Nano-scale surface modification of a segmented polyurethane with a phospholipid polymer

Surface functionalization of polyurethanes: A critical review

Synthetic polymers, particularly polyurethanes (PUs), have revolutionized bioengineering and biomedical devices due to their customizable mechanical properties and long-term stability. However, the inherent hydrophobic nature of PU surfaces arises common issues such as high friction, strong protein adsorption, and thrombosis, especially in the physiological environment of blood contact. To overcome these issues, researchers have explored various modification techniques to improve the surface biofunctionality of PUs. In this review, we have systematically summarized several typical surface modification methods including surface plasma modification, surface oxidation-induced grafting polymerization, isocyanate-based chemistry coupling, UV-induced surface grafting polymerization, adhesives-assisted attachment strategy, small molecules-bridge grafting, solvent evaporation technique, and hydrogen bonding interaction. Correspondingly, the advantages, limitations, and future prospects of these surface modification methods were discussed. This review provides an important guidance or tool for developing surface functionalized PUs in the fields of bioengineering and medical devices.

The synthesis of polyurethane with mechanical properties that are responsive to water retention states

Water-retention-state-responsive polyurethane was designed and synthesized via introducing zwitterionic sulfobetaine onto its polymer chains.

Surface modification and endothelialization of polyurethane for vascular tissue engineering applications: a review

Cardiovascular implants, especially vascular grafts made of synthetic polymers, find wide clinical applications in the treatment of cardiovascular diseases. However, cases of failure still exist, notably caused by restenosis and thrombus formation. Aiming to solve these problems, various approaches to surface modification of synthetic vascular grafts have been used to improve both the hemocompatibility and long-term patency of artificial vascular grafts. Surface modification using hydrophilic molecules can enhance hemocompatibility, but this may limit the initial vascular endothelial cell adhesion. Therefore, the improvement of endothelialization on these grafts with specific peptides and biomolecules is now an exciting field of research. In this review, several techniques to improve surface modification and endothelialization on vascular grafts, mainly polyurethane (PU) grafts, are summarized, together with the recent development and evolution of the different strategies: from the use of PEG, zwitterions, and polysaccharides to peptides and other biomolecules and genes; from in vitro endothelialization to in vivo endothelialization; and from bio-inert and bio-active to bio-mimetic approaches.

New Aliphatic Glycerophosphoryl-Containing Polyurethanes: Synthesis, Platelet Adhesion and Elution Cytotoxicity Studies

In this study new poly(ether)urethanes (PEUs) based on aliphatic diisocyanates were synthesized with phospholipid-like residues as chain extenders. The primary objective was to prepare new polyurethanes from diisocyanates that are less toxic than the aromatic ones widely used in medical-grade polyurethanes, in order to investigate the effect of the different aromatic or aliphatic hard segment content on the final properties of the materials. Some glycerophospho residues were simultaneously introduced to enhance the hemocompatibility of these materials. Polymers were prepared by a conventional two-step solution polymerization procedure using hexamethylene diisocyanate (HDI) and dodecametilendiisocyanate (DDI) and poly(1,4-butanediol) with molecular weight 1000 to form prepolymers, which were subsequently polymerized with 1-glycerophosphorylcholine (1-GPC) or glycerophosphorylserine (GPS) to act as chain extenders. The reference polymers bearing 1,4-butandiol (BD) were also synthesized. The polymers obtained were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (1H NMR), and differential scanning calorimetry (DSC). The hemocompatibility of synthesized segmented polyurethanes was preliminarily investigated by platelet-rich plasma contact studies and related scanning electron microscopy (SEM) photographs as well as by cell viability assay after cell exposure to material elutions to assess the effect of any toxic leachables coming out from the samples. Two of the polymers gave interesting results, suggesting the desirability of further investigation into their possible use in biomedical devices.

Biodegradable shape memory polymers functionalized with anti-biofouling interpenetrating polymer networks

A novel type of shape memory polyurethane (SMPU) with high mechanical properties and biodegradability was constructed using a lactone copolymer (poly(ε-caprolactone-co-γ-butyrolactone), PCLBL), a diol- or triol-based chain extender (1,5-pentanediol, glycerol and 2-amino-2-hydroxymethyl-1,3-propanediol) and a diisocyanate cross-linker (1,6-hexamethylene diisocyanate).

Delivery of AIB1 siRNA by Ca2+/PEI/heparin composite nanoparticles effectively inhibits the growth of human breast cancer

Here, a novel carrier fabricated by the interaction of negatively charged heparin and positively charged PEI and Ca²⁺ was investigated to deliver AIB1 siRNA into breast cancer cells both in vitro and in vivo. Ca²⁺/PEI/heparin nanoparticles were prepared by simply mixing heparin, PEI and CaCl₂ aqueous solution. Heparin in the Ca²⁺/PEI/heparin nanoparticles (40.9% heparin, w/w) decreased the cytotoxicity of PEI. According to the MTT assay, Ca²⁺/PEI/heparin NPs are superior to commercial Lipofectamine 2000 considering the safety. The Ca²⁺/PEI/heparin NPs are able to deliver siAIB1 into breast cancer cells as effectively as Lipofectamine 2000 both in vitro and in vivo. The in vivo experiment also indicated that the NF-κB/BCL-2 signal pathway might be the downstream signal pathway of AIB1 in regulating breast cancer proliferation and progression.

Quantification of aldehyde terminated heparin by SEC-MALLS-UV for the surface functionalization of polycaprolactone biomaterials

A straight forward strategy of heparin surface grafting employs a terminal reactive-aldehyde group introduced through nitrous acid depolymerization. An advanced method that allows simultaneously monitoring of both heparin molar mass and monomer/aldehyde ratio by size exclusion chromatography, multi-angle laser light scattering and UV-absorbance (SEC-MALLS-UV) has been developed to improve upon heparin surface grafting. Advancements over older methods allow quantitative characterization by direct (aldehyde absorbance) and indirect (Schiff-based absorbance) evaluation of terminal functional aldehydes. The indirect quantitation of functional aldehydes through labeling with aniline (and the formation of a Schiff-base) allows independent quantitation of both polymer mass and terminal functional groups with the applicable UV mass extinction coefficients determined. The protocol was subsequently used to synthesize an optimized heparin-aldehyde that had minimal polydispersity (PDI<2) and high reaction yields (yield >60% by mass). The 8 kDa weight averaged molar mass heparin-aldehyde was then grafted on polycaprolactone (PCL), a common implant material. This optimized heparin-aldehyde retained its antithrombin activity, assessed in freshly drawn blood or surface immobilized on PCL films. Anticoagulant activity was equal to or better than the 24 kDa unmodified heparin it was fragmented from.

Cell membrane-mimicking coating for blood-contacting polyurethanes

The aim of the present work was to develop simple modification technique for polyurethanes (PUs) intended for use in blood-contacting implants (vascular grafts, heart prosthesis, ventricular assist devices). PU surface was modified with soybean-derived phosphatidylcholine (PC) via one-step dip coating technique. In order to evaluate blood compatibility of the obtained materials, samples were contacted with human blood under static and arterial flow-simulated conditions. The PC-modified surfaces were thoroughly characterized and tested for fibrinogen resistance, the ability to resist platelet adhesion and activation, hemolysis percentage and plasma recalcification time. Results demonstrated significant, more than three-fold reduction in the amount of fibrinogen adsorbed to PC-modified materials as compared to non-modified PU. Analysis of the samples’ surface after incubation with blood showed high reduction in platelet adhesion. The results were confirmed by analysis of blood samples collected after shear-stress tests – the percentage of free (non-aggregated) platelets remaining in blood samples contacted with PC-coated materials exceeded 70%. The same parameter measured for non-modified PU was significantly lower and equaled 28%.

Surface modification of silicone for biomedical applications requiring long-term antibacterial, antifouling, and hemocompatible properties

Silicone has been used for peritoneal dialysis (PD) catheters for several decades. However, bacteria, platelets, proteins, and other biomolecules tend to adhere to its hydrophobic surface, which may lead to PD outflow failure, serious infection, or even death. In this work, a cross-linked poly(poly(ethylene glycol) dimethacrylate) (P(PEGDMA)) polymer layer was covalently grafted on medical-grade silicone surface to improve its antibacterial and antifouling properties. The P(PEGDMA)-grafted silicone (Silicone-g-P(PEGDMA)) substrate reduced the adhesion of Staphylococcus aureus , Escherichia coli , and Staphylococcus epidermidis , as well as 3T3 fibroblast cells by ≥90%. The antibacterial and antifouling properties were preserved after the modified substrate was aged for 30 days in phosphate buffer saline. Further immobilization of a polysulfobetaine polymer, poly((2-(methacryloyloxy)ethyl)dimethyl-(3-sulfopropyl)ammonium hydroxide) (P(DMAPS)), on the Silicone-g-P(PEGDMA) substrate via thiol-ene click reaction leads to enhanced antifouling efficacy and improved hemocompatibility with the preservation of the antibacterial property. Compared to pristine silicone, the so-obtained Silicone-g-P(PEGDMA)-P(DMAPS) substrate reduced the absorption of bovine serum albumin and bovine plasma fibrinogen by ≥80%. It also reduced the number of adherent platelets by ≥90% and significantly prolonged plasma recalcification time. The results indicate that surface grafting with P(PEGDMA) and P(DMAPS) can be potentially useful for the modification of silicone-based PD catheters for long-term applications.

Parinaric acid methyl ester polymer films with hill-structured features: fabrication and different sensitivities to normal and tumor cells

Parinaric acid methyl ester (PnA-Me) polymer films with hill-structured features were fabricated by a solvent volatilization in situ cross-linking method. Moreover, nuclear magnetic resonance, Fourier transform infrared, and oxidation kinetic analyses were successfully applied to monitor the formation process of PnA-Me polymer films. The role of PnA-Me monomer concentrations for growth control of the hill structures on a glass matrix had also been investigated. Also, the results demonstrated that size control of the resulting hill structure ranging from 0.56 ± 0.18 to 19.6 ± 3.5 μm could be realized by varying the concentration of the PnA-Me monomer from 0.0117 to 1.5 mg/mL. Additionally, the effects of polymer films with different surface topographical structures on the behaviors of rat mesenchymal stem cells and human pheochromocytoma cells were measured by morphological and metabolic methods. The results revealed that the cell activity of PnA-Me films was topographical structure- and cell-type-dependent. Furthermore, the selective sensitivity of the PnA-Me films to normal and tumor cells supported the potential value as the coatings for the tissue engineering substitutes.

Studies on bound water restrained by poly(2-methacryloyloxyethyl phosphorylcholine): Comparison with polysaccharide-water systems

The structural change of water restrained by poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) was investigated by differential scanning calorimetry (DSC), since the biocompatibility of PMPC and related biopolymers is affected by the structure of water on the polymer surface. The phase transition behaviour of PMPC-water systems with a water content (W(c)=mass of water/mass of dry sample, gg(-1)) in the range 0-2.0 was measured in the temperature range -150 to 50 degrees C. Glass transition, cold crystallization and melting were observed. Cold crystallization, which has been suggested as an index of biocompatibility, was detected for PMPC with a W(c) in the range 0.5-0.9. The amounts of two types of bound water, non-freezing water and freezing bound water, were calculated from the melting enthalpy. The amount of non-freezing water of PMPC was approximately 0.48. It was found that the phase transition behaviour and amount of bound water of PMPC were quite similar to those of water-soluble polysaccharide electrolytes. The results indicate that the bound water, not the free water, is restrained by PMPC.

Isopropyl Myristate-Modified Polyether-Urethane Coatings as Protective Barriers for Implantable Medical Devices

Polyurethane films have potential applications in medicine, especially for packaging implantable medical devices. Although polyether-urethanes have superior mechanical properties and are biocompatible, achieving water resistance is still a challenge. Polyether based polyurethanes with two different molecular weights (PTMO1000, PTMO2000) were prepared from 4,4’-diphenylmethane diisocyanate and poly(tetra-methylene oxide). Polymer films were introduced using different concentrations (0.5-10 wt %) of isopropyl myristate lipid (IPM) as a non-toxic modifying agent. The physical and mechanical properties of these polymers were characterised using physical and spectroscopy techniques (FTIR, Raman, DSC, DMA, tensile testing). Water contact angle and water uptake of the membranes as a function of IPM concentration was also determined accordingly. The FTIR and Raman data indicate that IPM is dispersed in polyurethane at ≤ 2wt% and thermal analysis confirmed this miscibility to be dependent on soft segment length. Modified polymers showed increased tensile strength and failure strain as well as reduced water uptake by up to 24% at 1-2 wt% IPM.

A small diameter, fibrous vascular conduit generated from a poly(ester urethane)urea and phospholipid polymer blend

The thrombotic and hyperplastic limitations associated with synthetic small diameter vascular grafts have generated sustained interest in finding a tissue engineering solution for autologous vascular segment generation in situ. One approach is to place a biodegradable scaffold at the site that would provide acute mechanical support while vascular tissue develops. To generate a scaffold that possessed both non-thrombogenic character and mechanical properties appropriate for vascular tissue, a biodegradable poly(ester urethane)urea (PEUU) and non-thrombogenic bioinspired phospholipid polymer, poly(2-methacryloyloxyethyl phosphorylcholine-co-methacryloyloxyethyl butylurethane) (PMBU) were blended at PMBU weight fractions of 0-15% and electrospun to create fibrous scaffolds. The composite scaffolds were flexible with breaking strains exceeding 300%, tensile strengths of 7-10MPa and compliances of 2.9-4.4 x 10(-4) mmHg(-1). In vitro platelet deposition on the scaffold surfaces significantly decreased with increasing PMBU content. Rat smooth muscle cell proliferation was also inhibited on PEUU/PMBU blended scaffolds with greater inhibition at higher PMBU content. Fibrous vascular conduits (1.3mm inner diameter) implanted in the rat abdominal aorta for 8 weeks showed greater patency for grafts with 15% PMBU blending versus PEUU without PMBU (67% versus 40%). A thin neo-intimal layer with endothelial coverage and good anastomotic tissue integration was seen for the PEUU/PMBU vascular grafts. These results are encouraging for further evaluation of this technique in larger diameter applications for longer implant periods.

Synthesis, platelet adhesion and cytotoxicity studies of new glycerophosphoryl-containing polyurethanes

In this work we synthesized new MDI -based poly(ether)urethanes (PEUs) with phospholipid-like residue as chain extender. Polymers were prepared by a conventional two-step solution polymerization procedure using 4,4' diphenylmethanediisocyanate (MDI) and poly(1,4- butanediol) with 1000 as molecular weight to form prepolymers which were successively polymerized with 1 glycerophosphorylcholine (1-GPC), 2-glycerophosphorylcholine (2-GPC) or glycerophosphorylserine (GPS) as chain extenders. Two reference polymers bearing 1,4-butandiol (BD) have been also synthesized. The polymers obtained were characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and modulated scanning calorimetry (MDSC). The biocompatibility of synthesized segmented polyurethanes was then investigated by platelet-rich plasma contact studies and related scanning electron microscopy (SEM) photographs for blood compatibility and cytotoxicity assay (MTT test) on material elution to assess the effect of any toxic leachables on cellular viability. Three polymers among all have given very satisfactory results suggesting to investigate more deeply their possible use in biomedical devices.

Development of Biocompatible Interpenetrating Polymer Networks Containing a Sulfobetaine-Based Polymer and a Segmented Polyurethane for Protein Resistance

Interpenetrating polymer networks (IPNs) were prepared by the modification of a segmented polyurethane (SPU) with a cross-linked sulfobetaine methacrylate (SBMA) polymer. The IPN films that were prepared can effectively resist nonspecific protein adsorption when the distribution of SBMA units within the SPU film is well controlled, and they retain high mechanical strengths inherent from the base SPU films. Furthermore, the zwitterionic and biomimetic nature of sulfobetaine and the ease of SBMA preparation make SBMA-based materials very attractive for a wide range of applications. It is challenging to control the diffusion of highly polar SBMA into the hydrophobic network of SPU. In this study, various parameters governing the formation of IPNs containing SBMA were studied. The chemical composition depth profile of the IPN films was determined by confocal Raman microscopy. The morphology and thickness of these IPN films were examined by atomic force microscopy and scanning electron microscopy. The amount of adsorbed proteins on the IPN films was determined by an enzyme-linked immunosorbent assay. Results show that the amount of adsorbed proteins on the IPN films depends on the incubation conditions, including solvent polarity, incubation time, SBMA monomer ratio, and incubation concentration. It appears that the IPN films prepared in a mixed solvent of higher polarity with long incubation time lead to very low protein adsorption. This study not only introduces a new IPN system containing SBMA, but also provides a fundamental understanding of various parameters governing the formation of IPNs.

Stress response of adherent cells on a polymer blend surface composed of a segmented polyurethane and MPC copolymers

To better understand the effect of 2-methacryloyloxyethyl phosphorylcholine (MPC) copolymer in improving the biocompatibility of segmented polyurethane (SPU), the expression of heat shock protein (HSP) mRNA in HeLa S3 cells adhered on SPU blended with MPC copolymers was measured. Conventionally, MPC copolymers (PMEH) were synthesized by changing the feed ratios of MPC and 2-ethylhexyl methacrylate. X-ray photoelectron spectroscopic analysis of the SPU/PMEH film indicated that the surface concentration of MPC units on the SPU/PMEH film increased with an increase in PMEH composition. HeLa S3 cells were cultured on SPU/PMEH films. The number of adherent cells on the SPU/PMEH films decreased with an increase in the concentration of PMEH. When the PMEH composition was greater than 0.5 wt %, cell adhesion and proliferation decreased markedly. Expressions of HSP27 and HSP47 mRNA were detected using the reverse transcription-polymerase chain reaction (RT-PCR). After incubation for 24 h, both the HSP mRNA expressions in the HeLa S3 cells showed no significant differences among all samples. In HeLa S3 cells that adhered to the SPU film for 48 h, the expressions of HSP27 and HSP47 mRNA increased significantly when compared with those incubated for 24 h. In contrast, the two kinds of mRNA expressions decreased in the HeLa S3 cells that adhered to the SPU/PMEH films for 48 h. From these results, we concluded that PMEH was quite important in suppressing the stress response of adherent HeLa S3 cells. Therefore, SPU/PMEH blend polymers are useful as implantable biomedical materials.

Segmented polyurethane modified by photopolymerization and cross-linking with 2-methacryloyloxyethyl phosphorylcholine polymer for blood-contacting surfaces of ventricular assist devices

To improve the biocompatibility of pulsatile ventricular assist devices (VADs), the blood-contacting surface of the segmented polyurethane (SPU) diaphragm employed in an electromechanical VAD was modified by introducing 2-methacryloyloxyethyl phosphorylcholine (MPC) units into its surface and forming an interpenetrating polymer network (IPN) structure, which contained independently cross-linked MPC polymer and SPU. The SPU diaphragm modified with an IPN structure was then assembled into a target test pump and underwent continuous pump operation at 37 degrees C for 2 weeks in a simulated systemic circulation using a mock circulatory loop. The surface characteristics of the pump diaphragm after 2 weeks of pump operation were then analyzed with an X-ray photoelectron spectroscope (XPS) and gold-colloid-labeled immunoassay. The XPS surface analysis of the IPN-modified SPU indicated the firm anchoring of MPC units even after 2 weeks of pump operation (the phosphor : carbon ratio was reduced by only 0.09%). The IPN-modified diaphragm prevented protein adsorption as well as cell adhesion in comparison to the unmodified SPU surface. This result thus validated that (1) the IPN structure could firmly secure MPC units to the SPU surface even in a high-mechanical-stress and high-shear environment, (2) the antithrombogenic power of MPC units remained unchanged after 2 weeks of continuous exposure to a high-shear environment, and (3) the IPN modified SPU cross-linked with MPC could be a powerful antithrombogenic surface for blood pumps used for chronic circulatory support of cardiac patients.