An official website of the United States government
Abstract Susceptibility of mammalian cells against harsh processing conditions limit their use in cell transplantation and tissue engineering applications. Besides modulation of the cell microenvironment, encapsulation of mammalian cells within hydrogel microbeads attract attention for cytoprotection through physical isolation of the encapsulated cells. The hydrogel formulations used for cell microencapsulation are largely dominated by ionically crosslinked alginate (Alg), which suffer from low structural stability under physiological culture conditions and poor cell–matrix interactions. Here the fabrication of Alg templated silk and silk/gelatin composite hydrogel microspheres with permanent or on‐demand cleavable enzymatic crosslinks using simple and cost‐effective centrifugation‐based droplet processing are demonstrated. The composite microbeads display structural stability under ion exchange conditions with improved mechanical properties compared to ionically crosslinked Alg microspheres. Human mesenchymal stem and neural progenitor cells are successfully encapsulated in the composite beads and protected against environmental factors, including exposure to polycations, extracellular acidosis, apoptotic cytokines, ultraviolet (UV) irradiation, anoikis, immune recognition, and particularly mechanical stress. The microbeads preserve viability, growth, and differentiation of encapsulated stem and progenitor cells after extrusion in viscous polyethylene oxide solution through a 27‐gauge fine needle, suggesting potential applications in injection‐based delivery and three‐dimensional bioprinting of mammalian cells with higher success rates.
more »
« less
Development of microbeads from unmodified biomass with tunable size and competitive mechanical properties
Despite national and international regulations, plastic microbeads are still widely used in personal care and consumer products (PCCPs) as exfoliants and rheological modifiers, causing significant microplastic pollution following use. As a sustainable alternative, microbeads were produced by extrusion of biomass solutions and precipitation into anti-solvent. Despite using novel blends of biodegradable, non-derivatized biomass including cellulose and Kraft lignin, resulting microbeads are within the shape, size, and stiffness range of commercial plastic microbeads, even without crosslinking. Solution processability and resulting bead shape and Young’s modulus can be tuned via biomass source, concentration, and degree of polymerization; biomass concentration, extrusion geometry, and precipitation and extraction conditions control the bead size. Lignin incorporation reduces the solution viscosity, which improves processability but also produces flatter beads with higher moduli than cellulose-only microbeads. While some lignin leaches from the beads when stored in water, adding surfactants like sodium dodecyl sulfate suppresses this effect, resulting in good mechanical stability over 2 months with no noticeable structural degradation. The stability of these mixed-source biomass microbeads—despite the absence of chemical crosslinking or derivatization—makes this route a promising, robust approach for obtaining environmentally-benign microbeads of tunable size and stiffness for use in PCCPs.
more »
« less
- Award ID(s):
- 1901635
- PAR ID:
- 10462341
- Date Published:
- Journal Name:
- Cellulose
- ISSN:
- 0969-0239
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Transient DNA loops occur throughout the genome due to thermal fluctuations of DNA and the function of SMC complex proteins such as condensin and cohesin. Transient crosslinking within and between chromosomes and loop extrusion by SMCs have profound effects on high-order chromatin organization and exhibit specificity in cell type, cell cycle stage, and cellular environment. SMC complexes anchor one end to DNA with the other extending some distance and retracting to form a loop. How cells regulate loop sizes and how loops distribute along chromatin are emerging questions. To understand loop size regulation, we employed bead–spring polymer chain models of chromatin and the activity of an SMC complex on chromatin. Our study shows that (1) the stiffness of the chromatin polymer chain, (2) the tensile stiffness of chromatin crosslinking complexes such as condensin, and (3) the strength of the internal or external tethering of chromatin chains cooperatively dictate the loop size distribution and compaction volume of induced chromatin domains. When strong DNA tethers are invoked, loop size distributions are tuned by condensin stiffness. When DNA tethers are released, loop size distributions are tuned by chromatin stiffness. In this three-way interaction, the presence and strength of tethering unexpectedly dictates chromatin conformation within a topological domain.more » « less
-
Abstract Teaching experiments involving edible, biodegradable calcium alginate beads serve as an attractive model system to introduce upper secondary age students to core chemistry topics through innovations in sustainable consumer products. A teaching experiment is described that engages students with the synthesis of calcium alginate hydrogel beads from sodium alginate and calcium lactate, two food-safe and renewable materials. The beads’ outer membranes are a result of ionic interactions between carboxylate groups from alginate strands and the divalent calcium cations between them, thus forming cross-linked polymers. Protonation of the carboxylate groups on the alginate strands decreases crosslinking density affecting bead formation. First, various concentrations of citric acid are used to lower the pH of the sodium alginate solution and the effect on the calcium alginate bead formation is observed. A correlation between pH and bead shape and firmness is derived. This information is then used to explore juices with varying natural acidities. The experiment is amenable to implementation in the classroom or as an at-home activity. Learning outcomes include acid-base reactions, chemical bonding, polymer structures, and green chemistry concepts. Students consider the environmental challenges of traditional plastics used in packaging and how innovative new commercial products are attempting to provide solutions.more » « less
-
Abstract BackgroundCellulose degradation by cellulases has been studied for decades due to the potential of using lignocellulosic biomass as a sustainable source of bioethanol. In plant cell walls, cellulose is bonded together and strengthened by the polyphenolic polymer, lignin. Because lignin is tightly linked to cellulose and is not digestible by cellulases, is thought to play a dominant role in limiting the efficient enzymatic degradation of plant biomass. Removal of lignin via pretreatments currently limits the cost-efficient production of ethanol from cellulose, motivating the need for a better understanding of how lignin inhibits cellulase-catalyzed degradation of lignocellulose. Work to date using bulk assays has suggested three possible inhibition mechanisms: lignin blocks access of the enzyme to cellulose, lignin impedes progress of the enzyme along cellulose, or lignin binds cellulases directly and acts as a sink. ResultsWe used single-molecule fluorescence microscopy to investigate the nanoscale dynamics of Cel7A fromTrichoderma reesei, as it binds to and moves along purified bacterial cellulose in vitro. Lignified cellulose was generated by polymerizing coniferyl alcohol onto purified bacterial cellulose, and the degree of lignin incorporation into the cellulose meshwork was analyzed by optical and electron microscopy. We found that Cel7A preferentially bound to regions of cellulose where lignin was absent, and that in regions of high lignin density, Cel7A binding was inhibited. With increasing degrees of lignification, there was a decrease in the fraction of Cel7A that moved along cellulose rather than statically binding. Furthermore, with increasing lignification, the velocity of processive Cel7A movement decreased, as did the distance that individual Cel7A molecules moved during processive runs. ConclusionsIn an in vitro system that mimics lignified cellulose in plant cell walls, lignin did not act as a sink to sequester Cel7A and prevent it from interacting with cellulose. Instead, lignin both blocked access of Cel7A to cellulose and impeded the processive movement of Cel7A along cellulose. This work implies that strategies for improving biofuel production efficiency should target weakening interactions between lignin and cellulose surface, and further suggest that nonspecific adsorption of Cel7A to lignin is likely not a dominant mechanism of inhibition.more » « less
-
This study demonstrated a sustainable, zero-waste approach to produce carboxylated lignin-containing cellulose nanofibers (LCNFs) directly from untreated sugarcane bagasse (SCB) using nitro-oxidation process (NOP) fol lowed by high-pressure homogenization. Systematic optimization of reaction parameters was conducted, including reaction time, HNO3-to-SCB ratio, HNO3 concentration, temperature, and co-oxidant addition (KNO₂). The results revealed that HNO3 concentration played the most dominant role in tailoring LCNF properties. Notably, the resulting LCNFs exhibited high dispersibility, with zeta potential values ranging from 38 to 65 mV due to the increasing surface carboxyl content (0.43 to 1.21 mmol/g) even under relatively mild conditions (e.g., 50 ◦C, 5 h). Lowering the acid concentration significantly increased the lignin content, enhancing the thermal stability. All LCNFs exhibited nanoscale diameters (7–13 nm), high crystallinity (54 to 70 %), and shear- thinning behavior. Elemental analysis of NOP effluents confirmed their enrichment with macro- and micro- nutrients, enabling their reuse as biofertilizers. This dual valorization of solid and liquid products positions NOP as a viable nanocellulose production and nutrient recovery pathway from lignocellulosic biomass. Resulting LCNFs, with their amphiphilic, biodegradable, and tunable surface properties, represent a compelling platform to make new materials to replace some synthetic polymers and reduce microplastic and chemical pollution.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s10570-023-05393-4
