Titan's Surface Research Articles

Self-assembled titanium-based macrostructures with hierarchical (macro-, micro-, and nano) porosities: A fundamental study

This study details the novel self-assembly of sodium titanate converted Ti-based microspheres into hierarchical porous 3D constructs, with macro-, micro-, and nanoporosity, for the first time. Ti6Al4V microspheres were suspended into 5 M NaOH (60 °C/24 h) solutions, with extensive variations in microsphere:solution ratios to modify microsphere interaction and initiate self-assembly through proximity merging of titanate surface dendritic growth. The formed structures, which either produced 1) unbonded, sodium titanate-converted microspheres; 2) flat (non-macroporous) scaffolds; or 3) open, hierarchically porous scaffolds, were then assessed in terms of their formation mechanism, chemical composition, porosity, as well as the effect of post-heat treatments on compressive mechanical properties. It was found that specific microsphere:solution ratios tended to form certain structures (<⅓ powder, 0.5 to 3 porous, >3 flat non-macroporous, >8 powder) due to a combination of microsphere freedom of movement, H2 gas bubble formation, and exposed surface reactivity. This promising discovery highlights the potential for lower temperature, simplistic production of 3D constructs with modifiable chemical properties due to the ion-exchange potential of titanate structures, with clear applications in a wide-range of fields, from medical materials to catalysts.

Evolution of Impact Melt Pools on Titan

AbstractTitan is an ocean world with a dense atmosphere, where photochemistry produces complex organic molecules that fall to the surface. An important astrobiological question is whether this material can mix with water and form molecules of biological interest. Large impacts heat the moon's subsurface and create liquid water melt pools. A recent study investigated impacts into Titan's clathrate‐covered ice shell. Methane clathrates are stable at Titan's surface conditions and have low thermal conductivity, making them efficient insulators that can lead to steep thermal gradients and a thin stagnant lid. The authors showed that the clathrate layer thickness primarily influences the melt distribution, while its volume is governed by the impactor size. Here, we investigate the fate of melt formed during an impact into a clathrate‐covered ice shell. Our results show two different behaviors: in cases when less melt is produced, the subsurface melt pool remains close to the surface and freezes on timescales ≲25 kyr; in cases when larger volumes of melt are produced, a downward‐oriented transport of the molten material occurs. As it descends, part of the melt freezes but some may reach the ocean within a few kyr under certain conditions; vertical impacts, high surface porosity, low viscosity, and tidal heating all favor this surface‐to‐ocean exchange. While providing insights on parameters that allow a subsurface melt pool to remain liquid beneath a Selk‐sized crater for a few kyr, this study suggests that Dragonfly may be able to sample melt deposits where organics reacted with liquid water to produce biomolecules.

Organic Input to Titan's Subsurface Ocean Through Impact Cratering.

Titan has an organic-rich atmosphere and surface with a subsurface liquid water ocean that may represent a habitable environment. In this work, we determined the amount of organic material that can be delivered from Titan's surface to its ocean through impact cratering. We assumed that Titan's craters produce impact melt deposits composed of liquid water that can founder in its lower-density ice crust and estimated the amount of organic molecules that could be incorporated into these melt lenses. We used known yields for HCN and Titan haze hydrolysis to determine the amount of glycine produced in the melt lenses and found a range of possible flux rates of glycine from the surface to the subsurface ocean. These ranged from 0 to 1011 mol/Gyr for HCN hydrolysis and from 0 to 1014 mol/Gyr for haze hydrolysis. These fluxes suggest an upper limit for biomass productivity of ∼103 kgC/year from a glycine fermentation metabolism. This upper limit is significantly less than recent estimates of the hypothetical biomass production supported by Enceladus's subsurface ocean. Unless biologically available compounds can be sourced from Titan's interior, or be delivered from the surface by other mechanisms, our calculations suggest that even the most organic-rich ocean world in the Solar System may not be able to support a large biosphere.

Nuclear quantum effects in the acetylene:ammonia plastic co-crystal.

Organic molecular solids can exhibit rich phase diagrams. In addition to structurally unique phases, translational and rotational degrees of freedom can melt at different state points, giving rise to partially disordered solid phases. The structural and dynamic disorder in these materials can have a significant impact on the physical properties of the organic solid, necessitating a thorough understanding of disorder at the atomic scale. When these disordered phases form at low temperatures, especially in crystals with light nuclei, the prediction of material properties can be complicated by the importance of nuclear quantum effects. As an example, we investigate nuclear quantum effects on the structure and dynamics of the orientationally disordered, translationally ordered plastic phase of the acetylene:ammonia (1:1) co-crystal that is expected to exist on the surface of Saturn's moon Titan. Titan's low surface temperature (∼90K) suggests that the quantum mechanical behavior of nuclei may be important in this and other molecular solids in these environments. By using neural network potentials combined with ring polymer molecular dynamics simulations, we show that nuclear quantum effects increase orientational disorder and rotational dynamics within the acetylene:ammonia (1:1) co-crystal by weakening hydrogen bonds. Our results suggest that nuclear quantum effects are important to accurately model molecular solids and their physical properties in low-temperature environments.

The Fate of Simple Organics on Titan's Surface: A Theoretical Perspective

AbstractAtmospheric photochemistry on Titan continuously transforms methane and nitrogen gases into various organic compounds. This study explores the fate of these molecules when they land on Titan's surface. Our analytical exploration reveals that most simple organics found in Titan's atmosphere, including all nitriles, triple‐bonded hydrocarbons, and benzene, land as solids. Only a few compounds are in the liquid phase, while only ethylene remains gaseous. For the simple organics that land as solids, we further examine their interactions with Titan's lake liquids. Utilizing principles of buoyancy, we found that flotation can be achieved via porosity‐induced (25%–60% porosity) or capillary force‐induced buoyancy for hydrogen cyanide ices on ethane‐rich lakes. Otherwise, these ices would sink and become lakebed sediments. By evaluating the timescale of flotation, our findings suggest that porosity‐induced flotation of millimeter‐sized and larger sediments is the only plausible mechanism for floating solids to explain the transient “magic islands” phenomena on Titan's lakes.

Vacuum-ultraviolet irradiation of pyridine:acetylene ices relevant to Titan astrochemistry.

Nitrogen-containing polycyclic aromatic hydrocarbons (NPAHs) are important molecules for astrochemistry and prebiotic chemistry, as their occurrence spans from interstellar molecular clouds to planetary systems. Their formation has been previously explored in gas phase experiments, but the role of solid-state chemical reactions in their formation under cryogenic conditions remains elusive. Here, we explore the formation of NPAHs through vacuum ultraviolet (VUV) irradiation of pyridine:acetylene ices in amorphous and co-crystalline phases, with the aim to simulate conditions relevant to the interstellar medium and Titan's atmosphere. Our results show that the synthesis of ethynylpyridines from VUV-irradiated pyridine:acetylene amorphous ices is achievable at 18 K. In the co-crystal phase, photolysis at 110 K leads to the formation of NPAHs such as quinolizinium+ and precursors, reflecting a dynamical system under our conditions. In contrast, irradiation at 90 K under stable conditions did not produce volatile photoproducts. These results suggest that such chemical processes can occur in Titan's atmosphere and potentially in its stratosphere, where the co-condensation of these molecules can form composite ices. Concurrently, the formation of stable co-crystals can influence the depletion rates of pyridine, which suggests that these structures can be preserved and potentially delivered to Titan's surface. Our findings provide insights into the molecular diversity and chemical evolution of organic matter on Titan, crucial for future space exploration missions, such as the Dragonfly mission, which may uncover higher-order organics derived from pyridine precursors on Titan's surface.

The impact of lake shape and size on lake breezes and air-lake exchanges on Titan

Titan, the largest moon of Saturn, has many lakes on its surface, formed mainly of liquid methane. Like water lakes on Earth, these methane lakes on Titan likely profoundly affect the local climate. Previous studies (Rafkin and Soto, 2020; Chatain et al., 2022) showed that Titan's lakes create lake breeze circulations with characteristic dimensions similar to the ones observed on Earth. However, such studies used a model in two dimensions; this work investigates the consequences of the addition of a third dimension to the model. Our results show that 2D simulations tend to overestimate the extension of the lake breeze over the land, and underestimate the strength of the subsidence over the lake, due to divergence/convergence geometrical effects in the mass conservation equations. In addition, 3D simulations including a large scale background wind show the formation of a pocket of accelerated wind behind the lake, which did not form in 2D simulations. An investigation of the effect of shoreline concavity on the resulting air circulation shows the formation of wind currents over peninsulas. Simulations with several lakes can either result in the formation of several individual lake breeze cells (during the day), or the emergence of a large merged cell with internal wind currents between lakes (during the night). Simulations of several real-shaped lakes located at a latitude of 74°N on Titan at the autumn equinox show that larger lakes trigger stronger winds, and that some sections of lakes might accumulate enough methane vapor to form a thin fog. Additionally, we adapted the Turbulent Kinetic Energy closure scheme of the model to better represent the extremely low turbulence at the surface of Titan, of 2 10−4 m2.s−2 above the land, and inferior to 3 10−5 m2.s−2 above the lake. The addition of a third dimension, along with adjustments in the parametrizations of turbulence and subsurface land temperature, results in a reduction in the magnitude of the average lake evaporate rate, namely to ∼6 cm/Earth year.

Charge Transfer and Orbital Reconstruction at an Organic-Oxide Interface.

The two-dimensional electron system (2DES) located at the surface of strontium titanate (STO) and at several other STO-based interfaces has been an established platform for the study of novel physical phenomena since its discovery. Here we report how the interfacing of STO and tetracyanoquinodimethane (TCNQ) results in a charge transfer that depletes the number of free carriers at the STO surface, with a strong impact on its electronic structure. Our study paves the way for efficient tuning of the electronic properties, which promises novel applications in the framework of oxide/organic-based electronics.

Synergistic polarization engineering on BaTiO3 bulk and surface for boosting redox kinetics of polysulfides in lithium–sulfur batteries

The notorious shuttle effect of intermediate lithium polysulfides and the sluggish kinetics of sulfur redox reactions restrict the further development of high-energy-density lithium-sulfur (Li–S) batteries. Herein, a strategy of synergistic polarization engineering on ferroelectric barium titanate (BaTiO3) bulk and surface is reported, aiming to collectively improve the adsorption-catalytic ability of ferroelectric BaTiO3 to polysulfides. Differential phase contrast-scanning transmission electron microscopy (DPC-STEM) demonstrates that the introduction of ultrathin heteroepitaxial TiOx surface can give rise to the surface local electric field differing from bulk internal polarization field. Experimental and theoretical results further reveal that synergistic polarization engineering by integrating the enhanced bulk internal polarization field with the surface local electric field can collaboratively realize excellent adsorption-catalytic activity resulting from rapid electrons transfer and optimized active sites. As a result, employing BaTiO3@TiOx modified separator can endow the batteries with favorable rate performance (the discharge specific capacity achieves 710 mAh g−1 at 4 C) and substantial enhancement on cyclic performance (64.5 % capacity retention at 2 C over 500 cycles). Impressively, even at high sulfur loading of 2.5 mg cm−2, the BaTiO3@TiOx-based cell still stabilizes 78 % capacity retention with at 1 C over 150 cycles, showing the practical potential of BaTiO3@TiOx in optimizing catalytic efficiency.

Noble metal nanoparticles and nanodiamond modified strontium titanate photocatalysts for room temperature CO production from direct hydrogenation of CO2

The activation and conversion of CO2 can be achieved on multifunctional catalytic sites at the metal/oxide interface by taking advantage of the synergy between noble metal nanoparticles and supports. Herein, sequential deposition of noble metals (Ru, Rh, and Pt) and nanodiamonds (NDs) was carried out on the surface of strontium titanates (STO). The noble metals and NDs were deposited in either 1 wt% or 10 wt%. The samples were characterized with in-situ as well as ex-situ spectroscopic and microscopic techniques and tested towards photocatalytic CO2 hydrogenation. The sequential deposition of the noble metals and NDs enhanced light absorption properties, which also led to higher photocatalytic activity. The STO-ND-Ru sample had the highest photocatalytic CO2 hydrogenation efficiency (47.5%) and showed improved selectivity for CH4 (14.5%). Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies showed that the hydrogenation of CO2 to CO and CH4 followed different mechanisms for pristine STO and STO-ND-Ru.

Characterizing phase transitions for titan's surface molecules: Implications for Dragonfly

The potential commonality of organic synthesis and prebiotic processes on the surface of Titan and primitive Earth makes Saturn's largest moon an indispensable location to seek answers for the origins of life on Earth and elsewhere. NASA's New Frontiers Mission, Dragonfly, is set to arrive on Titan's surface in the mid-2030s. Two of the main scientific goals of the Dragonfly mission are to identify chemical components and potential processes responsible for the production of biologically relevant compounds, and to search for potential biosignatures. To address these mission goals, Dragonfly is equipped with a linear ion trap mass spectrometer, called the Dragonfly Mass Spectrometer, or DraMS. This instrument will measure the molecular composition of Titan's surface at various locations inside and near Selk Crater, where prebiotic chemistry is expected to have occurred. Some molecules of interest on Titan's surface are thought to be sensitive to phase changes within the expected range of the sample handling chain, 94–165 K and 0.04–1.5 bar. A large abundance of such materials may therefore impact the capture efficiency and physical properties of the sampled materials within the DraMS system. In this work, we explore the potential for some of the hypothesized abundant organic molecules to be induced into phase transitions during the end-to-end sampling process by DraMS.

Evaluation of the interference of Tenax®TA adsorbent with dimethylformamide dimethyl acetal reagent for gas chromatography-Dragonfly mass spectrometry and future gas chromatography-mass spectrometry in situ analysis

Among future space missions, national aeronautics and space administration (NASA) selected two of them to analyze the diversity in organic content within Martian and Titan soil samples using a gas chromatograph – mass spectrometer (GC–MS) instrument. The Dragonfly space mission is planned to be launched in 2027 to Titan's surface and explore the Shangri-La surface region for years. One of the main goals of this mission is to understand the past and actual abundant prebiotic chemistry on Titan, which is not well characterized yet. The ExoMars space mission is planned to be launched in 2028 to Mars’ surface and explore the Oxia Planum and Mawrth Vallis region for years. The main objectives focus on the exploration of the subsurface soil samples, potentially richer in organics, that might be relevant for the search of past life traces on Mars where irradiation does not impact the matrices and organics. One recently used sample pre-treatment for gas chromatography – mass spectrometry analysis is planned on both space missions to detect refractory organic molecules of interest for astrobiology. This pre-treatment is called derivatization and uses a chemical reagent – called dimethylformamide dimethyl acetal (DMF-DMA) – to sublimate organic compounds keeping them safe from thermal degradation and conserving the chirality of the molecules extracted from Titan or Mars’ matrices. Indeed, the detection of building blocks of life or enantiomeric excess of some organics (e.g. amino acids) after DMF-DMA pre-treatment and GC–MS analyses would be both bioindicators. The main results highlighted by our work on DMF-DMA and Tenax®TA interaction and efficiency to detect organic compounds at ppb levels in a fast and single preparation are first that Tenax®TA did not show the onset of degradation until after 150 experiments – a 120 h at 300 °C experiment – which greatly exceeds the experimental lifetimes for the DraMS and GC-space in situ investigations. Tenax®TA polymer and DMF-DMA produce many by-products (about 70 and 46, respectively, depending on the activation temperature). Further, the interaction between the two leads to the production of 22 additional by-products from DMF-DMA degradation, but these listed by-products do not prevent the detection of trace-level organic molecules after their efficient derivatization and volatilization by DMF-DMA in the oven ahead the GC–MS trap and column.

Choice of Electrolyte Impacts the Selectivity of Proton-Coupled Electrochemical Reactions on Hydrogen Titanate

Proton-coupled electron transfer (PCET) reactions involving transition metal oxides are prevalent in aqueous electrochemical systems used for energy storage and conversion. Here, we elucidate the role of electrolyte on PCET mechanisms in transition metal oxides in aqueous acidic electrolytes using layered hydrogen titanate (H2Ti3O7) as an example. We identify three processes by which electrolyte protons interact with hydrogen titanate at the electrochemical interface: (1) adsorption at the surface and/or insertion into the bulk, (2) adsorption as part of the hydrogen evolution reaction (HER) at the surface, and (3) dissolution of the hydrogen titanate. We utilize a combined experimental and computational (ReaxFF) approach to probe how the competition for protons and electrons among these processes influences electrochemical properties, including the energy storage, Coulombic efficiency (CE), rate capability, and lifetime. In an acidic buffered electrolyte (1 M H3PO4), the CE increases from an average of 48% to 71% and the specific capacity increases from 83 to 90 mAh g–1 as compared to a strong acid electrolyte (1 M H2SO4). We propose that H3PO4 mitigates the HER and hydrogen titanate dissolution, thereby increasing the operating potential window for proton adsorption/insertion for charge storage in hydrogen titanate. Material characterization and computational results indicate that adsorption of phosphate species onto the surface of hydrogen titanate may decrease its dissolution upon reduction, thereby improving electrode performance. We offer a preliminary solution to improve energy storage performance via electrolyte tuning by decreasing the prevalence of the HER and electrode dissolution.

Ultrasound-triggered piezocatalytic composite hydrogels for promoting bacterial-infected wound healing.

Wound healing has become one of the basic issues faced by the medical community because of the susceptibility of skin wounds to bacterial infection. As such, it is highly desired to design a nanocomposite hydrogel with excellent antibacterial activity to achieve high wound closure effectiveness. Here, based on ultrasound-triggered piezocatalytic therapy, a multifunctional hydrogel is designed to promote bacteria-infected wound healing. Under ultrasonic vibration, the surface of barium titanate (BaTiO3, BT) nanoparticles embedded in the hydrogel rapidly generate reactive oxygen species (ROS) owing to the established strong built-in electric field, endowing the hydrogel with superior antibacterial efficacy. This modality shows intriguing advantages over conventional photodynamic therapy, such as prominent soft tissue penetration ability and the avoidance of serious skin phototoxicity after systemic administration of photosensitizers. Moreover, the hydrogel based on N-[tris(hydroxymethyl)methyl]acrylamide (THM), N-(3-aminopropyl)methacrylamide hydrochloride (APMH) and oxidized hyaluronic acid (OHA) exhibits outstanding self-healing and bioadhesive properties able to accelerate full-thickness skin wound healing. Notably, compared with the widely reported mussel-inspired adhesive hydrogels, OHA/THM-APMH hydrogel due to the multiple hydrogen bonds from unique tri-hydroxyl structure overcomes the shortage that catechol groups are easily oxidized, giving it long-term and repeatable adhesion performance. Importantly, this hybrid hydrogel confines BT nanoparticles to wound area and locally induced piezoelectric catalysis under ultrasound to eradicate bacteria, markedly improving the therapeutic biosafety and exhibits great potential for harmless treatment of bacteria-infected tissues.

Enhanced ion recognition through bi-directionally layered spacing regulation of 1D tubular titanate nanofilms

Titanate has been used to absorb heavy metal ions in wastewater. However, the selective adsorption driven by ion recognition remains a challenging task. In this paper, bidirectional layer spacing regulated titanate nanofilms were developed and the mechanism of layer spacing enhanced ion recognition was systematically studied. TEM, SEM, XRD, XPS, FTIR and BET were used to characterize and analyze the obtained titanate nanofilms, and the results showed that the adsorbent was successfully synthesized and the layer spacing of these nanofilms can be bidirectionally regulated. The adsorption kinetics and adsorption isotherm indicated a positive correlation between the layer spacing of titanate nanofilms and the ion recognition. DFT calculations and Bader program analysis were used to investigate the adsorption process of titanate nanofilms with different layer spacing. It can be concluded that the affinity between adsorbent and specific adsorbate and the electron transfer value on the titanate surface could be regulated by changing the layer spacing of titanate nanofilms, resulting in the enhanced ion recognition performance. Finally, an ion recognition mechanism was proposed based on the above experimental and calculative results.

Experimental Characterization of the Pyridine:Acetylene Co-crystal and Implications for Titan's Surface.

Titan, Saturn's largest moon, has a plethora of organic compounds in the atmosphere and on the surface that interact with each other. Cryominerals such as co-crystals may influence the geologic processes and chemical composition of Titan's surface, which in turn informs our understanding of how Titan may have evolved, how the surface is continuing to change, and the extent of Titan's habitability. Previous works have shown that a pyridine:acetylene (1:1) co-crystal forms under specific temperatures and experimental conditions; however, this has not yet been demonstrated under Titan-relevant conditions. Our work here demonstrates that the pyridine:acetylene co-crystal is stable from 90 K, Titan's average surface temperature, up to 180 K under an atmosphere of N2. In particular, the co-crystal forms via liquid-solid interactions within minutes upon mixing of the constituents at 150 K, as evidenced by distinct, new Raman bands and band shifts. X-ray diffraction (XRD) results indicate moderate anisotropic thermal expansion (about 0.5-1.1%) along the three principal axes between 90-150 K. Additionally, the co-crystal is detectable after being exposed to liquid ethane, implying stability in a residual ethane "wetting" scenario on Titan. These results suggest that the pyridine:acetylene co-crystal could form in specific geologic contexts on Titan that allow for warm environments in which liquid pyridine could persist, and as such, this cryomineral may preserve the evidence of impact, cryovolcanism, or subsurface transport in surface materials.

Floating Liquid Droplets on the Surface of Cryogenic Liquids: Implications for Titan Rain.

Saturn's moon, Titan, has a hydrocarbon-based hydrologic cycle with methane and ethane rainfall. Because of Titan's low gravity, "floating liquid droplets" (coherent droplets of liquid hydrocarbons that float upon a liquid surface) may form on the surface of Titan's hydrocarbon lakes and seas during rainfall. Floating liquid droplets, however, have not been investigated in the laboratory under conditions appropriate for the surface of Titan (cryogenic, hydrocarbon, liquids). We conducted a set of experiments to simulate methane and ethane rainfall under Titan surface conditions (89-94 K, 1.5 bar nitrogen atmosphere) and find that floating ethane droplets form in a wide range of bulk liquid compositions, yet floating methane droplets only form in a narrow compositional range and impact velocity. We find droplet formation is independent of the liquid density and hypothesize that dissolved atmospheric nitrogen in the bulk liquid may repel liquid ethane droplets at the surface. We propose that liquid droplets will form in Titan's methane-rich lakes and seas during ethane rainfall with a droplet radius of ≤3 mm and an impact velocity of ≤0.7 m/s. The presence of these droplets on Titan's lakes may result in a liquid surface layer that is dominated in rainfall composition.

Charges-Enhanced Molybdenum Disulfide Nanozyme Activity for Ultrasound-Mediated Cascade-Catalytic Tumor Ferroptosis.

Deficient catalytic activity of nanozyme and insufficient endogenous H2O2 in tumor microenvironment (TME) are major obstacles for nanozyme-mediated catalytic tumor therapy. Herein, since electron transfer is the basic essence of catalysis-mediated redox reaction, we explored the contributing factors of enzymatic activity based on positive and negative charges, which are experimentally and theoretically demonstrated to enhance the peroxidase (POD)-like activity of MoS2 nanozyme. Hence, an acidic TME-responsive and ultrasound-mediated cascade nanocatalyst (BTO/MoS2@CA) is presented by making few-layer MoS2 nanosheets grown on the surface of piezoelectric tetragonal barium titanate (T-BTO) and modified with pH-responsive cinnamaldehyde (CA). The integration of pH-responsive CA-mediated H2O2 self-supply, ultrasound-mediated charges enhanced enzymatic activity and GSH depletion enables out-of-balance redox homeostasis, leading to effective tumor ferroptosis with minimal side effects.

A Molybdenum Disulfide Nanozyme with Charge‐Enhanced Activity for Ultrasound‐Mediated Cascade‐Catalytic Tumor Ferroptosis

AbstractThe deficient catalytic activity of nanozymes and insufficient endogenous H2O2 in the tumor microenvironment (TME) are major obstacles for nanozyme‐mediated catalytic tumor therapy. Since electron transfer is the basic essence of catalysis‐mediated redox reactions, we explored the contributing factors of enzymatic activity based on positive and negative charges, which are experimentally and theoretically demonstrated to enhance the peroxidase (POD)‐like activity of a MoS2 nanozyme. Hence, an acidic tumor microenvironment‐responsive and ultrasound‐mediated cascade nanocatalyst (BTO/MoS2@CA) is presented that is made from few‐layer MoS2 nanosheets grown on the surface of piezoelectric tetragonal barium titanate (T‐BTO) and modified with pH‐responsive cinnamaldehyde (CA). The integration of pH‐responsive CA‐mediated H2O2 self‐supply, ultrasound‐mediated charge‐enhanced enzymatic activity, and glutathione (GSH) depletion enables out‐of‐balance redox homeostasis, leading to effective tumor ferroptosis with minimal side effects.

Dynamically evolving piezoelectric nanocomposites for antibacterial and repair-promoting applications in infected wound healing

Wound healing from bacterial infections is one of the major challenges in the biomedical field. The traditional single administration methods are usually accompanied with side effects or unsatisfactory efficacy. Herein, we design dynamically evolving antibacterial and repair-promoting nanocomposites (NCs) by in situ self-assembling of zeolitic imidazolate framework-8 (ZIF-8) on the surface of barium titanate (BTO), and further loading with a small amount of ciprofloxacin (CIP). The new strategy of combining pH-stimulated drug delivery and ultrasound-controlled sonodyamics has the potential to dynamically evolve in infected wound sites, offering a multifunctional therapy. In vitro study demonstrates that the enhancement generation of reactive oxygen species through the sonodynamic process due to the heterostructures and a small amount of CIP released in an acidic environment are synergistically antibacterial, and the inhibition rate was >99.9%. In addition, reduced sonodynamic effect and Zn2+ generated along with the gradual degradation of ZIF-8 simultanously promote cell migration and tissue regeneration. The invivo study of full-thickness skin wounds in mouse models demonstrate a healing rate of 99.3% could be achieved under the treatment of BTO@ZIF-8/CIP NCs. This work provides a useful improvement in rational design of multi-stimulus-responsive nanomaterials for wound healing. STATEMENT OF SIGNIFICANCE: A novel piezoelectric nanocomposite was proposed to realize sonodynamic therapy and pH-stimulated drug releasing simultaneously in wound healing treatment. The dynamically evolving structure of the piezoelectric nanocomposite in acidic microenvironment has been theoretically and experimentally verified to contribute to a continuous variation of sonodymanic strength, which accompanied with the gradual releasing of drug and biocompatible Zn2+effectively balanced antibacterial and repair-promoting effects. Both of the in vitro and in vivo study demonstrated that the strategy could significantly accelerate wound healing, inspiring researchers to optimize the design of multi-stimulus-responsive nanomaterials for various applications in biomedical and biomaterial fields.