Fabrication of Quasi-2D Shape-Tailored Microparticles using Wettability Contrast-Based Platforms

Patterned Surface Energy for Modulating Solid-Liquid Interfacial Properties

Surface energy, as an intrinsic property of solids, plays a crucial role in modulating the characteristics of solid surfaces, especially of the solid-liquid interface. Due to inevitable processes such as surface adsorption or contamination, the surface energy of practical solids is usually nonuniform. However, if this nonuniformity is rationally designed and effectively utilized, it is capable of endowing great potential for liquid manipulation. With the rapid development of microfabrication and surface modification techniques, a variety of artificial patterned surface energy surfaces (PSESs) have been fabricated, which extend the diversity, tunability, and precision of liquid-based applications. In this review, we discuss the regulation of solid-liquid interface properties with PSESs from a relatively macroscopic perspective, particularly focusing on how to control matter and energy through rational design. First, we provide a brief introduction about the definition and significance of PSESs. Then, matter selective adhesion by PSESs is summarized, including liquid dynamics regulation, crystallization inducement, and biosample self-distribution. In the following, we discuss how PSESs regulate physical fields, including the thermal field, electric field, and acoustic field, with an explanation centered on discontinuous solid-liquid contact on PSESs. Finally, associated challenges of surface energy regulation for liquid-based scenarios are included.

Advanced SERS Platform for Uniform and Reliable Molecular Detection

Signal uniformity is crucial for reliable and quantifiable surface-enhanced Raman scattering (SERS) measurements. However, challenges arise due to the continuous impact of localized hottest spots and the coffee ring effect on signal uniformity. In response to this, we developed a platform featuring a hierarchical structure with Ag nanopores and microbowls (HANM) and incorporated superhydrophobic/superhydrophilic (SHB/SHL) treatments. This design enhances the hottest spot area, ensuring a strong and consistent electromagnetic field while mitigating the coffee ring effect, which leads to an even analyte distribution. This was demonstrated by analyzing rhodamine 6G (R6G, 4 μL, 10-9 M to 10-12 M) molecules at different concentrations. The 2D mapping of the SERS signal intensities from the entire dried droplet exhibited excellent uniformity. The relative standard deviation of the intensities from 200 randomly selected points was calculated to be just 3.81%, laying the foundation for the quantitative detection capability. Additionally, through bisphenol A (BPA) detection in water samples collected from five different locations, the HANM-SHB/SHL structure consistently detected BPA with a uniform signal intensity across all water samples. In conclusion, we proposed a dual-function SERS platform featuring an improved hottest spot region and the ability to avoid the coffee ring effect, offering precise and reliable molecular analysis.

Self-Assembly of Platelet Lysates Proteins into Microparticles by Unnatural Disulfide Bonds for Bottom-Up Tissue Engineering

There is a demand to design microparticles holding surface topography while presenting inherent bioactive cues for applications in the biomedical and biotechnological fields. Using the pool of proteins present in human-derived platelet lysates (PLs), the production of protein-based microparticles via a simple and cost-effective method is reported, exploring the prone redox behavior of cysteine (Cy-SH) amino acid residues. The forced formation of new intermolecular disulfide bonds results in the precipitation of the proteins as spherical, pompom-like microparticles with adjustable sizes (15-50 µm in diameter) and surface topography consisting of grooves and ridges. These PL microparticles exhibit extraordinary cytocompatibility, allowing cell-guided microaggregates to form, while also working as injectable systems for cell support. Early studies also suggest that the surface topography provided by these PL microparticles can support osteogenic behavior. Consequently, these PL microparticles may find use to create live tissues via bottom-up procedures or injectable tissue-defect fillers, particularly for bone regeneration, with the prospect of working under xeno-free conditions.

Steering Stem Cell Fate within 3D Living Composite Tissues Using Stimuli-Responsive Cell-Adhesive Micromaterials

Engineered living microtissues such as cellular spheroids and organoids have enormous potential for the study and regeneration of tissues and organs. Microtissues are typically engineered via self-assembly of adherent cells into cellular spheroids, which are characterized by little to no cell-material interactions. Consequently, 3D microtissue models currently lack structural biomechanical and biochemical control over their internal microenvironment resulting in suboptimal functional performance such as limited stem cell differentiation potential. Here, this work report on stimuli-responsive cell-adhesive micromaterials (SCMs) that can self-assemble with cells into 3D living composite microtissues through integrin binding, even under serum-free conditions. It is demonstrated that SCMs homogeneously distribute within engineered microtissues and act as biomechanically and biochemically tunable designer materials that can alter the composite tissue microenvironment on demand. Specifically, cell behavior is controlled based on the size, stiffness, number ratio, and biofunctionalization of SCMs in a temporal manner via orthogonal secondary crosslinking strategies. Photo-based mechanical tuning of SCMs reveals early onset stiffness-controlled lineage commitment of differentiating stem cell spheroids. In contrast to conventional encapsulation of stem cell spheroids within bulk hydrogel, incorporating cell-sized SCMs within stem cell spheroids uniquely provides biomechanical cues throughout the composite microtissues' volume, which is demonstrated to be essential for osteogenic differentiation.

Ink-Drop Dynamics on Chemically Modified Surfaces

Inkjet printing provides an efficient routine for distributing functional materials into locations with well-designed arrangements. As one of the most critical factors in determining the printing quality, the impacting and depositing behaviors of ink drops largely depend on the wettability of the target surface. In addition to printing on solids with intrinsic wettability, various ink-drop impact dynamics and deposition morphologies have been reported through modifying the surface wettability including both homogeneous and heterogeneous, which opens up possibilities for applications such as advanced optic/electric device fabrication and highly sensitive detection. In this Perspective, we summarize recent progress in the modification methods of solid surface wettability and their capability in modulating the ink-drop impacting and depositing dynamics. The challenges facing ink-drop regulation by chemical modification methodologies are also envisaged at the end of the Perspective.

Hipster microcarriers: exploring geometrical and topographical cues of non-spherical microcarriers in biomedical applications

Structure and organisation are key aspects of the native tissue environment, which ultimately condition cell fate via a myriad of processes, including the activation of mechanotransduction pathways. By modulating the formation of integrin-mediated adhesions and consequently impacting cell contractility, engineered geometrical and topographical cues may be introduced to activate downstream signalling and ultimately control cell morphology, proliferation, and differentiation. Microcarriers appear as attractive vehicles for cell-based tissue engineering strategies aiming to modulate this 3D environment, but also as vehicles for cell-free applications, given the ease in tuning their chemical and physical properties. In this review, geometry and topography are highlighted as two preponderant features in actively regulating interactions between cells and the extracellular matrix. While most studies focus on the 2D environment, we focus on how the incorporation of these strategies in 3D systems could be beneficial. The techniques applied to design 3D microcarriers with unique geometries and surface topographical cues are covered, as well as specific tissue engineering approaches employing these microcarriers. In fact, successfully achieving a functional histoarchitecture may depend on a combination of fine-tuned geometrically shaped microcarriers presenting intricately tailored topographical cues. Lastly, we pinpoint microcarrier geometry as a key player in cell-free biomaterial-based strategies, and its impact on drug release kinetics, the production of steerable microcarriers to target tumour cells, and as protein or antibody biosensors.

Core-Shell Microcapsules: Biofabrication and Potential Applications in Tissue Engineering and Regenerative Medicine

The construction of biomaterial scaffolds that accurately recreate the architecture of living tissues in vitro is a major challenge in the field of tissue engineering and regenerative medicine. Core-shell microcapsules...

Microparticles orchestrating cell fate in bottom-up approaches

The modulation of cells in tissue formation is still one of the hardest tasks to achieve in Tissue Engineering. To control the cell response when undergoing their normal functions such as adhesion, differentiation, assembly, or maturation is vital the development of more successful solutions. Herein, we discuss how microparticles are being overlooked in their potential for controlling the cellular response. Until now, their role was quite often restricted to a reservoir of chemical compounds or as carriers for cell expansion. Nevertheless, microparticles design with the introduction of biophysical and biochemical cues can effectively modulate cell response.