Cellulose
nanocrystals (CNCs) are an emergent, sustainable nanomaterial
that are biosourced, abundant, and biodegradable. On account of their
high aspect ratio, low density, and mechanical rigidity, they have
been employed in numerous areas of biomedical research including as
reinforcing materials for bone or tissue scaffolds or as carriers
in drug delivery systems. Given the promise of these materials for
such use, characterizing and understanding their interactions with
biological systems is an important step to prevent toxicity or inflammation.
Reported herein are studies aimed at exploring the in vitro and in vivo effects that the source, length, and
charge of the CNCs have on cytotoxicity and immune response. CNCs
from four different biosources (cotton, wood, Miscanthus
x Giganteus, and sea tunicate) were prepared and functionalized
with positive or negative charges to obtain a small library of CNCs
with a range of dimensions and surface charge. A method to remove
endotoxic or other impurities on the CNC surface leftover from the
isolation process was developed, and the biocompatibility of the CNCs
was subsequently assayed in vitro and in
vivo. After subcutaneous injection, it was found that unfunctionalized
(uncharged) CNCs form aggregates at the site of injection, inducing
splenomegaly and neutrophil infiltration, while charged CNCs having
surface carboxylates, sulfate half-esters, or primary amines were
biologically inert. No effect of the particle source or length was
observed in the in vitro and in vivo studies conducted. The lack of an in vitro or in vivo immune response toward charged CNCs in these experiments
supports their use in future biological studies.
This research article will describe the design and use of polyelectrolyte hydrogel particles as internal curing agents in concrete and present new results on relevant hydrogel-ion interactions. When incorporated into concrete, hydrogel particles release their stored water to fuel the curing reaction, resulting in reduced volumetric shrinkage and cracking and thus increasing concrete service life. The hydrogel's swelling performance and mechanical properties are strongly sensitive to multivalent cations that are naturally present in concrete mixtures, including calcium and aluminum. Model poly(acrylic acid(AA)-acrylamide(AM))-based hydrogel particles with different chemical compositions (AA:AM monomer ratio) were synthesized and immersed in sodium, calcium, and aluminum salt solutions. The presence of multivalent cations resulted in decreased swelling capacity and altered swelling kinetics to the point where some hydrogel compositions displayed rapid deswelling behavior and the formation of a mechanically stiff shell. Interestingly, when incorporated into mortar, hydrogel particles reduced mixture shrinkage while encouraging the formation of specific inorganic phases (calcium hydroxide and calcium silicate hydrate) within the void space previously occupied by the swollen particle.
Poly(lactic acid) (PLA) is a commercially available bio‐based polymer that is a potential alternative to many commodity petrochemical‐based polymers. However, PLA's thermomechanical properties limit its use in many applications. Incorporating polymer‐grafted cellulose nanocrystals (CNCs) is one potential route to improving these mechanical properties. One key challenge in using these polymer‐grafted nanoparticles is to understand which variables associated with polymer grafting are most important for improving composite properties. In this work, poly(ethylene glycol)‐grafted CNCs are used to study the effects of polymer grafting density and molecular weight on the properties of PLA composites. All CNC nanofillers are found to reinforce PLA above the glass transition temperature, but non‐grafted CNCs and CNCs grafted with short PEG chains (<2 kg mol−1) are found to cause significant embrittlement, generally resulting in less than 3% elongation‐at‐break. By grafting higher molecular weight PEG (10 kg mol−1) onto the CNCs at a grafting density where the polymer chains are predicted to be in the semi‐dilute polymer brush conformation (~0.1 chains nm−2), embrittlement can be avoided.
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