Purpose <p>Tendon lengthening is a common lower limb surgical procedure in paediatric orthopaedics and deformity correction. Healing of a lengthened tendon is typically supported by casting and unloading of the operated limb. Although tendon rupture or overcorrection may adversely affect surgical outcomes, few studies have examined surgical means of improving post-operative stability of the tendon. We aim to evaluate a novel method for augmenting Z-Plasty tendon lengthening as a first step to clinical translation.</p> Methods <p>In this experimental ex vivo study, we employed a bovine flexor tendon model (<i>n</i> = 18) to examine a novel mechanical augmentation method after tendon lengthening by Z-plasty. Conventional surgical suturing of the imposed Z-plasty (<i>n</i> = 6) and an experimental group (<i>n</i> = 6), in which additional augmentation was performed by interlocking fibres of a biomaterial scaffold to the underlying tendon using a novel micro-needling technique, were compared to native tendons (<i>n</i> = 6).</p> Results <p>The needle interlocked scaffold successfully augmented the suture repair, showing more than doubled ultimate failure force compared to controls (482 ± 107 N vs. 206 ± 37 N, <i>p</i> &lt; 0.01), and more than 1.5-fold repair stiffness (41 ± 7 N/mm vs. 26 ± 9 N/mm, <i>p</i> &lt; 0.01). </p> Conclusion <p>We conclude that the use of an interpenetrating biomaterial scaffold represents a promising new approach for improving biomechanical tendon properties, which may have an implication on the stability of tendon suture, lengthening and tendon transfer procedures as well as on post-operative management and earlier mobilization.</p>