The amphiphilic chemical structure of native lignin, composed by a hydrophobic aromatic core and hydrophilic hydroxy groups, makes it a promising alternative for the development of bio‐based surface‐active compounds. However, the severe conditions traditionally needed during biomass fractionation make lignin prone to condensation and cause it to lose hydrophilic hydroxy groups in favour of the formation of C−C bonds, ultimately decreasing lignin's abilities to lower surface tension of water/oil mixtures. Therefore, it is often necessary to further functionalize lignin in additional synthetic steps in order to obtain a surfactant with suitable properties. In this work, multifunctional aldehyde‐assisted fractionation with glyoxylic acid (GA) was used to prevent lignin condensation and simultaneously introduce a controlled amount of carboxylic acid on the lignin backbone for its further use as surfactant. After fully characterizing the extracted GA‐lignin, its surface activity was measured in several water/oil systems at different pH values. Then, the stability of water/mineral oil emulsions was evaluated at different pH and over a course of 30 days by traditional photography and microscopy imaging. Further, the use of GA‐lignin as a surfactant was investigated in the formulation of a cosmetic hand cream composed of industrially relevant ingredients. Contrary to industrial lignins such as Kraft lignin, GA‐lignin did not alter the color or smell of the formulation. Finally, the surface activity of GA‐lignin was compared with other lignin‐based and fossil‐based surfactants, showing that GA‐lignin presented similar or better surface‐active properties compared to some of the most commonly used surfactants. The overall results showed that GA‐lignin, a biopolymer that can be made exclusively from renewable carbon, can successfully be extracted in one step from lignocellulosic biomass. This lignin can be used as an effective surfactant without further modification, and as such is a promising candidate for the development of new bio‐based surface‐active products.
Micrometer sized capsules are often used as single entities for the encapsulation and release of active ingredients, for example in food, cosmetics, and drug delivery. Important parameters that determine the stability of capsules and the release of reagents contained in them are the dimensions and composition of their shell. Most capsule shells are rather thick, thereby occupying a significant fraction of the capsule volume, or they are rigid, making the capsules fragile. This work introduces viscoelastic capsules with very thin shells of order 10 nm. Despite the thin nature of these shells, they are flexible, self‐healing, yet, for practical applications impermeable even to low molecular weight substances. These shells are formed by ionically crosslinking surfactants that are functionalized with catechol‐derivatives. This work investigates the influence of the number of chelators contained per surfactant and the crosslinking ion on the rheological properties of the membranes and relate it to the mechanical properties of the resulting capsules. This work demonstrates that these shells are impermeable to molecules as small as 340 Da even if loaded with cell culture media, indicating their potential for biomedical applications.
Nature fabricates hard functional materials from soft organic scaffolds that are mineralized. To enable an energy‐efficient locomotion of these creatures while maintaining their structural stability, nature often renders parts of these minerals porous. Unfortunately, methods to produce synthetic minerals with a similar degree of control over their multi length scale porous structure remain elusive. This level of control, however, would be required to design lightweight yet robust biominerals. Here, a room temperature process is presented that combines a localized mineralization with emulsion‐based 3D printing to form cm sized biominerals possessing pores whose diameters range from the 100 s of nm up to the mm length scale. The samples encompass up to 80 wt% of CaCO3 and display a specific compressive strength that is significantly higher than that of previously reported 3D printed porous biominerals and close to those of trabecular bones. The universality of this approach by forming different types of bioactive minerals, including calcite, aragonite, and brushite is demonstrated. The ability to 3D print these materials under benign conditions renders this energy‐efficient process well‐suited to construct cm‐sized lightweight yet load‐bearing structures that might find applications, for example, in the design of the next generation of flying or motile objects.
Ionically crosslinked hydrogels containing metal coordination motifs have piqued the interest of researchers in recent decades due to their self-healing and adhesive properties. In particular, catechol-functionalized bulk hydrogels have received a lot of attention because of their bioinspired nature. By contrast, very little is known about thin viscoelastic membranes made using similar chelator−ion pair motifs. This shortcoming is surprising because the unique interfacial properties of these membranes, namely, their self-healing and adhesion, would be ideal for capsule shells, adhesives, or for drug delivery purposes. We recently demonstrated the feasibility to fabricate 10 nm thick viscoelastic membranes from catechol-functionalized surfactants that are ionically crosslinked at the liquid/liquid interface. However, it is unclear if the vast know-how existing on the influence of the chelator−ion pair on the mechanical properties of ionically crosslinked three-dimensional (3D) hydrogels can be translated to two-dimensional (2D) systems. To address this question, we compare the dynamic mechanical properties of ionically crosslinked pyrogallol functionalized hydrogels with those of viscoelastic membranes that are crosslinked using the same chelator−ion pairs. We demonstrate that the storage and loss moduli of viscoelastic membranes follow a trend similar to that of the hydrogels, with the membrane becoming stronger as the ion−chelator affinity increases. Yet, membranes relax significantly faster than bulk equivalents. These insights enable the targeted design of viscoelastic, adhesive, self-healing membranes possessing tunable mechanical properties. Such capsules can potentially be used, for example, in cosmetics, as granular inks, or with additional work that includes replacing the fluorinated block by a hydrocarbon-based one in drug delivery and food applications.
Soft bodies of small creatures are frequently protected with hard shells whereas those of larger creatures are often supported with hard load-bearing structures. Nature usually fabricates these hard functional materials from soft organic scaffolds that are mineralized. To enable an energy-efficient locomotion of these creatures while maintaining the functionality of their protective or load-bearing components, nature minimizes the weight of these materials by making them porous. Unfortunately, methods that offer a similar degree of control over the nanometer up to the centimeter length scale structure of synthetic minerals remain elusive. Here we present a process that combines direct ink writing with emulsion templating to 3D print strong biominerals possessing pores whose diameters range from the 100s of nm up to the mm length scale at ambient temperature. After the structures have been stabilized through a second mineralization step, our samples encompass up to 80 wt% of CaCO3 and display a density and compressive strength close to those of human trabecular bones.
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