Agglomeration of human dermal fibroblasts with ECM mimicking nano-fragments and their effects on proliferation and cell/ECM interactions

E-cadherin biomaterials reprogram collective cell migration and cell cycling by forcing homeostatic conditions

Cells attach to the world through either cell-extracellular matrix adhesion or cell-cell adhesion, and traditional biomaterials imitate the matrix for integrin-based adhesion. However, materials incorporating cadherin proteins that mimic cell-cell adhesion offer an alternative to program cell behavior and integrate into living tissues. We investigated how cadherin substrates affect collective cell migration and cell cycling in epithelia. Our approach involved biomaterials with matrix proteins on one-half and E-cadherin proteins on the other, forming a "Janus" interface across which we grew a single sheet of cells. Tissue regions over the matrix side exhibited normal collective dynamics, but an abrupt behavior shift occurred across the Janus boundary onto the E-cadherin side, where cells attached to the substrate via E-cadherin adhesions, resulting in stalled migration and slowing of the cell cycle. E-cadherin surfaces disrupted long-range mechanical coordination and nearly doubled the length of the G0/G1 phase of the cell cycle, linked to the lack of integrin focal adhesions on the E-cadherin surface.

Bioassembly of multicellular spheroids to mimic complex tissue structure using surface-modified magnetized nanofibers

Advancements in biofabrication have led to major strides toward creating authentic organ models; however, replicating intricate organ structures without scaffolds remains challenging. In this study, we introduce a method utilizing surface-modifiable magnetic nanofibers to achieve precise control over spheroid functions and geometrical features, allowing the creation of multiple functional domains within a single microtissue. We generated magnetized nanofibers by electrospinning magnetic nanoparticles dispersed in poly-L-lactic acid solution. These fibers were then coated with polydopamine (PD) to enhance their biological functions, particularly reactive oxygen species (ROS) scavenging. These PD-coated magnetic fibers (PMFs) had magnetic-responsive properties when incorporated into human dermal fibroblast spheroids (0.019 ± 0.001 emu g-1). Furthermore, PMFs within the spheroids effectively regulated ROS levels by upregulating the expression of key anti-oxidative genes such assuperoxide dismutase-1(2.2 ± 0.1) andglutathione peroxidase-1(2.6 ± 0.1). By exploiting the magnetic responsiveness of spheroids, we were able to assemble them into various structures such as linear, triangular, and square structures using remotely applied magnetic forces. Within the assembled three-dimensional constructs, the cells in spheroids incorporating PMFs demonstrated resistance to ROS regulatory activity in the presence of hydrogen peroxide, while spheroids composed of bare fibers exhibited high ROS levels. Furthermore, we assembled spheroids containing fibroblasts and endothelial cells into complex tissue structures resembling vessels under magnetic manipulation. This innovative method holds tremendous promise for organ modeling and regenerative medicine due to the unprecedented control it allows in developing microtissues that closely emulate real organs.

E-cadherin biointerfaces reprogram collective cell migration and cell cycling by forcing homeostatic conditions

Cells attach to the world around them in two ways-cell:extracellular-matrix adhesion and cell:cell adhesion-and conventional biomaterials are made to resemble the matrix to encourage integrin-based cell adhesion. However, interest is growing for cell-mimetic interfaces that mimic cell-cell interactions using cadherin proteins, as this offers a new way to program cell behavior and design synthetic implants and objects that can integrate directly into living tissues. Here, we explore how these cadherin-based materials affect collective cell behaviors, focusing specifically on collective migration and cell cycle regulation in cm-scale epithelia. We built culture substrates where half of the culture area was functionalized with matrix proteins and the contiguous half was functionalized with E-cadherin proteins, and we grew large epithelia across this 'Janus' interface. Parts of the tissues in contact with the matrix side of the Janus interface exhibited normal collective dynamics, but an abrupt shift in behaviors happened immediately across the Janus boundary onto the E-cadherin side, where cells formed hybrid E-cadherin junctions with the substrate, migration effectively froze in place, and cell-cycling significantly decreased. E-cadherin materials suppressed long-range mechanical correlations in the tissue and mechanical information reflected off the substrate interface. These effects could not be explained by conventional density, shape index, or contact inhibition explanations. E-cadherin surfaces nearly doubled the length of the G0/G1 phase of the cell cycle, which we ultimately connected to the exclusion of matrix focal adhesions induced by the E-cadherin culture surface.

Chitin Nerve Conduits with Three-Dimensional Spheroids of Mesenchymal Stem Cells from SD Rats Promote Peripheral Nerve Regeneration

Peripheral nerve injury (PNI) is an unresolved medical problem with limited therapeutic effects. Epineurium neurorrhaphy is an important method for treating PNI in clinical application, but it is accompanied by inevitable complications such as the misconnection of nerve fibers and neuroma formation. Conduits small gap tubulization has been proved to be an effective suture method to replace the epineurium neurorrhaphy. In this study, we demonstrated a method for constructing peripheral nerve conduits based on the principle of chitosan acetylation. In addition, the micromorphology, mechanical properties and biocompatibility of the chitin nerve conduits formed by chitosan acetylation were further tested. The results showed chitin was a high-quality biological material for constructing nerve conduits. Previous reports have demonstrated that mesenchymal stem cells culture as spheroids can improve the therapeutic potential. In the present study, we used a hanging drop protocol to prepare bone marrow mesenchymal stem cell (BMSCs) spheroids. Meanwhile, spherical stem cells could express higher stemness-related genes. In the PNI rat model with small gap tubulization, BMSCs spheres exhibited a higher ability to improve sciatic nerve regeneration than BMSCs suspension. Chitin nerve conduits with BMSCs spheroids provide a promising therapy option for peripheral nerve regeneration.

Magnetism-controlled assembly of composite stem cell spheroids for the biofabrication of contraction-modulatory 3D tissue

Biofabrication of organ-like engineered 3D tissue through the assembly of magnetized 3D multi-cellular spheroids has been recently investigated in tissue engineering. However, the cytotoxicity of magnetic nanoparticles (MNPs) and contraction-induced structural deformation of the constructs have been major limitations. In this study, we developed a method to fabricate composite stem cell spheroids using MNP-coated fibers, alleviating MNP-mediated toxicity and controlling structural assembly under external magnetic stimuli. The MNP-coated synthetic fibers (MSFs) were prepared by coating various amounts of MNPs on the fibers via electrostatic interactions. The MSFs showed magnetic hysteresis and no cytotoxicity on 2D-cultured adipose-derived stem cells (ADSCs). The composite spheroids containing MSFs and ADSCs were rapidly formed in which the amount of impregnated MSFs modulated the spheroid size. The fusion ofin vitrocomposite spheroids was then monitored at the contacting interface; the fused spheroids with over 10μg of MSF showed minimal contraction after 7 d, retaining around 90% of total area ratio regardless of the number of cells, indicating that the presence of fibers within the composite spheroid supported its structural maintenance. The fusion of MSF spheroids was modulated by external magnetic stimulation, and the effect of magnetic force on the movement and fusion of the spheroids was investigated using COMSOL simulation. Finally, ring and lamellar structures were successfully assembled using remote-controlled MSF spheroids, showing limited deformation and high viability up to 50 d duringin vitroculture. In addition, the MSFs demonstrated no adverse effects on ADSC osteochondral differentiation. Altogether, we envision that our magnetic assembly system would be a promising method for the tissue engineering of structurally controlled organ-like constructs.

Microfluidic arrays of dermal spheroids: a screening platform for active ingredients of skincare products

Organotypic micrometre-size 3D aggregates of skin cells (multicellular spheroids) have emerged as a promising in vitro model that can be utilized as an alternative of animal models to test active ingredients (AIs) of skincare products; however, a reliable dermal spheroid-based microfluidic (MF) model with a goal of in vitro AI screening is yet to be developed. Here, we report a MF platform for the growth of massive arrays of dermal fibroblast spheroids (DFSs) in a biomimetic hydrogel under close-to-physiological flow conditions and with the capability of screening AIs for skincare products. The DFSs formed after two days of on-chip culture and, in a case study, were used in a time-efficient manner for screening the effect of vitamin C on the synthesis of collagen type I and fibronectin. The computational simulation showed that the uptake of vitamin C was dominated by the advection flux. The results of screening the benchmark AI, vitamin C, proved that DFSs can serve as a reliable in vitro dermal model. The proposed DFS-based MF platform offers a high screening capacity for AIs of skincare products, as well as drug discovery and development in dermatology.

Delivery of a spheroids-incorporated human dermal fibroblast sheet increases angiogenesis and M2 polarization for wound healing

Low cell engraftment is a major problem in tissue engineering. Although various methods related with cell sheets have been attempted to resolve the issue, low cell viability due to oxygen and nutrient depletion remains an obstacle toward advanced therapeutic applications. Cell therapy using fibroblasts is thought of as a good alternative due to the short doubling times of fibroblasts together with their immunomodulatory properties. Furthermore, three-dimensional (3D) fibroblasts exhibit unique angiogenic and inflammation-manipulating properties that are not present in two-dimensional (2D) forms. However, the therapeutic effect of 3D fibroblasts in tissue regeneration has not been fully elucidated. Macrophage polarization has been widely studied, as it stimulates the transition from the inflammation to the proliferation phase of wound healing. Although numerous strategies have been developed to achieve better polarization of macrophages, the low efficacy of these strategies and safety issues remain problematic. To this end, we introduced a biocompatible flat patch with specifically designed holes that form a spheroids-incorporated human dermal fibroblast sheet (SIS) to mediate the activity of inflammatory cytokines for M2 polarization and increase angiogenic efficacy. We further confirmed in vivo enhancement of wound healing with an SIS-laden skin patch (SISS) compared to conventional cell therapy.

Stem cell spheroid engineering with osteoinductive and ROS scavenging nanofibers for bone regeneration

Stem cell spheroids have been widely investigated to accelerate bone tissue regeneartion. However, the directed differentiation of stem cells into osteoblastic lineage and the prevention of cells from damage by reactive oxygen species (ROS) remain challenge. Here, we developed osteoinductive and ROS scavenging extracellular matrix (ECM)-mimicking synthetic fibers based on epigallocatechin gallate (EGCG) coating. They were then utilized to fabricate engineered spheroids with human adipose-derived stem cells (hADSCs) for bone tissue regeneation. The EGCG-mineral fibers (EMF) effectively conferred osteoinductive and ROS scavenging signals on the hADSCs within spheroids, demonstrating relative upregulation of antioxidant genes (SOD-1 (25.8±2.1) and GPX-1 (3.3±0.1) and greater level of expression of osteogenic markers, RUNX2 (5.8±0.1) and OPN (5.9±0.1), compared to hADSCs in the spheroids without EMF. The in vitro overexpression of osteogenic genes from hADSCs was achieved from absence of osteogenic supplenments. Furthermore, in vivo transplantation of hADSCs spheroids with the EMF significantly promoted calvarial bone regeneration (48.39±9.24%) compared to that from defect only (17.38±6.63%), suggesting that the stem cell spheroid biofabrication system with our novel mineralization method described here is a promising tool for bone tissue regeneration.

Engineering Multi-Cellular Spheroids for Tissue Engineering and Regenerative Medicine

Multi-cellular spheroids are formed as a 3D structure with dense cell-cell/cell-extracellular matrix interactions, and thus, have been widely utilized as implantable therapeutics and various ex vivo tissue models in tissue engineering. In principle, spheroid culture methods maximize cell-cell cohesion and induce spontaneous cellular assembly while minimizing cellular interactions with substrates by using physical forces such as gravitational or centrifugal forces, protein-repellant biomaterials, and micro-structured surfaces. In addition, biofunctional materials including magnetic nanoparticles, polymer microspheres, and nanofiber particles are combined with cells to harvest composite spheroids, to accelerate spheroid formation, to increase the mechanical properties and viability of spheroids, and to direct differentiation of stem cells into desirable cell types. Biocompatible hydrogels are developed to produce microgels for the fabrication of size-controlled spheroids with high efficiency. Recently, spheroids have been further engineered to fabricate structurally and functionally reliable in vitro artificial 3D tissues of the desired shape with enhanced specific biological functions. This paper reviews the overall characteristics of spheroids and general/advanced spheroid culture techniques. Significant roles of functional biomaterials in advanced spheroid engineering with emphasis on the use of spheroids in the reconstruction of artificial 3D tissue for tissue engineering are also thoroughly discussed.

Polydopamine-assisted one-step modification of nanofiber surfaces with adenosine to tune the osteogenic differentiation of mesenchymal stem cells and the maturation of osteoclasts

Adenosine and its receptors have emerged as alternative targets to control cellular functions for bone healing. However, the soluble delivery of adenosine has not proven effective because of its fast degradation in vivo. We therefore designed a stable coating of adenosine for biomaterial surfaces through polydopamine chemistry to control osteogenesis and osteoclastogenesis via A2bR signaling. First, we prepared electrospun poly (ι-lactic acid) (PLLA) nanofiber sheets, which were modified through a one-step adenosine polydopamine coating process. Scanning electron microscopy (SEM) revealed deposition of particles on the adenosine polydopamine-coated PLLA (AP-PL) sheets compared to the polydopamine-only sheets. Moreover, X-ray photoelectron spectroscopy analysis confirmed an increase in nitrogen signals due to adenosine. Furthermore, adenosine loading efficiency and retention were significantly enhanced in AP-PL sheets compared to polydopamine-only sheets. Human adipose-derived stem cells (hADSCs) cultured on AP-PL expressed A2bR (1.30 ± 0.19 fold) at significantly higher levels than those cultured on polydopamine-only sheets. This in turn significantly elevated the expression of Runx2 (16.94 ± 1.68 and 51.69 ± 0.07 fold), OPN (1.63 ± 0.16 and 30.56 ± 0.25 fold), OCN (1.16 ± 0.13 and 5.23 ± 0.16 fold), and OSX (10.01 ± 0.81 and 62.48 ± 0.25 fold) in cells grown in growth media on days 14 and 21, respectively. Similarly, mineral deposition was enhanced to a greater extent in the AP-PL group than the polydopamine group, while blocking of A2bR significantly downregulated osteogenesis. Finally, osteoclast differentiation of RAW 264.7 cells was significantly inhibited by growth on AP-PL sheets. However, osteoclast differentiation was significantly stimulated after A2bR was blocked. Taken together, we propose that polydopamine-assisted one-step coating of adenosine is a viable method for surface modification of biomaterials to control osteogenic differentiation of stem cells and bone healing.

Stem cell spheroids incorporating fibers coated with adenosine and polydopamine as a modular building blocks for bone tissue engineering

Although stem cell spheroids offer great potential as functional building blocks for bottom-up bone tissue engineering, delivery of bioactive signals remain challenging. Here, we engineered adenosine-ligand-modified fiber fragments to create a 3D cell-instructive microenvironment for bone. Briefly, the Poly(ι-lactic acid) (PLLA) nanofiber sheet was partially degraded into fragmented fibers (FFs) through aminolysis and adenosine was stably incorporated via one-step polydopamine coating. The SEM and XPS analysis demonstrated that polydopamine assisted adenosine coating efficiency was significantly increased, which led to high coating efficiency of adenosine and its significant retention. The engineered fibers were then assembled into stable spheroids with human-adipose-derived stem cells (hADSCs). The adenosine in the spheroids effectively stimulated A2bR (1.768 ± 0.08) signaling, which further significantly induced the expression of osteogenic markers such as Runx2 (3.216 ± 0.25), OPN (4.136 ± 0.14), OCN (10.16 ± 0.34), and OSX (2.27 ± 0.11) with improved mineral deposition (1.375 ± 0.05 μg per spheroid). In contrast, the adipogenic differentiation of hADSCs was significantly suppressed within the engineered spheroids. Transplantation of engineered spheroids strongly induced osteogenic differentiation of hADSCs in ectopic subcutaneous tissue. Finally, the bone regeneration was significantly enhanced by implanting AP-FF group (59.97 ± 18.33%) as compared to P-FF (27.96 ± 11.14) and defect only (7.97 ± 3.76%). We propose that stem cell spheroids impregnated with engineered fibers enabling adenosine delivery could be promising building blocks for a bottom-up approach to create large tissues for regeneration of damaged bone.