title: Immobilization of a phosphonated analog of matrix phosphoproteins within cross-linked collagen as a templating mechanism for biomimetic mineralization.
abstract: Immobilization of phosphoproteins on a collagen matrix is important for the induction of intrafibrillar apatite mineralization. Unlike phosphate esters, polyphosphonic acid has no reactive sites for covalent binding to collagen amine groups. Binding of poly(vinyl phosphonic acid) (PVPA), a biomimetic templating analog of matrix phosphoproteins, to collagen was found to be electrostatic in nature. Thus, an alternative retention mechanism was designed for immobilization of PVPA on collagen by cross-linking the latter with carbodiimide (EDC). This mechanism is based on the principle of size exclusion entrapment of PVPA molecules within the internal water compartments of collagen. By cross-linking collagen with EDC, a zero length cross-linking agent, the sieving property of collagen is increased, enabling the PVPA to be immobilized within the collagen. The absence of covalent cross-linking between PVPA and collagen was confirmed by Fourier transform infrared spectroscopy. Based on these results, a concentration range for immobilized PVPA to template intrafibrillar apatite deposition was established and validated using a single layer reconstituted type I collagen mineralization model. In the presence of a polyacrylic acid-containing mineralization medium optimal intrafibrillar mineralization of the EDC-cross-linked collagen was achieved using 500 and 1000 μg ml⁻¹ PVPA. The mineralized fibrils exhibited a hierarchical order of intrafibrillar mineral infiltration, as manifested by the appearance of electron-dense periodicity within unstained fibrils. Understanding the basic processes in intrafibrillar mineralization of reconstituted collagen creates opportunities for the design of tissue engineering materials for hard tissue repair and regeneration.
authors.affiliation: Department of Operative Dentistry and Endodontics, Sun Yat-sen University, Guangzhou, China.
authors.forename: Li-Sha
authors.initials: LS
authors.lastname: Gu
authors.forename: Young Kyung
authors.initials: YK
authors.lastname: Kim
authors.forename: Yan
authors.initials: Y
authors.lastname: Liu
authors.forename: Kei
authors.initials: K
authors.lastname: Takahashi
authors.forename: Senthil
authors.initials: S
authors.lastname: Arun
authors.forename: Courtney E
authors.initials: CE
authors.lastname: Wimmer
authors.forename: Raquel
authors.initials: R
authors.lastname: Osorio
authors.forename: Jun-Qi
authors.initials: JQ
authors.lastname: Ling
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Looney
authors.forename: David H
authors.initials: DH
authors.lastname: Pashley
authors.forename: Franklin R
authors.initials: FR
authors.lastname: Tay
mesh_terms: D000327:Adsorption / Q000187:drug effects; D001672:Biocompatible Materials / Q000378:metabolism*; D003094:Collagen / Q000378:metabolism* / Q000648:ultrastructure; D003432:Cross-Linking Reagents / Q000494:pharmacology*; D005022:Ethyldimethylaminopropyl Carbodiimide / Q000494:pharmacology; D005109:Extracellular Matrix / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D055767:Immobilized Proteins / Q000378:metabolism*; D007700:Kinetics; D008903:Minerals / Q000378:metabolism*; D063065:Organophosphonates / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D013997:Time Factors; D014753:Vinyl Compounds / Q000378:metabolism*
chemical_list: D001672:Biocompatible Materials; D003432:Cross-Linking Reagents; D055767:Immobilized Proteins; D008903:Minerals; D063065:Organophosphonates; D010750:Phosphoproteins; D014753:Vinyl Compounds; C433467:vinylphosphonic acid; D003094:Collagen; D005022:Ethyldimethylaminopropyl Carbodiimide