Multi-Directional Mechanofluorochromism of Acetyl Pyrenes and Pyrenyl Ynones.

A series of acetyl pyrenes and pyrenyl ynones with and without tert-butyl groups showed distinct mechanofluorochromism (MFC). Four pairs of polymorphic solids were found out of six compounds and interestingly, each of them showed hypsochromic, bathochromic or off-to-on MFC. The MFC properties were rationalized by categorizing the packing schemes into herringbone, sandwich, beta and gamma motifs depending on the relative contributions of C⋅⋅⋅C (or π-π) against C⋅⋅⋅H contacts. The bulky tert-butyl and trimethylsilyl groups served not only to reduce the number of aggregation patterns but also to prohibit the complete back reactions in solid state. Our results suggest that the simple pyrene derivatives may be promising candidates for a novel group of mechanically-sensitive materials.

Synthesis of Fluorinated Polyhydroxyalkanoates from Marine Bioresources as a Promising Biomaterial Coating.

By successive enzymatic and chemical modifications, novel fluorinated polyhydroxyalkanoates were synthesized and characterized. Unsaturated polyhydroxyalkanoate, PHAU, was first produced by fermentation using marine bacteria Pseudomonas raguenesii, and a graft copolymer PHAU-g-C8F17 was further prepared by controlled thiol-ene reaction in the presence of perfluorodecanethiol (PFDT). The PFDT grafting is realized by two different processes. In the first method, PHAU was previously solubilized in toluene. The grafting in solution is more efficient than the direct heterogeneous grafting onto a PHAU film. The degrees of grafting were determined by 1H NMR. The characterization of the microstructure by SEM-EDX and modulated and conventional DSC showed the formation of microdomains due to the organization of the hydrophobic segments of graft PFDT. Biomaterials prepared by 3D printing and coated by PHAU-g-C8F17 have the potential to be used as novel contrast agents as shown by Hahn echo experiments.

Blending Ferulic Acid Derivatives and Polylactic Acid into Biobased and Transparent Elastomeric Materials with Shape Memory Properties.

Thanks to its remarkable properties such as sustainability, compostability, biocompatibility, and transparency, poly-l-lactic acid (PLA) would be a suitable replacement for oil-based polymers should it not suffer from low flexibility and poor toughness, restricting its use to rigid plastic by excluding elastomeric applications. Indeed, there are few fully biobased and biodegradable transparent elastomers-PLA-based or not-currently available. In the last decades, many strategies have been investigated to soften PLA and enhance its toughness and elongation at break by using plasticizers, oligomers, or polymers. This work shows how a ferulic acid-derived biobased additive (BDF) blends with a common rigid and brittle commercial grade of polylactic acid to provide a transparent non-covalently cross-linked elastomeric material with shape memory behavior exhibiting an elongation at break of 434% (vs 6% for pristine PLA). Through a structure-activity relationship analysis conducted with BDF analogues and a modeling study, we propose a mechanism based on π-π stacking to account for the elastomeric properties. Blending ferulic acid derivatives with polylactic acid generates a new family of fully sustainable transparent elastomeric materials with functional properties such as shape memory.

Photoactive Polyoxometalate/DASA Covalent Hybrids for Photopolymerization in the Visible Range.

The synthesis of TBA-DASA-POM-DASA, the first photoactive covalent hybrid polyoxometalate (POM) incorporating a donor-acceptor Stenhouse adduct (DASA) reverse photochrome, is presented. It has been evidenced that in solution the equilibrium between the colorless cyclopentenone and the highly colored triene conformers is strongly dependent not only on the nature of the solvent but also the countercations, allowing to tune its optical properties. This complex has been further associated to photochromic spironaphtoxazine cations, resulting in a material which can be activated by two distinct optical stimuli. Moreover, when combined with N-methyldiethanolamine, TBA-DASA-POM-DASA constitutes a performing photoinitiating system for polyethylene glycol diacrylate polymerization and under visible light irradiation, a promising result in a domain scarcely developed in POM chemistry.

Design of Collagen and Gelatin-based Electrospun Fibers for Biomedical Purposes: An Overview.

Collagen and gelatin are essential natural biopolymers commonly utilized in biomaterials and tissue engineering because of their excellent physicochemical and biocompatibility properties. They can be used either in combination with other biomacromolecules or particles or even exclusively for the enhancement of bone regeneration or for the development of biomimetic scaffolds. Collagen or gelatin derivatives can be transformed into nanofibrous materials with porous micro- or nanostructures and superior mechanical properties and biocompatibility using electrospinning technology. Specific attention was recently paid to electrospun mats of such biopolymers, due to their high ratio of surface area to volume, as well as their biocompatibility, biodegradability, and low immunogenicity. The fiber mats with submicro- and nanometer scale can replicate the extracellular matrix structure of human tissues and organs, making them highly suitable for use in tissue engineering due to their exceptional bioaffinity. The drawbacks may include rapid degradation and complete dissolution in aqueous media. The use of gelatin/collagen electrospun nanofibers in this form is thus greatly restricted for biomedicine. Therefore, the cross-linking of these fibers is necessary for controlling their aqueous solubility. This led to enhanced biological characteristics of the fibers, rendering them excellent options for various biomedical uses. The objective of this review is to highlight the key research related to the electrospinning of collagen and gelatin, as well as their applications in the biomedical field. The review features a detailed examination of the electrospinning fiber mats, showcasing their varying structures and performances resulting from diverse solvents, electrospinning processes, and cross-linking methods. Judiciously selected examples from literature will be presented to demonstrate major advantages of such biofibers. The current developments and difficulties in this area of research are also being addressed.

Cyclodextrin-Calcium Carbonate Micro- to Nano-Particles: Targeting Vaterite Form and Hydrophobic Drug Loading/Release.

Tailor-made and designed micro- and nanocarriers can bring significant benefits over their traditional macroscopic counterparts in drug delivery applications. For the successful loading and subsequent release of bioactive compounds, carriers should present a high loading capacity, trigger release mechanisms, biodegradability and biocompatibility. Hydrophobic drug molecules can accumulate in fat tissues, resulting in drawbacks for the patient's recovery. To address these issues, we propose to combine the advantageous features of both host molecules (cyclodextrin) and calcium carbonate (CaCO3) particles in order to load hydrophobic chemicals. Herein, hybrid cyclodextrin-CaCO3 micro- to nano-particles have been fabricated by combining Na2CO3 solution and CaCl2 solution in the presence of an additive, namely poly (vinylsulfonic acid) (PVSA) or glycerol (gly). By investigating experimental parameters and keeping the Na2CO3 and CaCl2 concentrations constant (0.33 M), we have evidenced that the PVSA or gly concentration and mixing time have a direct impact on the final cyclodextrine-CaCO3 particle size. Indeed, by increasing the concentration of PVSA (5 mM to 30 mM) or gly (0.7 mM to 4 mM) or the reaction time (from 10 min to 4 h), particles with a size of 200 nm could be reached. Interestingly, the vaterite or calcite form could also be selected, according to the experimental conditions. We hypothesised that the incorporation of PVSA or gly into the precipitation reaction might reduce the nucleation rate by sequestering Ca2+. The obtained particles have been found to keep their crystal structure and surface charge after storage in aqueous media for at least 6 months. In the context of improving the therapeutic benefit of hydrophobic drugs, the developed particles were used to load the hydrophobic drug tocopherol acetate. The resulting particles are biocompatible and highly stable in a physiological environment (pH 7.4, 0.15 M NaCl). A selective release of the cargo is observed in acidic media (pH lower than 5).

Multilayer dextran derivative based capsules fighting bacteria resistant to Antibiotic: Case of Kanamycin-Resistant Escherichia coli.

Bacteria resistance to antibiotics has emerged as a major health problem. Developing new antibacterial systems is then of major interest. In this sense, we present biocapsules presenting inherent antibacterial capacity. The self-assembly of charged biopolymer, namely diethylaminoethyl-dextran hydrochloride (dex+) and dextran sulfate (dex-), were done on calcium carbonate microparticles, used as a template. Zeta potential measurements have shown the successful alternate adsorption of these biopolymers and related charge reversal upon the multilayer film construction onto the particles surface. The shape of the capsules was characterized by scanning electron microscopy (SEM). These particles were tested against bacteria resistant to antibiotics, namely kanamycin-resistant Escherichia coli. An inhibitory effect of the particles was observed during bacterial growth in liquid medium, i.e. in the range of 10 % for (dex+/dex-)n coated CaCO3 materials and of 50% for (dex+/dex-)n capsules. These findings evidence the high potential of capsules to act as antimicrobial agents in future and in treatments against infections.

Improved Processability and Antioxidant Behavior of Poly(3-hydroxybutyrate) in Presence of Ferulic Acid-Based Additives.

Poly(3-hydroxybutyrate), PHB, has gathered a lot of attention for its promising properties-in particular its biobased nature and high biodegradability. Although PHB is prime candidate for the packaging industry, the applications are still limited by a narrow processing window and thermal degradation during melt processing. In this work, three novel additives based on ferulic acid esterified with butanediol, pentanediol, and glycerol (BDF, PDF, and GTF, respectively) were used as plasticizers and antioxidative additives to improve mechanical properties of PHB. Elongation at break up to 270% was obtained in presence of BDF and the processing window was improved nearly 10-fold. The Pawley method was used to identify the monoclinic space group P2 of the BDF. The estimated crystallite size (71 nm) agrees with a crystalline additive. With PHB70BDF30 blends, even higher elongations at break were obtained though dwindled with time. However, these properties could be recovered after thermal treatment. The high thermal stability of this additive leads to an increase in the fire retardancy property of the material, and the phenolic structure induced antioxidant properties to the samples as demonstrated by radical scavenging tests, further highlighting the possibilities of the PHB/additive blends for packaging applications.

Efficient and Recyclable Heterogeneous Catalyst Based on PdNPs Stabilized on a Green-Synthesized Graphene-like Nanomaterial: Effect of Surface Functionalization.

This work reports for the first time a straightforward and efficient approach to covalent surface functionalization of a sustainable graphene-like nanomaterial with abundant carboxylic acid groups. This approach results in an efficient and robust chelatant platform for anchoring highly dispersed ultrasmall palladium particles with excellent catalytic activity in the reduction of both cationic (methylene blue, MB) and anionic (eosin-Y, Eo-Y) toxic organic dyes. The large-specific-surface-area (SBET = 266.94 m2/g) graphene-like nanomaterial (GHN) was prepared through a green and cost-effective pyrolysis process from saccharose using layered bentonite clay as a template. To introduce a high density of carboxylic acid functions, GHN was first doubly functionalized by successive grafting reaction using two different strategies: (i) in the first case, GHN was first grafted by (3-glycidyloxypropyl) trimethoxysilane (GPTMS) and then bifunctionalized by chemical grafting of tris(4-hydroxyphenyl)methane triglycidyl ether (TGE). In the second case, the grafting order of the two molecules has been reversed. GHN-GPTMS-TGE provided the highest number of grafted reactive epoxy groups, and it was selected for further functionalization with carboxylic acid functions via a ring-opening reaction through a two-step hydrolysis (H2SO4)/oxidation (KMnO4) approach. The GHN nanomaterial bearing carboxylic acid groups was then treated with sodium hydroxide to produce a deprotonated carboxylic acid-rich platform. Finally, due to a high density of accessible chelatant carboxylic acid groups, GHN-COO- binds strongly a great amount of Pd2+ ions to form stable complexes which after reduction by NaBH4 leads to highly dispersed, densely anchored, and uniformly distributed nanoscale Pd particles (d ∼ 4.5 nm) on the surface of the functionalized GHN. The GHN-COO-@PdNPs nanohybrid proved to be highly efficient for dye reduction by NaBH4 in aqueous solution at room temperature. Moreover, because of the high stability of the as-prepared graphene-like supported PdNPs, it exhibited very good reusability and could be recycled up to eight times without any significant loss in activity.

Antibiotic loading and development of antibacterial capsules by using porous CaCO3 microparticles as starting material.

Porous calcium carbonate (CaCO3) particles have been shown to be highly advantageous for biological applications, mainly due to their large surface area and their stability in physiological media. Also, developing appropriate antibacterial materials presenting the benefits of non-formation of harmful compounds is of major interest. Two characteristics of CaCO3 particles were investigated herein: (i) antibiotic-loading capacity and (ii) the possibility of using CaCO3 particles as a template for the fabrication of biocapsules presenting inherent antibacterial capacity. The particles were tested against two representative pathogenic bacteria (Staphylococcus aureus and Escherichia coli). On one hand, a method for antibiotic (namely penicillin, ampicillin and ciprofloxacin) loading inside calcium carbonate particles was developed and antibacterial activity was investigated. Encapsulation efficiency and loading content were 95% and 5%, respectively. We showed that antibiotics prevented bacterial growth within 2 h, with no evidence of bacterial regrowth within 16 h; bactericidal effects were also observed. On the other hand, the self-assembly of charged polysaccharides, namely chitosan (chi+) and dextran sulfate (dex-), were assessed on calcium carbonate microparticles used as a sacrificial matrix. During bacterial growth in a liquid medium, an inhibitory effect of these particles was observed, i.e. Staphylococcus aureus (Gram-positive) (from 16.3% to 48.8% for (chi+/dex-)n-chi+ coated CaCO3 materials and from 41.9% to 93.0% for (chi+/dex-)n-chi+ capsules) and Escherichia coli (Gram-negative) (from 18.2% to 45.5% for (chi+/dex-)n-chi+ coated CaCO3 materials and from 40.0% to 89.1% for (chi+/dex-)n-chi+ capsules). Staining with acridine orange highlighted the bactericidal effect of the designed particles. These findings demonstrate the excellent potential of using calcium carbonate particles in antibiotic therapy as a starting point for the development of smart materials.

Thermal Stability and Flammability Behavior of Poly(3-hydroxybutyrate) (PHB) Based Composites.

A series of samples based on poly(3-hydroxybutyrate) (PHB) containing five different additives were prepared and their thermal stability and flammability were discussed. The samples first underwent flammability screening by using Pyrolysis Combustion Flow Calorimeter (PCFC) analyses. Then, four samples were selected for further investigations. PHB composites containing sepiolite (Sep.) inorganic nanofiller, and also organic ammonium polyphosphate (APP) were examined for flammability and thermal behavior using PCFC, thermogravimetric analysis (TGA), flame test, and Differential Scanning Calorimetry (DSC) analyses. Moreover, burning behavior of samples were captured on a digital camera to give a deeper sense of their flammability character for comparison. The results revealed a significant improvement of flammability and thermal stability of composites, particularly in the presence of sepiolite with respect to the value obtained for unfilled PHB. Regarding TGA results, the char residue yield was increased to ca. 20.0 wt.% in the presence of sepiolite, while 0.0 wt.% was observed for PHB. PCFC measurements uncovered higher performance of PHB-Sep. sample as signaled by 40% reduction in the peak of heat release rate with respect to PHB. According to observations, PHB-Sep. sample showed non-dripping behavior with high capacity of charring in the presence of Sep. in a vertical flame test.