A facile approach toward protein-resistant biointerfaces based on photodefinable poly-p-xylylene coating

Characterization of Mechanical Stability and Immunological Compatibility for Functionalized Modification Interfaces

Surface modification layers are performed on the surfaces of biomaterials and have exhibited promise for decoupling original surface properties from bulk materials and enabling customized and advanced functional properties. The physical stability and the biological compatibility of these modified layers are equally important to ensure minimized delamination, debris, leaching of molecules, and other problems that are related to the failure of the modification layers and thus can provide a long-term success for the uses of these modified layers. A proven surface modification tool of the functionalized poly-para-xylylene (PPX) system was used as an example, and in addition to the demonstration of their chemical conjugation capabilities and the functional properties that have been well-documented, in the present report, we additionally devised the characterization protocols to examine stability properties, including thermostability and adhesive strength, as well as the biocompatibility, including cell viability and the immunological responses, for the modified PPX layers. The results suggested a durable coating stability for PPXs and firmly attached biomolecules under these stability and compatibility tests. The durable and stable modification layers accompanied by the native properties of the PPXs showed high cell viability against fibroblast cells and macrophages (MΦs), and the resulting immunological activities created by the MΦs exhibited excellent compatibility with non-activated immunological responses and no indication of inflammation.

Enhanced bone morphogenic property of parylene-C

The ability to induce osteointegration was introduced to a parylene-C surface via the simple and intuitive process of protein adsorption mediated by hydrophobic interactions. In this way, bone morphogenetic protein (BMP)-2, fibronectin, and platelet-rich plasma (PRP) could be immobilized on parylene-C surfaces. This approach alleviates concerns related to the use of potentially harmful substances in parylene-C modification processes. The adsorbed protein molecules were quantitatively characterized with respect to adsorption efficacy and binding affinity, and the important biological activities of the proteins were also examined using both early and late markers of osteogenetic activity, including alkaline phosphatase expression, calcium mineralization and marker gene expression. Additionally, the adsorbed PRP exhibited potential as a substitute for expensive recombinant growth factors by effectively inducing comparable osteogenetic activity. In addition to the excellent biocompatibility of parylene-C and its ability to coat a wide variety of substrate materials, the modification of parylene-C via protein adsorption provides unlimited possibilities for installing specific biological functions, expanding the potential applications of this material to include various biointerface platforms.

Development of Antifouling Hyperbranched Polyglycerol Layers on Hydroxyl Poly-p-xylylene Coatings

Antifouling surfaces that are resistant to protein adsorption and cell adhesion are desirable for many biomedical devices, such as diagnostic devices, biosensors, and implants. In this study, we developed an antifouling hyperbranched polyglycerol (hPG) surface on hydroxyl poly-p-xylylene (PPX-OH). PPX-OH was deposited via chemical vapor deposition (CVD), and an hPG film was then developed via the ring-opening reaction of glycidol. The hPG film greatly reduced the adhesion of L929 cells and platelets as well as protein adsorption. The addition of alkenyl groups in the hPG layer allows the conjugation of biomolecules, such as peptides and biotin, and elicits specific biological interactions. Since the CVD deposition of PPX-OH could be applied to most types of materials, our approach makes it possible to decorate an antifouling hPG film on most types of materials. Our method could be applied to biosensors, diagnostics, and biomedical devices in the future.

Micro- and nano-surface structures based on vapor-deposited polymers

Vapor-deposition processes and the resulting thin polymer films provide consistent coatings that decouple the underlying substrate surface properties and can be applied for surface modification regardless of the substrate material and geometry. Here, various ways to structure these vapor-deposited polymer thin films are described. Well-established and available photolithography and soft lithography techniques are widely performed for the creation of surface patterns and microstructures on coated substrates. However, because of the requirements for applying a photomask or an elastomeric stamp, these techniques are mostly limited to flat substrates. Attempts are also conducted to produce patterned structures on non-flat surfaces with various maskless methods such as light-directed patterning and direct-writing approaches. The limitations for patterning on non-flat surfaces are resolution and cost. With the requirement of chemical control and/or precise accessibility to the linkage with functional molecules, chemically and topographically defined interfaces have recently attracted considerable attention. The multifunctional, gradient, and/or synergistic activities of using such interfaces are also discussed. Finally, an emerging discovery of selective deposition of polymer coatings and the bottom-up patterning approach by using the selective deposition technology is demonstrated.

Tunable coverage of immobilized biomolecules for biofunctional interface design

Tunable biological responses can be controlled by the modifications of the density of the underlying chemical motifs and the density of the biomolecules immobilized.

Conjugation of monocarboxybetaine molecules on amino-poly-p-xylylene films to reduce protein adsorption and cell adhesion

A surface that resists protein adsorption and cell adhesion is highly desirable for many biomedical applications such as blood-contact devices and biosensors. In this study, we fabricated a carboxybetaine-containing surface and evaluated its antifouling efficacy. First, an amine-containing substrate was created by chemical vapor deposition of 4-aminomethyl-p-xylylene-co-p-xylylene (Amino-PPX). Aldehyde-ended carboxybetaine molecules were synthesized and conjugated onto Amino-PPX. The carboxybetaine-PPX surface greatly reduced protein adsorption and cell adhesion. The attachment of L929 cells on the carboxybetaine-PPX surface was reduced by 87% compared to the cell adhesion on Amino-PPX. Furthermore, RGD peptides could be conjugated on carboxybetaine-PPX to mediate specific cell adhesion. In conclusion, we demonstrate that a surface decoration with monocarboxybetaine molecules is useful for antifouling applications.

Evenly distributed thin-film Ag coating on stainless plate by tricomponent Ag/silicate/PU with antimicrobial and biocompatible properties

A tricomponent nanohybrid dispersion in water comprising silver nanoparticles (AgNP), nanometer-thick silicate platelets (NSP), and water-based polyurethane (PU) was developed for surface coating on orthopedic metal plates. The previously developed AgNP-on-NSP nanohybrid was homogeneously blended into a selected waterborne PU dispersion at varied weight ratios from 1/0.1 to 1/10 (w/w). PU was used to adhere the Ag nanohybrid to the metal surface. The resultant dispersions were analyzed and found to contain AgNP 2-18 nm in diameter and characterized by using UV absorption and TEM micrograph. The subsequent coating of AgNP/NSP-PU dispersion generated a film of 1.5 μm thickness on the metal plate surface, further characterized by an energy dispersive spectroscope (EDS) to show the homogeneous distribution of Ag, Si, and C elements on the metal plates. The surface antimicrobial efficacy was proven for the coating composition of AgNP/NSP to PU ranging from 1/1 to 1/5 by weight ratio but irrelevant to the thickness of the coated materials. The metal plate coated with the high Ag content at 1/1 (w/w) ratio was shown to have very low cytotoxicity toward the contacted mammal fibroblasts. Overall, the optimized tricomponent Ag/silicate/PU in water dispersion from 1/2 to 1/3 (w/w) could generate a stable film on a metal surface exhibiting both antimicrobial and biocompatible properties. The facile coating technique of the AgNP/NSP in waterborne PU is proven to be viable for fabricating infection- and cytotoxicity-free medical devices.

Compatibility balanced antibacterial modification based on vapor-deposited parylene coatings for biomaterials

An advanced antibacterial modification technique is conducted by immobilizing antibacterial agents to reduce bacterial attachment and show balanced biocompatibility.