Attenuated Total Reflection Fourier Transform Infrared Mapping Coupled With Principal Component Analysis For Studying Of The In Vitro Mineralization Of Poly(L-lactic Acid)/hydroxyapatite Nanocomposite

Poly(L-lactic acid)/hydroxyapatite(PLLA/HA)nanocomposite as an ideal scaffold material has good biocompatibility,biodegradability and excellent mechanical properties.Biodegradability is the main factor for evaluating the properties of scaffold materials.Generally,the biodegradation rate of scaffolds should match that of the new tissue formation.As far as PLLA/HA nanocomposites be concerned,the degradation of PLLA rests with a number of factors,including the polymer's crystallinity,molecular weight,crystalline morphology,wettability,the stereoisomeric content of PLLA and the content of HA.In this work,PLLA/HA nanocomposite with different structure were prepared by solvent casting/salt-leaching method and soked into simulated body fluid(SBF)at 37 ? for in vitro mineralization.Attenuated Total Reflection Fourier transformation Infrared(ATR FTIR)mapping coupled with principal component analysis(PCA)were employed to study the mineralization kinetics and PLLA's crystalline transformation of PLLA/HA nanocomponent during the in vitro mineralization.By univariate analysis of ATR FTIR images of PLLA/HA nanocomposite at different mineralization,we found that as the mineralization proceeds,the imaging area gradually changes from blue to red,suggesting an increase in the intensity ratio with mineralization.The in vitro mineralization kinetics of PLLA/HA nanocomposite materials with different architectures were further investigated by ATR FTIR mapping coupled with PCA.The results show that as the mineralization proceeds,PLLA was gradually degraded,while new formed HA were deposited on the pore walls and surface of p-and c-PLLA/HA nanocomposite,respectively.By analyzing the PC1 loading spectra of FTIR image of PLLA/HA nanocomposites and calculating the intensity ratio of the band at 1045 cm-1to the one at 1755 cm-1,we firstly report two mineralization kinetic models in different biomimetic solution.When in vitro mineralization was studied in SBF,both the porous and the compact nanocomposites followed a zero-order kinetic model,while the mineralization kinetics followed a second-order model when the PLLA/HA composite was immersed into PBS.In order to further understand the mineralization mechanism of PLLA/HA nanocomposite,we investigate the crystalline conformation change of PLLA matrix during the in vitro mineralization and propose two novel degradation mechanisms at molecular level for the first time.In this work,PLLAs with three different conformations were prepared on a differential scanning calorimeter(DSC).By analyzing their ATR FTIR spectra,we found that two band pairs(1384/1361 and 1211/1187)could be used for identifying the conformation of?-PLLA,?--PLLA and amor-PLLA.By calculating the ratios of the two bands of PC1 loading spectra of PLLA/HA nanocomposites at different mineralization days,and combining with the results of XRD and DSC,we conclude that the degradation and crystalline conformation change of PLLA matrix in PLLA/HA nanocomposite is an alternatively cyclic process.For p-PLLA/HA nanocomposite,the degradation occurred simultaneously both on the pore wall's surface and the interior of composite,and there is a transformation from?-PLLA to ?'-PLLA and vice versa with the increase of amor-PLLA.For c-PLLA/HA nanocomposite,however,the degradation of PLLA mainly occurred on the surface of composite.As the surface amor-PLLA of nanocomposite was degraded,SBF solution gradually penetrated into the interior of materials,and broke the original structure of PLLA.Our work provides a reliable theoretical basis and a new research idea for deep study of the in vitro mineralization of PLLA-based nanocomposite.