Polyglycolide (PGA) and poly(¿-caprolactone) (PCL) are currently two of the most employed biodegradable polymers. Tissue engineering , orthopaedic devices and drug delivery systems are representative examples were such polymers are extensively used. The repeat units of PGL and PCL differ on the number of methylene groups (i.e. one and five), a feature that leads to distinct chain flexibility, surface hydrophobicity and mechanical and thermal properties. For example, the melting points of PCL and PGA are 55 oC and 220 oC, namely a difference of more than 150 oC. In this way, materials with tuned properties could be obtained by a simple blend of different ratios of PGA and PCL if samples were well miscible. Electrospinning is one of the most versatile processes for preparing non-woven nanofibers that could be arranged into porous scaffolds. The process uses electrostatic forces (10–100 kV) to stretch a polymer dilute solution as it solidifies. The process is fast and allows an easy preparation of polymer mixtures if a common solvent is found . Furthermore, domains corresponding to the different polymers should be small due to the nanometric dimensions of the produced fibers and consequently an intimate contact between PCL and PGA molecules may be possible.
Incorporation of drugs into electrospun scaffolds is also an easy process since only minor modifications on the processing parameters are required, being also minimal the repercussion on the final geometry due to the usually low amount of loaded drug that is necessary to get a significant pharmacologic effect. Incorporation of several drugs can provide materials with multifunctional properties. In this work the use of a typical bactericide agent and an anticancer drug, which should provide a high added value, was assayed.
PHMB is a cationic oligomer having an average of 7–13 biguanide groups spaced by flexible hexamethylene segments. The high number of biguanide groups lead to a high effectiveness against microorganisms, although chemical characterization is hindered for the high dispersion of oligomer sizes. Curcumin (CUR) is a molecule constituted by two phenol groups connected by a,ß-unsaturated carbonyl groups. These diketones can form stable enols and are readily deprotonated to form enolates. Curcumin seems to have beneficial effects on various diseases, including multiple myeloma, pancreatic cancer, myelodysplastic syndromes, colon cancer, psoriasis, and Alzheimer's disease. Curcumin is also a pleiotropic molecule capable of interacting with molecular targets involved in inflammation. Electrospun scaffolds constituted by PGA/PCL ratios of 100/0, 80/20, 65/35, 50/50, 35/65 and 0/100 have been prepared, characterized and optimized in each case the processing conditions. 1,1,1,6,6,6-hexafluoroispropanol was employed as solvent and the total polymer concentration was kept in the 8-18 wt-% range. For loaded samples, solutions contained also 3 wt-% and 1 wt-% of PHMB and CUR, respectively. The electrospun nanofibers were collected on a target, which was placed 10 cm from the syringe tip (outer diameter 12 cm). A voltage of 20 kV was applied to the collecting target and the mass-flow rate was set at 3 mL/h.
Electrospun nanofibers were continuous, had smooth surfaces and a relatively homogeneous size (diameter around 900 nm). Formation of beads was the main problem, especially when the PCL content was higher.
FTIR and NMR spectra of the different scaffolds were in agreement with their theoretical composition. DSC heating traces and WAXD diffraction data indicate that crystalline domains of both polymers were present in the electrospun fibers, being also inferred a significant amorphous content.