Chemical Vapor Deposition Copolymerization Research Articles

Synthesis of Pigmented Parylene Coatings and Control of the Chromatism Based on Chemical Vapor Deposition Copolymerization

AbstractColoring and identification procedures for medical devices are important to reduce the risks of defective medical devices or incorrect operations and implantations. The study herein reports a novel platform of color pigment‐modified Parylene coatings to fulfill the needs of medical coatings, providing a surface modification route to alter the important property of color for an underlying material and/or device from its original color. Modification with a naphthalimide derivative is employed for the Parylene precursor. The synthesis of the final color Parylene coating is performed based on a vapor‐phase deposition polymerization process, and the coating is conformally coated on a variety of materials regardless of the shape or dimension. Furthermore, control of the color to create a series of color‐changing Parylene coatings is enabled by vapor deposition copolymerization with a second Parylene derivative source, and predictable color tuning from a primary to a secondary and/or tertiary color is achievable in the experiments and shows accordance with color theory. The reported coating platform represents a colored coating tool and is biocompatible for biotechnological applications.

Enhanced Growth Activities of Stem Cell Spheroids Based on a Durable and Chemically Defined Surface Modification Coating

Surface modification layers are needed for the precise definition of surface chemistries and are equally important for durable and stable adhesive properties to ensure long-term stability and effective performance for biotechnological applications. This study demonstrates a robust modification layer that is synthesized based on chemical vapor deposition copolymerization, and the resultant coating layer is composed of the side-by-side presentation of N-hydroxysuccinimide ester and maleimide functionalities with a controlled ratio to define the immobilization accessibility of chitosan and growth factor protein (FGF-2) molecules on the substrate surface for enhancing cellular activities of stem cells. Characterizations of the copolymer modification layer showed excellent durability, including adhesive strength and thermal stability, and the layer is free of concerns for delamination and/or unacceptable deformation/debris formation that can cause potential toxicity to the surrounding biological environment. Modifications using the copolymer layer on the cell culture surface have demonstrated synergistic activity by chitosan to support the formation of spheroids and by FGF-2 to enhance the proliferation of human adipose-derived stem cells (ADSCs) within the spheroids while increasing the spheroid size and cell numbers. Healthy and flourishing growth activities were discovered for ADSCs on the modified culture surfaces, and the results are useful for potential and related stem cell research and the interfaces of biomaterials.

Bioinstructive Coatings for Hematopoietic Stem Cell Expansion Based on Chemical Vapor Deposition Copolymerization.

We report the chemical vapor deposition (CVD) of dual-functional polymer films for the specific and orthogonal immobilization of two biomolecules (notch ligand delta-like 1 (DLL1) and an RGD-peptide) that govern the fate of hematopoietic stem and progenitor cells. The composition of the CVD polymer and thus the biomolecule ratio can be tailored to investigate and optimize the influence of the relative surface concentrations of biomolecules on stem cell behavior. Prior to cell experiments, all surfaces were characterized by infrared reflection adsorption spectroscopy, time-of-flight secondary ion mass spectrometry, and X-ray photoelectron spectroscopy to confirm the presence of both biomolecules. In a proof-of-principle stem cell culture study, we show that all polymer surfaces are cytocompatible and that the proliferation of the hematopoietic stem and progenitor cells is predominantly influenced by the surface concentration of immobilized DLL1.

Backbone-Degradable Polymers Prepared by Chemical Vapor Deposition.

Polymers prepared by chemical vapor deposition (CVD) polymerization have found broad acceptance in research and industrial applications. However, their intrinsic lack of degradability has limited wider applicability in many areas, such as biomedical devices or regenerative medicine. Herein, we demonstrate, for the first time, a backbone-degradable polymer directly synthesized via CVD. The CVD co-polymerization of [2.2]para-cyclophanes with cyclic ketene acetals, specifically 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), results in well-defined, hydrolytically degradable polymers, as confirmed by FTIR spectroscopy and ellipsometry. The degradation kinetics are dependent on the ratio of ketene acetals to [2.2]para-cyclophanes as well as the hydrophobicity of the films. These coatings address an unmet need in the biomedical polymer field, as they provide access to a wide range of reactive polymer coatings that combine interfacial multifunctionality with degradability.

Vapor‐Based Multicomponent Coatings for Antifouling and Biofunctional Synergic Modifications

A general concept is introduced featuring an ideal multifunctional surface that can avoid fouling problems while allowing the installed groups to perform with the high efficacy and accuracy necessary for delivering cascading and spontaneous biological activities. The idea is realized by using a direct synthesis of a multicomponent coating containing the two functionalities of 4‐methyl‐propiolate and 4‐N‐maleimidomethyl that is achieved via chemical vapor deposition copolymerization on various substrates. The novel coating can simultaneously perform specific bio‐orthogonal reactions, including the azide‐alkyne click reaction and a thiol‐maleimide coupling reaction. In the study, azide‐terminated polyethylene glycols are first immobilized on the methyl propiolate groups to impart an antifouling property, while bioactivity is enabled by tethering biotinylated thiols or Cys‐Arg‐Glu‐Asp‐Val (CREDV) peptides on the maleimide groups. The induced antifouling properties and bioactivities are confirmed by quartz crystal microbalance and cell culture studies. Finally, precisely manipulated endothelial cells, namely, human umbilical vein endothelial cells and bovine arterial endothelial cells, are observed on a complex stent substrate and on confined areas of the poly(methyl methacrylate) substrates.

Chemical vapor deposition copolymerization of 4-carboxyl-[2,2] paracyclophane and 4-amino-[2,2] paracyclophane

Chemical vapor deposition copolymerization (CVDCP) of 4-carboxyl-[2,2] paracyclophane (4-carboxyl-PCP) and 4-amino-[2,2] paracyclophane (4-amino-PCP) is carried out. It is shown in FTIR and 13C NMR spectra of the copolymer that an amide or imide bond is formed during the pyrolysis and the transportation of the pyrolysis products. Partial crosslinking, caused by the amidation or imidation of –COOH and –NH 2 among different chains in the copolymer, is possible during the transportation and deposition process. Compared with poly(carboxyl- p-xylylene-co- p-xylylene) (PPX-Carb), the thermal stability of the copolymer is improved. The crystallinity of the copolymer is reduced which is confirmed by transmittance and XRD results of the copolymer.

Multipotent Polymer Coatings Based on Chemical Vapor Deposition Copolymerization

The controlled and stable immobilization of one or multiple types of (bio)molecules to a surface has been identified as one of the critical challenges in several emerging research fields, such as the regulation of cell shape, the development of advanced biological assays and scaffolds for regenerative medicine, or the fabrication of increasingly complex micrototal analytical systems (lTAS). This is partly motivated by the need for defined surface architectures to simultaneously present multiple biological entities in controlled ratios. While a range of methods have been developed for the immobilization of a single type of biomolecule to artificial substrates, fewer concepts are available for the precise immobilization of multiple biomolecules in a controllable fashion. Recently, we established a suite of surface modification techniques based on chemical vapor deposition (CVD) polymerization of substituted [2.2]paracyclophanes. This novel coating technology resulted in a diverse class of functionalized poly p-xylylenes containing a wide variety of functional groups such as amines, esters, aldehydes, and alcohols. The resulting polymers provide a flexible solution to surface-engineering challenges, as they decouple surface design from bulk properties. In essence, CVD technology is a one-step coating procedure that generates functionalized surfaces without the need for further post-treatments once the films are deposited. In a significant extension of our previous work, we now report on the use of CVD copolymerization to fabricate multipotent and modular coatings. The term “multipotent coating” in this context, refers to a reactive coating that is compatible with the simultaneous presentation of multiple biomolecules in controllable ratios. Prior to CVD copolymerization, 4-trifluoroacetyl [2.2]paracyclophane (1) and 4-aminomethyl-[2.2]paracyclophane (2) were synthesized from commercially available [2.2]paracyclophane following established synthetic routes. CVD copolymerization of 1 and 2 was then conducted and resulted in a vacuum-deposited film of copolymer 3 on the substrate (Scheme 1). For CVD copolymerization, mixtures of carefully purified dimers 1 and 2 were initially sublimated under a reduced pressure of 56 Pa at 90–100 °C. The sublimation temperatures of 1 and 2 were sufficiently similar, and so to ensure that the compounds were exposed to comparable sublimation conditions they were placed near each other within the CVD system. Sublimated 1 and 2 were then transferred to the pyrolysis zone, which was heated to 670 °C to ensure cleavage of the aliphatic C–C bonds, resulting in the corresponding quinodimethanes (monomers). In the last step, monomers were adsorbed on the substrate at approximately 10 °C and spontaneously polymerized. CVD copolymerization of 1 and 2 resulted in transparent and topologically uniform polymer films (Figure S2, Supporting Information) with thicknesses between 50 and 200 nm. The film thickness is mainly determined by the total amount of [2.2]paracyclophanes used for polymerization. For instance, the thickness of a film produced by the deposition of 20 mg of equimolar amounts of 1 and 2 was determined by means of imaging ellipsometry to be 115 ± 15 nm. Moreover, the multifunctional coatings showed excellent chemical stability in a dry-air environment. No significant change in composition or chemical behavior was found for samples stored in a dry-air atmosphere for several weeks compared to freshly prepared samples. All copolymers as well as the two homopolymers 4 and 5 remained intact after rinsing with standard solvents such as water, chloroform, acetone, and ethanol. The elemental composition of the copolymer poly[4-aminomethyl-p-xylylene-co-4-trifluoroacetyl-p-xylylene-co-p-xylylene] (3) was studied by X-ray photoelectron spectroscopy (XPS). XPS is capable of detecting atomic composition within a depth of about 10 nm. Copolymer 3 was compared to the individual polymers, poly[4-trifluoroacetyl-p-xylylene-co-pxylylene] (4) and poly[4-aminomethyl-p-xylylene-co-p-xylylene] (5, see Table 1). Characteristic chemical elements detected for the individual polymers 4 and 5, such as oxygen (polymer 4), fluorine (polymer 4), and nitrogen (polymer 5), were simultaneously detected in the copolymer, indicating the presence of both functional groups on the surface. Because nitrogen is only present in the aminomethyl group of polymer 5, while fluorine is present in only the ketone function of polymer 4, the ratio of the elemental composition of nitrogen and fluorine is a good indicator of the chemical quality of the copolymer films. Using XPS, we found a N/F ratio of 0.332, which is in good acC O M M U N IC A IO N S