A Carbon Drug Delivery System for Lithium

Abstract

Lithium was introduced into pyrolyzed phenolic resins by dissolving lithium nitrate (5, 10, and 15% by mass) in a resol precursor. Impregnated specimens were pyrolyzed at 500°C, 575°C, and 650°C in inert atmosphere. After pyrolysis, samples were placed in 5 ml of phosphate buffered saline solution, refrigerated at 5°C, for various Li⁺ release times. Inductively coupled plasma-atomic spectroscopy was used to analyze these solutions, which were tested every 24 hours for 5 days; another set was tested after 60 days. Samples containing 5% lithium salt, fired to 500°C, released Li⁺ at a lower rate than those fired at higher temperature. At the early stages of exposure to saline, samples fired at 575°C and 650°C released Li⁺ at a higher rate, which fell to that of 500°C samples after many days. After leaching, nuclear reaction analysis using alpha radiation, with an exposure time of 1 hour, allowed us to analyze [Li⁺] and gradient up to 12 μm below the surface. This indicates that a smaller [Li⁺] remains in 650°C samples than in those fired at 575°C and 500°C. For 500°C samples, [Li⁺] near the surface was lower than that for samples fired at 575°C and 650°C. This indicates that 500°C samples release Li⁺ from near the surface, whereas samples fired at higher temperature release Li⁺ from deep below the surface, probably because of higher permeability. Li⁺ release rates of samples fired at 500°C and below 650°C follow a simple diffusion law, with diffusivities between 10⁻¹⁷ and 10⁻¹⁸ m²/s. Li⁺ rate may controlled over long time by a multilayered sprayed precursor with variable concentration.