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Phycocolloids are gelling polysaccharides extracted from algae that have found applications as microbiological culture media, food thickener, and cosmetic rheological modifiers. The extensive use of algae species that have not been yet domesticated has led to overexploitation or supply shortages. Thus, extending the library of phycocolloids would permit to support the industrial changes towards renewable polymer feedstocks but if the source of algae is limited to wild algae species, this might raise issue on the scalability and hinder the creation of a reliable supply chain. In this study, we have identified a new phycocolloid extracted from Chaetomorpha aerea, a green seaweed that can be cultivated in open ponds. Through elucidation of its chemical structure, we propose a gelation mechanism for an extracted sulfated polysaccharide fraction that form stable, transparent hydrogels that can be used for microbiological culture.

In multicellular organisms, cells are organized in a 3-dimensional framework and this is essential for organogenesis and tissue morphogenesis. Systems to recapitulate 3D cell growth are therefore vital for understanding development and cancer biology. Cells organized in 3D environments can evolve certain phenotypic traits valuable to physiologically relevant models that cannot be accessed in 2D culture. Cellular spheroids constitute an important aspect of in vitro tumor biology and they are usually prepared using the hanging drop method. Here a 3D printed approach is demonstrated to fabricate bespoke hanging drop devices for the culture of tumor cells. The design attributes of the hanging drop device take into account the need for high-throughput, high efficacy in spheroid formation, and automation. Specifically, in this study, custom-fit, modularized hanging drop devices comprising of inserts (Q-serts) were designed and fabricated using fused filament deposition (FFD). The utility of the Q-serts in the engineering of unicellular and multicellular spheroids-synthetic tumor microenvironment mimics (STEMs)—was established using human (cancer) cells. The culture of spheroids was automated using a pipetting robot and bioprinted using a custom bioink based on carboxylated agarose to simulate a tumor microenvironment (TME). The spheroids were characterized using light microscopy and histology. They showed good morphological and structural integrity and had high viability throughout the entire workflow. The systems and workflow presented here represent a user-focused 3D printing-driven spheroid culture platform which can be reliably reproduced in any research environment and scaled to- and on-demand. The standardization of spheroid preparation, handling, and culture should eliminate user-dependent variables, and have a positive impact on translational research to enable direct comparison of scientific findings.

Translational Bioinks for 3D Bioprinting 3D‐Bioprinting, a technology at the interface of additive manufacturing, biomaterials and cell biology, is poised to revolutionize regenerative medicine and drug screening. Bioinks are the lynchpin as they bridge bench to bedside. A biology‐based approach to engineering bioinks with pro‐regenerative attributes, with an emphasis on reproducibility, efficiency, and conformance to regulatory standards is essential for paving the way to clinical translation. More details can be found in article number 2103469 by V. Prasad Shastri and co‐workers. [Image: see text]

3D‐bioprinting (3DBP) possesses several elements necessary to overcome the deficiencies of conventional tissue engineering, such as defining tissue shape a priori, and serves as a bridge to clinical translation. This transformative potential of 3DBP hinges on the development of the next generation of bioinks that possess attributes for clinical use. Toward this end, in addition to physicochemical characteristics essential for printing, bioinks need to possess proregenerative attributes, while enabling printing of stable structures with a defined biological function that survives implantation and evolves in vivo into functional tissue. With a focus on bioinks for extrusion‐based bioprinting, this perspective review advocates a rigorous biology‐based approach to engineering bioinks, emphasizing efficiency, reproducibility, and a streamlined translation process that places the clinical endpoint front and center. A blueprint for engineering the next generation of bioinks that satisfy the aforementioned performance criteria for various translational levels (TRL1‐5) and a characterization tool kit is presented., 3D‐bioprinting (3DBP) is a promising technology that serves as a bridge to clinical translation. The translational potential of 3DBP depends on the development of the next generation of bioinks. Translational bioinks need to possess proregenerative attributes, while enabling printing of stable structures that survive implantation and evolve into functional tissue.

The limited potential of cartilage to regenerate itself has led to development of new strategies and biomaterials for cartilage tissue engineering and regenerative medicine. Although de novo strategies for cartilage repair have been realized, extrudable hydrogels that can be administered in minimally invasive manner while simultaneously supporting chondrogenic differentiation could lead to development of new systems to deliver cells to cartilage lesions. In this work, we explored the suitability of thermo-reversible, extrudable gels derived from carboxylated agarose for maintaining human articular chondrocyte (HAC) phenotype. Towards this objective, we have investigated the impact of hydrogel stiffness and presence of integrin-binding peptide sequence GGGGRGDSP on HAC differentiation potential. We discovered that stiffer hydrogels (5.8 kPa) are more efficient than softer counterparts (0.6 kPa) in promoting chondrogenesis. Interestingly, in GGGGRGDSP modified gels, a synergy between stiffness and RGD signaling led to enhanced expression of chondrogenic related genes (aggrecan, collagen type II and sox9). These findings were also supported by quantitative analysis of sulfated glycosaminoglycans. Since carboxylated agarose are highly suitable as bioink for 3D bioprinting, we propose that extrudable GGGGRGDSP-linked stiff carboxylated agarose as a medium for direct printing of chondrocyte into cartilage lesion.

3D bioprinting as a process has enabled the creation of complex structures laden with biological information including cells that is not realizable with conventional manufacturing techniques. Within this new manufacturing process, design strategies and design tools have to be adapted to deliver its full potential. In architecture, parametric design has allowed the creation of new shapes by expressing parameters in an algorithm that defines the relationship between design intent and design response. In this study, the application of this method to the bioprinting of hollow channel grown in silico within a porous scaffold is demonstrated. The final object was printed using a novel bioink formulation based on carboxylated agarose that is extrudable at ambient temperature. The hollow bioprinted object was imaged with X-ray computed tomography to obtain a 3D model for design validation. This proposed workflow “from design to validation” represents a new paradigm for realizing complex structures in 3D bioprinting through in silico optimization.

To study biological processes in vitro, biomaterials-based engineering solutions to reproduce the gradients observed in tissues are necessary. We present a platform for the 3D bioprinting of functionally graded biomaterials based on carboxylated agarose, a bioink amendable by extrusion bioprinting. Using this bioink, objects with a gradient of stiffness and gradient of cell concentration were printed. Functionalization of carboxylated agarose with maleimide moieties that react in minutes with a cysteine-terminated cell-adhesion peptide allowed us to print objects with a gradient of an immobilized peptide. This approach paves the way toward the development of tissue mimics with gradients.

With the increasing growth of the algae industry and the development of algae biorefinery, there is a growing need for high-value applications of algae-extracted biopolymers. The utilization of such biopolymers in the biomedical field can be considered as one of the most attractive applications but is challenging to implement. Historically, polysaccharides extracted from seaweed have been used for a long time in biomedical research, for example, agarose gels for electrophoresis and bacterial culture. To overcome the current challenges in polysaccharides and help further the development of high-added-value applications, an overview of the entire polysaccharide journey from seaweed to biomedical applications is needed. This encompasses algae culture, extraction, chemistry, characterization, processing, and an understanding of the interactions of soft matter with living organisms. In this review, we present algae polysaccharides that intrinsically form hydrogels: alginate, carrageenan, ulvan, starch, agarose, porphyran, and (nano)cellulose and classify these by their gelation mechanisms. The focus of this review further lays on the culture and extraction strategies to obtain pure polysaccharides, their structure-properties relationships, the current advances in chemical backbone modifications, and how these modifications can be used to tune the polysaccharide properties. The available techniques to characterize each organization scale of a polysaccharide hydrogel are presented, and the impact on their interactions with biological systems is discussed. Finally, a perspective of the anticipated development of the whole field and how the further utilization of hydrogel-forming polysaccharides extracted from algae can revolutionize the current algae industry are suggested.

Poly(2-alkyl-2-oxazoline) (PAOx) hydrogels are tailorable synthetic materials with demonstrated biomedical applications, thanks to their excellent biocompatibility and tunable properties. However, their use as injectable hydrogels is challenging as it requires invasive surgical procedures to insert the formed hydrogel into the body due to their nonsoluble 3D network structures. Herein, we introduce cyclooctyne and azide functional side chains to poly(2-oxazoline) copolymers to induce in situ gelation using strain promoted alkyne–azide cycloaddition. The gelation occurs rapidly, within 5 min, under physiological conditions when two polymer solutions are simply mixed. The influence of several parameters, such as temperature and different aqueous solutions, and stoichiometric ratios between the two polymers on the structural properties of the resultant hydrogels have been investigated. The gel formation within tissue samples was verified by subcutaneous injection of the polymer solution into an ex vivo model. The degradation study of the hydrogels in vitro showed that the degradation rate was highly dependent on the type of media, ranging from days to a month. This result opens up the potential uses of PAOx hydrogels in attempts to achieve optimal, injectable drug delivery systems and tissue engineering.

One of the challenges in 3D-bioprinting is the realization of complex, volumetrically defined structures, that are also anatomically accurate and relevant. Towards this end, in this study we report the development and validation of a carboxylated agarose (CA)-based bioink that is amenable to 3D printing of free-standing structures with high stiffness at physiological temperature using microextrusion printing without the need for a fugitive phase or post-processing or support material (FRESH). By blending CA with negligible amounts of native agarose (NA) a bioink formulation (CANA) which is suitable for printing with nozzles of varying internal diameters under ideal pneumatic pressure was developed. The ability of the CANA ink to exhibit reproducible sol-gel transition at physiological temperature of 37 °C was established through rigorous characterization of the thermal behavior, and rheological properties. Using a customized bioprinter equipped with temperature-controlled nozzle and print bed, high-aspect ratio objects possessing anatomically-relevant curvature and architecture have been printed with high print reproducibility and dimension fidelity. Objects printed with CANA bioink were found to be structurally stable over a wide temperature range of 4 °C to 37 °C, and exhibited robust layer-to-layer bonding and integration, with evenly stratified structures, and a porous interior that is conducive to fluid transport. This exceptional layer-to-layer fusion (bonding) afforded by the CANA bioink during the print obviated the need for post-processing to stabilize printed structures. As a result, this novel CANA bioink is capable of yielding large (5–10 mm tall) free-standing objects ranging from simple tall cylinders, hemispheres, bifurcated ‘Y’-shaped and ‘S’-shaped hollow tubes, and cylinders with compartments without the need for support and/or a fugitive phase. Studies with human nasal chondrocytes showed that the CANA bioink is amenable to the incorporation of high density of cells (30 million/mL) without impact on printability. Furthermore, printed cells showed high viability and underwent mitosis which is necessary for promoting remodeling processes. The ability to print complex structures with high cell densities, combined with excellent cell and tissue biocompatibility of CA bodes well for the exploitation of CANA bioinks as a versatile 3D-bioprinting platform for the clinical translation of regenerative paradigms.

Following ocular surgery, dressings are commonly applied to the surgical wound. These dressings need to combine medical properties with ease of use while maintaining comfort for the patient. For the ocular area, this means that the dressings need to act as a microbial barrier, allow good conformability to the contours of the eye, and provide evaporative cooling to the inflamed area. Furthermore, the dressings should be transparent to allow for the inspection of the wound site by healthcare professionals without the need for removal. In this paper, we investigate a blend of native agarose (NA) and carboxylated agarose (CA) for producing elastic hydrogels with high water content that can be supplemented with antibiotics. It was found that in comparison to pure agarose hydrogels, the NA hydrogels blended with CA had a reduced Young’s modulus, reduced evaporation rate when exposed to air, and accelerated release rate of antimicrobial agents, whilst maintaining the same degree of transparency. By altering the formulation from 2 wt.% pure NA to 1 wt.% NA blended with 1 wt.% CA, we were able to observe an approximately 55% reduction in Young’s modulus, 25% reduction in evaporation rate, as well as a significant acceleration in the release rate of cefazolin and doxycycline, making this hydrogel blend a potential material for topical treatment applications.

Porous biodegradable scaffolds have many applications in bioengineering, ranging from cell culture and transplantation, to support structures, to induce blood vessel and tissue formation in vivo. While numerous strategies have been developed for the manufacture of porous scaffolds, it remains challenging to control the spatial organization of the pores. In this study, we introduce the use of the granular convection effect, also known as the muesli or brazil nut effect, to rapidly engineer particulate templates with a vertical size gradient. These templates can then be used to prepare scaffolds with pore size gradients. To demonstrate this approach, we prepared templates with particle size gradients, which were then infused with a prepolymer solution consisting of the pentaerythritol ethoxylate (polyol), sebacoyl chloride (acid chloride), and poly(caprolactone). Following curing, the template was dissolved to yield biodegradable polyester‐ether scaffolds with pore size gradients that could be tuned depending on the size range of the particulates used. The application of these scaffolds was demonstrated using pancreatic islets, which were loaded via centrifugation and retained within the scaffold's pores without a decrease in viability. The proposed strategy provides a facile approach to prepare templates with spatially organized pores that could potentially be used for cell transplantation, or guided tissue formation. Refereed/Peer-reviewed

Hydrogel forming polysaccharides, such as the seaweed derived agarose, are well suited for wound dressing applications as they have excellent cell and soft tissue compatibility. For wound dressings, fibrous structure is desirable as the high surface area can favor adsorption of wound exudate and promote drug delivery. Although electrospinning offers a straightforward means to produce nonwoven fibrous polymeric structures, processing agarose and its derivatives into fibers through electrospinning is challenging as it has limited solubility in solvents other than water. In this study we describe the processing of carboxylated agarose (CA) fibers with antibacterial properties by electrospinning from a solution of the ionic liquid (IL) 1-butyl-3-methylimidazolium chloride ([Bmim]+Cl-) possessing antimicrobial properties. The extent of carboxylation was found to impact fiber diameter, mesh elastic modulus, fiber swelling, and the loading and release of IL. IL-bearing CA fibers inhibited the growth of Staphylococcus aureus and Pseudomonas aeruginosa, bacteria commonly found in wound exudate. In sum, nonwoven CA fibers processed from IL are promising as biomaterials for wound dressing applications. Refereed/Peer-reviewed

In tissue engineering, cell-adhesion peptides (CAPs) such as the ubiquitous arginine-glycine-aspartic acid (RGD) sequence have allowed the functionalization of synthetic materials to mimic macromolecules of the extracellular matrix (ECM). However, the variety of ECM macromolecules makes it challenging to reproduce all of the native tissue functions with only a limited variety of CAPs. Screening of libraries of CAPs, analogous to high-throughput drug discovery assays, can help to identify new sequences directing cell organization. However, challenges to this approach include the automation of cell seeding in three dimensions and characterization methods. Here, we report a method for robotically generating a library of 16 CAPs to identify a microenvironment capable of directing a chain-like morphology in olfactory ensheathing cells (OECs), a cell type of particular interest for guiding axon growth in spinal cord injury repair. This approach resulted in the identification of one CAP not previously reported to interact with OECs to direct their morphology into structures suitable for potential axon guidance. The same screening approach should be applicable to any range of cell types to discover new CAPs to direct cell fate or function.

A method is reported for making hollow channels within hydrogels decorated with cell‐adhesion peptides exclusively at the channel surface. Sacrificial fibers of different diameters are used to introduce channels within poly(ethylene glycol) hydrogels crosslinked with maleimide‐thiol chemistry, which are backfilled with a cysteine‐containing peptide solution which is conjugated to the lumen with good spatial efficiency. This allows for peptide patterning in only the areas of the hydrogel where they are needed when used as cell‐guides, reducing the amount of required peptide 20‐fold when compared to bulk functionalization. The power of this approach is highlighted by successfully using these patterned hydrogels without active perfusion to guide fibroblasts and olfactory ensheathing cells—the latter having unique potential in neural repair therapies.

Vascularization is a critical step in the restoration of cellular homeostasis. Several strategies including localized growth factor delivery, endothelial progenitor cells, genetically engineered cells, gene therapy, and prevascularized implants have been explored to promote revascularization. But, long-term stabilization of newly induced vessels remains a challenge. It has been shown that fibroblasts and mesenchymal stem cells can stabilize newly induced vessels. However, whether an injected biomaterial alone can serve as an instructive environment for angiogenesis remains to be elucidated. It is reported here that appropriate vascular branching, and long-term stabilization can be promoted simply by implanting a hydrogel with stiffness matching that of fibrin clot. A unique subpopulation of circulating CD11b

Islet transplantation is currently the only minimally invasive therapy available for patients with type 1 diabetes that can lead to insulin independence, however, it is limited to only a small number of patients Although clinical procedures have improved in the isolation and culture of islets, a large number of islets are still lost in the pretransplant period, limiting the success of this treatment Moreover, current practice includes islets being prepared at specialized centers, which are sometimes remote to the transplant location Thus, a critical point of intervention to maintain the quality and quantity of isolated islets is during transportation between isolation centers and the transplanting hospitals, during which 20-40% of functional islets can be lost The current study investigated the use of an oxygen-permeable PDMS microwell device for long-distance transportation of isolated islets. We demonstrate that the microwell device protected islets from aggregation during transport, maintaining viability and average islet size during shipping. Refereed/Peer-reviewed

As an alternative to natural extracellular matrix (ECM) macromolecules, cell-adhesion peptides (CAPs) have had tremendous impact on the design of cell culture platforms, implants, and wound dressings. However, only a handful of CAPs have been utilized. The discrepancy in ECM composition strongly affects cell behavior, so it is paramount to reproduce such differences in synthetic systems. This Opinion article presents strategies inspired from high-throughput screening techniques implemented in drug discovery to exploit the potential of a growing CAP library. These strategies are expected to promote the use of a broader spectrum of CAPs, which in turn could lead to improved cell culture models, implants, and wound dressings.

Correction for ‘Rapid fabrication of functionalised poly(dimethylsiloxane) microwells for cell aggregate formation’ by A. Forget et al., Biomater. Sci., 2017, 5, 828–836.

Cell aggregates reproduce many features of the natural architecture of functional tissues, and have therefore become an important in vitro model of tissue function. In this study, we present an efficient and rapid method for the fabrication of site specific functionalised poly(dimethylsiloxane) (PDMS) microwell arrays that promote the formation of insulin-producing beta cell (MIN6) aggregates. Microwells were prepared using an ice templating technique whereby aqueous droplets were frozen on a surface and PDMS was cast on top to form a replica. By employing an aqueous alkali hydroxide solution, we demonstrate exclusive etching and functionalisation of the microwell inner surface, thereby allowing the selective absorption of biological factors within the microwells. Additionally, by manipulating surface wettability of the substrate through plasma polymer coating, the shape and profile of the microwells could be tailored. Microwells coated with antifouling Pluronic 123, bovine serum albumin, collagen type IV or insulin growth factor 2 were employed to investigate the formation and stability of MIN6 aggregates in microwells of different shapes. MIN6 aggregates formed with this technique retained insulin expression. These results demonstrate the potential of this platform for the rapid screening of biological factors influencing the formation and response of insulin-producing cell aggregates without the need for expensive micromachining techniques. Refereed/Peer-reviewed

There is mounting evidence that the mechanical property of tissues provides important cues that control cell fate. However, implementation of hydrogels with tunable physicochemical properties is limited due to the challenges associated with crosslinking chemistries. It has been recently shown that mechanically well-defined injectable polysaccharide hydrogels can be engineered by switching their secondary structure from an α-helix to a β-sheet. Based on these findings, a new concept is presented to tailor the mechanical properties of agarose hydrogels via the blending with the β-sheet-rich carboxylated derivative. Using this simple strategy, gels with predictable roughness, fiber organization, and shear modulus ranging from 0.1 to 100 kPa can be formulated. Hydrogels whose mechanical properties can be precisely tailored in vivo without the recourse for chemical reactions are expected to play an important role in implementing mechanobiology paradigms in de novo tissue engineering.

Current organ transplantation protocols require the rapid transport of freshly isolated donor tissue to the recipient patient at the site where the procedure is to be conducted. During transport, the tissue graft can quickly deteriorate as a result of oxygen starvation. In this study, we report the fabrication of oxygen-releasing coatings for improved tissue preservation. The coatings were prepared via the encapsulation of calcium peroxide or urea peroxide microparticles between layers of octadiene plasma polymer films. By varying the thickness of the plasma polymer coating and type of peroxide, formulations were obtained that generate oxygen upon contact with aqueous solutions, while at the same time limiting the amount of toxic reactive oxygen species produced. The optimized coatings were tested under hypoxic conditions using the MIN6 β-cell line, which resulted in a 3-fold increase in the viability of cultured cells. These thin oxygen-releasing coatings can be deposited on a wide range of surfaces, creating a platform for oxygen delivery with the potential to extend the viability of transported tissues and increase the time frame available for graft transport. Refereed/Peer-reviewed

The mechanical properties of agarose-derived hydrogels depend on the scaffolding of the polysaccharide network. To identify and quantify such higher order structure, we applied Raman optical activity (ROA)a spectroscopic technique that is highly sensitive toward carbohydrateson native agarose and chemically modified agarose in the gel phase for the first time. By spectral global fitting, we isolated features that change as a function of backbone carboxylation (28, 40, 50, 60, 80, and 93 %) from other features that remain unchanged. We assigned these spectral features by comparison to ROA spectra calculated for different oligomer models. We found a 60:40 ratio of double- and single-stranded α-helix in the highly rigid hydrogel of native agarose, while the considerably softer hydrogels made from carboxylated agarose use a scaffold of unpaired β-strands.

Tissue engineering aims to gain mechanistic insights into human diseases and to develop new treatment protocols. Although 2-dimensional (2-D) flat petri dish culture and in vivo disease-based models are the industrial gold standards for understanding the underlying disease pathophysiology and for drug screening/testing, they are associated with certain limitations. While the 2-D cell culture systems fail to mimic in vivo signaling, animal-based disease models are associated with long incubation period, high cost, ethical constraints as well as depiction of human pathology in different species. Therefore, there has been a paradigm shift towards the development of 3-dimensional (3-D) based in vitro disease models. These models act as bridging gaps between the aforementioned conventional strategies thereby fastening clinical translation. In this regard, biomedical engineering plays a key role towards the development of tissue engineering based 3-D disease models. These models have demonstrated success in recapitulating human diseases in terms of in vivo morphology and signaling. This chapter will present examples of biomaterials-based 3-D engineered disease models with a focus on cancer. Refereed/Peer-reviewed

pH-sensitive hydrogels play an important role in controlled drug release applications and have the potential to impact the management of wounds. In this study, we report the fabrication of novel carboxylated agarose/tannic acid hydrogel scaffolds cross-linked with zinc ions for the pH-controlled release of tannic acid. The resulting hydrogels exhibited negligible release of tannic acid at neutral and alkaline pH and sustained release at acidic pH, where they also displayed maximum swelling. The hydrogels also displayed favorable antibacterial and anti-inflammatory properties, and a lack of cytotoxicity toward 3T3 fibroblast cell lines. In simulated wound assays, significantly greater cell migration and proliferation was observed for cells exposed to tannic acid hydrogel extracts. In addition, the tannic acid hydrogels were able to suppress NO production in stimulated human macrophages in a concentration-dependent manner, indicating effective anti-inflammatory activity. Taken together, the cytocompatibility, antibacterial, and anti-inflammatory characteristics of these novel pH-sensitive hydrogels make them promising candidates for wound dressings. Refereed/Peer-reviewed

PolyJet three-dimensional (3D) printing allows for the rapid manufacturing of 3D moulds for the fabrication of cross-linked poly(dimethylsiloxane) microwell arrays (PMAs). As this 3D printing technique has a resolution on the micrometer scale, the moulds exhibit a distinct surface roughness. In this study, the authors demonstrate by optical profilometry that the topography of the 3D printed moulds can be transferred to the PMAs and that this roughness induced cell adhesive properties to the material. In particular, the topography facilitated immobilization of endothelial cells on the internal walls of the microwells. The authors also demonstrate that upon immobilization of endothelial cells to the microwells, a second population of cells, namely, pancreatic islets could be introduced, thus producing a 3D coculture platform Refereed/Peer-reviewed

The synthesis of micro- and mesoporous organic materials with well-defined pore size and structure is currently a major challenge in materials science. Because of their purely organic nature, such systems are expected to introduce new opportunities that expand on those of their well-known inorganic analogues. Since the pioneering work on polystyrene-derived resins, macroporous polymers (pore diameter >50 nm) became a well-established family of porous materials. Here, the porosity arises mainly from microphase separation during the polymerization reaction. On the other hand, studies on hyper-crosslinked polystyrene networks further confirmed that it is also possible to generate microporous (pore diameter

High surface area organic materials featuring both micro- and mesopores were synthesized under ionothermal conditions via the formation of polyaryltriazine networks. While the polytrimerization of nitriles in zinc chloride at 400 degrees C produces microporous polymers, higher reaction temperatures induce the formation of additional spherical mesopores with a narrow dispersity. The nitrogen-rich carbonaceous polymer materials thus obtained present surface areas and porosities up to 3300 m(2) g(-1) and 2.4 cm(3) g(-1), respectively. The key point of this synthesis relies on the occurrence of several high temperature polymerization reactions, where irreversible carbonization reactions coupled with the reversible trimerization of nitriles allow the reorganization of the dynamic triazine network. The ZnCl2 molten salt fulfills the requirement of a high temperature solvent, but is also required as catalyst. Thus, this dynamic polymerization system provides not only highly micro- and mesoporous materials, but also allows controlling the pore structure in amorphous organic materials.

This study introduces a thermogelling bioink based on carboxylated agarose (CA) for bioprinting of mechanically defined microenvironments mimicking natural tissues. In CA system, by adjusting the degree of carboxylation, the elastic modulus of printed gels can be tuned over several orders of magnitudes (5-230 Pa) while ensuring almost no change to the shear viscosity (10-17 mPa) of the bioink solution; thus enabling the fabrication of 3D structures made of different mechanical domains under identical printing parameters and low nozzle shear stress. Human mesenchymal stem cells printed using CA as a bioink show significantly higher survival (95%) in comparison to when printed using native agarose (62%), a commonly used thermogelling hydrogel for 3D-bioprinting applications. This work paves the way toward the printing of complex tissue-like structures composed of a range of mechanically discrete microdomains that could potentially reproduce natural mechanical aspects of functional tissues. Refereed/Peer-reviewed

Mechanical aspects of the cellular environment can influence cell function, and in this context hydrogels can serve as an instructive matrix. Here we report that physicochemical properties of hydrogels derived from polysaccharides (agarose, κ-carrageenan) having an α-helical backbone can be tailored by inducing a switch in the secondary structure from α-helix to β-sheet through carboxylation. This enables the gel modulus to be tuned over four orders of magnitude (G′ 6 Pa–3.6 × 10 4 Pa) independently of polymer concentration and molecular weight. Using carboxylated agarose gels as a screening platform, we demonstrate that soft-carboxylated agarose provides a unique environment for the polarization of endothelial cells in the presence of soluble and bound signals, which notably does not occur in fibrin and collagen gels. Furthermore, endothelial cells organize into freestanding lumens over 100 μm in length. The finding that a biomaterial can modulate soluble and bound signals provides impetus for exploring mechanobiology paradigms in regenerative therapies.

When polymeric nanoparticles (NPs) are formed by nanoprecipitation, which is a nucleation−growth process, the control over size requires changing the polymer concentration or solvent composition. Here, we demonstrate that the NP size can be controlled independent of polymer variables by introducing a polyelectrolyte (PE) inthe aqueous phase. PEs that exhibit hydrogen bonding (H-bonding) yield a reduction in NP size, whereas PEs that do not possess this characteristic promote the formation of larger NPs. The observed effect can be attributed to the formation of a diffusional barrier around the NP in the form of a dense shell. This principle of controlling NP size is not limited to polymers and can also be employed in the production of lipid NPs. Refereed/Peer-reviewed