Laminated object manufacturing of bioactive ceramic implants

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Laminated object manufacturing of resorbable calcium phosphate ceramics for bone replacement and osteosynthesis implants will be explored. Multilayer implant structures of variable shape will be build up from ceramic tapes consisiting either of single phase ß-TCP (Ca3(PO4)2) or biphasic mixtures (BCP) of ß-TCP and HAP (Ca5(PO4)OH). Loading capacity of osteosynthesis implant devices will be improved by generation of compression surface stresses. Either a single surface layer sandwich or a gradient layer structure design both with an outer surface layer having a lower thermal expansion compared to the inner core layers will give rise for surface residual stresses upon cooling from sintering temperature. Tailoring of the thermal expansion behaviour will be envisaged by two approaches: i) partial substitution of Mg2+ for Ca2+ in the ß-TCP crystal lattice causes a reduction of thermal expansion coefficient from 20 x 10-6/°C at 0 wt. % Mg to 9 x 10-6/°C at 4.5 wt. % Mg. ii) biphasic mix-tures of ß-TCP with increasing amount of HAP show a decreasing thermal expansion co-efficient (HAP: 10 x 10-6 /°C) and an increasing Young´s modulus (HAP 80 GPa – TCP 30 GPa). A demonstrator device of a resorbable implant (osteosynthesis plate) will be manufactured. The resulting mechanical behaviour of multilayer implant design reinforced by surface stresses will be analysed and compared to residual stress free design of a homogeneous implant structure.