Biomechanical study of an additively manufactured NiTi patient-specific device for the treatment of craniosynostosis

Craniosynostosis, a pathological condition in which the fusion of cranial sutures prevents the normal development of the skull, may be treated by spring assisted surgery. The present work aims to employ additive manufacturing (AM) for the production of a novel NiTi spring distractor able to provide adequate and constant force during the treatment of nonsyndromic craniosynostosis. The use of AM allows to design patient-matched devices fitting the specific skull curvature of the new-borns, while the pseudoelastic behavior of NiTi can offer a constant force over a large deformation. The proposed novel device consists of three pairs of unit cells, the shape of which was optimised using finite element analysis. Thereafter, patient-specific NiTi springs were produced by laser powder bed fusion and the functional behaviour of the material was assessed by differential scanning calorimetry (DSC) and tensile testing. The AMed material reached as high relative density as 99.6 %. The AMed spring prototype was tested at 37 °C, exhibiting a pseudoelastic response at 350 MPa up to 4 % in strain: this functional behavior depended on the austenitic phase, that was detected at body temperature by the DSC scan. The proposed prototype paves the way for the design of a first AMed NiTi medical device for the treatment of unicoronal craniosynostosis, and could be further extended to other minimally invasive treatments requiring bone remodelling.