Cooling rate effects on thermal, structural, and microstructural properties of bio-hydroxyapatite obtained from bovine bone Cristian F. Ramirez-Gutierrez, 1 Anderzon F. Palechor-Ocampo, 1 Sandra M. Londo ~ no-Restrepo, 1 Beatriz M. Mill  an-Malo, 2 Mario E. Rodriguez-Garc  ıa 2 1 Posgrado en Ciencia e Ingenier  ıa de Materiales, Centro de F  ısica Aplicada y Tecnolog  ıa Avanzada, Universidad Nacional Aut  onoma de M exico Campus Juriquilla, Quer etaro, Qro., M exico 2 Departamento de Nanotecnolog  ıa, Centro de F  ısica Aplicada y Tecnolog  ıa Avanzada, Universidad Nacional Aut  onoma de M exico, Quer etaro, Qro., M exico Received 14 November 2014; revised 2 February 2015; accepted 16 February 2015 Published online 20 March 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/jbm.b.33401 Abstract: This article is focused on the study of cooling rate effects on the thermal, structural, and microstructural proper- ties of hydroxyapatite (HAp) obtained from bovine bone. A three-step process was used to obtain BIO-HAp: hydrothermal, calcinations, and cooling. Calcined samples in a furnace and cooling in air (HAp-CAir), water (HAp-CW), and liquid nitrogen (HAp-CN2), as well as an air cooled sample inside the furnace (HAp-CFAir), were studied. According to this study, the low cooling rate that was achieved for air cooled samples inside the furnace produce single crystal BIO-HAp with better crystal- line quality; other samples exhibited polycrystalline structures forming micron and submicron grains. V C 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 339–344, 2016. Key Words: hydroxyapatite, cooling rate, structural properties of bone, bio-hydroxyapatite How to cite this article: Ramirez-Gutierrez CF, Palechor-Ocampo AF, Londo~ no-Restrepo SM, Mill an-Malo BM, Rodriguez-Garc  ıa ME. 2016. Cooling rate effects on thermal, structural, and microstructural properties of bio-hydroxyapatite obtained from bovine bone. J Biomed Mater Res Part B 2016:104B:339–344. INTRODUCTION Hydroxyapatite (HAp) is a stoichiometric material formed of Ca 10 (PO 4 ) 6 (OH) 2 , while a mineral component of the bone called Bio-hydroxyapatite (Bio-HAp) is a non-stoichiometric HAp that contains other amounts of ions such as Na, Zn, Mg, K, Si, Ba, F, CO 3 . 1,2 Bio-HAp is growing in importance due to its potential applications in surgery, such as healing of segmental bone defects; but so far, it is a big problem due to the limited availability of bone processed material with special characteristics to be used in orthopedic, dental, and trauma surgery. The main application of Bio-HAp or Hap use is to fill the defects and promote bone growth. From a clinical standpoint, the best way to repair a bone defect that can usually be done through the replacement of a bone part or by the filling of a hole in the bone is by using autologous bone or by using biomaterial or xenograft with the similar characteristics, as is the case of bovine bone. This can be done with the use of Bio-HAp which con- tains almost all the ions present in the human bone. Some important aspects related to the crystallinity of Bio-Hap, chemical composition, and HAP crystal grain size are still an open problem that need to be addressed in terms of micro and structural studies. Usually, the HAP contained in the human bone does not have a high crystalline quality 1 ; there- fore, it is necessary to study different annealing and cooling processes to obtain Bio-HAp with similar structural and microstructural properties of the human bone. Bone from a biological source is composed of fat, pro- teins, water, and inorganic crystalline and amorphous com- pounds. In order to obtain a xenogenous bone, it is necessary to remove all organic components by using sol- vents or hydrothermal processes. The problem is that, in fact, organic and inorganic materials are forming a matrix in which these components are together. Several methods had been proposed in order to remove the organic phase. Giraldo-Betancur et al. 1 proposed a multistep process: first, the fat from the cortical bovine bone is removed; then, use an alkaline process to remove the protein in which some ions that are not part of the inorganic phase are removed; the final step is the calcination that removes any organic material for T > 700  C. In this study, a physicochemical comparison between commercial and calcined samples was done, and the most important aspect found in their work was that commercial BIO-HAp contains organic materials. Another process to obtain BIO-HAp begins with the depro- teination followed by calcination in air 3 ; but some ions, present in fat and protein, could be present for the calcina- tion process. Calcium phosphate (CP)-based biomaterials are a group of compounds having Ca/P molar ratios in the range of Correspondence to: M. E. Rodriguez-Garcia; e-mail: marioga@fata.unam.mx Contract grant sponsor: Consejo Nacional de Ciencia y Tecnolog  ıa (CONACYT) V C 2015 WILEY PERIODICALS, INC. 339