Due to well-known disadvantages of the autologous bone graft, many alternatives have been studied for a reliable spinal fusion. Herein, we aimed to investigate the effects of human recombinant epidermal growth factor (EGF) on posterolateral lumbar fusion in a rat model. 36 male SD rats underwent posterolateral fusion at L4-5 level. They were randomly assigned to 3 groups: Sham control group, Hydoxyapatite β-tricalcium phosphate (HA/β-TCP) group and HA/β-TCP + EGF group. Rats were euthanized at 8 weeks post-surgery. 6 rats from each group were selected for manual palpation examination, micro-computed tomography analysis and histologic analysis; and the rest was used for biomechanical analysis. Based on manual palpation, there was no fusion in the sham control group. Fusion rate was 33.3% in the HA/β-TCP group and 66.7% in the HA/β-TCP + EGF group (p=0.085). Micro-CT results revealed that new bone formation was higher in the HA/β-TCP + EGF group (BV/TV: 40% vs. 65%) (p=0.004). Histologically newly formed bone tissue was more pronounced in the EGF group and compacted and bridging bone spicules were observed. The median maximum bending moment values were 0.51 Nmm (0.42– 0.59), 0.73 Nmm (0.49– 0.88) and 0.91 Nmm (0.66– 1.03) in the sham control, HA/β-TCP and HA/β-TCP + EGF groups, respectively (p=0.013). The median stiffness values were 1.69 N/mm (1.12–2.18), 1.68 N/mm (1.13–2.74) and 3.10 N/mm (1.66–4.40) as in the previous order (p=0.087). This study demonstrates that EGF enhances posterolateral lumbar fusion in the rat model. EGF in combination with ceramic grafts increased the fusion rates.

During in vitro sub-culturing, tenocytes lose their phenotype which ultimately affects their functioning. As spindle-shaped fibroblasts, tenocytes have a unique thin elongated phenotype and they possess more spread-out shape through phenomena named dedifferentiation1. Given the link between cell shape and cell function, in this study, we first aimed to dedifferentiate tenocytes through in vitro sub-culturing in order to have a model system for dedifferentiation. For this, we isolated human flexor tendon cells from healthy female flexor digitorum longus and seeded at 5000 cells/cm² cell density, passaged every two days for six passages. In order to assess cell phenotype, we fixed with 4% paraformaldehyde and stained with phalloidin and DAPI to visualize the actin cytoskeleton and DNA respectively. We noted that in each passage, cells lost their spindle-shaped phenotype and became more pancake-shaped. At passage 1 and 2, the main cell phenotype is spindle-shaped. However, as the cells are further passaged, the phenotype of the cell population becomes more heterogeneous and at passage 5 and 6, they already display a more spread-out shape. Based on these results, we further hypothesized that they can be re-differentiated through matrix-mediated mechano-transduction and regain their morphology and function. For this aim, we generated decellularized tendon from porcine Achilles tendon and setup a mechanical loading system where we can provide mechanical loadings at physiological levels. This system will provide a new approach on in vitro tenocyte culturing.

Background context

Fusion is a fundamental procedure in spine surgery. Although autogenous grafts have ideal bone graft characteristics, their use may remain limited due to various morbidities. Even though ceramic based synthetic bone grafts are used commonly at present, in order to enhance their efficacy, their combined use with other materials has been investigated. The use of carbon nanotubes (CNTs) together with synthetic bone grafts such as hydroxyapatite (HA) has contributed to positive developments in bone tissue engineering.