## 1 Introduction  
The three middle ear ossicles (malleus, incus, and stapes), which are the smallest bones of the human body, are organized as a sound-conducting chain that connects the tympan to the cochlea [1]. Trauma, cancer surgery, or congenital malformations may lead to partial hear loss or total deafness, requiring ossicles replacement. Due to the highly personalized anatomy of these ossicles and of the surrounding tissues, finding cadaveric (or, even less available, from living donors) replacements to match them for heterologous transplantation is very difficult [2]. Besides using ossicles from humans, the most widely utilized method to restore conductive hearing is currently their total or partial replacement with a biocompatible metal implant [3], the most commonly used being titanium implants [4]. However, the choices of commercial prosthesis for ossicle replacement are limited to a few standard shapes and sizes, determined by the manufacturers.  
Besides metal bars, ceramic bridges have also been considered, showing good initial benefits but a high failure rate [5]. However, there is substantial interest in working with these materials, given that albeit fragile, these are mechanically quite sturdy when compact. More importantly, porous ceramics could be incorporated into osteogenic multi-material constructs and even potentially transformed in vitro into bone-like structures [6].  
With the advent of additive manufacturing and its medical applications, new avenues have been opened to solve the issue of ossicles availability, both for prosthetics (mainly by 3D printing) and for bio-implantology (by 3D bioprinting). Yet, surprisingly, the progress on these lines has been slow and limited so far to the early steps of high-resolution image acquisition [7] and CAD model generation [8], as well as to additive manufacturing with plastic materials, which are useful only for modeling or surgical planning [9].  
Here, we sought to develop more realistic aspects of the additive manufacturing technology by testing the available design and implementation options using biomaterials that are likely to be of value for next-generation biological, personalized otic implants. The current study is among the first ones to explore the use of 3D printing for the generation of ossicle models from biologically relevant materials such as osteogenic ceramics and hydrogels for bioprinting (bioinks), with the potential to be used in hearing restoration applications.  
This possibility was created by the availability of a printable (or 'plottable') calcium phosphate/hydroxyapatite cement (CPC) paste, also called 'Osteoink' [6], whose composition is close to that of human bone minerals [10]. Osteoink was specifically designed for 3D printers [11] and thus has been already assessed for osteo-inductive properties in vivo, when printed as a porous structure [6].  
The goal of this study was to assess the suitability of solid (CPC ceramic) and soft (alginate-based) biomaterials for the 3D printing of anatomically realistic models of human ear ossicles. To the best of our knowledge, work in this field has not been published yet, although there are precedents of creating implantable ceramic bridges for ossicle chain repair [5] or printing ossicle models with plastic materials [9].