# Personalized Bone Reconstruction and Regeneration in the Treatment of Craniosomiasis
## 2 Biomaterials and Tissue Engineering Approaches
### Tissue Engineering Strategies
In particular, a scaffold composed of a bioactive glass and a bioabsorbable 80:20 L-lactide:glycolide copolymer (PLGA 80) was developed and tested with both murine osteoblast cell lines expressing either the wild type or the mutated FGFR2 (namely, the FGFR2-C278F mutation found in Crouzon syndrome), and with human primary osteropgenitors from syndromic and nonsyndromic CS patients [111]. The composite scaffolds were able to support the homing, adhesion, and differentiation of both normal and mutated osteropgenitor cells, hence, proposed by the Authors as a suitable bone substitute to be implemented in the care of CS patients, undergoing extensive reconstructive surgery [111]. A revolutionizing approach has been introduced with the additive manufacturing techniques, which enable the precise and customized replication of the architecture of bone defects from medical image data (computerized tomography). In this way, the morphology of the synthetized scaffold perfectly matches the defect to be filled, hence facilitating its surgical implant and graft retention [112; 113]. A 3D scaffold based on polyethylene glycol (PEG) hydrogel-coated polycaprolactone (PCL) was developed using a novel computer-aided precision extrusion 3D printing system [114]. PCL shows excellent solubility, low melting point, biocompatibility and easy manufacturing [115; 116; 117; 118], while the PEG coating enables inhibiting osteoblast differentiation [119]. Indeed, in the cited study MC3T3E1(C4) calvarial cells adhered and differentiated into osteoblasts only on the uncoated portion of the scaffold [114]. Another group developed a new 3D-printed \(\beta\)-tricalcium phosphate (\(\beta\)-TCP) scaffold loaded with the osteogenic agent dipyridamole and evaluated the effects of this implants to support bone growing within bilateral calvarial defects in rabbit [120]. After the implantation, the Authors observed a volumetrically significant osteogenic regeneration of calvarial defects, with a favorable preservation of suture patency, at least in the short term [120]. The same group then reproduced the experiments in an immature rabbit model, evidencing a comparable responsiveness with respect to autologous bone grafts. They revealed a volumetrically and functionally significant osteogenic regeneration of calvarial defects, with a neoformed vascularized bone comparable to native tissue. Moreover, the Authors confirmed, using 3D morphometric facial surface analysis, that the 3D-printed \(\beta\)-TCP and dipyridamole scaffold does not lead to premature closure of sutures and allows to maintain the normal craniofacial growth [121]. Similar conclusions were reported by [PERSON] and coworkers [122], who tested the same scaffold in sheep calvarial defects, and observed no exuberant or ectopic bone formation, and no histologic evidence of inflammation within the defects, and higher osteogenesis in vivo. In the case of cranial defects characterized by irregular shape the use of injectable scaffolds is desirable, allowing to completely fill in the created void and to avoid invasive surgery [123], hence reducing the associated morbidities and costs [124]. The commonly used injectable scaffolds are based on hydrogels that consist of three-dimensional polymeric networks able to absorb a large amount of water, while maintaining their structural integrity. Hydrogels are widely used for many biomedical applications, such as scaffolds for tissue regeneration [125], cell encapsulation [126], drug delivery [127], and bioadhesives and biosealants [128]. Indeed, hydrogels can be designed to be responsive to environmental changes (e.g., temperature, pH, and ion concentration) and to encapsulate functional biomolecules and nanoparticles [129]. Shear thinning injectable hydrogels present several advantages over other systems, owing to their higher defect margin adaptability, easier handling and ability to be manually injected into deeper tissues.