Cyclodextrin-functional nanofibers as hormone delivery systems

Abstract

This thesis focuses on the development of cyclodextrin (CD)-functionalized polymer nanofibers for use in hormone delivery systems. Particular emphasis is placed on the rational selection of hydrophilic and hydrophobic polymers, the incorporation of hormones at varying concentrations, and the role of CD inclusion in modulating drug loading capacity, drug stability, and release kinetics. The study evaluates the release behavior of hormone-loaded nanofibers, with the aim of achieving both rapid and sustained release profiles. Hydrophilic polymers such as pullulan and gelatin are utilized to achieve rapid drug release via fast-disintegrating fibers, while hydrophobic cellulose acetate (CA) is employed to promote sustained drug release. In each formulation, the incorporation of CDs enhances the solubility and stability of the hormones, while simultaneously modulating their release profiles from the nanofibrous structures. Hormone delivery, especially oral administration of hormones such as progesterone (P4), estradiol (E2), and estriol (E3), presents significant therapeutic importance due to their central roles in regulating a wide range of physiological processes. These steroidal hormones, although endogenously produced, are frequently supplemented from external sources in clinical settings due to fluctuations, deficiencies, or dysfunctions in the body's natural hormone production. Their inclusion in this study is based on both their clinical relevance and their physicochemical challenges, such as poor aqueous solubility and instability, which complicate conventional oral delivery. P4 is a crucial hormone involved in regulating the menstrual cycle, maintaining pregnancy, and supporting embryogenesis. It is primarily secreted by the corpus luteum and later by the placenta during pregnancy. P4 prepares the endometrium for embryo implantation and sustains early pregnancy. However, progesterone levels may be insufficient due to luteal phase defects, anovulation, or during hormone replacement therapy (HRT) for peri- and postmenopausal women. Supplementation of P4 is essential in assisted reproductive technologies (ART), luteal phase support, and the treatment of conditions such as endometrial hyperplasia. E2, the most potent naturally occurring estrogen, is essential for reproductive health, maintaining bone density, cardiovascular protection, and neuroprotection. E2 levels significantly decline during menopause, leading to symptoms such as hot flashes, mood swings, and an increased risk of osteoporosis. Clinically, E2 is used in HRT for menopausal women, treatment of hypogonadism, and managing estrogen deficiencies following surgical removal of ovaries or other medical conditions. E3, while considered a weaker estrogen than E2, plays a vital role during pregnancy and is gaining recognition for its therapeutic potential due to its favorable safety profile. E3 is commonly used in HRT, particularly in women who cannot tolerate stronger estrogens. It exhibits tissue-selective activity with a lower risk of stimulating endometrial or breast tissue, making it a safer alternative for long-term use. Despite the body's inherent ability to synthesize these hormones, external supplementation is often required to restore physiological levels, manage hormone-related disorders, or compensate for age- or disease-related decline in endogenous production. Additionally, when hormones are administered orally, they often undergo significant first-pass metabolism in the liver, drastically reducing their bioavailability. The result is not only lower systemic levels but also greater interindividual variability in response and increased metabolic byproducts, which can lead to side effects. This thesis addresses these challenges by exploiting CD-functionalized nanofibers, which represent a novel approach to overcoming these obstacles. By combining the unique inclusion-complex-forming ability of CDs with the versatility of electrospinning, this work pioneers the development of advanced nanofiber systems capable of tailoring release profiles for both rapid and sustained delivery. The incorporation of hydrophilic and hydrophobic polymers in a single system further enhances the potential for personalized and efficient oral hormone therapy. The thesis begins by introducing the fundamentals of electrospinning and its application in fabricating electrospun fibers for oral drug delivery. It then examines the electrospinning process of hormone-loaded, CD-functionalized polymer fibers and their potential in hormone delivery systems. This is followed by an experimental section that provides a detailed overview of the materials used and the conducted experiments. The fourth chapter presents an investigation into the encapsulation and release behavior of the selected hormones— P4, E2, and E3—from hydrophilic electrospun pullulan-based fibers. These hormones, due to their hydrophobicity and poor aqueous solubility, were first complexed with CDs to improve their compatibility with the hydrophilic polymer matrix. The resulting inclusion complexes (ICs) were then incorporated into pullulan solutions and processed via electrospinning. Optimization of electrospinning parameters—such as polymer concentration, flow rate, voltage, and tip-to-collector distance—was carefully performed to obtain uniform, bead-free fibers. Fiber morphology was examined using optical microscopy and scanning electron microscopy (SEM), both of which confirmed the successful formation of continuous, smooth fibers with nanometer-scale diameters and no visible aggregates or crystalline hormone residues. The incorporation of hormone–CD complexes did not negatively affect fiber formation, indicating good compatibility between the drug complexes and the polymer matrix. FTIR analysis confirmed the successful encapsulation of P4, E2, and E3 within the fibers by identifying characteristic hormone peaks. TGA results demonstrated enhanced thermal stability of the encapsulated hormones, evidenced by higher decomposition temperatures compared to raw drugs and CD complexes. In vitro release studies were carried out in aqueous media to evaluate the drug release kinetics of the pullulan-based systems. The hydrophilic nature of pullulan enabled rapid fiber disintegration upon contact with simulated saliva, resulting in an immediate burst release of the encapsulated hormones. This fast-release profile is particularly valuable for buccal or sublingual administration, where rapid absorption through the mucosal membranes is desired. The data confirmed that hormone release was achieved within minutes, making these systems ideal for applications requiring quick onset of action, such as hormone deficiency crises or short-term therapeutic interventions. In the subsequent chapter, the thesis explores a more complex nanofiber design involving multilayered fibers with a sandwich structure to achieve controlled hormone release. This system consisted of hydrophobic CA as the outer layers and gelatin, a hydrophilic, biocompatible polymer, as the inner core layer. The inner gelatin layer contained the hormone–CD complexes, while the CA layers served as diffusion barriers to modulate the release rate. The fabrication of this multilayered structure was achieved through a sequential electrospinning process. Each layer was deposited with controlled thickness and alignment to ensure homogeneity and reproducibilityOptical microscopy was used to examine the fiber structure of each layer, while FTIR analysis verified the encapsulation of hormones at varying concentrations. Release studies demonstrated that the gelatin core facilitated an initial release phase upon hydration, followed by a more gradual hormone diffusion through the surrounding CA layers. The hydrophobicity of CA effectively slowed down water penetration, thereby reducing the rate of hormone diffusion. Comparative analysis between the pullulan fibers and the multilayered gelatin-CA systems highlighted the capacity to precisely tailor release kinetics through material selection and architectural design. The pullulan system was confirmed to be ideal for fast-dissolving applications, while the multilayered structure offered a promising strategy for sustained delivery. In conclusion, these chapters highlight the strategic integration of polymer science, drug delivery mechanisms, and nanotechnology in the development of advanced hormone delivery systems. The effective encapsulation, validated through FTIR, TGA, and SEM, along with the improved stability and controlled release profiles, demonstrates the potential of CD-functionalized electrospun nanofibers for both rapid and sustained hormone therapy. This work presents a flexible platform for oral or transmucosal hormone delivery, laying the groundwork for future translational studies and clinical applications.