Natural bone is a composite material composed of organic and inorganic components. The organic phase provides the elasticity and sclerenchyma, and inorganic phase provides rigidity, the mechanical support for human bone and the bioactivity, osteoconduction and osteoinduction. However, although bone is a thoroughly studied tissue with most of its biological and physical properties being well known, there is still an immense challenge when attempting to replicate these characteristics outside of living organisms. This is a consequence of the fact that bone regeneration is not only influenced by the biological and physical characteristics of scaffolds, but also by other aspects such as physical cues or signals that are generated by external factors. A strong interest in use of bioresorbable porous ceramics for biomedical applications appeared in the last 50 years as alternatives to permanent metallic implants. Nowadays this group of bioceramics is one of the most studied biomaterial, and specifically calcium phosphate (CaP) as hydroxyapatite (HA) are among the most common biodegradable materials currently employed in bone regeneration applications. However, if these synthetic 3D structures present promising properties in terms of bioactivity, they do not integrate the possibility of mimicking the dynamic bioelectrical signals present in vivo in the bone. Bioelectrical cues of natural living bone, such as, piezoelectricity, and ferroelectricity, etc. have been reported as some of the key factors in regulating metabolic activities like growth, structural remodeling as well as fracture healing. The emergence of organic conductive materials such as electronic conductive polymers as poly(3,4-ethylenedioxythiophene) (PEDOT) offers the opportunity to transform these synthetic and passive structures into 4D dynamic architectures which include electrical and mechanical cues.  The main objetives of this work is the development of new functional hybrid bioceramic-based materials for bone regeneration application, merging osteoregenerative properties of current bioceramic implants adding innovative functionalities as the electrical cues of conductive polymers.
Regarding the processing of this hybrid materials, despite the clear relevance of the properties of composite biomaterials both at a scientific level and in the bone graft market, even today their processing with innovative techniques as the Additive Manufacturing (AM) continues being an inconvenience that opens the possibility to the development of new processing routes. Among AM techniques, the fused filament fabrication (FFF) is one of the most simple and inexpensive techniques, however the main drawback is that traditionally is limited to thermoplastics polymers. FFF has been studied by the researcher group who has proposed an alternative colloidal processing technique patented to prepare a colloidal feedstock for FFF improving the load dispersion in a polymeric matrix. The successful printing of the hybrid composite using the colloidal chemistry allowed to stabilize and organize the HA and PEDOT phases without disturbing the printability of the composite. The possibility to print this new family of 4D biomaterials brings 3D printing closer to 4D printing and paves the way for a new understanding of the bone regeneration process.