The optical properties of hydroxyapatites (HAps) and bio HAps have been studied using Raman and infrared (IR) spectroscopies to describe their crystalline quality. However, the size of the HAp crystals and their crystalline order effects have not been considered yet. This paper focuses on the study of the effect of the change in the crystallites size have on the width of the IR and Raman spectra for defatted and deproteinized bones as well as incinerated biogenic HAp obtained from bovine, porcine, and human bones. Bone samples were analyzed through Raman and IR spectroscopies, X‐ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma (ICP), and scanning electron microscopy (SEM). The Raman and IR spectra for raw samples showed broad bands but, after calcination at 720 °C, became narrow and well defined. TEM images showed that all raw crystallites are ordered nanoplates contrary to the so far well‐established concept that biogenic HAps have low crystalline quality. XRD data confirmed that raw samples display broad peaks that correlated with the HRTEM images of ordered nanocrystals. This fact confirmed that the broad Raman and IR bands of raw clean bones come from nanocrystal plates. SEM analysis confirmed the increase in the crystal size after calcination from nanomicron to submicron dimensions due to a coalescence phenomenon. These results imply that the interpretation of Raman and IR spectra in the case of HAp nanoparticles has been erroneous. These results contribute to the design of biomaterials for tissue engineering based on biogenic HAp for bone regeneration.
19This work focuses on the analysis of the impact that raw and calcined biogenic 20 hydroxyapatite crystal size has on the Raman and infrared spectra. To this end, bovine, 21 porcine, and human bones samples were defatted and deproteinized as well as calcinated at 22 720°C and then analyzed through Raman and Infrared spectroscopies, Transmission 23 Electron Microscopy (TEM), Inductively Coupled Plasma (ICP), and Scanning Electron 24 Microscopy (SEM). Raman and IR spectra for raw samples showed broad bands while after 25 calcination bands became narrow and well defined. TEM images showed that all raw 26 crystallites are nano-plates with a high crystalline quality contrary to the so far well-27 established concept that biogenic hydroxyapatites have low crystalline quality. This fact 28 confirmed that the broad Raman and infrared bands of raw clean bones come from 29 nanocrystal-plates. SEM analysis confirmed the increase in the size of the crystals after 30 calcination from nano to sub-micron dimensions due to a coalescence phenomenon. 31 32 33 34 35 36 37 38 39 40Nowadays bio-ceramic materials like hydroxyapatites are growing in importance in 41 different fields, particularly in tissue engineering for medical and dental applications. The 42 hydroxyapatite obtained from natural sources is called bio-hydroxyapatite (BIO-HAp), and 43 its main difference with synthetic apatites is that it is a carbonated hydroxyapatite which 44 contains other elements such as Na, Mg, Mn, Fe, among others (1, 2).
45The physicochemical characterization of raw bone as well as BIO-HAp obtained through 46 different methodologies is still an open problem due to the complexity of the material.
47Infrared and Raman spectroscopies have been extensively used to study these materials to 48 monitor the removal of the organic matrix from the mineral phase as well as to identify 49 different mineral phases and to study the changes in the crystalline quality of HAp caused 50 by thermal processes (3, 4). However, no studies about the influence of the crystal size on 51 the vibrational properties of synthetic and natural hydroxyapatites have been reported in 52 detail. Usually, when these spectroscopies are used to study the vibrational states in 53 synthetic and natural hydroxyapatites (5), the full width at the half maximum (FWHM) of a 54 characteristic peak is used to determine the crystalline quality of HAp crystals and for 55 clinical diagnostic (6). However, this criterion must be discussed in detail in the case of 56 nanostructures.
57It is well established in the literature that nanosized crystals produce wider Raman bands 58 than micro-sized ones as can be found for semiconductors as Si (7, 8). The phonon 59 confinement model has been proposed to explain Raman spectra in nanosized systems 60 because the surface states must be considered (9-12). According to Gao et al. (13), the 61 underlying mechanism behind the size-dependent Raman shifts is still quite controversial 62 and an open problem. They proposed a theoretical method to explain th...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.