INTELLECTUAL MERIT: It is proposed to devise an oral drug delivery system, based on two polysaccharides that are regulated by the U.S. Food and Drug Administration and approved for oral administration. The proposed system is an ionic complex of chitosan, a positively charged polyelectrolyte, and cellulose nanocrystals, negatively charged, cylindrical macroions. Chitosan will impart to the system bioadhesive and bioabsorption-enhancing properties, whereas the cellulose nanocrystals (CNCs) will bind poorly soluble therapeutic molecules via surface complexation, thus preventing undesirable crystallization, and control their release rate through desorption. The long-term goal of the proposed research is a multifunctional oral delivery system for therapeutic agents that provides zero-order (constant rate) release while simultaneously enhancing the agent?s solubility and absorption and, thus, bioavailability. The specific objectives are: (1) Develop a detailed understanding of the factors governing the formation and properties of chitosan?CNC complexes, (2) Characterize the molecular interactions of selected model drugs with a cellulose surface, (3) Assess the drug loading and release efficiencies of chitosan?CNC complexes, (4) Assess the safety of ingestion of CNCs and chitosan?CNC complexes in vitro, (5) Assess the mucoadhesive properties of chitosan?CNC complexes in vitro, and (6) Assess the permeability-enhancing properties of chitosan?CNC complexes in vitro. The project will employ physicochemical and microscopy methods to study the formation and properties of the ionic complex and its interactions with and release of model drugs. Cell culture studies will be used to assess the toxicity of the ionic complex to human intestinal epithelial cells and the complexes effectiveness to enhance drug permeability.
BROADER IMPACTS: The proposal is inherently interdisciplinary, pairing a polymer chemist and molecular biologist. It thus benefits from the intrinsic information exchange arising from such collaborations. The proposed drug delivery system is highly versatile by reason of its oral safety, biocompatibility, and environmental biodegradability. As a result, the system could also be used for controlled release of functional molecules in foodstuffs, cosmetics, agricultural applications, and applications in the emerging field of functional textiles, to name a few. In addition to the technological impact, three graduate students will be trained in the interdisciplinary environment of the project and up to six undergraduate students will be trained on the project by providing them with summer undergraduate research experience. Undergraduate student participants, and intramural funding to supplement the NSF funding committed to support undergraduates, will be sought through the Virginia Tech Multicultural Academic Opportunities Program and an existing Virginia Tech REU program.
The project investigated an ionic complex between chitosan, a positively charged long-chain carbohydrate, and cellulose nanocrystals, negatively charged, plant-based, rod-like nanoparticles. The long-term goal of the project was a multifunctional oral delivery system for therapeutic agents that provides zero-order (constant rate) release while simultaneously enhancing the agent's solubility and absorption and, thus, bioavailability. The specific objectives of the project were: Develop a detailed understanding of the factors governing the formation and properties of chitosan-cellulose nanocrystal complexes Characterize the molecular interactions of selected model drugs with a cellulose surface Assess the drug loading and release efficiencies of chitosan-cellulose nanocrystal complexes Assess the safety of ingestion of cellulose nanocrystals and chitosan-cellulose nanocrystal complexes in vitro Assess the mucoadhesive properties of chitosan-cellulose nanocrystal complexes in vitro Assess the permeability-enhancing properties of chitosan-cellulose nanocrystal complexes in vitro This study of chitosan–cellulose nanocrystal complexes is one of the first experimental studies of polyelectrolyte–macroion systems. The major findings of this project are: Chitosan and sulfuric acid-hydrolyzed cellulose nanocrystals form an ionic complex when mixed at a solution pH between 2.6 and 5.6. The size, shape, and net charge of the ionic complex depend strongly on the concentrations of the two solutions, solution pH, and mixing ratio. The molecular weight of chitosan and the ionic strength of the solutions have a minor effect on the properties of the ionic complex. The size of the ionic complex is largest at very low pH levels (<2) because of the lack of ionization of the cellulose nanocrystal and smallest at very high pH levels (>8) because of the insolubility of chitosan in basic aqueous media. The size of the ionic complex decreases with increasing ionic strength in the range 0-0.5 M because of charge screening effects. The model drugs caffeine and chitosan interact only weakly with cellulose surfaces. Loading efficiencies and release rates are high for caffeine and low for ibuprofen. Cellulose nanocrystals are non-cytotoxic toward Caco-2 cells at concentrations of up to 10 mg/mL Chitosan is non-cytotoxic toward Caco-2 cells at concentrations of up to 1 mg/mL Both chitosan and cellulose nanocrystals have pH- and ionic strength-dependent mucoadhesive properties. Cellulose nanocrystals have no effect on the transepithelial electrical resistance (TEER) of Caco-2 cell monolayers within 2 h of exposure at concentrations between 0.01 and 1 mg/mL. Water-soluble chitosan (WSC) dose-dependently reduces the TEER of Caco-2 cell monolayers within 20 min of exposure. The TEER of Caco-2 cells that have been exposed to WSC for 2 hours at concentrations between 1 and 2.5 mg/mL recovers fully within 22 h. A decrease in tight junction protein occludin was observed in Caco-2 cell monolayers when treated with 5 mg/mL WSC for 2 hours. Chitosan-cellulose nanocrystal ionic complexes containing less than 50% by weight WSC do not significantly decrease TEER in Caco-2 cell monolayers. Complexes containing more than 50% by weight WSC can be obtained with surface-oxidized cellulose nanocrystals, containing carboxyl groups. The TEER of Caco-2 cells that have been exposed to 4 mg/mL chitosan-cellulose nanocrystal ionic complexes containing 2.1 mg/mL WSC for 2 h decreases during treatment similarly to the TEER of Caco-2 cells that have been exposed to 2.5 mg/mL WSC and fully recovers over the next 22 h. In summary, the ability of chitosan-cellulose nanocrystal ionic complexes to open up the tight junctions between intestinal epithelial cells and, thus, their potential for use as an oral drug delivery system has been demonstrated.
