Enzymatic grafting of chitosan onto Bombyx mori silk fibroin: kinetic and IR vibrational studies

Antimicrobial fibres derived from aryl-diazonium conjugation of chitosan with Harakeke (Phormium tenax) and Hemp (Cannabis sativa) Hurd

Surface functionalisation of natural materials to develop sustainable and environmentally friendly antimicrobial fibres has received great research interest in recent years. Herein, chitosan covalent conjugation via aryl-diazonium based chemistry onto Phormium tenax fibres (PTF) and hemp hurds (HH) was investigated. PTF are fibres derived from Harakeke/New Zealand flax, an indigenous and abundant plant source of leaf fibres, which served as an important 19th century export commodity of New Zealand. HH are obtained as a by-product from the hemp (Cannabis sativa) industry and find applications as traditional construction material, animal bedding, chemical absorbent, insulation, fireboard etc. This study reports aryl-diazonium covalent attachment of chitosan and PD13 (6-O-(3-(2-(N,N-dimethylamino)ethylamino)-2-hydroxypropyl)chitosan), a chitosan derivative with improved antibacterial activity, on to PTF and HH. The modification was confirmed using FTIR, XPS, SEM and water contact angle studies. Comparison of aryl-diazonium versus the use of succinic anhydride bridging for chitosan attachment was also investigated, with the diazonium method giving improved results. The treated PTF and HH fibres had good antibacterial activity against Staphylococcus aureus and this study contributes to the development of sustainable antibacterial fibres using bio-based materials.

Functional modification of silk fibroin from silkworms and its application to medical biomaterials: A review

Silk fibroin (SF) from the silkworm Bombyx mori is a fibrous protein identified as a widely suitable biomaterial due to its biocompatibility, tunable degradation, and mechanical strength. Various modifications of SF protein can give SF fibers new properties and functions, broadening their applications in textile and biomedical industries. A diverse array of functional modifications on various forms of SF has been reported. In order to provide researchers with a more systematic understanding of the types of functional modifications of SF protein, as well as the corresponding applications, we comprehensively review the different types of functional modifications, including transgenic modification, modifications with chemical groups or biologically active substance, cross-linking and copolymerization without chemical reactions, their specific modification methods and applications. Furthermore, recent applications of SF in various medical biomaterials are briefly discussed.

Hydrogels: An overview of its classifications, properties, and applications

The review paper starts with the introduction to hydrogels along with broad literature survey covering different modes of synthesis including high energy radiation methods. After that, paper covered broad classification of the hydrogels depending upon the basis of their source of origin, method of synthesis, type of cross-linking present and ionic charges on bound groups. Another advanced category response triggered hydrogels, which includes pH, temperature, electro, and light and substrate responsive hydrogels was also studied. Presented paper summarises chemical structure, properties, and synthesis of different kinds of hydrogels. Main focus was given to the preparation super absorbents such as: Semi-interpenetrating networks (semi-IPNs), Interpenetrating networks (IPNs) and cross-linked binary graft copolymers (BGCPs). The weak mechanical properties and easy degradation limit the uses of bio-based -hydrogels in biomedical field. Their properties can be improved through different chemical and physical methods. These methods were also discussed in the current research paper. Also, it includes development of hydrogels as controlled drug delivery devices, as implants and biomaterials to replace malfunctioned body parts along with their use in several other applications listed in the literature. Literature survey on the application of hydrogels in different fields like biomedical, nano-biotechnology, tissue engineering, drug delivery and agriculture was also carried out.

Biomedical applications of chitosan/silk fibroin composites: A review

Natural polymers have been used in the biomedical fields for decades, mainly derived from animals and plants with high similarities with biomacromolecules in the human body. As an alkaline polysaccharide, chitosan (CS) attracts much attention in tissue regeneration and drug delivery with favorable biocompatibility, biodegradation, and antibacterial activity. However, to overcome its mechanical properties and degradation behavior drawbacks, a robust fibrous protein-silk fibroin (SF) was introduced to prepare the CS/SF composites. Not only can CS be combined with SF via the amide and hydrogen bond formation, but also their functions are complementary and tunable with the blending ratio. To further improve the performances of CS/SF composites, natural (e.g., hyaluronic acid and collagen) and synthetic biopolymers (e.g., polyvinyl alcohol and hexanone) were incorporated. Also, the CS/SF composites acted as slow-release carriers for inorganic non-metals (e.g., hydroxyapatite and graphene) and metal particles (e.g., silver and magnesium), which could enhance cell functions, facilitate tissue healing, and inhibit bacterial growth. This review presents the state-of-the-art and future perspectives of different biomaterials combined with CS/SF composites as sponges, hydrogels, membranes, particles, and coatings. Emphasis is devoted to the biological potentialities of these hybrid systems, which look rather promising toward a multitude of applications.

Tyrosinase Magnetic Cross-Linked Enzyme Aggregates: Biocatalytic Study in Deep Eutectic Solvent Aqueous Solutions

In the field of biocatalysis, the implementation of sustainable processes such as enzyme immobilization or employment of environmentally friendly solvents, like Deep Eutectic Solvents (DESs) are of paramount importance. In this work, tyrosinase was extracted from fresh mushrooms and used in a carrier-free immobilization towards the preparation of both non-magnetic and magnetic cross-linked enzyme aggregates (CLEAs). The prepared biocatalyst was characterized and the biocatalytic and structural traits of free tyrosinase and tyrosinase magnetic CLEAs (mCLEAs) were evaluated in numerous DES aqueous solutions. The results showed that the nature and the concentration of the DESs used as co-solvents significantly affected the catalytic activity and stability of tyrosinase, while the immobilization enhanced the activity of the enzyme in comparison with the non-immobilized enzyme up to 3.6-fold. The biocatalyst retained the 100% of its initial activity after storage at -20 °C for 1 year and the 90% of its activity after 5 repeated cycles. Tyrosinase mCLEAs were further applied in the homogeneous modification of chitosan with caffeic acid in the presence of DES. The biocatalyst demonstrated great ability in the functionalization of chitosan with caffeic acid in the presence of 10% v/v DES [Bet:Gly (1:3)], enhancing the antioxidant activity of the films.

Preparation and Characterization of Phenolic Acid-Chitosan Derivatives as an Edible Coating for Enhanced Preservation of Saimaiti Apricots

In this study, caffeic acid (CA) and chlorogenic acid (CGA) were incorporated onto chitosan (CS) using free radical grafting initiated by a hydrogen peroxide/ascorbic acid (H₂O₂/Vc) redox system. The structural properties of the CA (CA-g-CS) and CGA (CGA-g-CS) derivatives were characterized by UV-Vis absorption, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and thermal stability analysis. Then, the antioxidant and antibacterial properties were evaluated, and the effect of CGA-g-CS on the postharvest quality of Saimaiti apricot was studied. It proved that phenolic acids were successfully grafted onto the CS. The grafting ratios of CA-g-CS and CGA-g-CS were 126.21 mg CAE/g and 148.94 mg CGAE/g. The antioxidation and antibacterial activities of CGA-g-CS were better than those of CA-g-CS. The MICs of CGA-g-CS against E. coli, S. aureus, and B. subtilis were 2, 1, and 2 mg/mL. The inhibitory zones of 20 mg/mL CGA-g-CS against the three bacteria were 19.16 ± 0.35, 16.33 ± 0.91, and 16.24 ± 0.05 mm. The inhibitory effects of 0.5% CGA-g-CS on the firmness, weight loss, SSC, TA, relative conductivity, and respiration rate of the apricot were superior. Our results suggest that CGA-g-CS can be potentially used as an edible coating material to preserve apricots.

Fiber-based photothermal, UV-resistant, and self-cleaning coatings fabricated by silicon grafted copolymers of chitosan derivatives and gallic acid

Superhydrophobic and hydrophobic properties are generally created by adopting low surface free energy materials. Therefore, most studies have focused on creating surface hydrophobicity by using hydrophobic or fluorinated materials. However, few studies are reported on realizing surface hydrophobicity by directly introducing hydrophilic molecules, which is also a challenge. Herein, with platinum nanozyme as the catalyst, the novel hydrophobic coatings have been rapidly gained via anchoring the polymer of hydrophilic gallic acid and chitosan or chitosan quaternary ammonium salt onto cotton fabric surface. Notably, the novel hydrophobic coatings exhibit significant advances compared with conventional hydrophobic ones created by utilizing fluorinated or hydrophobic materials, which breaks the limitation of employing low surface energy materials for gaining surface hydrophobicity. Subsequently, the sodium methyl silicate was grafted on the polymer's coatings to strengthen surface hydrophobicity and the abrasion resistance of hydrophobicity. Interestingly, the heating could induce the hydrophilicity of cotton fabric to recover to hydrophobicity. Moreover, the hydrophobic coatings also possess good photothermal conversion, UV resistance, and anti-oxidation activity for self-cleaning application and oil water separation. Briefly, the present work may open a new direction for preparing novel hydrophobic coatings by combining gallic acid and chitosan-based macromolecular carbohydrates.

Recent advances in bioprinting using silk protein-based bioinks

3D printing has experienced swift growth for biological applications in the field of regenerative medicine and tissue engineering. Essential features of bioprinting include determining the appropriate bioink, printing speed mechanics, and print resolution while also maintaining cytocompatibility. However, the scarcity of bioinks that provide printing and print properties and cell support remains a limitation. Silk Fibroin (SF) displays exceptional features and versatility for inks and shows the potential to print complex structures with tunable mechanical properties, degradation rates, and cytocompatibility. Here we summarize recent advances and needs with the use of SF protein from Bombyx mori silkworm as a bioink, including crosslinking methods for extrusion bioprinting using SF and the maintenance of cell viability during and post bioprinting. Additionally, we discuss how encapsulated cells within these SF-based 3D bioprinted constructs are differentiated into various lineages such as skin, cartilage, and bone to expedite tissue regeneration. We then shift the focus towards SF-based 3D printing applications, including magnetically decorated hydrogels, in situ bioprinting, and a next-generation 4D bioprinting approach. Future perspectives on improvements in printing strategies and the use of multicomponent bioinks to improve print fidelity are also discussed.

Dual-Stage Blue-Light-Guided Membrane and DNA-Targeted Photodynamic Inactivation Using Octyl Gallate for Ultraefficient Eradication of Planktonic Bacteria and Sessile Biofilms

This study aimed to investigate the synergistic bactericidal activity and mechanism of dual-stage light-guided membrane and DNA-targeted photodynamic inactivation (PDI) by the combination of blue light (BL, 420 nm) and the food additive octyl gallate (OG) against Vibrio parahaemolyticus in planktonic and biofilm growth modes. While OG serves as an outstanding exogenous photosensitizer, the planktonic cells were not visibly detectable after the OG-mediated PDI treatment with 0.2 mM OG within 15 min (191.7 J/cm²), and its biofilm was nearly eradicated within 60 min (383.4 J/cm²). Gram-positive Staphylococcus aureus was more susceptible to the PDI than Gram-negative V. parahaemolyticus. The cellular wall and proteins, as well as DNA, were the vulnerable targets for PDI. The membrane integrity could be initially disrupted by OG bearing a hydrophilic head and a hydrophobic tail via transmembrane insertion. The enhancement of OG uptake due to the first-stage light-assisted photochemical internalization (PCI) promoted the accumulation of OG in cells. It further boosted the second-stage light irradiation of the photosensitizer-inducing massive cell death. Upon the second-stage BL irradiation, reactive oxygen species (ROS) generated through the OG-mediated PDI in situ could extensively deconstruct membranes, proteins, and DNA, as well as biofilms, while OG could be activated by BL to carry out photochemical reactions involving the formation of OG-bacterial membrane protein (BMP) covalent conjugates and the interactions with DNA. This dual-stage light-guided subcellular dual-targeted PDI strategy exhibits encouraging effects on the eradication of planktonic bacteria and sessile biofilms, which provides a new insight into the development of an ultraeffective antimicrobial and biofilm removing/reducing technique to improve microbiological safety in the food industry.

Crosslinkers for polysaccharides and proteins: Synthesis conditions, mechanisms, and crosslinking efficiency, a review

Polysaccharides and proteins are important macromolecules for developing hydrogels devoted to biomedical applications. Chemical hydrogels offer chemical, mechanical, and dimensional stability than physical hydrogels due to the chemical bonds among the chains mediated by crosslinkers. There are many crosslinkers to synthesize polysaccharides and proteins based on hydrogels. In this review, we revisited the crosslinking reaction mechanisms between synthetic or natural crosslinkers and polysaccharides or proteins. The selected synthetic crosslinkers were glutaraldehyde, carbodiimide, boric acid, sodium trimetaphosphate, N,N'-methylene bisacrylamide, and polycarboxylic acid, whereas the selected natural crosslinkers included transglutaminase, tyrosinase, horseradish peroxidase, laccase, sortase A, genipin, vanillin, tannic acid, and phytic acid. No less important are the reactions involving click chemistry and the macromolecular crosslinkers for polysaccharides and proteins. Literature examples of polysaccharides or proteins crosslinked by the different strategies were presented along with the corresponding highlights. The general mechanism involved in chemical crosslinking mediated by gamma and UV radiation was discussed, with particular attention to materials commonly used in digital light processing. The evaluation of crosslinking efficiency by gravimetric measurements, rheology, and spectroscopic techniques was presented. Finally, we presented the challenges and opportunities to create safe chemical hydrogels for biomedical applications.

Rapid Antibacterial Effects of Silk Fabric Constructed through Enzymatic Grafting of Modified PEI and AgNP Deposition

Enzymatic antibacterial finishing is an eco-friendly alternative to develop functional silk-based materials. However, the low accessibility of tyrosine residues distributed in fibroin chains restricts the laccase-mediated functionalization of silk fibers (SF). To address this issue, a highly reactive p-hydroxyphenylacetic acid-modified polyethyleneimine (mPEI) was enzymatically grafted onto fibroin using laccase, aiming at constructing an antibacterial matrix of mPEI on the fiber surface. Subsequently, in situ deposition of silver nanoparticles (i.e., AgNPs) into the newly built mPEI network was performed to form a rapid antibacterial layer. The results indicated that laccase efficiently catalyzes the mPEI coupling, the zeta potential of SF-g-mPEI increases from -32 to 21.70 mV, and the silver content reaches 1.81% after AgNP embedment. Based on the combined two-step treatments, the obtained silk fabric exhibited excellent antibacterial abilities against two bacteria, including Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The antibacterial rates of both bacteria reached 99.9% within 30 min of contact, remaining over 99.9% within 18 h of contact even after washing 10 times. The present work provides an enzyme-mediated method for construction of silk fabric with durable and rapid antibacterial activity.

Biopolymer Matrices Based on Chitosan and Fibroin: A Review Focused on Methods for Studying Surface Properties

For the creation of tissue-engineered structures based on natural biopolymers with the necessary chemical, physical, adhesive, morphological, and regenerative properties, biocompatible materials based on polysaccharides and proteins are used. This work is devoted to a problem of the technology of polymeric materials for biomedical purposes: the creation of biopolymer tissue engineering matrix and the development of a methodology for studying morphology and functional properties of their surface to establish the prospects for using the material for contact with living objects. The conditions for the formation of scaffolds based on composite materials of chitosan and fibroin determine the structure of the material, the thickness and orientation of molecular layers, the surface morphology, and other parameters that affect cell adhesion and growth. The analysis of studies of the morphology and properties of the surface of biopolymer matrices obtained using different methods of molding from solutions of chitosan and fibroin is carried out.

Alginate Bioconjugate and Graphene Oxide in Multifunctional Hydrogels for Versatile Biomedical Applications

In this work, we combined electrically-conductive graphene oxide and a sodium alginate-caffeic acid conjugate, acting as a functional element, in an acrylate hydrogel network to obtain multifunctional materials designed to perform multiple tasks in biomedical research. The hybrid material was found to be well tolerated by human fibroblast lung cells (MRC-5) (viability higher than 94%) and able to modify its swelling properties upon application of an external electric field. Release experiments performed using lysozyme as the model drug, showed a pH and electro-responsive behavior, with higher release amounts and rated in physiological vs. acidic pH. Finally, the retainment of the antioxidant properties of caffeic acid upon conjugation and polymerization processes (Trolox equivalent antioxidant capacity values of 1.77 and 1.48, respectively) was used to quench the effect of hydrogen peroxide in a hydrogel-assisted lysozyme crystallization procedure.

Chitosan grafted/cross-linked with biodegradable polymers: A review

Public perception of polymers has been drastically changed with the improved plastic management at the end of their life. However, it is widely recognised the need of developing biodegradable polymers, as an alternative to traditional petrochemical polymers. Chitosan (CH), a biodegradable biopolymer with excellent physiological and structural properties, together with its immunostimulatory and antibacterial activity, is a good candidate to replace other polymers, mainly in biomedical applications. However, CH has also several drawbacks, which can be solved by chemical modifications to improve some of its characteristics such as solubility, biological activity, and mechanical properties. Many chemical modifications have been studied in the last decade to improve the properties of CH. This review focussed on a critical analysis of the state of the art of chemical modifications by cross-linking and graft polymerization, between CH or CH derivatives and other biodegradable polymers (polysaccharides or proteins, obtained from microorganisms, synthetized from biomonomers, or from petrochemical products). Both techniques offer the option of including a wide variety of functional groups into the CH chain. Thus, enhanced and new properties can be obtained in accordance with the requirements for different applications, such as the release of drugs, the improvement of antimicrobial properties of fabrics, the removal of dyes, or as scaffolds to develop bone tissues.

Enzyme Cascade Reaction Involving Lytic Polysaccharide Monooxygenase and Dye-Decolorizing Peroxidase for Chitosan Functionalization

In situ H₂O₂ generation systems are efficient for H₂O₂-dependent biocatalytic oxidation reactions. Here, we report that lytic polysaccharide monooxygenases (LPMOs), copper-dependent polysaccharide monooxygenases, can efficiently supply H₂O₂ in situ to dye-decolorizing peroxidases (DyPs) using substrate gallic acid (GA) for chitosan functionalization. The maximum grafting ratio induced by the cascade reaction was significantly higher than that achieved by a reaction with initial exogenous H₂O₂. The maximum grafting ratio was obtained with 12 g/L GA, 5.6 mg/L DyP, 20-30 mg/L LPMO, and pH 4.5-5.0. UV-vis, Fourier transform infrared (FT-IR), and nuclear magnetic resonance (¹H NMR) spectroscopy confirmed GA grafting onto chitosan. X-ray diffraction (XRD) analysis and thermogravimetric analysis (TGA) indicated that GA-chitosan conjugates had lower thermal stability and crystallinity than chitosan. The GA-chitosan conjugates had significantly higher antioxidant activity than chitosan. This study supplies a green and high-efficiency approach to achieve an enzymatic cascade reaction for chitosan functionalization and has potential applications in H₂O₂-dependent biocatalytic oxidation reactions.

Antimicrobial Chitosan Conjugates: Current Synthetic Strategies and Potential Applications

As a natural polysaccharide, chitosan possesses good biocompatibility, biodegradability and biosafety. Its hydroxyl and amino groups make it an ideal carrier material in the construction of polymer-drug conjugates. In recent years, various synthetic strategies have been used to couple chitosan with active substances to obtain conjugates with diverse structures and unique functions. In particular, chitosan conjugates with antimicrobial activity have shown great application prospects in the fields of medicine, food, and agriculture in recent years. Hence, we will place substantial emphasis on the synthetic approaches for preparing chitosan conjugates and their antimicrobial applications, which are not well summarized. Meanwhile, the challenges, limitations, and prospects of antimicrobial chitosan conjugates are described and discussed.

Insect Cuticle-Mimetic Hydrogels with High Mechanical Properties Achieved via the Combination of Chitin Nanofiber and Gelatin

By mimicking the natural sclerotization process of insect cuticles, a novel nanofiber-reinforced gelatin hydrogel was developed with improved mechanical properties, which was further strengthened through quinone cross-linking. Because quinone cross-linking reacts between amino groups by increasing the amino group content on the chitin crystalline surface through alkali treatment, surface-deacetylated chitin nanofibers (SD-ChNFs) were prepared to facilitate the cross-linking reaction between SD-ChNF and gelatin. This technique resulted in a tough hydrogel with a dark color. In comparison to a non-cross-linked version, the quinone-cross-linked SD-ChNF/gelatin hydrogel exhibited significantly improved tensile performance. Notably, by controlling the cross-linking reaction time from 6 to 48 h, the tensile strength of the quinone-cross-linked hydrogels can be modified and can reach as high as 2.96 MPa while displaying a variable brown color. Given the eco-friendly, biocompatible, and sustainable properties of chitin and gelatin, these bioinspired hydrogels provide potential applications in the agricultural and biomedical fields.

Thiolation and characterization of regenerated Bombyx mori silk fibroin films with reduced glutathione

Bombyxmori silk fibroin-based materials have good biocompatibility and biodegradability. In order to maximize their utility while maintain appropriate features, silk fibroin (SF) films were modified with reduced glutathione (GSH) (NH₂)–ECG–(COOH), using the carbodiimide chemistry method, for the introduction of thiol groups onto surfaces. The effects of this modification on SF films’ chemical and physical properties, and cytotoxicity were assessed. The chemical and elemental composition analysis results suggested that reduced glutathione (GSH) was covalently coupled onto the surface of silk fibroin films. Atomic force microscopy (AFM) results indicated the surface roughness of silk fibroin film was increased after the modification by GSH. The GSH-modified silk fibroin films also showed the smaller contact angle due to the hydrophilic peptides coupled on the film surface. Through MTT assay, it was shown that the chemically modified SF film was not cytotoxic to HEK293 cells, and it had no adverse influence on the growth of HEK293 cells. Our approach provides a new option to engineer SF-based material surface with thiol groups in order to allow for secondary reactions and holds great promise for applications of SF-based materials in the biomedical field.

Effect of tyrosinase-catalyzed crosslinking on the structure and allergenicity of turbot parvalbumin mediated by caffeic acid

BACKGROUND

Enzymatic treatment of allergenic protein can alter their functional properties under a mild reaction condition due to specificity of enzymes. Phenolic compounds act as mediators and enhance the crosslinking reactions. The study aimed to assess the changes in the structure and immunoglobulin G (IgG) binding capacity of turbot parvalbumin (PV) upon crosslinking with tyrosinase (Tyr) in the absence and presence of caffeic acid.

RESULTS

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis revealed the appearance of higher molecular weight bands (24, 36 kDa) in the crosslinked PV. The secondary structure of crosslinked PV became loosened and disordered. The results of intrinsic fluorescence and ultraviolet absorption spectral analyses, as well as surface hydrophobicity and free amino group analyses also revealed structural changes. As observed by western blot analysis, the intensity of the PV bands reduced upon Tyr treatment, indicating reduced binding of specific IgG to PV. Moreover, the indirect ELISA (enzyme-linked immunosorbent assay) analysis confirmed that the IgG binding ability of crosslinked PV was reduced 34.94%.

CONCLUSION

Enzymatic treatment mitigated the allergenicity of fish PV, which was closely related to the alterations in the conformational structure. This treatment showed potential for developing hypoallergenic fish products under mild reaction conditions. © 2019 Society of Chemical Industry.

Evaluation of a Novel Collagenous Matrix Membrane Cross-Linked with Catechins Catalyzed by Laccase: A Sustainable Biomass

Collagen, a sustainable and biodegradable biomass material, has many applications in different scope including application in food packaging. However, owing to its poor mechanical properties, this kind of application is limited. In this work, collagen was cross-linked with catechin under the incubation of laccase to improve the mechanical properties of collagen, and the cross-linked collagen exhibited properties of excellent antioxidant capacity and lower swelling ratio. Meanwhile, Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) results provide evidence for changes in the structure of collagen after being cross-linked with the catechin. From the aspects of the thermal stability, tensile strength, elongation, antioxidant capacity, swelling, solubility, and morphological analysis, the cross-linked collagen has better physical properties in comparison with natural collagen. This indicates that the physical properties and antioxidant capacity of collagen after being cross-linked with catechins were improved significantly. Therefore, the cross-linked collagen can be used as green food-packaging materials.

Combining antioxidant hydrogels with self-assembled microparticles for multifunctional wound dressings

A multi-functional composite to be employed as a dressing material was prepared by combining hydrogel and microparticle systems.

Nanostructure-Enabled and Macromolecule-Grafted Surfaces for Biomedical Applications

Advances in nanotechnology and nanomaterials have enabled the development of functional biomaterials with surface properties that reduce the rate of the device rejection in injectable and implantable biomaterials. In addition, the surface of biomaterials can be functionalized with macromolecules for stimuli-responsive purposes to improve the efficacy and effectiveness in drug release applications. Furthermore, macromolecule-grafted surfaces exhibit a hierarchical nanostructure that mimics nanotextured surfaces for the promotion of cellular responses in tissue engineering. Owing to these unique properties, this review focuses on the grafting of macromolecules on the surfaces of various biomaterials (e.g., films, fibers, hydrogels, and etc.) to create nanostructure-enabled and macromolecule-grafted surfaces for biomedical applications, such as thrombosis prevention and wound healing. The macromolecule-modified surfaces can be treated as a functional device that either passively inhibits adverse effects from injectable and implantable devices or actively delivers biological agents that are locally based on proper stimulation. In this review, several methods are discussed to enable the surface of biomaterials to be used for further grafting of macromolecules. In addition, we review surface-modified films (coatings) and fibers with respect to several biomedical applications. Our review provides a scientific update on the current achievements and future trends of nanostructure-enabled and macromolecule-grafted surfaces in biomedical applications.

Oxidation of municipal wastewater by free radicals mechanism. A UV/Vis spectroscopy study

This study investigates the oxidation of municipal wastewater (WW) by complexation with natural polyphenols having radical scavenging activity, such as (3,4,5 tri-hydroxy-benzoic acid) gallic acid (GA) in alkaline pH (>7), under ambient O₂ and temperature. Physicochemical and structural characteristics of GA-WW complex-forming are evaluated by UV/Vis spectroscopy. The comparative analysis among UV/Vis spectra of GA monomer, GA-GA polymer, WW compounds, and GA-WW complex reveals significant differences within 350-450 and 500-900 nm. According to attenuated total reflectance (ATR) spectroscopy and thermogravimetric analysis (TGA), these spectra differences correspond to distinct complexes formed. This study suggests a novel role of natural polyphenols on the degradation and humification of wastes.

A comparative investigation of Bombyx mori silk fibroin hydrogels generated by chemical and enzymatic cross-linking

Fibroin, the major proteinaceous component of the silk fiber produced by larvae of the domesticated silk moth (Bombyx mori), has been widely investigated as a biomaterial for potential applications in tissue engineering and regenerative medicine. Following sol-gel transition, silk fibroin solutions can generate hydrogels that present certain advantages when employed as biomaterials, especially if they are cross-linked. The subject of this study was the self-cross-linking of silk fibroin through a process induced by the enzyme horseradish peroxidase (HRP) in the presence of hydrogen peroxide, a method only recently proposed and scarcely reported. The hydrogels were prepared either by physical cross-linking, by cross-linking with a natural compound (genipin), or by enzymatic cross-linking. The products were comparatively characterized in regard to their synthesis and background chemical aspects, physical and optical properties, mechanical properties, secondary structure, swelling/deswelling behavior, enzymatic degradation, and compatibility as substrates for cell adhesion and proliferation. The study confirmed the advantages of the HRP-induced cross-linking, which included considerably shorter gelation times, enhanced elasticity of the resulting hydrogels, and improved cytocompatibility. Discrepancies between certain results of this investigation and those reported previously were discussed in detail.

Self-Crosslinking of Silk Fibroin Using H2O2-Horseradish Peroxidase System and the Characteristics of the Resulting Fibroin Membranes

Silk fibroin has been widely used in biomedical and clinical fields owing to its good biocompatibility. In the present work, self-crosslinking of fibroin molecules was carried out using the hydrogen peroxide (H₂O₂)-horseradish peroxidase system, followed by preparation of the fibroin membranes, aiming at improving the mechanical property of fibroin-based material and expanding its applications. P-Hydroxyphenylacetamide (PHAD), as the model compound of tyrosine residues in fibroins, was used to investigate the possibility of horseradish peroxidase (HRP)-catalyzed crosslinking. The results were characterized by means of 1H NMR and UPLC-TQD. The efficacy of enzymatic crosslinking of silk fibroins was examined by determining the changes in the relative viscosity, amino acid compositions, and SEC chromatogram. The obtained data indicated that H₂O₂-HRP incubation led to PHAD polymerization, and the molecular weight of fibroin proteins was also noticeably increased after the enzymatic treatment. CD and ATR-FTIR spectra revealed that H₂O₂-HRP treatments had an evident impact on the conformational structure of silk fibroins. The mechanical property and thermal behavior for the modified fibroin membrane were noticeably improved compared to the untreated. Meanwhile, the obtained membrane exhibited good biocompatibility according to the cell growth experiment. The present work provides a novel method for preparation of the fibroin-based materials for biomedical applications.

Enzymes as Green Catalysts for Precision Macromolecular Synthesis

The present article comprehensively reviews the macromolecular synthesis using enzymes as catalysts. Among the six main classes of enzymes, the three classes, oxidoreductases, transferases, and hydrolases, have been employed as catalysts for the in vitro macromolecular synthesis and modification reactions. Appropriate design of reaction including monomer and enzyme catalyst produces macromolecules with precisely controlled structure, similarly as in vivo enzymatic reactions. The reaction controls the product structure with respect to substrate selectivity, chemo-selectivity, regio-selectivity, stereoselectivity, and choro-selectivity. Oxidoreductases catalyze various oxidation polymerizations of aromatic compounds as well as vinyl polymerizations. Transferases are effective catalysts for producing polysaccharide having a variety of structure and polyesters. Hydrolases catalyzing the bond-cleaving of macromolecules in vivo, catalyze the reverse reaction for bond forming in vitro to give various polysaccharides and functionalized polyesters. The enzymatic polymerizations allowed the first in vitro synthesis of natural polysaccharides having complicated structures like cellulose, amylose, xylan, chitin, hyaluronan, and chondroitin. These polymerizations are "green" with several respects; nontoxicity of enzyme, high catalyst efficiency, selective reactions under mild conditions using green solvents and renewable starting materials, and producing minimal byproducts. Thus, the enzymatic polymerization is desirable for the environment and contributes to "green polymer chemistry" for maintaining sustainable society.

Chemoenzymatic modification of silk fibroin with poly(2,6-dimethyl-1,5-phenylene ether) using horseradish peroxidase

Hydrophobic modification of silk fibroin with poly(2,6-dimethyl-1,5-phenylene ether) (PPE) chains is achieved by the chemoenzymatic polymerization of 2,6-dimethylphenol.

Enzymatic processing of protein-based fibers

Wool and silk are major protein fiber materials used by the textile industry. Fiber protein structure-function relationships are briefly described here, and the major enzymatic processing routes for textiles and other novel applications are deeply reviewed. Fiber biomodification is described here with various classes of enzymes such as protease, transglutaminase, tyrosinase, and laccase. It is expected that the reader will get a perspective on the research done as a basis for new applications in other areas such as cosmetics and pharma.

Highly tunable elastomeric silk biomaterials

Elastomeric, fully degradable and biocompatible biomaterials are rare, with current options presenting significant limitations in terms of ease of functionalization and tunable mechanical and degradation properties. We report a new method for covalently crosslinking tyrosine residues in silk proteins, via horseradish peroxidase and hydrogen peroxide, to generate highly elastic hydrogels with tunable properties. The tunable mechanical properties, gelation kinetics and swelling properties of these new protein polymers, in addition to their ability to withstand shear strains on the order of 100%, compressive strains greater than 70% and display stiffness between 200 - 10,000 Pa, covering a significant portion of the properties of native soft tissues. Molecular weight and solvent composition allowed control of material mechanical properties over several orders of magnitude while maintaining high resilience and resistance to fatigue. Encapsulation of human bone marrow derived mesenchymal stem cells (hMSC) showed long term survival and exhibited cell-matrix interactions reflective of both silk concentration and gelation conditions. Further biocompatibility of these materials were demonstrated with in vivo evaluation. These new protein-based elastomeric and degradable hydrogels represent an exciting new biomaterials option, with a unique combination of properties, for tissue engineering and regenerative medicine.

Building an antifouling zwitterionic coating on urinary catheters using an enzymatically triggered bottom-up approach

Catheter associated urinary tract infections are common during hospitalization due to the formation of bacterial biofilms on the indwelling device. In this study, we report an innovative biotechnology-based approach for the covalent functionalization of silicone catheters with antifouling zwitterionic moieties to prevent biofilm formation. Our approach combines the potential bioactivity of a natural phenolics layer biocatalytically conjugated to sulfobetaine-acrylic residues in an enzymatically initiated surface radical polymerization with laccase. To ensure sufficient coating stability in urine, the silicone catheter is plasma-activated. In contrast to industrial chemical methods, the methacrylate-containing zwitterionic monomers are polymerized at pH 5 and 50 °C using as an initiator the phenoxy radicals solely generated by laccase on the phenolics-coated catheter surface. The coated catheters are characterized by X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared (FTIR) analysis, atomic force microscopy (AFM), and colorimetrically. Contact angle and protein adsorption measurements, coupled with in vitro tests with the Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus in static and dynamic conditions, mimicking the operational conditions to be faced by the catheters, demonstrate reduced biofilm formation by about 80% when compared to that of unmodified urinary catheters. The zwitterionic coating did not affect the viability of the human fibroblasts (BJ-5ta) over seven days, corresponding to the extended useful life of urinary catheters.