In vivo testing of biphasic scaffold design parameters for integrative tendon repair

Abstract

Event Abstract Back to Event In vivo testing of biphasic scaffold design parameters for integrative tendon repair Xinzhi Zhang1*, Jon-Michael E. Caldwell1, Nicole H. Goldhaber1, Yelena Akelina1, Stephen B. Doty2*, Louis J. Soslowsky3, William N. Levine1* and Helen H. Lu1* 1 Columbia University, United States 2 Hospital for Special Surgery, United States 3 University of Pennsylvania, United States Introduction: Functional tendon-bone integration post rotator cuff repair remains a clinical challenge. To regenerate the tendon-bone interface, which consists of non-calcified and calcified fibrocartilage[1]-[3], a biphasic, fiber-based scaffold of poly lactide-co-glycolide (PLGA, Phase A) atop a layer of PLGA-hydroxyapatite (PLGA-HA, Phase B) has been developed[4]. The objective of this study is to determine the effect of scaffold design parameters such as fiber alignment, diameter, and composition on interface regeneration in a rat rotator cuff repair model. Methods: Scaffold Fabrication: By changing collection mode or increasing polymer concentration, bilayer scaffolds based on aligned, unaligned, nano- or microfibers of PLGA 85:15 and PLGA-HA were formed via electrospinning[4]. Biphasic scaffold of a blend of polycaprolactone (PCL) with PLGA (5:1, PCL-PLGA) were also formed. SEM and FTIR were performed to characterize the scaffolds (n=3). In Vivo Model: Bilateral rotator cuff repair[5] were performed in male Lewis rats (n=6/group, 310±8g). The supraspinatus tendon was cut at the tendon-bone junction followed by enthesis removal. Scaffold was inserted between the bone and distal end of tendon, sutured to the bone, followed by tendon re-attachment. End-Point Analyses: At week 5, rat shoulders (n=6/group) were processed for collagen distribution (picrosirius red), alignment (polarized microscopy), and type (Col II&X immunohistology), glycosaminoglycan (GAG, alcian blue), and mineral distribution (von Kossa). Statistical Analysis: Two-way ANOVA and all pair-wise comparisons were made with Tukey Kramer post-hoc test (p< 0.05). Results: The aligned, biphasic, nanofiber scaffold enabled the formation of a fibrocartilage-like interface rich in GAG and positive for types II, X collagen (Fig. 1), while only disorganized fibrous tissue were seen at the tendon-bone junction for the unaligned group. When the biphasic scaffold is made of aligned microfibers, minimal matrix deposition was observed at the healing site post repair (Fig. 2). A similar outcome was observed when the composition of the bilayer nanofiber scaffold is changed to PCL-PLGA (Fig. 2). Discussion: These results show that fiber alignment, diameter and composition all contribute to the regeneration of the tendon-bone interface. Specifically, the bilayer scaffold of PLGA and PLGA-HA nanofibers enabled interface regeneration, as the alignment and size of the nanofibers closely resembles those of the native interface. Interestingly, the relatively slower degradation of the PLGA microfibers and PCL-PLGA nanofibers was sufficient to hinder healing and inhibit tendon-bone integration. Optimal degradation enables the bilayer scaffold to provide the needed initial mechanical strength post repair while encouraging neo-interface deposition. Collectively these results demonstrate that both fiber diameter and polymer degradation rate are key design parameters in engineering tendon-bone integration. NIH-PECASE (HHL), NSERC (XZ)