Biomimetic Mineralization of Hierarchical Nanofiber Shish-Kebabs in a Concentrated Apatite-Forming Solution

Abstract

Recently, hierarchical polymer nanostructures called nanofiber shish-kebabs (NFSKs) have shown great potential in directing the distribution of minerals for biomineralization. In this work, we report controlled biomimetic mineralization in block copolymer-containing NFSKs. NFSKs were formed by crystallizing polycaprolactone-block-poly­(acrylic acid) (PCL-b-PAA) kebabs on PCL fiber backbones. The block copolymer kebabs were periodically distributed on PCL nanofibers with a spacing of ∼100–300 nm. Free ions could infiltrate into anionic PAA nanodomains and initiate the NFSK-templated biomimetic mineralization process. A concentrated calcium phosphate solution was used in the present study, which led to significantly accelerated mineralization kinetics compared with the previously studied simulated body fluid systems. Electron microscopy, Fourier-transform infrared spectroscopy, and wide-angle X-ray diffraction were used to characterize the structure and morphology of the mineralized NFSKs. A three-stage mineralization process was identified, and carbonated nonstoichiometric hydroxyapatite was observed after stage 2 with the mineral location templated within kebabs. This accelerated mineralization process yielded a periodic mineral distribution of a biomimetic calcium phosphate phase along the fibers, and the decrease in mineral formation time allows for more efficient biomineralization study and composite formation.

Insight on the Role of Poly(acrylic acid) for Directing Calcium Phosphate Mineralization of Synthetic Polymer Bone Scaffolds

“…PCL-b-PAA was synthesized, with methods and block copolymer characterization previously reported. 43 To form kebab crystals, a 1 w/ v% solution of PCL-b-PAA was dissolved in a mixed solvent of 1:1 PA:EtOH by heating it to 70 °C. After being cooled to room temperature, a 1.5 cm × 1.5 cm square of PCL nanofibers was added to 1 mL of the block copolymer solution.…”

“…This is consistent with the stage 3 mineralization (as defined in the Introduction) that was previously reported for the same mineralization solution and 12 h time point. 43 PAA 100 (100 kDa) was added to the mineralization solution at low concentration (10 μg/mL), and NFSKs were incubated in these PAA-ion solutions for up to 7 days. Figure 3c−f shows the NFSK mat morphology after mineralizing in the PAA 100 -containing solution.…”

“…In particular, when a block copolymer such as poly(caprolactone)-b-PAA (PCL-b-PAA) containing an ionic block (PAA) is used as the kebab-forming material, controlled polymer crystallization and block copolymer phase separation lead to the formation of sub-10 nm ionic domains that recruit mineral ions for confined mineralization. 38,43 NFSKs have demonstrated great utility in controlling both mineral spatial distribution and crystalline orientation, which are the two key characteristics in collagen-mediated biomineralization. Both unmineralized and mineralized NSFK mats have demonstrated excellent potential applications in bone tissue engineering.…”

Formation mechanism of zigzag patterned P(NIPAM-co-AA)/CuS composite microspheres by in situ biomimetic mineralization for morphology modulation

“…Their narrow size distribution combined with their advantages mentioned above makes them ideal templates for preparing spherical inorganic–organic composite materials. 16 For example, synthetic polymer hydrogels composed of poly(acrylamide), 17 PNIPAM, 18 polycaprolactone- block -poly(acrylic acid), 19 and other materials have been used as the template for mineralization. Although there are a number of reports in the literature about the hydrogel with special patterned morphology, the pattern morphology of the composites formed on the surface of materials is derived from the oriented growth of crystals caused by additives or self-assembled templates.…”

Core–Shell Nanofibers with a Shish-Kebab Structure Simulating Collagen Fibrils for Bone Tissue Engineering

“…The shish-kebab (SK) structure is a special interface crystal structure in semicrystalline polymers, which consists of straight-chain crystals and folded-chain crystals. Electrospun nanofibers can be used as a straight-chain crystal, which induces the periodic growth of polymers perpendicular to its surface at a certain temperature to form lamellae. − When nanofibers and the polymer matrix are similar in geometry, such as lattice parameters, orientation, or some crystal plane spacing, polymer chains can form a kebab or coating on the surface of nanofibers. , Yu et al confirmed that the crystallization behavior of polymers significantly increased the proliferation and alkaline phosphatase (ALP) activity of MC3T3-E1 cells . Chen et al found that the SK structure improved the mechanical properties of nanofibrous membranes …”