. Microscopy videos reveal a new mechanism whereby the glycocalyx-mimetic nanostructures eliminate the formation of fibrin networks on the surfaces. This approach shows for the first time that the nanoscale structure and organization of glycosaminoglycans in the glycocalyx are essential to (i) reduce protein adsorption, (ii) reversibly bind fibrin(ogen), and (iii) inhibit fibrin network formation on surfaces. The insights gained from this work suggest new design principles for blood-compatible surfaces. New surfaces developed using these design principles could reduce risk of catastrophic failures of blood-contacting medical devices.

Heparin as a molecular spacer immobilized on microspheres to improve blood compatibility in hemoperfusion

Heparin, a highly sulfated linear polysaccharide, with anticoagulation function and blood compatibility is widely used as a biomaterials in medical application, but the most importance of heparin is its structure function as the macromolecular space arm. In this study, heparin as a spacer was covalently immobilized on the chloromethylated polystyrene microspheres (Ps) and then connected with l-phenylalanine forming the Ps-Hep-Phe structure, which was developed for endotoxin adsorption in hemoperfusion. The grafting density of heparin reach the maximum when the initial concentration of heparin solution was 5 mg/mL. The adsorbents with the heparin as a spacer showed the prolonged clotting times, low protein adsorption, and reduced the hemolysis rate, indicating that heparin-modified adsorbents have great blood compatibility. The adsorption capacity of Ps-Hep-Phe for endotoxin was 25.15 EU/g in dynamic adsorption, higher than that of Ps. Therefore, this study imply that heparin would be promising for modification of adsorbents in hemoperfusion.

Blood-Contacting Biomaterials: In Vitro Evaluation of the Hemocompatibility

Hemocompatibility of blood-contacting biomaterials is one of the most important criteria for their successful in vivo applicability. Thus, extensive in vitro analyses according to ISO 10993-4 are required prior to clinical applications. In this review, we summarize essential aspects regarding the evaluation of the hemocompatibility of biomaterials and the required in vitro analyses for determining the blood compatibility. Static, agitated, or shear flow models are used to perform hemocompatibility studies. Before and after the incubation of the test material with fresh human blood, hemolysis, cell counts, and the activation of platelets, leukocytes, coagulation and complement system are analyzed. Furthermore, the surface of biomaterials are evaluated concerning attachment of blood cells, adsorption of proteins, and generation of thrombus and fibrin networks.

Superhydrophobic Blood-Repellent Surfaces

Superhydrophobic surfaces repel water and, in some cases, other liquids as well. The repellency is caused by topographical features at the nano-/microscale and low surface energy. Blood is a challenging liquid to repel due to its high propensity for activation of intrinsic hemostatic mechanisms, induction of coagulation, and platelet activation upon contact with foreign surfaces. Imbalanced activation of coagulation drives thrombogenesis or formation of blood clots that can occlude the blood flow either on-site or further downstream as emboli, exposing tissues to ischemia and infarction. Blood-repellent superhydrophobic surfaces aim toward reducing the thrombogenicity of surfaces of blood-contacting devices and implants. Several mechanisms that lead to blood repellency are proposed, focusing mainly on platelet antiadhesion. Structured surfaces can: (i) reduce the effective area exposed to platelets, (ii) reduce the adhesion area available to individual platelets, (iii) cause hydrodynamic effects that reduce platelet adhesion, and (iv) reduce or alter protein adsorption in a way that is not conducive to thrombus formation. These mechanisms benefit from the superhydrophobic Cassie state, in which a thin layer of air is trapped between the solid surface and the liquid. The connections between water- and blood repellency are discussed and several recent examples of blood-repellent superhydrophobic surfaces are highlighted.

Investigation on the Linker Length of Synthetic Zwitterionic Polypeptides for Improved Nonfouling Surfaces

Zwitterionic polymers are outstanding nonfouling materials widely used for surface modification. However, works that systematically evaluate the structure-activity relationship of the side chain linker effect with related antifouling abilities are sparse. Here, we generate a series of well-defined zwitterionic polypeptides bearing oligoethylene glycol (EG) linkers in the side chain (P(CB-EG _xGlu), x = 1-3) and anchor them on gold surfaces via the grafting-to approach to compare their antifouling performances. The surface properties are characterized by X-ray photoelectron spectroscopy (XPS), circular dichroism spectroscopy (CD), variable angle spectroscopic ellipsometry (VASE), static water contact angle (SCA), and atomic force microscopy (AFM). By use of quartz crystal microbalance with dissipation (QCM-D), confocal microscopy, and scanning electron microscope, our results convincingly demonstrate the excellent antifouling performance of all zwitterionic polypeptides. Importantly, the surface coated with P(CB-EG₃Glu), the one with the longest EG linker, exhibits the best resistance to single protein (below the detection limit of QCM) and blood serum (∼96-98% reduction) adsorption, which largely outperforms those of the PEG positive control and the two P(CB-EG _xGlu) analogues with shorter EG _x linkers. The same P(CB-EG₃Glu) surface also gives the highest degree of prevention of cell/platelet/bacterial attachment (∼99% reduction) among all samples tested. Together, our study highlights the linker effect to the nonfouling performance of zwitterionic polypeptides, and the results strongly support P(CB-EG₃Glu) as a robust nonfouling material for numerous applications.

A facile method to prepare a versatile surface coating with fibrinolytic activity, vascular cell selectivity and antibacterial properties

Clot and thrombus formation on surfaces that come into contact with blood is still the most serious problem for blood contacting devices. Despite many years of continuous efforts in developing hemocompatible materials, it is still of great interest to develop multifunctional materials to enable vascular cell selectivity (to favor rapid endothelialization while inhibiting smooth muscle cell proliferation) and improve hemocompatibility. In addition, biomaterial-associated infections also cause the failure of biomedical implants and devices. However, it remains a challenging task to design materials that are multifunctional, since one of their functions will usually be compromised by the introduction of another function. In the present work, the gold substrate was first layer-by-layer (LbL) deposited with a multilayered polyelectrolyte film containing chitosan (positively charged) and a copolymer of sodium 4-vinylbenzenesulfonate (SS) and the "guest" adamantane monomer 1-adamantan-1-ylmethyl methacrylate (P(SS-co-Ada), negatively charged) via electro-static interactions, referred to as Au-LbL. The chitosan and P(SS-co-Ada) were intended to provide, respectively, resistance to bacteria and heparin-like properties. Then, "host" β-cyclodextrin derivatives bearing seven lysine ligands (CD-L) were immobilized on the Au-LbL surface by host-guest interactions between adamantane residues and CD-L, referred to as Au-LbL/CD-L. Finally, a versatile surface coating with fibrinolytic activity (lysis of nascent clots), vascular cell selectivity and antibacterial properties was developed.

Influence of dynamic flow conditions on adsorbed plasma protein corona and surface-induced thrombus generation on antifouling brushes

The information regarding the nature of protein corona (and its changes) and cell binding on biomaterial surface under dynamic conditions is critical to dissect the mechanism of surface-induced thrombosis. In this manuscript, we investigated the nature of protein corona and blood cell binding in heparinized recalcified human plasma, platelet rich plasma and whole blood on three highly hydrophilic antifouling polymer brushes, (poly(N, N-dimethylacrylamide) (PDMA), poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly[N-(2-hydroxypropyl) methacrylamide] (PHPMA) using an in vitro blood loop model at comparable arterial and venous flow, and static conditions. A fluid dynamics model was used initially to better understand the resulting flow patterns in a vertical channel containing the substrates to arrive at the placement of the substrates within the blood loop. The protein binding on the brush modified substrates was determined using ellipsometry, fluorescence microscopy and the nature of the protein corona was investigated using mass spectrometry based proteomics. The flow elevated fouling on brush coated surface from blood. The extent of plasma protein adsorption and platelet adhesion onto PDMA brush was lower than other surfaces in both static and flow conditions. The profiles of adsorbed protein corona showed strong dependence on the test conditions (static vs. flow), and the chemistry of the polymer brushes. Specially, the PDMA brush under flow conditions was more enriched with coagulation proteins, complement proteins, vitronectin and fibronectin but was less enriched with serum albumin. Apolipoprotein B-100 and complement proteins were the most abundant proteins seen on PMPC and PHPMA surfaces under both flow and static conditions, respectively. Unlike PDMA brush, the flow conditions did not affect the composition of protein corona on PMPC and PHPMA brushes. The nature of the protein corona formed in flow conditions influenced the platelet and red blood cell binding. The dependence of shear stress on platelet adhesion from platelet rich plasma and whole blood highlights the contribution of red blood cells in enhancing platelet adhesion on the surface under high shear condition.

Sulfonate Groups and Saccharides as Essential Structural Elements in Heparin-Mimicking Polymers Used as Surface Modifiers: Optimization of Relative Contents for Antithrombogenic Properties

Blood compatibility is a long sought-after goal in biomaterials research, but remains an elusive one, and in spite of extensive work in this area, there is still no definitive information on the relationship between material properties and blood responses such as coagulation and thrombus formation. Materials modified with heparin-mimicking polymers have shown promise and indeed may be seen as comparable to materials modified with heparin itself. In this work, heparin was conceptualized as consisting of two major structural elements: saccharide- and sulfonate-containing units, and polymers based on this concept were developed. Copolymers of 2-methacrylamido glucopyranose, containing saccharide groups, and sodium 4-vinylbenzenesulfonate, containing sulfonate groups, were graft-polymerized on vinyl-functionalized polyurethane (PU) surfaces by free radical polymerization. This graft polymerization method is simple, and the saccharide and sulfonate contents are tunable by regulating the feed ratio of the monomers. Homopolymer-grafted materials, containing only sulfonate or saccharide groups, showed different effects on cell-surface interactions including platelet adhesion, adhesion and proliferation of vascular endothelial cells, and adhesion and proliferation of smooth muscle cells. The copolymer-grafted materials showed effects due to both sulfonate and saccharide elements with respect to blood responses, and the optimum composition was obtained at a 2:1 ratio of sulfonate to saccharide units (material designated as PU-PS1M1). In cell adhesion experiments, this material showed the lowest platelet and human umbilical vein smooth muscle cell density and the highest human umbilical vein endothelial cell density. Among the materials investigated, PU-PS1M1 also had the longest plasma clotting time. This material was thus shown to be multifunctional with a combination of properties, suggesting thromboresistant behavior in blood contact.

Manipulation of the response of human endothelial colony-forming cells by focal adhesion assembly using gradient nanopattern plates

Nanotopography plays a pivotal role in the regulation of cellular responses. Nonetheless, little is known about how the gradient size of nanostructural stimuli alters the responses of endothelial progenitor cells without chemical factors. Herein, the fabrication of gradient nanopattern plates intended to mimic microenvironment nanotopography is described. The gradient nanopattern plates consist of nanopillars of increasing diameter ranges [120-200 nm (GP 120/200), 200-280 nm (GP 200/280), and 280-360 nm (GP 280/360)] that were used to screen the responses of human endothelial colony-forming cells (hECFCs). Nanopillars with a smaller nanopillar diameter caused the cell area and perimeter of hECFCs to decrease and their filopodial outgrowth to increase. The structure of vinculin (a focal adhesion marker in hECFCs) was also modulated by nanostructural stimuli of the gradient nanopattern plates. Moreover, Rho-associated protein kinase (ROCK) gene expression was significantly higher in hECFCs cultured on GP 120/200 than in those on flat plates (no nanopillars), and ROCK suppression impaired the nanostructural-stimuli-induced vinculin assembly. These results suggest that the gradient nanopattern plates generate size-specific nanostructural stimuli suitable for manipulation of the response of hECFCs, in a process dependent on ROCK signaling. This is the first evidence of size-specific nanostructure-sensing behavior of hECFCs.

SIGNIFICANCE

Nano feature surfaces are of growing interest as materials for a controlled response of various cells. In this study, we successfully fabricated gradient nanopattern plates to manipulate the response of blood-derived hECFCs without any chemical stimulation. Interestingly, we find that the sensitive nanopillar size for manipulation of hECFCs is range between 120 nm and 200 nm, which decreased the area and increased the filopodial outgrowth of hECFCs. Furthermore, we only modulate the nanopillar size to increase ROCK expression can be an attractive method for modulating the cytoskeletal integrity and focal adhesion of hECFCs.

Honeycomb-structured metasurfaces for the adaptive nesting of endothelial cells under hemodynamic loads

The thrombogenicity of artificial materials comprising ventricular assist devices (VADs) limits their long-term integration in the human body.

Polycaprolactone nanofibers functionalized with placental derived extracellular matrix for stimulating wound healing activity

Impaired wound healing is primarily associated with inadequate angiogenesis, repressed cell migration, deficient synthesis of extracellular matrix (ECM) component/growth factors, and altered inflammatory responses in the wound bed environment.

A Positively Charged Surface Triggers Coagulation Activation Through Factor VII Activating Protease (FSAP)

Contact between biomedical materials and blood often initiates undesirable pro-coagulant and pro-inflammatory processes. On negatively charged materials, blood coagulation is known to be triggered through autoactivation of Factor XII, while activation on cationic surfaces follows a distinct and so far enigmatic mechanism. Because Factor VII activating protease (FSAP) is known to be activated on positively and on negatively charged macromolecules in plasma, we have investigated its interaction with charged biomaterials and its consequences for coagulation. Several activation processes in blood and plasma were characterized after contact with material surfaces with varied charge. FSAP was found to be exclusively activated by the positively charged surfaces polyethylenimine (PEI) and poly-l-lysine (PLL), not by the negatively charged glass or self-assembled monolayer with carboxyl group termination (SAM-COOH), as well as uncharged (Teflon AF) surfaces. Whole blood incubation on PEI showed that this activation was concomitant with coagulation as determined by thrombin and fibrin formation, which was high for glass (F1+2, 138 nM) and PEI (F1+2, 44 nM) but low for Teflon AF (F1+2, 3.3 nM) and SAM COOH (F1+2, 5.8 nM). Contact phase inhibitor diminished coagulation to background levels for all surfaces except PEI (F1+2: ^PEI 43 to 25 nM; glass, 58 to 1.5 nM) indicating that coagulation activation is not dependent on FXII activation on the PEI surface. A decisive role of endogenous FSAP for coagulation however was confirmed with the use of FSAP inhibitory antibodies which showed no influence on Teflon AF, glass and SAM COOH but diminished F1+2 on PEI to less than 50%. We propose that FSAP activation could be a novel mechanism of surface-driven coagulation. An inhibition of this protease might improve hemocompatibility of cationic surfaces and therefore facilitate the application of polycationic surfaces in blood.

Protein Resistant Polymeric Biomaterials

Toward improving implantable medical devices as well as diagnostic performance, the development of polymeric biomaterials having resistance to proteins remains a priority. Herein, we highlight key strategies reported in the recent literature that have relied upon improvement of surface hydrophilicity via direct surface modification methods or with bulk modification using surface modifying additives (SMAs). These approaches have utilized a variety of techniques to incorporate the surface hydrophilization agent, including physisorption, hydrogel network formation, surface grafting, layer-by-layer (LbL) assembly and blending base polymers with SMAs. While poly(ethylene glycol) (PEG) remains the gold standard, new alternatives have emerged such as polyglycidols, poly(2-oxazoline)s (POx), polyzwitterions, and amphiphilic block copolymers. While these new strategies provide encouraging results, the need for improved correlation between in vitro and in vivo protein resistance is critical. This may be achieved by employing complex protein solutions as well as strides to enhance the sensitivity of protein adsorption measurements.

Effect of crystalline phase changes in titania (TiO2) nanotube coatings on platelet adhesion and activation

OBJECTIVE

To explore the relationship between various crystalline phases of titania (TiO₂) nanotube (TNT) coatings and platelet adhesion and activation.

METHODS

TNT coatings were fabricated on pure titanium foils by anodization and then randomly divided into four groups. Three groups were annealed at 350°C, 450°C and 550°C in order to obtain different crystalline phases. The remaining group was not annealed and served as the control group. X-ray diffraction (XRD) was used to define the crystalline phases of different groups. Surface morphology, elemental composition, surface roughness, and contact angles were measured by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), laser scanning confocal microscopy (LSCM) and contact angle analysis, respectively. Platelets were cultured on the TNT coatings for 30min and 60min to assess the number, viability, distribution, and morphology of the adhered platelets. CD62P fluorescence expression and the amount of released platelet-derived growth factor (PDGF) were detected to evaluate platelet activation.

RESULTS

The un-annealed TNT coatings were amorphous and part of TNT converted to anatase after the 350°C annealing treatment. The quantity of anatase increased upon annealing at 450°C and transformed to rutile at 550°C. Nanotubes of all four groups maintained a well-ordered structure, but the wall thickness of the nanotubes increased from (11.874±1.660) nm for the un-annealed TNTs to (26.126±2.130) nm for the 550°C annealed TNTs. The surface roughness of the 550°C annealed TNT coatings was the lowest and the water contact angle was the largest at (28.117±1.182) °. The number and viability of adhered platelets after 30min and 60min were the highest on TNT coatings annealed at 450°C. LSCM and SEM images revealed that the platelets that adhered on the 450°C annealed TNT coatings aggregated, transformed, and spread most obviously. CD62P fluorescence expression results showed that the platelets on the 350°C and 450°C annealed TNT coating groups expressed the strongest fluorescence, followed by platelets on the 550°C annealed group and the un-annealed group. The quantity of released PDGF was highest for the 450°C annealed group at (4719±86) pg/mL, and lowest for the un-annealed group at (4241±74) pg/mL.

CONCLUSION

Crystalline TNT coatings encourage improved platelet adhesion and activation over amprphous analogues. The TNT coatings annealed at 450°C resulted in the most improved platelet behavior. The TNT crystalline phase was the predominant influencing factor in platelet adhesion and activation.

Evaluation of platelet adhesion and activation on polymers: Round-robin study to assess inter-center variability

The regulatory agencies provide recommendations rather than protocols or standard operation procedures for the hemocompatibility evaluation of novel materials e.g. for cardiovascular applications. Thus, there is a lack of specifications with regard to test setups and procedures. As a consequence, laboratories worldwide perform in vitro assays under substantially different test conditions, so that inter-laboratory and inter-study comparisons are impossible. Here, we report about a prospective, randomized and double-blind multicenter trial which demonstrates that standardization of in vitro test protocols allows a reproducible assessment of platelet adhesion and activation from fresh human platelet rich plasma as possible indicators of the thrombogenicity of cardiovascular implants. Standardization of the reported static in vitro setup resulted in a laboratory independent scoring of the following materials: poly(dimethyl siloxane) (PDMS), poly(ethylene terephthalate) (PET) and poly(tetrafluoro ethylene) (PTFE). The results of this in vitro study provide evidence that inter-laboratory and inter-study comparisons can be achieved for the evaluation of the adhesion and activation of platelets on blood-contacting biomaterials by stringent standardization of test protocols.

Manufacture and property research of heparin grafted electrospinning PCU artificial vascular scaffolds

PCU (polycarbonate polyurethane) is supposed to be an ideal elastomer for manufacturing artificial vessel scaffold with perfect mechanical strength and biocompatibility. Surface grafting by heparin sodium can increase its anticoagulant hemorrhagic, achieving a better application in artificial vessels. Artificial vessels were preliminarily prepared by electrostatic spinning, treated by NH₃ plasma and cross-linked with the anticoagulant heparin sodium chemically. Performances of the PCU-Hep (heparin sodium grafted purethane artificial vessels) artificial vessel were calculated through the physical and chemical property tests, evaluation of blood and biocompatibility. Results manifested that heparin sodium was successfully grafted to the vascular surface, porosity, pore diameter and water permeability of the vascular prosthesis fitted the requirements of artificial vessels, the blood test results demonstrated that the vascular material had a low hemolysis, in vitro cytotoxicity experiment and animal experiments proved an excellent biocompatibility. Thus the heparin sodium grafted electrospinning vessels could reduce intravascular thrombus and had potential clinical application.

Effect of construction of TiO2 nanotubes on platelet behaviors: Structure-property relationships

Blood compatibility of TiO₂ nanotubes (TNTs) has been assessed in rabbit platelet-rich plasma (PRP), which combines activation of both blood plasma coagulation and platelets. We find that (i) amorphous TiO₂ nanotubes (TNTs) with relatively larger outer diameters led to reduced platelet adhesion/activation, (ii) TNTs with relatively smaller outer diameters in a predominately rutile phase also inhibited platelet adhesion and activation, and (iii) a pervasive fibrin network formed on larger outer diameter TNTs in a predominately anatase phase. Thus, this study suggests that combined effect of crystalline phase and surface chemistry controls blood-contact behavior of TNTs. A more comprehensive mechanism is proposed for understanding hemocompatibility of TiO₂ which might prove helpful as a guide to prospective design of TiO₂-based biomaterials.

STATEMENT OF SIGNIFICANCE

To realize optimal design and construction of biomaterials with desired properties for blood contact materials, a comprehensive understanding of structure-property relationships is required. In the existing literature, TiO₂ nanotube has been reported to be a good candidate for biomedical applications. However, it is noticeable that the blood compatibility of TiO₂ nanotubes (TNTs) remains obscure or even inconsistent in the previously published works. The inconsistency could derive from different research protocols, material properties or blood sources. Thus, a thorough investigation of the effect of surface properties on blood compatibility is crucial to the development of titanium based materials. In this paper, we explored the effect of surface properties on the response of platelet-rich plasma, especially surface morphology, chemistry, wettability and crystalline phase. The results indicated that crystalline phase was a dominant factor in platelet behaviors. Reduced adhesion and activation of platelets were observed on amorphous and rutile dominated TNTs, whereas anatase dominated TNTs activated the formation of fibrin network. We further proposed a hypothetical mechanism for better understanding of how surface properties affect the response of platelet-rich plasma. Therefore, this study expands the fundamental understanding of the structure-property relationships of titanium based materials.