High-performance multimode elastocaloric cooling system

Synergistic Interface Engineering and Band Alignment Enable High-Temperature Capacitive Performance in PAEK-Based Polymer Nanocomposites

Polymer dielectric capacitors are crucial devices of high-power electrical systems for capacitive energy storage. The large conduction loss of polymer dielectrics at elevated temperatures and electric fields is the main challenge. Herein, dielectric nanocomposites of BNNS/poly(aryl ether ketone) (PAEK) regulated by interfacial engineering and band alignment are presented, significantly restraining the conduction loss and greatly enhancing the energy storage density at high temperatures and high electric fields. Dual-functionalized BNNS with -NH2 and -F groups (F-BNNS-NH2) were prepared and incorporated into carboxylate-functionalized PAEK (PAEK-COOH) to form robust interfacial bonding via an amino-carboxyl reaction, enabling excellent thermal stability and mechanical properties of the composites. Meanwhile, the electron-withdrawing nature of the -F group regulated the BNNS band structure to achieve widened Eg, which is responsible for the generation of electrons and holes trappings. At optimal conditions, a record-high breakdown strength of 600 MV/m with an energy density of 5.58 J/cm3 and an energy density of 5.01 J/cm3 at an efficiency of 90% is realized at 150 °C, which surpasses most reported nanocomposite dielectrics. This work establishes a paradigm for harmonizing interfacial reinforcement with electronic structure regulation in extreme-condition energy storage dielectrics.

Large thermoelastic effect in martensitic phase of ferroelastic alloys for high efficiency heat pumping

Solid state heat pumping using latent heat from first order ferroic phase transitions is a promising green alternative to traditional vapor compression technology. However, the intrinsic phase transition hysteresis poses a limitation on heat pumping energy efficiency. Here, we propose heat pumping using reversible heat from anhysteretic elastic deformation in martensitic phase of ferroelastic alloys. Conventionally, this thermoelastic effect (TeE) is considered too weak to be practical. But we find that in [100]-textured Ti78Nb22 martensitic polycrystals, the TeE can produce a large adiabatic temperature change (∆Tad) of 4-5 K at 413-473 K due to macroscopic large linear thermal expansion (αl = 10-4/K). This large TeE not only far exceeds those of ordinary metals ( Δ T a d ≈ 0.2 K ) but also brings a material-level energy efficiency that reaches about 90% of the Carnot theoretical limit. In other ferroelastic martensitic alloys with larger intrinsic αl (up to 5.4 × 10-4/K), the TeE is predicted to bring an even larger ∆Tad (up to 22 K) while maintaining relatively high efficiency. Our findings offer a non-phase-transition-based way for high efficiency solid state heat pumping.

Alcogel-Based Interfacial Evaporation for Vertical Thermal Diode-Structured Smart Walls with Radiant Cooling

Traditional building envelopes with constant thermophysical properties constrain their capabilities in temperature regulation. Whether it is possible to achieve single-direction heat transfer along building envelopes with climate-adaptative thermophysical properties to enhance passive heat gain in winter and thermal dissipation in summer? In this work, through the capillary effect in interfacial evaporation and thermal diode structure, single-direction heat transfer with passively adjustable thermal properties in a vertical building envelope is practically achieved. An evaporation-condensation-based smart wall (ECSW) is manufactured for spontaneous and continuous cooling/heating supply to the built environment. The ECSW features climate-adaptative heat transfer characteristics with heat transfer coefficient transiting from 3.33 to ≈30 W m-2 K-1. Additionally, coupling with radiant cooling and photothermal capabilities, ECSW shows excellent thermal performances, i.e., a heat transfer at 5.44 W m-2 by radiant cooling with a 5 °C cooler surface, and a heat transfer at 387.68 W m-2 under solar illumination at 1000 W m-2. Simulation results show that the ECSW enables building energy savings at 66.47% in Kunming. This study first reports vertical thermal diode building envelopes utilizing natural heating/cooling sources through interfacial evaporation for passive temperature regulation with low costs, performance stability and energy-saving potentials for smart and sustainable buildings.

Bulk Bi-Sb polycrystals underpinned by high electron/phonon mean free path ratio enabling thermoelectric cooling under 77 K

Bi-Sb alloy, as a promising thermoelectric material at cryogenic temperatures, has seen stagnant progress due to challenges in understanding the transport behaviors of energy carriers, and difficulties in synthesizing high-homogeneity, large-grain samples. In this study, an inherent electron-phonon decoupling in Bi-Sb is revealed using the first-principles calculations based on the virtual crystal approximation. The mean free path of the dominant electrons (λele ~ 103 nm) is found of two orders of magnitude larger than that of phonons (λph ~ 101 nm), suggesting that a grain size greater than 10 μm would be favorable for thermoelectric transport. Bulk Bi-Sb polycrystals with highly elemental homogeneity and large grain size (~80 μm) are successfully synthesized through an ultra-fast quenching method combined with annealing, delivering superior thermoelectric performance. A prototype module based on the Bi0.88Sb0.12 polycrystal, with a ZTmax of 0.48 at 150 K, is fabricated and demonstrates a ΔTmax of 4 K at a Th of 75 K. This marks the first report of n-p paired thermoelectric cooling modules operating below liquid nitrogen temperature.

Recent Advances in Polyvinylidene Fluoride with Multifunctional Properties in Nanogenerators

Amid the global energy crisis and rising emphasis on sustainability, efficient energy harvesting has become a research priority. Nanogenerators excel in converting abundant mechanical and thermal energy into electricity, offering a promising path for sustainable solutions. Among various nanogenerator's materials, Polyvinylidene fluoride (PVDF), with its distinctive molecular structure, exhibits multifunctional electrical properties including dielectric, piezoelectric and pyroelectric characteristics. These properties combined with its excellent flexibility make PVDF a prime candidate material for nanogenerators. In nanogenerators, this material is capable of efficiently collecting and converting energy. This paper discusses how PVDF's properties are manifested in three types of nanogenerators and compares the performance of these nanogenerators. In addition, strategies to improve the output performance of nanogenerators are demonstrated, including physical and chemical modification of materials, as well as structural optimization strategies such as hybrid structures and external circuits. It also introduces the application of this material in natural and human energy harvesting, as well as its promising prospects in medical technologies and smart home systems. The aim is to promote the use of PVDF in self-powered sensing, energy harvesting and smart monitoring, thereby providing valuable insights for designing more efficient and versatile nanogenerators.

Overcoming Energy Storage-Loss Trade-Offs in Polymer Dielectrics Through the Synergistic Tuning of Electronic Effects in π-Conjugated Polystyrenes

Achieving high-performance dielectric materials remains a significant challenge due to the inherent trade-offs between high energy storage density and low energy loss. A central difficulty lies in identifying a suitable dipolar unit that can enhance the polarity and dielectric constant of the material while effectively suppressing the high energy losses associated with polarization relaxation, charge injection, and conduction. To address this, a novel strategy is proposed that introduces electron-donating and electron-withdrawing substituents on the benzene ring of polystyrene-based polymers, creating bulky dipole groups that are resistant to reorientation under an electric field. This approach mitigates relaxation losses associated with dipole reorientation and manipulates the band structure via substituent modification to suppress conduction losses. Additionally, the deformation of the π-electron cloud under an electric field enhances the dielectric constant and energy storage density. Ultimately, the optimized chlorostyrene-methyl methacrylate (MMA) copolymer exhibits an 85% discharge efficiency and an energy storage density of 18.3 J cm- 3, nearly three times that of styrene-based copolymers under the same conditions. This study introduces a new approach for designing high-energy density, low-loss polymer dielectric materials by precisely controlling electron-donating and electron-withdrawing effects to modulate the distribution of π-conjugated electron clouds.

Tenon-and-Mortise Structure-Inspired MOF/PVDF Composites with Enhanced Piezocatalytic Performance via Dipole-Engineering Strategy

Fabricating poly(vinylidene fluoride) (PVDF) and its composite ferroelectrics are essential for the development of next-generation lightweight, portable, wearable, and implantable intelligent devices. However, integrating and maximizing spontaneous polarization and interfacial electromechanical conversion efficiency remain major challenges in the contemporary PVDF-based composites field. Herein, inspired by the tenon-and-mortise structure associated with ancient Chinese architecture, an amino-anchored metal-organic framework (MOF)/PVDF piezoelectric composite using a dipole-engineering strategy to deliver enhanced piezocatalytic performance is constructed. Homogeneous and long-range ordered hydrogen-bond networks have been formed with the PVDF matrix after introducing periodically arranged amino anchors into the NH2-HU MOF. The NH2-HU10wt%/PVDF composite exhibits a 40% greater β-phase content and a remnant polarization value more than 550% higher than that of the bare PVDF fibers. These amino anchors synergistically enhance both the local electric field and collaborative dipole alignment resulting in a piezocatalytic bactericidal performance of 97.4% when irradiated under clinical ultrasound conditions. Moreover, the enhanced polarizability within the MOF/PVDF composite simultaneously improves its responsiveness to X-rays via its periodic amino anchoring networks, thereby doubling CT imaging efficacy for implants at lower voltages. Integrating piezoelectric MOFs and polymer matrices through molecular design presents a viable approach for optimizing ferroelectric properties and expanding piezoelectric-composite applications.

Achieving kilowatt-scale elastocaloric cooling by a multi-cell architecture

Elastocaloric cooling using shape memory alloys (SMAs) has attracted considerable interest as an environmentally friendly, energy-efficient alternative to conventional vapour-compression refrigeration1,2. However, the limited cooling power of existing devices (≤300 W) hampers the commercialization of this technology3,4. Here we constructed a kilowatt-scale elastocaloric cooling device using compressive tubular NiTi in an 'SMAs in series-fluid in parallel' architecture, referred to as the multi-cell architecture. A large specific cooling power of 12.3 W g-1 was achieved by the large surface-area-to-volume ratio of thin-walled tubular NiTi at high-frequency operation (3.5 Hz), complemented by graphene nanofluid as an efficient heat transfer agent. Furthermore, the multi-cell architecture ensures a sufficient elastocaloric mass for tight assembly while maintaining a low system fluid pressure. Our device achieves a cooling power of 1,284 W on the fluid side at zero temperature lift during the initial 500,000 cycles, demonstrating the potential of this green cooling technology for a decarbonized future5,6.

Bioinspired thermally conducting packaging for heat management of high performance electronic chips

Conventional electronic chip packaging generates a huge thermal resistance due to the low thermal conductivity of the packaging materials that separate chip dies and coolant. Here we propose and fabricate a closed high-conducting heat chip package based on passive phase change, using silicon carbide which is physically and structurally compatible with chip die materials. Our "chip on vapor chamber" (CoVC) concept realizes rapid diffusion of hot spots, and eliminates the high energy consumption of refrigeration ordinarily required for heat management. Multi-scale wicks and bionic vein structures are applied to CoVC leading to an increase of 164% in heat transfer performance. The thermal resistance of the package was only a third that of traditional packaging systems. This means that the structure of CoVC has a good thermal conducting ability and can reduce energy consumption for heat dissipation.

Dilute Nanocomposites: Tuning Polymer Chain Local Nanostructures to Enhance Dielectric Responses

Dielectric polymers possessing high energy and low losses are of great interest for electronic and electric devices and systems. Nanocomposites in which high dielectric constant (high-K) nanofillers at high loading (>10 vol%) are admixed with polymer matrix have been investigated for decades, aiming at enhancing the dielectric performance, but with limited success. In 2017, it is discovered that reducing nanofiller loading to less than 0.5 vol% in polymer matrix can lead to marked enhancement in dielectric performance. Here, we reviewed the discoveries and advances of this unconventional approach to enhance dielectric performance of polymers. Experimental studies uncover that nanofillers lead to interfaces changes over distances larger than 100 nm. Experimental and modeling results show that introducing free volume in polymers reduces the constraints of glass matrix on dipoles in polymers, leading to enhanced K without affecting breakdown. Moreover, low-K nanofillers at low-volume loading serve as deep traps for charges, lowering conduction losses and increasing breakdown strength. The dilute nanocomposites provide new avenues for designing dielectric polymers with high K, minimal losses, and robust breakdown fields, thus achieving high energy and power density and low loss for operation over a broad temperature regime.

Mechanocaloric Effects Characterization of Low-Crystalline Thermoplastic Polyurethanes Fiber

Mechanocaloric cooling/heat pumping with zero carbon emission and high efficiency shows great potential for replacing traditional refrigeration with vapor compression. Mechanocaloric prototypes that are developed using shape memory alloys (SMAs) face the problems of a large driving force and high cost. In this work, we report a low-crystalline thermoplastic polyetherurethane (TPU) elastomer fiber with a low actuation force and good mechanocaloric performance. We fabricate the TPU fiber and develop a multifunctional mechanical tester to measure both the elastocaloric and twistocaloric effects. In the experiments, the applied stress required to induce mechanocaloric effects of the TPU fiber is only 10~30 MPa, which is much lower than that of widely used NiTi elastocaloric SMAs (600~1200 MPa). The TPU fiber produces a maximum twistocaloric adiabatic temperature change of 10.2 K, which is 78.9% larger than its elastocaloric effect of 5.7 K. The wide-angle X-ray scattering (WAXS) results show that the strain-induced amorphous chain alignment and associated configurational entropy change are the main causes of the good mechanocaloric effects of the TPU fiber, rather than the strain-induced crystallization. This work demonstrates the potential of achieving low-force heat-efficient mechanocaloric cooling using thermoplastic elastomer fibers.

Elastocaloric Heat Pump by Twist Induced Periodical Non-Linear Stress for Low Hysteresis and High Carnot Efficiency

Elastocaloric cooling is one of the most promising solid-state cooling approaches to address the issues of energy shortage and global warming. However, the cooling efficiency and cycle life of this technology need to be improved, and the required driving force shall be reduced. Here, a novel elastocaloric heat pump by periodic non-linear stress is developed by employing fiber twisting and separated cooling and heating media. The non-linear stress generated by fiber twisting yields a hierarchical, rigid-yet-flexible architecture and a periodic entropy spatial distribution, which result in a low mechanical hysteresis work and a high cooling efficiency (a maximum material coefficient of performance (COP) of 30.8 and a maximum Carnot efficiency of 82%). The torsional non-linear stress inhibits crack propagation and results in a highly extended cycle life (14752 cycles, more than ten times of fiber stretching). The heat pump exhibits a maximum average temperature span of 25.6 K, a maximum specific cooling power of 1850 W Kg-1, a maximum device COP of 19.5, and a maximum device power of 5.0 W, under each optimal condition.

Enhancement of the Elastocaloric Performance of Natural Rubber by Forced Air Convection

We study the enhancement of the elastocaloric effect in natural rubber by using forced air convection to favour heat extraction during the elongation stage of a stretching-unstretching cycle. Elastocaloric performance is quantified by means of the adiabatic undercooling that occurs after fast removal of the stress, measured by infrared thermography. To ensure accuracy, spatial averaging on thermal maps of the sample surface is performed since undercooled samples display heterogeneities caused by various factors. The influence of the stretching velocity and the air velocity is analysed. The findings indicate that there is an optimal air velocity that maximises adiabatic undercooling, with stretching velocities needing to be high enough to enhance cooling power. Our experiments allowed the characterisation of the dependence of the Newton heat transfer coefficient on the air convection velocity, which revealed an enhancement up to 600% for air velocities around 4 m/s.

Efficient roller-driven elastocaloric refrigerator

Elastocaloric cooling has experienced fast development over the past decade owing to its potential to reshape the refrigeration industry. While the solid-state elastocaloric refrigerant is emission-free, the efficiency of the state-of-the-art elastocaloric cooling systems is not sufficient yet to reduce carbon emissions during operation. In this study, we double the coefficient of performance, the most commonly used efficiency metric, via the synergy of material-level advances in TiNiCu and the system-level roller-driven mechanism capable of recovering kinetic energy. On the materials level, a 125% improvement in coefficient of performance is illustrated in TiNiCu compared to NiTi, empowered by the B2-B19 martensitic transformation with improved lattice compatibility and the grain boundary strengthening from the nanocrystalline structure. On the system level, owing to the properly sized angular momentum in rotating parts, 78% work recovery efficiency is reported, transcending the theoretical limit previously unattainable without kinetic energy recovery. This confluence of materials and mechanical innovations propels elastocaloric cooling systems into a new realm of efficiency and paves the way for their practical application.

Shearo-caloric effect enhances elastocaloric responses in polymer composites for solid-state cooling

Room-temperature elastocaloric cooling is considered as a zero-global-warming-potential alternative to conventional vapor-compression refrigeration technology. However, the limited entropy and large-deformation features of elastocaloric polymers hinder the creation of the breakthrough in their caloric responses and device development. Herein, we report that the addition of a small amount of inorganic nanofillers into the polymer induces the aggregate of the effective elastic chains via shearing the interlaminar molecular chains, which provides an additional contribution to the entropy in elastocaloric polymers. Consequently, the adiabatic temperature change of -18.0 K and the isothermal entropy change of 187.4 J kg-1 K-1 achieved in the polymer nanocomposites outperform those of current elastocaloric polymers. Moreover, a large-deformation cooling system with a work recovery efficiency of 56.3% is demonstrated. This work opens a new avenue for the development of high-performance elastocaloric polymers and prototypes for solid-state cooling applications.

Sizing up caloric devices

Emerging solid-state cooling technologies may help reduce overall carbon emissions.

3D Printing Elastocaloric TiNiCu Thermoelectric Shape Memory Alloys

The development of new thermoelectric conversion and cooling materials is an important means of addressing global climate and heat emissions in the future. While heavy and toxic elements like tellurium and lead are traditionally used to make thermoelectric materials with poor mechanical properties, recent decades have seen a gradual push towards greener and more sustainable alternatives. One such potential alternative material for thermoelectric and thermal management applications would be the Nitinol (TiNi) shape memory alloy, due to their superior mechanical properties. In this study, we have investigated the use of 3D melt printing techniques that can be used to achieve thermoelectric performance and efficiency of elastic memory alloys below 500 °C. The electrical and thermal properties of TiNiCu materials and their relation to morphology were investigated. All the alloys show similar effect sizes, their fatigue behavior is however different. By adjusting the composition of Ti and Ni elements and we have obtained memory alloys with high thermoelectric properties, with a 50% increase in power factor and a 100% increase in ZT values. This work demonstrates the feasibility of using novel 3D-printed SMAs for thermoelectric and cooling applications, providing an experimental basis for the future preparation of low-cost, efficient, long service lifetime and stable materials for thermal energy harvesting and management.

Elastocaloric, barocaloric and magnetocaloric effects in spin crossover polymer composite films

Giant barocaloric effects were recently reported for spin-crossover materials. The volume change in these materials suggests that the transition can be influenced by uniaxial stress, and give rise to giant elastocaloric properties. However, no measurements of the elastocaloric properties in these compounds have been reported so far. Here, we demonstrated the existence of elastocaloric effects associated with the spin-crossover transition. We dissolved particles of ([Fe(L)2](BF4)2, [L=2,6di(pyrazol-1-yl)pyridine]) into a polymeric matrix. We showed that the application of tensile uniaxial stress to a composite film resulted in a significant elastocaloric effect. The elastocaloric effect in this compound required lower applied stress than for other prototype elastocaloric materials. Additionally, this phenomenon occurred for low values of strain, leading to coefficient of performance of the material being one order of magnitude larger than that of other elastocaloric materials. We believe that spin-crossover materials are a good alternative to be implemented in eco-friendly refrigerators based on elastocaloric effects.

A full solid-state conceptual magnetocaloric refrigerator based on hybrid regeneration

The environmental friendliness and high efficiency of magnetocaloric refrigeration make it a promising substitute for vapor compression refrigeration. However, the common use of heat transfer fluid in conventional passive magnetic regenerators (PMRs) and active magnetic regenerators (AMRs) makes only partial materials contribute to the regeneration process, which produces large regeneration loss and greatly limits the regeneration efficiency and refrigeration performance at high frequency. Herein, we propose a new conceptual hybrid magnetic regenerator (HMR) composed of multiple solid-state high thermal conductivity materials (HTCMs) and magnetocaloric materials (MCMs), in which both HTCM and MCM elements participate in the regeneration process. This novel working mode could greatly reduce regeneration losses caused by dead volume, pressure losses, and temperature nonuniformity in heat transfer substances to markedly improve regeneration efficiency at high working frequencies. Using the experimentally obtained adiabatic temperature change and magnetic work and with the help of finite element simulation, a maximum temperature of 26 K, a dramatically large cooling power of 8.3 kW/kg, and a maximum ideal exergy efficiency of 54.2% are achieved at the working frequency of 10 Hz for an ideal prototype device of a rotary HMR magnetocaloric refrigerator, which shows potential for achieving an integrative, advanced performance against current AMR/PMR systems.

Hybrid magnon-phonon localization enhances function near ferroic glassy states

Ferroic materials on the verge of forming ferroic glasses exhibit heightened functionality that is often attributed to competing long- and short-range correlations. However, the physics underlying these enhancements is not well understood. The Ni45Co5Mn36.6In13.4 Heusler alloy is on the edge of forming both spin and strain glasses and exhibits magnetic field-induced shape memory and large magnetocaloric effects, making it a candidate for multicaloric cooling applications. We show using neutron scattering that localized magnon-phonon hybrid modes, which are inherently spread across reciprocal space, act as a bridge between phonons and magnons and result in substantial magnetic field-induced shifts in the phonons, triple the caloric response, and alter phase stability. We attribute these modes to the localization of phonons and magnons by antiphase boundaries coupled to magnetic domains. Because the interplay between short- and long-range correlations is common near ferroic glassy states, our work provides general insights on how glassiness enhances function.

Self-oscillating polymeric refrigerator with high energy efficiency

Electrocaloric1,2 and electrostrictive3,4 effects concurrently exist in dielectric materials. Combining these two effects could achieve the lightweight, compact localized thermal management that is promised by electrocaloric refrigeration5. Despite a handful of numerical models and schematic presentations6,7, current electrocaloric refrigerators still rely on external accessories to drive the working bodies8-10 and hence result in a low device-level cooling power density and coefficient of performance (COP). Here we report an electrocaloric thin-film device that uses the electro-thermomechanical synergy provided by polymeric ferroelectrics. Under one-time a.c. electric stimulation, the device is thermally and mechanically cycled by the working body itself, resulting in an external-driver-free, self-cycling, soft refrigerator. The prototype offers a directly measured cooling power density of 6.5 W g-1 and a peak COP exceeding 58 under a zero temperature span. Being merely a 30-µm-thick polymer film, the device achieved a COP close to 24 under a 4 K temperature span in an open ambient environment (32% thermodynamic efficiency). Compared with passive cooling, the thin-film refrigerator could immediately induce an additional 17.5 K temperature drop against an electronic chip. The soft, polymeric refrigerator can sense, actuate and pump heat to provide automatic localized thermal management.

Continuous and efficient elastocaloric air cooling by coil-bending

Elastocaloric cooling has emerged as an eco-friendly technology capable of eliminating greenhouse-gas refrigerants. However, its development is limited by the large driving force and low efficiency in uniaxial loading modes. Here, we present a low-force and energy-efficient elastocaloric air cooling approach based on coil-bending of NiTi ribbons/wires. Our air cooler achieves continuous cold outlet air with a temperature drop of 10.6 K and a specific cooling power of 2.5 W g-1 at a low specific driving force of 26 N g-1. Notably, the cooler shows a system coefficient of performance of 3.7 (ratio of cooling power to rotational mechanical power). These values are realized by the large specific heat transfer area (12.6 cm2 g-1) and the constant cold zone of NiTi wires. Our coil-bending system exhibits a competitive performance among caloric air coolers.

Evaluation of the mechanical properties and clinical application of nickel-titanium shape memory alloy anal fistula clip

Objective

The study investigates the mechanical properties of a nickel-titanium shape memory alloy anal fistula clip (NiTi-AFC), studies the surgical method of treating anal fistula, and evaluates its clinical efficacy.

Methods

The anal fistula clip was formed in nickel-titanium alloy with a titanium content of 50.0%-51.8%. The mechanical properties and chemical properties were tested. A total of 31 patients with anal fistula were enrolled between 1 January 2020 and 1 January 2023. All patients underwent internal orifice closure surgery using NiTi-AFC, and anorectal magnetic resonance or ultrasound was performed before surgery and 6 months after surgery for diagnosis and evaluation. Fistula cure rates, length of stay, perianal pain, and Wexner incontinence scores were retrospectively compared between patients treated with NiTi-AFC and patients treated with other surgical methods.

Result

NiTi-AFC has a density of 6.44-6.50 g·cm-3, with a shape-restoring force of 63.8 N. The corrosion rate of NiTi-AFC in 0.05% hydrochloric acid solution at atmospheric pressure and 20°C is approximately 6.8 × 10-5 g·(m·h)-1. A total of 31 patients (male/female: 19/12, age: 43.7 ± 17.8 years) were included. Among them, 22.6% (7) had multiple anal fistula, 16.1% (5) had high anal fistula, and 48.3% (15) had perianal fistula Crohn's disease. In total, 12.9% (4/31) did not achieve primary healing, underwent fistula resection, and eventually recovered. A retrospective analysis showed that the fistula healing rate, length of stay, and anal pain of NiTi-AFC treatment were similar to those of other traditional surgeries, but the Wexner incontinence score was significantly lower.

Conclusion

NiTi-AFC has shape memory properties, corrosion resistance, superelastic effect, and surface cell adhesion. It is applied to internal orifice closure surgery of anal fistula, with good therapeutic effect, and can protect the anal function.