Surface Curvature Differentially Regulates Stem Cell Migration and Differentiation via Altered Attachment Morphology and Nuclear Deformation

3D printing calcium phosphate ceramics with high osteoinductivity through pore architecture optimization

The osteoinductivity of 3D printed calcium phosphate (CaP) ceramics has a large gap compared with those prepared by conventional foaming methods, and improving the osteoinductivity of 3D printing CaP ceramics is crucial for successful application in bone regeneration. Pore architecture plays a critical role in osteoinductivity. In this study, CaP ceramics with a hexagonal close-packed (HCP) spherical pore structure were successfully fabricated using DLP printing technology. Additionally, octahedral (Octahedral), diamond (Diamond), and helical (Gyroid) structures were constructed with similar porosity and macropore diameter. CaP ceramics with the HCP structure exhibited higher compression strength (8.39 ± 1.82 MPa) and lower permeability (6.41 × 10-11 m2) compared to the Octahedral, Diamond, and Gyroid structures. In vitro cellular responses indicated that the macropore architecture strongly influenced the local growth rate of osteoblast-formed cell tissue; cells grew uniformly and formed circular rings in the HCP group. Furthermore, the HCP group promoted the expression of osteogenic genes and proteins more effectively than the other three groups. The outstanding osteoinductivity of the HCP group was confirmed in canine intramuscular implantation studies, where the new bone area reached up to 8.02 ± 1.94 % after a 10-week implantation. Additionally, the HCP group showed effective bone regeneration in repairing femoral condyle defects. Therefore, our findings suggest that 3D printed CaP bioceramics with an HCP structure promote osteoinductivity and can be considered as candidates for personalized precise treatment of bone defects in clinical applications. STATEMENT OF SIGNIFICANCE: 1. 3D printing BCP ceramics with high osteoinductivity were constructed through pore architecture optimization. 2. BCP ceramics with HCP structure exhibited relatively higher mechanical strength and lower permeability than those with Octahedral, Diamond and Gyroid structures. 3. BCP ceramics with HCP structure could promote the osteogenic differentiation of MC3T3-E1, and showed the superior in-vivo osteoinductivity and bone regeneration comparing with the other structures.

Micropatterned shape-memory polymer substrate containing hydrogen bonds creates a long-term dynamic microenvironment for regulating nerve-cell fate

Peripheral nerve injuries (PNIs) caused by mechanical contusion are frequently encountered in clinical practice, using nerve guidance conduits (NGCs) is now a promising therapy. An NGC creates a microenvironment for cell growth and differentiation, thus understanding physical and biochemical cues that can affect nerve-cell fate is a prerequisite for rationally designing NGCs. However, most of the previous works were focused on some static cues, the dynamic nature of the nerve microenvironment has not yet been well captured. Herein, we develop a micropatterned shape-memory polymer as a programmable substrate for providing a dynamic cue for nerve-cell growth. The shape-memory properties enable temporal programming of the substrate, and a dynamic microenvironment is created during standard cell culturing at 37 °C. Unlike most of the biomedical shape-memory polymers that recover rapidly at 37 °C, the proposed substrate shows a slow recovery process lasting 3-4 days and creates a long-term dynamic microenvironment. Results demonstrate that the vertically programmed substrates provide the most suitable dynamic microenvironment for PC12 cells as both the differentiation and maturity are promoted. Overall, this work provides a strategy for creating a long-term dynamic microenvironment for regulating nerve-cell fate and will inspire the rational design of NGCs for the treatment of PNIs.

Structurally and mechanically tuned macroporous hydrogels for scalable mesenchymal stem cell-extracellular matrix spheroid production

Mesenchymal stem cells (MSCs) are essential in regenerative medicine. However, conventional expansion and harvesting methods often fail to maintain the essential extracellular matrix (ECM) components, which are crucial for their functionality and efficacy in therapeutic applications. Here, we introduce a bone marrow-inspired macroporous hydrogel designed for the large-scale production of MSC-ECM spheroids. Through a soft-templating approach leveraging liquid-liquid phase separation, we engineer macroporous hydrogels with customizable features, including pore size, stiffness, bioactive ligand distribution, and enzyme-responsive degradability. These tailored environments are conducive to optimal MSC proliferation and ease of harvesting. We find that soft hydrogels enhance mechanotransduction in MSCs, establishing a standard for hydrogel-based 3D cell culture. Within these hydrogels, MSCs exist as both cohesive spheroids, preserving their innate vitality, and as migrating entities that actively secrete functional ECM proteins. Additionally, we also introduce a gentle, enzymatic harvesting method that breaks down the hydrogels, allowing MSCs and secreted ECM to naturally form MSC-ECM spheroids. These spheroids display heightened stemness and differentiation capacity, mirroring the benefits of a native ECM milieu. Our research underscores the significance of sophisticated materials design in nurturing distinct MSC subpopulations, facilitating the generation of MSC-ECM spheroids with enhanced therapeutic potential.

Multi-parameter design of triply periodic minimal surface scaffolds: from geometry optimization to biomechanical simulation

This study introduces a multi-parameter design methodology to create triply periodic minimal surface (TPMS) scaffolds with predefined geometric characteristics. The level-set constant and unit cell lengths are systematically correlated with targeted porosity and minimum pore sizes. Network and sheet scaffolds featuring diamond, gyroid, and primitive level-set structures are generated. Three radially graded schemes are applied to each of the six scaffold type, accommodating radial variations in porosity and pore sizes. Computer simulations are conducted to assess the biomechanical performance of 18 scaffold models. Results disclose that diamond and gyroid scaffolds exhibit more expansive design ranges than primitive counterparts. While primitive scaffolds display the highest Young's modulus and permeability, their lower yield strength and mesenchymal stem cell (MSC) adhesion render them unsuitable for bone scaffolds. Gyroid scaffolds demonstrate superior mechanical and permeability performances, albeit with slightly lower MSC adhesion than diamond scaffolds. Sheet scaffolds, characterized by more uniform material distribution, exhibit superior mechanical performance in various directions, despite slightly lower permeability. The higher specific surface area of sheet scaffolds contributes to elevated MSC adhesion. The stimulus factor analysis also revealed the superior differentiation potential of sheet scaffolds over network ones. The diamond sheet type demonstrated the optimal differentiation. Introducing radial gradations enhances axial mechanical performance at the expense of radial mechanical performance. Radially decreasing porosity displays the highest permeability, MSC adhesion, and differentiation capability, aligning with the structural characteristics of human bones. This study underscores the crucial need to balance diverse biomechanical properties of TPMS scaffolds for bone tissue engineering.

Manufacturing mesenchymal stromal cells in a microcarrier-microbioreactor platform can enhance cell yield and quality attributes: case study for acute respiratory distress syndrome

Mesenchymal stem and stromal cells (MSCs) hold potential to treat a broad range of clinical indications, but clinical translation has been limited to date due in part to challenges with batch-to-batch reproducibility of potential critical quality attributes (pCQAs) that can predict potency/efficacy. Here, we designed and implemented a microcarrier-microbioreactor approach to cell therapy manufacturing, specific to anchorage-dependent cells such as MSCs. We sought to assess whether increased control of the biochemical and biophysical environment had the potential to create product with consistent presentation and elevated expression of pCQAs relative to established manufacturing approaches in tissue culture polystyrene (TCPS) flasks. First, we evaluated total cell yield harvested from dissolvable, gelatin microcarriers within a microbioreactor cassette (Mobius Breez) or a flask control with matched initial cell seeding density and culture duration. Next, we identified 24 genes implicated in a therapeutic role for a specific motivating indication, acute respiratory distress syndrome (ARDS); expression of these genes served as our pCQAs for initial in vitro evaluation of product potency. We evaluated mRNA expression for three distinct donors to assess inter-donor repeatability, as well as for one donor in three distinct batches to assess within-donor, inter-batch variability. Finally, we assessed gene expression at the protein level for a subset of the panel to confirm successful translation. Our results indicated that MSCs expanded with this microcarrier-microbioreactor approach exhibited reasonable donor-to-donor repeatability and reliable batch-to-batch reproducibility of pCQAs. Interestingly, the baseline conditions of this microcarrier-microbioreactor approach also significantly improved expression of several key pCQAs at the gene and protein expression levels and reduced total media consumption relative to TCPS culture. This proof-of-concept study illustrates key benefits of this approach to therapeutic cell process development for MSCs and other anchorage-dependent cells that are candidates for cell therapies.

Focal adhesion and actin orientation regulated by cellular geometry determine stem cell differentiation via mechanotransduction

Tuning cell adhesion geometry can affect cytoskeleton organization and the distribution of cytoskeleton forces, which play critical roles in controlling cell functions. To elucidate the geometrical relationship with cytoskeleton force distribution, it is necessary to control cell morphology. In this study, a series of dextral vortex micropatterns were prepared to precisely control cell morphology for investigating the influence of the curvature degree of adhesion curves on intracellular force distribution and stem cell differentiation at a sub-cellular level. Peripherial actin filaments of micropatterned cells were assembled along the adhesion curves and showed different orientations, filament thicknesses and densities. Focal adhesion and cytoskeleton force distribution were dependent on the curvature degree. Intracellular force distribution was also regulated by adhesion curves. The cytoskeleton and force distribution affected the osteogenic differentiation of mesenchymal stem cells through a YAP/TAZ-mediated mechanotransduction process. Thus, regulation of cell adhesion curvature, especially at cytoskeletal filament level, is critical for cell function manipulation. STATEMENT OF SIGNIFICANCE: In this study, a series of dextral micro-vortexes were prepared and used for the culture of human mesenchymal stem cells (hMSCs) to precisely control adhesive curvatures (0°, 30°, 60°, and 90°). The single MSCs on the micropatterns had the same size and shape but showed distinct focal adhesion (FA) and cytoskeleton orientations. Cellular nanomechanics were observed to be correlated with the curvature degrees, subsequently influencing nuclear morphological features. As a consequence, the localization of the mechanotransduction sensor and activator-YAP/TAZ was affected, influencing osteogenic differentiation. The results revealed the pivotal role of adhesive curvatures in the manipulation of stem cell differentiation via the machanotransduction process, which has rarely been investigated.

Propelling Minimally Invasive Tissue Regeneration With Next-Era Injectable Pre-Formed Scaffolds

The growing aging population, with its associated chronic diseases, underscores the urgency for effective tissue regeneration strategies. Biomaterials play a pivotal role in the realm of tissue reconstruction and regeneration, with a distinct shift toward minimally invasive (MI) treatments. This transition, fueled by engineered biomaterials, steers away from invasive surgical procedures to embrace approaches offering reduced trauma, accelerated recovery, and cost-effectiveness. In the realm of MI tissue repair and cargo delivery, various techniques are explored. While in situ polymerization is prominent, it is not without its challenges. This narrative review explores diverse biomaterials, fabrication methods, and biofunctionalization for injectable pre-formed scaffolds, focusing on their unique advantages. The injectable pre-formed scaffolds, exhibiting compressibility, controlled injection, and maintained mechanical integrity, emerge as promising alternative solutions to in situ polymerization challenges. The conclusion of this review emphasizes the importance of interdisciplinary design facilitated by synergizing fields of materials science, advanced 3D biomanufacturing, mechanobiological studies, and innovative approaches for effective MI tissue regeneration.

Polishing methods for composites restoration: the influence on human gingival fibroblasts behaviour

BACKGROUND

Carious/Non-carious cervical lesions with gingival recessions may require both dental and periodontal reconstructive therapy, where flaps/grafts may be placed in contact with a dental filling material. Human Gingival Fibroblasts (HGF-1) response during the early phase of healing could vary according to the procedures employed to cure the dental composite. Moreover, oxygen diffusion into dental composite inhibits the polymerization reaction, creating an oxygen-inhibited layer (OIL) that presents residual unreacted monomers. The aim of this study was to assess the effect of different polishing techniques and OIL on HGF-1.

METHODS

Composite discs polished with different techniques (diamond rubber, abrasive discs and tungsten carbide burr) were used. An additional not polished smooth group obtained with and without OIL was used as control. Samples were physically characterized through the analysis of their hydrophilicity and surface topography through contact angle measurement and SEM, respectively; afterwards the biologic response of HGF-1 when cultured on the different substrates was analyzed in terms of cytotoxicity and gene expression.

RESULTS

The finishing systems caused alterations to the wettability, even if without a proportional relation towards the results of the proliferation essay, from which emerges a greater proliferation on surfaces polished with one-step diamond rubber and with abrasive discs as well as a direct effect of the glycerin layer, confirming that surface roughness can heavily influence the biological response of HGF-1.

CONCLUSIONS

Surfaces wettability as well as cellular behavior seem to be affected by the selection of the finishing system used to lastly shape the restoration. Especially, the presence of OIL act as a negative factor in the regards of human gingival fibroblasts. The present study may provide the first clinical instruction regarding the best polishing system of composite material when the restoration is placed directly in contact with soft tissue cells. Understanding HGF-1 behavior can help identifying the polishing treatment for direct restoration of carious/non-carious cervical lesions associated with gingival recessions.

Nuclear curvature determines Yes-associated protein localization and differentiation of mesenchymal stem cells

Controlling mesenchymal stem cell (MSC) differentiation remains a critical challenge in MSCs' therapeutic application. Numerous biophysical and mechanical stimuli influence stem cell fate; however, their relative efficacy and specificity in mechanically directed differentiation remain unclear. Yes-associated protein (YAP) is one key mechanosensitive protein that controls MSC differentiation. Previous studies have related nuclear mechanics with YAP activity, but we still lack an understanding of what nuclear deformation specifically regulates YAP and its relationship with mechanical stimuli. Here, we report that maximum nuclear curvature is the most precise biophysical determinant for YAP mechanotransduction-mediated MSC differentiation and is a relevant parameter for stem cell-based therapies. We employed traction force microscopy and confocal microscopy to characterize the causal relationships between contractility and nuclear deformation in regulating YAP activity in MSCs. We observed that an increase in contractility compresses nuclei anisotropically, whereby the degree of asymmetric compression increased the bending curvature of the nuclear membrane. We then examined membrane curvature and tension using thin micropatterned adhesive substrate lines and an FRET-based tension sensor, revealing the direct role of curvature in YAP activity driven by both active and passive nuclear import. Finally, we employed micropatterned lines to control nuclear curvature and precisely direct MSC differentiation. This work illustrates that nuclear curvature subsumes other biophysical aspects to control YAP-mediated differentiation in MSCs and may provide a deterministic solution to some of the challenges in mesenchymal stem cell therapies.

Twisted-plywood-like tissue formation in vitro. Does curvature do the twist?

Little is known about the contribution of 3D surface geometry to the development of multilayered tissues containing fibrous extracellular matrix components, such as those found in bone. In this study, we elucidate the role of curvature in the formation of chiral, twisted-plywood-like structures. Tissues consisting of murine preosteoblast cells (MC3T3-E1) were grown on 3D scaffolds with constant-mean curvature and negative Gaussian curvature for up to 32 days. Using 3D fluorescence microscopy, the influence of surface curvature on actin stress-fiber alignment and chirality was investigated. To gain mechanistic insights, we did experiments with MC3T3-E1 cells deficient in nuclear A-type lamins or treated with drugs targeting cytoskeleton proteins. We find that wild-type cells form a thick tissue with fibers predominantly aligned along directions of negative curvature, but exhibiting a twist in orientation with respect to older tissues. Fiber orientation is conserved below the tissue surface, thus creating a twisted-plywood-like material. We further show that this alignment pattern strongly depends on the structural components of the cells (A-type lamins, actin, and myosin), showing a role of mechanosensing on tissue organization. Our data indicate the importance of substrate curvature in the formation of 3D tissues and provide insights into the emergence of chirality.

Investigation of cell infiltration and colonization in 3D porous scaffolds via integrated experimental and computational strategies

This study aimed to integrate experimental and computational methods to systematically investigate cell infiltration and colonization within porous scaffolds. Poly(lactic acid) discs (Diameter: 6 mm; Thickness: 500 µm) with open pores (Diameter: 400-1100 µm), corners (Angle: 30-120°) and gaps (Distance: 100-500 µm), and cellulosic scaffolds with irregular pores (Diameter: 50-300 µm) were situated in tissue culture plates and cultured with human dermal fibroblasts (HDFs). Both phase contrast and scanning electron microscopy revealed that HDFs initially proliferated on scaffold surfaces, then infiltrated into the porous structures via cell bridging and stacking strategies, which was affected by the initial cell seeding densities, porous structures and culture times. Based on the density-dependent cell growths in two-dimensional cell cultures, power law models were developed to quantitatively simulate cell growths on scaffold surfaces. Model analysis predicted the effect of cell seeding efficiency on cell infiltrations into the porous scaffolds, which was further validated via series cell seeding experiments. The novelty of this research lies in the incorporation of multiple experimental and computational strategies, which enables the mechanistic insights of cell invasion and colonization in porous scaffolds, also facilitates the development of suitable bioprocesses for cell seeding and tissue manufacturing in Tissue Engineering and Regenerative Medicine.

Engineering periodontal tissue interfaces using multiphasic scaffolds and membranes for guided bone and tissue regeneration

Periodontal diseases are one of the greatest healthcare burdens worldwide. The periodontal tissue compartment is an anatomical tissue interface formed from the periodontal ligament, gingiva, cementum, and bone. This multifaceted composition makes tissue engineering strategies challenging to develop due to the interface of hard and soft tissues requiring multiphase scaffolds to recreate the native tissue architecture. Multilayer constructs can better mimic tissue interfaces due to the individually tuneable layers. They have different characteristics in each layer, with modulation of mechanical properties, material type, porosity, pore size, morphology, degradation properties, and drug-releasing profile all possible. The greatest challenge of multilayer constructs is to mechanically integrate consecutive layers to avoid delamination, especially when using multiple manufacturing processes. Here, we review the development of multilayer scaffolds that aim to recapitulate native periodontal tissue interfaces in terms of physical, chemical, and biological characteristics. Important properties of multiphasic biodegradable scaffolds are highlighted and summarised, with design requirements, biomaterials, and fabrication methods, as well as post-treatment and drug/growth factor incorporation discussed.

Mechanoresponse of Curved Epithelial Monolayers Lining Bowl-Shaped 3D Microwells

The optimal functioning of many organs relies on the curved architecture of their epithelial tissues. However, the mechanoresponse of epithelia to changes in curvature remains misunderstood. Here, bowl-shaped microwells in hydrogels are designed via photopolymerization to faithfully replicate the shape and dimensions of lobular structures. Leveraging these hydrogel-based microwells, curved epithelial monolayers are engineered, and how in-plane and Gaussian curvatures at the microwell entrance influence epithelial behavior is investigated. Cells and nuclei around the microwell edge display a more pronounced centripetal orientation as the in-plane curvature decreases, and enhanced cell straightness and speed. Moreover, cells reorganize their actin cytoskeleton by forming a supracellular actin cable at the microwell edge, with its size becoming more pronounced as the in-plane curvature decreases. The Gaussian curvature at the microwell entrance enhances the maturation of the supracellular actin cable architecture and leads to a vertical orientation of nuclei toward the bottom of the microwell. Increasing Gaussian curvature results in flattened and elongated nuclear morphologies characterized by highly compacted chromatin states. This approach provides better understanding of the mechanoresponse of curved epithelial monolayers curvatures lining lobular structures. In addition, bowl-shaped microwells offer a powerful platform to study curvature-dependent mechanotransduction pathways in anatomically relevant 3D structures.

Extracellular Matrix Cues Regulate Mechanosensing and Mechanotransduction of Cancer Cells

Extracellular biophysical properties have particular implications for a wide spectrum of cellular behaviors and functions, including growth, motility, differentiation, apoptosis, gene expression, cell-matrix and cell-cell adhesion, and signal transduction including mechanotransduction. Cells not only react to unambiguously mechanical cues from the extracellular matrix (ECM), but can occasionally manipulate the mechanical features of the matrix in parallel with biological characteristics, thus interfering with downstream matrix-based cues in both physiological and pathological processes. Bidirectional interactions between cells and (bio)materials in vitro can alter cell phenotype and mechanotransduction, as well as ECM structure, intentionally or unintentionally. Interactions between cell and matrix mechanics in vivo are of particular importance in a variety of diseases, including primarily cancer. Stiffness values between normal and cancerous tissue can range between 500 Pa (soft) and 48 kPa (stiff), respectively. Even the shear flow can increase from 0.1-1 dyn/cm2 (normal tissue) to 1-10 dyn/cm2 (cancerous tissue). There are currently many new areas of activity in tumor research on various biological length scales, which are highlighted in this review. Moreover, the complexity of interactions between ECM and cancer cells is reduced to common features of different tumors and the characteristics are highlighted to identify the main pathways of interaction. This all contributes to the standardization of mechanotransduction models and approaches, which, ultimately, increases the understanding of the complex interaction. Finally, both the in vitro and in vivo effects of this mechanics-biology pairing have key insights and implications for clinical practice in tumor treatment and, consequently, clinical translation.

Active Osteoblasts or Quiescent Bone Lining Cells? Preosteoblasts Fate Orchestrated by Curvature and Stiffness of an In Vitro 2.5D Biomimetic Culture System

Biomimetic cell culture systems are required to provide more physiologically relevant microenvironments for bone cells. Here, a simple 2.5D culture platform is proposed, combining adjustable stiffness and surface features that mimic bone topography by using sandpaper grits as master molds with two stiffness formulations of polydimethylsiloxane (PDMS). The subsequent replicas perfectly conform the grits and reproduce the corresponding negative relief with cavities separated by convex edges. Biomimicry is also provided by an extracellular matrix (ECM)-like thin film coating, using the layer-by-layer (LbL) method. The topographical features, alternating concave, and convex structures drive preosteoblasts organization and morphology. Strikingly, curvature orchestrates the commitment of preosteoblasts, with i) maturation to active osteoblasts able to produce a dense collagenous matrix that ultimately mineralizes in the cavities, and ii) edges hosting quiescent cells that synthetize a very thin immature collagen layer with no mineralization. In summary, the present in vitro culture system model offers a cell-instructive 2.5D microenvironment that controls preosteoblasts fate, leading to two coexisting subpopulations: mature osteoblasts and bone lining cells (BLC). This promising culture system opens new avenues to advanced tissue-engineered modeling and can be applied to precellularized bone biomaterials.

Double-Network DNA Macroporous Hydrogel Enables Aptamer-Directed Cell Recruitment to Accelerate Bone Healing

Recruiting endogenous bone marrow mesenchymal stem cells (BMSCs) in vivo to bone defect sites shows great promise in cell therapies for bone tissue engineering, which tackles the shortcomings of delivering exogenous stem cells, including limited sources, low retention, stemness loss, and immunogenicity. However, it remains challenging to efficiently recruit stem cells while simultaneously directing cell differentiation in the dynamic microenvironment and promoting neo-regenerated tissue ingrowth to achieve augmented bone regeneration. Herein, a synthetic macroporous double-network hydrogel presenting nucleic acid aptamer and nano-inducer enhances BMSCs recruitment, and osteogenic differentiation is demonstrated. An air-in-water template enables the rapid construction of highly interconnective macroporous structures, and the physical self-assembly of DNA strands and chemical cross-linking of gelatin chains synergistically generate a resilient double network. The aptamer Apt19S and black phosphorus nanosheets-specific macroporous hydrogel demonstrate highly efficient endogenous BMSCs recruitment, cell differentiation, and extracellular matrix mineralization. Notably, the enhanced calvarial bone healing with promising matrix mineralization and new bone formation is accompanied by adapting this engineered hydrogel to the bone defects. The findings suggest an appealing material approach overcoming the traditional limitations of cell-delivery therapy that can inspire the future design of next-generation hydrogel for enhanced bone tissue regeneration.

Effects of Space Dimensionality within Scaffold for Bone Regeneration with Large and Oriented Blood Vessels

The internal structure of the scaffolds is a key factor for bone regeneration. In this study, we focused on the space dimensionality within the scaffold that may control cell migration and evaluated the effects on the size and orientation of blood vessels and the amount of bone formation in the scaffold. The carbonate apatite scaffolds with intrascaffold space allowing one-dimensional (1D), two-dimensional (2D), or three-dimensional (3D) cell migration were fabricated by 3D printing. These scaffolds had the same space size, i.e., distances between the struts (~300 µm). The scaffolds were implanted into the medial condyle of rabbit femurs for four weeks. Both the size and orientation degree of the blood vessels formed in the scaffolds allowing 1D cell migration were 2.5- to 4.0-fold greater than those of the blood vessels formed in the scaffolds allowing 2D and 3D cell migration. Furthermore, the amount of bone formed in the scaffolds allowing 1D cell migration was 1.4-fold larger than that formed in the scaffolds allowing 2D and 3D cell migration. These are probably because the 1D space limited the direction of cell migration and prevented the branching of blood vessels, whereas 2D and 3D spaces provided the opportunity for random cell migration and blood vessel branching. Thus, scaffolds with 1D space are advantageous for inducing large and oriented blood vessels, resulting in a larger amount of bone formation.

Geometry-structure models for liquid crystal interfaces, drops and membranes: wrinkling, shape selection and dissipative shape evolution

We review our recent contributions to anisotropic soft matter models for liquid crystal interfaces, drops and membranes, emphasizing validations with experimental and biological data, and with related theory and simulation literature. The presentation aims to illustrate and characterize the rich output and future opportunities of using a methodology based on the liquid crystal-membrane shape equation applied to static and dynamic pattern formation phenomena. The geometry of static and kinetic shapes is usually described with dimensional curvatures that co-mingle shape and curvedness. In this review, we systematically show how the application of a novel decoupled shape-curvedness framework to practical and ubiquitous soft matter phenomena, such as the shape of drops and tactoids and bending of evolving membranes, leads to deeper quantitative insights than when using traditional dimensional mean and Gaussian curvatures. The review focuses only on (1) statics of wrinkling and shape selection in liquid crystal interfaces and membranes; (2) kinetics and dissipative dynamics of shape evolution in membranes; and (3) computational methods for shape selection and shape evolution; due to various limitations other important topics are excluded. Finally, the outlook follows a similar structure. The main results include: (1) single and multiple wavelength corrugations in liquid crystal interfaces appear naturally in the presence of surface splay and bend orientation distortions with scaling laws governed by ratios of anchoring-to-isotropic tension energy; adding membrane elasticity to liquid crystal anchoring generates multiple scales wrinkling as in tulips; drops of liquid crystals encapsulates in membranes can adopt, according to the ratios of anchoring/tension/bending, families of shapes as multilobal, tactoidal, and serrated as observed in biological cells. (2) Mapping the liquid crystal director to a membrane unit normal. The dissipative shape evolution model with irreversible thermodynamics for flows dominated by bending rates, yields new insights. The model explains the kinetic stability of cylinders, while spheres and saddles are attractors. The model also adds to the evolving understanding of outer hair cells in the inner ear. (3) Computational soft matter geometry includes solving shape equations, trajectories on energy and orientation landscapes, and shape-curvedness evolutions on entropy production landscape with efficient numerical methods and adaptive approaches.

Injectable Microporous Annealed Crescent-Shaped (MAC) Particle Hydrogel Scaffold for Enhanced Cell Infiltration

Hydrogels are widely used for tissue engineering applications to support cellular growth, yet the tightly woven structure often restricts cell infiltration and expansion. Consequently, granular hydrogels with microporous architectures have emerged as a new class of biomaterial. Particularly, the development of microporous annealed particle (MAP) hydrogel scaffolds has shown improved stability and integration with host tissue. However, the predominant use of spherically shaped particles limits scaffold porosity, potentially limiting the level of cell infiltration. Here, a novel microporous annealed crescent-shaped particle (MAC) scaffold that is predicted to have improved porosity and pore interconnectivity in silico is presented. With microfluidic fabrication, tunable cavity sizes that optimize interstitial void space features are achieved. In vitro, cells incorporated into MAC scaffolds form extensive 3D multicellular networks. In vivo, the injectable MAC scaffold significantly enhances cell infiltration compared to spherical MAP scaffolds, resulting in increased numbers of myofibroblasts and leukocytes present within the gel without relying on external biomolecular chemoattractants. The results shed light on the critical role of particle shape in cell recruitment, laying the foundation for MAC scaffolds as a next-generation granular hydrogel for diverse tissue engineering applications.

Identification and analysis of 3D pores in packed particulate materials

We took the classic 'guess the number of beans in a jar game' and amplified the research question. Rather than estimate the quantity of particles in the jar, we sought to characterize the spaces between them. Here we present an approach for delineating the pockets of empty space (three-dimensional pores) between packed particles, which are hotspots for activity in applications and natural phenomena that deal with particulate materials. We utilize techniques from graph theory to exploit information about particle configuration that allows us to locate important spatial landmarks within the void space. These landmarks are the basis for our pore segmentation, where we consider both interior pores as well as entrance and exit pores into and out of the structure. Our method is robust for particles of varying size, form, stiffness and configuration, which allows us to study and compare three-dimensional pores across a range of packed particle types. We report striking relationships between particles and pores that are described mathematically, and we offer a visual library of pore types. With a meaningful discretization of void space, we demonstrate that packed particles can be understood not by their solid space, but by their empty space.

Shape-Morphing Photoresponsive Hydrogels Reveal Dynamic Topographical Conditioning of Fibroblasts

The extracellular environment defines a physical boundary condition with which cells interact. However, to date, cell response to geometrical environmental cues is largely studied in static settings, which fails to capture the spatiotemporally varying cues cells receive in native tissues. Here, a photoresponsive spiropyran-based hydrogel is presented as a dynamic, cell-compatible, and reconfigurable substrate. Local stimulation with blue light (455 nm) alters hydrogel swelling, resulting in on-demand reversible micrometer-scale changes in surface topography within 15 min, allowing investigation into cell response to controlled geometry actuations. At short term (1 h after actuation), fibroblasts respond to multiple rounds of recurring topographical changes by reorganizing their nucleus and focal adhesions (FA). FAs form primarily at the dynamic regions of the hydrogel; however, this propensity is abolished when the topography is reconfigured from grooves to pits, demonstrating that topographical changes dynamically condition fibroblasts. Further, this dynamic conditioning is found to be associated with long-term (72 h) maintenance of focal adhesions and epigenetic modifications. Overall, this study offers a new approach to dissect the dynamic interplay between cells and their microenvironment and shines a new light on the cell's ability to adapt to topographical changes through FA-based mechanotransduction.

Fractional and scaled Brownian motion on the sphere: The effects of long-time correlations on navigation strategies

We analyze fractional Brownian motion and scaled Brownian motion on the two-dimensional sphere S^{2}. We find that the intrinsic long-time correlations that characterize fractional Brownian motion collude with the specific dynamics (navigation strategies) carried out on the surface giving rise to rich transport properties. We focus our study on two classes of navigation strategies: one induced by a specific set of coordinates chosen for S^{2} (we have chosen the spherical ones in the present analysis), for which we find that contrary to what occurs in the absence of such long-time correlations, nonequilibrium stationary distributions are attained. These results resemble those reported in confined flat spaces in one and two dimensions [Guggenberger et al. New J. Phys. 21, 022002 (2019)1367-263010.1088/1367-2630/ab075f; Vojta et al. Phys. Rev. E 102, 032108 (2020)2470-004510.1103/PhysRevE.102.032108]; however, in the case analyzed here, there are no boundaries that affect the motion on the sphere. In contrast, when the navigation strategy chosen corresponds to a frame of reference moving with the particle (a Frenet-Serret reference system), then the equilibrium distribution on the sphere is recovered in the long-time limit. For both navigation strategies, the relaxation times toward the stationary distribution depend on the particular value of the Hurst parameter. We also show that on S^{2}, scaled Brownian motion, distinguished by a time-dependent diffusion coefficient with a power-scaling, is independent of the navigation strategy finding a good agreement between the analytical calculations obtained from the solution of a time-dependent diffusion equation on S^{2}, and the numerical results obtained from our numerical method to generate ensemble of trajectories.

Effects of Zinc and Strontium Doping on In Vitro Osteogenesis and Angiogenesis of Calcium Silicate/Calcium Phosphate Cement

Based on multiple biological functions (mainly osteogenesis and angiogenesis) of bioactive ions, Zn/Sr-doped calcium silicate/calcium phosphate cements (Zn/Sr-CS/CPCs, including 10Zn-CS/CPC, 20Sr-CS/CPC, and 10Zn/20Sr-CS/CPC) were prepared by the addition of Zn and Sr dual active ions into CS/CPC to further accelerate its bone regeneration in this study. The physicochemical and biological properties of the Zn/Sr-CS/CPCs were systematically investigated. The results showed that the setting time was slightly prolonged, the compressive strength and porosity did not change much, and all groups maintained good injectability after the doping of Zn and Sr. Besides, the doping of Zn and Sr had little effect on the phase and microstructure of hydrated products of CS/CPC. The degradation rate of Zn/Sr-CS/CPCs decreased after doping with Zn and Sr. In mouse bone marrow mesenchymal stem cells (mBMSC) experiments, all Zn/Sr-CS/CPCs stimulated the viability, adhesion, proliferation, and alkaline phosphatase (ALP) activity together with osteogenesis-related genes (ALP, Runx2, Col-I, OCN, and OPN). The further addition of Zn and Sr played better and synergistic roles in in vitro osteogenesis. Thereinto, 10Zn/20Sr-CS/CPC manifested the optimum in vitro osteogenic performance. As for human umbilical vein endothelial cell (HUVEC) experiments, the incorporation of CS doped with Zn and Sr into CPC possessed good vascularization properties of proliferation, NO secretion, tube formation, and the expression of angiogenesis-related genes (VEGF, bFGF, and eNOS). In conclusion, the doping of Zn and Sr into CS/CPC could exhibit excellent osteogenesis and good angiogenesis potentials and 10Zn/20Sr-CS/CPC could be considered as a promising candidate in bone repair.

Harnessing mechanical cues in the cellular microenvironment for bone regeneration

At the macroscale, bones experience a variety of compressive and tensile loads, and these loads cause deformations of the cortical and trabecular microstructure. These deformations produce a variety of stimuli in the cellular microenvironment that can influence the differentiation of marrow stromal cells (MSCs) and the activity of cells of the MSC lineage, including osteoblasts, osteocytes, and chondrocytes. Mechanotransduction, or conversion of mechanical stimuli to biochemical and biological signals, is thus part of a multiscale mechanobiological process that drives bone modeling, remodeling, fracture healing, and implant osseointegration. Despite strong evidence of the influence of a variety of mechanical cues, and multiple paradigms proposed to explain the influence of these cues on tissue growth and differentiation, even a working understanding of how skeletal cells respond to the complex combinations of stimuli in their microenvironments remains elusive. This review covers the current understanding of what types of microenvironmental mechanical cues MSCs respond to and what is known about how they respond in the presence of multiple such cues. We argue that in order to realize the vast potential for harnessing the cellular microenvironment for the enhancement of bone regeneration, additional investigations of how combinations of mechanical cues influence bone regeneration are needed.

Mechanical stress confers nuclear and functional changes in derived leukemia cells from persistent confined migration

Nuclear deformability plays a critical role in cell migration. During this process, the remodeling of internal components of the nucleus has a direct impact on DNA damage and cell behavior; however, how persistent migration promotes nuclear changes leading to phenotypical and functional consequences remains poorly understood. Here, we described that the persistent migration through physical barriers was sufficient to promote permanent modifications in migratory-altered cells. We found that derived cells from confined migration showed changes in lamin B1 localization, cell morphology and transcription. Further analysis confirmed that migratory-altered cells showed functional differences in DNA repair, cell response to chemotherapy and cell migration in vivo homing experiments. Experimental modulation of actin polymerization affected the redistribution of lamin B1, and the basal levels of DNA damage in migratory-altered cells. Finally, since major nuclear changes were present in migratory-altered cells, we applied a multidisciplinary biochemical and biophysical approach to identify that confined conditions promoted a different biomechanical response of the nucleus in migratory-altered cells. Our observations suggest that mechanical compression during persistent cell migration has a role in stable nuclear and genomic alterations that might handle the genetic instability and cellular heterogeneity in aging diseases and cancer.

High-Throughput Bioprinting of Geometrically-Controlled Pre-Vascularized Injectable Microgels for Accelerated Tissue Regeneration

Successful integration of cell-laden tissue constructs with host vasculature depends on the presence of functional capillaries to provide oxygen and nutrients to the embedded cells. However, diffusion limitations of cell-laden biomaterials challenge regeneration of large tissue defects that require bulk-delivery of hydrogels and cells. Herein, a strategy to bioprint geometrically controlled, endothelial and stem-cell laden microgels in high-throughput is introduced, allowing these cells to form mature and functional pericyte-supported vascular capillaries in vitro, and then injecting these pre-vascularized constructs minimally invasively in-vivo. It is demonstrated that this approach offers both desired scalability for translational applications as well as unprecedented levels of control over multiple microgel parameters to design spatially-tailored microenvironments for better scaffold functionality and vasculature formation. As a proof-of-concept, the regenerative capacity of the bioprinted pre-vascularized microgels is compared with that of cell-laden monolithic hydrogels of the same cellular and matrix composition in hard-to-heal defects in vivo. The results demonstrate that the bioprinted microgels have faster and higher connective tissue formation, more vessels per area, and widespread presence of functional chimeric (human and murine) vascular capillaries across regenerated sites. The proposed strategy, therefore, addresses a significant issue in regenerative medicine, demonstrating a superior potential to facilitate translational regenerative efforts.

Sequence-Encoded Differences in Phase Separation Enable Formation of Resilin-like Polypeptide-Based Microstructured Hydrogels

Microstructured hydrogels are promising platforms to mimic structural and compositional heterogeneities of the native extracellular matrix (ECM). The current state-of-the-art soft matter patterning techniques for generating ECM mimics can be limited owing to their reliance on specialized equipment and multiple time- and energy-intensive steps. Here, a photocross-linking methodology that traps various morphologies of phase-separated multicomponent formulations of compositionally distinct resilin-like polypeptides (RLPs) is reported. Turbidimetry and quantitative 1H NMR spectroscopy were utilized to investigate the sequence-dependent liquid-liquid phase separation of multicomponent solutions of RLPs. Differences between the intermolecular interactions of two different photocross-linkable RLPs and a phase-separating templating RLP were exploited for producing microstructured hydrogels with tunable control over pore diameters (ranging from 1.5 to 150 μm) and shear storage moduli (ranging from 0.2 to 5 kPa). The culture of human mesenchymal stem cells demonstrated high viability and attachment on microstructured hydrogels, suggesting their potential for developing customizable platforms for regenerative medicine applications.

3D micropattern force triggers YAP nuclear entry by transport across nuclear pores and modulates stem cells paracrine

Biophysical cues of the cellular microenvironment tremendously influence cell behavior by mechanotransduction. However, it is still unclear how cells sense and transduce the mechanical signals from 3D geometry to regulate cell function. Here, the mechanotransduction of human mesenchymal stem cells (MSCs) triggered by 3D micropatterns and its effect on the paracrine of MSCs are systematically investigated. Our findings show that 3D micropattern force could influence the spatial reorganization of the cytoskeleton, leading to different local forces which mediate nucleus alteration such as orientation, morphology, expression of Lamin A/C and chromatin condensation. Specifically, in the triangular prism and cuboid micropatterns, the ordered F-actin fibers are distributed over and fully transmit compressive forces to the nucleus, which results in nuclear flattening and stretching of nuclear pores, thus enhancing the nuclear import of YES-associated protein (YAP). Furthermore, the activation of YAP significantly enhances the paracrine of MSCs and upregulates the secretion of angiogenic growth factors. In contrast, the fewer compressive forces on the nucleus in cylinder and cube micropatterns cause less YAP entering the nucleus. The skin repair experiment provides the first in vivo evidence that enhanced MSCs paracrine by 3D geometry significantly promotes tissue regeneration. The current study contributes to understanding the in-depth mechanisms of mechanical signals affecting cell function and provides inspiration for innovative design of biomaterials.

3D printed pore morphology mediates bone marrow stem cell behaviors via RhoA/ROCK2 signaling pathway for accelerating bone regeneration

Bone bionics and structural engineering have sparked a broad interest in optimizing artificial scaffolds for better bone regeneration. However, the mechanism behind scaffold pore morphology-regulated bone regeneration remains unclear, making the structure design of scaffolds for bone repair challenging. To address this issue, we have carefully assessed diverse cell behaviors of bone mesenchymal stem cells (BMSCs) on the β-tricalcium phosphate (β-TCP) scaffolds with three representative pore morphologies (i.e., cross column, diamond, and gyroid pore unit, respectively). Among the scaffolds, BMSCs on the β-TCP scaffold with diamond pore unit (designated as D-scaffold) demonstrated enhanced cytoskeletal forces, elongated nucleus, faster cell mobility, and better osteogenic differentiation potential (for example, the alkaline phosphatase expression level in D-scaffold were 1.5-2 times higher than other groups). RNA-sequencing analysis and signaling pathway intervention revealed that Ras homolog gene family A (RhoA)/Rho-associated kinase-2 (ROCK2) has in-depth participated in the pore morphology-mediated BMSCs behaviors, indicating an important role of mechanical signaling transduction in scaffold-cell interactions. Finally, femoral condyle defect repair results showed that D-scaffold could effectively promote endogenous bone regeneration, of which the osteogenesis rate was 1.2-1.8 times higher than the other groups. Overall, this work provides insights into pore morphology-mediated bone regeneration mechanisms for developing novel bioadaptive scaffold designs.

Superiority of Triply Periodic Minimal Surface Gyroid Structure to Strut-Based Grid Structure in Both Strength and Bone Regeneration

The aging population has rapidly driven the demand for bone regeneration. The pore structure of a scaffold is a critical factor that affects its mechanical strength and bone regeneration. Triply periodic minimal surface gyroid structures similar to the trabecular bone structure are considered superior to strut-based lattice structures (e.g., grids) in terms of bone regeneration. However, at this stage, this is only a hypothesis and is not supported by evidence. In this study, we experimentally validated this hypothesis by comparing gyroid and grid scaffolds composed of carbonate apatite. The gyroid scaffolds possessed compressive strength approximately 1.6-fold higher than that of the grid scaffolds because the gyroid structure prevented stress concentration, whereas the grid structure could not. The porosity of gyroid scaffolds was higher than that of the grid scaffolds; however, porosity and compressive strength generally have a trade-off relationship. Moreover, the gyroid scaffolds formed more than twice the amount of bone as grid scaffolds in a critical-sized bone defect in rabbit femur condyles. This favorable bone regeneration using gyroid scaffolds was attributed to the high permeability (i.e., larger volume of macropores or porosity) and curvature profile of the gyroid structure. Thus, this study validated the conventional hypothesis using in vivo experiments and revealed factors that led to this hypothetical outcome. The findings of this study are expected to contribute to the development of scaffolds that can achieve early bone regeneration without sacrificing the mechanical strength.

Integrating physicomechanical and biological strategies for BTE: biomaterials-induced osteogenic differentiation of MSCs

Large bone defects are a major global health concern. Bone tissue engineering (BTE) is the most promising alternative to avoid the drawbacks of autograft and allograft bone. Nevertheless, how to precisely control stem cell osteogenic differentiation has been a long-standing puzzle. Compared with biochemical cues, physicomechanical stimuli have been widely studied for their biosafety and stability. The mechanical properties of various biomaterials (polymers, bioceramics, metal and alloys) become the main source of physicomechanical stimuli. By altering the stiffness, viscoelasticity, and topography of materials, mechanical stimuli with different strengths transmit into precise signals that mediate osteogenic differentiation. In addition, externally mechanical forces also play a critical role in promoting osteogenesis, such as compression stress, tensile stress, fluid shear stress and vibration, etc. When exposed to mechanical forces, mesenchymal stem cells (MSCs) differentiate into osteogenic lineages by sensing mechanical stimuli through mechanical sensors, including integrin and focal adhesions (FAs), cytoskeleton, primary cilium, ions channels, gap junction, and activating osteogenic-related mechanotransduction pathways, such as yes associated proteins (YAP)/TAZ, MAPK, Rho-GTPases, Wnt/β-catenin, TGFβ superfamily, Notch signaling. This review summarizes various biomaterials that transmit mechanical signals, physicomechanical stimuli that directly regulate MSCs differentiation, and the mechanical transduction mechanisms of MSCs. This review provides a deep and broad understanding of mechanical transduction mechanisms and discusses the challenges that remained in clinical translocation as well as the outlook for the future improvements.

Human disease models in drug development

Biomedical research is undergoing a paradigm shift towards approaches centred on human disease models owing to the notoriously high failure rates of the current drug development process. Major drivers for this transition are the limitations of animal models, which, despite remaining the gold standard in basic and preclinical research, suffer from interspecies differences and poor prediction of human physiological and pathological conditions. To bridge this translational gap, bioengineered human disease models with high clinical mimicry are being developed. In this Review, we discuss preclinical and clinical studies that benefited from these models, focusing on organoids, bioengineered tissue models and organs-on-chips. Furthermore, we provide a high-level design framework to facilitate clinical translation and accelerate drug development using bioengineered human disease models.

Programmable Tissue Folding Patterns in Structured Hydrogels

Folding of mucosal tissues, such as the tissue within the epithelium of the upper respiratory airways, is critical for organ function. Studying the influence of folded tissue patterns on cellular function is challenging mainly due to the lack of suitable cell culture platforms that can recreate dynamic tissue folding in vitro. Here, a bilayer hydrogel folding system, composed of alginate/polyacrylamide double-network (DN) and hyaluronic acid (HA) hydrogels, to generate static folding patterns based on mechanical instabilities, is described. By encapsulating human fibroblasts into patterned HA hydrogels, human bronchial epithelial cells form a folded pseudostratified monolayer. Using magnetic microparticles, DN hydrogels reversibly fold into pre-defined patterns and enable programmable on-demand folding of cell-laden hydrogel systems upon applying a magnetic field. This hydrogel construction provides a dynamic culture system for mimicking tissue folding in vitro, which is extendable to other cell types and organ systems.

Emergent collective organization of bone cells in complex curvature fields

Individual cells and multicellular systems respond to cell-scale curvatures in their environments, guiding migration, orientation, and tissue formation. However, it remains largely unclear how cells collectively explore and pattern complex landscapes with curvature gradients across the Euclidean and non-Euclidean spectra. Here, we show that mathematically designed substrates with controlled curvature variations induce multicellular spatiotemporal organization of preosteoblasts. We quantify curvature-induced patterning and find that cells generally prefer regions with at least one negative principal curvature. However, we also show that the developing tissue can eventually cover unfavorably curved territories, can bridge large portions of the substrates, and is often characterized by collectively aligned stress fibers. We demonstrate that this is partly regulated by cellular contractility and extracellular matrix development, underscoring the mechanical nature of curvature guidance. Our findings offer a geometric perspective on cell-environment interactions that could be harnessed in tissue engineering and regenerative medicine applications.

Curvature in Biological Systems: Its Quantification, Emergence, and Implications across the Scales

Surface curvature both emerges from, and influences the behavior of, living objects at length scales ranging from cell membranes to single cells to tissues and organs. The relevance of surface curvature in biology is supported by numerous experimental and theoretical investigations in recent years. In this review, first, a brief introduction to the key ideas of surface curvature in the context of biological systems is given and the challenges that arise when measuring surface curvature are discussed. Giving an overview of the emergence of curvature in biological systems, its significance at different length scales becomes apparent. On the other hand, summarizing current findings also shows that both single cells and entire cell sheets, tissues or organisms respond to curvature by modulating their shape and their migration behavior. Finally, the interplay between the distribution of morphogens or micro-organisms and the emergence of curvature across length scales is addressed with examples demonstrating these key mechanistic principles of morphogenesis. Overall, this review highlights that curved interfaces are not merely a passive by-product of the chemical, biological, and mechanical processes but that curvature acts also as a signal that co-determines these processes.

Static and Dynamic: Evolving Biomaterial Mechanical Properties to Control Cellular Mechanotransduction

The extracellular matrix (ECM) is a highly dynamic system that constantly offers physical, biological, and chemical signals to embraced cells. Increasing evidence suggests that mechanical signals derived from the dynamic cellular microenvironment are essential controllers of cell behaviors. Conventional cell culture biomaterials, with static mechanical properties such as chemistry, topography, and stiffness, have offered a fundamental understanding of various vital biochemical and biophysical processes, such as cell adhesion, spreading, migration, growth, and differentiation. At present, novel biomaterials that can spatiotemporally impart biophysical cues to manipulate cell fate are emerging. The dynamic properties and adaptive traits of new materials endow them with the ability to adapt to cell requirements and enhance cell functions. In this review, an introductory overview of the key players essential to mechanobiology is provided. A biophysical perspective on the state-of-the-art manipulation techniques and novel materials in designing static and dynamic ECM-mimicking biomaterials is taken. In particular, different static and dynamic mechanical cues in regulating cellular mechanosensing and functions are compared. This review to benefit the development of engineering biomechanical systems regulating cell functions is expected.

Enhancement of acellular biomineralization, dental pulp stem cell migration, and differentiation by hybrid fibrin gelatin scaffolds

OBJECTIVE

The current in vitro study aims to evaluate cross-linked hydrogels with and without the addition of fibrin that could potentially be used in endodontic regeneration as a scaffold material.

METHODS

Synthesis of gelatin/fibrin scaffold, and performing nanoscale characterization using cryo-electron microscopy, dynamic rheology, and XRF for structure property relations; plating dental pulp stem cells and determining mineralization, migration, and differentiation using rt-PCR, XRF, and Raman spectroscopy.

RESULTS

Cryo electron imaging shows gelatin and fibrin, when gelled separately to form classical rectangular cross-linked networks, where the modulus scales inversely with the cube root of the mesh size. When gelled together, a network with a fundamentally different structure is formed, which has higher ductility and when placed as a scaffold in osteogenic media, produces twice the mineral content. Immunofluorescence, RT-PCR and Rahman Spectroscopy indicate that the hybrid gel enhances cell migration, induces odontogenic differentiation of dental pulp stem cells, and promotes formation of dentin.

SIGNIFICANCE

The mechanical properties of the hybrid gel scaffold enhance in-migration of stem cells and subsequent differentiation, which are critical for regenerative procedures. Under acellular conditions, placement of the hybrid gel enhances biomineralization, which would strengthen the root if used as a scaffold for endodontic regeneration. Our in vitro findings are consistent with previous in vivo studies which show improved mineralization when bleeding is induced into the canal, given that fibrin is a primary component in blood clotting. Therefore, insertion of the hybrid gelatin-fibrin scaffold could enable more reproducible and consistent outcomes if used for regenerative endodontic treatment (RET).

Curvature-dependent adhesion of vesicles

The morphology and motion behavior of a cell are highly influenced by its external biological, chemical, and physical stimuli, and geometric confinement. In this paper, it is revealed that the mean curvature of the substrate significantly influences the adhesion of vesicles. By employing the variational method and investigating the Helfrich free energy, the configuration of axisymmetric vesicles adhered to curved spherical substrates is obtained theoretically. Moreover, numerical simulations based on the finite element method are also carried out to investigate the adhesion of vesicles on curved substrates with complex shapes. It is found that for a fixed area of a vesicle, its total free energy depends mainly on the mean curvature of the adhesion region but is insensitive to the specific shape of the substrate, and the total free energy monotonically decreases with the increase in the mean curvature. In addition, possible biological significances of the curvature-dependent adhesion, such as the shape of the cell and antibiofouling, are discussed. This study may deepen our understanding of the underlying mechanisms of adhesion in cellular activities.

The Effect of Tortuosity on Permeability of Porous Scaffold

In designing porous scaffolds, permeability is essential to consider as a function of cell migration and bone tissue regeneration. Good permeability has been achieved by mimicking the complexity of natural cancellous bone. In this study, a porous scaffold was developed according to the morphological indices of cancellous bone (porosity, specific surface area, thickness, and tortuosity). The computational fluid dynamics method analyzes the fluid flow through the scaffold. The permeability values of natural cancellous bone and three types of scaffolds (cubic, octahedron pillar, and Schoen's gyroid) were compared. The results showed that the permeability of the Negative Schwarz Primitive (NSP) scaffold model was similar to that of natural cancellous bone, which was in the range of 2.0 × 10^-11 m² to 4.0 × 10^-10 m². In addition, it was observed that the tortuosity parameter significantly affected the scaffold's permeability and shear stress values. The tortuosity value of the NSP scaffold was in the range of 1.5-2.8. Therefore, tortuosity can be manipulated by changing the curvature of the surface scaffold radius to obtain a superior bone tissue engineering construction supporting cell migration and tissue regeneration. This parameter should be considered when making new scaffolds, such as our NSP. Such efforts will produce a scaffold architecturally and functionally close to the natural cancellous bone, as demonstrated in this study.

Review on Porous Scaffolds Generation Process: A Tissue Engineering Approach

Porous scaffolds have been widely explored for tissue regeneration and engineering in vitro three-dimensional models. In this review, a comprehensive literature analysis is conducted to identify the steps involved in their generation. The advantages and disadvantages of the available techniques are discussed, highlighting the importance of considering pore geometrical parameters such as curvature and size, and summarizing the requirements to generate the porous scaffold according to the desired application. This paper considers the available design tools, mathematical models, materials, fabrication techniques, cell seeding methodologies, assessment methods, and the status of pore scaffolds in clinical applications. This review compiles the relevant research in the field in the past years. The trends, challenges, and future research directions are discussed in the search for the generation of a porous scaffold with improved mechanical and biological properties that can be reproducible, viable for long-term studies, and closer to being used in the clinical field.

Bone regeneration strategies based on organelle homeostasis of mesenchymal stem cells

The organelle modulation has emerged as a crucial contributor to the organismal homeostasis. The mesenchymal stem cells (MSCs), with their putative functions in maintaining the regeneration ability of adult tissues, have been identified as a major driver to underlie skeletal health. Bone is a structural and endocrine organ, in which the organelle regulation on mesenchymal stem cells (MSCs) function has most been discovered recently. Furthermore, potential treatments to control bone regeneration are developing using organelle-targeted techniques based on manipulating MSCs osteogenesis. In this review, we summarize the most current understanding of organelle regulation on MSCs in bone homeostasis, and to outline mechanistic insights as well as organelle-targeted approaches for accelerated bone regeneration.

Mechanical properties of triply periodic minimal surface (TPMS) scaffolds: considering the influence of spatial angle and surface curvature

Triply periodic minimal surface (TPMS) has a promising application in the design of bone scaffolds due to its relevance in bone structure. Notably, the mechanical properties of TPMS scaffolds can be affected by many factors, including the spatial angle and surface curvature, which, however, remain to be discovered. This paper illustrates our study on the mechanical properties of tissue scaffolds consisting of TPMS structures (Primitive and I-WP) by considering the influence of spatial angle and surface curvature. Also, the development of a novel model representative of the mechanical properties of scaffolds based on the entropy weight fuzzy comprehensive evaluation method is also presented. For experimental investigation and validation, we employed the selective laser melting technology to manufacture scaffolds with varying structures from AlSi10Mg powder and then performed mechanical testing on the scaffolds. Our results show that for a given porosity, the Gaussian curvature of the stretched TPMS structures is more concentrated and have a higher elastic modulus and fatigue life. At the spatial angle θ = 27°, the shear modulus of the primitive unit reaches its largest value; the shear modulus of the I-WP unit is positively correlated with the spatial angle. Additionally, it is found that the comprehensive mechanical properties of TPMS structures can be significantly improved after changing the surface curvature. Taken together, the identified influence of spatial angle and surface curvature and the developed models of scaffold mechanical properties would be of significant advance and guidance for the design and development of bone scaffolds.

Recent advances in regenerative biomaterials

Nowadays, biomaterials have evolved from the inert supports or functional substitutes to the bioactive materials able to trigger or promote the regenerative potential of tissues. The interdisciplinary progress has broadened the definition of 'biomaterials', and a typical new insight is the concept of tissue induction biomaterials. The term 'regenerative biomaterials' and thus the contents of this article are relevant to yet beyond tissue induction biomaterials. This review summarizes the recent progress of medical materials including metals, ceramics, hydrogels, other polymers and bio-derived materials. As the application aspects are concerned, this article introduces regenerative biomaterials for bone and cartilage regeneration, cardiovascular repair, 3D bioprinting, wound healing and medical cosmetology. Cell-biomaterial interactions are highlighted. Since the global pandemic of coronavirus disease 2019, the review particularly mentions biomaterials for public health emergency. In the last section, perspectives are suggested: (i) creation of new materials is the source of innovation; (ii) modification of existing materials is an effective strategy for performance improvement; (iii) biomaterial degradation and tissue regeneration are required to be harmonious with each other; (iv) host responses can significantly influence the clinical outcomes; (v) the long-term outcomes should be paid more attention to; (vi) the noninvasive approaches for monitoring in vivo dynamic evolution are required to be developed; (vii) public health emergencies call for more research and development of biomaterials; and (viii) clinical translation needs to be pushed forward in a full-chain way. In the future, more new insights are expected to be shed into the brilliant field-regenerative biomaterials.

Micro-Topographies Induce Epigenetic Reprogramming and Quiescence in Human Mesenchymal Stem Cells

Biomaterials can control cell and nuclear morphology. Since the shape of the nucleus influences chromatin architecture, gene expression and cell identity, surface topography can control cell phenotype. This study provides fundamental insights into how surface topography influences nuclear morphology, histone modifications, and expression of histone-associated proteins through advanced histone mass spectrometry and microarray analysis. The authors find that nuclear confinement is associated with a loss of histone acetylation and nucleoli abundance, while pathway analysis reveals a substantial reduction in gene expression associated with chromosome organization. In light of previous observations where the authors found a decrease in proliferation and metabolism induced by micro-topographies, they connect these findings with a quiescent phenotype in mesenchymal stem cells, as further shown by a reduction of ribosomal proteins and the maintenance of multipotency on micro-topographies after long-term culture conditions. Also, this influence of micro-topographies on nuclear morphology and proliferation is reversible, as shown by a return of proliferation when re-cultured on a flat surface. The findings provide novel insights into how biophysical signaling influences the epigenetic landscape and subsequent cellular phenotype.

Scalable and high-throughput production of an injectable platelet-rich plasma (PRP)/cell-laden microcarrier/hydrogel composite system for hair follicle tissue engineering

Background

Tissue engineering of hair follicles (HFs) has enormous potential for hair loss treatment. However, certain challenges remain, including weakening of the dermal papilla cell (DPC) viability, proliferation, and HF inducibility, as well as the associated inefficient and tedious preparation process required to generate extracellular matrix (ECM)-mimicking substrates for biomolecules or cells. Herein, we utilized gelatin methacryloyl (GelMA) and chitosan hydrogels to prepare scalable, monodispersed, and diameter-controllable interpenetrating network GelMA/chitosan-microcarriers (IGMs) loaded with platelet-rich plasma (PRP) and seeded with DPCs, on a high-throughput microfluidic chip.

Results

The ECM-mimicking hydrogels used for IGMs exhibited surface nano-topography and high porosity. Mass production of IGMs with distinct and precise diameters was achieved by adjusting the oil and aqueous phase flow rate ratio. Moreover, IGMs exhibited appropriate swelling and sustained growth factor release to facilitate a relatively long hair growth phase. DPCs seeded on PRP-loaded IGMs exhibited good viability (> 90%), adhesion, spreading, and proliferative properties (1.2-fold greater than control group). Importantly, PRP-loaded IGMs presented a higher hair inducibility of DPCs in vitro compared to the control and IGMs group (p < 0.05). Furthermore, DPC/PRP-laden IGMs were effectively mixed with epidermal cell (EPC)-laden GelMA to form a PRP-loaded DPC/EPC co-cultured hydrogel system (DECHS), which was subcutaneously injected into the hypodermis of nude mice. The PRP-loaded DECHS generated significantly more HFs (~ 35 per site) and novel vessels (~ 12 per site) than the other groups (p < 0.05 for each).

Conclusion

Taken together, these results illustrate that, based on high-throughput microfluidics, we obtained scalable and controllable production of ECM-mimicking IGMs and DECHS, which simulate an effective micro- and macro-environment to promote DPC bioactivity and hair regeneration, thus representing a potential new strategy for HF tissue engineering.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01671-8.

Characterizing cell recruitment into isotropic and anisotropic biomaterials by quantification of spatial density gradients in vitro

The success of cell-free in situ tissue engineering approaches depends on an appropriate recruitment of autologous cells from neighboring tissues. This identifies cellular migration as a critical parameter for the pre-clinical characterization of biomaterials. Here, we present a new method to quantify both the extent and the spatial anisotropy of cell migration in vitro. For this purpose, a cell spheroid is used as a cell source to provide a high number of cells for cellular invasion and, at the same time, to guarantee a controlled and spatially localized contact to the material. Therefore, current limitations of assays based on 2D cell sources can be overcome. We tested the method on three biomaterials that are in clinical use for soft tissue augmentation in maxilla-facial surgery and a substrate used for 3D in vitro cell culture. The selected biomaterials were all collagen-derived, but differed in their internal architecture. The analysis of cellular isodensity profiles within the biomaterials allowed the identification of the extent and the preferential directions of migration, as well as their relation to the biomaterials and their specific pore morphologies. The higher cell density within the biomaterials resulting from the here-introduced cell spheroid assay compared to established 2D cell layer assays suggests a better representation of the in vivo situation. Consequently, the presented method is proposed to advance the pre-clinical evaluation of cell recruitment into biomaterials, possibly leading to an improved prediction of the regeneration outcome.

Myofibroblast transdifferentiation of keratocytes results in slower migration and lower sensitivity to mesoscale curvatures

Functional tissue repair after injury or disease is governed by the regenerative or fibrotic response by cells within the tissue. In the case of corneal damage, keratocytes are a key cell type that determine the outcome of the remodeling response by either adapting to a fibroblast or myofibroblast phenotype. Although a growing body of literature indicates that geometrical cues in the environment can influence Myo(fibroblast) phenotype, there is a lack of knowledge on whether and how differentiated keratocyte phenotype is affected by the curved tissue geometry in the cornea. To address this gap, in this study we characterized the phenotype of fibroblastic and transforming growth factor β (TGFβ)-induced myofibroblastic keratocytes and studied their migration behavior on curved culture substrates with varying curvatures. Immunofluorescence staining and quantification of cell morphological parameters showed that, generally, fibroblastic keratocytes were more likely to elongate, whereas myofibroblastic keratocytes expressed more pronounced α smooth muscle actin (α-SMA) and actin stress fibers as well as more mature focal adhesions. Interestingly, keratocyte adhesion on convex structures was weak and unstable, whereas they adhered normally on flat and concave structures. On concave cylinders, fibroblastic keratocytes migrated faster and with higher persistence along the longitudinal direction compared to myofibroblastic keratocytes. Moreover, this behavior became more pronounced on smaller cylinders (i.e., higher curvatures). Taken together, both keratocyte phenotypes can sense and respond to the sign and magnitude of substrate curvatures, however, myofibroblastic keratocytes exhibit weaker curvature sensing and slower migration on curved substrates compared to fibroblastic keratocytes. These findings provide fundamental insights into keratocyte phenotype after injury, but also exemplify the potential of tuning the physical cell environments in tissue engineering settings to steer towards a favorable regeneration response.

Metallic Scaffold with Micron-Scale Geometrical Cues Promotes Osteogenesis and Angiogenesis via the ROCK/Myosin/YAP Pathway

The advent of precision manufacturing has enabled the creation of pores in metallic scaffolds with feature size in the range of single microns. In orthopedic implants, pore geometries at the micron scale could regulate bone formation by stimulating osteogenic differentiation and the coupling of osteogenesis and angiogenesis. However, the biological response to pore geometry at the cellular level is not clear. As cells are sensitive to curvature of the pore boundary, this study aimed to investigate osteogenesis in high- vs low-curvature environments by utilizing computer numerical control laser cutting to generate triangular and circular precision manufactured micropores (PMpores). We fabricated PMpores on 100 μm-thick stainless-steel discs. Triangular PMpores had a 30° vertex angle and a 300 μm base, and circular PMpores had a 300 μm diameter. We found triangular PMpores significantly enhanced the elastic modulus, proliferation, migration, and osteogenic differentiation of MC3T3-E1 preosteoblasts through Yes-associated protein (YAP) nuclear translocation. Inhibition of Rho-associated kinase (ROCK) and Myosin II abolished YAP translocation in all pore types and controls. Inhibition of YAP transcriptional activity reduced the proliferation, pore closure, collagen secretion, alkaline phosphatase (ALP), and Alizarin Red staining in MC3T3-E1 cultures. In C166 vascular endothelial cells, PMpores increased the VEGFA mRNA expression even without an angiogenic differentiation medium and induced tubule formation and maintenance. In terms of osteogenesis-angiogenesis coupling, a conditioned medium from MC3T3-E1 cells in PMpores promoted the expression of angiogenic genes in C166 cells. A coculture with MC3T3-E1 induced tubule formation and maintenance in C166 cells and tubule alignment along the edges of pores. Together, curvature cues in micropores are important stimuli to regulate osteogenic differentiation and osteogenesis-angiogenesis coupling. This study uncovered key mechanotransduction signaling components activated by curvature differences in a metallic scaffold and contributed to the understanding of the interaction between orthopedic implants and cells.

Directing Multicellular Organization by Varying the Aspect Ratio of Soft Hydrogel Microwells

Multicellular organization with precise spatial definition is essential to various biological processes, including morphogenesis, development, and healing in vascular and other tissues. Gradients and patterns of chemoattractants are well-described guides of multicellular organization, but the influences of 3D geometry of soft hydrogels are less well defined. Here, the discovery of a new mode of endothelial cell self-organization guided by combinatorial effects of stiffness and geometry, independent of protein or chemical patterning, is described. Endothelial cells in 2 kPa microwells are found to be ≈30 times more likely to migrate to the edge to organize in ring-like patterns than in stiff 35 kPa microwells. This organization is independent of curvature and significantly more pronounced in 2 kPa microwells with aspect ratio (perimeter/depth) < 25. Physical factors of cells and substrates that drive this behavior are systematically investigated and a mathematical model that explains the organization by balancing the dynamic interaction between tangential cytoskeletal tension, cell-cell, and cell-substrate adhesion is presented. These findings demonstrate the importance of combinatorial effects of geometry and stiffness in complex cellular organization that can be leveraged to facilitate the engineering of bionics and integrated model organoid systems with customized nutrient vascular networks.

Heterogeneity of In Vitro Expanded Mesenchymal Stromal Cells and Strategies to Improve Their Therapeutic Actions

Beneficial properties of mesenchymal stromal cells (MSCs) have prompted their use in preclinical and clinical research. Accumulating evidence has been provided for the therapeutic effects of MSCs in several pathologies, including neurodegenerative diseases, myocardial infarction, skin problems, liver disorders and cancer, among others. Although MSCs are found in multiple tissues, the number of MSCs is low, making in vitro expansion a required step before MSC application. However, culture-expanded MSCs exhibit notable differences in terms of cell morphology, physiology and function, which decisively contribute to MSC heterogeneity. The changes induced in MSCs during in vitro expansion may account for the variability in the results obtained in different MSC-based therapy studies, including those using MSCs as living drug delivery systems. This review dissects the different changes that occur in culture-expanded MSCs and how these modifications alter their therapeutic properties after transplantation. Furthermore, we discuss the current strategies developed to improve the beneficial effects of MSCs for successful clinical implementation, as well as potential therapeutic alternatives.