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Transparent cobalt‐doped yttrium aluminum garnet (Co2+:YAG) ceramics—An innovatory fast saturable absorber

Agnieszka Szysiak, Kamila Leśniewska‐Matys, Helena Węglarz, Przemysław Gołębiewski, Dariusz Podniesiński, Anna Kozłowska

Abstract

Highly transparent Y3Al5O12 (YAG) ceramics doped with 0.025 and 0.05 at.% Co ions were prepared for the first time by the freeze granulation process and reaction sintering. Scanning electron microscopy (SEM) and X‐ray diffraction (XRD) were performed to analyze the microstructure and crystal structure of the samples. The absorption spectra of the Co2+:YAG ceramics were measured at room temperature, and significant absorption bands at 600 nm, as well as at 1535 nm, were observed. The nonlinear behavior of the received material was experimentally demonstrated. Due to the short relaxation time of investigated ceramics, we considered them as fast saturable absorbers. The influence of the postsintering annealing process was examined. The values of saturation intensities of YAG ceramics with different concentrations of cobalt were estimated by fitting experimental data to the theoretical model for fast saturable absorbers.

Keywords

Co:YAG ceramics, Fast saturable absorber, Freeze granulation, Transparent ceramics

Spray freeze granulation of submicrometre α-alumina using ultrasonication

Shaghayegh Ghanizadeh, Prabhu Ramanujam, Bala Vaidhyanathan, Jon Binner

Abstract

Granulation is a key factor towards improvement of the flowability of fine ceramic powders to make them suitable for industrial dry pressing. Controlled granulation of fine alumina particles with a primary particle size of ∼150 nm was carried out using spray-freeze drying, which led to the production of flowable granules with high crushability. The fracture surface of uniaxially die-pressed green bodies made from granules with density values of ≥50 % of theoretical showed a uniform microstructure. Sintering experiments were performed using conventional single- and two-stage radiant heating methods followed by density and grain size measurement and characterisation of the final dense compacts to study the efficiency of two-stage sintering in grain growth elimination. The results have been compared with those of alumina bodies prepared using similar suspension by the slip-casting route.

Photocatalytic Oxidation of HMF under Solar Irradiation: Coupling of Microemulsion and Lyophilization to Obtain Innovative TiO2-Based Materials

Alessandro Allegri, Valeriia Maslova, Magda Blosi, Anna Luisa Costa, Simona Ortelli, Francesco Basile, Stefania Albonetti

Abstract

The photocatalytic oxidation of biomass-derived building blocks such as 5-hydroxymethylfurfural (HMF) is a promising reaction for obtaining valuable chemicals and the efficient long-term storage of solar radiation. In this work, we developed innovative TiO2-based materials capable of base-free HMF photo-oxidation in water using simulated solar irradiation. The materials were prepared by combining microemulsion and spray-freeze drying (SFD), resulting in highly porous systems with a large surface area. The effect of titania/silica composition and the presence of gold-copper alloy nanoparticles on the properties of materials as well as photocatalytic performance were evaluated. Among the lab-synthesized photocatalysts, Ti15Si85 SFD and Au3Cu1/Ti15Si85 SFD achieved the higher conversions, while the best selectivity was observed for Au3Cu1/Ti15Si85 SFD. The tests with radical scavengers for both TiO2-m and Au3Cu1/Ti15Si85 SFD suggested that primary species responsible for the selective photo-oxidation of HMF are photo-generated electrons and/or superoxide radicals.

Keywords

5-hydroxymethyl furfural, spray-freeze drying, photocatalysis, TiO2, microemulsion

Synergistic effects in oxygen evolution activity of mixed iridium-ruthenium pyrochlores

Rebecca K. Pittkowski, Daniel F. Abbott, Roman Nebel, Spyridon Divanis, Emiliana Fabbri, Ivano E. Castelli, Thomas J. Schmidt, Jan Rossmeisl, Petr Krtil

Abstract

Pyrochlore oxides (A₂B₂O₇) simultaneously containing iridium and ruthenium in the B-site are promising catalysts for oxygen evolution reaction (OER) in acid media. The catalytic activity of the pyrochlore based catalysts is increased by the coexistence of Ir and Ru in the B-site of the pyrochlore structure. Lanthanide (Yb, Gd, or Nd) stabilized mixed pyrochlores with a fraction of Ru in the B-site of x_Ru =0.2, 0.4, 0.6, 0.8 were synthesized by the spray-freeze freeze-dry approach. All prepared mixed pyrochlore catalysts are surpassing the OER activity of the corresponding iridium and ruthenium analogues featuring no cation mixing as well as that of the benchmark IrO₂ catalyst. The synergy of Ir and Ru in the B-site of the pyrochlore structure suppresses the effect of the A-site cation radius on the OER activity. The observed OER activity scales with the Ir-Ru bond distance which represents the local structure of the prepared materials. The most active ytterbium catalyst also shows a significant stability improvement under OER operando conditions over the benchmark IrO₂

Keywords

Electrocatalysis, Oxygen evolution, Pyrochlores, Local structure optimization, Synergy

Production of bromelain aerosols using spray-freeze-drying technique for pulmonary supplementation

M. N. Lavanya, R. Preethi, J. A. Moses, C. Anandharamakrishnan

Abstract

Spray-freeze-drying (SFD) is a promising technique to produce inhalable dry powder formulations that able to retain the integrity of bioactive compounds. Therefore, in this study bromelain aerosols were developed using SFD by varying core-to-wall ratios (1:10, 1:25 and 1:50). The maltodextrin was used to protect the bromelain during freezing and drying stages had a significant effect on the developed aerosols; as the concentration increased, the emitted dosage level increased to around 97.2%. The particles were found to be spherical and highly porous, with geometric diameter ranging between 4.71 to 7.46 µm. All formulations were low in density, had excellent flowability and the theoretical mass median aerodynamic diameter (MMADt) ranged between 2.97 to 3.33 µm. The total bromelain concentration ranged between 413.73 to 462 mg/g and the activity was found to be between 333.22 to 404.64 casein digestion units−1 (CDU)−1 for all three formulations. The XRD patterns explained the crystalline nature of these formulations. The in-vitro release profile showed that the release of bromelain was slow and sustained for 12 h and 46 to 55% of release was estimated. In-vitro aerosol performance of particles showed 84.28% fine particle fraction (FPF) and MMAD of 3.2 µm for the 1:25 formulation. Thus, this study confirmed that SFD can produce aerosols with desired properties and the approach can be used for pulmonary supplementation of food bioactives with good retention and activity.

Keywords

Pulmonary supplementation, aerosol delivery system, mass median aerodynamic diameter, spray-freeze-drying, in-vitro release

Fabrication and microstructure analysis of continuous C fibers reinforced SiC-Cnfs hybrid composite tubes

Shaik Mubina, M. Ilaiyaraja, Asit Kumar Khanra, Bhaskar Prasad Saha

Abstract

The carbon nanofibers (Cnfs) dispersed SiC-Cnfs composite powder has been produced by spray freeze-granulation technique. SiC-based hybrid composite tubes (BN-C_f/SiC-Cnfs) were fabricated by systematically laying of boron nitride-coated continuous carbon fiber (BN-C_f) in the SiC-Cnfs composite matrix. High-density hybrid composite tubes were processed by cold isostatically pressing (CIP) of the afore-mentioned powder in a specially designed mold followed by pressureless sintering. The detailed processing techniques highlighting the criticality of each processing-step have been discussed. The implication of the processing techniques on the structure and properties of the composites were analyzed by using SEM, FTIR, and XRD, highlighting the matrix microstructure and the interfacial bonding of fiber with the matrix. In addition, the influence of newly evolved secondary-phases, Cnfs dispersion, long C_f reinforcement on optimization of properties of the hybrid composites was discussed in detail highlighting TEM analysis. The fractographic analysis of the hybrid composite tubes was carried out to understand the influence of long fibers on the improvement of fracture toughness of the nanofibers containing hybrid composite matrix. The fracture toughness and the other mechanical properties of the base matrix were found to improve significantly due to the combined contribution of specially laid long fibers in nanofibers containing matrix.

Keywords

BN-coated long C fibers, SiC-Cnfs powder, hybrid composite tubes, CIP, pressureless sintering

Comparison of Strategies in Development and Manufacturing of Low Viscosity, Ultra-High Concentration Formulation for IgG1 Antibody

Vaibhav Deokar, Alok Sharma, Rustom Mody, Subrahmanyam M. Volety

Abstract

Monoclonal antibodies requiring higher doses for exerting therapeutic effect but having lower stability, are administered as dilute infusions, or as two (low concentration) injections both resulting in reduced patient compliance. Present research summarizes impact of manufacturing conditions on ultra-high concentration (≥150 mg/mL) IgG1 formulation, which can be administered as one subcutaneous injection. IgG1 was concentrated to ~200 mg/mL using tangential flow filtration (TFF). Alternatively, spray dried (SPD) and spray freeze dried (SFD) IgG1, was reconstituted in 30%v/v propylene glycol to form ultra-high concentration (~200 mg/mL) injectable formulation. Reconstituted, SPD and SFD IgG1 formulations, increased viscosity beyond an acceptable range for subcutaneous injections (<20 cP). Formulations developed by reconstitution of SPD IgG1, demonstrated increase in high and low molecular weight impurities, at accelerated and stressed conditions. Whereas, the stability data suggested reconstituted SFD IgG1 was comparable to control IgG1 formulation concentrated by TFF. Also, formulation of IgG1 diafiltered with proline using TFF, reduce viscosity from ~21.9 cP to ~11 cP at 25 °C and had better stability. Thus, conventional TFF technique stands to be one of the preferred methods for manufacturing of ultra-high concentration IgG1 formulations. Additionally, SFD could be an alternative method for long term storage of IgG1 in a dry powder state.

Keywords

High concentration, IgG antibody(s), Monoclonal antibody(s), Injectable(s), Protein formulation(s), Tangential flow filtration, Viscosity modifiers, Spray drying, Spray freeze-drying

Targeted Pulmonary Delivery of the Green Tea Polyphenol Epigallocatechin Gallate Controls the Growth of Mycobacterium tuberculosis by Enhancing the Autophagy and Suppressing Bacterial Burden

Ankur Sharma, Kalpesh Vaghasiya, Eupa Ray, Pushpa Gupta, Umesh Datta Gupta, Amit Kumar Singh, Rahul Kumar Verma

Abstract

Growing rates of tuberculosis (TB) superbugs are alarming, which has hampered the progress made to-date to control this infectious disease, and new drug candidates are few. Epigallocatechin gallate (EGCG), a major polyphenolic compound from green tea extract, shows powerful efficacy against TB bacteria in in vitro studies. However, the therapeutic efficacy of the molecule is limited due to poor pharmacokinetics and low bioavailability following oral administration. Aiming to improve the treatment outcomes of EGCG therapy, we investigated whether encapsulation and pulmonary delivery of the molecule would allow the direct targeting of the site of infection without compromising the activity. Microencapsulation of EGCG was realized by scalable spray-freeze-drying (SFD) technology, forming free-flowing micrometer-sized microspheres (epigallocatechin-3-gallate-loaded trehalose microspheres, EGCG-t-MS) of trehalose sugar. These porous microspheres exhibited appropriate aerodynamic parameters and high encapsulation efficiencies. In vitro studies demonstrated that EGCG-t-MS exhibited dose- and time-dependent killing of TB bacteria inside mouse macrophages by cellular mechanisms of lysosome acidification and autophagy induction. In a preclinical study on TB-infected Balb/c mice model (4 weeks of infection), we demonstrate that the microencapsulated EGCG, administered 5 days/week for 6 weeks by pulmonary delivery, showed exceptional efficacy compared to oral treatment of free drug. This treatment approach exhibited therapeutic outcomes by resolution of inflammation in the infected lungs and significant reduction (P < 0.05) in bacterial burden (up to ∼2.54 Log10 CFU) compared to untreated control and orally treated mice groups. No pathological granulomas, lesions, and inflammation were observed in the histopathological investigation, compared to untreated controls. The encouraging results of the study may pave the avenues for future use of EGCG in TB therapeutics by targeted pulmonary delivery and lead to its translational success.

Keywords

tuberculosis, epigallocatechin gallate, trehalose microspheres, pulmonary drug delivery, autophagy

Drying of Vaccines and Biomolecules

Bhaskar N. Thorat Institute of Chemical Technology, Bhubaneswar, India Correspondencebn.thorat@ictmumbai.edu.in, Ayantika Sett Department of Chemical Engineering, Institute of Chemical Technology, Bhubaneswar, India & A. S. Mujumdar Institute of Chemical Technology, Matunga(E), Mumbai, India

Abstract

Vaccines are the most important life-saving prophylactic medicines administered in maintaining global health. In a pandemic situation, the manufacturing, formulation followed by preservation of vaccine are challenging areas of concern looking at the dire need of administering it to several billion people on the planet in a pandemic like situation. An important area of major concern is the potential loss of vaccine activity during storage and transportation. Scientists have developed several innovative ideas to store vaccines for a longer period of time. This article focuses on a critical overview of various methods of vaccine storage in dry powder form. Conventional vaccine drying processes, such as freeze drying under different conditions, spray drying along with the upcoming novel technologies such as spray freeze drying are described in detail for the application in vaccine drying. Some other emerging methods, such as, microwave freeze drying and atmospheric freeze drying techniques are also discussed; these could be the game changers in the future. Several drying techniques make use of protective agents during the process of drying and storage. This review also highlights a comparative study of various technological challenges in drying of vaccines in support of the current global health scenario affected by COVID19.

Keywords

Vacuum freeze drying, heat pump, spray drying, atmospheric freeze drying, microwave drying, adjuvants

Ceramic binder jetting additive manufacturing: Effects of granulation on properties of feedstock powder and printed and sintered parts

Guanxiong Miao, Wenchao Du, Mohammadamin Moghadasi, Zhijian Pei, Chao Ma

Abstract

Because of its high sinterability, nanopowder could be beneficial for ceramic binder jetting additive manufacturing to achieve a high density on printed and sintered parts. However, the flowability of nanopowder is poor because of the large interparticle cohesion. This poor flowability prohibits the usage of nanopowder in ceramic binder jetting. In this study, to improve the flowability of nanopowder, alumina nanoparticles were granulated into micron-sized granules through spray freeze drying. The raw nanopowder and granulated powder were compared by characterizing their flowability and printability. Results showed that the granulated powder had a much better flowability than the raw nanopowder. Because of the superior flowability, the granulated powder formed a denser and smoother powder bed than the raw nanopowder and resulted in denser and smoother printed and sintered samples. These improvements indicated that the printability of nanopowder was improved by granulation.

Keywords

Additive manufacturing, Binder jetting, Ceramics, Granulation, Density