Chitosan is an abundant biopolymer derived from food waste with attractive properties, particularly its high biocompatibility and easy chemical processability. Here, we review the rapidly expanding ...literature on chitosan‐based porous materials with a focus on the gelation mechanisms, the three‐dimensional multiscale structural control, and the diverse chemical functionality not accessible by other biopolymers. The properties vary widely: from supercritically dried, mesoporous chitosan aerogels to very light, freeze‐dried macroporous scaffolds. Porous chitosan displays impressive performance at the laboratory scale, but the highly (meso)porous nature amplifies not only the beneficial functionality of chitosan, but also its drawbacks, resulting in serious barriers to industrialization. In order to facilitate technology transfer, we critically discuss the practical feasibility of chitosan aerogels in potential applications compared to conventional and other biopolymer‐based porous or nonporous materials.
Chitosan aerogels and freeze‐dried gels—these fascinating bio‐derived materials, with tailored porous structures and otherwise inaccessible functionalities, recently emerged from the biomedical field into the realm of materials science and chemistry. Chitosan aerogels are a hot topic in academic research, but what are the barriers to industrial production and commercialization?
Biopolymer aerogels were among the first aerogels produced, but only in the last decade has research on biopolymer and biopolymer–composite aerogels become popular, motivated by sustainability ...arguments, their unique and tunable properties, and ease of functionalization. Biopolymer aerogels and open‐cell foams have great potential for classical aerogel applications such as thermal insulation, as well as emerging applications in filtration, oil–water separation, CO2 capture, catalysis, and medicine. The biopolymer aerogel field today is driven forward by empirical materials discovery at the laboratory scale, but requires a firmer theoretical basis and pilot studies to close the gap to market. This Review includes a database with over 3800 biopolymer aerogel properties, evaluates the state of the biopolymer aerogel field, and critically discusses the scientific, technological, and commercial barriers to the commercialization of these exciting materials.
Air gel: The last decade has seen a strong acceleration in biopolymer and biopolymer–composite aerogel research, motivated by sustainability arguments, their unique and tunable properties, and ease of functionalization. This Review evaluates the field of biopolymer aerogels, including its potential and barriers for applications in thermal insulation, filtration, oil–water separation, CO2 capture, catalysis, drug delivery, and nutrition.
Silica aerogels are highly porous (~95%), predominantly mesoporous (20–50 nm) materials with very high surface area (~800 m2/g), but applications that valorize the chemical properties linked to the ...high surface area lag behind those that valorize the pore structure (thermal insulation). Here, we present widely applicable protocols to synthesize and characterize organo-functionalized silica aerogels with high surface area (356–1177 m2/g) and high mass loadings of surface functional groups (1.0–4.9 mmol/g, 0.9–3.9 molecules/nm2). Wet silica gels are soaked into dilute solutions containing pre-hydrolyzed organofunctional trialkoxysilanes, followed by supercritical CO2 drying. The retention of the various functional groups in the dry aerogels is confirmed by FTIR and their concentrations quantified by solid-state NMR spectroscopy. The mild reaction conditions are compatible with all tested functional groups (silanol, ethoxy, trimethylsilyl, amino, vinyl, methyl methacrylate, epoxy, phosphonate), without the need to optimize for each specific functional silane, making the synthesis of organofunctionalized aerogels a routine task.
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•A flexible protocol to produce organo-functionalized silica aerogels is presented.•Grafting and retention of functional groups are validated by FTIR and solid-state NMR.•Content of functional groups are determined by quantitative NMR spectroscopy.•Potential applications are systemically reviewed for the investigated functionalities.
We demonstrate a general approach to the preparation of layered graphene oxide structures with sandwiched conducting polymers of different morphologies. The approach is conceptualized on the basis of ...the electrostatic interactions between negatively charged graphene oxide sheets and positively charged surfactant micelles. A graphene oxide−polypyrrole composite prepared from this approach exhibited an excellent electrocapacitive performance with a high specific capacitance over 500 F g−1. Good rate performance and cycle ability were realized by the composite electrode. The simple method described here opens up a generalized route to making a wide range of graphene oxide-based and graphene-based composite materials for applications beyond electrochemical energy storage.
With their low thermal conductivity (λ), silica aerogels can reduce carbon emissions from heating and cooling demands, but their widespread adoption is limited by the high production cost. A one‐pot ...synthesis for silica aerogel granulate is presented that drastically reduces solvent use, production time, and global warming potential. The inclusion of the hydrophobization agent prior to gelation with a post‐gelation activation step, enables a complete production cycle of less than four hours at the lab scale for a solvent use close to the theoretical minimum, and limits the global warming potential. Importantly, the one‐pot aerogel granulate retains the exceptional properties associated with silica aerogel, mostly λ=14.4±1.0 mW m−1⋅K−1 for the pilot scale materials, about half that of standing air (26 mW m−1⋅K−1). The resource‐, time‐, and cost‐effective production will allow silica aerogels to break out of its niche into the mainstream building and industrial insulation markets.
Solving the solvent problem: Silica aerogels are ideal thermal insulation materials, but are expensive owing to the large solvent consumption during their production. A simplified synthesis combines all reagents in a single step and minimizes the production time, solvent use, and carbon footprint, but retains the outstanding properties associated with silica aerogels.
Silica aerogels are amongst the lightest mesoporous solids known and well recognized for their superinsulating properties, but the weak mechanical properties of the inorganic network structure has ...often narrowed their field of application. Here, the inherent brittleness of dried inorganic gels is tackled through the elaboration of a strong mesoporous silica aerogel interpenetrated with a silylated nanocellulosic scaffold. To this avail, a functionalized scaffold is synthesized by freeze‐drying an aqueous suspension of nanofibrillated cellulose (NFC)—a bio‐based nanomaterial mechanically isolated from renewable resources—in the presence of methyltrimethoxysilane sol. The silylated NFC scaffold displays a high porosity (>98%), high flexibility, and reduced thermal conductivity (λ) compared with classical cellulosic structures. The polysiloxane layer decorating the nanocellulosic scaffold is exploited to promote the attachment of the mesoporous silica matrix onto the nanofibrillated cellulose scaffold (NFCS), leading to a reinforced silica hybrid aerogel with improved thermomechanical properties. The highly porous (>93%) silica‐NFC hybrids displays meso‐ and macroporosity with pore diameters controllable by the NFCS mass fraction, reduced linear shrinkage, improved compressive properties (55% and 126% increase in Young's modulus and tensile strength, respectively), while maintaining superinsulating properties (λ ≤ 20 mW (m K)–1). This study details a new direction for the synthesis of multiscale hybrid silica aerogel structures with tailored properties through the use of alkyltrialkoxysilane prefunctionalized nanocellulosic scaffolds.
A strong multiscale silica aerogel is obtained through the interpenetration of silica nanoparticles with a silylated nanocellulosic scaffold. The polysiloxane layer decorating the scaffold is exploited to promote the attachment of the mesoporous silica matrix onto the nanofibrillated cellulose scaffold, leading to highly porous silica hybrid aerogel displaying reduced linear shrinkage, improved compressive properties but maintaining its superinsulating properties.
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•Effect of solvent systems on chitosan gel shrinkage and aerogel properties.•SAXS identifies the step during which the gel/aerogel structure forms (solid phase).•The structure can ...form at any synthesis step, including supercritical drying.•New concept of aerogel structure control using solvent–polymer affinity.
The functionality of biopolymer aerogels is inherently linked to its microstructure, which in turn depends on the synthesis protocol. Detailed investigations on the macroscopic size change and nanostructure formation during chitosan aerogel synthesis reveal a new aspect of biopolymer aerogels that increases process flexibility. Formaldehyde-cross-linked chitosan gels retain a significant fraction of their original volume after solvent exchange into methanol (50.3 %), ethanol (47.1 %) or isopropanol (26.7 %), but shrink dramatically during subsequent supercritical CO2 processing (down to 4.9 %, 3.5 % and 3.7 %, respectively). In contrast, chitosan gels shrink more strongly upon exchange into n-heptane (7.2 %), a low affinity solvent, and retain this volume during CO2 processing. Small-angle X-ray scattering confirms that the occurrence of the volumetric changes correlates with mesoporous network formation through physical coagulation in CO2 or n-heptane. The structure formation step can be controlled by solvent–polymer and polymer–drying interactions, which would be a new tool to tailor the aerogel structure.
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•Comprehensive review of all approaches used to assemble aerogel-fiber materials.•“In situ sol-gel” and “via pre-formed aerogel” approaches are described and evaluated.•Enhanced ...mechanical/physical properties are obtained while keeping low thermal conductivity.•Anoverviewofthemarketandfuture researchtrends areidentified.
Silica aerogels have a unique structure that makes them promising materials for variable applications. However, they are brittle due to weak inter-particle necks, and also expensive. Combining aerogel with fibers can not only enhance the mechanical/insulation properties, but also reduce dust release, and ease practical application. The majority of review articles in this field have been on the aerogel/textile systems' application or on textile impregnation in silica sol utilizing the sol–gel technique, with a few papers also addressing the use of aerogel as filler. This review for the first time highlights all strategies to assemble silica aerogel with textile materials. For sol–gel approaches, the fibers can be impregnated in a silica precursor sol to form the aerogel in situ between the fibers, but the sol itself can also be spun into aerogel fibers. Other strategies employ pre-formed silica aerogel, mixed in polymer or solvent matrices/slurries, to form aerogel injected blankets, aerogel-filled material coated fibers, and aerogel-filled composite fibers. Aerogel particles-filled textile packages have also been proposed. The emerging activities on simulations of aerogel-fiber combinations are reviewed. The advantages/disadvantages of various approaches are evaluated, and the current market situation and an outlook for the future of the field are summarized.
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•Reviewing popular bioprinting technologies employed in craniofacial and dental tissue regeneration.•Evaluating existing biomaterials for 3D printing in dental ...applications.•Emphasizing the importance of printing materials with both excellent mechanical and biological properties for craniofacial and dental purposes.•Providing an overview of identified future research trends in the field.
The rising incidence of defects in oral and maxillofacial tissues, linked to factors such as trauma, tumors, periodontal disease, and aging, poses significant challenges. Current treatments, involving autografts, allografts, and synthetic graft materials, face obstacles like secondary trauma, inflammation, and inadequate biocompatibility. Tissue engineering, integrating cell biology and material science since the 1990s, relies heavily on biomaterial scaffolds to promote cell adhesion, proliferation, and differentiation. Traditional scaffold fabrication, including 3D printing, methods lack precision, hindering effective tissue repair by controlling cell distribution and the extracellular matrix. Biomedical engineering advancements have introduced 3D bioprinting as an innovative solution, overcoming constraints of conventional scaffolds. 3D bioprinting technology enables rapid and precise reconstruction of damaged tissues with loaded cells, mimicking in vivo environments. This paper explores key 3D bioprinting technologies such as inkjet-based, extrusion-based, fused deposition modeling, laser-assisted, VAT photopolymerization, freeform reversible embedding of suspended hydrogels, and sacrificial template printing. The selection of materials with suitable mechanical and biological properties is crucial, considering the distinct requirements of each technique. This review provides a comprehensive survey of research progress on 3D printing biomaterial applications in craniofacial and dental tissue engineering, serving as a valuable reference for future medical research.
Abstract
Ice-templating technology holds great potential to construct industrial porous materials from nanometers to the macroscopic scale for tailoring thermal, electronic, or acoustic transport. ...Herein, we describe a general ice-templating technology through freezing the material on a rotating cryogenic drum surface, crushing it, and then re-casting the nanofiber slurry. Through decoupling the ice nucleation and growth processes, we achieved the columnar-equiaxed crystal transition in the freezing procedure. The highly random stacking and integrating of equiaxed ice crystals can organize nanofibers into thousands of repeating microscale units with a tortuous channel topology. Owing to the spatially well-defined isotropic structure, the obtained Al
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nanofiber aerogels exhibit ultralow thermal conductivity, superelasticity, good damage tolerance, and fatigue resistance. These features, together with their natural stability up to 1200 °C, make them highly robust for thermal insulation under extreme thermomechanical environments. Cascading thermal runaway propagation in a high-capacity lithium-ion battery module consisting of LiNi
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cathode, with ultrahigh thermal shock power of 215 kW, can be completely prevented by a thin nanofiber aerogel layer. These findings not only establish a general production route for nanomaterial assemblies that is conventionally challenging, but also demonstrate a high-energy-density battery module configuration with a high safety standard that is critical for practical applications.
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