"Tissue engineering proposes an innovative therapeutic approach to support and induce regenerative processes in damaged tissues. Scaffolds should provide a suitable environment for proliferation, differentiation, and maturation of cells and formation of new tissue and blood vessels. Furthermore, scaffolds should be gradually resorbed at a rate commensurate with bone formation. Calcium phosphates (CaPs) are commonly used in bone tissue engineering due to their chemical composition similarity to the main component of the inorganic part of bone. Among CaPs, β tricalcium phosphate (β-TCP) exhibits a suitable resorption rate for tissue engineering applications . However, highly porous ceramics demonstrate high brittleness and poor surgical handling. Polymeric coatings tend to improve the durability of bioceramic scaffolds and may serve as carriers of biologically active substances . Poly(3-hydroxybutyrate) (P(3HB)) is a biocompatible and biodegradable biopolymer, which degradation products are harmless to the surrounding tissues. For these reasons, we used P(3HB) as a coating on β-TCP scaffolds. The physicochemical and biological properties of the obtained materials have been examined.
β-TCP scaffolds were fabricated by a foam replication method using three types of polyurethane matrices with different pore sizes (S-small, M-medium, L-large). The bioceramic scaffolds were soaked in the P(3HB) solution, dried, and subjected to further studies. Obtained materials were assessed by X-ray diffraction, scanning electron microscopy, hydrostatic weighing, compression tests, and chemical stability in vitro. Degradation products of P(3HB) were analysed via UHPLC-MS. Furthermore, hMSC adhesion, growth, and differentiation were assessed.
The ceramic scaffolds were uniformly covered with the biopolymer, which was evidenced by SEM observations. The P(3HB) coating did not significantly influence the total porosity of the materials obtained ( Ptotal~70 vol%). Composites possessed higher comprehensive strength (up to 4.5 ± 0.5 MPa) compared to uncoated β-TCP. The degradation of P(3HB) during incubation in water was confirmed by UHPLC-MS as (R)-3-hydroxybutyric acid and its oligomers were identified in the extracts. In vitro studies revealed that hMSCs adhere, grow, and proliferate on both uncoated and coated scaffolds (viability over 85% at 7 and 21 days). The number of cells increased in day 21 if compared to day 7 on all materials. The pore size affected the depth of penetration of the cells. The cells efficiently penetrate the materials (even 650-700 µm into the scaffold with large pores).
P(3HB) can serve as a coating on ceramic-polymer composites improving mechanical properties and the durability of the scaffolds. In addition, the released (R)-3-hydroxyacids may nourish the surrounding tissues. Preliminary in vitro studies using hMSC revealed no cytotoxicity of β-TCP as well as β-TCP/P(3HB) scaffolds. Developed materials can act as scaffolds for bone tissue regeneration. Further in vivo studies are necessary.
ACKNOWLEDGEMENTS: Research funded by the National Centre for Research and Development, Poland, grant Techmatstrateg no. TECHMATSTRATEG2/407507/1/NCBR/2019
REFERENCES:  Putri, et al., Journal of Biomedical Materials Research Part A, 108(3) (2020), 625-632.  Skibiński, et al., Ceramics International 47(3) (2021), 3876-3883."