# Personalized Bone Reconstruction and Regeneration in the Treatment of Craniosomiasis
## 2 Biomaterials and Tissue Engineering Approaches
### Tissue Engineering Strategies
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Commercial Fixation System** & **Composition** &
\begin{tabular}{c} **Post-Operative** \\ **Infection Rate** \\ \end{tabular} & **References** \\ \hline \multirow{2}{*}{LactoSorb®} & 82\% poly-l-lactic acid (PLLA), & \multirow{2}{*}{0–3\%} & [54; 55; 56; 57; 58; 59; 60; 61; 62; 73] \\  & 18\% polyglycolic acid (PGA) & & \\ Biosorb® PDX & 80\% PLLA 20\% PGA & 4\% & [63] \\ PolyMax® RAPID & 85\% PLLA, 15\% PGA & None & [74] \\  & Trimethylene carbonate, PLA, & & \\ Inion® CPS baby & PDLLA, Polyglycolide & 0–1.6\% & [65; 66; 67; 68] \\ RapidSorb® & 85\% PLLA, 15\% PGA & 0–1.4\% & [75; 76] \\ MacroPore® FRP & 85\% PLLA, 15\% PGA & 2–4\% & [55; 64] \\ Resorb-X® & 50\% PLLA, 50\% PDLLA & 0–2.6\% & [77; 78] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Commercial rigid fixation systems based on biodegradable materials. size cranial defects in this age group is actually still lacking. The cranial repair in these cases require a careful approach considering the need to accommodate the still growing brain in order to avoid secondary constriction and a failure of the craniplasty. Exchange cranioplasty may represent an effective option. This consists of harvesting a graft from the unaffected skull to repair the contralateral cranial defect, and relying on the spontaneous healing of the donor site if the dura mater and periosteum are well preserved [81, 95]. Tissue engineering has been introduced in CS care, to cope with the severe drawbacks associated with the use of \"non-growing\", non-biological metallic and bio-ceramic-based implants, yielding poor and unsatisfactory long-term results in paediatric patients [46]. The tissue engineering approaches involve the combination of three main components, i.e., scaffold, biomolecules (e.g., growth factors and bone-inducing agents, drugs, such as antimicrobials, etc. ), and cells, in order to fulfil the key requirements of an ideal bone regenerative strategy: osteoconduction, osteoinduction, and osteogenesis [96]. The design and development of temporary biomimetic scaffolds is pivotal in determining the success of a tissue engineering approach. The ideal scaffold should be biodegradable, able to promote the bone regeneration by supporting cell colonization and growth (osteoconduction), and/or to induce stem cells to differentiate towards the osteoblast phenotype (osteoinduction). Hence, two different strategies can be followed: (i) a conductive approach based on the use of passive three-dimensional supports on which cells may attach, migrate, and differentiate; (ii) an inductive approach, based on the use of active supports, loaded with bioactive signals, aimed at promoting cell migration and guiding the cell responsiveness. To these aims, the designed scaffolds have to satisfy multiple requirements, in terms of chemical-physical properties (composition, microstructure, mechanical properties, bio-desorption degree) and biological features (biocompatibility, ability to promote cellular and vascular colonization, angiogenesis, etc.) [97]. Biodegradable materials, both natural and synthetic, provide many advantages over metals and other non-degradable materials commonly used in maxillofacial surgery, avoiding the related disadvantages, i.e., growth disturbance [98], plate migration [99], the need for subsequent removal [100], long-term palpability and thermal sensitivity [101], and compatibility with imaging investigations. However, natural polymers, e.g., collagen, alginate, agarose, chitosan, and fibrin, present poor mechanical behaviour and inconsistent degradation rates, whereas the synthetic polymers, i.e., polycarbonates, polyesters, polyorthoesters, polyanhydrides, polyurethanes, and polyphophagranes [102], are characterized by higher mechanical strength. In detail, the physical (i.e., mechanical and degradation) properties of polymers strongly depend on their molecular weight, crystallinity degree, physical aging time, test, and environmental conditions.