There is a need for spinal implants that have nonlinear stiffness to provide stabilization if the spine loses stiffness through injury, degeneration, or surgery. There is also a need for spinal implants to be customizable for individual needs, and to be small enough to be unobtrusive once implanted. Past and ongoing work that defines the effects of degeneration on the torque rotation curve of a functional spinal unit (FSU) were used to produce a spinal implant which could meet these requirements. This thesis proposes contact-aided inserts to be used with the FlexSuRe™ spinal implant to create a nonlinear stiffness. Moreover, different inserts can be used to create customized behaviors. An analytical model is introduced for insert design, and the model is verified using a finite element model and tests of physical prototypes both on a tensile tester and cadaveric testing on an in-house spine tester. Testing showed the inserts are capable of creating a non-linear force-deflection curve and it was observed that the device provided increased stiffness to a spinal segment in flexion-extension and lateral-bending. This thesis further proposes that the FlexSuRe™ spinal implant can be reduced in size by joining LET joint geometries in series in a serpentine nature. An optimization procedure was performed on the new geometry and feasible designs were identified. Moreover, due to maintaining LET joint geometry, the contact-aided insert could be implemented in conjunction with this new device geometry.