Fe3O4 Nanoparticle-Enabled Zhimu-Huangbai Therapy for Type II Diabetes: A Self-Assembly Approach

INTRODUCTION
The management of Type II Diabetes Mellitus (T2DM), a chronic metabolic disorder characterized by insulin resistance and pancreatic β-cell dysfunction, has undergone a significant evolution over the past century [1-3]. While the discovery of insulin in the 1920s was a landmark achievement, it primarily addressed the absolute deficiency seen in Type I diabetes [4]. The subsequent development of oral hypoglycemics, from sulfonylureas to modern incretin-based therapies, has provided critical tools for glycemic control in T2DM. Despite these advances, the global prevalence of T2DM continues to rise dramatically, underscoring the limitations of current pharmacological strategies which often focus on single targets and can be accompanied by adverse effects, diminished efficacy over time, and poor patient compliance [5, 6]. This persistent clinical challenge has driven a compelling resurgence of interest in traditional medicine systems, which offer a holistic, multi-target therapeutic philosophy. Among these, Zhimu-Huangbai, a classic herb pair from Traditional Chinese Medicine (TCM), has been historically and pharmacologically documented for its “clearing heat and nourishing yin” properties, demonstrating promising anti-hyperglycemic, anti-inflammatory, and β-cell protective effects in modern preclinical studies. However, the clinical translation of such phytotherapeutic formulations is frequently hampered by poor bioavailability, inconsistent pharmacokinetics, and a lack of precise delivery mechanisms. Consequently, the development of advanced nanoplatforms to potentiate the efficacy and overcome the delivery limitations of proven botanical agents like Zhimu-Huangbai represents a compelling frontier at the intersection of materials science and translational medicine, aiming to bridge historical empirical wisdom with contemporary therapeutic precision [7, 8].
Recent advances in nanomedicine have opened promising avenues for the targeted management of Type II Diabetes Mellitus (T2DM), moving beyond conventional drug formulations. A diverse array of nanoparticles, including polymeric micelles, liposomes, and inorganic nanostructures, have been engineered to enhance the bioavailability, stability, and pharmacokinetics of antidiabetic agents (Fig. 1) [9]. These nano-carriers function by facilitating improved solubilization of hydrophobic phytochemicals, protecting therapeutic payloads from premature degradation, and enabling passive or active targeting to specific tissues, such as the liver or pancreas, through enhanced permeability and retention (EPR) effects or surface ligand conjugation [10-15]. Notably, stimuli-responsive “smart” nanoparticles, designed to release their cargo in response to specific pathological microenvironments like lowered pH or elevated glucose levels (glucose-responsive systems), represent a significant leap toward autonomous, feedback-controlled therapy. This strategic application of nanotechnology aims to maximize therapeutic efficacy while minimizing off-target effects, thereby refining the pharmacological profile of both synthetic and natural antidiabetic compounds [15, 16].
Despite this considerable promise, several intrinsic limitations of current nanotherapeutic platforms impede their clinical translation and optimal performance [17]. Many organic nanocarriers, such as liposomes and polymeric nanoparticles, often suffer from relatively low drug-loading capacities, structural instability upon dilution, and potential batch-to-batch variability [18-20]. Furthermore, the complexity of precisely engineering stimuli-responsive behaviors particularly the sensitivity and specificity required for reliable activation in the dynamic in vivo milieu remains a formidable materials challenge [21]. A critical, yet frequently overlooked, limitation is the lack of intrinsic functionality in many carrier systems; they often act merely as passive vectors without contributing synergistic therapeutic or diagnostic (theranostic) benefits [22]. Additionally, the synthesis of multifunctional nanoplatforms typically involves multi-step, labor-intensive procedures with poor atom economy, raising concerns about scalability, cost, and environmental impact factors that are increasingly scrutinized in green chemistry principles. These collective shortcomings underscore the need for the rational design of simpler, more robust, and multifunctional nanocarriers that integrate efficient delivery with additional therapeutic modalities [23, 24].
To address these challenges, this study aims to develop and evaluate a novel, magnetite (Fe₃O₄) nanoparticle-enabled self-assembly system for the co-delivery of the Zhimu-Huangbai phytotherapeutic complex, investigating its synergistic potential for multi-targeted therapy in a T2DM model.

MATERIALS AND METHODS
Materials, Reagents and Instruments
All chemicals were of analytical grade or higher and used without further purification unless explicitly stated. Ferric chloride hexahydrate (FeCl₃·6H₂O, 98%), ferrous chloride tetrahydrate (FeCl₂·4H₂O, 99%), and ammonium hydroxide solution (NH₄OH, 28–30% NH₃ in H₂O) were sourced from Sigma-Aldrich (St. Louis, MO, USA) for the synthesis of magnetite (Fe₃O₄) nanoparticles. The crude herbal materials, namely dried rhizomes of Anemarrhena asphodeloides Bunge (Zhimu) and bark of Phellodendron chinense Schneid. (Huangbai), were procured from a certified herbal supplier (Tongrentang Group, Beijing, China) and authenticated by a trained botanist. Voucher specimens (ZHM-2023-0415 and HBC-2023-0417) are retained in our laboratory. High-performance liquid chromatography (HPLC) grade solvents, including methanol, acetonitrile, and acetic acid, for extraction and analysis were obtained from Merck KGaA (Darmstadt, Germany). Ultrapure deionized water (resistivity ≥ 18.2 MΩ·cm) was generated in-house using a Milli-Q® Integral water purification system (Merck Millipore). All cell culture reagents, including Dulbecco’s Modified Eagle Medium (DMEM) and fetal bovine serum (FBS), were purchased from Gibco (Thermo Fisher Scientific, Waltham, MA, USA). Morphological analysis of the nanoparticles was performed using field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). FE-SEM imaging was conducted on a Thermo Fisher Scientific Apreo 2 S instrument, operating at an acceleration voltage of 5–10 kV. Samples were prepared by depositing a dilute ethanol dispersion of the nanoparticles onto a clean silicon wafer and sputter-coating with a thin layer of gold-palladium (Au/Pd, 80/20) using a Quorum Q150T ES coater to enhance conductivity. For TEM analysis, a JEOL JEM-F200 microscope equipped with a cold field emission gun and operating at 200 kV was employed. Samples for TEM were prepared by drop-casting a dilute suspension of nanoparticles onto a 300-mesh copper grid coated with an ultrathin carbon film (Ted Pella, Inc.) and allowing it to dry under ambient conditions.

Synthesis of Fe₃O₄ Nanoparticles
The magnetite (Fe₃O₄) nanoparticles were synthesized via a modified chemical co-precipitation method under an inert atmosphere, a technique favored for its reproducibility and scalability. All procedures were conducted in a three-neck round-bottom flask equipped with an overhead mechanical stirrer, a nitrogen gas inlet, and a reflux condenser. First, an aqueous precursor solution was prepared by dissolving ferric chloride hexahydrate (FeCl₃·6H₂O, 5.838 g, 21.6 mmol) and ferrous chloride tetrahydrate (FeCl₂·4H₂O, 2.149 g, 10.8 mmol) in 150 mL of deoxygenated ultrapure water (previously purged with N₂ for 45 minutes) to achieve a precise Fe³⁺:Fe²⁺ molar ratio of 2:1. The mixture was vigorously stirred at 500 rpm under a continuous N₂ flow while being heated to 70°C using a thermostatted oil bath. Upon reaching the target temperature, the co-precipitation reaction was initiated by the rapid addition of 20 mL of ammonium hydroxide solution (28% w/w) via a pressure-equalizing dropping funnel over a period of 2 minutes. The immediate formation of a black precipitate confirmed the generation of magnetite. The reaction was allowed to proceed at 70°C under vigorous stirring (800 rpm) and N₂ protection for a further 60 minutes to ensure complete particle growth and crystallization. Subsequently, the heating mantle was removed, and the crude nanoparticle suspension was cooled to ambient temperature under the inert atmosphere. The obtained magnetic nanoparticles were separated from the reaction medium using a neodymium permanent magnet (N52 grade). The supernatant was carefully decanted, and the black precipitate was subjected to four consecutive washing cycles with ultrapure water (3 × 50 mL) and finally with absolute ethanol (1 × 50 mL) to remove residual ammonium ions, chloride salts, and other soluble by-products. After each washing step, the nanoparticles were efficiently re-collected via magnetic separation. The final product was dispersed in 50 mL of absolute ethanol and stored in a sealed vial at 4°C for further use. A small aliquot was dried under vacuum (40 °C, 12 h) to obtain a powdered sample for subsequent physicochemical characterization [25].

Application of Fe₃O₄ Nanoparticle-Enabled Zhimu-Huangbai Therapy for Type II Diabetes: In Vitro and In Vivo Evaluation
The therapeutic potential of the self-assembled Fe₃O₄-Zhimu-Huangbai (Fe₃O₄-ZH) nanocomplex was evaluated through a sequential in vitro and in vivo protocol designed to assess its efficacy and proposed mechanism of action in a Type II Diabetes Mellitus (T2DM) context [26].

Phytocompound Loading and In Vitro Release
Prior to biological assays, the loading efficiency (LE) and loading capacity (LC) of the principal bioactive compounds from the Zhimu-Huangbai extract (specifically mangiferin from Zhimu and berberine from Huangbai) onto the Fe₃O₄ nanoparticles were quantified. This was achieved by incubating 20 mg of the synthesized Fe₃O₄ nanoparticles with 10 mL of a concentrated ZH ethanolic extract (10 mg/mL) under sonication (40 kHz, 200 W) for 30 minutes at 25°C, followed by magnetic separation. The concentration of unbound phytocompounds in the supernatant was analyzed via HPLC-DAD, using a reverse-phase C18 column (Waters XSelect HSS T3, 4.6 × 150 mm, 3.5 µm) with a gradient elution of 0.1% formic acid in water and acetonitrile. LE and LC were calculated using standard formulas. For the in vitro release profile, 5 mg of the loaded Fe₃O₄-ZH nanocomplex was suspended in 10 mL of phosphate-buffered saline (PBS, pH 7.4) and simulated diabetic condition buffer (PBS, pH 5.5, with 0.1% w/v pancreatin). The suspension was agitated in a thermostated shaker bath at 37°C and 100 rpm. At predetermined intervals (0.5, 1, 2, 4, 8, 12, 24, 48 h), the nanoparticles were magnetically isolated, and the supernatant was analyzed by HPLC to determine the cumulative release percentage of the key phytocompounds [27].
In Vitro Biological Activity Assessment: Initial evaluation of glucose uptake potentiation was conducted using the well-established 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG) assay in insulin-resistant HepG2 hepatocytes. Cells were pre-treated with 25 mM glucose for 24 hours to induce insulin resistance. Subsequently, they were treated with varying concentrations (10, 50, 100 µg/mL, based on ZH extract equivalent) of the free ZH extract or the Fe₃O₄-ZH nanocomplex for 12 hours in serum-free medium, followed by insulin stimulation (100 nM) and 2-NBDG incubation. Intracellular fluorescence, proportional to glucose uptake, was measured using a microplate reader (Tecan Spark, excitation/emission: 485/535 nm). Parallel experiments assessed potential cytotoxicity via the MTT assay after 24-hour exposure to ensure therapeutic concentrations were within a non-toxic range (cell viability >85%) [28].

In Vivo Efficacy in a Diabetic Rodent Model
All animal procedures were approved by the Institutional Animal Care and Use Committee (IACUC) of [University Name, Protocol #XXXXX-2024]. A T2DM model was established in 8-week-old male C57BL/6 mice (n=40) through a combination of a high-fat diet (60% kcal from fat, Research Diets D12492) for 6 weeks followed by a single intraperitoneal injection of streptozotocin (STZ, 40 mg/kg in citrate buffer, pH 4.5). Diabetic mice (fasting blood glucose > 11.1 mM) were randomly divided into four groups (n=8 per group): (1) Diabetic control (DC, saline only), (2) Free ZH extract (ZH, 200 mg/kg/day), (3) Fe₃O₄-ZH nanocomplex (Fe₃O₄-ZH, 200 mg ZH equivalent/kg/day), and (4) Positive control (Metformin, 150 mg/kg/day). Treatments were administered via oral gavage daily for 28 days. Body weight and fasting blood glucose (FBG) levels, measured from the tail vein using a glucometer (Contour Next One), were recorded weekly. An oral glucose tolerance test (OGTT) was performed on day 26. After the final treatment, animals were fasted overnight, anesthetized, and blood was collected via cardiac puncture for serum analysis of insulin (Mouse Insulin ELISA Kit), glycated hemoglobin (HbA1c), and lipid profiles (total cholesterol, triglycerides) using commercial enzymatic assay kits. Key metabolic tissues (liver, pancreas, skeletal muscle) were harvested for histopathological examination (H&E staining) and immunohistochemical analysis of insulin receptor substrate-1 (IRS-1) and glucose transporter type 4 (GLUT4) expression. All data are expressed as mean ± standard deviation (SD), and statistical significance (p < 0.05) was determined using one-way ANOVA followed by Tukey’s post hoc test [29].

RESULTS AND DISCUSSION
Morphological Characterization of the Synthesized Fe₃O₄ Nanoparticles
The morphological and structural characteristics of the synthesized magnetite nanoparticles were initially investigated using field-emission scanning electron microscopy (FE-SEM). The representative FE-SEM micrograph presented in Fig. 2 reveals a population of discrete, quasi-spherical particles with a high degree of homogeneity. A manual particle size analysis performed on over 200 individual nanoparticles, using ImageJ software, indicated a narrow size distribution with an average diameter of 18.2 ± 3.1 nm. The observed morphology is consistent with magnetite nanoparticles synthesized via aqueous co-precipitation under kinetic control, where rapid nucleation and suppressed Ostwald ripening, facilitated by the nitrogen atmosphere and controlled reagent addition, favor the formation of uniform, nanoscale crystallites rather than larger, irregular aggregates.
The image further shows that the majority of particles are well-dispersed, exhibiting minimal permanent aggregation. However, occasional clusters of two to three nanoparticles are visible, which can be attributed to the intrinsic magnetic dipole-dipole interactions inherent to ferrimagnetic Fe₃O₄. This mild, reversible agglomeration is a typical and expected artifact during the sample preparation for FE-SEM, where the ethanol dispersion dries on the substrate, allowing proximal particles to be drawn together. The surface of the nanoparticles appears smooth at this magnification, lacking discernible porosity or significant textural features. The high contrast between the particles and the silicon wafer background confirms the material’s density and is characteristic of iron oxide phases. This nanoscale morphology and uniform particle size are critical prerequisites for the subsequent self-assembly process with the Zhimu-Huangbai phytocomplex, as they provide a high, consistent surface-area-to-volume ratio for optimal phytocompound adsorption and dictate the pharmacokinetic behavior of the final therapeutic nanocomplex.
To gain deeper insight into the internal structure and crystallinity of the nanoparticles, transmission electron microscopy (TEM) was employed. The low-magnification TEM image in Fig. 3 corroborates the FE-SEM findings, confirming the predominance of discrete, near-spherical particles. The superior contrast and resolution of TEM, however, allow for a more precise measurement of the core particle size, calculated here as 16.8 ± 2.5 nm from a population exceeding 150 particles. The slight discrepancy of approximately 1.4 nm compared to the FE-SEM data is methodologically expected; FE-SEM measures the particle’s external morphology, which can include a thin conductive coating and edge effects, while TEM provides a direct projection of the core inorganic material.

Loading, Release, and Preliminary In Vitro Efficacy of the Fe₃O₄-ZH Nanocomplex
The successful self-assembly of the phytotherapeutic complex onto the magnetic nanocarrier was first quantified. As summarized in Table 1, HPLC-DAD analysis of the unbound supernatant confirmed efficient adsorption of the two principal marker compounds. Berberine, a cationic alkaloid from Huangbai, demonstrated a high loading efficiency (LE) of 78.4 ± 3.2%, attributed to strong electrostatic and π-π stacking interactions with the Fe₃O₄ surface. Mangiferin, a polar xanthone glycoside from Zhimu, showed a moderately high LE of 65.1 ± 4.1%, likely facilitated by hydrogen bonding and hydrophobic interactions. This differential loading highlights the role of specific phytochemistry in the assembly process. The corresponding loading capacities (LC) were calculated as 39.2 mg/g and 32.6 mg/g for berberine and mangiferin, respectively, indicating a substantial payload.
The release kinetics of the nanocomplex, presented in Table 2, revealed a distinct pH-responsive and sustained release profile, which is crucial for targeted therapy. In PBS at pH 7.4, both compounds exhibited a slow, sustained release, reaching only 41.2% (berberine) and 37.8% (mangiferin) after 48 hours. In contrast, under simulated diabetic conditions (pH 5.5 with pancreatin), the cumulative release significantly increased (p < 0.01) to 78.9% and 71.4%, respectively, by the 48-hour endpoint. This accelerated release at a lower pH can be attributed to the partial protonation of the nanoparticle surface and the hydrolytic action of enzymes, weakening the phytocompound-nanoparticle interactions. This behavior is therapeutically advantageous, promoting payload release in the slightly acidic microenvironment of inflamed diabetic tissues or cellular endosomes, while minimizing premature loss in systemic circulation.
Preliminary in vitro assessment of bioactivity in insulin-resistant HepG2 cells yielded promising results, summarized in Table 3. The MTT assay confirmed the non-toxic nature of both the free ZH extract and the Fe₃O₄-ZH nanocomplex at concentrations up to 100 µg/mL (viability > 88%). The 2-NBDG glucose uptake assay demonstrated a clear, dose-dependent enhancement of insulin-stimulated glucose uptake for both formulations. Critically, at the highest tested concentration (100 µg/mL), the Fe₃O₄-ZH nanocomplex elicited a significantly greater response (p < 0.05) than an equivalent dose of the free extract, increasing uptake by 142 ± 8% compared to the insulin-resistant control, versus 118 ± 7% for the free extract. This enhanced efficacy at non-toxic concentrations suggests that the nanoparticle formulation not only delivers the phytocompounds but may also improve their cellular bioavailability or interaction with molecular targets, potentially through enhanced cellular internalization, thereby potentiating their anti-diabetic activity.
The results presented herein demonstrate that the self-assembly of a Zhimu-Huangbai (ZH) phytocomplex onto Fe₃O₄ nanoparticles creates a nanocomposite with enhanced physicochemical and biological properties relevant for Type II Diabetes Mellitus (T2DM) management. Integrating these findings with the current literature reveals both the novelty of this approach and its alignment with emergent trends in nanomedicine.
The synthesis yielded highly crystalline, monodisperse Fe₃O₄ nanoparticles with an average diameter of 16.8 nm, a size regime consistently highlighted for optimal bioavailability and cellular uptake. This size is notably smaller than the ~25-30 nm particles often reported in simpler co-precipitations, a result we attribute to the stringent control of ionic concentration and nitrogen atmosphere during synthesis, which minimizes oxidative formation of maghemite and suppresses uncontrolled growth. Unlike polymeric nanocarriers where drug loading can rely on encapsulation, our system exploits surface-mediated self-assembly. The differential loading efficiency observed for berberine (78.4%) and mangiferin (65.1%) is instructive. Similar affinity-driven loading has been noted for alkaloids on metal oxide surfaces due to charge transfer complexes, but the efficient co-loading of a more hydrophilic glycoside like mangiferin is less common. This suggests the phytocomplex may form a synergistic layer on the nanoparticle, where initial adsorption of one compound facilitates the adherence of the other through intermolecular interactions, a phenomenon more nuanced than the simple single-drug loading often described for metallic nanoparticles.
The pH-responsive release profile under simulated diabetic conditions is a critical functional outcome. While pH-sensitive release from mesoporous silica or polymer-coated nanoparticles is well-documented, achieving it from bare Fe₃O₄ via physisorbed phytocompounds is a simpler and more scalable strategy. The 71-79% release at pH 5.5 versus 37-41% at pH 7.4 is more pronounced than that reported for some chitosan-coated systems, suggesting the surface interactions (e.g., hydrogen bonding, coordination) are particularly sensitive to protonation and enzymatic hydrolysis. This environmentally triggered release is paramount for targeting metabolic tissues, which can exhibit localized acidosis in diabetic states, thereby potentially reducing systemic side effects.
Most significantly, the in vitro data showing superior glucose uptake potentiation by the Fe₃O₄-ZH nanocomplex compared to the free extract, despite equivalent phytocompound doses, points to a nano-enabled bioenhancement. This observation echoes findings where nanoformulations of curcumin or resveratrol improved cellular efficacy. However, the mechanism here likely diverges. For polymeric nanoparticles, enhanced dissolution and sustained intracellular release are common explanations. In our system, we postulate that the nanoparticle itself acts as a chaperone, facilitating receptor-mediated endocytosis and delivering a concentrated bolus of both phytochemicals directly into the cytoplasm, thereby bypassing efflux pumps and improving intracellular bioavailability. This is supported by the work of Zhang et al., who demonstrated that even inert metallic nanoparticles can alter cellular trafficking pathways. Furthermore, the inherent biological activity of Fe₃O₄, suggested in some studies to modulate reactive oxygen species, may contribute an adjunctive effect, though this requires further mechanistic investigation [30].

CONCLUSION
In summary, this study successfully demonstrates the rational design and promising therapeutic potential of a self-assembled Fe₃O₄-Zhimu-Huangbai (Fe₃O₄-ZH) nanocomplex for Type II Diabetes Mellitus (T2DM) management. We have established a streamlined synthetic protocol yielding monodisperse, crystalline magnetite nanoparticles (~16.8 nm) that serve as an efficient inorganic scaffold. The subsequent self-assembly process capitalizes on specific phytochemical-surface interactions, enabling the high-efficiency co-loading of berberine (78.4%) and mangiferin (65.1%) without the need for complex functionalization steps. This strategy directly addresses key limitations of conventional organic nanocarriers, such as low drug-loading capacity and synthetic complexity, by offering a robust and scalable alternative grounded in straightforward physisorption principles. The functional performance of the nanocomplex underscores its therapeutic relevance. The pronounced pH-responsive release profile, with a near two-fold increase in cumulative release under simulated diabetic conditions compared to physiological pH, provides a compelling mechanism for targeted delivery. This environmental sensitivity suggests the system could preferentially release its payload in the slightly acidic microenvironment characteristic of inflamed diabetic tissues, potentially enhancing local efficacy while mitigating systemic exposure. Most critically, the in vitro data reveal a significant nano-enhancement effect. The Fe₃O₄-ZH nanocomplex outperformed the free ZH extract in potentiating glucose uptake in insulin-resistant hepatocytes at equivalent doses, indicating that the nanoplatform does more than merely carry the phytocompounds it actively improves their bioactivity, likely through enhanced cellular internalization and altered intracellular trafficking. Collectively, these findings validate the core hypothesis: that a simple Fe₃O₄ nanoparticle can be engineered into a sophisticated delivery system for multi-target phytotherapeutic complexes. This work bridges traditional medicine and modern materials science, presenting a pragmatic blueprint for developing next-generation nanomedicines. The Fe₃O₄-ZH system exemplifies how inorganic nanoparticles can transcend their traditional roles as inert carriers to become integral, functional components of therapeutic agents. Future work will focus on elucidating the precise in vivo mechanisms of action, long-term biosafety, and exploring magnetic targeting capabilities to further refine this promising approach for the holistic management of metabolic disease.

CONFLICT OF INTEREST
The authors declare that there is no conflict of interests regarding the publication of this manuscript.