Hydroxyapatite (HAp) particles with very different surface charges and compositions (i.e. different Ca/P and CO₃ ²⁻/PO₄ ³⁻ ratios) have been obtained by varying the experimental conditions used during the chemical precipitation process. The DNA adsorption capacity and protection imparted against the attack of nucleases of HAp particles have been proved to depend on the surface charge while the buffering capacity is affected by the chemical composition. On the basis of both the surface charge and the crystallinity, the predominant planes at the surfaces of HAp particles have been identified. Atomistic molecular dynamics simulations of surfaces constructed with these planes (i.e. (001) and the two terminations of (010)) with the adsorbed B-DNA double helix have been performed to get microscopic understanding of the influence of the mineral in the biomolecule structure and the interaction energies. The results indicate that the DNA secondary structure is perfectly preserved on the (001) surface, this stability being accompanied by an attractive binding energy. In contrast, the (010) surface with PO₄ ³⁻, OH⁻ and Ca²⁺ ions in the termination induces significant local and global deformations in the double helix, repulsive OH⁻(HAp)⋯PO₄ ³⁻ (DNA) interactions provoking the desorption of the biomolecule. Finally, although the termination of the (010) surface with PO₄ ³⁻ and Ca²⁺ ions also deforms the double helix, it forms very strong attractive interactions with the biomolecule. These binding characteristics are in excellent agreement with the DNA adsorption and protection abilities experimentally determined for the HAp samples. Finally, the surface charge has been found less decisive than the chemical composition in the efficacy of the transfection process.

Permanently polarized hydroxyapatite (HAp) particles have been prepared by applying a constant DC of 500 V at 1000 °C for 1 h to the sintered mineral. This process causes important chemical changes, as the formation of OH⁻defects (vacancies), the disappearance of hydrogenophosphate ions at the mineral surface layer, and structural variations reflected by the increment of the crystallinity. As a consequence, the electrochemical properties and electrical conductivity of the polarized mineral increase noticeably compared with as‐prepared and sintered samples. Moreover, these increments remain practically unaltered after several months. In addition, permanent polarization favours significantly the ability of HAp to adsorb inorganic bioadsorbates in comparison with as‐prepared and sintered samples. The adsorbates cause a significant increment of the electrochemical stability and electrical conductivity with respect to bare polarized HAp, which may have many implications for biomedical applications of permanently polarized HAp.

The adsorption of orthophosphate, pyrophosphate, triphosphate and a trisphosphonate onto hydroxyapatite has been examined using experiments and quantum mechanical calculations. Adsorption studies with FTIR and X-ray photoelectron spectroscopies have been performed considering both crystalline hydroxyapatite (HAp) and amorphous calcium phosphate particles, which were specifically prepared and characterized for this purpose. Density functional theory (DFT) calculations have been carried out considering the (100) and (001) surfaces of HAp, which were represented using 1 × 2 × 2 and 3 × 3 × 1 slab models, respectively. The adsorption of phosphate onto the two crystallographic surfaces is very much favored from an energetic point of view, which is fully consistent with current interpretations of the HAp growing process. The structures calculated for the adsorption of pyrophosphate and triphosphate evidence that this process is easier for the latter than for the former. Thus, the adsorption of pyrophosphate is severely limited by the surface geometry while the flexibility of triphosphate allows transforming repulsive electrostatic interactions into molecular strain. On the other hand, calculations predict that the trisphosphonate only adsorbs onto the (001) surface of HAp. Theoretical predictions are fully consistent with experimental data. Thus, comparison of DFT results and spectroscopic data suggests that the experimental conditions used to prepare HAp particles promote the predominance of the (100) surface. Accordingly, experimental identification of the adsorption of trisphosphonate onto such crystalline particles is unclear while the adsorption of pyrophosphate and triphosphate is clearly observed.

Image convolution operations in digital computer systems are usually very expensive operations in terms of resource consumption (processor resources and processing time) for an efficient Real-Time application. In these scenarios the visual information is divided into frames and each one has to be completely processed before the next frame arrives in order to warranty the real-time. A spike-based philosophy for computing convolutions based on the neuro-inspired Address-Event-Representation (AER) is achieving high performances. In this paper we present two FPGA implementations of AER-based convolution processors for relatively small Xilinx FPGAs (Spartan-II 200 and Spartan-3 400), which process 64×64 images with 11×11 convolution kernels. The maximum equivalent operation rate that can be reached is 163.51 MOPS for 11×11 kernels, in a Xilinx Spartan 3 400 FPGA with a 50MHz clock. Formulations, hardware architecture, operation examples and performance comparison with frame-based convolution processors are presented and discussed.