Use of nano-enabled approaches to advance acupuncture therapy for disease management

Abstract

Acupuncture is an ancient form of therapy, which has long been part of traditional Chinese medicine (TCM); however, its use has spread globally, to the point where it is currently practiced worldwide. Although metal needles continue to be used most commonly, through multidisciplinary research, novel technologies, including nanotechnology, have allowed acupuncture to evolve to the point of achieving greater efficiency and more sophisticated functions in clinical practice. We summarized recent advancements in the literature using nano-enabled strategies to create novel needles that enhance and expand their therapeutic effects and found that nanotechnology may help provide new evidence to verify acupuncture theory, improve the features of acupuncture needles and their clinical effects by combining with drug delivery, and even enable new therapeutic methods when combined with acupuncture needles. The use of nano-technology with acupuncture delivery looks very promising for potential clinical applications. We also envisage that with nanotechnology, innovations in acupuncture needles could generate a multi-functional toolbox for use in both diagnostic and therapeutic medicine. Such new types of acupuncture needles could be used at acupoints and data collected to guide the planning of clinical trials may be more consistent with acupuncture theory and traditional clinical applications of this therapeutic modality.

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1. Introduction of modern acupuncture

Acupuncture is an ancient form of therapy, which has long been part of traditional Chinese medicine (TCM), with its history in China spanning more than 3000 years. More recently, however, its use has spread globally, to the point where it is currently practiced worldwide. It is characterized by the insertion of fine needles through a patient's skin at designated acupuncture points (acupoints) following basic principles of classic TCM theory. Although achieving pain relief is the most common reason for acupuncture to be used, numerous other health conditions have been shown to improve with this therapy.¹ In 1979, the World Health Organization (WHO) listed 43 diseases and conditions that can be treated with acupuncture, a number that increased to 63 in 1996. Such conditions include migraine headaches, facial nerve palsy, ischemic stroke, knee osteoarthritis, nausea and vomiting, dysmenorrhea, obesity, anxiety, depression, and insomnia.²

With over three millennia of clinical use, acupuncture's accuracy and effectiveness in clinical practice have improved. The meridian and acupoint theories of TCM attribute acupuncture's effectiveness to body physiology being modulated when specific acupoints are stimulated, with modern science increasingly providing evidence demonstrating the activation of peripheral nerves, transmission of sensory information from the spinal cord to brain, and activation of peripheral autonomic pathways, among other physiological changes.³ In a recent study, the researchers provided a neuroanatomical basis for the selectivity and specificity of acupoints in driving specific autonomic pathways based on data generation in animals.⁴

Along with mechanistic research into its underlying physiology and its increasingly wide clinical use, clinical research on acupuncture has also grown and increasingly become standard. Since 1975, more than 10 000 randomized controlled trials on acupuncture have been published, with these studies having been conducted all over the world. In a recent systematic review of acupuncture, of 77 diseases investigated, acupuncture was found to have a moderate or large effect, with moderate- or high-certainty evidence, in eight diseases or conditions: improved functional communication in patients with post-stroke aphasia; relief of neck and shoulder pain; relief of myofascial pain; relief of fibromyalgia-related pain; relief of non-specific lower back pain; increased lactation success rate within 24 hours of delivery; reduced severity of vascular dementia symptoms; and improved allergic rhinitis nasal symptoms.⁵

Based on the published literature in 2013, the WHO reported that 103 of its 194 member countries were using acupuncture as a treatment, that 29 had enacted laws to regulate TCM, and that 18 had included acupuncture in their medical insurance systems. Thus, acupuncture, the most popular alternative medical therapy, plays an important role in healthcare systems worldwide.²

In China, acupuncture is a longstanding, legal medical practice that is used extensively by doctors with certifications in Chinese Medicine acupuncture. The number of acupuncture practitioners has exploded in recent years, such that there were an estimated 18 404 doctors certified in acupuncture in Mainland China in 2018.^2,6 Acupuncture was introduced to the United States in the early 19th century, but it was not until the late 1970s that its practice has gained popularity in the country. The National Institutes of Health (NIH) approved acupuncture as a treatment for patients in 1991, while the Food and Drug Administration (FDA) approved acupuncture needles as a medical device in 1996. Moreover, 47 US states and Washington, D.C. have passed acupuncture laws, ensuring the legal use and development of acupuncture since 2014. There are currently approximately 17 000 acupuncturists in the United States, most having been trained as Oriental Medical Doctors, Doctors of Oriental Medicine, or Licensed Acupuncturists. The American Academy of Medical Acupuncture (AAMA) is the professional association that oversees a national board certification examination for physician acupuncturists, and physicians can only practice acupuncture within the scope of their medical license.^2,7

In Europe, acupuncture has had a similar developmental history. It first became popular in France, then spread to neighboring Western European countries and, ultimately, the whole of Europe. In 2006, the United Kingdom had more than 3000 licensed acupuncturists, according to the data from the British Acupuncture Council. In Australia, a national registration standard for TCM was implemented in 2012, making Australia the first Western country to legislate it. In Japan and South Korea, acupuncture is commonly practiced as routine treatment, and traditional medicine plays much the same important role as modern medicine. In summary, acupuncture has entered a new era worldwide.

As mentioned above, acupuncture relies on the appropriate insertion and manipulation of needles of various gauges and lengths into the skin at specific acupoints. In ancient China, the very first needles were constructed from stones. Over time, acupuncture needles have evolved from their stone roots to be constructed from bamboo, ceramic bone (a ceramic composed of bone ash, feldspathic material, and kaolin), plant thorns, and later, metals, as depicted in Fig. 1(a) and (b). As acupuncture technology has spread globally, acupuncture treatments have evolved into several distinct styles, which include Japanese acupuncture, Korean hand acupuncture, Leamington Five-Element acupuncture, and French energetic acupuncture, though the traditional Chinese form continues to predominate. There are also specialized approaches, such as hand and foot acupuncture, auricular acupuncture, and scalp acupuncture.⁸ With special materials like needles plated with gold, fire needle acupuncture has also become widely used in clinical practice. These specialized techniques and the theories behind them have been advanced by generations of acupuncturists.

Fig. 1 Different types of acupuncture needles: (a) ancient needles made of special stones, (b) filiform needles, (c) electroacupuncture needles and (d) red-laser needles. Reproduced with permission from ref. 9 Copyright 2019, Mary Ann Liebert, Inc.

Although metal needles continue to be used most commonly, both electricity and lasers (as shown in Fig. 1(c) and (d)) are now used to replace handheld needles in certain circumstances. Electric acupuncture improves therapeutic outcomes and shortens treatment duration by enhancing the flow of electric currents between needles. Laser acupuncture, however, is well-suited for specific patient demographics, including geriatric and pediatric populations, as well as for individuals with needle phobias, due to its non-invasive nature that eliminates the risk of infection and bleeding complications associated with skin penetration. Although their use remains controversial, both electrical and laser acupuncture therapies have been shown to achieve similar or even better effects than traditional manual acupuncture.^2,8,9 This indicates that, through multidisciplinary research, novel technologies have allowed acupuncture to evolve to the point of achieving greater efficiency and more sophisticated functions in clinical practice.

Nanotechnology is the engineering of materials that are from 1 to 100 nm in at least one dimension for use in technological or scientific applications. The brilliance of nanotechnology lies in the miniscule size of the nanoparticles. Reducing the size of a structure to a nanoscale results in completely different properties, like unique performances in fields like chemistry, photology, electricity, and magnetism. This application has laid an important foundation for innovations in acupuncture needles.¹⁰ From this perspective, we will summarize recent advancements in the literature using nano-enabled strategies to create novel needles that enhance and expand their therapeutic effects. While promising, this field remains in a juvenile stage, which opens up numerous possibilities. Thus, the authors also provide personal perspectives on how to enhance the synergistic functions of nanotechnology and acupuncture therapeutics and what is required to reveal the mechanisms behind this enhanced effectiveness.

2. Recent advances in acupuncture through nano-technology

Despite the long history and widespread use of acupuncture, challenges remain in achieving any consensus regarding its use. Some classic TCM theories – like meridian theory – have a well-established place guiding the clinical practice of acupuncture. However, the anatomy of meridians remains inadequately understood.¹⁰

Nanotechnology enables novel nanochips/nanoneedles to generate new evidence to verify such theories and may provide new insights into the mechanisms behind acupuncture. Acupuncture needles combined with nanotechnology could be employed as a multifunctional toolbox and used for such purposes as specialized drug delivery, adopting the minimally-invasive and positionally-precise characteristics of acupuncture to enhance the efficiency and reproducibility of drug delivery. Nanotechnology could also enable different, new types of nanoneedles to deliver novel therapies, in vivo and in real time.

2.1 Nanotechnology may help provide new evidence to verify acupuncture theory

As already discussed, although acupuncture has achieved promising clinical effects over thousands of years, it still lacks detailed, empirically-based evidence to explain the mechanisms underlying its effectiveness, which understandably creates doubt in the minds of those who are unsure and fodder for denial among those who already are critical. Research on the mechanisms and underlying physio-biology of acupuncture remains popular throughout the TCM field. Nanotechnology could help to generate new evidence to verify acupuncture theory.

The meridian, a concept lacking a known anatomical basis, has become the subject of scientific inquiry, propelled by advancements in technology. The discovery of the primo vascular system (PVS) by Bong-Han Kim in the 1960s has shed light on an anatomical structure believed to correspond to acupoints and meridians.^11,12 Recent endeavors, particularly leveraging nanotechnology, have revitalized interest in PVS research. The Nano Primo Research Centre,^11,13 established at Seoul National University, has spearheaded groundbreaking experiments utilizing Mercox¹⁴ and fluorescent nanoparticles¹⁵ to map meridian pathways, presenting compelling visualization techniques.

The manual manipulation of acupuncture needles remains the most frequently practiced clinical procedure, and observational results indicate that employing thicker needles and/or deeper insertion may produce increased stimuli intensity, potentially enhancing therapeutic effects. However, due to the discomfort caused by inserting larger-diameter acupuncture needles, this effect remained largely theoretical until nanotechnology permitted the production of special needles.

S.-L. In et al.¹⁶ hypothesized that increasing needle surface area with no significant variation in needle diameter may lead to increased interactions in the surrounding tissue, leading to enhanced acupuncture stimuli. Motivated by this, they fabricated a new class of acupuncture needles that possessed a novel surface morphology, creating the so-called porous acupuncture needles (PANs), with hierarchical micro/nano-scale conical pores upon the surface of conventional stainless steel acupuncture needles. These fabricated PANs have approximately 20 times the surface area of conventional needles. How well these high-surface-area PANs perform has been evaluated by monitoring electrophysiological and behavioral responses during the in vivo stimulation of Shenmen (HT7) points in Wistar rats, revealing PANs to be more effective at controlling electrophysiological and tremor behavioral responses in ethanol-withdrawn rats than conventional acupuncture needles. Comparative analysis of cocaine-induced locomotor activity using PANs and thick acupuncture needles has also demonstrated that PANs can better attenuate hyper-locomotor activity with significantly less pain sensation. Such work offers a unique pathway for achieving a less discomfortable, yet enhanced therapeutic effect, verifying the acupuncture theory that inserting thicker needles could yield stronger stimuli and better clinical effects (shown in Fig. 2).

Fig. 2 Surface images of porous acupuncture needles (PANs). (a) Surface image of a conventional stainless steel needle. (b) Surface image of a porous anodized needle. (c) Enlarged image of (b). (d) Cross-sectional image of the porous anodized needle. Insets of (a and b) show needle tips. (e) Compared to the control diet rats group (normal as represented by 100%), the alcohol treatment group (alcohol) showed greatly increased tremor activity. The PAN group with acupuncture stimulation at HT7 significantly attenuated alcohol-induced tremor activity compared to the alcohol group. *p < 0.05 stands for control and alcohol groups, #p < 0.05 stands for alcohol and PAN groups. (f) Comparison of PANs and thick (1.6 mm diameter) acupuncture needles in attenuation of cocaine induced hyper-locomotion by the HT-7 acupuncture test. (g)–(i) The movement of an individual rat in a square open field black acrylic box was recorded by a video camera. Blue square indicates the start position of the rat. Reproduced with permission from ref. 16. Copyright 2016, Nature Publishing group.

2.2 Nanotechnology improves acupuncture needles and their clinical effects

One of the most important advantages of nanomedicine is enhanced drug delivery. Nanoparticles have been designed to treat many diseases, but the greatest focus has been on cancer. Anticancer drugs are typically small organic molecules, but there are ongoing efforts to increase their delivery and, hence, therapeutic efficacy through enhanced nano-delivery systems. Besides cancer, nanomedicines are also being developed for diagnosing and treating infectious, neurodegenerative, and cardiovascular diseases. Thus, the number and impact of macromolecular biopharmaceuticals (i.e., polypeptides and polynucleotides) are increasing enormously. However, the size and complexity of nano-compounds impose significant challenges to their safe and effective use. Furthermore, this class of compounds suffer notoriously from limited permeability across biological barriers, such as cellular membranes or epithelial tissues like those of the gastrointestinal (GI) tract, skin, and lungs.¹⁷ The delivery of macromolecular biopharmaceuticals is preferentially via noninvasive (“needle free”) approaches. Meanwhile, for lesion-positioning therapy, which has the advantage of being able to precisely localize drugs in and/or around a lesion of interest and enrich their effect, nanomedicines must overcome physical barriers, especially within certain tissues or organs – like intervertebral discs and cartilage, both largely avascular tissues – using specialized needles. Therefore, designing a drug-delivery system that can reliably penetrate the physical barriers of various tissues and organs and achieve accurate localization within lesions is a major problem in urgent need of a solution.

Microneedles, which are sharp and sturdy microstructures designed for skin penetration, offer expanded possibilities for the delivery of various active pharmaceutical ingredients (APIs) such as vaccines and therapeutic agents. In comparison to hypodermic needles, microneedle arrays present advantages in terms of ease of use and painless applications for blood collection or drug delivery.¹⁸ Extensive research has been conducted on the design, fabrication and application of microneedle systems. For instance, Zhang et al. developed nano-plum-blossom needles that combine microneedles with plum-blossom needle technology, delivering diclofenac diethylamine emulsion and providing instant pain relief and alleviation of symptoms associated with acute gouty arthritis.^19,20 Another example is that Gu et al. designed a core–shell structured microneedle array patch with programmed functions (PF-MNs) to dynamically modulate the wound immune microenvironment according to the varied healing phases.²¹

While both acupuncture needles and microneedles involve skin penetration, they are designed based on different purposes that are used in traditional medicine and modern medical technologies, respectively. The major differences include: (i) materials and shape: acupuncture needles are typically made of metals such as stainless steel and are rigid to penetrate deeper tissues. Microneedles, however, can be made from polymers, silicon, or sometimes metals. They are designed to be flexible and minimally invasive, suitable for skin applications. While acupuncture needles have a uniform thickness along their length, microneedles often have a tapered or pyramid-shaped structure with a sharp tip; (ii) length and thickness: acupuncture needles are typically longer, ranging from a few millimeters to several centimeters, and thicker. Microneedles, on the other hand, are usually shorter in length, ranging from hundreds of micrometers to a few millimeters. Microneedles are specifically designed for skin penetration and drug delivery at or near the skin's surface, while acupuncture needles could reach deep tissue; and (iii) purposes: acupuncture needles are used in traditional Chinese medicine for therapeutic purposes, such as balancing the body's energy flow (Qi) and treating various health conditions. They are inserted into specific acupuncture points along the meridians of the body. Microneedles are primarily designed for drug delivery, vaccination, and cosmetic applications.

Normal acupuncture needles are made of metals and, as such, are physically rigid. They can also be constructed to be hundreds of millimeters long, lengths that can easily reach tissues deep within the human body and penetrate tough physical barriers when inserted through the skin. However, administering targeted treatment with normal acupuncture needles made of metals is difficult, due to their single-chemical composition and lack of chemical groups that can be used for chemical modification. Therefore, Feng Lin etc.²² designed normal acupuncture needles with a screw-thread structure at the tip (ST needles) and hydrogel to function as an adhesive to permit the sustained-release of drugs. Through minimally-invasive yet precise positioning of ST needles within lesions, the dry-to-wet conversion of hydrogel when in contact with body fluids and inflammation, and rotation of the ST needles as they penetrate the lesion, the hydrogel can be precisely positioned within, for example, subchondral bone, thereby permitting the continuous release of the therapeutic drug (as shown in Fig. 3). Investigators have performed in vitro experiments confirming that ST needles penetrate the physical barrier of cartilage to enter subchondral bone. Simultaneously, the hydrogel-transfer efficiency of the ST needle is significantly higher than that of the standard normal acupuncture needle, due to the drug-protective effect of the screw-thread structure.

Fig. 3 Schematic diagram of lesion positioning therapy by special acupuncture needles (ST-needles). (a) Chinese normal acupuncture needles (CA-needles) with a screw-thread structure at the tip (ST-needles) were designed to penetrate the subchondral bone and transport the hydrogel. (b) The pores left by the ST-needles promoted mesenchymal stem cell (MSC) migration, and the hydrogel continuously released baicalein (BAI) to regulate cytokine secretion. (c) Schematic diagram of the hydrogel-modified ST-needle. (d) 360° display of the CA-needle tip with the hydrogel. (e) 360° display of the ST-needle tip with the hydrogel. Reproduced with permission from ref. 22. Copyright 2022, Wiley-VCH GmbH, Weinheim.

The efficacy of lesion-positioning therapy with ST needles has been verified in an osteoarthritis rat model, in which precise positioning was achieved in subchondral bone, inhibiting the secretion of abnormal cytokines, promoting the migration of mesenchymal stem cells to cartilage defects, and repairing cartilage. Overall, the ST needle and hydrogel system can greatly expand the clinical application of precision-positioning therapy, giving strong evidence that nanotechnology could improve the features of acupuncture needles and their effects.

2.3 Nanotechnology enables new therapeutic methods when combined with acupuncture based therapy

Pre-clinical efforts focused on integrating nanotechnology into cancer diagnosis and treatment have been substantial, with the field continuing to mature while waiting for its full impact to be realized.²³ In addition to single- or combined-modality therapy with surgery, chemotherapy, and/or radiotherapy, all of which are commonly used clinically, a number of promising therapeutic strategies have recently been put forward, including immunotherapy and gene therapy, photothermal therapy (PTT), photo-dynamic therapy (PDT), and other therapeutic methods. However, these techniques usually rely on chemical and genetic drugs or exotic nanomaterials to actualize treatment, making them quite difficult or debatable for practical clinical applications in the near future, due to uncertainties relating to potential biotoxicity and biohazards and related genetic and ethical issues.²⁴ Such issues have arisen with other non-neoplastic diseases as well. Therefore, there is an urgent need for simple, natural, efficient, and less-expensive treatments to combat disease.

Acupuncture is well known for being simple, more natural, and convenient to administer, while also being inexpensive and, for some diseases, documented as effective; and nanotechnology enables new therapeutic methods like hydrogen (H₂) therapy when delivered through acupuncture. Through the combined use of traditional Chinese acupuncture, iron needle electrodes, and in vivo electrochemistry, Guohua Qi et al.²⁴ achieved in vivo H₂ generation in tumors in a controlled fashion and utilized this to effectively treat tumors for the first time. Cathode acupuncture electrodes, administering an applied voltage of ∼3 V (with minimal damage to living tissues), effectively generate an electrochemical reaction within the acidic environment of a tumor, generating sufficient H₂ locally to cause cancer cells to burst and die. With puncture positioning, the acidic tumor microenvironment, and gas diffusion effect, H₂ generation electrochemotherapy (H₂-ECT) enables precise and large-scale tumor therapy, as already demonstrated through the in vivo treatment of mice with gliomas and breast cancer. From this research, it is apparent that, despite the theoretical potential of H₂ therapy to cure cancer, the current lack of effective methods to control the production and release of enough H₂ in the body has resulted in cancer cures from H₂ therapy to be rarely reported. Combining the use of Chinese acupuncture iron needle electrodes and in vivo electrochemistry, natural and conceptually new in vivo H₂ generation electrochemotherapy of tumors has come into reality (as shown in Fig. 4). Although this technique is not strictly nanotechnology, it nonetheless suggests the potential to treat cancers with novel methods that combine nano-enabled approaches and Chinese acupuncture needles.

Fig. 4 Schematic diagram of a new way of treating cancer by combining acupuncture needles with iron needle electrodes and in vivo electrochemistry. (a) Schematic diagram of green H₂-ETC therapy in vivo. (b) Schematic EC processes of two acupuncture Fe electrode systems showing anodic Fe dissolution and cathodic H₂ production. (c) The microscopic imaging of the acupuncture anode electrode after the H₂-ETC treatment at various voltages for 10 min. The red circles indicate the corrosion location of the electrode. (d) Schematic diagram of C6 tumor xenograft establishment, black and green H₂-ETC procedures, and therapeutic outcome in mice (n = 3). (e) and (f) Typical photographs of the tumor-bearing mice and tumor lumps, and their control groups, before and after 15 days of first treatment under different conditions (black, NS = needle stimulation + 0 V, NS + 1.2 V, NS + 2.1 V, NS + 3.0 V, 10 min twice a day for the first 3 days and observed for over 12 days). The red circle indicates the eliminated tumor in this case. Scale bar: 1.5 cm. Reproduced with permission from ref. 24. Copyright 2020, Oxford University Press.

Another example involves an acupoint nanocomposite hydrogel, simulating acupuncture and delivering triptolide (TP) for treating rheumatoid arthritis (RA). Given the toxicity concerns of long-term analgesic and anti-inflammatory drug use in RA patients, acupuncture's analgesic benefits with fewer side-effects are advantageous. Ren²⁵et al. innovatively developed an acupoint nanocomposite hydrogel, combining TP-human serum albumin nanoparticles (TP@HSA NPs) and 2-chloro-N(6)-cyclopentyl adenosine for RA treatment. This approach exhibits prolonged analgesic effects, improvement in joint inflammation, and alleviation of side effects associated with TP. This groundbreaking attempt at combining acupuncture and drug delivery presents a novel therapeutic method for RA and potentially other diseases.

3. Perspective on the future of nano-enabled approaches with improved acupuncture needles

Nano-enabled approaches advance acupuncture therapy for the management of diseases like colorectal cancer,²⁶ osteoarthritis, and glioma and breast cancer.²⁴ Since all these studies were conducted in vivo and yielded positive results, despite being mostly restricted to animal models, the use of nano-technology with acupuncture delivery looks very promising for potential clinical applications. Whether new models of acupuncture needles and nano-based methodology will also be both feasible and effective in clinical practice will be a major emphasis of future research. Through our review of the literature, however, research on the combination of nanotechnology and Chinese acupuncture remains at a preliminary stage. The possibilities for application nonetheless appear vast.

First, employing fluorescent magnetic nanoparticles may provide new insights into acupuncture meridians. Both meridians and acupoints are dynamic, in that they both receive stimuli and regulate body functions. Nanotechnology-based molecular imaging, combined with the insertion of acupuncture needles, could be a powerful tool to provide more reliable and accurate data on dynamic changes in meridians and acupoints. Under these circumstances, scientific support for the underlying mechanisms behind acupuncture's effectiveness and the theoretical basis for meridian theory may arise.

Second, with nanotechnology, innovations in acupuncture needles could generate a multi-functional toolbox for use in both diagnostic and therapeutic medicine. The range of nano-systems that have been proposed is very extensive, including the use of very different materials (natural or synthetic) ranging from polymers or lipids to systems derived from microorganisms.²⁷ In studies that have been conducted so far, acupuncture needles are generally treated more like the medium holding nano-material than the therapeutic element itself. However, as per TCM theory, when acupuncturists treat patients with acupuncture needles, they choose acupoints based upon meridians and acupoints theory and upon pattern identification rules. Thus, acupuncture is considered multifunctional therapy in itself, dynamically altering acupoints on its own. Besides nanodrug delivery, the surface of acupuncture needles could also be filled with nano-particulate photothermal, magnetothermal, and photodynamic agents (as depicted in Fig. 5).

Fig. 5 Schematic models of different types of nano-acupuncture needles. Traditional acupuncture needles can be loaded with nano-drugs, fluorescent nanoparticles, magnetic nanoparticles and infrared radiation.

Third, recently developed nano-acupuncture needles have been inserted directly into lumbar spinal dorsal horn neurons, subchondral bone, and tumors in animal experiments, which is not the usual acupuncture practice, since such needle insertion is not into acupoints. In future research, such new types of acupuncture needles could be used at acupoints and data collected to guide the planning of clinical trials may be more consistent with acupuncture theory and traditional clinical applications of this therapeutic modality. This approach has the potential to broaden the scope of acupuncture applications, extending its utility beyond pain management to address conditions such as stroke, obesity, allergic rhinitis, and beyond.

Utilizing nano-enabled approaches to advance acupuncture therapy for disease management may result in a series of novel acupuncture needles. However, before these new needles are applied in clinical practice, in addition to clinical trials to confirm their effectiveness in treating disease, basic research is necessary to reveal the mechanisms behind how they work. In general, taking a drug-delivery needle as an example, the following components and procedures are required. First, we need to prepare each new type of nano-acupuncture needle and provide sufficient description of its characteristics – like size, structure, and chemical composition – as well as of the synthesis procedure. Second, the needle's drug-release performance and drug retention time in tissue should be tested penetrating different anatomical barriers, like skin, intestinal or lung mucosa, bone, and cartilage in in vitro experiments. Third, the ability of needles to transport nano-drugs like nanoparticles, liposomes, and hydrogels should be determined and, when necessary, tested for any cytotoxicity caused by the injected material. The fourth step, which is the most important, will be to evaluate the therapeutic effectiveness and cellular and molecular mechanisms of nano-acupuncture treatment. In this stage, if we focus on one specific disease, a standardized animal model should be chosen. Since we are observing the effectiveness of nano-acupuncture needles, an appropriate control condition should be selected, whether that is a traditional acupuncture needle, a sham needle, or some other control condition.

Acupoints can be chosen by experts, based upon either their experience treating the specific disease or by following established clinical guidelines for that disease, while considering the traditional theory that stimulating acupoints causes both a local and systemic response. Stimulation frequency, time, and intensity during acupuncture can also influence the effects of treatment, and so the procedures followed when performing acupuncture must be reported. Electroacupuncture is more stable, in that it results in more continuous stimulation, relative to acupuncture, as currently used worldwide, in vivo, in both animal models and clinically. The evaluation index should be multidimensional – from macro to micro – and include behavioral data like tremor degree, blood and body liquid testing (biochemical assays), histological analysis, and immunofluorescence labeling. Medical tools – like multi-omics, sequencing, and high throughput screening – can also be chosen to discern the molecular mechanisms behind such treatment. This is the research work our research team just finished, as shown in Fig. 6.²⁸

Fig. 6 Schematic diagram of effective treatment of knee osteoarthritis using a nano-enabled drug acupuncture (nd-Acu) technology in mice. (a) Schematic of nd-Acu design. (b) Images of dye release under UV lighting (365 nm), which show the ability of nd-Acu to load and release the drug. (c) FITC release curves. Left: fluorescence intensity, Ex: 495 nm, Em: 525 nm. FITC release from nd-Acu needles (green) and pristine needles (gray) in 0.01 mol L⁻¹ PBS at room temperature (n = 2). Snapshot of fluorescence image of FITC release at 5 min under UV (right, 365 nm). (d) Schematic illustration of electroacupuncture treatment using lidocaine-laden nd-Acu in MIA-induced KOA mice. (e) At the conclusion stage of the efficacy study, IL-1β, IL-6, and TNF-α levels in knee articular cavity fluid were determined by ELISA (n = 6). (f) Normalized levels of HMGB1 and TLR4 mRNA in knee articular cavity fluid in different treatment groups (n = 5). (g) Possible mechanism finding of lidocaine-laden nd-Acu treated KOA mice by WB and proteomics assay. Reproduced with permission from ref. 28. Copyright 2023, Wiley-VCH GmbH, Weinheim.

In our research, we developed a nano-enabled drug delivery acupuncture technology (nd-Acu) based on traditional acupuncture needles, with the stainless-steel surface designed for delivering various payload molecules. The nd-Acu platform involves an electrochemical procedure to attach methyl salicylate-modified cyclodextrin, enabling the encapsulation of single or multiple payload molecules via an inclusion complexation process. Initial studies on drug loading and release profiles were conducted using fluorescent dyes both abiotically and at the intact animal level. Compared to pristine needles without cyclodextrin modification, nd-Acu demonstrated more efficient dye loading and time-dependent release. A proof-of-principle efficacy study utilized our platform to load a local anesthetic, lidocaine, for treating knee osteoarthritis (KOA) in mice. Lidocaine-laden nd-Acu effectively alleviated pain, reduced inflammation, and slowed down KOA development, as demonstrated biochemically and histologically. Mechanistic investigations using hypothesis-driven and proteomic approaches revealed in vivo modulation of the HMGB1/TLR4 signaling pathway as a key contributor to the therapeutic outcome, with preliminary evidence suggesting the involvement of mitochondria and small GTPase, such as cdc42, during the treatment with lidocaine nd-Acu.

While the combination of nanotechnology and acupuncture technology holds great potential, significant challenges still persist. The first challenge relates to nano-safety. Despite the low risk of serious adverse events associated with acupuncture,²⁹ there is limited research on the biosafety of combining acupuncture and nanotechnology, especially involving nanoparticles and hydrogels. Comprehensive biosafety assessments, encompassing skin irritation tests and blood and organ safety tests, are necessary.

The second challenge revolves around the methodology of combining nanotechnology and acupuncture. Nanomaterials, owing to their small size and large specific surface area, demand technologies that can easily attach and release drugs on the needle within tissues, synchronizing the drug's effects with acupuncture treatment. Commonly used techniques include the electrochemical procedure and laser engraving. Evaluation of biocompatibility, including tissue compatibility, blood compatibility, inflammatory compatibility and mechanical characteristics, is needed. From a tech-transfer perspective, it would be advantageous to prioritize the use of FDA-approved drugs or drug combinations in designing a drug delivery acupuncture platform.

The third challenge is about the methodology of mechanistic studies. The already complex physiological process of acupuncture becomes even more intricate when combined with a drug delivery platform. Hypothesis-driven approaches to investigate the working mechanism of nano-enabled drug acupuncture could be useful, especially when the drug or acupuncture treatment of the disease is well researched. However, the use of multi-omics, sequencing, and high throughput screening could also be highly advantageous and informative, given these non-biased assays can unveil potential and non-obvious mechanisms at the intact organism level.

4. Conclusion

All the effort that is being expended to produce novel nano-enabled techniques and tools combined with acupuncture is being directed towards developing more natural, efficient, and precise therapies. Traditional Chinese Medicine (TCM) is regarded as more natural, convenient, efficient, and less expensive than most modern medicine, and traditional acupuncture only using needles is more popular than herbal therapy because of its proven effectiveness and reduced side effects.

In China, traditional Chinese medicine accounts for a sizeable proportion of all healthcare and its share of the healthcare market continues to grow, with its annual revenue reaching 691.9 billion yuan in 2021, according to national pharmaceutical industry statistics. Such common use contrasts sharply with its very sparse use in the United States and other Western countries, where TCM remains on the fringe of healthcare, largely due to inadequate public awareness, much less acceptance by Western medicine practitioners, and the relative lack of level I research documenting its effectiveness published in high-profile, peer-reviewed, Western scientific/medical journals. This leads to the question of how acupuncture can make inroads into accepted Western medical practice and become more popular and accessible worldwide in the future. We believe that the incorporation of nanotechnology into acupuncture practices will both advance everyone's understanding of how and why acupuncture works, from a physiological perspective, and greatly expand the range of its clinical applications.

Author contributions

W. X. contributed to the project conceptualization of the work and the manuscript writing and revision. Y. X. contributed to the discussion of the work. H. M. contributed to the project conceptualization. P. W. and Q. L. contributed to the project conceptualization and writing and revising the manuscript and supervised the project. All authors have given approval to the final version of the manuscript.

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgements

This work was supported by the National Key Research and Development Program of China (2022YFA1207300), the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB36000000) and National Natural Science Foundation of China (32271452).

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