Fabrication of a new physiological macroporous hybrid biomaterial/bioscaffold material based on polyphosphate and collagen by freeze-extraction

Abstract

We describe the fabrication of a new scaffold, an inorganic–organic hybrid biomaterial, consisting of the physiological polymers: the inorganic polymer polyphosphate (polyP), as well as the organic macromolecules collagen and chondroitin sulfate. The polyP polymer is composed of multiple phosphate orthophosphate units linked together by high-energy phosphoanhydride bonds. Chondroitin sulfate has been included due to its hydrogel-forming properties. In the presence of Ca²⁺ ions, the randomly coiled polyP reorganizes together with collagen and chondroitin sulfate to linear molecules which undergo hardening. This scaffold is deposited as amorphous Ca–polyP nanoparticles (size ≈20–40 nm large) around the collagen fibers. Applying the method of freeze-extraction a stable macroporous 3D hydrogel scaffold with a Young's modulus of ≈0.4 MPa is formed comprising cavities/channels larger than 75 μm. The scaffold exhibits a pronounced capacity for induction of cell proliferation (primary human osteoblasts, phOSB) and differentiation (alkaline phosphatase gene expression). We propose that incorporation of the physiological polymer polyP into the collagen-based scaffold might allow a dynamic opening and resealing and by that facilitates the exchange of nutrients for the growth of cells. This physiological hybrid biomaterial might have the potential to be used in bone and cartilage repair.