The core engineering insight is deceptively simple: increase the surface area of the needle and you amplify everything the needle does. Electrochemical anodic oxidation achieves this by placing the stainless-steel needle—typically SUS304, an alloy of iron, chromium, and nickel chosen for its biocompatibility and electrochemical stability—as the anode in an electrolyte cell. In the widely used protocol, an ethylene glycol-based solvent containing 0.5 weight percent ammonium fluoride and a small amount of deionized water serves as the electrolyte, with carbon paper acting as the cathode. As voltage is applied, metal ions released from the needle surface react with hydroxide ions to form oxides of iron, chromium, and nickel. In most anodizing conditions these oxide films are dense, but fluoride ions selectively dissolve 20 to 50 percent of the growing film, carving out a nanoporous architecture instead.

Getting the porosity right depends on a delicate balance of processing parameters. Fluoride concentrations that are too low fail to generate sufficient pores, while excessive concentrations trigger structural collapse through over-etching. Ethylene glycol, with its high viscosity, helps optimize oxide growth rates and improve structural alignment compared with aqueous electrolytes. Voltage proved equally decisive: experiments measuring surface area by both methylene blue dye adsorption and Brunauer–Emmett–Teller analysis found that 30 volts maximized the nanoporous surface area, achieving a BET value of 0.0328 square meters per gram. Above 40 volts, the needles simply broke. At the optimum, the effective surface area of a needle increased up to twentyfold compared with a conventional smooth needle, with pores ranging from 1.0 to 2.6 micrometers in diameter and oxide layer thickness growing from roughly 693 nanometers after five minutes of anodization to 4.25 micrometers after 25 minutes.

These porous surfaces serve as ideal substrates for a second modification strategy: electrodeposition of noble metal nanoparticles. By applying an external current or voltage to reduce metal ions in solution onto the porous framework, researchers can control particle size, density, and distribution with considerable precision. Silver, gold, and platinum nanoparticles deposited on anodized needles produced average particle diameters of 32.9, 57.7, and 49.3 nanometers respectively, each conferring distinct advantages. Silver’s dense, small particles deliver high conductivity and antibacterial properties; gold’s uniform distribution enhances biocompatibility and biomolecule binding, suiting drug delivery and biosensing applications; and platinum’s larger, sparser particles offer superior heat resistance and electrochemical stability for long-term stimulation environments. Together, the deposited nanoparticles can expand the effective reaction area of a needle by tens of times, transforming it from a passive stimulation tool into a functional bioelectrode.

The therapeutic consequences of this surface engineering are striking. In a rat model of inflammatory pain induced by complete Freund’s adjuvant, nanoporous needles inserted at the ST36 acupoint—located over the tibialis anterior muscle—generated significantly greater rotational torque and withdrawal resistance than conventional needles, a reflection of the enhanced needle grasp phenomenon in which tissue winds around the rotating shaft. Histological analysis confirmed the mechanical story: subcutaneous connective tissue thickness increased from 58.0 to 339.2 micrometers and muscle layer thickness from 524.7 to 942.7 micrometers after porous needle treatment. Functionally, the porous needles extended meaningful analgesia to roughly two hours, compared with only 30 to 60 minutes for conventional needles, and ten days of repeated treatment produced cumulative reductions in mechanical hypersensitivity. The authors suggest that amplified mechanical stimulation may boost local adenosine release, activate transient receptor potential channels such as TRPV1, and intensify crosstalk between subcutaneous fibroblasts and peripheral nerve endings, while observed collagen fiber realignment may further prolong antinociceptive signaling.

Perhaps most provocatively, the modified needles show promise against substance use disorders. In animal studies, porous needle acupuncture at HT7—a point on the inner wrist crease—significantly reduced cocaine-induced hyperlocomotion in rats, with the effect persisting far longer than that achieved by thicker conventional needles. Against ethanol withdrawal, nanoporous needle treatment reduced tremors more effectively than conventional acupuncture as measured by automated force-transducer monitoring, and elevated plus maze testing revealed anxiolytic effects during withdrawal. When different electrode types were compared—conventional, porous, and porous needles sensitized with silver, gold, or platinum—the silver-sensitized variant performed best, increasing open-arm exploration time by 20 percent relative to the unsensitized porous group. This hints that noble-metal-enhanced charge transfer may synergize with acupuncture-induced stimulation in brain regions governing anxiety and reward, offering a possible low-cost, surgery-free neuromodulation strategy for addiction.

The cancer data add another dimension. In a chemically induced rat model of colorectal cancer, porous needle acupuncture reduced aberrant crypt foci, an early warning sign of tumorigenesis, most markedly when treatment was delivered at HT7 rather than the SI5 acupoint on the wrist. Genetic analysis showed the porous needles reversed a greater number of cancer-related transcriptional changes than conventional needles. In late-stage disease, repeatedly treated animals bore fewer and smaller tumors and displayed lower circulating levels of carcinoembryonic antigen, a standard colorectal cancer biomarker. Immunohistochemical staining revealed reduced beta-catenin expression in treated tissues, suggesting suppression of the Wnt/beta-catenin signaling pathway, a major driver of colon cancer progression. Notably, acupoint selection mattered as much as needle type, underscoring that clinical optimization will require attention to both device engineering and anatomical targeting.

Beyond therapy, the engineered needles are emerging as serious candidates for neural interfacing. Conventional neural electrodes face an uncomfortable trade-off: larger surfaces yield better signal-to-noise ratios but inflict more tissue damage, while miniaturized electrodes are gentler but suffer high impedance. Porous needle electrodes dissolve this dilemma. Electrochemical impedance spectroscopy showed smaller semicircle diameters in Nyquist plots for porous needles, indicating lower charge transfer resistance, and local field potential signals in the 1 to 49 hertz range—associated with motor cortex activity—were captured more reliably than with conventional electrodes, while noise in the 59 to 61 hertz band was significantly reduced. Because the porous architecture interlocks with surrounding tissue, electrode stability improves over time, and the stainless-steel platform can be fabricated cheaply and reproducibly. Previous biocompatibility work in dermal and subcutaneous applications, along with evidence that nanoscale pores promote protein adsorption and cellular integration, strengthens the case for chronic implantation.

Remarkably, the same properties that make these needles good neural electrodes also make them viable electrocatalysts. In alkaline potassium hydroxide solutions, anodized porous needles exhibited lower charge transfer resistance and enhanced current density for the oxygen evolution reaction compared with conventional polished electrodes, with a Tafel slope of 67.6 millivolts per decade indicating favorable catalytic kinetics. The hydrogen evolution reaction proved more demanding, requiring noble metal coatings such as silver nanoparticles, though even then performance remains below standard catalysts, highlighting a clear optimization target in particle size and coating homogeneity. Cross-sectional electron microscopy revealed conical nanopores between 0.81 and 1.92 micrometers in diameter and 0.51 to 1.33 micrometers deep, topography that improves wettability and ion transport—the very parameters that govern water-splitting efficiency. The implication is that defective or waste acupuncture needles could be repurposed as low-cost electrochemical materials, improving economic efficiency across their lifecycle.

The review’s authors, led by Su-Il In of the Daegu Gyeongbuk Institute of Science and Technology, are candid about the field’s limitations. Most studies rest on rodent models with few human trials, and research has concentrated narrowly on pain, addiction, and cancer-related symptoms. Fabrication has likewise stagnated around a single ammonium fluoride–ethylene glycol–water electrolyte recipe, leaving the morphological consequences of alternative chemistries largely unexplored. Their prescription is systematic optimization of anodization conditions, functionalization with photothermal agents, semiconducting nanomaterials, or biosensitive coatings, and large-scale clinical validation. If those steps succeed, the two-thousand-year-old acupuncture needle may complete an extraordinary journey—from ritual instrument to precision medicine platform, bioelectronic interface, and component of sustainable energy technology.

Subject of Research: Surface engineering of acupuncture needles for biomedical and electrochemical applications

Article Title: Nanostructured acupuncture needles: recent progress in surface engineering and biomedical and electrochemical applications

Article References: Lee, J., Park, J., Park, S., Kim, H., & In, S.-I. (2025). Nanostructured acupuncture needles: recent progress in surface engineering and biomedical and electrochemical applications. Advances in Industrial and Engineering Chemistry, 1(1), Article 35. https://doi.org/10.1007/s44405-025-00037-6

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00037-6

Keywords: acupuncture needles, electrochemical anodization, nanoporous surfaces, noble metal nanoparticles, neural electrodes, local field potential, pain management, addiction treatment, colorectal cancer, oxygen evolution reaction, hydrogen evolution reaction, surface engineering

The technical premise of ICMS is deceptively simple. By passing carefully shaped pulses of electrical current through microelectrodes positioned in cortical tissue, researchers can evoke neural activity in targeted populations of neurons without requiring any natural sensory input. The timing, amplitude, frequency and spatial pattern of those pulses determine what the brain perceives. In a functioning brain-computer interface, this creates the possibility of a true two-way channel: the device decodes neural signals to infer intent, and it writes information back into the cortex through stimulation. The Tianjin University review, authored by Pengfei Hu, Chong Chen, Yunliang Zang, Xiaohong Li and Dong Ming, organizes the field around this delivery-and-parameter framework, tracing how pulse design and electrode placement jointly shape both perception and long-term circuit change.

The most direct and best-documented application is artificial touch. When electrodes stimulate the primary somatosensory cortex, human participants report localized sensations described as touch, pressure or tingling at specific points on the body, even though no peripheral nerve is involved. Early experiments established that individual electrodes reliably produce perceptible, place-specific sensations. More recent work has pushed further, using multiple electrodes and engineered spatiotemporal patterns to convey richer tactile information, including edges, curvature and even apparent motion across the skin. Human studies have shown that such patterned stimulation improves the controllability and internal structure of artificial touch, allowing users to discriminate features that single-pulse stimulation cannot convey. Yet the review is candid about the gap that remains: synthetic tactile signals still do not reproduce the complexity of natural touch, which combines thousands of mechanoreceptors firing with precisely coordinated timing.

Vision follows a parallel logic. Electrical stimulation of the primary visual cortex produces phosphenes, the perceived spots or lines of light that appear even in people who have been blind for years. Because phosphenes can be evoked across a grid of electrodes, coordinated stimulation of multiple sites can be composed into recognizable shapes and letters, much as individual pixels combine into an image. Experiments with blind participants have demonstrated simple two-dimensional visual patterns and basic object-localization tasks, offering proof of principle that cortical prostheses can deliver usable visual information. Still, the researchers note that current visual prosthesis studies remain confined to relatively simple shapes, letters and localization. Predicting how a given stimulation will be perceived, identifying which electrode combinations produce the most useful phosphenes, and maintaining stable stimulation over long implantation periods remain the field’s most stubborn engineering challenges.

One of the most consequential findings the review synthesizes is that the brain can learn. Animals trained with intracortical stimulation learn to interpret artificial patterns and use them to guide behavior, even when those patterns bear no direct resemblance to natural sensory codes. This observation suggests that the nervous system does not demand an exact mimicry of biology; it can assign meaning to an entirely synthetic neural signal through experience. The implications for future bidirectional brain-computer interfaces are substantial. Rather than painstakingly reverse-engineering natural sensory encoding, engineers may be able to design stimulation schemes that are simpler, more robust and more flexible, and trust cortical plasticity to do the interpretive work. The brain, in effect, becomes a co-designer of the interface.

The review then examines a more ambitious possibility: using ICMS not merely to create momentary sensations but to change how neural circuits function over longer periods. Repeated or precisely timed stimulation can induce plasticity-like changes in cortical networks, the same class of modifications through which the brain normally stores skills and recovers from injury. The authors discuss studies in which paired or activity-dependent stimulation altered functional connectivity between cortical regions. In one particularly striking closed-loop paradigm, spontaneous neural activity recorded from the motor cortex was used to trigger stimulation of the somatosensory cortex with a controlled delay. Because the stimulation arrived at a biologically meaningful time relative to the spontaneous activity, the temporally matched pairing strengthened intercortical coupling and was associated with improved motor recovery in a rat model of brain injury. The result points toward stimulation therapies that reshape circuits rather than simply activating them.

Despite these advances, the authors are explicit that such applications remain largely experimental. Reliable biomarkers that confirm a circuit has actually changed, reproducible stimulation parameters that work across individuals, implantation procedures that are safe over years, and therapeutic benefits that endure all require further validation before any clinical translation. The history of neuromodulation is littered with promising animal results that failed to survive the transition to human trials, and ICMS researchers are aware that plasticity induction, in particular, is exquisitely sensitive to timing, dosage and the state of the tissue being stimulated. What works in a healthy rat motor-sensory loop may behave very differently in an injured or aged human cortex.

A parallel challenge is the hardware itself. Conventional microwire and silicon electrodes are far stiffer than the soft, delicate tissue of the brain, and this mechanical mismatch has consequences. Micromotion between implant and tissue causes damage, inflammation and glial scar formation, which progressively isolate the electrode from the neurons it needs to reach and degrade signal quality over time. Flexible electrodes soften the mechanical mismatch, and the review describes the field’s migration from rigid probes toward flexible, biomimetic designs. But flexibility alone cannot eliminate the biological barrier between an artificial material and living neural tissue, which is why the researchers highlight a further step: biohybrid neural interfaces. These incorporate living biological components, including neural stem cells, neural progenitor cells and other neural cells, directly into the implanted device. The goal is twofold: improve integration with host tissue so the interface survives longer, and allow living tissue to participate in signal transmission itself. More advanced designs can even guide axon growth, creating new biological connections between neural tissue and the electronic device. In the most optimistic framing, biohybrid interfaces could extend beyond better electrodes to repairing damaged neural circuits, combining electronics, living cells and host tissue into a single functioning system.

None of this, the review stresses, makes ICMS a plug-and-play technology. Long-term performance depends on the stability of implanted electrodes, and stimulation effects vary between individuals and can drift over time within the same person. The authors therefore call for coordinated progress across electrode design, stimulation encoding, closed-loop calibration and safety evaluation, together with longer follow-up periods, cross-species validation, standardized safety assessments and reproducible behavioral and neural-network outcomes. Rather than replacing existing neuromodulation technologies, they argue, ICMS may ultimately serve as a complementary tool offering far finer control over local neural populations than surface stimulation or pharmacological approaches can achieve. Its long-term promise lies in combining several capabilities at once: delivering artificial sensory information, letting the brain learn entirely new information channels, reshaping dysfunctional circuits and integrating electronic devices more naturally with living neural tissue. As the review concludes, translating intracortical microstimulation from an experimental technique into durable brain-computer interface systems will require progress not in any single technology, but simultaneously across interface reliability, stimulation encoding, closed-loop control, safety and biohybrid integration. The work was supported by the National Key Research and Development Program of China, the Major Program of the National Natural Science Foundation of China and the National Natural Science Foundation of China.

Subject of Research: Intracortical microstimulation as a technique for evoking artificial perception and inducing plasticity in brain-computer interfaces

Article Title: Intracortical microstimulation in brain–computer interfaces: Evoking perception and plasticity

Article References: Intracortical microstimulation in brain–computer interfaces: Evoking perception and plasticity. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: intracortical microstimulation, brain-computer interfaces, sensory feedback, phosphenes, neuroplasticity, closed-loop neuromodulation, biohybrid neural interfaces, somatosensory cortex, visual prosthesis, neural electrodes, Intracortical, microstimulation