BioSpring™:  Promoting Orthopedic Healing Through Small-Scale Spring Implantables

Abstract

Rigid spinal implants are commonly used to treat pediatric deformities, but are poorly suited to ongoing growth, resulting in asymmetric bone development and poor tissue integration. A clinical need exists for orthopedic implants that correct deformities while accommodating growth without repeat intervention. The BioSpring™ addresses this need with a compact, biocompatible spring embedded in a segmented spinal rod system, designed to provide high elastic compressibility to passively modulate force over time. This internal element enables surgeons to apply an initial distraction force that gradually relaxes as the spine grows. By expanding the range of elastic motion delivering consistent force, the BioSpring supports bone growth and reduces reliance on rigid fixation. Its simple cylindrical geometry minimizes slippage, shear, and stiffness, enabling smooth, self-regulating force modulation without active adjustment. We selected candidate polymers based on biocompatibility, tunable elasticity, and scalable fabrication. Mechanical testing confirmed the device’s ability to deliver target distraction forces within both functional and peak loading ranges, consistent force response, and limited diametric deformation under load. Additional assessments, including swelling ratio and cell viability analyses, demonstrated stability in physiological environments and initial biocompatibility. Device-level testing showed that the BioSpring could replicate the desired force profile of a stainless steel spring while eliminating common mechanical drawbacks. These findings establish proof of concept for the BioSpring: a compact, low-cost, and removable implant that passively modulates force within orthopedic fixation systems. It offers a simple, manufacturable solution for growth-responsive fixation with translational potential in pediatric spinal correction and other dynamic musculoskeletal applications.

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