Composited electrospun nanofibers made of temperature-responsive poly(N-isopropylacrylamide) (pNIPAM) and biodegradable poly (ε-caprolactone) (PCL) can be utilized for 'on-demand' and controlled drug release of ibuprofen without burst effect for potential pharmaceutical applications. Three types of nanofibers, PCL, pNIPAM and pNIPAM/ PCL composite NFs containing ibuprofen were fabricated using electrospinning techniques. Ibuprofen release rates from PCL NFs are not affected by the temperature in the range of 22-34°C (less than 10%). In contrast, the ibuprofen release rates from pNIPAM NFs are very sensitive to the change in temperature, which is five times higher at 22°C compared to 34°C. However, there is a serious burst effect at 22°C. Compared to other two types of NFs, pNIPAM/PCL composite NFs prepared demonstrated a variable and controlled release at both room and higher temperature, due to the extra protection from the hydrophobic poly (ε-caprolactone). The rate at 22°C is 75% faster compared to that at 34°C. This kind of composite design can provide a novel approach to suppress the burst effect in drug delivery systems for potential pharmaceutical applications.

Electrospun microfibers (MFs) composed of pH and temperature responsive polymers can be used for controllable and variable delivery of ibuprofen. First, electrospinning technique was employed to prepare poly( -caprolactone) (PCL) and poly(Nisopropylacrylamide-co-methacrylic acid) (pNIPAM-co-MAA) MFs containing ibuprofen. It was found that drug release rates from PCL MFs cannot be significantly varied by either temperature (22-40 ∘ C) or pH values (1.7-7.4). In contrast, the ibuprofen (IP) diffusion rates from pNIPAM-co-MAA MFs were very sensitive to changes in both temperature and pH. The IP release from pNIPAM-co-MAA MFs was highly linear and controllable when the temperature was above the lower critical solution temperature (LCST) of pNIPAM-co-MAA (33 ∘ C) and the pH was lower than the pK of carboxylic acids (pH 2). At room temperature, however, the release rate was dramatically increased by nearly ten times compared to that at higher temperature and lower pH. Such a unique and controllable drug delivery system could be naturally envisioned to find many practical applications in biomedical and pharmaceutical sciences such as programmable transdermal drug delivery.

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