CaP-electrodeposition in electrospun PLLA/ZnO nanofiber nonwovens

Abstract

Solid bioactive calcium phosphate (CaP)-based coatings on metallic substrates are established to improve osseointegration of bone implants. Less work is published on highly porous pre-mineralized fiber structures for coatings or scaffolds. In this study, research on electrochemically mineralized poly-L-lactic acid (PLLA) nanofiber covers is introduced. This work focusses on the feasibility of the manufacture of porous osteoconductive scaffolds with adjustable mineral content. Aqueous solutions of calcium nitrate and ammonium diphosphate were used as electrolyte for electrochemical deposition of CaP. The performance of carbon (C), magnesium (Mg) and titanium (Ti) electrode pairs was investigated (voltage: 2 - 20 V). Ti electrodes proved to be advantageous regarding erosion, deposition homogeneity, gas generation, and mineral adhesion, and therefore were covered by electrospun PLLA nonwovens for electrochemical mineralization. Recordings of voltage and current revealed a stable operating process. The nanofiber covers were homogenously penetrated by mineral crystals, which enclosed fibers. Investigations on morphology and chemical composition were performed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and optical microscopy. Chemically reactive electrode materials (e.g. Mg) can be included in the deposited crystals, if desired. EDX revealed Mg in deposited crystals when using Mg electrodes. In addition, EDX analysis is suitable for indirect detecting electrode erosion by identifying electrode elements in mineral deposits. Using Ti electrodes, the expected elements with relative Ca/P ratio of 1.2 ± 0.3 were detected. The degree of mineral fraction can be adjusted by processing time. A voltage of 15 V proved to be the best compromise between deposition rate and process time for the introduced setting with Ti electrodes. A high porosity as well as premineralization is intended, which assumedly allows good cell infiltration and rapid osseointegration of the implant. Further work is intended to involve studies on mineral filling density, other polymer scaffolds, and biological testing.