Diffusion and Binding of Laponite Clay Nanoparticles into Collagen Fibers for the Formation of Leather Matrix

A novel method to enhance the efficiency of aldehyde tanning agents via collagen amination

The utilization of chromium free tanning agents generates lots of pollutants such as chromium containing wastewater and sludge. Besides, trivalent chromium may be converted into carcinogenic hexavalent chromium under certain conditions, causing permanent harm to the human body. Therefore, the promotion of chromium free tanning technology is extremely significant. In this study, it reports a green strategy to build a novel tanning system via the amination of collagen fibers. Leather collagen was aminated by diethanolamine to improve the positive charge and number of amino groups. This allowed the regulation of functional groups in collagen fibers and enabled the high employment of aldehyde tanning agents. On this matter, experimental work combined with molecular dynamics simulation was used to investigate the enhancement mechanism of amination. Collagen fibers aminated by diethanolamine achieved better aldehyde tanning effect than untreated collagen fibers, such as a higher shrinkage temperature (87.5 °C), dyeing absorption (74.6 %), and lower free formaldehyde content (160.8 mg/kg). This work provided a novel strategy for the establishment of a green and efficient chromium free tanning system.

Covalently surface-grafting α‑zirconium phosphate nanoplatelets enables collagen fiber matrix with ultraviolet barrier, antibacterial, and flame-retardant properties

Manipulating the dispersibility and reactivity of two-dimensional nanomaterials in collagen fibers (CFs) matrix has aroused attention in the fabrication of multifunctional collagen-based nanocomposites. Here, α‑zirconium phosphate nanoplatelets (ZrP NPs) were surface-functionalized with gallic acid (GA) to afford ZrP-GA NPs for engineering CFs matrix. The influence of ZrP-GA NPs on the ultraviolet barrier, antibacterial, and flame-retardant properties of resultant CFs matrix were investigated. Microstructural analysis revealed that ZrP-GA NPs were dispersed and bound within the collagen fibrils and onto the collagen strands in the CFs matrix. The resultant CFs matrix also maintained typical D-periodic structures of collagen fibrils and native branching and interwoven structures of CFs networks with increased porosity and enhanced ultraviolet barrier properties. Inhibition zone testing presented excellent antibacterial activities of the CFs matrix owing to surface grafting of antibacterial GA. Thanks to enhanced dispersion and binding of ZrP NPs with the CFs matrix by surface-functionalization with GA, the resultant CFs matrix reduced the peak heat release rate and the total heat release by 42.9 % and 39.0 %, respectively, highlighting improved flame-retardant properties. We envision that two-dimensional nanomaterials possess great potential in developing reasonable collagen-based nanocomposites towards the manufacture of emergent multifunctional collagen fibers-based wearable electronics.

Solid waste collagen-associated fabrication of magnetic hematite nanoparticle@collagen nanobiocomposite for emission-adsorption of dyes

The strategic utilization of hazardous particulate waste in eliminating environmental pollution is an important research hotspot. Herein, abundantly available hazardous solid collagenic waste of leather industry is converted into stable hybrid nanobiocomposite (HNP@SWDC) comprising magnetic hematite nanoparticles (HNP) and solid waste derived collagen (SWDC) via co-precipitation method. The structural, spectroscopic, surface, thermal, and magnetic properties; fluorescence quenching; dye selectivity; and adsorption are explored via microstructural analyzes of HNP@SWDC and dye adsorbed-HNP@SWDC using ¹H nuclear magnetic resonance, Raman, ultraviolet-visible, Fourier-transform infrared (FTIR), X-ray photoelectron, and fluorescence spectroscopies; thermogravimetry; field-emission scanning electron microscopy; and vibrating-sample magnetometry (VSM). The intimate interaction of SWDC with HNP and elevated magnetic properties of HNP@SWDC are apprehended via amide-imidol tautomerism associated nonconventional hydrogen bondings, disappearance of goethite specific -OH def. in HNP@SWDC, and VSM. The as-fabricated reusable HNP@SWDC is employed for removing methylene blue (MB) and rhodamine B (RhB). Chemisorption of RhB/MB in HNP@SWDC via ionic, electrostatic, and hydrogen bonding interactions alongside dimerization of dyes are realized by ultraviolet-visible, FTIR, and fluorescence studies; pseudosecond order fitting; and activation energies. The adsorption capacity = 46.98-56.14/22.89-27.57 mg g^-1 for RhB/MB is noted using 0.01 g HNP@SWDC within 5-20 ppm dyes and 288-318 K.

Sustainable metal-free leather manufacture via synergistic effects of triazine derivative and vegetable tannins

Restrictions on heavy metals, especially chromium, have encouraged alternative tanning systems that can reduce environmental and human health risks from conventional chrome-based tanning. In this work, metal-free combination tanning was developed by using vegetable tannins and a triazine-based syntan containing active chlorine groups (SACC). Specifically, the relationship between leather performance (e.g., hydrothermal stability and organoleptic properties) and technical protocols (e.g., types and dose of tannins) was systematically established. The optimized protocol involving a unique procedure (i.e., 10% SACC pre-tanning, shaving, and 25% wattle tanning) endowed the leather with high shrinkage temperature (~ 92 °C) and met the Chinese standards for shoe upper leather (QB/T 1873-2010). Our method not only produces zero chrome-containing solid wastes, but also uses ~ 75% less tannin for leather manufacture. The excellent leather performance was ascribed to the synergistic effects, where SACC and wattle diffused into collagen fibrils and may bind to collagen via covalent, hydrogen and ionic bonding, locking the hierarchical structure of collagen from microfibrils to fiber bundles. Moreover, we summarized these findings and proposed a diffusion-binding-locking mechanism, providing new insights for current tanning theory. Together with the biodegradable spent tanning liquor, this approach will underpin the development of sustainable leather manufacture.

Graphical Abstract

Compact glyoxal tanning system: a chrome-free sustainable and green approach towards tanning-cum-upgradation of low-grade raw materials in leather processing

Increased concern over the use of metal salts such as chromium, zirconium, and aluminum for tanning of hides and skins has made the leather production industry to be constantly on the lookout for organic tanning agents in place of the inorganic system. Though glutaraldehyde has been looked at as a viable option, it still lags in imparting superior strength properties to the leather and also it has been reported to have inherent toxicity. With that concept in view, this research work focuses on the usage of glyoxal along with synthetic tanning agents as a replacement for glutaraldehyde and other inorganic tanning systems. The offer level and starting pH for the glyoxal tanning process was optimized as 6% (w/w) and 5.0, respectively, and the shrinkage temperature of the collagen was found to be around 80 °C. Additionally, the controlled shrunken grain effect of the aldehyde tanning system was explored by changing the pH of the process, which helped to improve the thickness of low-grade thinner raw materials by up to 40%. The mechanism for the shrunken grain effect has also been proposed in this work by studying the dimensional changes occurring in the leather matrix upon treating skin/hide with glyoxal at different pH levels. The mechanical and strength properties of the leather were found to be better than the glutaraldehyde tanning system. The BOD/COD ratio of wastewater generated from the glyoxal process was found to be greater than 0.3 making them easily treatable. Considering all these factors, compact glyoxal-based tanning along with synthetic tanning agents can be a game-changing technology for the leather processing industry.

Supramolecular Assembly of Multifunctional Collagen Nanocomposite Film via Polyphenol-Coordinated Clay Nanoplatelets

Functional bionanocomposites have evoked immense research interests in many fields including biomedicine, food packaging, and environmental applications. Supramolecular self-assembled bionanocomposite materials fabricated by biopolymers and two-dimensional (2D) nanomaterials have particularly emerged as a compelling material due to their biodegradable nature, hierarchical structures, and designable multifunctions. However, construction of these materials with tunable properties has been still challenging. Here, we report a self-assembled, flexible, and antioxidative collagen nanocomposite film (CNF) via regulating supramolecular interactions of type I collagen and tannic acid (TA)-functionalized 2D synthetic clay nanoplatelets Laponite (LAP). Specifically, TA-coordinated LAP (LAP-TA) complexes were obtained via chelation and hydrogen bonding between TA and LAP clay nanoplatelets and further used to stabilize the triple-helical confirmation and fibrillar structure of the collagen via hydrogen bonding and electrostatic interactions, forming a hierarchical microstructure. The obtained transparent CNF not only exhibited the reinforced thermal stability, enzymatic resistance, tensile strength, and hydrophobicity but also good water vapor permeability and antioxidation. For example, the tensile strength was improved by over 2000%, and the antioxidant property was improved by 71%. Together with the simple fabrication process, we envision that the resulting CNF provides greater opportunities for versatile bionanocomposites design and fabrication serving as a promising candidate for emerging applications, especially food packaging and smart wearable devices.

Manipulate the nano-structure of layered double hydroxides via calcination for enhancing immobilization of anionic dyes on collagen fibers

In this work, we present an effective approach for promoting the immobilization of anionic dyes on the collagen fibers of the leather matrix via introducing layered double oxide (LDO), which is obtained by calcining layered double hydroxides (LDH), inspired by incorporating their memory effect and charge effect. The results indicate that the calcination increases specific surface area, oxygen vacancies, and Al³⁺ defects of LDH nanosheets, and the structure of LDH nanosheets can be reconstructed by rehydration. Diffusion behavior of both LDH and LDO nanosheets into the collagen fibers follows the Langmuir model. The LDO nanosheets can penetrate into the collagen fibers more easily and evenly than that of the LDH nanosheets. Moreover, the formation of ionic bonds, hydrogen bonds, and coordination bonds between the nanosheets and the collagen stabilizing the collagen microstructures can endow the collagen fibers with improved thermal stability. Increased porosity of the collagen fibers results in enhanced adsorption and immobilization capacity for anionic dyes on the collagen fibers of the leather matrix in leather post-tanning process. Furthermore, adsorption behavior of anionic dye on the collagen fibers can be well accorded with pseudo-second-order and Langmuir model, exhibiting a monolayer adsorption process. This established cooperative approach will be helpful to extend the application of clay for improving the dyeing performance of leather matrix towards eco-leather manufacture and effectively reduce emission of dyes from the source in leather manufacturing.

A cleaner approach to tanning process of cattle hide upper suede leather: chrome-less polycarboxylate/montmorillonite nanocomposites as tanning agent

In this study, a cleaner approach to a 'sandwich' chrome-less tanning for cattle hide upper suede leather based on polycarboxylate/montmorillonite nanocomposite (PCM) has been developed. The chromium was reduced both in tanning process and retanning process. Hydrothermal stability, mechanical strength, and organoleptic properties of the leather were closed to traditional chrome tanning. The important advantage of the cleaner tanning approach is that the chromium load in wastewater decreased from 2302 mg/L in tanning process and 2919 mg/L in retanning process to 131 and 257 mg/L, respectively. Moreover, SEM analyses demonstrated that the leather tanned by PCM achieved loose fiber structure and flaky montmorillonite deposition both in intra-triple and inter-triple helix. XRD results suggested that basic chromium sulfate and PCM may form more complexation with the helix chain of collagen fiber, resulting in structural distortion of collagen molecules without destroying the triple helical structure. EDS liner scanning indicated the distribution of chromium on the cross section of the leather. Trypsin degradation curves revealed the cleaner approach might increase the degradation of leather, and the economic analysis results showed that the tanning costs could be reduced and increased the economic benefits.

De Novo Design of Functional Coassembling Organic-Inorganic Hydrogels for Hierarchical Mineralization and Neovascularization

Synthetic nanostructured materials incorporating both organic and inorganic components offer a unique, powerful, and versatile class of materials for widespread applications due to the distinct, yet complementary, nature of the intrinsic properties of the different constituents. We report a supramolecular system based on synthetic nanoclay (Laponite, Lap) and peptide amphiphiles (PAs, PAH3) rationally designed to coassemble into nanostructured hydrogels with high structural integrity and a spectrum of bioactivities. Spectroscopic and scattering techniques and molecular dynamic simulation approaches were harnessed to confirm that PAH3 nanofibers electrostatically adsorbed and conformed to the surface of Lap nanodisks. Electron and atomic force microscopies also confirmed an increase in diameter and surface area of PAH3 nanofibers after coassembly with Lap. Dynamic oscillatory rheology revealed that the coassembled PAH3-Lap hydrogels displayed high stiffness and robust self-healing behavior while gas adsorption analysis confirmed a hierarchical and heterogeneous porosity. Furthermore, this distinctive structure within the three-dimensional (3D) matrix provided spatial confinement for the nucleation and hierarchical organization of high-aspect ratio hydroxyapatite nanorods into well-defined spherical clusters within the 3D matrix. Applicability of the organic-inorganic PAH3-Lap hydrogels was assessed in vitro using human bone marrow-derived stromal cells (hBMSCs) and ex vivo using a chick chorioallantoic membrane (CAM) assay. The results demonstrated that the organic-inorganic PAH3-Lap hydrogels promote human skeletal cell proliferation and, upon mineralization, integrate with the CAM, are infiltrated by blood vessels, stimulate extracellular matrix production, and facilitate extensive mineral deposition relative to the controls.

3D bioprinting of mechanically tuned bioinks derived from cardiac decellularized extracellular matrix

3D bioprinting is a powerful technique for engineering tissues used to study cell behavior and tissue properties in vitro. With the right formulation and printing parameters, bioinks can provide native biological and mechanical cues while allowing for versatile 3D structures that recapitulate tissue-level organization. Bio-based materials that support cellular adhesion, differentiation, and proliferation - including gelatin, collagen, hyaluronic acid, and alginate - have been successfully used as bioinks. In particular, decellularized extracellular matrix (dECM) has become a promising material with the unique ability to maintain both biochemical and topographical micro-environments of native tissues. However, dECM has shown technical limitations for 3D printing (3DP) applications posed by its intrinsically low mechanical stability. Herein, we report hydrogel bioinks composed of partially digested, porcine cardiac decellularized extracellular matrix (cdECM), Laponite-XLG nanoclay, and poly(ethylene glycol)-diacrylate (PEG-DA). The Laponite facilitated extrusion-based 3DP, while PEG-DA enabled photo-polymerization after printing. Improving upon previously reported bioinks derived from dECM, our bioinks combine extrudability, shape fidelity, rapid cross-linking, and cytocompatibility in a single formulation (> 97% viability of encapsulated human cardiac fibroblasts and > 94% viability of human induced pluripotent stem cell derived cardiomyocytes after 7 days). The compressive modulus of the cured hydrogel bioinks was tunable from 13.4-89 kPa by changing the concentration of PEG-DA in the bioink formulation. Importantly, this span of mechanical stiffness encompasses ranges of tissue stiffness from healthy (compressive modulus ~5-15 kPa) to fibrotic (compressive modulus ~30-100 kPa) cardiac tissue states. The printed constructs demonstrated shape fidelity, adaptability to different printing conditions, and high cell viability following extrusion and photo-polymerization, highlighting the potential for applications in modeling both healthy and fibrotic cardiac tissue.

Hierarchical Incorporation of Surface-Functionalized Laponite Clay Nanoplatelets with Type I Collagen Matrix

Unraveling the interaction mechanisms of type I collagen with various inorganic nanoparticles is of pivotal importance to construct collagen-based bionanocomposites with hierarchical structures for biomedical, pharmaceutical, and other industrial applications. In this study, synthetic two-dimensional Laponite nanoplatelets (LAP NPs) are surface-functionalized with tetrakis(hydroxymethyl) phosphonium sulfate (THPS) for reinforcing their incorporation with type I collagen matrix by focusing on the influences of the interactions on the hierarchical structures of the collagen. Our results indicate that the LAP NPs can be successfully surface-functionalized with THPS via covalent bonds between the amine-functionalized NPs and the hydroxymethyl groups of THPS. Moreover, the resulting NPs can be well dispersed into the collagen matrix and evenly bound onto the collagen fiber strands and between the collagen fibrils, preserving the native D-periodic banding patterns of the collagen fibrils. The formation of covalent and hydrogen bonds between the collagen and the functionalized NPs can stabilize the intrinsic triple-helical conformation of the collagen, conferring the resulting collagen-based nanocomposites with improved thermal stability and enhanced mechanical properties. We anticipate that a fundamental understanding of the interactions between the collagen and functionalized inorganic nanoparticles would contribute to the design, fabrication, and further application of hierarchical collagen-based bionanocomposites with multifunctions.

Interaction between retanning agents and wet white tanned by a novel bimetal complex tanning agent

Abstract

A promising and practical chrome-free tanning system has been developed based on a novel Al–Zr bimetal complex tanning agent. However, to achieve satisfactory resultant leather, the retanning process that is compatible with this emerging tannage needs to be investigated systematically. This paper aims to explore the interaction between the bimetal complex tanned wet white and retanning agents. The isoelectric point (pI) of wet white was 7.2, which was nearly the same as wet blue. The electropositivity of wet white was even higher than that of wet blue during post-tanning processes, resulting in higher uptake rate of retanning agents. The distribution of various retanning agents in wet white was analyzed by pI measurement of layered leather and fluorescent tracing technique. The retanning agents were unevenly distributed throughout the cross-section, which might be an important restriction factor in obtaining satisfactory organoleptic properties of the crust leather. This fact is mainly due to the strong electrostatic interaction between anionic retanning agents and wet white. Applying a high dosage of multiple retanning agents in a proper sequence of addition benefited the full penetration of retanning agents in leather matrix and thus improved the organoleptic properties of crust leather. This work provides guidance for optimizing retanning process of the wet white leather.

Graphical abstract

Marinobacter sp. Stable Hydrous Titanium Oxide-Functionalized Bovine Serum Albumin Nanospheres for Uranium Capture from Spiked Seawater

A novel nanospherical hydrous titanium oxide adsorbent (hydrous titanium oxide-immobilized bovine serum albumin nanospheres, HTO-BSA-NSs) was prepared by immobilizing HTOs with a manipulated molecular mass and number of active sites for uranium on the surface of BSA-NSs. The adsorption performances of HTO-BSA-NSs were investigated in spiked natural seawater with extra 8 ppm uranium. The results demonstrated that HTO-BSA-NSs are capable of uranium capture from a complex aqueous matrix with a low uranium concentration. Meanwhile, the microbial stability of HTO-BSA-NSs in sterilized natural seawater with Marinobacter sp. was investigated and observed through an optical microscope and TEM, revealing that the wrapped HTOs could protect the BSA-NSs from the decomposition of microorganisms, and the structure and functional groups of HTO-BSA-NSs remain stable compared with the BSA-NSs. In addition, the uranium adsorption mechanism of HTO-BSA-NSs is mainly recognized as dehydrated complexation, which was concluded from characterization analysis, adsorption model fitting, and theoretical calculations based on density functional theory. The remarkable uranium adsorption performance and microbial stability of HTO-BSA-NSs indicated that they have the potential to be a low-cost and environmentally friendly adsorbent for uranium extraction from complex environments such as seawater or uranium-containing industrial wastewater.