Passive microfluidic devices for cell separation

Shape-based separation of micro- and nanoparticles has emerged as a powerful yet underdeveloped strategy in microfluidics, offering distinct advantages over conventional size-based methods, particularly for biomedical and functional material applications. Unlike size-based separation, shape-based approaches enable discrimination between particles of identical volume but differing morphology, an essential capability for isolating pathological cells, engineered particles, or anisotropic biological entities whose function is inherently linked to shape. This review provides a comprehensive and critical overview of recent progress in both passive and active microfluidic platforms tailored for shape-selective separation. Passive systems such as deterministic lateral displacement, pinched flow fractionation, inertial, and viscoelastic microfluidics exploit hydrodynamic and flow-structure interactions, while active methods including dielectrophoresis, magnetophoresis, optophoresis, and acoustophoresis utilize external fields to modulate particle trajectories based on geometric anisotropy. For example, recent advancements demonstrate high purities often exceeding 95%, with throughput rates ranging from several microliters to milliliters per minute depending on the device configuration, achieving shape-based cell and particle sorting efficiencies above 90% under optimal conditions. For each technique, we highlight the underlying mechanisms enabling shape sensitivity, key technological advancements, and emerging trends in experimental and computational approaches. We also discuss the challenges in capturing complex particle behaviors such as rotation, alignment, and deformability and emphasize the need for integrated modeling, real-time control, and system-level optimization. Finally, we outline future directions and opportunities for advancing shape-based microfluidic separation toward scalable, high-precision applications in diagnostics, therapeutics, and materials science.

Maintenance and modulation of stem cells stemness based on biomaterial designing via chemical and physical signals

Recent research in the vaccine and immunotherapy fields has revealed that biomaterials have the ability to activate immune pathways, even in the absence of other immune‐stimulating signals. Intriguingly, new studies reveal these responses are influenced by the physicochemical properties of the material. Nearly all of this work has been done in the vaccine and immunotherapy fields, but there is tremendous opportunity to apply this same knowledge to tissue engineering and regenerative medicine. This review discusses recent findings that reveal how material properties—size, shape, chemical functionality—impact immune response, and links these changes to emerging opportunities in tissue engineering and regenerative medicine. We begin by discussing what has been learned from studies conducted in the contexts of vaccines and immunotherapies. Next, research is highlighted that elucidates the properties of materials that polarize innate immune cells, including macrophages and dendritic cells, toward either inflammatory or wound healing phenotypes. We also discuss recent studies demonstrating that scaffolds used in tissue engineering applications can influence cells of the adaptive immune system—B and T cell lymphocytes—to promote regenerative tissue microenvironments. Through greater study of the intrinsic immunogenic features of implantable materials and scaffolds, new translational opportunities will arise to better control tissue engineering and regenerative medicine applications.

Lattice Boltzmann simulations of pinched flow fractionation

Deterministic lateral displacement (DLD) is a microfluidic technique for size fractionation of particles/cells in continuous flow with a great potential for biological and clinical applications. Growing interest of DLD devices in enabling high-throughput operation for practical applications, such as circulating tumor cell (CTC) separation, necessitates employing higher flow rates, leading to operation at moderate to high Reynolds number (Re) regimes. Recently, it has been shown that symmetric airfoil shaped pillars with neutral angle-of-attack (AoA) can be used for high-throughput design of DLD devices due to their mitigation of vortex effects and preservation of flow symmetry under high Re conditions. While high-Re operation with symmetric airfoil shaped pillars has been established, the effect of AoAs on the DLD performance has not been investigated. In this paper, we have characterized the airfoil DLD device with various AoAs. The transport behavior of microparticles has been observed and analyzed with various AoAs in realistic high-Re. Furthermore, we have modeled the flow fields and anisotropy in a representative airfoil pillar array, for both positive and negative AoA configurations. Unlike the conventional DLD device, lateral displacement has been suppressed with +5° and + 15° AoA configurations regardless of particle sizes. On the other hand, stronger lateral displacement has been seen with -5° and - 15° AoAs. This can be attributed to growing flow anisotropy as Re climbs, and significant expansion or compression of streamlines between airfoils with AoAs. The findings in this study can be utilized for the design and optimization of airfoil DLD microfluidic devices with various AoAs.

The advent of microfluidics in the 1990s promised a revolution in multiple industries from healthcare to chemical processing. Deterministic lateral displacement (DLD) is a continuous-flow microfluidic particle separation method discovered in 2004 that has been applied successfully and widely to the separation of blood cells, yeast, spores, bacteria, viruses, DNA, droplets, and more. Deterministic lateral displacement is conceptually simple and can deliver consistent performance over a wide range of flow rates and particle concentrations. Despite wide use and in-depth study, DLD has not yet been fully elucidated or optimized, with different approaches to the same problem yielding varying results. We endeavor here to provide up-to-date expert opinion on the state-of-art and current fundamental, practical, and commercial challenges with DLD as well as describe experimental and modeling opportunities. Because these challenges and opportunities arise from constraints on hydrodynamics, fabrication, and operation at the micro- and nanoscale, we expect this Perspective to serve as a guide for the broader micro- and nanofluidic community to identify and to address open questions in the field.

In recent decades, regenerative medicine has merited substantial attention from scientific and research communities. One of the essential requirements for this new strategy in medicine is the production of biocompatible and biodegradable scaffolds with desirable geometric structures and mechanical properties. Despite such promise, it appears that regenerative medicine is the last field to embrace green, or environmentally-friendly, processes, as many traditional tissue engineering materials employ toxic solvents and polymers that are clearly not environmentally friendly. Scaffolds fabricated from plant proteins (for example, zein, soy protein, and wheat gluten), possess proper mechanical properties, remarkable biocompatibility and aqueous stability which make them appropriate green biomaterials for regenerative medicine applications. The use of plant-derived proteins in regenerative medicine has been especially inspired by green medicine, which is the use of environmentally friendly materials in medicine. In the current review paper, the literature is reviewed and summarized for the applicability of plant proteins as biopolymer materials for several green regenerative medicine and tissue engineering applications.

Nanofiber-embedded 3D hydrogel constructs have garnered significant attention due to their versatile applications in drug delivery, cell therapy, tissue engineering, and regenerative medicine. These constructs are especially prized for their capacity to mimic the composition of the extracellular matrix (ECM) found in living tissues and organs. The unique chemical and mechanical properties of hydrogel microcapsules have made them particularly notable among various biomaterial constructs for their effectiveness in cell encapsulation, which aims to improve cell growth and proliferation. In this study, we developed alginate hydrogel microcapsules embedded with chitin nanofibrils, using divalent calcium ions and trivalent iron ions as crosslinking agents. An electrostatic encapsulation technique was utilized to create microcapsules with diameters ranging from 200-500 μm, and their physicochemical properties, rheological properties, size, and mechanical stability were evaluated. The rheological analysis demonstrated that the Fe3+ crosslinked hydrogel (AF0) and Fe3+/Ca2+ cross-linked hydrogel (AFC) have higher storage modulus than the Ca2+ crosslinked hydrogel (AC0). Additionally, FTIR analyses of AF0 and AFC demonstrated a broader -O-H stretching peak compared to that of AC0, suggesting that more hydroxyl groups of alginate chains are involved in crosslinking with ferric ions exhibiting extended mechanical stability compared to those crosslinked with calcium ions under in vitro physiological conditions. We also investigated the cellular responses to the composite hydrogels crosslinked with these divalent and trivalent metal ions through in vitro studies involving the seeding and encapsulation of NIH/3T3 fibroblast cells. Remarkably, both types of crosslinked microcapsules maintained excellent cell viability for up to 5 days. Our in vitro scratch assay demonstrated that media extracted from AF0 microcapsules facilitated faster wound closure compared to that extracted from AC0, suggesting that hydrogels crosslinked with Fe3+ ions promote enhanced cellular proliferation. These results suggest that calcium and ferric ion crosslinked alginate-chitin composite microcapsules provide a promising platform for developing 3D hydrogel constructs suitable for various biomedical applications, including wound healing models, tissue engineering, and drug toxicity testing.

Circulating tumor cells (CTCs) are cancer cells shed from primary tumor and circulating in the peripheral blood. CTCs initiate secondary tumor colonies and result in more than 90% of cancer death. Isolation and enumeration of CTCs have exhibited promising clinical applications in cancer early diagnosis, prognosis and personalized therapy. However, owing to the extremely low rarity (as low as one CTC in one billion blood cells), CTCs isolation remains a great technical challenge. Current CTCs isolation approaches are based either on their biological properties, including immunoassay, magnetic-activated cell sorting, fluorescence-activated cell sorting, or physical properties, including filtering, inertial microfluidics, deterministic lateral displacement and etc. In general, biology-based techniques are characterized as high purity but low throughput; while physical property based techniques have advantages of low cost and high throughput. In this work, we reported the fabrication of a multilayer crossflow device and demonstrated the capability of isolating CTCs from whole blood based on lateral-flow filtration. The device was consisted of a filter membrane sandwiched between two microfluidic channel layers and fabricated with standard PDMS soft lithography and multilayer bonding technique. A 77.3% filtration efficiency with 4.5um polystyrene beads and a 97% cancer cells recovery rate have been achieved for a single-pass filtration. To further enhance the enrichment ratio(concentration of CTCs prior to filtration over that post-filtration) of CTCs over blood cells, a recirculating filtration system was built by combing the crossflow device with pressure pump and electromagnetic valves. In this system, 1 ml blood sample was treated for 10 times within 40 minutes, with an enrichment ratio of more than 104.

There is a great demand of suitable biomaterials for tissue engineering applications in regenerative medicine. Decellularized extracellular matrix scaffolds derived from different organs and tissues have been successfully applied for human use as therapeutic agents in many tissue defects. The aim of the present study was to establish histological and ultrastructural characterisation as minimal criteria for assessing the suitability of decellularised bioscaffolds in tissue engineering applications. The study was performed on bovine omentum processed by a natural bovine bile based decellularisation protocol. Histological analysis and scanning electron microscopy examinations were performed and compared with an established decellularised bovine pericardial scaffold. Gross examination revealed that the decellularisation process did not alter the shape of the omentum. Histological examination confirmed the preservation of the collagenous fibres without any observable cell nuclei following decellularisation. Further, scanning electron microscopy examination demonstrated the arrangement and ultrastructure of collagen fibrils in the bioscaffolds. Our results suggest that histological and ultrastructural characterisation provide preliminary data on determining the biocompatibility of scaffolds before planning in vivo studies in tissue engineering applications.

Deterministic lateral displacement (DLD) devices have great potential for the separation and sorting of various suspended particles based on their size, shape, deformability, and other intrinsic properties. Currently, the basic idea for the separation mechanism is that the structure and geometry of DLDs uniquely determine the flow field, which in turn defines a critical particle size and the particle lateral displacement within a device. We employ numerical simulations using coarse-grained mesoscopic methods and two-dimensional models to elucidate the dynamics of both rigid spherical particles and deformable red blood cells (RBCs) in different DLD geometries. Several shapes of pillars, including circular, diamond, square, and triangular structures, and a few particle sizes are considered. The simulation results show that a critical particle size can be well defined for rigid spherical particles and depends on the details of the DLD structure and the corresponding flow field within the device. However, non-isotropic and deformable particles such as RBCs exhibit much more complex dynamics within a DLD device, which cannot properly be described by a single parameter such as the critical size. The dynamics and deformation of soft particles within a DLD device become also important, indicating that not only size sorting, but additional sorting targets (e.g., shape, deformability, internal viscosity) are possible.

Latest advancements and trends in biomedical polymers for disease prevention, diagnosis, treatment, and clinical application.

Manufacturing of hydrogel biomaterials with controlled mechanical properties for tissue engineering applications.

Hydrogels are water-swollen polymeric matrices with properties that are remarkably similar in function to the extracellular matrix. For example, the polymer matrix provides structural support and adhesion sites for cells in much of the same way as the fibers of the extracellular matrix. In addition, depending on the polymer used, bioactive sites on the polymer may provide signals to initiate certain cell behavior. However, despite their potential as biomaterials for tissue engineering and regenerative medicine applications, fabricating hydrogels that truly mimic the physicochemical properties of the extracellular matrix to physiologically-relevant values is a challenge. Recent efforts in the field have sought to improve the physicochemical properties of hydrogels using advanced materials science and engineering methods. In this review, we highlight some of the most promising methods, including crosslinking strategies and manufacturing approaches such as 3D bioprinting and granular hydrogels. We also provide a brief perspective on the future outlook of this field and how these methods may lead to the clinical translation of hydrogel biomaterials for tissue engineering and regenerative medicine applications.

We prepared 3D poly (ε-caprolactone) (PCL) nanofibre scaffolds and tested their use for seeding, proliferation, differentiation and migration of mesenchymal stem cell (MSCs). 3D nanofibres were prepared using a special collector for common electrospinning; simultaneously, a 2D PCL nanofibre layer was prepared using a classic plain collector. Both scaffolds were seeded with MSCs and biologically tested. MSC adhesion, migration, proliferation and osteogenic differentiation were investigated. The 3D PCL scaffold was characterized by having better biomechanical properties, namely greater elasticity and resistance against stress and strain, thus this scaffold will be able to find broad applications in tissue engineering. Clearly, while nanofibre layers of the 2D scaffold prevented MSCs from migrating through the conformation, cells infiltrated freely through the 3D scaffold. MSC adhesion to the 3D nanofibre PCL layer was also statistically more common than to the 2D scaffold (P < 0.05), and proliferation and viability of MSCs 2 or 3 weeks post-seeding, were also greater on the 3D scaffold. In addition, the 3D PCL scaffold was also characterized by displaying enhanced MSC osteogenic differentiation. We draw the conclusion that all positive effects observed using the 3D PCL nanofibre scaffold are related to the larger fibre surface area available to the cells. Thus, the proposed 3D structure of the nanofibre layer will find a wide array of applications in tissue engineering and regenerative medicine.