Enzymatically Triggered Drug Release from Microgels Controlled by Glucose Concentration.

This study aims to design microgels for controlled drug release via enzymatically generated pH changes in the presence of glucose. Modern medicine is focused on developing smart delivery systems with controlled release capabilities. In response to this demand, we present the synthesis, characterization, and enzymatically triggered drug release behavior of microgels based on poly(acrylic acid) modified with glucose oxidase (GOx) (p(AA-BIS)-GOx). TEM images revealed that the sizes of air-dried p(AA-BIS)-GOx microgels were approximately 130 nm. DLS measurements showed glucose-triggered microgel size changes upon glucose addition, which depended on buffer concentration. Enzymatically triggered drug release experiments using doxorubicin-loaded microgels with immobilized GOx demonstrated that drug release is strongly dependent on glucose and buffer concentration. The highest differences in release triggered by 5 and 25 mM glucose were observed in HEPES buffer at concentrations of 3 and 9 mM. Under these conditions, 80 and 52% of DOX were released with 25 mM glucose, while 47 and 28% of DOX were released with 5 mM glucose. The interstitial glucose concentration in a tumor ranges from ∼15 to 50 mM. Normal fasting blood glucose levels are about 5.5 mM, and postprandial (2 h after a meal) glucose levels should be less than 7.8 mM. The obtained results highlight the microgel's potential for drug delivery using the enhanced permeability and retention (EPR) effect, where drug release is controlled by enzymatically generated pH changes in response to elevated glucose concentrations.

Structure-property relationship of pea protein microgels as fat analogues in Pickering oil-in-water emulsions: effect of salt addition.

BACKGROUND: The design of plant-based microgels provides a platform for food ingredients to enhance palatability and functionality. This work aimed to explore the modifying effect of salt addition (KCl) on the structure of pea protein microgel particles (PPI MPs), on the interfacial adsorption and characteristics of formed emulsions as fat analogues. RESULTS: Salt addition (0-200 mmol L-1) promoted a structural transformation from α-helix to ß-sheet, increased the surface hydrophobicity (from 1160.8 to 2280.7), and increased the contact angle (from 56.73° to 96.47°) of PPI MPs. The electrostatic shielding effect led to the tighter packing of MPs with irregular structures and lowered the adsorption energy barrier. Notably, salt-treated PPI MPs could adjust their adsorption state at the interface. The discernible adsorption of PPI MPs with 200 mmol L-1 salt addition that possessed enhanced anti-deformation ability dominated the interfacial stabilization, whereas a relatively rougher stretched continuous interfacial film formed after spreading and deformation of 0 mmol L-1 MPs. A tribological test suggested that emulsion stabilized by MPs at 0 (0.0053) and 80 mmol L-1 (0.0068) had similar friction coefficients to commercial mayonnaise (0.0058), whereas a higher salt concentration (200 mmol L-1) lowered its oral sensation due to the adsorption layer and enhanced the resistance to droplet coalescence during oral processing. CONCLUSION: Salt could be a modifier to tune the structure of microgels, and further promote the formation and attributes of emulsions. This study would improve application attributes of PPI MPs in the design of realistic fat analogues. © 2024 Society of Chemical Industry.

Carboxyl-functionalized dual pH/temperature-responsive poly(N-vinylcaprolactam) microgels based on isogenous comonomers for smart window applications.

Stimuli-responsive poly(N-vinylcaprolactam) (PVCL)-based microgels, which could response to small external environmental changes, have attracted great interests in the fields of biomedicine and nanotechnology. However, the preparation of such microgels meets severe challenge due to their low incorporation efficiency and thermoresponsivity passivation. To address these issues, we select 3-(tert-butoxycarbonyl)-N-vinylcaprolactam (TBVCL), a carboxyl-functionalized VCL derivative, as a comonomer to develop pH/temperature dual-responsive microgels. TBVCL, with a structure similar to VCL, enhances incorporation efficiency and colloidal stability, while reducing thermoresponsivity passivation. The volume phase transition temperature (VPTT) of the microgels can be adjusted over a broad range (19.0-49.5 °C). Notably, the radial swelling ratios of the microgels can be modulated by pH, achieving a maximum swelling ratio of 3. The distinct changes in dissolution-precipitation behavior under different temperatures or pH conditions make these microgels suitable for applications such as smart windows and sensors. Furthermore, this novel approach for fabricating microgels with pH-tunable phase-transition temperatures demonstrates significant potential for the controlled release of nanoparticles (e.g., drugs, catalysts, and quantum dots) and the development of smart nanocrystal-polymer composite sensors.

Microgel delivery systems of functional substances for precision nutrition.

Microgels delivery system have great potential in functional substances encapsulation, protection, release, precise delivery and nutritional intervention. Microgel is a three-dimensional network structure formed by physical or chemical crosslinking of biopolymers, whose characteristics include dispersion and swelling, stable structure, small volume and high specific surface area, and is a special kind of colloid. In this chapter, the common wall materials for preparing food grade microgels, and the main preparation principles, methods, advantages and disadvantages of microgels loaded with functional substances were firstly reviewed. Then the main characteristics of microgel as delivery system, such as deformability, high encapsulation, stimulus-responsive release and targeted delivery, and its potential benefits in intervening chronic diseases were summarized. Finally, the applications of microgel delivery system for functional substance in the field of precision nutrition were discussed. This chapter will help to design of next-generation advanced targeting microgel delivery system, and realize precision nutrition intervention of food functional substances on body health.

Soft and Deformable Thermoresponsive Hollow Rod-Shaped Microgels.

Depending on their aspect ratio, rod-shaped particles exhibit a much richer 2D and 3D phase behavior than their spherical counterparts, with additional nematic and smectic phases accompanied by defined orientational ordering. While the phase diagram of colloidal hard rods is extensively explored, little is known about the influence of softness in such systems, partly due to the absence of appropriate model systems. Additionally, investigating higher volume fractions for long rods is usually complicated because non-equilibrium dynamical arrest is likely to precede the formation of more defined states. This has motivated us to develop micrometric rod-like microgels with limited sedimentation that can respond to temperature and reversibly reorganize into defined phases via annealing and seeding procedures. A detailed procedure is presented for synthesizing rod-shaped hollow poly(N-isopropylacrylamide) microgels using micrometric silica rods as sacrificial templates. Their morphological characterization is conducted through a combination of microscopy and light scattering techniques, evidencing the unconstrained swelling of rod-shaped hollow microgels compared to core-shell microgel rods. Different aspects of their assembly in dispersion and at interfaces are further tested to illustrate the opportunities and challenges offered by such systems that combine softness, anisotropy, and thermoresponsivity.

FLIM nanoscopy resolves the structure and preferential adsorption in the co-nonsolvency of PNIPAM microgels in methanol-water.

Polymer microgels are swollen macromolecular networks with a typical size of hundred of nanometers to several microns that show an extraordinary open and responsive architecture to different external stimuli, being therefore important candidates for nanobiotechnology and nanomedical applications such as biocatalysis, sensing and drug delivery. It is therefore crucial to understand the delicate balance of physical-chemical interactions between the polymer backbone and solvent molecules that to a high extent determine their responsivity. In particular, the co-nonsolvency effect of poly(N-isopropylacrylamide) in aqueous alcohols is highly discussed, and there is a disagreement between molecular dynamics (MD) simulations (from literature) of the preferential adsorption of alcohol on the polymer chains and the values obtained by several empirical methods that mostly probe the bulk solvent properties. It is our contention that the most efficacious method for addressing this problem requires a nanoscopic method that can be combined with spectroscopy and record fluorescence spectra and super-resolved fluorescence lifetime images of microgels labeled covalently with the solvatochromic dye Nile Red. By employing this approach, we could simultaneously resolve the structure of sub-micron size objects in the swollen and in the collapsed state and estimate the solvent composition inside of them in - mixtures for two very different polymer architectures. We found an outstanding agreement between the MD simulations and our results that estimate a co-solvent molar fraction excess of approximately 3 with a very flat profile in the lateral direction of the microgel.

Closed-loop theranostic microgels for immune microenvironment modulation and microbiota remodeling in ulcerative colitis.

Inflammatory bowel disease (IBD) is characterized by the upregulation of reactive oxygen species (ROS) and dysfunction of gut immune system, and microbiota. The conventional treatments mainly focus on symptom control with medication by overuse of drugs. There is an urgent need to develop a closed-loop strategy that combines in situ monitoring and precise treatment. Herein, we innovatively designed the 'cluster munition structure' theranostic microgels to realize the monitoring and therapy for ulcerative colitis (a subtype of IBD). The superoxide anion specific probe (tetraphenylethylene-coelenterazine, TPC) and ROS-responsive nanogels consisting of postbiotics urolithin A (UA) were loaded into alginate and ion-crosslinked to obtain the theranostic microgels. The theranostic microgels could be delivered to the inflammatory site, where the environment-triggered breakup of the microgels and release of the nanogels were achieved in sequence. The TPC-UA group had optimal results in reducing inflammation, repairing colonic epithelial tissue, and remodeling microbiota, leading to inflammation amelioration and recovery of tight junction between the colonic epithelium, and maintenance of gut microbiota. During the recovery process, the local chemiluminescence intensity, which is proportional to the degree of inflammation, was gradually inhibited. The cluster munition of theranostic microgels displayed promising outcomes in monitoring inflammation and precise therapy, and demonstrated the potential for inflammatory disease management.

Microgels sense wounds' temperature, pH and glucose.

Wound healing concerns almost all bed-side related diseases. With our increasing comprehension of healing nature, the physical and chemical natures behind the wound microenvironment have been decoupled. Wound care demands timely screening and prompt diagnosis of wound complications such as infection and inflammation. Biosensor by the way of exhaustive collection, delivery, and analysis of data, becomes indispensable to arrive at an ideal healing upshot and controlling complications by capturing in-situ wound status. Electrochemical based sensors carry some potential unstable performance subjected to the electrical circuitry and power access and contamination. The colorimetric sensors are free from those concerns. We report that microsensors designed from O/W/O of capillary fluids can continuously monitor wound temperature, pH and glucose concentration. We combined three different types of microgels to encapsulate liquid crystals of cholesterol, nontoxic fuel litmus and two glucose-sensitizing enzymes. A smartphone applet was then developed to convert wound healing images to RGB of digitalizing data. The microgel dressing effectively demonstrates the local temperature change, pH and glucose levels of the wound in high resolution where a microgel is a 'pixel'. They are highly responsive, reversible and accurate. Monitoring multiple physicochemical and physiological indicators provides tremendous potential with insight into healing processing.

Raman spectroscopy and molecular dynamics simulations of protein microgels at the oil-water interface.

The real-time structural changes of the molecular space conformation of myofibrillar protein microgels (MPM) after heat treatment (90 °C, 30 min) were analyzed by molecular dynamics simulation, and the structural properties and changes of MPM at the oil-water interface were analyzed by the combination of Raman spectroscopy and molecular dynamics simulation. The shift in the oil ratio had a major impact on the transformation of disulfide bonds within the protein molecule. Simultaneously, it caused tryptophan and tyrosine residues (I850 cm-1/ I850 cm-1 > 1) to become exposed, increasing the locations of amino acid residues in the protein that interact with the oil phase. HIPE with different oil phases influenced the change in spatial structural conformation of MPM, and there was a flexible structural change in the molecular space. The HIPE system, which was stabilized by 3.0 wt% MPM and 0.75 oil phase, exhibited a thixotropic recovery of >70 % and the highest elastic modulus G' (822.14 Pa) based on the rheological behavior. It is expected to provide a theoretical basis for the development and utilization of high internal phase emulsion stabilized by microgel protein in food industry.

Amphiphilic Nanogels as Versatile Stabilizers for Pickering Emulsions.

Pickering emulsions (PEs) are stabilized by particles at the water/oil interface and exhibit superior long-term stability compared to emulsions with molecular surfactants. Among colloidal stabilizers, nano/microgels facilitate emulsification and can introduce stimuli responsiveness. While increasing their hydrophobicity is connected to phase inversion from oil-in-water (O/W) to water-in-oil (W/O) emulsions, a predictive model to relate this phase inversion to the molecular structure of the nano/microgel network remains missing. Addressing this challenge, we developed a library of amphiphilic nanogels (ANGs) that enable adjusting their hydrophobicity while maintaining similar colloidal structures. This enabled us to systematically investigate the influence of network hydrophobicity on emulsion stabilization. We found that W/O emulsions are preferred with increasing ANG hydrophobicity, oil polarity, and oil/water ratio. For nonpolar oils, increasing emulsification temperature enabled the formation of W/O PEs that are metastable at room temperature. We connected this behavior to interfacial ANG adsorption kinetics and quantified ANG deformation and swelling in both phases via atomic force microscopy. Importantly, we developed a quantitative method to predict phase inversion by the difference in Flory-Huggins parameters between ANGs with water and oil (χwater - χoil). Overall, this study provides crucial structure-property relations to assist the design of nano/microgels for advanced PEs.

Effect of inulin on structural, physicochemical, and in vitro gastrointestinal tract release properties of core-shell hydrogel beads as a delivery system for vitamin B12.

In this study, core-shell hydrogel beads were developed as a controlled-release delivery system for vitamin B12. Vitamin B12-loaded microgels (MG) were prepared using gellan gum (GG). Core-shell hydrogel beads were produced by incorporating MG into pea protein isolate (PPI) and sodium alginate (AL) matrix filled/coated with different concentrations (0 %, 1 %, 3 %, 5 %, and 10 %) of inulin (IN). Based on XRD analysis, MG was successfully incorporated into core-shell hydrogel beads. In FE-SEM and FT-IR analyses, the smoother surface and denser structure of the beads were observed as IN concentration increased due to hydrogen bonds between IN and the beads. The encapsulation efficiency increased from 68.64 % to 82.36 % as IN concentration increased from 0 % to 10 %, respectively. After exposure to simulated oral and gastric conditions, core-shell hydrogel beads exhibited a lower cumulative release than MG, and a more sustained release was observed as IN concentration increased in simulated intestinal conditions.

On the Relation between the Viscoelastic Properties of Granular Hydrogels and Their Performance as Support Materials in Embedded Bioprinting.

Granular hydrogels, formed by jamming microgels suspension, are promising materials for three-dimensional bioprinting applications. Despite their extensive use as support materials for embedded bioprinting, the influence of the particle's physical properties on the macroscale viscoelasticity on one hand and on the printing performance on the other hand remains unclear. Herein, we investigate the linear and nonlinear rheology of κ-carrageenan granular hydrogel through small- and large-amplitude oscillatory shear measurements. We tuned the granular hydrogel's properties by changing the stiffness (soft, medium, stiff) and the packing density of the individual microgels. Characterizations in the linear viscoelasticity regime revealed that the storage modulus of granular hydrogels is not a simple function of microgel stiffness and depends on the microgel packing density. At larger strains, increasing the microgel stiffness reduced the energy dissipation of the granular beds and increased the solid-fluid transition point. To understand how the different rheological properties of granular support materials influence embedded bioprinting, we examined the printing fidelity and cellular filament shrinkage within the granular beds. We found that microgels with low packing density diminished the printing quality, while stiff microgels promoted filament roughness. In addition, we found that highly packed stiff microgels significantly reduced the postprinting contraction of cellular filaments. Overall, this work provides a comprehensive knowledge of the rheology of granular hydrogels that can be used to rationally design support beds for bioprinting applications with specific characteristics.

Cartilage-derived cells display heterogeneous pericellular matrix synthesis in agarose microgels.

The pericellular matrix (PCM) surrounding chondrocytes is essential for articular cartilage tissue engineering. As the current isolation methods to obtain chondrocytes with their PCM (chondrons) result in a heterogeneous mixture of chondrocytes and chondrons, regenerating the PCM using a tissue engineering approach could prove beneficial. In this study, we aimed to discern the behavior of articular chondrocytes (ACs) in regenerating the PCM in such an approach and whether this would also be true for articular cartilage-derived progenitor cells (ACPCs), as an alternative cell source. Bovine ACs and ACPCs were encapsulated in agarose microgels using droplet-based microfluidics. ACs were stimulated with TGF-ß1 and dexamethasone and ACPCs were sequentially stimulated with BMP-9 followed by TGF-ß1 and dexamethasone. After 0, 3, 5, and 10 days of culture, PCM components, type-VI collagen and perlecan, and ECM component, type-II collagen, were assessed using flow cytometry and fluorescence microscopy. Both ACs and ACPCs synthesized the PCM before the ECM. It was seen for the first time that synthesis of type-VI collagen always preceded perlecan. While the PCM synthesized by ACs resembled native chondrons after only 5 days of culture, ACPCs often made less well-structured PCMs. Both cell types showed variations between individual cells and donors. On one hand, this was more prominent in ACPCs, but also a subset of ACPCs showed superior PCM and ECM regeneration, suggesting that isolating these cells may potentially improve cartilage repair strategies.

Rational Designing Microenvironment of Gas-Diffusion Electrodes via Microgel-Augmented CO2 Availability for High-Rate and Selective CO2 Electroreduction to Ethylene.

Efficient electrochemical CO2 reduction reaction (CO2RR) requires advanced gas-diffusion electrodes (GDEs) with tunned microenvironment to overcome low CO2 availability in the vicinity of catalyst layer. Herein, for the first time, pyridine-containing microgels-augmented CO2 availability is presented in Cu2O-based GDE for high-rate CO2 reduction to ethylene, owing to the presence of CO2-phil microgels with amine moieties. Microgels as three-dimensional polymer networks act as CO2 micro-reservoirs to engineer the GDE microenvironment and boost local CO2 availability. The superior ethylene production performance of the GDE modified by 4-vinyl pyridine microgels, as compared with the GDE with diethylaminoethyl methacrylate microgels, indicates the bifunctional effect of pyridine-based microgels to enhance CO2 availability, and electrocatalytic CO2 reduction. While the Faradaic efficiency (FE) of ethylene without microgels was capped at 43% at 300 mA cm-2, GDE with the pyridine microgels showed 56% FE of ethylene at 700 mA cm-2. A similar trend was observed in zero-gap design, and GDEs showed 58% FE of ethylene at -4.0 cell voltage (>350 mA cm-2 current density), resulting in over 2-fold improvement in ethylene production. This study showcases the use of CO2-phil microgels for a higher rate of CO2RR-to-C2+, opening an avenue for several other microgels for more selective and efficient CO2 electrolysis.

Droplet Microfluidics for High-Throughput Screening and Directed Evolution of Biomolecules.

Directed evolution is a powerful technique for creating biomolecules such as proteins and nucleic acids with tailor-made properties for therapeutic and industrial applications by mimicking the natural evolution processes in the laboratory. Droplet microfluidics improved classical directed evolution by enabling time-consuming and laborious steps in this iterative process to be performed within monodispersed droplets in a highly controlled and automated manner. Droplet microfluidic chips can generate, manipulate, and sort individual droplets at kilohertz rates in a user-defined microchannel geometry, allowing new strategies for high-throughput screening and evolution of biomolecules. In this review, we discuss directed evolution studies in which droplet-based microfluidic systems were used to screen and improve the functional properties of biomolecules. We provide a systematic overview of basic on-chip fluidic operations, including reagent mixing by merging continuous fluid streams and droplet pairs, reagent addition by picoinjection, droplet generation, droplet incubation in delay lines, chambers and hydrodynamic traps, and droplet sorting techniques. Various microfluidic strategies for directed evolution using single and multiple emulsions and biomimetic materials (giant lipid vesicles, microgels, and microcapsules) are highlighted. Completely cell-free microfluidic-assisted in vitro compartmentalization methods that eliminate the need to clone DNA into cells after each round of mutagenesis are also presented.

Facile One Pot Synthesis of Hybrid Core-Shell Silica-Based Sensors for Live Imaging of Dissolved Oxygen and Hypoxia Mapping in 3D Cell Models.

Fluorescence imaging allows for noninvasively visualizing and measuring key physiological parameters like pH and dissolved oxygen. In our work, we created two ratiometric fluorescent microsensors designed for accurately tracking dissolved oxygen levels in 3D cell cultures. We developed a simple and cost-effective method to produce hybrid core-shell silica microparticles that are biocompatible and versatile. These sensors incorporate oxygen-sensitive probes (Ru(dpp) or PtOEP) and reference dyes (RBITC or A647 NHS-Ester). SEM analysis confirmed the efficient loading and distribution of the sensing dye on the outer shell. Fluorimetric and CLSM tests demonstrated the sensors' reversibility and high sensitivity to oxygen, even when integrated into 3D scaffolds. Aging and bleaching experiments validated the stability of our hybrid core-shell silica microsensors for 3D monitoring. The Ru(dpp)-RBITC microparticles showed the most promising performance, especially in a pancreatic cancer model using alginate microgels. By employing computational segmentation, we generated 3D oxygen maps during live cell imaging, revealing oxygen gradients in the extracellular matrix and indicating a significant decrease in oxygen level characteristics of solid tumors. Notably, after 12 h, the oxygen concentration dropped to a hypoxic level of PO2 2.7 ± 0.1%.

Magneto-Enzymatic Microgels for Precise Hydrogel Sculpturing.

The inclusion of hollow channels in tissue-engineered hydrogels is crucial for mimicking the natural physiological conditions and facilitating the delivery of nutrients and oxygen to cells. Although bio-fabrication techniques provide diverse strategies to create these channels, many require sophisticated equipment and time-consuming protocols. Herein, collagenase, a degrading agent for methacrylated gelatin hydrogels, and magnetic nanoparticles (MNPs) are combined and processed into enzymatically active spherical structures using a straightforward oil bath emulsion methodology. The generated microgels are then used to microfabricate channels within biomimetic hydrogels via a novel sculpturing approach that relied on the precise coupling of protein-enzyme pairs (for controlled local degradation) and magnetic actuation (for directional control). Results show that the sculpting velocity can be tailored by adjusting the magnetic field intensity or concentration of MNPs within the microgels. Additionally, varying the magnetic field position or microgel size generated diverse trajectories and channels of different widths. This innovative technology improves the viability of encapsulated cells through enhanced medium transport, outperforming non-sculpted hydrogels and offering new perspectives for hydrogel vascularization and drug/biomolecule administration. Ultimately, this novel concept can help design fully controlled channels in hydrogels or soft materials, even those with complex tortuosity, in a single wireless top-down biocompatible step.

Selective Segregation of Thermo-Responsive Microgels via Microfluidic Technology.

Separation of equally sized particles distinguished solely by material properties remains still a very challenging task. Here a simple separation of differently charged, thermo-responsive polymeric particles (for example microgels) but equal in size, via the combination of pressure-driven microfluidic flow and precise temperature control is proposed. The separation principle relies on forcing thermo-responsive microgels to undergo the volume phase transition during heating and therefore changing its size and correspondingly the change in drift along a pressure driven shear flow. Different thermo-responsive particle types such as different grades of ionizable groups inside the polymer matrix have different temperature regions of volume phase transition temperature (VPTT). This enables selective control of collapsed versus swollen microgels, and accordingly, this physical principle provides a simple method for fractioning a binary mixture with at least one thermo-responsive particle, which is achieved by elution times in the sense of particle chromatography. The concepts are visualized in experimental studies, with an intend to improve the purification strategy of the broad distribution of charged microgels into fractioning to more narrow distribution microgels distinguished solely by slight differences in net charge.

Nanogels: Recent Advances in Synthesis and Biomedical Applications.

In the context of advanced nanomaterials research, nanogels (NGs) have recently gained broad attention for their versatility and promising biomedical applications. To date, a significant number of NGs have been developed to meet the growing demands in various fields of biomedical research. Summarizing preparation methods, physicochemical and biological properties, and recent applications of NGs may be useful to help explore new directions for their development. This article presents a comprehensive overview of the latest NG synthesis methodologies, highlighting advances in formulation with different types of hydrophilic or amphiphilic polymers. It also underlines recent biomedical applications of NGs in drug delivery and imaging, with a short section dedicated to biosafety considerations of these innovative nanomaterials. In conclusion, this article summarizes recent innovations in NG synthesis and their numerous applications, highlighting their considerable potential in the biomedical field.

Evolution of the Active Phase of Pt/Sn-Al2O3 Catalysts During Acidic Impregnation and Their Use in Propane Dehydrogenation.

Alumina-supported PtSn is an industrialized catalyst for propane dehydrogenation. During the catalyst impregnation, the acidic impregnation solution with chloroplatinic acid as a precursor inevitably leads to the partial dissolution of the surface of amphoteric alumina support and finally varies catalytic performance. Herein, the structure evolution of the active phase, induced by an impregnated acidic solution, was studied with special care. According to the diffused double layer theory, we proposed a model of microgels during impregnation. The microgels formed in the solution with suitable acidity on the surface of the catalysts evolved into a structure of Al2O3-coated oxidized Pt by reprecipitation during drying and calcination. The covered Pt species could be exposed by Ar+ sputtering or migrate to the surface during reduction to serve as active sites for propane dehydrogenation. Noticeably, the surface Sn0 species was generated when the pH of the impregnated solution was around 0.56, which is solid proof for the unique active phase with the PtSn alloy present on SnOx species existing on the surface of the Sn-Al2O3 support. The synthesized catalyst exhibited high propylene selectivity (99.4%) and superior stability (kd = 0.002 h-1). This study provides new insight for the precise preparation of Pt/Sn-Al2O3 catalysts.