**Author details**

**5. Conclusions and future prospects**

186 Modern Technologies for Creating the Thin-film Systems and Coatings

proteins, mammalian cells and microorganisms.

overcome in the future.

to the desired application.

**Conflict of interest**

**Acknowledgements**

The authors declare no competing interests.

Doctoral School and Nucleus program—contract 4N/2016.

In this chapter, the new and rapidly emerging importance of smart-coating engineering was introduced, with focused attention on smart thermoresponsive pNIPAm interfaces obtained by matrix-assisted laser evaporation-based method. In this chapter, the thermoresponsivecoatings characteristics obtained by MAPLE-based method were emphasized along with some of the deposition parameters and used for biological assays *in vitro* implying BSA model

MAPLE as technique for obtaining smart polymeric coatings with specific characteristics envisaging biological application provides the advantage of tailoring not only the thickness of the pNIPAm layer, which is an important parameter in the cell attachment, but also the morphology of the deposited thin films for influencing protein and cells detachment and its increased stability in the fluid medium. Although significant progress has been achieved in the field of smart coatings based on stimuli-responsive materials, the materials and methods discussed within this chapter still have limitations in practical applications that need to be

Although the majority of the previous works in this field have used insoluble pNIPAm-based coatings, future research should be more directed toward biomimetic bio-interfaces, with integrated analysis platforms able to address the complexity of bio-environments accordingly

Considering the abovementioned advantages of the MAPLE method on tuning not only the surface characteristics and properties but also the chemical composition and film functionality, this approach could provide a new strategy to engineer multifunctional films for biological

The research leading to these results has received funding from the Romanian National Authority for Scientific Research (CNCS – UEFISCDI), under the projects PN-II-PT-PCCA-2013-4-1643, PNII- PT-PCCA-2013-4-199, PN-II-RU-TE-2014-4-2434, Romanian Academy Project 1/2015-2016 of the Institute of Biochemistry, University of Bucharest-Biology

studies, regenerative medicine, tissue engineering and industrial applications.

Laurentiu Rusen1 , Valentina Dinca1\*, Cosmin Mustaciosu2,3, Madalina Icriverzi4,5, Livia Elena Sima4 , Anca Bonciu1,6, Simona Brajnicov1,7, Natalia Mihailescu1 , Nicoleta Dumitrescu1,7, Alexandru I. Popovici8 , Anca Roseanu4 and Maria Dinescu1

\*Address all correspondence to: valentina.dinca@inflpr.ro

1 National Institute for Lasers, Plasma and Radiation Physics, Măgurele, Romania

2 Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering (IFIN-HH), Măgurele, Romania

3 Department of Science and Engineering of Oxide Materials and Nanomaterials, Faculty of Applied Chemistry and Materials Science, Politehnica University of Bucharest, Bucharest, Romania

4 Institute of Biochemistry of the Romanian Academy, Bucharest, Romania

5 Department of Biochemistry and Molecular Biology, Faculty of Biology, University of Bucharest, Bucharest, Romania

6 Faculty of Physics, University of Bucharest, Bucharest-Măgurele, Romania

7 Faculty of Mathematics and Natural Sciences, University of Craiova, Craiova, Romania

8 University of Medicine and Pharmacy Carol Davila, Bucharest, Romania

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#### **Controlled Rate Thermal Analysis (CRTA) as New Method to Control the Specific Surface in Hydroxyapatite Thin Coatings Controlled Rate Thermal Analysis (CRTA) as New Method to Control the Specific Surface in Hydroxyapatite Thin Coatings**

E. Peón, A. El hadad, F.R. García‐Galván, E. Peón, A. El hadad, F.R. García‐Galván, A. Jiménez‐Morales and J.C. Galván

A. Jiménez‐Morales and J.C. Galván

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/66468

#### **Abstract**

The control of the texture in synthetic hydroxyapatite ceramics had limited their appli‐ cation in the field of the materials for bone implantation, even more when it is used as a filling in cements and other formulations in orthopedic surgery. The present article shows preliminary results demonstrating the effectiveness of a modification of the con‐ trolled rate thermal analysis (CRTA), developed by J. Rouquerol, used for the prepara‐ tion of ceramic materials with controlled textural characteristics, during the formation of ceramic powders of synthetic hydroxyapatite at low temperatures. The thermal treat‐ ments of the hydroxyapatite were carried out in a device connected to a computer, to control temperature and pressure system, keeping the decomposition speed constant. Results, reported when preparing ceramic powders of hydroxyapatite at 300 and 850°C under controlled pressure, using synthetic hydroxyapatite with a Ca/P molar ratio equal to 1.64, were checked using IR spectroscopy and X‐ray diffraction, showed that the formed phase corresponds to that of crystalline hydroxyapatite, even at 300°C of maxi‐ mum temperature. Values of specific surface (BET) between 17 and 66 m<sup>2</sup> /g, with pore size in the range of 50–300 Å in both cases are obtained by N<sup>2</sup> absorption isotherms, when analyzing the isotherms of nitrogen absorption.

**Keywords:** hydroxyapatite, formation, thermal analysis to controlled speed, specific surface, pore size

and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, © 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

### **1. Introduction**

It is known the diversity of materials in use today as bone substitutes. Among them the hydroxyapatite (HA) has deserved special attention because of its excellent biocompatibil‐ ity, almost the same of that of natural bone. Most of commercial HA used in clinical and research applications are in solid and granulated forms with pore sizes between 100 and 150 μm. It has been demonstrated that such a range of pore dimension is appropriate to cause tissue growth in direct applications as bone substitutes [1–5]. HA ceramics and thin films can be synthesized by many methods [3, 4]. The conventional chemical precipitation method is the more extended method [6]. Following chemical precipitation, combination methods and the hydrothermal process are the next most well‐known methods of preparing HA [6–10]. Nevertheless, the scientific community is devoting great efforts looking for new alternative methods in order to obtain hydroxyapatite ceramics with improved microstructural and cor‐ rosion properties. In this way, laser‐assisted bioprinting and pulsed laser deposition tech‐ niques are very promising methods to obtain this kind of hydroxyapatite ceramics and thin films [11–14]. Also, alternating current electric field modified synthesis [15] and magnetron sputtering techniques (MST) [16, 17].

In this context, several methods of synthesis of HA with appropriately controlled textural characteristics as well as its use as a filler in formulations for systems in orthopedic sur‐ gery have been reported, however, the uniformity of the pore size is a problem unsolved up to now [18–20]. The sol‐gel synthesis of HA thin films and ceramics has attracted much attention because it offers a molecular‐level mixing of the calcium and phosphorus pre‐ cursors, which is capable of improving chemical homogeneity of the resulting HA to a significant extent, in comparison with conventional methods [18–20]. Fortunately, Vila et al*.* have obtained significant progress in recent years using the sol‐gel process [22]. In the context of the present work, they have obtained a bimodal porous process for nanocrystal‐ line hydroxyapatite (HA) coatings with pore sizes in the range of meso/macrometer scale deposited onto Ti6Al4V substrates by the sol‐gel method using nonionic surfactants as the porous former agent [22].

When phosphates are treated at several temperatures important changes occur in their properties, in particular, in their chemical contents and physicochemical characteristics, which permit an assessment of admixtures in the phosphates and the effects of substitution of the fundamental elements with others. But, on the other hand, the thermal treatment of the material poses a serious problem, due to difficulties to effectively control the gradients of pressure and temperature originated in different parts of the sample in most experi‐ ments [23–25].

The method for the thermal analysis developed by Rouquerol [26, 27], known as "control rate thermal analysis" (CRTA), has been tested in formulations for the control of textures in solids [28–30]. This method is very useful in cases of complex thermolysis usually lapses through superimposed, parallel or serial reactions. Thermal treatment at a controlled speed can allow the formation of homogeneous porosity and a homogeneous surface in its chemical composi‐ tion and distribution of defects.

In previous studies, we have prepared organic‐inorganic hybrid sol‐gel films with nanocrys‐ talline hydroxyapatite as a filler and triethylphosphite (TEP)as a network forming agent to enhance the *in vitro* biocompatibility and corrosion protection of these coatings deposited on Ti6Al4V alloys [31, 32]. Now, the purpose of this new study is to apply the CRTA technique to crystallize synthetic HA with a controlled specific surface and homogeneous distribution of pores, appropriate to be used in bone implantation and other formulations for orthopedic surgery. These parameters may be very important in different situations. For example, when HA is used as a filler in cement‐based composites, the superficial specific area must be small because a frail material may be obtained due to the presence of microfracture centers when are too big. Taking into account thermogravimetric analysis results, several pressures and temperatures of control were tested in the preparation of ceramic powders.
