Active Nucleation Sites Research Articles

Boosting Electrode Performance and Bubble Management via Direct Laser Interference Patterning.

Laser-structuring techniques like Direct Laser Interference Patterning show great potential for optimizing electrodes for water electrolysis. Therefore, a systematic experimental study is performed to analyze the influence of the spatial period and the aspect ratio between spatial period and structure depth on the electrode performance for pure Ni electrodes. Using a statistical design of experiments approach, it is found that the spatial distance between the laser-structures is the decisive processing parameter for the improvement of the electrode performance. Thus, the electrochemically active surface area could be increased by a factor of 12 compared to a nonstructured electrode. For oxygen evolution reaction, a significantly lower onset potential and overpotential (≈ -164 mV at 100mAcm-2) is found. This is explained by the superhydrophilic surface of the laser-structures and the influence of the structured surface on the bubble growth, which leads to a lower number of active nucleation sites and, simultaneously, larger detached bubbles. Combined with the fully wetted electrode surface, this results in reduced electrode blocking and thus, lower ohmic resistance.

Micro‐/Nanohierarchical Surfaces for Enhanced Pool Boiling in Large‐Area Silicon Multichips

With the rising demand for data centers, the need for an efficient thermal management approach becomes increasingly critical. This study examines the enhancement in pool boiling heat transfer on a customized multichip module, designed to mimic artificial intelligence chip layouts for high‐performance computing. Experiments are conducted on smooth surfaces and hierarchical structures integrating micropillars and porous copper, specifically copper inverse opal (CuIO) and copper nanowire (NW). The results demonstrate significant enhancements in critical heat flux (CHF) and heat transfer coefficient (HTC) through these hierarchical structures. Notably, the NW‐CuIO‐integrated hierarchical structure exhibits the highest CHF (234 W cm−2), achieving a 166% enhancement over smooth silicon. The HTC enhancement is more pronounced for the CuIO‐integrated hierarchical structure; this structure achieves an HTC of 70.3 kW m−2 K−1, which represents a 166% improvement. The heater layout, engineered surfaces, and their synergistic effects are analyzed through visualization. The observed boiling inversion phenomena further underscore the importance of sequential activation of nucleation sites in improving boiling performance. This study provides valuable insights into the mechanisms governing the enhancement of boiling heat transfer and offers practical guidance for developing efficient thermal management solutions for data centers.

Pool boiling experiments in graphene, graphene oxide and reduced graphene oxide nanofluid

The research focusing on two-phase heat transfer through pool boiling has been significantly advancing because of its high heat dissipation at small surface superheat temperatures. In the current research, pool boiling heat transfer characteristics of graphene, graphene oxide, and reduced graphene oxide at concentrations of 0.01, 0.05, and 0.1 vol. % are analyzed and compared with the base fluid. The experiments are conducted at saturated boiling and atmospheric conditions using copper as a boiling surface. An enhanced pool boiling heat transfer is observed with all considered nanofluid as compared to the base fluid regardless of the nanofluid concentration and it is enhanced with a rise in concentration. The earliest and latest onset of nucleate boiling was observed with graphene and graphene oxide respectively due to its hydrophobic and hydrophilic wettability respectively. The graphene, graphene oxide, and reduced graphene oxide nanofluid at 0.1 vol.% showed enhancement in critical heat flux of 44.49%, 81.96%, and 103.37% respectively, and heat transfer coefficient of 53.09%, 109.38%, and 165.27% respectively as related to the base fluid. The supreme heat transfer characteristics of reduced graphene oxide nanofluid were mainly because of the boiling-induced nanoparticle coating, enhanced wettability, and presence of high active nucleation sites.

Electrochemical Nucleation and Growth of Silver on Carbon Screen Printed Electrodes: Interpretation of Current Transients Obtained at Low Overpotentials

Potentiostatic current transients of silver nucleation and growth were obtained on carbon screen printed electrodes (SPE) consisting of single walled carbon nanotubes, carbon nanofibers, and mesoporous carbon. Data for the number of deposited silver particles were obtained by field-emission scanning electron microscopy. All three types of SPE show the presence of large (μm-sized) crystals with surface density of about 105 cm−2 together with much smaller silver particles with sizes typically below 80 nm and surface density in the 108 cm−2 range. The different carbon structures do not affect the shape and size of the large crystals but influence the size and extent of aggregation of the nanometer-sized ones. The current transients are interpreted by the Scharifker-Mostany model for multiple nucleation and diffusion limited growth and data for the nucleation rate per active site (A) and number of active sites for nucleation (N0) were obtained. It was found that the numbers of micron-sized crystals correspond to the calculated data for N0. The physical meaning of the quantities A and N0, obtained by fitting current transients with maxima, was critically assessed. The long-time behavior of the current transients was analyzed and evidence for diffusion at nonzero surface concentration of the silver ions was obtained.

Boiling performance enhancement and self-recovery of nucleate boiling regime on micro- and nanostructured porous surfaces

In this paper, we report the pool boiling experimental results for significant enhancements in the boiling heat transfer coefficient (BHTC) and CHF on various microporous surfaces. The microporous surfaces were fabricated by metal (Copper) powder sintering process, and nanostructured porous surfaces were additionally fabricated through the thermal oxidation of the metal porous surfaces. Among the examined substrates, a boiling surface with a thin metal porous layer and millimeter-sized porous pillar structures exhibited optimal boiling performance; the BHTC and CHF of the microporous surface were measured to be approximately 500 % and 270 % higher than those of a smooth reference surface, respectively. We conjecture that the results come from the combined effect of active nucleation site density enhancement, capillary wicking promotion, and separation of liquid-vapor flow paths on the microporous surface with porous pillars. On the other hands, the porous pillar surface with needle-like nanostructures showed the interesting phenomena that can be regarded to the recovery of the boiling regime from transition boiling to nucleate boiling. At the CHF, the temperature increase on the surface was slower than that on the other surfaces. Additionally, at high heat fluxes below the CHF, the overheated surface self-recovered to the nucleate boiling state, indicating the rewetting of local dry spots. We consider that the capillary wicking capability strongly improved by the nanostructures on the surface was presumably responsible for inhibiting the irreversible expansion of local dry spots. From the experimental observations throughout this study, we propose the following key requirements to design an ideal boiling surface: increasing the nucleation site density, ensuring a liquid supply path by capillary wicking, separating the liquid and vapor flow paths, and improving the liquid wettability of the solid surface by forming nanostructures.

Highly Reversible Sodium Metal Batteries Enabled by Extraordinary Alloying Reaction of Single‐Atom Antimony

AbstractThe unique coordination configuration of single‐atom materials (SAMs) allows precise reaction control at atomic‐level and a potential of unusual electrochemical reaction. Nevertheless, it is a big challenge to prepare main group element with high loading content. Here, multifield‐regulated synthesis (MRS) technology is utilized to rapidly produce single‐atom antimony (Sb) metal with a high loading of 15 wt.%. Ab initio molecular dynamics simulations reveal the significantly enhanced reaction kinetics of Sb and nitrogen‐doped graphene by multi‐physics field coupling. Compared with common metallic Sb nanoparticles, atomically dispersed Sb displays remarkably improved electrochemical reaction kinetics and stable structure due to the negligible variation of stresses and volume expansion during the pseudocapacitive alloying‐dealloying process. Such extraordinary alloying reaction in well‐dispersed Sb atoms enabling homogeneous ion flow can serve as active nucleation sites for regulating even Na metal nucleation and growth. As a result, copper foil coated with only ≈3 µm thickness of such material exhibits a high Coulombic efficiency of up to 99.99%, an ultra‐low overpotential of 3 mV, and a long lifetime exceeding 2500 h in symmetrical cells. Furthermore, an anode‐free MRS‐SbSA||Na3V2(PO4)3 battery is constructed, which demonstrates exceptionally high energy density (≈362 Wh Kg−1), outstanding rate capability and good cycling stability.

Design and Synthesis of Sb-Doped CuS@C Hollow Nanocubes as Efficient Anode Materials for Sodium-Ion Battery.

Copper sulfide has received widespread attention for application as anode materials in sodium-ion batteries due to their potent capabilitiess and eco-friendly properties. However, it is a challenge to achieve a high rate capability and long cycle stability owing to the heterogeneous transfer of sodium ions during charge-discharge, the interior poor electron conductivity and repeated volumetric expansion of copper sulfide. In this study, Sb-doped copper sulfide hollow nanocubes coated with carbon shells (Sb-CuS@C) was designed and constructed as anode nanomaterials in sodium-ion batteries. Thanks to the intrinsic good electron conductivity and chemical stability of carbon shells, Sb-CuS@C possesses a higher overall electron transfer as anode material, avoids agglomeration and structural destruction during the cycling. As a result, the synthesized Sb-CuS@C achieved an excellent reversible capacity of 595 mA h g-1 after 100 cycles at 0.5 A g-1 and a good rate capability of 340 mA h g-1 at a higher 10 A g-1. DFT calculations clarify that the uniformly doped Sb would act as active sodiophilic nucleation sites to help adsorbing sodium-ion during discharging and leading uniform sodium deposition. This work provides a new insight into the structural and componential modification for common transition-metal sulfides towards application as anode materials in sodium-ion battery.

Roller-like Spore Carbon Sphere-Orientated Graphene Fibers Prepared via Rheological Engineering for Lithium Sulfur Batteries.

Flexible batteries with large energy densities, lightweight nature, and high mechanical strength are considered as an eager goal for portable electronics. Herein, we first propose free-standing graphene fiber electrodes containing roller-like orientated spore carbon spheres via rheological engineering. With the help of the orientated microfluidic cospinning technology and the plasma reduction method, spore carbon spheres are self-assembled and orientedly dispersed into numerous graphene flakes, forming graphene fiber electrodes enriched with internal rolling woven structures, which cannot only enhance the electrical contact between active materials but also effectively improve the mechanical strength and structure stability of graphene fiber electrodes. When the designed graphene fibers are combined with the active sulfur cathode and lithium metal anode, the assembled flexible lithium sulfur batteries possess superior electrochemical performance with high capacity (>1000 mA h g-1) and excellent cycling life as well as good mechanical properties. According to density functional theory and COMSOL simulations, the roller-like spore carbon sphere-orientated graphene fiber hosts provide reinforced trapping-catalytic-conversion behavior to soluble polysulfides and nucleation active sites to lithium metal, thus synergistically suppressing the shuttle effect of polysulfides at the cathode side and lithium dendrite growth at the anode side, thereby boosting the whole electrochemical properties of lithium sulfur batteries.

Dynamic fractal ice nano-nucleators for cancer cryotherapy

We present cryo-responsive dynamic fractal ice nano-nucleators (DF-INNs) for cryo-cancer therapy applications. Our development of DF-INNs leverages their structural advantages, which inherently maximizes the number of active sites for heterogeneous ice nucleation. Owing to their radially attached nanocrystalline structure, DF-INNs expose an extensive array of grain boundaries. The rapid precipitation and subsequent radial attachments of nanocrystallites promote the exposure of facets with high Miller indices, intrinsically strained, five-fold twinned nanocrystals, and increasing point defects due to kinetically-limited precipitation. This unique fractal structure culminates in the elevating of freezing temperature compared to Euclidean-shaped ice nucleators. Additionally, the branched fractal structure of DF-INNs facilitates heterogenic ice formation within its nanoconfined region, leading to the production of numerous self-similar small fractal fragments. This fragmentation is primarily driven by nanoconfinement-induced delayed ice nucleation, similar to frost heaving. The shear stress can be easily relieved through grain boundary sliding within the radially stacked DF-INN, making itself prone to cryo-responsive fragmentation. Such dynamic attributes significantly enhance ice nucleating activity, presenting a powerful strategy to increase the efficacy of cryotherapy by enhancing cellular ice formation and in vivo tumor coverage.

Performance of surface structures in enhancing heat transfer rates of miniaturized pulsating heat pipe

Enhancement of the thermal performance by modifying the evaporator surface of a miniaturized pulsating heat pipe (PHP) is the primary target of the present work. Four PHPs having different evaporator surface types i.e., smooth, dimple cavity array, tunnel cavity, and rectangular cavity array were investigated numerically to compare the gas-liquid interfacial behavior and evaluate the role of bubble nucleation, slug-plug movement, and drop-film condensation on the thermal performance. Detailed modeling of evaporating and condensing interfaces shows that activation of nucleation sites at all defined discrete structures and undisturbed liquid flow path at the evaporator promote heat transfer rate. Through thermo fluidic analysis around different surface structures, evaporation dynamics is analyzed to understand the suitability of a structure type for enhancement of heat transfer. Associated slug-plug motion through the adiabatic zone and processes at the condenser have been also discussed to propose the characteristics of an ideal enhanced PHP. The capacity to transfer heat has been also characterized using thermal resistance for different structured PHPs which may be a guiding factor for the design of heat sinks for thermal applications.

The novel Auricularia-like MoS2 as binder-free electrodes for enhanced capacitive deionization

Molybdenum disulfide (MoS2) has been proven to be an effective and promising electrode material for capacitive deionization (CDI) due to its unique architectures and excellent electrochemical activity. However, MoS2-based electrodes still suffer from the high contact electrical resistance between MoS2 and the current collectors because of the necessity of adding binder during their fabrication. In this work, a flexible MoS2-based electrode with no binders was successfully fabricated. It was found that the frameworks of stainless-steel mesh with surface treatment could serve as an ideal substrate to provide plenty of active nucleation sites for the growth of MoS2. Consequently, a novel morphology of MoS2 with Auricularia-like architectures was produced. Based on electrochemical impedance spectroscopy (EIS), the charge transfer resistance was reduced to nearly zero after the treatment, highly increasing the transportation of charges inside the electrodes compared to the common MoS2-based electrodes. As a result, the binder-free MoS2-based electrodes demonstrated a superior desalination performance of 28.76 mg g-1 (1.2 V) for NaCl solution, which was superior to that of common MoS2-based and many other advanced materials-based electrodes. The novel MoS2-based electrode not only facilitates the utilization of MoS2 in CDI but also paves the way for its application in other electrochemical domains.

Flow boiling heat transfer enhancement of R134a in additively manufactured minichannels with microengineered surfaces

Additive manufacturing (AM) of metal components has opened new frontiers in heat transfer applications owing to its wide design freedom, which enables previously unexplored geometries with enhanced thermal performance to be developed. Open minichannels, on the other hand, consist of an extra manifold situated above the common flow channels, have been demonstrated to effectively reduce pressure drop and two-phase flow instability by mitigating backflow and maldistribution. In this paper, we synergized open minichannel design methodology with an ultrascalable surface microstructuring method for AM AlSi10Mg to improve flow boiling heat transfer performance of R134a. Experiments were conducted at the refrigerant mass flow rates (ṁ) of 0.005 kg/s to 0.01 kg/s (corresponding to mass fluxes of 73 to 146 kg/m2⋅s), and effective heat fluxes (qeff) of 1.8 kW/m2 to 141 kW/m2, by supplying 2 ℃ subcooled liquid to the minichannel inlet at saturation pressure (Psat) of 7.27 bar. The effects of heat flux, nucleation site density, mass flow rate and location of nucleation sites on the harmonic-average heat transfer coefficient (have) and pressure drop (ΔP) along the flow direction are investigated and compared against a conventionally manufactured (Al6061) counterpart. Our results show that the proposed etching process significantly improves the cooling performance of AM microstrucured minichannels, resulting in 210% higher have than Al6061 with negligible pressure drop penalty. The flow visualization results reveal a sequential order of nucleation site activation with increasing heat flux for microstructured open minichannels, which starts from the top of fins, followed by the corners and other three surfaces within the channels. This also results in the non-negligible effects of mass flow rate on cooling performance for microstructured minichannels, with approximately 10%–66% higher have at the lowest mass flow rate. Besides, the pressure drop penalty resulting from plain AM rough surface is also reduced by up to 13% through the proposed microstructuring process. In all, this work not only successfully identifies the dominant mechanisms in AM microstructured open minichannels, but it also provides useful minichannel design guidelines for high-performance two-phase cooling devices by AM.

Bi-Directional Modification to Quench Detrimental Redox Reactions and Minimize Interfacial Energy Offset for NiOX/Perovskite-Based Solar Cells.

The quality of the buried heterojunction of nickel oxide (NiOX)/perovskite is crucial for efficient charge carrier extraction and minimizing interfacial non-radiative recombination in inverted perovskite solar cells (PSCs). However, NiOX has limitations as a hole transport layer (HTL) due to energy level mismatch, low conduction, and undesirable redox reactions with the perovskite layer, which impede power conversion efficiency (PCE) and long-term stability. In this study, para-amino 2,3,5,6-tetrafluorobenzoic acid (PATFBA) is proposed as a bifacial defect passivator to tailor the NiOX/perovskite interface. The acid group and adjacent fluorine atoms of PATFBA effectively passivate NiOX surface defects, thereby improving its Ni3+/Ni2+ ratio, hole extraction capability, and energy band alignment with perovskite, while also providing active sites for homogenous nucleation. Meanwhile, the amine and adjacent fluorine atomsstabilize the buried perovskite interface by passivating interfacial defects, resulting in higher crystalline perovskite films with supressed non-radaitive recombination. Furthermore, the PATFBA buffer layer prevents redox reactions between Ni3+ and perovskite.These synergistic bi-directional interactions lead to optimized inverted PSCs with a PCE of 20.51% compared to 16.89% for pristine devices and the unencapsulated PATFBA-modified devices exhibit outstanding thermal and long-term stability. This work provides a new engineering approach to buried interfaces through the synergy of functional groups.

Spontaneous grain refinement effect of rare earth zinc alloy anodes enables stable zinc batteries.

Irreversible interfacial reactions at the anodes pose a significant challenge to the long-term stability and lifespan of zinc (Zn) metal batteries, impeding their practical application as energy storage devices. The plating and stripping behavior of Zn ions on polycrystalline surfaces is inherently influenced by the microscopic structure of Zn anodes, a comprehensive understanding of which is crucial but often overlooked. Herein, commercial Zn foils were remodeled through the incorporation of cerium (Ce) elements via the 'pinning effect' during the electrodeposition process. By leveraging the electron-donating effect of Ce atoms segregated at grain boundaries (GBs), the electronic configuration of Zn is restructured to increase active sites for Zn nucleation. This facilitates continuous nucleation throughout the growth stage, leading to a high-rate instantaneous-progressive composite nucleation model that achieves a spatially uniform distribution of Zn nuclei and induces spontaneous grain refinement. Moreover, the incorporation of Ce elements elevates the site energy of GBs, mitigating detrimental parasitic reactions by enhancing the GB stability. Consequently, the remodeled ZnCe electrode exhibits highly reversible Zn plating/stripping with an accumulated capacity of up to 4.0Ah cm-2 in a Zn symmetric cell over 4000h without short-circuit behavior. Notably, a ∼0.4Ah Zn||NH4V4O10 pouch cell runs over 110 cycles with 83% capacity retention with the high-areal-loading cathode (≈20mg cm-2). This refining-grains strategy offers new insights into designing dendrite-free metal anodes in rechargeable batteries.

Research on boiling heat transfer of aqueous extracts vacuum drying based on fractal theory

Traditional Chinese Medicine (TCM) aqueous extracts are highly viscous pseudoplastic porous media that boiling during vacuum drying, and the drying mechanism significantly differs from that of conventional solid materials. To reveal the heat transfer mechanism, a simulation model of aqueous extracts nucleate boiling was built based on fractal theory, and the effects of superheat, material temperature, viscosity and contact angle on fractal characteristics and heat transfer were studied. Results demonstrate that within a superheat range from 11 °C and 74 °C, the fractal dimension of active nucleation sites on the drying wall ranges between 1.75 and 1.86. The nuclear boiling heat flux increases with the increase in superheat, material temperature, specific heat capacity, thermal conductivity, and contact angle; or with the decrease in viscosity. The research can offer theoretical guidance for the development of drying processes and the optimization of technology in high viscosity pseudoplastic porous media.

Nucleation, growth and bubble detachment in liquid-vapor phase change on structured surfaces

Comprehensive grasp of heat and mass transfer, particularly in applications involving liquid-vapor phase change, hinges on management of nucleation, growth, and detachment of vapor bubbles. Various parameters influence the dynamics of phase-change heat and mass transfer and thus dictate the interactions between the surface, the liquid, and the vapor, profoundly impacting the underlying processes. To tailor these phenomena and harness them for technical applications involving high heat flux densities and intense mass transfer, such as boiling and electrolysis, surface functionalization is under intense development. By designing structured surfaces and creating preferential nucleation sites that promote heterogeneous nucleation, it is possible to exert control over the location and density of active nucleation sites on the surface. This, in turn, enables the regulation of bubble growth and detachment from the surface. With the aim of identifying optimal surface treatments for functionalizing surfaces and enhancing their performance in phase-change applications, we evaluated the nucleation, growth and detachment of a single bubble in a liquid-vapor phase change on untextured and laser-textured surfaces during water electrolysis. Platinum was chosen as the preferential material due to its favourable electrochemical properties for the hydrogen evolution reaction in acidic media. Electrolysis was performed at various voltages and the bubble dynamics were evaluated through high-speed imaging to investigate the intricacies of bubble growth and their mutual interactions. At 3.5 V using the laser textured surface, hydrogen bubbles detaching from the electrode surface had on average 40% smaller diameter, while the frequency of their detachment was 2,5-times higher compared to the untextured surface. This opens the possibility for further research that could lead to improving the efficiency of electrolysis.

Study of nucleate boiling growth regime on thin surfaces.

In a context of energy transition, heat exchanges are a key for energy sobriety. Among those exchanges, nucleate boiling is the preferred heat transfer method for high heat flux. Vaporisation plays an important role in the nuclear industry, but also in thermal machines such as cooling systems in data centers. In spite of decades studying boiling thermodynamics, modelling heat transfers in the nucleate boiling is still a major difficulty because of its numerous parameters. In the 1960s, scientists developed promising models called heat flux partitioning models. These models have been improved over the years, but they need closure laws about bubbles dynamics and nucleation site density. For the purpose of improving those models, we took part in an international collaboration (ANR TraThI) to study interface heat transfer. Project focuses on boiling with a controlled nucleation site density with a strong emphasis on studying isolated bubbles in water pool boiling, and later addressing multiple bubble interactions in pool and flow boiling. This work focuses on the bubble growth regimes on thin metallic foil observed in a water pool boiling experiment, with a distinction between microlayer and contact line growth regime. Pulsed nanosecond laser was used to create active nucleation site, while high-speed infrared thermography and shadowgraphy were implemented to record transient wall temperatures and bubble dynamics, respectively. This work shows that our experimental configuration induced two different bubble growth regimes, depending on the imposed heat flux and the recent past at the nucleation site and its vicinity. Study provides a framework for further in-depth investigations with different experimental configurations.

Boiling heat flux partitioning model with bubble tracking method considering bubble merger and stochastic characteristics

This study presents the development and validation of a numerical tool of heat partitioning model for boiling heat transfer using a bubble tracking method. It was aimed to account for the effect of stochastic phenomena in the boiling process by simulating individual bubbles. Saturated pool boiling conditions on a horizontal plate heater were analyzed to demonstrate the effectiveness of the proposed model. The model was devised based on the observations from high-resolution pool boiling experiments, assuming a truncated sphere for bubble shape and using simplified microlayer size and thickness models. The developed heat partitioning model was verified by comparisons with the conventional heat partitioning model. Afterward, the validation of the model was conducted by comparing the result of the simulation with the experimental data of the saturated pool boiling. In this validation, measured values of nucleation site density, departure diameter, single-phase heat transfer coefficients, etc. were applied. Additionally, the effect of stochastic phenomena on boiling heat transfer was evaluated using the bubble tracking method, focusing on nucleation timing and nucleation site distribution. Stochastic nucleation was found to reduce the bubble merger probability compared to simultaneous nucleation, leading to increased microlayer evaporation. Stochastic site distribution, on the other hand, decreased active nucleation sites due to the site suppression effect, resulting in reduced microlayer evaporation compared to uniform site distribution.

Effect of Evaporation Temperature and Mg2+ Concentration on the Crystallization of Ammonium Sulfate

AbstractThis study investigates the influences of the evaporation temperature and Mg2+ concentration on the crystallization of an ammonium sulfate mother liquor. Specifically, their effects on the solubility, metastable zone width, crystallization amount, average particle size, and coefficient of variation of ammonium sulfate are examined through the laser and evaporation crystallization methods. Results show that solubility increases and the metastable zone width narrows with an increase in the evaporation temperature. At an evaporation temperature of 338.15 K, the controllability of the crystallization process improves and explosive nucleation does not easily occur. In this case, crystals with large average particle sizes, regular morphologies, and high crystallinity are obtained. With an increase in the Mg2+ concentration in the solvent, solubility decreases. The added Mg2+ covers the active nucleation sites, thus hindering the nucleation of ammonium sulfate and widening the metastable zone width. At a Mg2+ concentration of 0.9 g L−1 or higher, Mg2+ covers the active surfaces of the grains. This inhibits normal crystal growth and hinders the nucleation and growth of ammonium sulfate crystals, so the crystallization amount of ammonium sulfate significantly reduces.

Calcium crosslinked macroporous bacterial cellulose scaffolds with enhanced in situ mineralization and osteoinductivity for cranial bone regeneration

The inherent biological inertness and lack of three-dimensional (3D) macroporous structures greatly hinder the use of pristine bacterial cellulose (BC) as a tissue engineering scaffold for bone regeneration. To address this issue, we developed a simple and effective strategy to fabricate a BC-based scaffold with excellent bioactivity and macroporous structure by crosslinking short-cut BC nanofibers using Ca2+. The Ca2+ crosslinked macroporous BC scaffold (MPBC@Ca) presents better structural stability due to the enhanced cellulose hydration. Importantly, the Ca2+ on the surface of BC nanofibers can serve as an active nucleation site to accelerate the deposition of hydroxyapatite (HAp), which is beneficial for the construction of biomimetic bone tissue extracellular matrix (ECM) microenvironment. The HAp-deposited MPBC@Ca scaffolds (HAp-MPBC@Ca) with biomimetic ECM microenvironment have excellent cytocompatibility and enhanced osteogenic differentiation of stem cells in vitro. Furthermore, the results of in vivo tests revealed that the HAp-MPBC@Ca scaffold has favorable osteoinductivity and accelerates cranial bone tissue regeneration. This study proposes a novel strategy to improve the bioactivity of BC and presents the great potential of biomimetic ECM microenvironment BC-based scaffold for repairing large cranial bone defects.