Thermoresponsive Worms for Expansion and Release of Human Embryonic Stem Cells

RGD Density on Tadpole Nanostructures Regulates Cancer Stem Cell Proliferation and Stemness

Cancer stem cells (CSCs) make up a small population of cancer cells, primarily responsible for tumor initiation, metastasis, and drug resistance. They overexpress Arg-Gly-Asp (RGD) binding integrin receptors that play crucial roles in cell proliferation and stemness through interaction with the extracellular matrix. Here, we showed that monodisperse polymeric tadpole nanoparticles covalently coupled with different RGD densities regulated colon CSC proliferation and stemness in a RGD density-dependent manner. These tadpoles penetrated deeply and evenly into tumor spheroids and specifically entered cells with cancer stem markers CD24 and CD133. Low RGD density tadpoles triggered integrin α5 expression that further activated TGF-β3 and TGF-β2 signaling pathways, confirmed by the increase of pERK and Bcl-2 protein levels. This process is associated with the RGD cluster presentation controlled by the RGD density on the tadpole surface.

Synthesis of Poly(propylene oxide)-Poly(N,N'-dimethylacrylamide) Diblock Copolymer Nanoparticles via Reverse Sequence Polymerization-Induced Self-Assembly in Aqueous Solution

Sterically-stabilized diblock copolymer nanoparticles comprising poly(propylene oxide) (PPO) cores are prepared via reverse sequence polymerization-induced self-assembly (PISA) in aqueous solution. N,N'-Dimethylacrylamide (DMAC) acts as a cosolvent for the weakly hydrophobic trithiocarbonate-capped PPO precursor. Reversible addition-fragmentation chain transfer (RAFT) polymerization of DMAC is initially conducted at 80% w/w solids with deoxygenated water. At 30-60% DMAC conversion, the reaction mixture is diluted to 5-25% w/w solids. The PPO chains become less solvated as the DMAC monomer is consumed, which drives in situ self-assembly to form aqueous dispersions of PPO-core nanoparticles of 120-190 nm diameter at 20 °C. Such RAFT polymerizations are well-controlled (Mw/Mn ≤ 1.31), and more than 99% DMAC conversion is achieved. The resulting nanoparticles exhibit thermoresponsive character: dynamic light scattering and transmission electron microscopy studies indicate the formation of more compact spherical nanoparticles of approximately 33 nm diameter on heating to 70 °C. Furthermore, 15-25% w/w aqueous dispersions of such nanoparticles formed micellar gels that undergo thermoreversible (de)gelation on cooling to 5 °C.

Efficient Synthesis of Hydrolytically Degradable Block Copolymer Nanoparticles via Reverse Sequence Polymerization-Induced Self-Assembly in Aqueous Media

Hydrolytically degradable block copolymer nanoparticles are prepared via reverse sequence polymerization-induced self-assembly (PISA) in aqueous media. This efficient protocol involves the reversible addition-fragmentation chain transfer (RAFT) polymerization of N,N'-dimethylacrylamide (DMAC) using a monofunctional or bifunctional trithiocarbonate-capped poly(ϵ-caprolactone) (PCL) precursor. DMAC monomer is employed as a co-solvent to solubilize the hydrophobic PCL chains. At an intermediate DMAC conversion of 20-60 %, the reaction mixture is diluted with water to 10-25 % w/w solids. The growing amphiphilic block copolymer chains undergo nucleation to form sterically-stabilized PCL-core nanoparticles with PDMAC coronas. 1 H NMR studies confirm more than 99 % DMAC conversion while gel permeation chromatography (GPC) studies indicate well-controlled RAFT polymerizations (Mw /Mn ≤1.30). Transmission electron microscopy (TEM) and dynamic light scattering (DLS) indicate spheres of 20-120 nm diameter. As expected, hydrolytic degradation occurs within days at 37 °C in either acidic or alkaline solution. Degradation is also observed in phosphate-buffered saline (PBS) (pH 7.4) at 37 °C. However, no degradation is detected over a three-month period when these nanoparticles are stored at 20 °C in deionized water (pH 6.7). Finally, PDMAC30 -PCL16 -PDMAC30 nanoparticles are briefly evaluated as a dispersant for an agrochemical formulation based on a broad-spectrum fungicide (azoxystrobin).

RGD-Coated Polymer Nanoworms for Enriching Cancer Stem Cells

Cancer stem cells (CSCs) are primarily responsible for tumour drug resistance and metastasis; thus, targeting CSCs can be a promising approach to stop cancer recurrence. However, CSCs are small in numbers and readily differentiate into matured cancer cells, making the study of their biological features, including therapeutic targets, difficult. The use of three-dimensional (3D) culture systems to enrich CSCs has some limitations, including low sphere forming efficiency, enzymatic digestion that may damage surface proteins, and more importantly no means to sustain the stem properties. A responsive 3D polymer extracellular matrix (ECM) system coated with RGD was used to enrich CSCs, sustain stemness and avoid enzymatic dissociation. RGD was used as a targeting motif and a ligand to bind integrin receptors. We found that the system was able to increase sphere forming efficiency, promote the growth of spheric cells, and maintain stemness-associated properties compared to the current 3D culture. We showed that continuous culture for three generations of colon tumour spheroid led to the stem marker CD24 gradually increasing. Furthermore, the new system could enhance the cancer cell sphere forming ability for the difficult triple negative breast cancer cells, MBA-MD-231. The key stem gene expression for colon cancer also increased with the new system. Further studies indicated that the concentration of RGD, especially at high doses, could inhibit stemness. Taken together, our data demonstrate that our RGD-based ECM system can facilitate the enrichment of CSCs and now allow for the investigation of new therapeutic approaches for colorectal cancer or other cancers.

Cardiac Cell Therapy with Pluripotent Stem Cell-Derived Cardiomyocytes: What Has Been Done and What Remains to Do?

PURPOSE OF REVIEW

Exciting pre-clinical data presents pluripotent stem cell-derived cardiomyocytes (PSC-CM) as a novel therapeutic prospect following myocardial infarction, and worldwide clinical trials are imminent. However, despite notable advances, several challenges remain. Here, we review PSC-CM pre-clinical studies, identifying key translational hurdles. We further discuss cell production and characterization strategies, identifying markers that may help generate cells which overcome these barriers.

RECENT FINDINGS

PSC-CMs can robustly repopulate infarcted myocardium with functional, force generating cardiomyocytes. However, current differentiation protocols produce immature and heterogenous cardiomyocytes, creating related issues such as arrhythmogenicity, immunogenicity and poor engraftment. Recent efforts have enhanced our understanding of cardiovascular developmental biology. This knowledge may help implement novel differentiation or gene editing strategies that could overcome these limitations. PSC-CMs are an exciting therapeutic prospect. Despite substantial recent advances, limitations of the technology remain. However, with our continued and increasing biological understanding, these issues are addressable, with several worldwide clinical trials anticipated in the coming years.

Design of chemically defined synthetic substrate surfaces for the in vitro maintenance of human pluripotent stem cells: A review

Human pluripotent stem cells (hPSCs) have the potential of long-term self-renewal and differentiation into nearly all cell types in vitro. Prior to the downstream applications, the design of chemically defined synthetic substrates for the large-scale proliferation of quality-controlled hPSCs is critical. Although great achievements have been made, Matrigel and recombinant proteins are still widely used in the fundamental research and clinical applications. Therefore, much effort is still needed to improve the performance of synthetic substrates in the culture of hPSCs, realizing their commercial applications. In this review, we summarized the design of reported synthetic substrates and especially their limitations in terms of cell culture. Moreover, much attention was paid to the development of promising peptide displaying surfaces. Besides, the biophysical regulation of synthetic substrate surfaces as well as the three-dimensional culture systems were described.

Nonionic Polymer with Flat Upper Critical Solution Temperature Behavior in Water

We rationally designed a monomer that when polymerized formed a well-defined nonionic polymer [poly(2-(methacryloyloxy) ethylureido glycinamide), PMEGA] by reversible addition fragmentation chain transfer with a flat and tunable upper critical solution temperature (UCST) in water. The monomer was made in one pot from commercially available compounds and with ease of purification. Strong hydrogen-bonding side groups on the polymer produced sharp coil-to-globule transitions upon cooling below its UCST. Ideal random copolymers produced with butyl methacrylate also showed flat UCST profiles, in which the UCST increased with a greater butyl methacrylate copolymer composition from 7 to 65 °C. In the presence of NaCl, the UCST decreased linearly with NaCl concentration due to the "salting-in" effect, and it was found that the slopes from the linear decrease of UCST were nearly identical for all copolymer compositions. This new polymer and its copolymers support the hypothesis that strong hydrogen bonding between the side groups allowed the flat UCST to be readily tuned with a high level of predictability. We postulate that this polymer system may provide wide biological applicability similar to that found for the well-used flat lower critical solution temperature (LCST) of poly(N-isopropylacrylamide).

Temperature-Induced Formation of Uniform Polymer Nanocubes Directly in Water

Conventional self-assembly methods of block copolymers in cosolvents (i.e., usually water and organic solvents) has yet to produce a pure and monodisperse population of nanocubes. The requirement to assemble a nanocube is for the second block to have a high molecular weight. However, such high molecular weight block copolymers usually result in the formation of kinetically trapped nanostructures even with the addition of organic cosolvents. Here, we demonstrate the rapid production of well-defined polymer nanocubes directly in water by utilizing the thermoresponsive nature of the second block (with 263 monomer units), in which the block copolymer was fully water-soluble below its lower critical solution temperature (LCST) and would produce a pure population of nanocubes when heated above this temperature. Incorporating a pH-responsive monomer in the second block allowed us to control the size of the nanocubes in water with pH and the LCST of the block copolymer. We then used the temperature and pH responsiveness to create an adaptive system that changes morphology when using a unique fuel. This fuel (H₂O₂ + MnO₂) is highly exothermic, and the solution pH increases with the consumption of H₂O₂. Initially, a nonequilibrium spherical nanostructure formed, which transformed over time into nanocubes, and by controlling the exotherm of the reaction, we controlled the time for this transformation. This block copolymer and the water-only method of self-assembly have provided some insights into designing biomimetic systems that can readily adapt to the environmental conditions.

3D Extracellular Matrix Mimics: Fundamental Concepts and Role of Materials Chemistry to Influence Stem Cell Fate

Synthetic 3D extracellular matrices (ECMs) find application in cell studies, regenerative medicine, and drug discovery. While cells cultured in a monolayer may exhibit unnatural behavior and develop very different phenotypes and genotypes than in vivo, great efforts in materials chemistry have been devoted to reproducing in vitro behavior in in vivo cell microenvironments. This requires fine-tuning the biochemical and structural actors in synthetic ECMs. This review will present the fundamentals of the ECM, cover the chemical and structural features of the scaffolds used to generate ECM mimics, discuss the nature of the signaling biomolecules required and exploited to generate bioresponsive cell microenvironments able to induce a specific cell fate, and highlight the synthetic strategies involved in creating functional 3D ECM mimics.

Fibronectin-conjugated thermoresponsive nanobridges generate three dimensional human pluripotent stem cell cultures for differentiation towards the neural lineages

Production of 3-dimensional neural progenitor cultures from human pluripotent stem cells offers the potential to generate large numbers of cells. We utilised our nanobridge system to generate 3D hPSC aggregates for differentiation towards the neural lineage, and investigate the ability to passage aggregates while maintaining cells at a stem/progenitor stage. Over 38 days, aggregate cultures exhibited upregulation and maintenance of neural-associated markers and demonstrated up to 10 fold increase in cell number. Aggregates undergoing neural induction in the presence or absence of nanobridges demonstrated no differences in marker expression, proliferation or viability. However, aggregates formed without nanobridges were statistically significantly fewer and smaller by passage 3. Organoids, cultured from aggregates, and treated with retinoic acid or rock inhibitor demonstrated terminal differentiation as assessed by immunohistochemistry. These data demonstrate that nanobridge 3D hPSC can differentiate to neural stem/progenitor cells, and be maintained at this stage through serial passaging and expansion.

Fabrication of Polymer-Protein Hybrids

Rapid developments in organic chemistry and polymer chemistry promote the synthesis of polymer-protein hybrids with different structures and biofunctionalities. In this feature article, recent progress achieved in the synthesis of polymer-protein conjugates, protein-nanoparticle core-shell structures, and polymer-protein nanogels/hydrogels is briefly reviewed. The polymer-protein conjugates can be synthesized by the "grafting-to" or the "grafting-from" approach. In this article, different coupling reactions and polymerization methods used in the synthesis of bioconjugates are reviewed. Protein molecules can be immobilized on the surfaces of nanoparticles by covalent or noncovalent linkages. The specific interactions and chemical reactions employed in the synthesis of core-shell structures are discussed. Finally, a general introduction to the synthesis of environmentally responsive polymer-protein nanogels/hydrogels by chemical cross-linking reactions or molecular recognition is provided.

Methods for Expansion of Three-Dimensional Cultures of Human Embryonic Stem Cells Using a Thermoresponsive Polymer

Human pluripotent stem cells (hPSCs) are viewed as promising candidates for applications in regenerative medicine and therapy due to their proliferative and pluripotent properties. However, obtaining clinically significant numbers of hPSCs remains a limiting factor and impedes their use in therapeutic applications. Conventionally, hPSCs are cultured on two-dimensional surfaces coated with a suitable substrate, such as Matrigel™. This method, however, requires a large surface area to generate sufficient cell numbers to meet clinical needs and is therefore impractical as a manufacturing platform for cell expansion. In addition, the use of enzymes for cell detachment and small molecule inhibitors to increase plating efficiency may impact future cell behavior when used for routine subculturing. In this study, we describe a protocol to generate and maintain hPSC aggregates in a three-dimensional suspension culture by utilizing thermoresponsive nanobridges. The property of the polymer used in the nanobridges enables passaging and expansion through a temperature change in combination with mechanically applied shear to dissociate aggregates; thus, we eliminate the need of enzymes or small molecules for cell dissociation and viability, respectively. Utilizing this platform, maintenance of human embryonic stem cells for three continuous passages demonstrated high expression levels in key pluripotent markers.

Surfactant-Free RAFT Emulsion Polymerization of Styrene Using Thermoresponsive macroRAFT Agents: Towards Smart Well-Defined Block Copolymers with High Molecular Weights

The combination of reversible addition⁻fragmentation chain transfer (RAFT) and emulsion polymerization has recently attracted much attention as a synthetic tool for high-molecular-weight block copolymers and their micellar nano-objects. Up to recently, though, the use of thermoresponsive polymers as both macroRAFT agents and latex stabilizers was impossible in aqueous media due to their hydrophobicity at the usually high polymerization temperatures. In this work, we present a straightforward surfactant-free RAFT emulsion polymerization to obtain thermoresponsive styrenic block copolymers with molecular weights of around 100 kDa and their well-defined latexes. The stability of the aqueous latexes is achieved by adding 20 vol % of the cosolvent 1,4-dioxane (DOX), increasing the phase transition temperature (PTT) of the used thermoresponsive poly(N-acryloylpyrrolidine) (PAPy) macroRAFT agents above the polymerization temperature. Furthermore, this cosolvent approach is combined with the use of poly(N,N-dimethylacrylamide)-block-poly(N-acryloylpiperidine-co-N-acryloylpyrrolidine) (PDMA-b-P(APi-co-APy)) as the macroRAFT agent owning a short stabilizing PDMA end block and a widely adjustable PTT of the P(APi-co-APy) block in between 4 and 47 °C. The temperature-induced collapse of the latter under emulsion polymerization conditions leads to the formation of RAFT nanoreactors, which allows for a very fast chain growth of the polystyrene (PS) block. In dynamic light scattering (DLS), as well as cryo-transmission electron microscopy (cryoTEM), moreover, all created latexes indeed reveal a high (temperature) stability and a reversible collapse of the thermoresponsive coronal block upon heating. Hence, this paper pioneers a versatile way towards amphiphilic thermoresponsive high-molecular-weight block copolymers and their nano-objects with tailored corona switchability.

Xeno-free culture of human pluripotent stem cells on oligopeptide-grafted hydrogels with various molecular designs

Establishing cultures of human embryonic (ES) and induced pluripotent (iPS) stem cells in xeno-free conditions is essential for producing clinical-grade cells. Development of cell culture biomaterials for human ES and iPS cells is critical for this purpose. We designed several structures of oligopeptide-grafted poly (vinyl alcohol-co-itaconic acid) hydrogels with optimal elasticity, and prepared them in formations of single chain, single chain with joint segment, dual chain with joint segment, and branched-type chain. Oligopeptide sequences were selected from integrin- and glycosaminoglycan-binding domains of the extracellular matrix. The hydrogels grafted with vitronectin-derived oligopeptides having a joint segment or a dual chain, which has a storage modulus of 25 kPa, supported the long-term culture of human ES and iPS cells for over 10 passages. The dual chain and/or joint segment with cell adhesion molecules on the hydrogels facilitated the proliferation and pluripotency of human ES and iPS cells.

A Critical Appraisal of RAFT-Mediated Polymerization-Induced Self-Assembly

Recently, polymerization-induced self-assembly (PISA) has become widely recognized as a robust and efficient route to produce block copolymer nanoparticles of controlled size, morphology, and surface chemistry. Several reviews of this field have been published since 2012, but a substantial number of new papers have been published in the last three years. In this Perspective, we provide a critical appraisal of the various advantages offered by this approach, while also pointing out some of its current drawbacks. Promising future research directions as well as remaining technical challenges and unresolved problems are briefly highlighted.

Long-term xeno-free culture of human pluripotent stem cells on hydrogels with optimal elasticity

The tentative clinical application of human pluripotent stem cells (hPSCs), such as human embryonic stem cells and human induced pluripotent stem cells, is restricted by the possibility of xenogenic contamination resulting from the use of mouse embryonic fibroblasts (MEFs) as a feeder layer. Therefore, we investigated hPSC cultures on biomaterials with different elasticities that were grafted with different nanosegments. We prepared dishes coated with polyvinylalcohol-co-itaconic acid hydrogels grafted with an oligopeptide derived from vitronectin (KGGPQVTRGDVFTMP) with elasticities ranging from 10.3 to 30.4 kPa storage moduli by controlling the crosslinking time. The hPSCs cultured on the stiffest substrates (30.4 kPa) tended to differentiate after five days of culture, whereas the hPSCs cultured on the optimal elastic substrates (25 kPa) maintained their pluripotency for over 20 passages under xeno-free conditions. These results indicate that cell culture matrices with optimal elasticity can maintain the pluripotency of hPSCs in culture.

Molecular characterisation of stromal populations derived from human embryonic stem cells: Similarities to immortalised bone marrow derived stromal stem cells

Human bone marrow-derived stromal (skeletal) stem cells (BM-hMSC) are being employed in an increasing number of clinical trials for tissue regeneration. A limiting factor for their clinical use is the inability to obtain sufficient cell numbers. Human embryonic stem cells (hESC) can provide an unlimited source of clinical grade cells for therapy. We have generated MSC-like cells from hESC (called here hESC-stromal) that exhibit surface markers and differentiate to osteoblasts and adipocytes, similar to BM-hMSC. In the present study, we used microarray analysis to compare the molecular phenotype of hESC-stromal and immortalised BM-hMSC cells (hMSC-TERT). Of the 7379 genes expressed above baseline, only 9.3% of genes were differentially expressed between undifferentiated hESC-stromal and BM-hMSC. Following ex vivo osteoblast induction, 665 and 695 genes exhibited ≥ 2-fold change (FC) in hESC-stromal and BM-hMSC, respectively with 172 genes common to both cell types. Functional annotation of significantly changing genes revealed similarities in gene ontology between the two cell types. Interestingly, genes in categories of cell adhesion/motility and epithelial–mesenchymal transition (EMT) were highly enriched in hESC-stromal whereas genes associated with cell cycle processes were enriched in hMSC-TERT. This data suggests that while hESC-stromal cells exhibit a similar molecular phenotype to hMSC-TERT, differences exist that can be explained by ontological differences between these two cell types. hESC-stromal cells can thus be considered as a possible alternative candidate cells for hMSC, to be employed in regenerative medicine protocols.

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hESC-derived MSC-like cells were compared to immortalised BM-MSC.

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Comparison was performed using microarrays on non-induced and OB induced cells.

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Analysis demonstrated close hierarchical relationships and molecular phenotypes.

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90.7% of genes were similarly expressed in non-induced cells.

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73% of OB induced genes for both cell lines correlated with GO ontology analysis.

Smart hybrid materials by conjugation of responsive polymers to biomacromolecules

The chemical structure and function of biomacromolecules has evolved to fill many essential roles in biological systems. More specifically, proteins, peptides, nucleic acids and polysaccharides serve as vital structural components, and mediate chemical transformations and energy/information storage processes required to sustain life. In many cases, the properties and applications of biological macromolecules can be further expanded by attaching synthetic macromolecules. The modification of biomacromolecules by attaching a polymer that changes its properties in response to environmental variations, thus affecting the properties of the biomacromolecule, has led to the emergence of a new family of polymeric biomaterials. Here, we summarize techniques for conjugating responsive polymers to biomacromolecules and highlight applications of these bioconjugates reported so far. In doing so, we aim to show how advances in synthetic tools could lead to rapid expansion in the variety and uses of responsive bioconjugates.

Thermoresponsive hydrogel maintains the mouse embryonic stem cell “naïve” pluripotency phenotype

A chemically defined hydrogel HG21, which allows enzyme-free passaging, is a substitute for gelatin allowing standardised and inexpensive mESC culture.