Switching the Biointerface of Displaceable Poly‑<i>p</i>‑xylylene Coatings

A new class of functionalized poly-<i>p</i>-xylyene coating has been synthesized to provide switchable and displaceable surface properties for biomaterials. The switchability is achieved through a mechanism for detaching/attaching biomolecules and/or a mechanism through which the programmed restoration of functions or their replacement by other functions can be carried out. This advanced version of poly-<i>p</i>-xylylene comprises an integrated disulfide moiety within the functional side group, and the switching phenomenon between the immobilized functional molecules is triggered by the redox thiol–disulfide interchange reaction. These dynamically well-defined molecules on the surfaces respond simultaneously to altered biological properties and controlled biointerfacial functions, for example, switching wettability or reversibly altered cell adhesion activity. Poly-<i>p</i>-xylylenes are a key player in controlling surface properties for many important applications, such as medical implants, biosensors, bioMEMS devices, and microfluidics. The introduction of this new facet of poly-<i>p</i>-xylylenes enables the dynamic mimicry of biological functions relevant to the design of new biomaterials

Fabrication of Functional Polymer Structures through Bottom-Up Selective Vapor Deposition from Bottom-Up Conductive Templates

An electrically induced bottom-up process was introduced for the fabrication of multifunctional nanostructures of polymers. Without requiring complicated photolithography or printing techniques, the fabrication process first produced a conducting template by colloidal lithography to create an interconnected conduction pathway. By supplying an electrical charge to the conducting network, the conducting areas were enabled with a highly energized surface that generally deactivated the adsorbed reactive species and inhibited the vapor deposition of poly-<i>p</i>-xylylene polymers. However, the template allowed the deposition of ordered poly-<i>p</i>-xylylene nanostructures only on the confined and negative areas of the conducting template, in a relatively large centimeter-scale production. The wide selection of functionality and multifunctional capability of poly-<i>p</i>-xylylenes naturally rendered the synergistic and orthogonal chemical reactivity of the resulting nanostructures. With only a few steps, the construction of a nanometer topology with the functionalization of multiple chemical conducts can be achieved, and the selected deposition process represents a state-of-the-art nanostructure fabrication in a simple and versatile approach from the bottom up

Topologically Controlled Cell Differentiation Based on Vapor-Deposited Polymer Coatings

In addition to the widely adopted method of controlling cell attachment for cell patterning, pattern formation via cell proliferation and differentiation is demonstrated using precisely defined interface chemistry and spatial topology. The interface platform is created using a maleimide-functionalized parylene coating (maleimide-PPX) that provides two routes for controlled conjugation accessibility, including the maleimide–thiol coupling reaction and the thiol–ene click reaction, with a high reaction specificity under mild conditions. The coating technology is a prime tool for the immobilization of sensitive molecules, such as growth factor proteins. Conjugation of fibroblast growth factor 2 (FGF-2) and bone morphogenetic protein (BMP-2) was performed on the coating surface by elegantly manipulating the reaction routes, and confining the conjugation reaction to selected areas was accomplished using microcontact printing (μCP) and/or UV irradiation photopatterning. The modified interface provides chemically and topologically defined signals that are recognized by cultured murine preosteoblast cells for proliferation (by FGF-2) and osteogenesis (by BMP-2) activities in specific locations. The reported technique additionally enabled synergistic pattern formation for both osteogenesis and proliferation activities on the same interface, which is difficult to perform using conventional cell attachment patterns. Because of the versatility of the coating, which can be applied to a wide range of materials and on curved and complex devices, the proposed technology is extendable to other prospective biomaterial designs and material interface modifications

Customizable Optical and Biofunctional Properties of a Medical Lens Based on Chemical Vapor Deposition Encapsulation of Liquids

An innovative intraocular lens (IOL) device was fabricated based on a chemical vapor deposition encapsulation process using functionalized poly-<i>p</i>-xylylenes. The advanced IOL device provides noncompromised design parameters for both its optical and biological properties. As an excellent optical device, it provides a high refractive index and a tunable effective focal length that is realized by manipulating the wetting properties of the encapsulated liquids; the device also offers protection from UV radiation. As a key medical device, it exhibits excellent biocompatibility and reduced postoperative calcification through the intrinsic properties of poly-<i>p</i>-xylylenes. In addition, these synergic functions are provided with precise surface chemistry for location to a guided attachment or repellent properties for eye epithelial cells, which is important in preventing device-associated complications

IRRAS characterization of (a) coating 5 modified surface and (b) coating 5/BMP-2 modified surface.

<p>Both of the modifications were on a gold-coated silicon substrate. Three significant peaks, which are characters of asymmetric stretching bands of NHS ester C = O were detected as 1770, 1739, and 1716 cm^-1 in S1(a). Peaks at 1217 cm^-1 and 1072 cm^-1 were attributed to N-O and C-O stretch, respectively. In S1 (b), peak of N-O (1207 cm^-1) and C-O (1067 cm^-1) stretch were reduced and one of the C = O peak (1716 cm^-1 in (a) and 1709 cm^-1 in (b)) strongly reduced after immobilization of BMP-2. The characterization peaks of BMP-2 appeared on the bands around 3247 cm^-1 for N-H and 3490 cm^-1 for O-H.</p

QCM analysis of coating 5 modified surface.

<p>Curve (a) is the result of BMP-2 solution injected and flowing through coating <b>5</b> modified surface, and at the end of the measurement, the amount of BMP-2 adsorption on coating <b>5</b> modified surface is 6.04·10⁻¹² mol cm^-2. Curve (b) is the result of BMP-2 solution injected and flowing through parylene C-modified surface, and at the end of the measurement, the amount of BMP-2 adsorption on parylene C surface is 3.81·10⁻¹² mol cm^-2. Curve (c) is the result of BMP-2 solution injected and flowing through PEG5000 modified surface, and at the end of the measurement, only 1.62·10⁻¹⁴ mol cm^-2 of BMP-2 adsorbed on the surface. Curve (d) is the result of BMP-2 primary antibody solution injected and flowing through coating <b>5</b>/BMP-2 modified surface, and at the end of the measurement, the amount of BMP-2 primary antibody adsorption on coating <b>5</b> modified surface is 2.43·10⁻¹² mol cm^-2. Curve (e) is the result of BMP-2 primary antibody solution injected and flowing through coating <b>5</b> modified surface, and at the end of the measurement, the amount of BMP-2 primary antibody adsorption on coating <b>5</b> modified surface is 2.35·10⁻¹² mol cm^-2.</p

XPS survey spectra of (a) coating 5 modified surface and (b) coating 5/BMP-2 modified surface.

<p>The atomic concentration of C, N and O are 77.3%, 4.55% and 18.22% on the coating <b>5</b> modified surface and 65.0%, 9.5% and 25.5% on the coating <b>5</b>/BMP-2 modified surface. The N composition significantly increased due to immobilization of BMP-2.</p

Sustained Immobilization of Growth Factor Proteins Based on Functionalized Parylenes

Protein molecules immobilized on biomaterial surfaces are performed based on oriented conjugation or replaced mimicking peptides. The sustainable immobilization of growth factor proteins using functionalized parylene coatings is demonstrated in this study. Site-specific and nonspecific immobilization approaches are realized to conjugate bone morphogenetic protein (BMP-2). The binding affinities and conformational changes of BMP-2 are confirmed by QCM and SPR characterizations. Osteoinduction of stem cells is examined by ALP activity on the BMP-2 modified surfaces. Finally, immobilizations and equally sustained biological functions of vascular endothelial growth factor (VEGF) and a mimicking peptide of KLTWQELYQLKYKG (QK) are also examined and confirmed

Relative gene expression of (a) Alpl (gene marker of ALP) and (b) Bglap3 (gene marker of osteocalcin).

<p>The effect of coating <b>5</b>/BMP-2 modified, coating <b>5</b> modified and unmodified surface on relative mRNA expression was assayed on days 0, 4, 7, 11, and 14. The asterisks indicate significant differences (*P<0.05 and **P<0.01) between coating <b>5</b>/BMP-2 modified, coating <b>5</b> modified and unmodified surface at each time point.</p