Boutinguiza et al. Nanoscale Research Letters 2011, 6:255 http://www.nanoscalereslett.com/content/6/1/255 Page 4 of 5 Figure 4 HRTEM micrograph showing amorphous nanoparticles and submicronic particles obtained from fish bones by laser ablation in water using CW laser. Laser irradiance: 6 × 105 W/cm2. amorphous, while the obtained in the former case are crystalline; other authors have obtained crystalline hydro- xylapatite particles using pulsed laser ablation at higher irradiance [24,25]. Concerning the composition, crystalline particles obtained by the use of pulsed laser still preserve the com- position of precursor material, although some of them undergo transformation phase from precursor HA to b- TCP promoted by longer pulse and high temperature. The effect of laser irradiation is expected to induce struc- tural changes in material precursor constituted by HA due to the elevated temperature. Investigations in enamel irradiated with laser reported the formation of traces of a-TCP phase [26] when CO2 laser is used and the pre- sence of traces of a-TCP and b-TCP when the source is Nd:YAG laser [27], which are in accordance with the Figure 5 SEM micrograph of micrometric particles obtained from fish bones by laser ablation in water using CW laser. Laser irradiance: 6 × 105 W/cm2. obtained results. The amorphous particles obtained when using CW laser are calcium phosphate compounds, prob- ably formed by melting and rapid solidification due the low irradiance delivered by the CW laser. Conclusions In summary, we have been obtained HA and b-TCP nanoparticles by the use of laser ablation of targets from fish bones suspended in de-ionized water. The particles were obtained using pulsed as well as continuous wave laser. The use of the first one promotes the crystalline nanoparticles formation due to the high irradiance, while the latter one favors the formation of amorphous particles. The formation mechanism of particles can be attributed to explosive ejection. Abbreviations CW: continuous wave; SAED: selected area electron diffraction; SEM: scanning electron microscopy; TEM: transmission electron microscopy; XRD: X-ray diffraction; XRF: X-ray fluorescence. Acknowledgements This work was partially supported by the European Union program POCTEP project (0330_IBEROMARE_1_P), the Spanish government (CICYT/FEDER MAT2006-10481) and by Xunta de Galicia (INCITE08PXIB303225PR, INCITE09E2R303103ES). The authors gratefully appreciate the technical assistance of the CACTI staff (Análisis Instrumental and Microscopía Electrónica). Authors’ contributions MB and JP conceived the work. MB and RC performed the experiments with the Nd:YAG laser. MB and AR performed the experiments with the fiber laser. Characterization of materials was carried out by FL. JP directed the work and wrote the draft paper. All authors contributed to the interpretation of results, discussion and read, corrected and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Received: 5 November 2010 Accepted: 25 March 2011 Published: 25 March 2011 References 1. Wang W, Shi D, Lian J, Liu G, Wang L, Ewing RC: Luminescent hydroxylapatite nanoparticles by surface functionalization. Appl Phys Lett 2006, 89:183106. 2. Aronov D, Rosenman G, Karlov A, Shashkin A: Wettability patterning of hydroxyapatite nanobioceramics induced by surface potential modification. Appl Phys Lett 2006, 88:163906. 3. Xu HHK, Weir MD, Sun L, Takagi S, Chow LC: Effects of calcium phosphate nanoparticles on Ca-PO4 composite. J Dent Res 2007, 86:378-383. 4. Barinov SM, Baschenko YV: Application of ceramic composites as implants: result and problem. In Bioceramics and the human body. Edited by: Krajewski A. UK: Elsevier Science Publishers; 1992:206-210. 5. Koshino T, Murase T, Takagi T, Saito T: New bone formation around porous hydroxyapatite wedge implanted in opening wedge high tibial osteotomy in patients with osteoarthritis. Biomaterials 2001, 22:1579-1582. 6. Schneider OD, Loher S, Brunner TJ, Uebersax L, Simonet M, Grass RN, Merkle HP, Stark WJ: Cotton wool-like nanocomposite biomaterials prepared by electrospinning: in vitro bioactivity and osteogenic differentiation of human mesenchymal stem cells. J Biomed Mater Res B Appl Biomater 2007, 84B:350-362. 7. Roohani-Esfahani SI, Nouri-Khorasani S, Lu Z, Appleyard R, Zreiqat H: The influence hydroxyapatite nanoparticle shape and size on the properties