Recent Advances in Continuous MOF Membranes for Gas Separation and Pervaporation.

Metal-organic frameworks (MOFs), a sub-group of porous crystalline materials, have been receiving increasing attention for gas separation and pervaporation because of their high thermal and chemical stability, narrow window sizes, as well as tuneable structural, physical, and chemical properties. In this review, we comprehensively discuss developments in the formation of continuous MOF membranes for gas separation and pervaporation. Additionally, the application performance of continuous MOF membranes in gas separation and pervaporation are analysed. Lastly, some perspectives for the future application of continuous MOF membranes for gas separation and pervaporation are given.

Advances in Extrusion 3D Bioprinting: A Focus on Multicomponent Hydrogel-Based Bioinks.

3D bioprinting involves the combination of 3D printing technologies with cells, growth factors and biomaterials, and has been considered as one of the most advanced tools for tissue engineering and regenerative medicine (TERM). However, despite multiple breakthroughs, it is evident that numerous challenges need to be overcome before 3D bioprinting will eventually become a clinical solution for a variety of TERM applications. To produce a 3D structure that is biologically functional, cell-laden bioinks must be optimized to meet certain key characteristics including rheological properties, physico-mechanical properties, and biofunctionality; a difficult task for a single component bioink especially for extrusion based bioprinting. As such, more recent research has been centred on multicomponent bioinks consisting of a combination of two or more biomaterials to improve printability, shape fidelity and biofunctionality. In this article, multicomponent hydrogel-based bioink systems are systemically reviewed based on the inherent nature of the bioink (natural or synthetic hydrogels), including the most current examples demonstrating properties and advances in application of multicomponent bioinks, specifically for extrusion based 3D bioprinting. This review article will assist researchers in the field in identifying the most suitable bioink based on their requirements, as well as pinpointing current unmet challenges in the field.

NIPAM-based Microgel Microenvironment Regulates the Therapeutic Function of Cardiac Stromal Cells.

To tune the chemical, physical, and mechanical microenvironment for cardiac stromal cells to treat acute myocardial infarction (MI), we prepared a series of thermally responsive microgels with different surface charges (positive, negative, and neutral) and different degrees of hydrophilicity, as well as functional groups (carboxyl, hydroxyl, amino, and methyl). These microgels were used as injectable hydrogels to create an optimized microenvironment for cardiac stromal cells (CSCs). Our results indicated that a hydrophilic and negatively charged microenvironment created from poly( N-isopropylacrylamide- co-itaconic acid) was favorable for maintaining high viability of CSCs, promoting CSC proliferation and facilitating the formation of CSC spheroids. A large number of growth factors, such as vascular endothelial growth factor (VEGF), insulin-like growth factor I (IGF-1), and stromal-derived factor-1 (SDF-1) were released from the spheroids, promoting neonatal rat cardiomyocyte activation and survival. After injecting the poly( N-isopropylacrylamide- co-itaconic acid) microgel into mice, we examined their acute inflammation and T-cell immune reactions. The microgel itself did not elicit obvious immune response. We then injected the same microgel-encapsulated with CSCs into MI mice. The result revealed the treatment-promoted MI heart repair through angiogenesis and inhibition of apoptosis with an improved cell retention rate. This study will open a door for tailoring poly( N-isopropylacrylamide)-based microgel as a delivery vehicle for CSC therapy.

Tuning microenvironment for multicellular spheroid formation in thermo-responsive anionic microgel scaffolds.

Tumor spheroids are considered to be effective in drug screening and evaluation. Three-dimensional scaffold-based cell culture becomes very promising in producing multicellular spheroids. Different from other approaches, 3D scaffolds mimic in vivo cellular microenvironment which encourages intercellular and extracellular interactions. The properties of the cellular microenvironment include the surface wettability, chemistry, and charge of the scaffolds which may influence cell attachment, proliferation as well as migration and these properties are essential for multicellular spheroids formation. Through co-polymerization with different carboxylic acids, we demonstrate that the surface charge density and hydrophobicity of the microenvironment have a great impact on the tumor spheroids formation progress and their size distribution. Our results show that a scaffold with a moderate negative charge density and a highly hydrophilic surface promotes cell proliferation, resulting in quicker and larger spheroids formation. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2899-2909, 2018.

Heart Repair Using Nanogel-Encapsulated Human Cardiac Stem Cells in Mice and Pigs with Myocardial Infarction.

Stem cell transplantation is currently implemented clinically but is limited by low retention and engraftment of transplanted cells and the adverse effects of inflammation and immunoreaction when allogeneic or xenogeneic cells are used. Here, we demonstrate the safety and efficacy of encapsulating human cardiac stem cells (hCSCs) in thermosensitive poly(N-isopropylacrylamine-co-acrylic acid) or P(NIPAM-AA) nanogel in mouse and pig models of myocardial infarction (MI). Unlike xenogeneic hCSCs injected in saline, injection of nanogel-encapsulated hCSCs does not elicit systemic inflammation or local T cell infiltrations in immunocompetent mice. In mice and pigs with acute MI, injection of encapsulated hCSCs preserves cardiac function and reduces scar sizes, whereas injection of hCSCs in saline has an adverse effect on heart healing. In conclusion, thermosensitive nanogels can be used as a stem cell carrier: the porous and convoluted inner structure allows nutrient, oxygen, and secretion diffusion but can prevent the stem cells from being attacked by immune cells.

Thermoresponsive Acidic Microgels as Functional Draw Agents for Forward Osmosis Desalination.

Thermoresponsive microgels with carboxylic acid functionalization have been recently introduced as an attractive draw agent for forward osmosis (FO) desalination, where the microgels showed promising water flux and water recovery performance. In this study, various comonomers containing different carboxylic acid and sulfonic acid functional groups were copolymerized with N-isopropylacrylamide (NP) to yield a series of functionalized thermoresponsive microgels possessing different acidic groups and hydrophobicities. The purified microgels were examined as the draw agents for FO application, and the results show the response of water flux and water recovery was significantly affected by various acidic comonomers. The thermoresponsive microgel with itaconic acid shows the best overall performance with an initial water flux of 44.8 LMH, water recovery up to 47.2% and apparent water flux of 3.1 LMH. This study shows that the incorporation of hydrophilic dicarboxylic acid functional groups into the microgels leads to the enhancement on water adsorption and overall performance. Our work elucidates in detail on the structure-property relationship of thermoresponsive microgels in their applications as FO draw agents and would be beneficial for future design and development of high performance FO desalination.

Functionalized thermo-responsive microgels for high performance forward osmosis desalination.

Stimuli-responsive hydrogels were recently proposed for energy-saving forward osmosis (FO) process. However, their low water flux and dewatering ability for reuse make them less attractive for industrial desalination process. In this work, the co-polymer microgels of N-isopropylacrylamide and acrylic acid with different mixing ratios were synthesized using surfactant-free emulsion polymerization to produce submicron-size hydrogels with high surface area and fast swelling-deswelling response. The microgels were employed as draw agents in a laboratory scale FO desalination system. The microgel-based FO process performed a high water flux up to 23.8 LMH and high water recovery ability of 72.4%. In addition, we explored a new conductivity measurement method to online analyze water flux of the FO system. This on-line conductivity analysis approach appeared to be an accurate and efficient method for evaluating microgel-based FO desalination performance. Our experimental data revealed that the stimuli-responsive microgel was an efficient draw agent for FO desalination.