Formation of Hydroxyapatite Skeletal Materials from Hydrogel Matrices via Artificial Biomineralization

Abstract

Several kinds of hydrogels were prepared as mimics for the collagen/acidic protein hydrogel employed as the polymer matrix for mineralization in natural bone formation. The hydrogels prepared as mineralization matrices were employed for synthesizing artificial bones. The artificial bone made from a network of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) prepared by heating (PVA/PAA-h-network) exhibited mechanical properties comparable with those of fish scales. To elucidate the formation mechanism of the artificial bone, we synthesized four further kinds of matrix. Artificial bones were obtained from both a PVA/PAA network prepared by repeated freezing and thawing (PVA/PAA-ft-network) and a chitosan/PAA network, in which hydrogen bonding exists between the two constituent polymers, similar to that observed in a natural collagen/acidic protein network. The artificial bone made from the chitosan/PAA network was confirmed to be formed by the phase transformation of a cartilaginous precursor by a process similar to the transformation of cartilaginous tissue to natural bone. In addition, skeletal phase material, i.e., a homogeneous solid phase of hydroxyapatite/polymers, was formed in the cartilaginous phase, i.e., the hypercomplex gel. The skeletal phase grew thicker at the expense of the cartilaginous phase until it formed the entirety of the composite. Artificial bones were also obtained from a gelatin/PAA network and a poly[N-(2-hydroxyethyl)acrylamide]-co-(acrylic acid) network. These experimental results suggested that the coexistence of proton donor and proton acceptor functions in the hydrogel is a key factor for bone formation. The hydroxyapatite content of our artificial bones was almost conterminous with those of natural bones.

Calcium Carbonate Skeletal Material Is Synthesized via Phase Transition of the Calcium Carbonate Cartilaginous Material

“…60 to 95% in weight in the dry state, which are similar to the compositions of vertebrate bony tissues. 12 These results indicate that the polymer network in bone biomineralization will consist of collagen and acidic proteins. Instead of the hole zone of fibril, 14 the proton-donating function of collagen is important, because gelatin is also an effective network-forming polymer.…”

“…The chitosan/PAA network (chitosan/PAA), PVA/PAA physically cross-linked network (PVA/PAA-p), and PVA/PAA chemically cross-linked network (PVA/PAA-c) were prepared by the method described in detail in previous reports. 12 Chitosan/PAA was prepared by mixing water-insoluble chitosan and water-soluble PAA ( M w ≈ 5 kDa) solutions at the polymer weight ratio of 2:1 under an acidic condition. After drying, this network film turned out to be insoluble without further treatment in the CC solution.…”

Siliceous‐based monolithic materials coated with a hydroxyapatite layer: Preparation and investigation of drug affinity by Raman spectroscopy

“…In situ mineralization of HA on monolith was carried out according to method described by Jongwattanapisan et al, Pietrzyńska et al, Iwatsubo et al, Barros et al, and Wei et al with modifications.…”

Natural marine sponges for bone tissue engineering: The state of art and future perspectives

“…As previously described, spongin is the main organic component of sponge fibrous skeletons and it is analogous to collagen type XIII . Collagen is one of the most widely used natural polymers for tissue bioregeneration . Human collagens vary greatly in terms of size, function, and tissue distribution, but all contain one characteristic feature: a triple helix of three polypeptide chains .…”

“…13 Collagen is one of the most widely used natural polymers for tissue bioregeneration. 56 Human collagens vary greatly in terms of size, function, and tissue distribution, but all contain one characteristic feature: a triple helix of three polypeptide chains. 57 In general, collagen has maintained a highly conserved amino acid sequence throughout the course of evolution.…”