Electromagnetic metamaterials for biomedical applications: short review and trends

This mini-review examines the most prominent features and usages of metamaterials, such as metamaterial-based and metamaterial-inspired RF components used for biomedical applications. Emphasis is given to applications on sensing and imaging systems, wearable and implantable antennas for telemetry, and metamaterials used as flexible absorbers for protection against extreme electromagnetic (EM) radiation. A short discussion and trends on the metamaterial composition, implementation, and phantom preparation are presented. This review seeks to compile the state-of-the-art biomedical systems that utilize metamaterial concepts for enhancing their performance in some form or another. The goal is to highlight the diverse applications of metamaterials and demonstrate how different metamaterial techniques impact EM biomedical applications from RF to THz frequency range. Insights and open problems are discussed, illuminating the prototyping process

Fabrication of sub-micron pillars on curved surfaces using thermal nanoimprint lithography

Studies have shown that pillars of specific dimensions and spatial arrangement can promote osteogenic differentiation of stem cells and kill bacteria that cause infections. Other studies have shown that surface curvature can also serve as a mechanical cue to modulate cell behavior. Therefore, the fabrication of pillars on curved surfaces would allow researchers to investigate the synergistic effect of pillars and curvature on cell behavior. In this project, a process was developed based on thermal nanoimprint lithography (TNL) and dry etching techniques for the fabrication of pillars into curved substrates made of hard materials. To this aim, a fused silica specimen containing sub-micron pillars was used as the master mold in a molding process to replicate the pillars as pits into a hybrid polydimethylsiloxane (PDMS) mold. The dimensions and morphology of the replicated patterns were assessed using a scanning electron microscope (SEM). Thereafter, TNL was employed to imprint the pits of the hybrid PDMS mold on the surface of the desired planar/ curved substrates. Finally, etching processes were employed to transfer the patterns into the bulk of the substrates. The process was first developed on planar fused silica substrates and then, on curved substrates. The interspace of the resultant pillars on the planar substrates was no more than 3% different than the interspace of the original pillars on the master mold. The diameter was also close to the values of the diameter of the original pillars (the maximum difference was 23%). The height of the pillars differed slightly (mo more than 16%) for the specific process conditions that were used. On the curved substrates, the interspace increased by 5% and 10%, and the diameter by 57% and 11%

Nanoimprinting for high-throughput replication of geometrically precise pillars in fused silica to regulate cell behavior

Developing high-throughput nanopatterning techniques that also allow for precise control over the dimensions of the fabricated features is essential for the study of cell-nanopattern interactions. Here, we developed a process that fulfills both of these criteria. Firstly, we used electron-beam lithography (EBL) to fabricate precisely controlled arrays of submicron pillars with varying values of interspacing on a large area of fused silica. Two types of etching procedures with two different systems were developed to etch the fused silica and create the final desired height. We then studied the interactions of preosteoblasts (MC3T3-E1) with these pillars. Varying interspacing was observed to significantly affect the morphological characteristics of the cell, the organization of actin fibers, and the formation of focal adhesions. The expression of osteopontin (OPN) significantly increased on the patterns, indicating the potential of the pillars for inducing osteogenic differentiation. The EBL pillars were thereafter used as master molds in two subsequent processing steps, namely soft lithography and thermal nanoimprint lithography for high-fidelity replication of the pillars on the substrates of interest. The molding parameters were optimized to maximize the fidelity of the generated patterns and minimize the wear and tear of the master mold. Comparing the replicated feature with those present on the original mold confirmed that the geometry and dimensions of the replicated pillars closely resemble those of the original ones. The method proposed in this study, therefore, enables the precise fabrication of submicron- and nanopatterns on a wide variety of materials that are relevant for systematic cell studies. Statement of significance: Submicron pillars with specific dimensions on the bone implants have been proven to be effective in controlling cell behaviors. Nowadays, numerous methods have been proposed to produce bio-instructive submicron-topographies. However, most of these techniques are suffering from being low-throughput, low-precision, and expensive. Here, we developed a high-throughput nanopatterning technique that allows for control over the dimensions of the features for the study of cell-nanotopography interactions. Assessing the adaptation of preosteoblast cells showed the potential of the pillars for inducing osteogenic differentiation. Afterward, the pillars were used for high-fidelity replication of the bio-instructive features on the substrates of interest. The results show the advantages of nanoimprint lithography as a unique technique for the patterning of large areas of bio-instructive surfaces.Biomaterials & Tissue Biomechanic