Design of oriented mesoporous silica films for guiding protein adsorption states

Self-Assembly of Cyclic-Bending Collagen Fibrils by Polyimide Films

The cyclic-bending morphologies of the fibrils formed by the self-assembly of type I collagen (Col) are closely related to the mechanisms of various diseases. Therefore, studies that allow the self-assembly of Col molecules to form cyclic-bending fibrils in vitro are vitally important. In this study, we successfully achieved the cyclic-bending shapes (specifically, a regular hexagonal shape) of Col molecules by controlling the steric structures of polyimide (PI) molecular chains through the film formation process. Specifically, when a single layer of PI film was baked, the PI molecular chains within the film bent in the direction parallel to the substrate surface plane. Repeating the layering and baking processes resulted in 3D structures of the PI molecular chains, which were oriented in the direction perpendicular to the substrate surface plane. This three-dimensional bending would result from the PI molecular chain interactions between the upper and lower layers. When the Col molecules were reacted on these film surfaces, they recognized the structures of the PI molecular chains and self-assembled to form cyclic-bending Col fibrils. Especially, in PI films subjected to three cycles of layering and baking, hemicircular-shaped Col fibrils were observed to be regularly arrayed. Additionally, these regularly cyclic-bending fibrils were aligned in the uniaxial direction through a uniaxial rubbing treatment of the PI films. This successful research is significant both as a method for controlling the morphologies of Col fibrils and as a study that explores the biomedical implications of Col fibril cyclic-bending in the living body.

Investigation into self-assembled collagen arrays guided by the surface properties of polyimide films

The mechanism of highly-oriented collagen (Col) fibril arrays on rubbed polyimide (PI) films was investigated in order to understand the interfacial Col-PI interactions. It was found that the orientation of the surface functional groups of the rubbed PI films was most effectively controlled and optimized by the rubbing conditions. In particular, nano-grooves with a width of 100-600 nm and a depth of 2-10 nm were formed on the rubbed PI films at a rubbing strength of 2.4 m, leading to the formation of the highest density of the Col fibril array. Moreover, highly-oriented Col fibrils were formed inside the nano-grooves by the formation of hydrogen bonds between the CO of the imide groups (@ rubbed PI films) and the N-H of the amino groups (@ β-Sheets of Col molecules), resulting in the orientation of the Col molecules and subsequent assembly to the fibrils. Thus, the orientation and density of the fibril arrays on the rubbed PI films were successfully controlled by the interfacial interactions between the β-Sheet component of Col and the nano-groove surfaces of the rubbed PI films. Therefore, the novel technology of this study will provide an effective method to fabricate the one-directional fibrous nanostructures and to understand how to control the orientation of biomolecules in vitro.

Rubbing-Assisted Approach for Fabricating Oriented Nanobiomaterials

The highly-oriented structures in biological tissues play an important role in determining the functions of the tissues. In order to artificially fabricate oriented nanostructures similar to biological tissues, it is necessary to understand the oriented mechanism and invent the techniques for controlling the oriented structure of nanobiomaterials. In this review, the oriented structures in biological tissues were reviewed and the techniques for producing highly-oriented nanobiomaterials by imitating the oriented organic/inorganic nanocomposite mechanism of the biological tissues were summarized. In particular, we introduce a fabrication technology for the highly-oriented structure of nanobiomaterials on the surface of a rubbed polyimide film that has physicochemical anisotropy in order to further form the highly-oriented organic/inorganic nanocomposite structures based on interface interaction. This is an effective technology to fabricate one-directional nanobiomaterials by a biomimetic process, indicating the potential for wide application in the biomedical field.

Nanostructural control of transparent hydroxyapatite nanoparticle films using a citric acid coordination technique

Hydroxyapatite (HA), as the main mineral component in hard tissues, has good biocompatibility. In particular, HA films are widely used as bioactive coatings for artificial bones and dental implants in biomedical fields. However, it is currently difficult to prepare a nanostructure-controlled HA film by a wet process for further applications. Herein, we report the synthesis of HA nanoparticles coordinated by citric acid (Cit/HA) based on the interactions between carboxylate and calcium ions to control the sizes and shapes of the hybrid nanoparticles, to improve their dispersibility in water and to eventually form uniform transparent films with nanospaces, and investigated the film formation mechanism. As compared with the well-known rod-like HA nanoparticles (size: 48 × 15 nm²), we successfully synthesized spherical and negatively charged Cit/HA nanoparticles (size: 25 × 23 nm²) to achieve highly transparent Cit/HA films using the spin-coating technique. The Cit/HA films had uniform and crack-free appearance. About the nanostructures, we found that the Cit/HA film surfaces had meso-scaled nanospaces with a diameter of 4.2 nm based on the regular arrangement of spherical nanoparticles, instead of the HA film with a nanospace diameter of 24.5 nm formed by non-uniform accumulation. Therefore, we successfully achieved the control of the nanospace sizes of the films with the nanoparticle arrangement and realized transparent nanoparticle film formation in a very simple way, which will provide more convenient bioceramic films for biomedical applications.