Elucidation of bio-inspired hydroxyapatie crystallization on oxygen-plasma modified 3D printed poly-caprolactone scaffolds.

Bioapatite formation in bones is a slow process starting with deposition of calcium phosphate and then its nucleation and crystallization into hydroxyapatite crystals. If the same process can be replicated on tissue engineered scaffolds, it will result in the formation of biomimetic bone constructs that will have comparable mechanical properties to native tissue. To mimic the same process on 3D printed polycaprolactone (PCL) scaffolds oxygen plasma treatment was performed to modify their surface chemistry. The attenuated total reflectance-fourier transform infrared (ATR-FTIR) analysis showed formation of carboxyl groups on the PCL surface with corresponding increase in roughness as analyzed by atomic force microscope (AFM) studies. A biomimetic acellular mineralization procedure was then utilized to deposit calcium minerals on these scaffolds. Though amorphous calcium phosphate was deposited on all the scaffolds with highest amount on PCL scaffolds with tricalcium phosphate (TCP), biomimetic hydroxyapatite crystals were only formed on oxygen plasma treated scaffolds, as shown by X-ray diffraction (XRD) analysis. The COOH groups on the plasma treated scaffolds acted as nucleation sites for amorphous calcium phosphate and the crystal growth was observed in the (211) plane simulating the crystal growth in developing bones. The ATR-FTIR study demonstrated the carbonated nature of these hydroxyapatite crystals mimicking that of bioapatite. The electronegative COOH groups mimic the negative amino acid side chains in collagen Type I present in bone tissue and the carbonated environment helps in creating bioapatite like deposits. The present study demonstrated the important role of PCL surface chemistry in mimicking a bone like mineralization process in vitro. This work details novel insights regarding improved mineralization of 3D printed PCL scaffolds useful for the development of more biomimetic bone constructs with improved mechanical properties.