Antimicrobial coating is of great important in leather finishing. Herein, we report a newly synthesized polyurethane with zwitterionic sulfobetaine side groups and evaluate their performance in the antifouling leather coatings. The microstructure of the synthesized zwitterionic polyurethane (iNPU) films has been examined by Fourier transform infrared (FTIR), X-ray diffraction (XRD) and atomic force microscopy (AFM) in order to understand how it influences the mechanical and surface properties. Our results show that introduction of zwitterionic groups into polyurethane can markedly increase the degree of micro-phase separation between the hard and soft segments of the PU chains since the incorporated zwitterionic group leads to more hydrogen bonding and polar interactions, making the hard components to be more thermodynamically incompatible with the soft segments. As the content of the incorporated zwitterionic content increases, the ordered structure in PU chains is reduced, and the micro-phase separation degree is increased. Therefore, the tensile strength and elongation at break of the iNPU films are significantly improved. Dynamic mechanical thermal analysis (DMTA) results further indicate that the Tg of the iNPU coatings decreases, and the deformability greatly increases at a higher content of zwitterionic group. Water contact angle (WCA) measurements reveal the improved surface wetting property due to the presence of zwitterionic group. The antibacterial testing shows that the iNPU coated leather surfaces exhibit reasonably good anti-mold adhesion performance, although the iNPU films do not show apparent contact-killing antibacterial property against E. coli and S. aureus. The present zwitterionic polyurethane is thus can be potentially used as antimicrobial adhesive leather coating materials.

In recent years, inorganic nanoparticles such as Laponite have frequently been incorporated into polymer matrixes to obtain nanocomposite hydrogels with hierarchical structures, ultrastrong tensibilities, and high transparencies. Despite their unique physical and chemical properties, only a few reports have evaluated Laponite-based nanocomposite hydrogels for biomedical applications. This article presents the synthesis and characterization of a novel, hemocompatible nanocomposite hydrogels by in situ polymerization of acrylamide (AAm) in a mixed suspension containing Laponite and gelatin. The compatibility, structure, thermal stability, and mechanical properties of the resulting NC gels with varied gel compositions were investigated. Our results show that the prepared nanocomposite hydrogels exhibit good thermal stability and mechanical properties. The introduction of a biocompatible polymer, gelatin, into the polymer matrix did not change the transparency and homogeneity of the resulting nanocomposite hydrogels, but it significantly decreased the hydrogel’s pH-responsive properties. More importantly, gelatins that were incorporated into the PAAm network resisted nonspecific protein adsorption, improved the degree of hemolysis, and eventually prolonged the clotting time, indicating that the in vitro hemocompatibility of the resulting nanocomposite hydrogels had been substantially enhanced. Therefore, these nanocomposite hydrogels provide opportunities for potential use in various biomedical applications.Keywords: gelatin; hemocompatible; Laponite; nanocomposite hydrogels; PAAm

•The Mw of water soluble DCMC is 2.38 × 105 g/mol measured by LLS.•Incorporation of minute DCMC can induce cross-linked collagen cryogel.•Crosslinking reaction and cryogenic treatment do not destroy collagen triple helix.•The cryogel has a heterophase structure and displays good biological properties.We present the use of a natural derivative, dialdehyde carboxymethyl cellulose (DCMC) as the cross-linker for the preparation of spongy collagen cryogels by freezing-thawing method. The DCMC has been characterized by laser light scattering (LLS), showing the molecular weight of 2.38 × 105 g/mol. FT-IR studies demonstrate that the cross-linking reaction and the cryogenic treatment do not destroy the triple helix of collagen. SEM images indicate that the cryogel has a heterophase structure with interconnecting macropores. DSC measurements reveal that the incorporation of a very small amount of DCMC can significantly improve the thermal stability of collagen. Moreover, the cryogels exhibit fast swelling rate, and their equilibrium swelling ratio is related to DCMC content and pH-dependent. The in vitro blood-compatibility tests prove that the introduction of DCMC does not cause the reducing performance in hemolysis and blood clotting compared with pure collagen. Hence, the low-cost and non-toxic nature of DCMC confers the cryogel great potential in tissue engineering and other biomedical applications.

We have developed a novel approach to introduce zwitterions into polyurethane for the preparation of antibiofouling coating. First, the thiol–ene click reaction between 2-(dimethylamino)ethyl methacrylate (DMAEMA) and 3-mercapto-1,2-propanediol (TPG) is used to synthesize dihydroxy-terminated DMAEMA (DMA(OH)2) under UV catalysis. The product has been proved by gel permeation chromatography (GPC), Fourier transform infrared spectrum (FT-IR), proton nuclear magnetic resonance (1H NMR), and high resolution mass spectrometry (HRMS). DMA(OH)2 is then incorporated into polyurethane as side groups by polyaddition with diisocyanate and further reacts with 1,3-propane sultone to obtain the zwitterionic polyurethanes. The presence of sulfobetaine zwitterions side groups has been demonstrated by FT-IR and X-ray photoelectron spectroscopy (XPS). Thermal analysis indicates that the thermal stability is decreased with the increasing content of zwitterionions. The antibiofouling property of polyurethanes has been investigated by the measurement of adsorption of fibrinogen, bovine serum albumin (BSA), and lysozyme on the polyurethanes surface using quartz crystal microbalance with dissipation (QCM-D). The results show that the polyurethane coatings exhibit effective nonspecific protein resistance at higher content of zwitterionic side groups.

Ultrasensitive differential scanning calorimetry (US-DSC) was used to directly measure the thermal transition temperature and energy change of acid soluble collagen in the presence of Cr3 + and Al3 + sulfates. The behavior of Cr3 + was analogous to kosmotropes in the cation Hofmeister series and increased the stability of collagen in dilute solutions. Meanwhile, the denaturational enthalpy change (ΔH) of collagen was substantially reduced with change to increasing Cr3 + concentration. This is likely due to the uni-point binding of Cr3 + with carboxyl groups of collagen side chains that could decrease the hydrogen-bonding in collagen and result in the increase of protein hydrophobicity. In the case of Al3 +, the interactions between the ions and collagen showed very different properties: at low and medium ion concentrations, the stability of the collagen was decreased; however, a further increase of Al3 + concentration led to a salting-out effect of collagen, indicating the Al3 + is a typical chaotropic ion. This striking difference of the two ions in the stabilization of collagen can be explained in terms of the different interactions between the cations and the carboxyl groups of collagen side chains. Additionally, we studied metal ion induced conformational change by the combination of circular dichroism (CD) and atomic force microscopy (AFM). CD measurements revealed that neither metal ion interactions of collagen with Cr3 + nor Al3 + ions destroyed the triple-helical backbone structure of collagen in the solution. AFM results further confirmed that the dehydration of collagen by Cr3 + is more significant than Al3 +, thus inducing the aggregation of collagen fibrils.US-DSC thermograms showed significantly different effects of Cr3 + and Al3 + on acid soluble collagen (ΔH, Tm, Cp). These differences can be explained by specific ion effect following the concept of matching water affinities. Neither Cr3 + nor Al3 + destroyed the collagen triple helix but induced different molecular aggregation morphologies.Highlights► Cr3 + increased collagen thermostability but decreased its denaturational enthalpy. ► Al3 + decreased collagen stability at low and medium ion concentrations. ► The behavior of Cr3 + was analogous to kosmotropes, whereas Al3 + was chaotropic. ► Neither Cr3 + nor Al3 + destroyed the triple helix conformation of collagen. ► Cr3 + and Al3 + induced different morphological changes of collagen.

In the past, many thermoanalytical studies revealed that the denaturation of type I collagen solution in acetic acid exhibited a bimodal transition with a pre-transition endothermal peak before a distinct major one. This pre-transition peak has been assigned to various origins, but there has no well-accepted explanation. Herein, by using ultrasensitive differential scanning calorimetry, we have comparatively measured the thermal denaturation of type I and II collagens in dilute solutions and reexamined their structural transitions. Our results show that the pre-transition is not because of previously suggested defibrillation of collagen in solution. It is however related to the thermally labile regions with hydroxyproline deficient sequences. More interestingly, a minor new peak is created near the position of previous pre-transition, being at the expense of the major transition. Our US-DSC results thereby demonstrate that the consecutive two-stage denaturational transitions for type I collagen correspond to different structural origins, respectively.Graphical abstractHighlights► The thermal denaturation of type I and II collagens has been measured by US-DSC. ► Pre-transition of type I is related to thermally labile regions with deficient Hyp. ► The two-stage denaturation of type I corresponds to different structural origins.

Conversion of carboxymethyl cellulose (CMC) to its dialdehyde derivatives by periodate oxidization in acid solutions has been investigated as a function of pH, temperature, reaction time and periodate dosage. Our results show that the stoichiometric ratio of NaIO4 to CMC and the pH of aqueous medium are substantially responsible for the aldehyde content and yield of the product. Laser light scattering (LLS) and wide angle X-ray diffraction (WAXD) measurements demonstrate that physical and chemical degradations concomitant with the oxidization process occur, leading to the decrease in 〈Rh〉 and crystallinity, respectively. The degradation mechanism for acid-catalyzed cleavage of β-1-4-glycosidic bond is proposed. Atomic force microscopy (AFM) images reveal the morphological changes of CMC with the degree of oxidization. The present study quantitatively indicates the substantial degradation in derivatization of cellulose by periodate oxidization method, and is helpful for exploring novel carboxymethyl polysaccharide derivatives.

The application of ultrasonic irradiation (40 KHz, 120 W) in the enzymatic extraction of bovine tendon collagen has been investigated. Our results show that using the ultrasonic irradiation increases the yield of collagen up to ∼124% and significantly shortens the extraction time in comparison with the conventional pepsin isolation method. Such improvements are attributed to the enhancement of the enzyme activity and the dissolution of collagen substrate because the ultrasonic irradiation disperses the pepsin aggregates and opens up the collagen fibrils, thus the enzymatic hydrolysis is facilitated. AFM imaging shows the same fibrillar structure of tendon collagens generated from both the methods. The CD and FT-IR measurements reveal that the triple helix structure of collagen remains intact even after the ultrasonic irradiation. This study shows that the mild ultrasound irradiation can effectively improve the efficiency of pepsin extraction of natural collagen without any compromise of the resultant collagen quality.

We have investigated the effects of Cr3+ on the hierarchical structure of pigskin collagen fibers by use of scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), wide-angle X-ray diffraction (WAXD), confocal laser micro-Raman spectroscopy (CLRS), and circular dichroism (CD). Our results demonstrate that the introduction of Cr3+ leads to the formation of a cluster of 20−40 nm between collagen fibrils, while the unique axial periodic structure (D periodicity) of the fibrils does not change. As the Cr3+ concentration increases, the order of intermolecular lateral packing, crystallite structure within helical chains, and N and C telopeptide regions decrease. The present study reveals that Cr3+ only cross-links with collagen but does not disrupt its triple helical structure.