Abstract
A recent study has shown that demineralized cortical bone (DCB) did not improve the healing of tendon-bone interface. Considering that there is a gradient of mineral content in the tendon-bone interface, we designed a segmentally demineralized cortical bone (sDCB) scaffold with two different regions: undemineralized cortical bone section within the scaffold (sDCB-B) and complete demineralized cortical bone section within the scaffold (sDCB-D), to mimic the natural structure of the tendon-bone interface. Furthermore, the extracellular matrix (ECM) from tendon-derived stem cells (TDSCs) was used to modify the sDCB-D region of sDCB to construct a novel scaffold (sDCB-ECM) for enhancing the bioactivity of the sDCB-D. The surface topography, elemental distribution, histological structure, and surface elastic modulus of the scaffold were observed using scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, histological staining and atomic force microscopy. Cell proliferation of bone marrow mesenchymal stem cells (BMSCs) and TDSCs cultured on scaffolds was evaluated using the Cell Counting kit-8, and cell viability was assessed by Live/Dead cell staining. Cell morphology was detected by fluorescent staining. The ability of the scaffolds to recruit stem cells was tested using transwell migration assay. The expression levels of bone-, cartilage- and tendon-related genes and proteins in stem cells were assessed by the polymerase chain reaction and western blotting. Our results demonstrated that there was a gradient of Ca and P elements in sDCB, and TDSC-derived ECM existed on the surface of the sDCB-D region of sDCB. The sDCB-ECM could promote stem cell proliferation and migration. Moreover, the sDCB-B region of sDCB-ECM could stimulate osteogenic and chondrogenic differentiation of BMSCs, and the sDCB-D-ECM region of sDCB-ECM could stimulate chondrogenic and tenogenic differentiation of TDSCs when compared to DCB. Our study indicated that sDCB-ECM might be a potential bioscaffold to enhance the tendon-bone interface regeneration.
Highlights
The tendon-bone interface is difficult to repair because of its highly heterogeneous and complex structure with gradually increasing mineral content (Isaac et al, 2012)
The SEM results showed that segmentally demineralized cortical bone (sDCB) contained two different regions, and energy dispersive X-ray (EDX) elemental mapping demonstrated that there was a gradient of Ca and P elements in the sDCB (Figures 2A,B)
After tendon-derived stem cells (TDSCs) were cultured for 2 weeks, a thin layer of cells with their extracellular matrix (ECM) could be observed on the surface of the sDCB-D region (Figures 3A,B, middle panels)
Summary
The tendon-bone interface is difficult to repair because of its highly heterogeneous and complex structure with gradually increasing mineral content (Isaac et al, 2012). This unique area consists of four different regions: tendon, fibrocartilage, mineralized fibrocartilage and bone (Genin et al, 2009). Sundar et al (2009) found that DBM could improve the healing of the tendon-bone interface of the ovine patellar tendon, and the DBM group showed better functional weight-bearing than the control group. A recent study reported that DBM did not improve the healing of the tendon-bone interface in a rat rotator cuff tear model (Thangarajah et al, 2017)
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