Antifouling Polymer Brushes Displaying Antithrombogenic Surface Properties

High-density zwitterionic polymer brushes exhibit robust lubrication properties and high antithrombotic efficacy in blood-contacting medical devices

High-performance catheters are essential for interventional surgeries, requiring reliable anti-adhesive and lubricated surfaces. This article develops a strategy for constructing high-density sulfobetaine zwitterionic polymer brushes on the surface of catheters, utilizing dopamine and sodium alginate as the primary intermediate layers, where dopamine provides mussel-protein-like adhesion to anchor the polymer brushes to the catheter surface. Hydroxyl-rich sodium alginate increases the number of grafting sites and improves the grafting mass by more than 4 times. The developed high-density zwitterionic polymer brushes achieve long-lasting and effective lubricity (μ<0.0078) and are implanted in rabbits for four hours without bio-adhesion and thrombosis in the absence of anticoagulants such as heparin. Experiments and molecular dynamics simulations demonstrate that graft mass plays a decisive role in the lubricity and anti-adhesion of polymer brushes, and it is proposed to predict the anti-adhesion of polymer brushes by their lubricity to avoid costly and time-consuming bioassays during the development of amphoteric polymer brushes. A quantitative influence of hydration in the anti-adhesion properties of amphiphilic polymer brushes is also revealed. Thus, this study provides a new approach to safe, long-lasting lubrication and anticoagulant surface modification for medical devices in contact with blood. STATEMENT OF SIGNIFICANCE: High friction and bioadhesion on medical device surfaces can pose a significant risk to patients. In response, we have developed a safer, simpler, and more application-specific surface modification strategy that addresses both the lubrication and anti-bioadhesion needs of medical device surfaces. We used dopamine and sodium alginate as intermediate layers to drastically increase the grafting density of the zwitterionic brushes and enabled the modified surfaces to have an extremely low coefficient of friction (μ = 0.0078) and to remain non-bioadhesive for 4 hours in vivo. Furthermore, we used molecular dynamics simulations to gain insight into the mechanisms behind the superior anti-adhesion properties of the high-density polymer brushes. Our work contributes to the development and application of surface-modified coatings.

Tackling the Root Cause of Surface-Induced Coagulation: Inhibition of FXII Activation to Mitigate Coagulation Propagation and Prevent Clotting

Factor XII (FXII) is a zymogen present in blood that tends to adsorb onto the surfaces of blood-contacting medical devices. Once adsorbed, it becomes activated, initiating a cascade of enzymatic reactions that lead to surface-induced coagulation. This process is characterized by multiple redundancies, making it extremely challenging to prevent clot formation and preserve the properties of the surface. In this study, a novel modulatory coating system based on C1-esterase inhibitor (C1INH) functionalized polymer brushes, which effectively regulates the activation of FXII is proposed. Using surface plasmon resonance it is demonstrated that this coating system effectively repels blood plasma proteins, including FXII, while exhibiting high activity against activated FXII and plasma kallikrein under physiological conditions. This unique property enables the modulation of FXII activation without interfering with the overall hemostasis process. Furthermore, through dynamic Chandler loop studies, it is shown that this coating significantly improves the hemocompatibility of polymeric surfaces commonly used in medical devices. By addressing the root cause of contact activation, the synergistic interplay between the antifouling polymer brushes and the modulatory C1INH is expected to lay the foundation to enhance the hemocompatibility of medical device surfaces.

Green Solvent-Based Antifouling Polymer Brushes Demonstrate Excellent Hemocompatibility

Medical devices are crucial for patient care, yet even the best biomaterials lead to infections and unwanted activation of blood coagulation, potentially being life-threatening. While hydrophilic polymer brushes are the best coatings to mitigate these issues, their reliance on fossil raw materials underscores the urgency of bio-based alternatives. In this work, we introduce polymer brushes of a green solvent-based monomer, prohibiting protein adsorption, bacterial colonization, and blood clot formation at the same level as fossil-based polymer brushes. The polymer brushes are composed of N,N-dimethyl lactamide acrylate (DMLA), can be polymerized in a controlled manner, and show strong hydrophilicity as determined by thermodynamic analysis of the surface tension components. The contact of various challenging protein solutions results in repellency on the poly(DMLA) brushes. Furthermore, the poly(DMLA) brushes completely prevent the adhesion and colonization of Escherichia coli. Remarkably, upon blood contact, the poly(DMLA) brushes successfully prevent the formation of a fibrin network and leukocyte adhesion on the surface. While showcasing excellent antifouling properties similar to those of N-hydroxypropyl methacrylamide (HPMA) polymer brushes as one of the best antifouling coatings, the absence of hydroxyl groups prevents activation of the complement system in blood. We envision the polymer brushes to contribute to the future of hemocompatible coatings.

Ring-Opening Polymerization of Trimethylene Carbonate with Phosphazene Organocatalyst

Aliphatic polycarbonate (APC) compounds are an important class of biodegradable materials with excellent biocompatibility, good biodegradability, and low toxicity, and the study of these compounds and their modification products aims to obtain biodegradable materials with better performance. In this context, the ring-opening polymerization (ROP) of trimethylene carbonate (TMC) from a low nucleophilic organic superbase of phosphazene (t-BuP₄) as a catalyst and benzyl alcohol (BnOH) as an initiator at room temperature was carefully studied to prepare poly(trimethylene carbonate) (PTMC) which is one of the most studied APC. ¹H NMR and SEC measurements clearly demonstrate the presence of a benzyloxy group at the α-terminus of the obtained PTMC homopolymers while investigation of the polymerization kinetics confirms the controlled/living nature of t-BuP₄-catalyzed ROP of TMC. On the basis of this, the block copolymerization of TMC and δ-valerolactone (VL)/ε-caprolactone (CL) was successfully carried out to give PTMC-b-PCL and PTMC-b-PVL copolymers. Furthermore, PTMC with terminal functionality was also prepared with the organocatalytic ROP of TMC through functional initiators. We believe that the present ROP system is a robust, highly efficient, and practical strategy for producing excellent biocompatible and biodegradable PTMC-based materials.

Polyzwitterionic Coating of Porous Adsorbents for Therapeutic Apheresis

Adsorbents for whole blood apheresis need to be highly blood compatible to minimize the activation of blood cells on the biomaterial surface. Here, we developed blood-compatible matrices by surface modification with polyzwitterionic polysulfobetainic and polycarboxybetainic coatings. Photoreactive zwitterionic terpolymers were synthesized by free-radical polymerization of zwitterionic, photoreactive, and fluorescent monomers. Upon UV irradiation, the terpolymers were photodeposited and mutually crosslinked on the surface of hydrophobic polystyrene-co-divinylbenzene and hydrophilic polyacrylamide-co-polyacrylate (DALI) beads. Fluorescent microscopy revealed coatings with an average thickness of 5 µm, which were limited to the bead surface. Blood compatibility was assessed based on polymer-induced hemolysis, coagulation parameters, and in vitro tests. The maintenance of the adsorption capacity after coating was studied in human whole blood with cytokines for polystyrene beads (remained capacity 25-67%) and with low-density lipoprotein (remained capacity 80%) for polyacrylate beads. Coating enhanced the blood compatibility of hydrophobic, but not of hydrophilic adsorbents. The most prominent effect was observed on coagulation parameters (e.g., PT, aPTT, TT, and protein C) and neutrophil count. Polycarboxybetaine with a charge spacer of five carbons was the most promising polyzwitterion for the coating of adsorbents for whole blood apheresis.

Bottlebrush inspired injectable hydrogel for rapid prevention of postoperative and recurrent adhesion

Postsurgical adhesion is a common clinic disease induced by surgical trauma, accompanying serious subsequent complications. Current non-surgical approaches of drugs treatment and biomaterial barrier administration only show limited prevention effects and couldn't effectively promote peritoneum repair. Herein, inspired by bottlebrush, a novel self-fused, antifouling, and injectable hydrogel is fabricated by the free-radical polymerization in aqueous solution between the methacrylate hyaluronic acid (HA-GMA) and N-(2-hydroxypropyl) methacrylamide (HPMA) monomer without any chemical crosslinkers, termed as H-HPMA hydrogel. The H-HPMA hydrogel can be tuned to perform excellent self-fused properties and suitable abdominal metabolism time. Intriguingly, the introduction of the ultra-hydrophilic HPMA chains to the H-HPMA hydrogel affords an unprecedented antifouling capability. The HPMA chains establish a dense hydrated layer that rapidly prevents the postsurgical adhesions and recurrent adhesions after adhesiolysis in vivo. The H-HPMA hydrogel can repair the peritoneal wound of the rat model within 5 days. Furthermore, an underlying mechanism study reveals that the H-HPMA hydrogel significantly regulated the mesothelial-to-mesenchymal transition (MMT) process dominated by the TGF-β-Smad2/3 signal pathway. Thus, we developed a simple, effective, and available approach to rapidly promote peritoneum regeneration and prevent peritoneal adhesion and adhesion recurrence after adhesiolysis, offering novel design ideas for developing biomaterials to prevent peritoneal adhesion.

Detection of E. coli Bacteria in Milk by an Acoustic Wave Aptasensor with an Anti-Fouling Coating

Milk is a significant foodstuff around the world, being produced and consumed in large quantities. The safe consumption of milk requires that the liquid has an acceptably low level of microbial contamination and has not been subjected to spoiling. Bacterial safety limits in milk vary by country but are typically in the thousands per mL of sample. To rapidly determine if samples contain an unsafe level of bacteria, an aptamer-based sensor specific to Escherichia coli bacteria was developed. The sensor is based on an ultra-high frequency electromagnetic piezoelectric acoustic sensor device (EMPAS), with the aptamer being covalently bound to the sensor surface by the anti-fouling linker, MEG-Cl. The sensor is capable of the selective measurement of E. coli in PBS and in cow’s milk samples down to limits of detection of 35 and 8 CFU/mL, respectively, which is well below the safe limits for commercial milk products. This sensing system shows great promise for the milk industry for the purpose of rapid verification of product safety.

Grafting density and antifouling properties of poly[N-(2-hydroxypropyl) methacrylamide] brushes prepared by “grafting to” and “grafting from”

Poly(HPMA) brushes prepared by a grafting-from method suppress fouling from blood plasma by an order of magnitude better than the polymer brushes of the same molecular weight prepared by a grafting-to method.

Preparation of thermosensitive PNIPAm-based copolymer coated cytodex 3 microcarriers for efficient nonenzymatic cell harvesting during 3D culturing

Enzymatic detachment of cells might damage important features and functions of cells and could affect subsequent cell-based applications. Therefore, nonenzymatic cell detachment using thermosensitive polymer matrix is necessary for maintaining cell quality after harvesting. In this study, we prepared thermosensitive PNIPAm-co-AAc-b-PS and PNIPAm-co-AAm-b-PS copolymers and low critical solution temperature (LCST) was tuned near to body temperature. Then, spin coated polymer films were prepared for cell adhesion and thermal-induced cell detachment. The alpha-step analysis and scanning electron microscope image of the films suggested that the thickness of the films depends on the molecular weight and concentration which ranged from 206 to 1330 nm for PNIPAm-co-AAc-b-PS and 97.5-497 nm for PNIPAm-co-AAm-b-PS. The contact angles of the films verified that the polymer surface was moderately hydrophilic at 37°C. Importantly, RAW264.7 cells were convincingly proliferated on the films to a confluent of >80% within 48 h and abled to detach by reducing the temperature. However, relatively more cells were grown on PNIPAm-co-AAm-b-PS (5%w/v) films and thermal-induced cell detachment was more abundant in this formulation. As a result, PNIPAm-co-AAm-b-PS (5%w/v) was further used to coat commercial cytodex 3 microcarriers for 3D cell culturing and interestingly enhanced cell detachment with preserved potential of recovery was observed at a temperature of below LCST. Thus, surface modification of microcarriers with thermosensitive PNIPAm-co-AAm-b-PS could be vital strategy for nonenzymatic cell detachment and to achieve adequate number of cells with maximum cell viability and functionality.

Unraveling the Mechanism and Kinetics of Binding of an LCI-eGFP-Polymer for Antifouling Coatings

The ability of proteins to adsorb irreversibly onto surfaces opens new possibilities to functionalize biological interfaces. Herein, the mechanism and kinetics of adsorption of protein-polymer macromolecules with the ability to equip surfaces with antifouling properties are investigated. These macromolecules consist of the liquid chromatography peak I peptide from which antifouling polymer brushes are grafted using single electron transfer-living radical polymerization. Surface plasmon resonance spectroscopy reveals an adsorption mechanism that follows a Langmuir-type of binding with a strong binding affinity to gold. X-ray reflectivity supports this by proving that the binding occurs exclusively by the peptide. However, the lateral organization at the surface is directed by the cylindrical eGFP. The antifouling functionality of the unimolecular coatings is confirmed by contact with blood plasma. All coatings reduce the fouling from blood plasma by 8894% with only minor effect of the degree of polymerization for the studied range (DP between 101 and 932). The excellent antifouling properties, combined with the ease of polymerization and the straightforward coating procedure make this a very promising antifouling concept for a multiplicity of applications.

Anti-biofouling assembly strategies for protein & cell repellent surfaces: a mini-review

The protein/cell interactions with the surface at the blood-biomaterial interface generally control the efficiency of biomedical devices. A wide range of active processes and slow kinetics occur simultaneously with many biomaterials in healthcare applications, leading to multiple biological reactions and reduced clinical functions. In this work, we present a brief review of studies as the interface between proteins and biomaterials. These include mechanisms of resistance to proteins, protein-rejecting polyelectrolyte multilayers, and coatings of hydrophilic, polysaccharide and phospholipid nature. The mechanisms required to attain surfaces that resist adhesion include steric exclusion, water-related effects, and volume effects. Also, approaches in the use of hydrophilic, highly hydrated, and electrically neutral coatings have demonstrated a good ability to decrease cell adhesion. Moreover, amongst the available methods, the approach of layer-by-layer deposition has been known as an interesting process to manipulate protein and cell adhesion behavior.

Improving Hemocompatibility: How Can Smart Surfaces Direct Blood To Fight against Thrombi

Nature utilizes endothelium as a blood interface that perfectly controls hemostasis, preventing the uncontrolled formation of thrombi. The management of positive and negative feedback that finely tunes thrombosis and fibrinolysis is essential for human life, especially for patients who undergo extracorporeal circulation (ECC) after a severe respiratory or cardiac failure. The exposure of blood to a surface different from healthy endothelium inevitably initiates coagulation, drastically increasing the mortality rate by thromboembolic complications. In the present study, an ultrathin antifouling fibrinolytic coating capable of disintegrating thrombi in a self-regulated manner is reported. The coating system is composed of a polymer brush layer that can prevent any unspecific interaction with blood. The brushes are functionalized with a tissue plasminogen activator (tPA) to establish localized fibrinolysis that solely and exclusively is active when it is required. This interactive switching between the dormant and active state is realized through an amplification mechanism that increases (positive feedback) or restores (negative feedback) the activity of tPA depending on whether a thrombus is detected and captured or not. Thus, only a low surface density of tPA is necessary to lyse real thrombi. Our work demonstrates the first report of a coating that self-regulates its fibrinolytic activity depending on the conditions of blood.

Antifouling Silicone Hydrogel Contact Lenses with a Bioinspired 2-Methacryloyloxyethyl Phosphorylcholine Polymer Surface

Inspired by the cell membrane surface as well as the ocular tissue, a novel and clinically applicable antifouling silicone hydrogel contact lens material was developed. The unique chemical and biological features on the surface on a silicone hydrogel base substrate were achieved by a cross-linked polymer layer composed of 2-methacryloyloxyethyl phosphorylcholine (MPC), which was considered important for optimal on-eye performance. The effects of the polymer layer on adsorption of biomolecules, such as lipid and proteins, and adhesion of cells and bacteria were evaluated and compared with several conventional silicone hydrogel contact lens materials. The MPC polymer layer provided significant resistance to lipid deposition as visually demonstrated by the three-dimensional confocal images of whole contact lenses. Also, fibroblast cell adhesion was decreased to a 1% level compared with that on the conventional silicone hydrogel contact lenses. The movement of the cells on the surface of the MPC polymer-modified lens material was greater compared with other silicone hydrogel contact lenses indicating that lubrication of the contact lenses on ocular tissue might be improved. The superior hydrophilic nature of the MPC polymer layer provides improved surface properties compared to the underlying silicone hydrogel base substrate.

Electromagnetic Piezoelectric Acoustic Sensor Detection of Extracellular Vesicles through Interaction with Detached Vesicle Proteins

An electromagnetic piezoelectric acoustic sensor (EMPAS) was used to study the non-specific adsorption of human red blood cell-derived extracellular vesicle preparations. Vesicle storage history (temperature and duration) highly affected the obtained results: The signal change, namely the frequency decrease of the crystal measured at 20 °C, was negligibly small (<1 s⁻²) when the vesicle solutions had previously been stored at 4 °C, and was in the order of 10 s⁻² when the vesicle solutions had been stored at −30 °C. Moreover, the rate of frequency decrease increased exponentially with the storage time at −30 °C. Upon a 4 °C storage period following the −30 °C storage period of the same sample, the measured frequency decrease dropped, suggesting a partial relaxation of the system. The results are explained by the disintegration of the vesicles triggered by the freeze–thaw cycle, likely due to the detachment of proteins from the vesicle surface as was proved by size-exclusion chromatography. Surface modification of the sensor crystal provided the possibility of signal enhancement, as the maximum rate of the frequency change for the same vesicle concentrations was higher on hydrophobic, octadecyl trichlorosilane–modified quartz than on hydrophilic, bare quartz. The EMPAS signal has been associated with the amount of detached proteins, which in turn is proportional to the originating vesicle concentration.

Surface Design of Antifouling Vascular Constructs Bearing Biofunctional Peptides for Tissue Regeneration Applications

Antifouling polymer layers containing extracellular matrix-derived peptide motifs offer promising new options for biomimetic surface engineering. In this contribution, we report the design of antifouling vascular grafts bearing biofunctional peptide motifs for tissue regeneration applications based on hierarchical polymer brushes. Hierarchical diblock poly(methyl ether oligo(ethylene glycol) methacrylate-block-glycidyl methacrylate) brushes bearing azide groups (poly(MeOEGMA-block-GMA-N₃)) were grown by surface-initiated atom transfer radical polymerization (SI-ATRP) and functionalized with biomimetic RGD peptide sequences. Varying the conditions of copper-catalyzed alkyne-azide “click” reaction allowed for the immobilization of RGD peptides in a wide surface concentration range. The synthesized hierarchical polymer brushes bearing peptide motifs were characterized in detail using various surface sensitive physicochemical methods. The hierarchical brushes presenting the RGD sequences provided excellent cell adhesion properties and at the same time remained resistant to fouling from blood plasma. The synthesis of anti-fouling hierarchical brushes bearing 1.2 × 10³ nmol/cm² RGD biomimetic sequences has been adapted for the surface modification of commercially available grafts of woven polyethylene terephthalate (PET) fibers. The fiber mesh was endowed with polymerization initiator groups via aminolysis and acylation reactions optimized for the material. The obtained bioactive antifouling vascular grafts promoted the specific adhesion and growth of endothelial cells, thus providing a potential avenue for endothelialization of artificial conduits.

Amyloid-Like Protein Aggregates: A New Class of Bioinspired Materials Merging an Interfacial Anchor with Antifouling

Surfaces that resist nonspecific protein adsorption in a complex biological milieu are required for a variety of applications. However, few strategies can achieve a robust antifouling coating on a surface in an easy and reliable way, regardless of material type, morphology, and shape. Herein, the preparation of an antifouling coating by one-step aqueous supramolecular assembly of bovine serum albumin (BSA) is reported. Based on fast amyloid-like protein aggregation through the rapid reduction of the intramolecular disulfide bonds of BSA by tris(2-carboxyethyl)phosphine, a dense proteinaceous nanofilm with controllable thickness (≈130 nm) can be covered on virtually arbitrary material surfaces in tens of minutes by a simple dipping or spraying. The nanofilm shows strong stability and adhesion with the underlying substrate, exhibiting excellent resistance to the nonspecific adsorption of a broad-spectrum of contaminants including proteins, serum, cell lysate, cells, and microbes, etc. In vitro and in vivo experiments show that the nanofilm can prevent the adhesion of microorganisms and the formation of biofilm. Compared with native BSA, the proteinaceous nanofilm coating exposes a variety of functional groups on the surface, which have more-stable adhesion with the surface and can maintain the antifouling in harsh conditions including under ultrasound, surfactants, organic solvents, and enzymatic digestion.

Efficacy of A Poly(MeOEGMA) Brush on the Prevention of Escherichia coli Biofilm Formation and Susceptibility

Urinary tract infections are one of the most common hospital-acquired infections, and they are often associated with biofilm formation in indwelling medical devices such as catheters and stents. This study aims to investigate the antibiofilm performance of a polymer brush—poly[oligo(ethylene glycol) methyl ether methacrylate], poly(MeOEGMA)—and evaluate its effect on the antimicrobial susceptibility of Escherichia coli biofilms formed on that surface. Biofilms were formed in a parallel plate flow chamber (PPFC) for 24 h under the hydrodynamic conditions prevailing in urinary catheters and stents and challenged with ampicillin. Results obtained with the brush were compared to those obtained with two control surfaces, polydimethylsiloxane (PDMS) and glass. The polymer brush reduced by 57% the surface area covered by E. coli after 24 h, as well as the number of total adhered cells. The antibiotic treatment potentiated cell death and removal, and the total cell number was reduced by 88%. Biofilms adapted their architecture, and cell morphology changed to a more elongated form during that period. This work suggests that the poly(MeOEGMA) brush has potential to prevent bacterial adhesion in urinary tract devices like ureteral stents and catheters, as well as in eradicating biofilms developed in these biomedical devices.

Surface Probe Linker with Tandem Anti-Fouling Properties for Application in Biosensor Technology

This paper describes the anti-fouling capability of the novel monolayer-forming surface linker 3-(3-(trichlorosilylpropyloxy) propanoyl chloride (MEG-Cl). This compound was successfully attached to quartz crystal surfaces which are employed in an electromagnetic piezoelectric acoustic sensor (EMPAS) configuration. The MEG-Cl coated surface was both employed with Ni-NTA for the binding of recombinant proteins and for the tandem property of the avoidance of fouling from serum and milk. The MEG-Cl coated surfaces were found to provide a large degree of anti-fouling on the EMPAS device, and were comparable to previously studied MEG-OH surfaces. Importantly, the monolayer continued to provide anti-fouling capability to the biosensor following extension with Ni-NTA in place. Accordingly, this surface linker provides an attractive system for use in biosensor technology in terms of both its anti-fouling and linking properties.

In Pursuit of Zero 2.0: Recent Developments in Nonfouling Polymer Brushes for Immunoassays

"Nonfouling" polymer brush surfaces can greatly improve the performance of in vitro diagnostic (IVD) assays due to the reduction of nonspecific protein adsorption and consequent improvement of signal-to-noise ratios. The development of synthetic polymer brush architectures that suppress adventitious protein adsorption is reviewed, and their integration into surface plasmon resonance and fluorescent sandwich immunoassay formats is discussed. Also, highlighted is a novel, self-contained immunoassay platform (the D4 assay) that transforms time-consuming laboratory-based assays into a user-friendly and point-of-care format with a sensitivity and specificity comparable or better than standard enzyme-linked immunosorbent assay (ELISA) directly from unprocessed samples. These advancements clearly demonstrate the utility of nonfouling polymer brushes as a substrate for ultrasensitive and robust diagnostic assays that may be suitable for clinical testing, in field and laboratory settings.

Synthesis of a conductive polymer thin film having a choline phosphate side group and its bioadhesive properties

A conductive polymer thin film having choline phosphate as the side group was prepared. The polymer thin film can prevent bovine serum albumin binding while present nice fibroblast cell adhesion.

Blend scaffolds with polyaspartamide/polyester structure fabricated via TIPS and their RGDC functionalization to promote osteoblast adhesion and proliferation

Target of this work was to prepare a RGDC functionalized hybrid biomaterial via TIPS technique to achieve a more efficient control of osteoblast adhesion and diffusion on the three-dimensional (3D) scaffolds. Starting from a crystalline poly(l-lactic acid) (PLLA) and an amorphous α,β-poly(N-2-hydroxyethyl) (2-aminoethylcarbamate)-d,l-aspartamide-graft-polylactic acid (PHEA-EDA-g-PLA) copolymer, blend scaffolds were characterized by an appropriate porosity and pore interconnection. The PHEA-EDA-PLA interpenetration with PLLA improved hydrolytic susceptibility of hybrid scaffolds. The presence of free amino groups on scaffolds allowed to tether the cyclic RGD peptide (RGDC) via Michael addition using the maleimide chemistry. Cell culture test carried out on preosteoblastic cells MC3T3-E1 incubated with scaffolds, has evidenced cell adhesion and proliferation. Furthermore, the presence of distributed bone matrix on all scaffolds was evaluated after 70 days compared to PLLA only samples.

Polymeric Approaches to Reduce Tissue Responses Against Devices Applied for Islet-Cell Encapsulation

Immunoisolation of pancreatic islets is a technology in which islets are encapsulated in semipermeable but immunoprotective polymeric membranes. The technology allows for successful transplantation of insulin-producing cells in the absence of immunosuppression. Different approaches of immunoisolation are currently under development. These approaches involve intravascular devices that are connected to the bloodstream and extravascular devices that can be distinguished in micro- and macrocapsules and are usually implanted in the peritoneal cavity or under the skin. The technology has been subject of intense fundamental research in the past decade. It has co-evolved with novel replenishable cell sources for cure of diseases such as Type 1 Diabetes Mellitus that need to be protected for the host immune system. Although the devices have shown significant success in animal models and even in human safety studies most technologies still suffer from undesired tissue responses in the host. Here we review the past and current approaches to modulate and reduce tissue responses against extravascular cell-containing micro- and macrocapsules with a focus on rational choices for polymer (combinations). Choices for polymers but also choices for crosslinking agents that induce more stable and biocompatible capsules are discussed. Combining beneficial properties of molecules in diblock polymers or application of these molecules or other anti-biofouling molecules have been reviewed. Emerging are also the principles of polymer brushes that prevent protein and cell-adhesion. Recently also immunomodulating biomaterials that bind to specific immune receptors have entered the field. Several natural and synthetic polymers and even combinations of these polymers have demonstrated significant improvement in outcomes of encapsulated grafts. Adequate polymeric surface properties have been shown to be essential but how the surface should be composed to avoid host responses remains to be identified. Current insight is that optimal biocompatible devices can be created which raises optimism that immunoisolating devices can be created that allows for long term survival of encapsulated replenishable insulin-producing cell sources for treatment of Type 1 Diabetes Mellitus.

Current Understanding of How Extracorporeal Membrane Oxygenators Activate Haemostasis and Other Blood Components

Extracorporeal membrane oxygenators are used in critical care for the management of severe respiratory and cardiac failure. Activation of the coagulation system is initiated by the exposure of blood to synthetic surfaces and the shear stresses of the circuit, especially from device pumps. Initial fibrinogen deposition and subsequent activation of coagulation factors and complement allow platelets and leucocytes to adhere to oxygenator surfaces and enhance thrombin generation. These changes and others contribute to higher rates of thrombosis seen in these patients. In addition, bleeding rates are also high. Primary haemostasis is impaired by platelet dysfunction and loss of their key adhesive molecules and shear stress causes an acquired von Willebrand defect. In addition, there is also altered fibrinolysis and lastly, administration of systemic anticoagulation is required to maintain circuit patency. Further research is required to fulyl establish the complexities of the haemostatic changes with these devices, and to elucidate the mechanistic changes that are mainly responsible so that plans can be made to reduce their complications and improve management.

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.

Effect of shear stress on the reduction of bacterial adhesion to antifouling polymers

In this work, two antifouling polymer brushes were tested at different shear stress conditions to evaluate their performance in reducing the initial adhesion of Escherichia coli. Assays were performed using a parallel plate flow chamber and a shear stress range between 0.005 and 0.056 Pa. These shear stress values are found in different locations in the human body where biomedical devices are placed. The poly(MeOEGMA) and poly(HPMA) brushes were characterized and it was shown that they can reduce initial adhesion up to 90% when compared to glass. Importantly, the performance of these surfaces was not affected by the shear stress, which is an indication that they do not collapse under this shear stress range. The brushes displayed a similar behavior despite the differences in their chemical composition and surface energy. Both surfaces have shown ultra-low adsorption of macromolecules from the medium when tested with relevant biological fluids (urine and serum). This indicates that these surfaces can potentially be used in biomedical devices to reduce initial bacterial colonization and eventually reduce biofilm formation on these devices.

Introduction of Nature's Complexity in Engineered Blood-compatible Biomaterials

Biomaterials with excellent blood-compatibility are needed for applications in vascular replacement therapies, such as vascular grafts, heart valves and stents, and in extracorporeal devices such as hemodialysis machines and blood-storage bags. The modification of materials that are being used for blood-contacting devices has advanced from passive surface modifications to the design of more complex, smart biomaterials that respond to relevant stimuli from blood to counteract coagulation. Logically, the main source of inspiration for the design of new biomaterials has been the endogenous endothelium. Endothelial regulation of hemostasis is complex and involves a delicate interplay of structural components and feedback mechanisms. Thus, challenges to develop new strategies for blood-compatible biomaterials now lie in incorporating true feedback controlled mechanisms that can regulate blood compatibility in a dynamic way. Here, supramolecular material systems are highlighted as they provide a promising platform to introduce dynamic reciprocity, due to their inherent dynamic nature.

Active quinine-based films able to release antimicrobial compounds via melt quaternization at low temperature

The fabrication of antibacterial films based on renewable materials (e.g., chitosan) has attracted significant interest in fields such as food packaging, health care and medicine. However, exploiting the antibacterial properties of cinchona alkaloids to design active nanostructured films able to release quinine-based antimicrobial compounds has not been considered previously. Herein, we develop two different routes to produce active quinine-based nanostructured cross-linked films by exploiting the multiple reactive sites of quinine and, specifically, both the nitrogen atom and the vinyl group of the quinuclidine portion of the molecule, as well as their corresponding orthogonal quaternization and thiol-ene coupling reactions. The first synthetic strategy produces stiff and brittle nanostructured quinine-based films of limited utility for practical applications. Conversely, the second approach produces active, flexible and nanostructured quinine-based films (T_g = -14 °C, Young's modulus = 1.3 GPa), which are able to release antimicrobial compounds against E. coli that, remarkably, are noncytotoxic against mouse macrophage and human dermal fibroblast cells. These kinds of active cinchona alkaloid-based coatings are easy to prepare by means of simple, solvent-free, melt quaternization/spreading procedures at a relatively low temperature (120 °C), making this second approach one of the most facile reported procedures to date to produce active nanostructured bio-based films.

Lotus-on-chip: computer-aided design and 3D direct laser writing of bioinspired surfaces for controlling the wettability of materials and devices

In this study we present the combination of a math-based design strategy with direct laser writing as high-precision technology for promoting solid free-form fabrication of multi-scale biomimetic surfaces. Results show a remarkable control of surface topography and wettability properties. Different examples of surfaces inspired on the lotus leaf, which to our knowledge are obtained for the first time following a computer-aided design with this degree of precision, are presented. Design and manufacturing strategies towards microfluidic systems whose fluid driving capabilities are obtained just by promoting a design-controlled wettability of their surfaces, are also discussed and illustrated by means of conceptual proofs. According to our experience, the synergies between the presented computer-aided design strategy and the capabilities of direct laser writing, supported by innovative writing strategies to promote final size while maintaining high precision, constitute a relevant step forward towards materials and devices with design-controlled multi-scale and micro-structured surfaces for advanced functionalities. To our knowledge, the surface geometry of the lotus leaf, which has relevant industrial applications thanks to its hydrophobic and self-cleaning behavior, has not yet been adequately modeled and manufactured in an additive way with the degree of precision that we present here.

Tyrosinase-Mediated Surface Coimmobilization of Heparin and Silver Nanoparticles for Antithrombotic and Antimicrobial Activities

Thrombus and infections are the most common causes for the failure of medical devices, leading to higher hospitalization costs and, in some cases, patient morbidity. It is, therefore, necessary to develop novel strategies to prevent thrombosis and infection caused by medical devices. Herein, we report a simple and a highly efficient strategy to impart antithrombotic and antimicrobial properties to substrates, by simultaneously immobilizing heparin and in situ-synthesized silver nanoparticles (Ag NPs) via a tyrosinase-catalyzed reaction. This consists of tyrosinase-oxidized phenolic groups of a heparin derivative (heparin-grafted tyramine, HT) to catechol groups, followed by immobilizing heparin and inducing the in situ Ag NP formation onto poly(urethane) (PU) substrates. The successful immobilization of both heparin and in situ Ag NPs on the substrates was confirmed by analyses of water contact angles, XPS, SEM, and AFM. The sustained silver release and the surface stability were observed for 30 days. Importantly, the antithrombotic potential of the immobilized surfaces was demonstrated by a reduction in fibrinogen absorption, platelet adhesion, and prolonged blood clotting time. Additionally, the modified PU substrates also exhibited remarkable antibacterial properties against both Gram-positive and Gram-negative bacteria. The results of this work suggest a useful, effective, and time-saving method to improve simultaneous antithrombotic and antibacterial performances of a variety of substrate materials for medical devices.

Polymer Brush-Functionalized Chitosan Hydrogels as Antifouling Implant Coatings

Implantable sensor devices require coatings that efficiently interface with the tissue environment to mediate biochemical analysis. In this regard, bioinspired polymer hydrogels offer an attractive and abundant source of coating materials. However, upon implantation these materials generally elicit inflammation and the foreign body reaction as a consequence of protein fouling on their surface and concomitant poor hemocompatibility. In this report we investigate a strategy to endow chitosan hydrogel coatings with antifouling properties by the grafting of polymer brushes in a "grafting-from" approach. Chitosan coatings were functionalized with polymer brushes of oligo(ethylene glycol) methyl ether methacrylate and 2-hydroxyethyl methacrylate using photoinduced single electron transfer living radical polymerization and the surfaces were thoroughly characterized by XPS, AFM, water contact angle goniometry, and in situ ellipsometry. The antifouling properties of these new bioinspired hydrogel-brush coatings were investigated by surface plasmon resonance. The influence of the modifications to the chitosan on hemocompatibility was assessed by contacting the surfaces with platelets and leukocytes. The coatings were hydrophilic and reached a thickness of up to 180 nm within 30 min of polymerization. The functionalization of the surface with polymer brushes significantly reduced the protein fouling and eliminated platelet activation and leukocyte adhesion. This methodology offers a facile route to functionalizing implantable sensor systems with antifouling coatings that improve hemocompatibility and pave the way for enhanced device integration in tissue.

Biomimetic Principles to Develop Blood Compatible Surfaces

Functionalized biomaterial surface patterns capable of resisting nonspecific adsorption while retaining their bioactivity are crucial in the advancement of biomedical technologies, but currently available biomaterials intended for use in whole blood frequently suffer from nonspecific adsorption of proteins and cells, leading to a loss of activity over time. In this review, we address two concepts for the design and modification of blood compatible biomaterial surfaces, zwitterionic modification and surface functionalization with glycans – both of which are inspired by the membrane structure of mammalian cells – and discuss their potential for biomedical applications.

Reduced Blood Cell Adhesion on Polypropylene Substrates through a Simple Surface Zwitterionization

To overcome the thrombogenic reactions of hydrocarbon-based biomaterials in clinical blood treatment, we introduce a model study of surface zwitterionization of a polypropylene (PP) substrate using a set of well-defined copolymers for controlling the adhesion of blood cells in vitro. Random and block copolymers containing zwitterionic units of 2-methacryloyloxyethyl phosphorylcholine (MPC), [3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt (SBAA), or nonionic units of 2-hydroxyethyl methacrylate (HEMA) with a controlled hydrophobic segment of 70% n-butyl methacrylate (BMA) units in these polymers were synthesized through reversible addition-fragmentation chain transfer polymerization. A systematic study of how zwitterionic and nonionic copolymer architectures associated with controlled chain orientation via hydration processes affect blood compatibility is reported. The surface wettability of PP substrates coated with the block copolymer with poly(MPC) (PMPC) segments was higher than that of the random copolymer poly(MPC-random-BMA). However, only the random copolymers with SBAA units demonstrate a higher surface wettability. The PP substrate coated with nonionic copolymers containing HEMA units showed relatively lower hydration capability associated with higher protein adsorption, platelet adhesion, and leukocyte attachment than those with zwitterionic copolymers. The random copolymer poly(SBAA-random-BMA) coated on the PP substrates exhibited resistance to cell adhesion in human whole blood at a level comparable to that of MPC copolymers. An ideal zwitterionic PP substrate could be obtained by coating it with a block copolymer composed of PMPC and poly(BMA) (PBMA) segments, PMPC-block-PBMA. The water contact angle decreased dramatically from approximately 100° on the original PP substrate to 11° within 30 s. The number of blood cells attached on PMPC-block-PBMA decreased significantly to less than 2.5% of that on original PP. These results prove that the rational design of zwitterionic polymers incorporated with a hydrophobic anchoring portion provides a promising approach to reduce blood cell adhesion and protein adsorption of hydrocarbon-based biomaterials applied in direct contact with human whole blood.

Hydrophilic Polymer Brush Layers on Stainless Steel Using Multilayered ATRP Initiator Layer

Thin polymer coatings (in tens of nanometers to a micron thick) are desired on industrial surfaces such as stainless steel. In this thickness range coatings are difficult to produce using conventional methods. In this context, surface-initiated controlled polymerization method can offer a promising tool to produce thin polymer coatings via bottom-up approach. Furthermore, the industrial surfaces are chemically heterogeneous and exhibit surface features in the form of grain boundaries and grain surfaces. Therefore, the thin coatings must be equally effective on both the grain surfaces and the grain boundary regions. This study illustrates a novel "periodic rejuvenation of surface initiation" process using surface-initiated ATRP technique to amplify the graft density of poly(oligoethylene glycol)methacrylate (POEGMA) brush layers on stainless steel 316L surface. The optimized conditions demonstrate a controlled, macroscopically homogeneous, and stable POEGMA brush layer covering both the grain surface and the grain boundary region. Various relevant parameters-surface cleaning methods, controllability of thickness, graft density, homogeneity and stability-were studied using techniques such as ellipsometer, X-ray photoelectron spectroscopy, scanning electron microscopy-energy-dispersive X-ray, surface zeta potential, and infrared reflection-adsorption spectroscopy.

Hepatitis B plasmonic biosensor for the analysis of clinical serum samples

A plasmonic biosensor for rapid detection of protein biomarkers in complex media is reported. Clinical serum samples were analyzed by using a novel biointerface architecture based on poly[(N-(2-hydroxypropyl) methacrylamide)-co-(carboxybetaine methacrylamide)] brushes functionalized with bioreceptors. This biointerface provided an excellent resistance to fouling even after the functionalization and allowed for the first time the direct detection of antibodies against hepatitis B surface antigen (anti-HBs) in clinical serum samples using surface plasmon resonance (SPR). The fabricated SPR biosensor allowed discrimination of anti-HBs positive and negative clinical samples in 10min. Results are validated by enzyme-linked immunoassays of the sera in a certified laboratory. The sensor could be regenerated by simple treatment with glycine buffer.

A strategy for constructing anti-adhesion surfaces based on interfacial thiol–ene photoclick chemistry between DOPA derivatives with a catechol anchor group and zwitterionic betaine macromolecules

A novel route to construct stable anti-adhesion surfaces was explored via click chemistry between the anti-adhesion macromolecules and the anchoring compound DMA to various substrates.