Tissue engineered mimetic periosteum for efficient delivery of rhBMP-2

Background: Despite its unique regenerative capacity, bone healing can be compromised, leading to delayed fracture regeneration and consequently nonunion. Due to the scarcity of autografts and the problems associated with a supraphysiological use of rhBMP-2, novel tissue engineering strategies arise as a promising solution to overcome nonunions and related bone pathologies. Purpose: To clinically deal with fracture nonunion, we designed engineered mimetic autografts consisting of a personalized polycaprolactone (PCL) scaffold surrounded by a porous PCL membrane mimicking the periosteum synthesized by melt electrowriting (MEW) (Figure 1). Methods: MEW membrane was functionalized with poly ethyl acrylate (PEA) and Fibronectin for efficient rhBMP-2 binding and delivery. The regenerative capacity and therapeutic potential of these scaffolds were tested in vitro for osteoblast differentiation and vivo in a critical size femur defect in Sprague Dawley rats (n=6-7 animals/group) (ethical approval 073-20). Regenerative effects were assessed by qPCR, q-mCT and histological analysis. Non-parametric Kruskal Wallis test was used for statistical analysis. Results: We selected the two lowest dose implants (10 mg/ml, 51.94±8.84 ng and 25 mg/ml, 186.8±17.33) to assess release profile over time and for in vivo therapeutic effect. In vitro, single loading of 186 ng of rhBMP-2 allows similar differentiation potential that standard osteogenic differentiation medium where fresh rhBMP-2 was added twice weekly (Figure 2). In vivo, regarding bone regeneration, quantitative μCT analysis shows great bone healing of defects treated with rhBMP-2 at concentrations of 25 μg/ml (186 ng) and 10 μg/ml (52 ng). Control group, 6.80±2.47 mm3; 10 μg/ml BMP-2 group 19.53±4.266 mm3, *p=0.0324; 25 μg/ml BMP-2 group 24.48±11.30 mm3, **p=0.0087. In addition, histological analysis was carried out to determine the osteoconductive potential of our PCL core (Figure 3). Conclusion: In conclusion, PEA functionalized mimetic periosteum show an unpreceded increase in bone healing, greatly enhancing rhBMP-2 effects