In the rst case, for example, porous silk broin scaold showed a Targetmol’s Butylated hydroxyanisole hierarchical organization similar to the physiologic extracellular matrix characterized by high porosity and controlled pore sizes. In vivo tests using silk broin membrane in rabbit calvarial model, reported a complete bony union across the defects after weeks.To further improve the silk broin osteogenesis induction, other researchers covered the bulk structure with dierent materials.Instead, other researchers tested nanohydroxyapatitecoated silk substrates in rabbit model.They reported good scaold stability, cell attachments and new bone formation in four weeks. The hydroxyapatite inclusion has been also used to enhance the mechanical properties of the silk broin scaold, promoting mesenchymal stem cells dierentiation and bone regeneration. From both in vivo and in vitro studies, silk bres inclusion improves the compressive strength and reduces the setting time with no negative eect on the injectability and cytocompatibility. From a dierent point of view, other researchers focalized their studies on the silk usage as coating for composite scaold. Thanks to the enhanced scaold mechanical properties obtained by the multiple coatings, in vitro tests showed an increased proliferation and enhanced osteogenic dierentiation of human mesenchymal stem cells.In particular, among the three scaolds with increased number of coating, the X multiple coated scaolds showed optimal combination of structural and mechanical properties for bone regeneration.Even if far from native bone mechanical stiness, the X coating led to a relevant increase in compressive strength consistent with the trabecular bone one. In general, silk broin revealed a bone formation ecacy comparable with the commercial membranes that makes it one of the most promising material for medical application and in particular for bone regeneration. Among the natural polymers, the chitosan represents another valid candidate usable in bone tissue regeneration.Due to its charge, chitosan facilitates the interaction with several reasch Acacetin negatively charged molecules and membranes.Chitosan is characterized by cytocompatibility, biodegradability, nontoxicity, and mucoadhesivity. Moreover, it promotes osteoblasts growth and matrix mineralization.Unfortunately, as much as collagen, the limit in mechanical strength requires its combination with dierent materials. An explicative example is represented by a mixture of hydroxyapatitechitosan and gelatin that returned a compressive strength of these scaolds close to the lower limit of compressive strength in spongy bone. To further increase the osteoactivity, several studies tested the addition of the BMP chemical factor.The BMP release from the spheres improved the bone formation and the osseointegration in dog models, in four weeks. After weeks, in rabbit model, the scaold showed complete healing and recanalization of the bonemarrow cavity. Moreover, the chitosan is also suitable in drug delivery eld, as evident from both the in vitro and in vivo results.In particular, while adiposederived stem cells, cultured on matrix of poly nanohydroxyapatitealendronateloaded chitosan microspheres, showed good drug release and enhanced osteogenic dierentiation, in vivo results on rabbit models conrmed the osteogenic eect showing total bone repair within eight weeks. All these results conrmed the chitosan suitability for drug delivery application, suggesting its possible application in hydrogel form.In particular, the recent improvements in manufacturing techniques led the researches in testing the chitosan in the form of bioprinted hydrogel structure.