Well-ordered biphasic calcium phosphate–alginate scaffolds fabricated by multi-channel 3D plotting under mild conditions

Abstract

Herein, we present a new type of biphasic organic–inorganic scaffold, which can be fabricated by multi-channel 3D plotting under mild conditions based on a highly concentrated alginate paste and a ready-to-use calcium phosphate cement (CPC) for bone and osteochondral tissue engineering. The structures of scaffolds were characterised by light and scanning electron microscopy (SEM). Results indicated that the concentrated alginate and CPC pastes had comparable plotting consistency, and therefore could be combined in one (biphasic) scaffold by applying predesigned plotting parameters. After crosslinking of alginate and setting of CPC, the biphasic scaffold obtained mechanical and structural stability. Mechanical test data revealed that biphasic CPC–alginate scaffolds had significantly increased compressive strength and modulus compared to pure alginate as well as mixed calcium phosphate (CaP)–alginate scaffolds in a wet state and improved strength and toughness compared to pure CPC scaffolds in both dry and wet conditions. Culture of human mesenchymal stem cells (hMSCs) on these scaffolds over 3 weeks demonstrated the good cytocompatibility of the selected materials. Because of the mild preparation conditions, bovine serum albumin (BSA) as a model protein was loaded in alginate and CPC pastes prior to plotting with high loading efficiency. Release studies in vitro showed that BSA released much faster from alginate strands than from CPC strands, which might allow amount-controlled protein release from biphasic CPC–alginate scaffolds. Furthermore, an upgraded bipartite osteochondral scaffold consisting of an alginate part for chondral and a biphasic CPC–alginate part for bony repair was fabricated based on this technique. This scaffold showed a strong organic–inorganic interface binding due to interlocking and crosslinking of the alginate strands.