## 2 Materials and Methods
### Experimental Tests  
The experimental tests are composed of mechanical tests and strain measurements of the sample. The former consisted of applying both longitudinal compressive (\(\mathrm{F_{L}}\)) and transversal compressive (\(\mathrm{F_{T}}\)) forces to the prepared sample (Figure 2a). The \(\mathrm{F_{L}}\) was applied in the direction of the larger side of the specimen by means of a push-pull testing machine (KEELAVITE(r) 50 kN) (Figure 2b). This machine consists of a hydraulic actuator directed by an automatic control (MTS 407(r)), which allows to apply loads up to 50 kN (Figure 2b). The longitudinal system is equipped with an [PERSON] 20 Klbf load cell (model: 3174-20K) for force measurement. The piston of the machine, threaded to the inferior end of the sample, compresses the sample, whose superior end is threaded to the fixed frame. In addition, a complementary device [55] allows to apply transversal compressive force (\(\mathrm{F_{T}}\)) in the mid-section of the specimen as shown in Figure 2a. This device consists of a linear screw type actuator controlled manually [55], in which forces up to 1500 N are measured with a load cell connected in series (Interface 2 Klbf, model: WMC-2000). Figure 1: (**a**) Horse femur after extracting a piece from the mid diaphysis for machining; (**b**) one of the four specimens after milling; (**c**) embedding process; (**d**) spray speckle for digital image correlation strain measurements. A total of eight different loading states were simulated for transversal and longitudinal force values 0, 250 and 500 N as indicated in Table 1. For each loading state, transversal and longitudinal loads were applied from 0 to the desired level of load in static conditions. The load was applied very slowly, below 10 N/s. During load application, the strain in the region of interest was measured as described below. During the 6 h required to complete the test, from the moment that the samples are taken out of the freezer, the sample was not hydrated. To determine the strain of the bone sample during the biaxial test, an optical non-contact system (Limess(r), Q400; Vic Snap Image Acquisition(r), version 2010, build 902; and Vic2D 2009(r), version 2009.1.0, build 345M) was used (Figure 3a). This system allows to obtain the history of deformations in real time on the outer surface of the sample. Strain measurements were performed in the \(10\times 10\) mm region of interest located in the middle of the sample (see Figure 2a). The resolution of the system allows to measure strains in points with a separation of 57 \(\upmu\)m within the region of interest. It means \begin{table}
\begin{tabular}{c c c c} \hline \hline \(\mathbf{F_{L}}\) [N] & \(\mathbf{F_{T}}\) [N] & \(\epsilon_{L}\)\(\times\)**10\({}^{-3}\) [\%]** & \(\epsilon_{T}\)\(\times\)**10\({}^{-3}\) [\%]** \\ \hline
0 & \(-\)250 & 5.8 & \(-\)17.6 \\
0 & \(-\)500 & 21.4 & \(-\)35.9 \\ \(-\)250 & 0 & \(-\)16.5 & 9.5 \\ \(-\)250 & \(-\)250 & \(-\)9.8 & \(-\)8.8 \\ \(-\)250 & \(-\)500 & 0.55 & \(-\)27.7 \\ \(-\)500 & 0 & \(-\)36.3 & 16.8 \\ \(-\)500 & \(-\)250 & \(-\)28.2 & \(-\)0.025 \\ \(-\)500 & \(-\)500 & \(-\)17.9 & \(-\)20.3 \\ \hline \hline \end{tabular} Note: Table notes. \(\mathbf{F_{L}}\): Overall longitudinal force. \(\mathbf{F_{T}}\): Overall transversal force. \(\epsilon_{L}\) : Averaged longitudinal component of the strain tensor. \(\epsilon_{T}\) : Averaged transversal component of the strain tensor.  
\end{table} 
Table 1: Macroscopic results of the mechanical tests. Figure 2: (a) Scheme of the loads applied to the specimen, longitudinal forces, \(\mathbf{F_{L}}\), and transversal forces, \(\mathbf{F_{T}}\); (b) picture of the system during experiments. The push-pull testing machine may be observed in the back ground. The piston and the load cell above, attached to the green frame, can be observed. The system that applies the transversal load can be seen below, while the DIC camera appears in front. that the analysed region generates a strain field of around 34,000 points.