PEG-coated large mesoporous silicas as smart platform for protein delivery and their use in a collagen-based formulation for 3d printing

Silica-based mesoporous systems have gained great interest in drug delivery applications due to their excellent biocompatibility and high loading capability. However, these materials face challenges in terms of pore-size limitations since they are characterized by nanopores ranging between 6–8 nm and thus unsuitable to host large molecular weight molecules such as proteins, enzymes and growth factors (GFs). In this work, for an application in the field of bone regeneration, large-pore mesoporous silicas (LPMSs) were developed to vehicle large biomolecules and release them under a pH stimulus. Considering bone remodeling, the proposed pH-triggered mechanism aims to mimic the release of GFs encased in the bone matrix due to bone resorption by osteoclasts (OCs) and the associated pH drop. To this aim, LPMSs were prepared by using 1,3,5-trimethyl benzene (TMB) as a swelling agent and the synthesis solution was hydrothermally treated and the influence of different process temperatures and durations on the resulting mesostructure was investigated. The synthesized particles exhibited a cage-like mesoporous structure with accessible pores of diameter up to 23 nm. LPMSs produced at 140◦C for 24 h showed the best compromise in terms of specific surface area, pores size and shape and hence, were selected for further experiments. Horseradish peroxidase (HRP) was used as model protein to evaluate the ability of the LPMSs to adsorb and release large biomolecules. After HRP-loading, LPMSs were coated with a pH-responsive polymer, poly(ethylene glycol) (PEG), allowing the release of the incorporated biomolecules in response to a pH decrease, in an attempt to mimic GFs release in bone under the acidic pH generated by the resorption activity of OCs. The reported results proved that PEG-coated carriers released HRP more quickly in an acidic environment, due to the protonation of PEG at low pH that catalyzes polymer hydrolysis reaction. Our findings indicate that LPMSs could be used as carriers to deliver large biomolecules and prove the effectiveness of PEG as pH-responsive coating. Finally, as proof of concept, a collagen-based suspension was obtained by incorporating PEG-coated LPMS carriers into a type I collagen matrix with the aim of designing a hybrid formulation for 3D-printing of bone scaffolds

Electrophoretic deposition of Sr-containing mesoporous bioactive glass particles produced by spray-drying

Introduction Mesoporous bioactive glasses (MBGs) are gaining increasing interest in the biomedical field thanks to their exceptional textural characteristics (high surface area, high pore volume and highly ordered mesoporosity). These properties lead to an improved apatite kinetics formation, which allow these glasses to be successfully applied in bone tissue regeneration [1]. In this work we adopted an aerosol-based spray drying process in order to have high control and reproducibility over the morphology of particles. In order to increase their regenerative potential, the particles have been doped with strontium, element known for its osteogenic and bone antiresorptive properties [2]. Later the particles have been deposed by electrophoretic deposition (EPD) on glass-ceramic scaffolds fabricated by the polymer sponge replication method. EPD is a versatile technique which allows an easy control of the thickness of the deposited film through simple adjustment of the applied voltage and the deposition time. The scaffolds, based on a quaternary silicate glass (SCNA, SiO2–CaO–Na2O–Al2O3 oxide system), have good mechanical properties but low bioactivity [3]. Thanks to MBG particle deposition, they acquire a pronounced bioactive behaviour, thus becoming an excellent solution for bone tissue regeneration. Results and Discussion MBGs synthesized with the aerosol-based spray-drying process have a basic composition on the SiO2-CaO system and have been doped with the 1% molar of strontium (SD_Sr1). FESEM image of particles shows micro-sized spherical particles, with size mostly ranging between 500 nm and 5 µm. N2 adsorption analysis gives back a high specific surface area value, 160 m2/g, and a pore size distribution between 5 and 9 nm, which confirms the mesoporosity of the sample. Strontium incorporation inside the binary composition does not modify the bioactive behaviour of the glass: after 14 days in SBF nanoparticles are completely covered by a layer of hydroxyapatite.The EDS quantitative analysis shows that the amount of strontium effectively incorporated in the microparticles was 70% of the theoretical one, probably because of the high dimension of the ion which hinders its entrance into the glass network. Nevertheless, most of the Sr incorporated has been released after 14 days of immersion in SBF, as the coupled plasma-atomic emission spectrometry (ICP-AES) reveals. On the basis of literature data, the released concentrations are suitable for inducing osteogenesis [4]. EPD has been performed in ethanol, applying a voltage of 120 V for 5 minutes. The scaffolds, being not conductive, have been suspended between two stainless steel electrodes through a clamp. A dispersant (TEA, triethanolamine) has been used to keep the particles in suspension during the whole deposition time. The deposited layer was abundant but not uniform on the scaffold surface. After immersion for 7 days in SBF, hydroxyapatite formation has been observed on the surface of the microparticles deposited on the scaffold struts. This demonstrates that MBGs not only maintain their bioactivity after deposition but also transfer this property to scaffolds. Conclusions MBGs synthetized with aerosol-based spray-drying process and doped with strontium have excellent textural properties and a bioactive behaviour. After electrophoretic deposition, they maintain these properties and consequently they improve the bioactivity of SCNA scaffolds, which initially are almost biologically inert. In this way we demonstrate that it is possible to obtain a successful construct for bone tissue engineering with both excellent regenerative and mechanical properties

Isolation and characterisation of colistin-resistant Enterobacterales from chickens in Southeast Nigeria.

ABSTRACT Objectives Resistance to colistin (CST) mediated by mobile genetic elements has had a broad impact worldwide. There is an intensified call for epidemiological surveillance of mcr in different reservoirs to preserve CST for future generations. In Nigeria, the poultry industry is a key livestock sector. This study was undertaken to screen putative colistin-resistant Enterobacterales (CST-r-E) from poultry birds in Southeast Nigeria and to determine the genetic relatedness of mcr-harbouring isolates. Methods Faecal and cloacal swab samples (n = 785) were collected from chickens in 17 farms located in three contiguous states in Southeast Nigeria between March–November 2018. Following selective culture, CST-r-E were isolated. Confirmation of CST resistance, antimicrobial susceptibility testing, molecular detection of genes mcr-1 to mcr-10, multilocus sequence typing (MLST) and randomly amplified polymorphic DNA (RAPD) analysis were performed on the isolates. A questionnaire was distributed to investigate the knowledge about CST and its use of chicken farm caretakers. Results Of the 785 samples evaluated, 45 (5.7%) were positive for 48 CST-r-E, among which 23 harboured the mcr-1 gene (22 Escherichia coli and 1 Klebsiella pneumoniae). In two E.coli isolates, a new allelic variant (mcr-1.22) was detected. RAPD analysis allowed the identification of 11 different fingerprints. MLST also revealed 11 STs, with 3 of them being novel. Conclusion mcr has significantly spread in poultry birds of Southeast Nigeria, which poses a worrisome risk to veterinary and human health. Strategies to prevent indiscriminate use of CST in farms should be quickly adopted before CST resistance becomes a huge global health issue

Dissolution susceptibility of glass-like carbon versus crystalline graphite in high-pressure aqueous fluids and implications for the behavior of organic matter in subduction zones

Organic matter, showing variable degrees of crystallinity and thus of graphitization, is an important source of carbon in subducted sediments, as demonstrated by the isotopic signatures of deep and ultra-deep diamonds and volcanic emissions in arc settings. In this experimental study, we investigated the dissolution of sp2 hybridized carbon in aqueous fluids at 1 and 3 GPa, and 800\ub0C, taking as end-members i) crystalline synthetic graphite and ii) X-ray amorphous glass-like carbon. We chose glass-like carbon as an analogue of natural \u201cdisordered\u201d graphitic carbon derived from organic matter, because unlike other forms of poorly ordered carbon it does not undergo any structural modification at the investigated experimental conditions, allowing approach to thermodynamic equilibrium. Textural observations, Raman spectroscopy, synchrotron X-ray diffraction and dissolution susceptibility of char produced by thermal decomposition of glucose (representative of non-transformed organic matter) at the same experimental conditions support this assumption. The redox state of the experiments was buffered at \u394FMQ 48 \u20130.5 using double capsules and either fayalite-magnetite-quartz (FMQ) or nickel-nickel oxide (NNO) buffers. At the investigated P\u2013T\u2013fO2 conditions, the dominant aqueous dissolution product is carbon dioxide, formed by oxidation of solid carbon. At 1 GPa and 800\ub0C, oxidative dissolution of glass-like carbon produces 16\u201319 mol% more carbon dioxide than crystalline graphite. In contrast, fluids interacting with glass-like carbon at the higher pressure of 3 GPa show only a limited increase in CO2 (fH2NNO) or even a lower CO2 content (fH2FMQ) with respect to fluids interacting with crystalline graphite. The measured fluid compositions allowed retrieving the difference in Gibbs free energy (\u394G) between glass-like carbon and graphite, which is +1.7(1) kJ/mol at 1 GPa\u2013800\ub0C and +0.51(1) kJ/mol (fH2NNO) at 3 GPa\u2013800\ub0C. Thermodynamic modeling suggests that the decline in dissolution susceptibility at high pressure is related to the higher compressibility of glass-like carbon with respect to crystalline graphite, resulting in G\u2013P curves crossing at about 3.4 GPa at 800\ub0C, close to the graphite\u2013diamond transition. The new experimental data suggest that, in the presence of aqueous fluids that flush subducted sediments, the removal of poorly crystalline \u201cdisordered\u201d graphitic carbon is more efficient than that of crystalline graphite especially at shallow levels of subduction zones, where the difference in free energy is higher and the availability of poorly organized metastable carbonaceous matter and of aqueous fluids produced by devolatilization of the downgoing slab is maximized. At depths greater than 110 km, the small differences in \u394G imply that there is minimal energetic drive for transforming \u201cdisordered\u201d graphitic carbon to ordered graphite; \u201cdisordered\u201d graphitic carbon could even be energetically slightly favored in a narrow P interval

Hydrogenation reactions of carbon on Earth: Linking methane, margarine, and life

Hydrogenation reactions are a major route of electron and proton flow on Earth. Interfacing geology and organic chemistry, hydrogenations occupy pivotal points in the Earth’s global geochemical cycles. Some examples of hydrogenation reactions on Earth today include the production and consumption of methane in both abiotic and biotic reactions, the reduction of protons in hydrothermal settings, and the biological synthesis and degradation of fatty acids. Hydrogenation reactions were likely important for prebiotic chemistry on the early Earth, and today serve as one of the fundamental reaction classes that enable cellular life to construct biomolecules. An understanding and awareness of hydrogenation reactions is helpful for comprehending the larger web of molecular and material inter-conversions on our planet. In this brief review we detail some important hydrogenation and dehydrogenation reactions as they relate to geology, biology, industry, and atmospheric chemistry. Such reactions have implica- tions ranging from the suite of reactions on early Earth to industrial applications like the production of hydrocarbon fuel