Surface modification with affinity ligands capable of capturing bioactive molecules in situ is a widely used strategy for developing biofunctional materials. However, many bioactive molecules, for example zymogens, exist naturally in a "quiescent" state, and become active only when "triggered" by specific activators. In the present study, in situ activation of a surface-integrated zymogen was achieved by introducing affinity ligands for both the zymogen and its activator. Specifically a dual affinity surface was designed for the integration of plasminogen (Plg) and tissue plasminogen activator (t-PA). This surface was expected to have plasmin-generating and, therefore, fibrinolytic properties. A polyurethane surface was modified with a copolymer of 2-hydroxyethyl methacrylate and 1-adamantan-1-ylmethyl methacrylate poly(HEMA-co-AdaMA). The affinity ligands, ARMAPE peptide (for t-PA) and ε-lysine-containing β-cyclodextrin (β-CD-(Lys)7) (for Plg), were attached in sequence via covalent bonding and host-guest interactions, respectively. The resulting surfaces were shown to have high binding capacities for both t-PA and Plg while resisting nonspecific protein adsorption. Pre-loading with t-PA followed by Plg uptake from plasma generated plasmin and thus endowed the surface with fibrinolytic activity. In general the incorporation of dual affinity ligands to achieve surface-promoted bioactivity is a promising approach for the development of biofunctional materials. The method reported herein for the sequential attachment of plasminogen and t-PA affinity ligands can be extended to systems of multiple ligands generally.
Biomaterial-associated infections often arise from contaminating bacteria adhering to an implant surface that are introduced during surgical implantation and not effectively eradicated by antibiotic treatment. Whether or not infection develops from contaminating bacteria depends on an interplay between bacteria contaminating the biomaterial surface and tissue cells trying to integrate the surface with the aid of immune cells. The biomaterial surface plays a crucial role in defining the outcome of this race for the surface. Tissue integration is considered the best protection of a biomaterial implant against infectious bacteria. This paper aims to determine whether and how macrophages aid osteoblasts and human mesenchymal stem cells to adhere and spread over gold nanoparticle (GNP)-coatings with different hydrophilicity and roughness in the absence or presence of contaminating, adhering bacteria. All GNP-coatings had identical chemical surface composition, and water contact angles decreased with increasing roughness. Upon increasing the roughness of the GNP-coatings, the presence of contaminating Staphylococcus epidermidis in biculture with cells gradually decreased surface coverage by adhering and spreading cells, as in the absence of staphylococci. More virulent Staphylococcus aureus fully impeded cellular adhesion and spreading on smooth gold- or GNP-coatings, while Escherichia coli allowed minor cellular interaction. Murine macrophages in monoculture tended toward their pro-inflammatory “fighting” M1-phenotype on all coatings to combat the biomaterial, but in bicultures with contaminating, adhering bacteria, macrophages demonstrated Ym1 expression, indicative of polarization toward their anti-inflammatory “fix-and-repair” M2-phenotype. Damage repair of cells by macrophages improved cellular interactions on intermediately hydrophilic/rough (water contact angle 30 deg/surface roughness 118 nm) GNP-coatings in the presence of contaminating, adhering Gram-positive staphylococci but provided little aid in the presence of Gram-negative E. coli. Thus, the merits on GNP-coatings to influence the race for the surface and prevent biomaterial-associated infection critically depend on their hydrophilicity/roughness and the bacterial strain involved in contaminating the biomaterial surface.
This work reports a simple and robust strategy for synthesis of polydopamine nanocapsules (PDA NCs). First, polymer assemblies were synthesized by a γ-ray-induced liquid-liquid (H2O-acrylate) interface polymerization strategy, in the absence of any surfactants. 1H nuclear magnetic resonance analysis and molecular dynamics simulation reveal that the generation of polymer assemblies largely depends on the hydrophilicity of acrylate and gravity of the oligomers at the interface. By virtue of the spherical structure and mechanic stability of the polymer assemblies, PDA NCs are next prepared by the interfacial polymerization of dopamine onto the assemblies, followed by the removal of templates by using ethanol. The polydopamine nanocapsules are shown to load and release ciprofloxacin (CIP, a model drug), such that the CIP-loaded PDA NCs are able to inhibit the growth of Escherichia coli.
The extent of protein adsorption is an important consideration in the biocompatibility of biomaterials. Various experimental methods can be used to determine the quantity of protein adsorbed, but the results usually differ. In the present work, self-assembled monolayers (SAMs) were used to prepare a series of model gold surfaces varying systematically in water wettability, from hydrophilic to hydrophobic. Three commonly used methods, namely, surface plasmon resonance (SPR), quartz crystal microbalance with dissipation (QCM-D), and (125)I-radiolabeling, were employed to quantify fibrinogen (Fg) adsorption on these surfaces. This approach allows a direct comparison of the mass of Fg adsorbed using these three techniques. The results from all three methods showed that protein adsorption increases with increasing surface hydrophobicity. The increase in the mass of Fg adsorbed with increasing surface hydrophobicity in the SPR data was parallel to that from (125)I-radiolabeling, but the absolute values were different and there does not seem to be a "universally congruent" relationship between the two methods for surfaces with varying wettability. For QCM-D, the variation in protein adsorption with wettability was different from that for SPR and radiolabeling. On the more hydrophobic surfaces, QCM-D gave an adsorbed mass much higher than from the two other methods, possibly because QCM-D measures both the adsorbed Fg and its associated water. However, on the more hydrophilic surfaces, the adsorbed mass from QCM-D was slightly greater than that from SPR, and both were smaller than from (125)I-radiolabeling; this was true no matter whether the Sauerbrey equation or the Voigt model was used to convert QCM-D data to adsorbed mass.
A hexapeptide derived from an enzyme inhibitor was used to conjugate a hydrophilic polymer to the inhibitor “berth” in the enzyme, affording the enzyme resistance to the inhibitor.
Abstract A novel biomaterial based on polyurethane (PU) was prepared through physical incorporation of lysine‐containing copolymer to improve its hemocompatibility and surface recognition of plasminogen. The lysine‐containing copolymer was synthesized via the copolymerization of 2‐ethylhexyl methacrylate (EHMA), oligo (ethylene glycol) methyl ether methacrylate (OEGMA) and 6‐ tert ‐butoxycarbonyl amino‐2‐(2‐methyl‐acryloylamino)‐hexanoic acid tert ‐butyl ester (Lys(P)MA), followed by the deprotection of COOH and ε ‐NH 2 groups on lysine residues in the copolymer. The composition of the copolymer can be adjusted by varying the monomer feed ratio. The three components contribute to improving the compatibility with PU, resistance to nonspecific protein adsorption and specific binding of plasminogen, respectively. The binding capacity towards plasminogen increased with the lysine content in the copolymer. This approach illustrates a simple way for the generation of novel biomaterials with improved hemocompatibility and surface recognition of specific biomolecules.
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