## 2 Materials and Methods  
Commercially pure titanium (cp Ti) powder produced by a hydrogenation/dehydrogeneration process has been used as the starting powder (SE-JONG Materials Co. Ltd., Incheon, Korea). Its chemical composition is equivalent to cp Ti ASTM F67-00 Grade IV. Two different space holders have been employed: sodium chloride, NaCl (Panreac Quimica S.A.U., Barcelona, Spain, purity > 99.5%) and ammonium bicarbonate, NH\({}_{4}\)HCO\({}_{3}\), (Cymit Quimica S.L., Barcelona, Spain, with a purity of 99.9%). The space-holder granules, NaCl and NH\({}_{4}\)HCO\({}_{3}\), with a large particle size (according to Table 1) were selected to promote a higher degree of interconnectivity of the pores, and a high average size of space holder (>100 \(\upmu\)m) would fulfil the requirements to ensure the bone ingrowth. In order to obtain the green bodies, conventional PM at low pressure (including its particular limits: loose sintering, LS) and space-holder techniques have been implemented. In an LS route, the metal powder has been poured and vibrated into a cylindrical mould of alumina for 2 min, which has then been heated to the sintering temperature chosen (1000 \({}^{\circ}\)C and 1200 \({}^{\circ}\)C) under high vacuum (\(\sim\)10\({}^{-5}\) mbar). In the space-holder technique: (1) the blends of cp Ti powder and space-holder particles [cp Ti+NaCl or cp Ti + NH\({}_{4}\)HCO\({}_{3}\)], only powder mixtures with 30 and 40 volume percent of space holders were prepared in a Turbula(r) T2C, blended for 40 min to ensure good homogenization; (2) afterwards, the compaction of the mixture takes place (800 MPa, pressure defined according to the compressibility curve of the material and the results of a previous work [26]), (3) subsequently, regarding to the space holder used, the elimination step has been performed. The NH\({}_{4}\)HCO\({}_{3}\) is thermally removed (60 \({}^{\circ}\)C + 110 \({}^{\circ}\)C; both stages of the thermal treatment are carried out for 10-12 h and at low vacuum conditions 10\({}^{-2}\) mbar) [26], while the salt has dissolved in distilled water (temperature between 50 and 60 \({}^{\circ}\)C, without agitation and during 4-5 immersion cycles) [19]. Sintering was carried out under high vacuum in a CARBOLYTE STF 15/75/450 ceramic furnace with a horizontal tube (2 h at 1250 \({}^{\circ}\)C under high vacuum conditions: \(\sim\)10\({}^{-5}\) mbar) [26]. The manufacturing parameters have been stablished in order to obtain mechanical properties (Young's modulus, \(E\), and yield strength, \(\sigma_{y}\)) similar to the cortical bone. The powder mass has been calculated to produce specimens with fit dimensions for compression tests (height/diameter = 0.8). The compaction stage in conventional PM and space-holder technique has been carried out in an INSTRON 5505 machine (Instron, Massachusetts, United State). Density measurement has been performed out through the Archimedes' method with distilled water impregnation, due to its experimental simplicity and reasonable reliability (ASTM C373-88). Total porosity \(P\)(Arch) and interconnected porosity (\(Pi\)) have been calculated from the density measurements. For the image analysis, sectioned parts have been prepared by a sequence of conventional metallographic steps (resin mounting and grinding) followed by a mechanic-chemical polishing with magnesium oxide and hydrogen peroxide. The porosity evaluation by image analysis has been performed by using an optical microscope Nikon Epiphot (Nikon, Tokyo, Japan) coupled with a camera Jenoptik Progres C3 (Jenoptik, Jena, Germany), and the software Image-Pro Plus 6.2, Mediacibernetic, Bethesda, MD, USA. Image analysis has been evaluated with 10 pictures of 5\(\times\) and 20\(\times\) for each processing condition.