**7. Conclusions and future perspectives**

The progressive population aging and the younger people modern behaviors, which expose to serious injuries and traumas, are concerns of large and continuously increasing socioeconomic impact. The continual advances in materials science and nanotechnology allowed great progress in biomedical device development for bone regeneration. Nevertheless, the development of bio-devices mimicking biological tissue structure and composition with high complexity and load-bearing properties, such as extended bone and osteochondral parts or segmental bones, still presents serious limitations. In fact, the related clinical needs remain unmet because of the absence of well-established regenerative devices for such applications. Many possibilities for solving these concerns are offered by the recent advances in materials science: the new-generation smart multifunctional device development could

*Bio-Inspired Technology*

mances [8].

The main goal is the implantation of osteoinducting and osteoconducting scaffolds with spatially organized macroporosity and mechanical strength sufficient for early in vivo loading upon implantation and elastic properties close to those of the bone. This may enable scaffolds to respond to the biomechanical loads and activate mechano-transduction mechanisms, yielding remodeling and formation of new functional bone [90]. The complex structure of bones, hierarchically organized from the nano- to the macro-scale, and the interaction taking place across all levels of organization are the reasons of the outstanding mechanical performances of bones. For this reason, long-bone regeneration should be assisted by scaffolds endowed with bone-like composition and similar structural complexity; however, the common manufacturing methods do not produce mechanically resistant scaffolds with the required hierarchical pore organization and bioactivity. The chemical biomimesis in scaffolds for long-bone regeneration is influenced by the mechanical strength of HA-based materials. There are several studies about scaffolds based on composite materials, making use of strong bioactive or bioinert phases [36, 37] that were dispersed in a calcium-phosphate matrix. However, the limitation in the

achievement of hierarchically organized structures still remains [8].

ized by a biomimetic hierarchical structure [20].

*Scheme of the multi-scale structure of wood and bone tissue.*

This problem can reside in nature, so the attention of scientists has been moved to find and observing complex morphologies that exist in nature, and then try to reproduce them. In particular, the ligneous structures strongly resemble bones in their structural organization and morphology which affect the mechanical perfor-

Like bone, wood can be considered as a cellular material at the scale of hundred micrometers to centimeters (**Figure 4**). At the cell level, the mechanical properties are governed by the shape and diameter of the cell cross section, as well as by the thickness of the cell wall. In particular, the apparent density of wood, which in turn is a determining factor for the performance of lightweight structures, is directly related to the ratio of cell wall thickness to cell diameter. The particular hierarchical architecture of the cellular microstructure gives wood an exceptional combination of high stiffness, toughness, and strength at low density [91]. The alternation of channel-like porous and fiber bundle areas makes the wood an elective material to be used as a template in the preparation of a new bone substitute that is character-

**44**

**Figure 4.**

be enabled by new fabrication approaches that get inspired from the multitude of outstanding biological structures and phenomena. The preliminary steps that have already been taken in this direction are very promising, and the development of bioinspired materials is rapidly becoming a priority to achieve nanotechnological solutions facing critical societal needs.
