Hyaluronic acid hydrogel for controlled self-renewal and differentiation of human embryonic stem cells

Biomaterial-based microstructures fabricated by two-photon polymerization microfabrication technology

Two-photon polymerization (TPP) microfabrication technology can freely prepare micro/nano structures with different morphologies and high accuracy for micro/nanophotonics, micro-electromechanical systems, microfluidics, tissue engineering and drug delivery.

Hyaluronic acid/PEGylated amphiphilic nanoparticles for pursuit of selective intracellular doxorubicin release

The mechanism of nanomedicine possessing anticancer and antimicrobial agents to combat microbes in tumor tissues to alleviate cancer-drugs resistance.

Smart injectable biogels based on hyaluronic acid bioconjugates finely substituted with poly(β-amino ester urethane) for cancer therapy

In situ-forming injectable biogels (IBGs) have been developed for the programmed delivery of potent chemotherapeutic drugs.

Modulating stiffness with photo-switchable supramolecular hydrogels

Supramolecular hyaluronic acid hydrogels formed via 2 : 1 homoternary complexes of coumarin and cucurbit[8]uril can reversibly toggle between physical and covalent states.

Lymphatic Tissue Engineering and Regeneration

The lymphatic system is a major circulatory system within the body, responsible for the transport of interstitial fluid, waste products, immune cells, and proteins. Compared to other physiological systems, the molecular mechanisms and underlying disease pathology largely remain to be understood which has hindered advancements in therapeutic options for lymphatic disorders. Dysfunction of the lymphatic system is associated with a wide range of disease phenotypes and has also been speculated as a route to rescue healthy phenotypes in areas including cardiovascular disease, metabolic syndrome, and neurological conditions. This review will discuss lymphatic system functions and structure, cell sources for regenerating lymphatic vessels, current approaches for engineering lymphatic vessels, and specific therapeutic areas that would benefit from advances in lymphatic tissue engineering and regeneration.

Stem cell niche: Dynamic neighbor of stem cells

Stem cell niche is a specialized and dynamic microenvironment around the stem cells which plays a critical role in maintaining the stemness properties of stem cells. Over the years, advancement in the research activity has revealed the various important aspects of stem cell niche including cell-cell interaction, cell-extracellular matrix interaction, a large number of soluble signaling factors and various biochemical and biophysical cues (such as oxygen tension, flow, and shear and pore size). Stem cells have the potential to be a powerful tool in regenerative medicine due to their self-renewal property and immense differentiation potential. Recent progresses in in vitro culture conditions of embryonic stem cells, adult stem cells and induced pluripotent stem cells have enabled the researchers to investigate and understand the role of the microenvironment in stem cell properties. The engineered artificial stem cell niche has led to a better execution of stem cells in regenerative medicine. Here we elucidate the key components of stem cell niche and their role in niche engineering and stem cell therapeutics.

Differential Effects of Heparin and Hyaluronic Acid on Neural Patterning of Human Induced Pluripotent Stem Cells

A lack of well-established animal models that can efficiently represent human brain pathology has led to the development of human induced pluripotent stem cell (hiPSC)-derived brain tissues. Brain organoids have enhanced our ability to understand the developing human brain and brain disorders (e.g., Schizophrenia, microcephaly), but the organoids still do not accurately recapitulate the anatomical organization of the human brain. Therefore, it is important to evaluate and optimize induction and signaling factors in order to engineer the next generation of brain organoids. In this study, the impact of hyaluronic acid (HA), a major brain extracellular matrix (ECM) component that interacts with cells through ligand-binding receptors, on the patterning of brain organoids from hiPSCs was evaluated. To mediate HA- binding capacity of signaling molecules, heparin was added in addition to HA or conjugated to HA to form hydrogels (with two different moduli). The neural cortical spheroids derived from hiPSCs were treated with either HA or heparin plus HA (Hep- HA) and were analyzed for ECM impacts on neural patterning. The results indicate that Hep-HA has a caudalizing effect on hiPSC-derived neural spheroids, in particular for stiff Hep-HA hydrogels. Wnt and Hippo/Yes-associated protein (YAP) signaling was modulated (using Wnt inhibitor IWP4 or actin disruption agent Cytochalasin D respectively) to understand the underlying mechanism. IWP4 and cytochalasin D promote forebrain identity. The results from this study should enhance the understanding of influence of biomimetic ECM factors for brain organoid generation.

Programming Niche Accessibility and In Vitro Stemness with Intercellular DNA Reactions

Stem cells generally exist in low abundance and tend to lose stemness in the absence of self-renewal signals. While extracellular-matrix-mimicking techniques have been developed to support stem cell proliferation, the lack of niche cells in these synthetic systems often hampers continuous stem cell expansion and maintenance of pluripotency, which are indispensable for regenerative medicine. Here, an intercellular DNA-reaction-programmed ESPN (expansion of stem cells with pairing niches) strategy is developed for 3D culture of mammary stem cells (MaSCs). Boolean logic operations are implemented to confer DNA-programmed mechanical signaling and genetically engineered morphogen signaling by niche cells, resulting in sustained expansion of MaSCs in vitro. The creation of stem cell niches improves the proliferation of pluripotent cells by four times during one-week culture. This method thus provides a novel approach for logical regulation of stemness and proliferation of stem cells for biomedicine.

Tissue and organ decellularization in regenerative medicine

The advancement and improvement in decellularization methods can be attributed to the increasing demand for tissues and organs for transplantation. Decellularized tissues and organs, which are free of cells and genetic materials while retaining the complex ultrastructure of the extracellular matrix (ECM), can serve as scaffolds to subsequently embed cells for transplantation. They have the potential to mimic the native physiology of the targeted anatomic site. ECM from different tissues and organs harvested from various sources have been applied. Many techniques are currently involved in the decellularization process, which come along with their own advantages and disadvantages. This review focuses on recent developments in decellularization methods, the importance and nature of detergents used for decellularization, as well as on the role of the ECM either as merely a physical support or as a scaffold in retaining and providing cues for cell survival, differentiation and homeostasis. In addition, application, status, and perspectives on commercialization of bioproducts derived from decellularized tissues and organs are addressed. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1494-1505, 2018.

Bi-directional cell-pericellular matrix interactions direct stem cell fate

Modifiable hydrogels have revealed tremendous insight into how physical characteristics of cells' 3D environment drive stem cell lineage specification. However, in native tissues, cells do not passively receive signals from their niche. Instead they actively probe and modify their pericellular space to suit their needs, yet the dynamics of cells' reciprocal interactions with their pericellular environment when encapsulated within hydrogels remains relatively unexplored. Here, we show that human bone marrow stromal cells (hMSC) encapsulated within hyaluronic acid-based hydrogels modify their surroundings by synthesizing, secreting and arranging proteins pericellularly or by degrading the hydrogel. hMSC's interactions with this local environment have a role in regulating hMSC fate, with a secreted proteinaceous pericellular matrix associated with adipogenesis, and degradation with osteogenesis. Our observations suggest that hMSC participate in a bi-directional interplay between the properties of their 3D milieu and their own secreted pericellular matrix, and that this combination of interactions drives fate.

Cartilage regeneration using arthroscopic flushing fluid-derived mesenchymal stem cells encapsulated in a one-step rapid cross-linked hydrogel

Many attempts have been made to repair articular cartilage defects, including mesenchymal stem cell (MSC)-based tissue engineering strategies. Although this approach shows promise, optimizing MSC sources and their delivery is challenging. This study was designed to test the feasibility of using MSCs found in the human arthroscopic flushing fluid (AFF) for cartilage regeneration, by incorporating them into a newly developed one-step rapid cross-linking hyper-branched polyPEGDA/HA hydrogel. AFF-MSCs were isolated from the original intra-articular flushing fluid of 10 patients prior to arthroscopic procedures. The hydrogel was fabricated with hyper-branched polyPEGDA and thiolated hyaluronic acid (HA). In vitro assays demonstrated that AFF-MSCs possessed the typical MSC morphology and phenotype, and maintained chondrogenic differentiation properties when encapsulated within the hydrogel. The AFF-MSC/hydrogel composite could significantly repair full-thickness cartilage defects generated in a rat model after 8 weeks of implantation; smooth cartilage was formed with evidence of hyaline cartilage formation. These data suggest that human AFF-MSCs are a novel and abundant MSC source that have high therapeutic value for cartilage regeneration.

STATEMENT OF SIGNIFICANCE

Many attempts have been made to repair the defects of articular cartilage, including mesenchymal stem cell (MSC)-based tissue engineering strategies. Optimizing MSC sources and their delivery approaches still remain clinically challenging. Recent studies determined that MSCs derived from synovium and synovial fluid exhibited superior chondrogenic potential. However, no feasible methods to harvest these human tissues and cells have been impeding them for clinical application. Hereby, we explored a simple and easy accessible approach to obtain a new stem cell source from arthroscopic flushing fluid (AFF-MSCs), which probably contains plenty of MSCs from synovium and synovial fluid. Further experiments demonstrated that encapsulation of these stem cells with one-step rapid cross-linked polyPEGDA/HA hydrogel held very encouraging potential for cartilage regeneration.

Acceleration of Diabetic Wound Regeneration using an In Situ-Formed Stem-Cell-Based Skin Substitute

Chronic diabetic ulcers are a common complication in patients with diabetes, often leading to lower limb amputations and even mortality. Stem cells have shown promise in promoting cutaneous wound healing by modulating inflammation, angiogenesis, and re-epithelialization. However, more effective delivery and engraftment strategies are needed to prolong transplanted stem cell lifespan and their pro-healing functions in a chronic wound environment to improve skin regeneration. In this study, an injectable poly(ethylene glycol) (PEG)-gelatin-based hydrogel system is examined to create a functional stem cell niche for the delivery of adipose-derived stem cells (ASCs) into diabetic wounds. Human ASCs are encapsulated into the in situ crosslinked hydrogels and cultured in a 3D topography. The encapsulated cells are well attached and spread inside the hydrogels, retaining viability, proliferation, and metabolic activity up to three weeks in vitro. Allogeneic ASCs are delivered to diabetic wounds by this hydrogel vehicle. It is found that stem cell retention is significantly improved in vivo with vehicle-mediated delivery. The ASC-hydrogel-based treatment decreases inflammatory cell infiltration, enhances neovascularization, and remarkably accelerates wound closure in diabetic mice. Together, these findings suggest this conveniently-applicable ASC-hydrogel-based skin substitute provides a promising potential for the treatment of chronic diabetic wounds.

Targeting Breast Cancer Stem Cells to Overcome Treatment Resistance

Despite advances in breast cancer diagnosis and treatment, many patients still fail therapy, resulting in disease progression, recurrence, and reduced overall survival. Historically, much focus has been put on the intrinsic subtyping based in the presence (or absence) of classical immunohistochemistry (IHC) markers such as estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-related protein (HER2). However, it is widely understood that tumors are composed of heterogeneous populations of cells with a hierarchical organization driven by cancer stem cells (CSCs). In breast tumors, this small population of cells displaying stem cell properties is known as breast CSCs (BCSCs). This rare population exhibit a CD44⁺/CD24-/low phenotype with high ALDH activity (ALDH⁺), and possesses higher tolerability to chemotherapy, hormone therapy, and radiotherapy and is able to reproduce the bulk of the tumor after reduction of cell populations sensitive to first-line therapy leading to disease relapse. In this review, we present special attention to BCSCs with future directions in the establishment of a therapy targeting this population. Drugs targeting the main BCSCs signaling pathways undergoing clinical trials are also summarized.

Near-physiological microenvironment simulation on chip to evaluate drug resistance of different loci in tumour mass

Developing a bio-functional model in vitro to study cancer resistance, which is a big challenge for clinical cancer therapy, is of great interest. Such reliable model requires appropriate drug diffusion kinetics simulation and a microenvironment that allows cell-cell and cell-matrix interactions. In this work, a special hydrogel-based three-dimensional (3D) microfluidic chip was constructed to simulate tumour-vascular microenvironment. The self-healing hydrogel supports long-time cell survival and proliferation, effective cellular metabolism of cancer drugs and cell-cell interaction between different types of cells. In the effective near-physiological tumour-vascular microenvironment, the endothelial and fibroblast cells are spread on different sides of a porous membrane, while sensitive and resistant breast tumour cells are separately cultured in the dynamic hydrogel consisting of glycol chitosan and telechelic difunctional poly (ethylene glycol) in the upper chambers. Nutrients and drugs are introduced through the bottom channel and diffuse into the cancer cells. Doxorubicin molecules pass first through blood vessel endothelial cells and act on the tumour cells surrounded by fibroblasts. Tumour cells respond differently to drug when they are cultured in the microenvironment. Sensitive breast tumour cells have a 47% increase in viability than those cultured without fibroblasts and endothelial cells. Both sensitive and resistant tumour cells can be analysed under the same chemical environment. This work represents a multi-functional in vitro platform that allows near-physiological simulation, effective drug metabolism and cellular response to extracellular stimuli and has great potential to make drug discovery speedy and precise.

Hemostatic properties of in situ gels composed of hydrophobically modified biopolymers

Hemorrhaging often occurs during cardiac surgery, and postoperative bleeding is associated with medical complications or even death. Medical complications resulting from hemorrhaging can lead to longer hospital stays, thus increasing costs. Hemostatic agents are the main treatment for bleeding. In the present study, hemostatic agents composed of aldehyde groups and hydrophobically modified with hyaluronic acid (ald-hm-HyA) and hydrophobically modified gelatin (hm-ApGltn) were developed and their hemostatic effects were evaluated. These modified hemostatic agents formed more stable blood clots compared with the nonhydrophobically modified HyA-based hemostatic agent. The bulk strength of the whole blood clot using the aldehyde and stearoyl group-modified hyaluronic acid (ald-C18-HyA)/hm-ApGltn-based hemostatic agent was higher than that of the aldehyde group only modified HyA (ald-HyA)/hm-ApGltn-based hemostatic agent. Rheological experiments using α-cyclodextrin showed that hydrophobic modification of HyA with C18 groups effectively enhanced anchoring to the red blood cell surface. Therefore, the ald-hm-HyA/hm-ApGltn-based hemostatic agent has potential applications in cardiac surgery.

Recent Advances in Engineering the Stem Cell Microniche in 3D

Conventional 2D cell culture techniques have provided fundamental insights into key biochemical and biophysical mechanisms responsible for various cellular behaviors, such as cell adhesion, spreading, division, proliferation, and differentiation. However, 2D culture in vitro does not fully capture the physical and chemical properties of the native microenvironment. There is a growing body of research that suggests that cells cultured on 2D substrates differ greatly from those grown in vivo. This article focuses on recent progress in using bioinspired 3D matrices that recapitulate as many aspects of the natural extracellular matrix as possible. A range of techniques for the engineering of 3D microenvironment with precisely controlled biophysical and chemical properties, and the impact of these environments on cellular behavior, is reviewed. Finally, an outlook on future challenges for engineering the 3D microenvironment and how such approaches would further our understanding of the influence of the microenvironment on cell function is provided.

Zero-dimensional, one-dimensional, two-dimensional and three-dimensional biomaterials for cell fate regulation

The interaction of biological cells with artificial biomaterials is one of the most important issues in tissue engineering and regenerative medicine. The interaction is strongly governed by physical and chemical properties of the materials and displayed with differentiated cellular behaviors, including cell self-renewal, differentiation, reprogramming, dedifferentiation, or transdifferentiation as a result. A number of engineered biomaterials with micro- or nano-structures have been developed to mimic structural components of cell niche and specific function of extra cellular matrix (ECM) over past two decades. In this review article, we briefly introduce the fabrication of biomaterials and their classification into zero-dimensional (0D), one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) ones. More importantly, the influence of different biomaterials on inducing cell self-renewal, differentiation, reprogramming, dedifferentiation, and transdifferentiation was discussed based on the progress at 0D, 1D, 2D and 3D levels, following which the current research limitations and research perspectives were provided.

Engineering Hydrogel Microenvironments to Recapitulate the Stem Cell Niche

Stem cells are a powerful resource for many applications including regenerative medicine, patient-specific disease modeling, and toxicology screening. However, eliciting the desired behavior from stem cells, such as expansion in a naïve state or differentiation into a particular mature lineage, remains challenging. Drawing inspiration from the native stem cell niche, hydrogel platforms have been developed to regulate stem cell fate by controlling microenvironmental parameters including matrix mechanics, degradability, cell-adhesive ligand presentation, local microstructure, and cell-cell interactions. We survey techniques for modulating hydrogel properties and review the effects of microenvironmental parameters on maintaining stemness and controlling differentiation for a variety of stem cell types. Looking forward, we envision future hydrogel designs spanning a spectrum of complexity, ranging from simple, fully defined materials for industrial expansion of stem cells to complex, biomimetic systems for organotypic cell culture models.

Designing well-defined photopolymerized synthetic matrices for three-dimensional culture and differentiation of induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are of interest for the study of disease, where these cells can be derived from patients and have the potential to be differentiated into any cell type; however, three-dimensional (3D) culture and differentiation of iPSCs within well-defined synthetic matrices for these applications remains limited. Here, we aimed to establish synthetic cell-degradable hydrogels that allow precise presentation of specific biochemical cues for 3D culture of iPSCs with relevance for hypothesis testing and lineage-specific differentiation. We synthesized poly(ethylene glycol)-(PEG)-peptide-based hydrogels by photoinitiated step growth polymerization and used them to test the hypothesis that the viability of iPSCs within these matrices could be rescued with appropriate biochemical cues inspired by proteins and integrins important for iPSC culture on Matrigel. Specifically, we selected a range of motifs inspired by iPSC binding to Matrigel, including laminin-derived IKVAV and YIGSR, α5β1-binding PHSRNG10RGDS, αvβ5-binding KKQRFRHRNRKG, and RGDS that is known to bind a variety of integrins for generally promoting cell adhesion. YIGSR and PHSRNG10RGDS resulted in the highest iPSC viability, where binding of β1 integrin was key, and these permissive compositions also allowed iPSC differentiation into neural progenitor cells (NPCs) (decreased oct4 expression and increased pax6 expression) in response to soluble factors. The resulting NPCs formed clusters of different sizes in response to each peptide, suggesting that matrix biochemical cues affect iPSC proliferation and clustering in 3D culture. In summary, we have established photopolymerizable synthetic matrices for the encapsulation, culture, and differentiation of iPSCs for studies of cell-matrix interactions and deployment in disease models.

hPSC-Derived Striatal Cells Generated Using a Scalable 3D Hydrogel Promote Recovery in a Huntington Disease Mouse Model

Huntington disease (HD) is an inherited, progressive neurological disorder characterized by degenerating striatal medium spiny neurons (MSNs). One promising approach for treating HD is cell replacement therapy, where lost cells are replaced by MSN progenitors derived from human pluripotent stem cells (hPSCs). While there has been remarkable progress in generating hPSC-derived MSNs, current production methods rely on two-dimensional culture systems that can include poorly defined components, limit scalability, and yield differing preclinical results. To facilitate clinical translation, here, we generated striatal progenitors from hPSCs within a fully defined and scalable PNIPAAm-PEG three-dimensional (3D) hydrogel. Transplantation of 3D-derived striatal progenitors into a transgenic mouse model of HD slowed disease progression, improved motor coordination, and increased survival. In addition, the transplanted cells developed an MSN-like phenotype and formed synaptic connections with host cells. Our results illustrate the potential of scalable 3D biomaterials for generating striatal progenitors for HD cell therapy.

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3D-generated striatal cells rapidly achieve functional maturity

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Transplanted cells delayed disease onset and alleviated symptoms in HD mice

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Transplanted striatal cells increased lifespan in HD mice

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HTT aggregates were observed in striatal cells transplanted into HD mice

Polyisocyanopeptide hydrogels: A novel thermo-responsive hydrogel supporting pre-vascularization and the development of organotypic structures

Molecular and mechanical interactions with the 3D extracellular matrix are essential for cell functions such as survival, proliferation, migration, and differentiation. Thermo-responsive biomimetic polyisocyanopeptide (PIC) hydrogels are promising new candidates for 3D cell, tissue, and organ cultures. This is a synthetic, thermo-responsive and stress-stiffening material synthesized via polymerization of the corresponding monomers using a nickel perchlorate as a catalyst. It can be tailored to meet various demands of cells by modulating its stiffness and through the decoration of the polymer with short GRGDS peptides using copper free click chemistry. These peptides make the hydrogels biocompatible by mimicking the binding sites of certain integrins. This study focuses on the optimization of the PIC polymer properties for efficient cell, tissue and organ development. Screening for the optimal stiffness of the hydrogel and the ideal concentration of the GRGDS ligand conjugated with the polymer, enabled cell proliferation, migration and differentiation of various primary cell types of human origin. We demonstrate that fibroblasts, endothelial cells, adipose-derived stem cells and melanoma cells, do survive, thrive and differentiate in optimized PIC hydrogels. Importantly, these hydrogels support the spontaneous formation of complex structures like blood capillaries in vitro. Additionally, we utilized the thermo-responsive properties of the hydrogels for a rapid and gentle recovery of viable cells. Finally, we show that organotypic structures of human origin grown in PIC hydrogels can be successfully transplanted subcutaneously onto immune-compromised rats, on which they survive and integrate into the surrounding tissue.

STATEMENT OF SIGNIFICANCE

Molecular and mechanical interactions with the surrounding environment are essential for cell functions. Although 2D culture systems greatly contributed to our understanding of complex biological phenomena, they cannot substitute for crucial interaction that take place in 3D. 3D culture systems aim to overcome limitations of the 2D cultures and answer new questions about cell functions. Thermo-responsive biomimetic polyisocyanopeptide (PIC) hydrogels are promising new candidates for 3D cell, tissue, and organ cultures. They are synthetic and can be tailor to meet certain experimental demands. Additionally, they are characterized by strain-stiffening, a feature crucial for cell behaviour, but rare in hydrogels. Their thermos-responsive properties enable quick recovery of the cells by a simple procedure of lowering the temperature.

Scalable and physiologically relevant microenvironments for human pluripotent stem cell expansion and differentiation

Human pluripotent stem cells (hPSCs) are required in large numbers for various biomedical applications. However, the scalable and cost-effective culturing of high quality hPSCs and their derivatives remains very challenging. Here, we report a novel and physiologically relevant 3D culture system (called the AlgTube cell culture system) for hPSC expansion and differentiation. With this system, cells are processed into and cultured in microscale alginate hydrogel tubes that are suspended in the cell culture medium in a culture vessel. The hydrogel tubes protect cells from hydrodynamic stresses in the culture vessel and limit the cell mass smaller than 400 μm in diameter to ensure efficient mass transport, creating cell-friendly microenvironments for growing cells. This system is simple, scalable, highly efficient, defined and compatible with the current good manufacturing practices. Under optimized culture conditions, the AlgTubes enabled long-term culture of hPSCs (>10 passages, >50 days) with high cell viability, high growth rate (1000-fold expansion over 10 days per passage), high purity (>95% Oct4+) and high yield (5.0 × 10⁸ cells ml^-1), all of which offer considerable advantages compared to current approaches. Moreover, the AlgTubes enabled directed differentiation of hPSCs into various tissue cells. This system can be readily scaled to support research from basic biological study to clinical development and the future industry-scale production.

Hyaluronan size alters chondrogenesis of adipose-derived stem cells via the CD44/ERK/SOX-9 pathway

Hyaluronan (HA) is a natural linear polymer that is one of the main types of extracellular matrix during the early stage of chondrogenesis. We found that the chondrogenesis of adipose-derived stem cells (ADSCs) can be initiated and promoted by the application of HA to mimic the chondrogenic niche. The aim of this study is to investigate the optimal HA molecular weight (Mw) for chondrogenesis of ADSCs and the detailed mechanism. In this study, we investigated the relationships among HA Mw, CD44 clustering, and the extracellular signal-regulated kinase (ERK)/SOX-9 pathway during chondrogenesis of ADSCs. Human ADSCs (hADSCs) and rabbit ADSCs (rADSCs) were isolated and expanded. Chondrogenesis was induced in rADSCs by culturing cells in HA-coated wells (HA Mw: 80 kDa, 600 kDa and 2000 kDa) and evaluated by examining cell aggregation, chondrogenic gene expression (collagen type II and aggrecan) and sulfated glycosaminoglycan (sGAG) deposition in vitro. Cartilaginous tissue formation in vivo was confirmed by implanting HA/rADSCs into joint cavities. CD44 clustering, ERK phosphorylation, SOX-9 expression and SOX-9 phosphorylation in cultured hADSCs were further evaluated. Isolated and expanded rADSCs showed multilineage potential and anchorage-independent growth properties. Cell aggregation, chondrogenic gene expression, and sGAG deposition increased with increasing HA Mw in rADSCs. The 2000 kDa HA had the most pronounced chondrogenic effect on rADSCs in vitro, and implanted 2000 kDa HA/rADSCs exhibited marked cartilaginous tissue formation in vivo. CD44 clustering and cell aggregation of hADSCs were enhanced by an increase in HA Mw. In addition, higher HA Mws further enhanced CD44 clustering, ERK phosphorylation, and SOX-9 expression and phosphorylation in hADSCs. Inhibiting CD44 clustering in hADSCs reduced HA-induced chondrogenic gene expression. Inhibiting ERK phosphorylation also simultaneously attenuated HA-induced SOX-9 expression and phosphorylation and chondrogenic gene expression in hADSCs. Our results indicate that HA initiates ADSC chondrogenesis and that higher Mw HAs exhibit stronger effects, with 2000 kDa HA having the strongest effect. These effects may be mediated through increased CD44 clustering and the ERK/SOX-9 signaling pathway.

STATEMENT OF SIGNIFICANCE

HA-based biomaterials have been studied in stem cell-based articular cartilage tissue engineering. However, little is known about the optimal HA size for stem cell chondrogenesis and the mechanism of how HA size modulates stem cell chondrogenesis. Accordingly, we used HAs with various Mws (80-2000 kDa) as culture substrates and tested their chondrogenic effect on ADSCs. Our results demonstrated that HAs with a Mw of 2000 kDa showed the optimal effect for chondrogenesis of ADSCs. Moreover, we found that HA size can regulate ADSC chondrogenesis via the CD44/ERK/SOX-9 pathway. This finding provides new information regarding the biochemical control of chondrogenesis by HA substrates that may add value to the development of HA-based biomaterials for articular cartilage regeneration.

Bacterial adaptability of enzyme and pH dual-responsive surface for infection resistance

A major challenge in antibacterial surface preparation is the elaborated implement of controlled antibacterial agent delivery on demand. We present a bacterial hyaluronidase (HAase) and pH dual-responsive antimicrobial surface, with excellent biocompatibility under physiological conditions and releasing vancomycin (Van) once bacteria invade.

Zwitterionic starch-based hydrogel for the expansion and "stemness" maintenance of brown adipose derived stem cells

Brown adipose derived stem cells (BADSCs) have become a promising stem cell treatment candidate for myocardial infarction because of their efficiently spontaneous differentiation capacity towards cardiomyocytes. The lack of existing cell passage protocols motivates us to develop a neotype 3D cell expansion technique for BADSCs. In this study, "clickable" zwitterionic starch based hydrogels are developed using methacrylate modified sulfobetaine derived starch with dithiol-functionalized poly (ethylene glycol) as crosslinker via the "thiol-ene" Michael addition reaction. Moreover, CGRGDS peptide is immobilized into the hydrogel via a similar "clickable" approach. Their Young's moduli range from 22.28 to 74.81 kPa depending on the concentration of precursor solutions. Excellent anti-fouling property is also presented owing to the introduction of zwitterionic moieties. BADSCs are homogeneously encapsulated in the hydrogels and then routinely cultured for 10 days. Results suggest a capacious cell proliferation and the extent increases with either the decrease of mechanical strength or the introduction of CGRGDS. More excitingly, the cell "stemness" is well maintained during this period and the expanded cells released from the hydrogels well keep the efficiently spontaneous cardiomyogenic differentiation capacity. Therefore, it is suggested that zwitterionic starch based hydrogel is able for the expansion and "stemness " maintenance of BADSCs.

Maintenance of neural progenitor cell stemness in 3D hydrogels requires matrix remodelling

Neural progenitor cell (NPC) culture within three-dimensional (3D) hydrogels is an attractive strategy for expanding a therapeutically relevant number of stem cells. However, relatively little is known about how 3D material properties such as stiffness and degradability affect the maintenance of NPC stemness in the absence of differentiation factors. Over a physiologically relevant range of stiffness from ∼0.5 to 50 kPa, stemness maintenance did not correlate with initial hydrogel stiffness. In contrast, hydrogel degradation was both correlated with, and necessary for, maintenance of NPC stemness. This requirement for degradation was independent of cytoskeletal tension generation and presentation of engineered adhesive ligands, instead relying on matrix remodelling to facilitate cadherin-mediated cell-cell contact and promote β-catenin signalling. In two additional hydrogel systems, permitting NPC-mediated matrix remodelling proved to be a generalizable strategy for stemness maintenance in 3D. Our findings have identified matrix remodelling, in the absence of cytoskeletal tension generation, as a previously unknown strategy to maintain stemness in 3D.

Engineering Concepts in Stem Cell Research

The field of regenerative medicine integrates advancements made in stem cells, molecular biology, engineering, and clinical methodologies. Stem cells serve as a fundamental ingredient for therapeutic application in regenerative medicine. Apart from stem cells, engineering concepts have equally contributed to the success of stem cell based applications in improving human health. The purpose of various engineering methodologies is to develop regenerative and preventive medicine to combat various diseases and deformities. Explosion of stem cell discoveries and their implementation in clinical setting warrants new engineering concepts and new biomaterials. Biomaterials, microfluidics, and nanotechnology are the major engineering concepts used for the implementation of stem cells in regenerative medicine. Many of these engineering technologies target the specific niche of the cell for better functional capability. Controlling the niche is the key for various developmental activities leading to organogenesis and tissue homeostasis. Biomimetic understanding not only helped to improve the design of the matrices or scaffolds by incorporating suitable biological and physical components, but also ultimately aided adoption of designs that helped these materials/devices have better function. Adoption of engineering concepts in stem cell research improved overall achievement, however, several important issues such as long-term effects with respect to systems biology needs to be addressed. Here, in this review the authors will highlight some interesting breakthroughs in stem cell biology that use engineering methodologies.

3D neural tissue models: From spheroids to bioprinting

Three-dimensional (3D) in vitro neural tissue models provide a better recapitulation of in vivo cell-cell and cell-extracellular matrix interactions than conventional two-dimensional (2D) cultures. Therefore, the former is believed to have great potential for both mechanistic and translational studies. In this paper, we review the recent developments in 3D in vitro neural tissue models, with a particular focus on the emerging bioprinted tissue structures. We draw on specific examples to describe the merits and limitations of each model, in terms of different applications. Bioprinting offers a revolutionary approach for constructing repeatable and controllable 3D in vitro neural tissues with diverse cell types, complex microscale features and tissue level responses. Further advances in bioprinting research would likely consolidate existing models and generate complex neural tissue structures bearing higher fidelity, which is ultimately useful for probing disease-specific mechanisms, facilitating development of novel therapeutics and promoting neural regeneration.

Injectable silk fibroin hydrogels functionalized with microspheres as adult stem cells-carrier systems

Hydrogels are good candidate materials for cell delivery scaffolds because they can mimic the physical, chemical, electrical and biological properties of most of the native tissues. In this study, composite biosynthetic hydrogels were produced by combining the bio-functionality of silk fibroin (SF) with the structural versatility of polyethylene-glycol-diacrylated (PEGDa). The formation of a photopolymerizable PEGDa-SF hydrogel (PSFHy) was optimized for 3D-cell culture. Functionalization of the 3D-PSFHy with protein microspheres (MS) was required to increase the porosity and cell-adhesive properties of the material. Cardiac mesenchymal stem cells, which were cultured within the MS-embedding PSFHy, exhibited good viability and expression of proteins that are characteristic of the initial phases of the cardiac muscle differentiation process. Further, the addition of chondroitin sulfate into the scaffolds improved the cell viability. A cell-preconditioning of the scaffold was also performed, suggesting a potential application of these sponge-like scaffolds for analysing the effects of several extracellular microenvironments, produced by different kinds of cells, on the stem cells fate. The results presented herein highlight on the possibility to use the PSFHys functionalized with MS as stem cell-carrier systems with sponge-like properties, potential ultrasound-imaging contrast agents and controlled biochemical factor delivery.

Independently Tuning the Biochemical and Mechanical Properties of 3D Hyaluronan-Based Hydrogels with Oxime and Diels-Alder Chemistry to Culture Breast Cancer Spheroids

For native breast cancer cell growth to be mimicked in vitro as spheroids, a well-defined matrix that mimics the tumor microenvironment is required. Finding a biomimetic material for 3D cell culture other than Matrigel has challenged the field. Because hyaluronan is naturally abundant in the tumor microenvironment and can be chemically modified, we synthesized a hyaluronan (HA) hydrogel with independently tunable mechanical and chemical properties for 3D culture of breast cancer cells. By modifying HA with distinct bioorthogonal functional groups, its mechanical properties are controlled by chemical cross-linking via oxime ligation, and its biochemical properties are controlled by grafting bioactive peptides via Diels-Alder chemistry. A series of hydrogels were screened in terms of stiffness and peptide composition for cancer spheroid formation. In the optimal hydrogel formulation, the 3D breast cancer spheroids showed decreased drug diffusion into their core and upregulation of cellular multidrug-resistant efflux pumps similar to what is observed in drug-resistant tumors. Our results highlight the potential of these tunable and well-defined gels in drug screening assays.

Cardiosphere-Derived Cells Demonstrate Metabolic Flexibility That Is Influenced by Adhesion Status

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Cell adhesion status regulates energy metabolism in adult stem cells

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Adherent adult stem cells (CDCs, MSCs, ASCs) utilize glycolysis to generate majority (70% to 85%) of their cellular ATP needs

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Akt phosphorylation transduces adhesion-mediated regulation of energy metabolism by regulating membrane translocation of glucose transporters (GLUT1) and thus, cellular glucose uptake and glycolysis

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Cell dissociation/suspension leads to Akt de-phosphorylation, >3-fold reduction in the number of cell surface GLUT1 receptors, downregulation of cellular glucose uptake, glycolysis, cellular ATP levels, and loss of cell viability

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Encapsulation of dissociated cells in hydrogels that provide cell adhesion motifs, promotes Akt phosphorylation, rapidly restores glycolysis, and cellular ATP levels

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^99mTc-pertechnetate uptake (by cells genetically engineered to express the Na-Iodide symporter) reflects cellular ATP levels, thus permitting in vivo monitoring of energetics of transplanted cells by SPECT imaging.

Adult stem cells demonstrate metabolic flexibility that is regulated by cell adhesion status. The authors demonstrate that adherent cells primarily utilize glycolysis, whereas suspended cells rely on oxidative phosphorylation for their ATP needs. Akt phosphorylation transduces adhesion-mediated regulation of energy metabolism, by regulating translocation of glucose transporters (GLUT1) to the cell membrane and thus, cellular glucose uptake and glycolysis. Cell dissociation, a pre-requisite for cell transplantation, leads to energetic stress, which is mediated by Akt dephosphorylation, downregulation of glucose uptake, and glycolysis. They designed hydrogels that promote rapid cell adhesion of encapsulated cells, Akt phosphorylation, restore glycolysis, and cellular ATP levels.