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

Bone is a complex tissue with robust mechanical and biological properties originating from its nanoscale composite structure. Although much research has been conducted on designing bioinspired artificial bone, the role of biological macromolecules such as noncollagenous proteins (NCPs) in influencing the formation of biominerals is not fully understood. In this work, we have designed nanofiber shish-kebab (NFSK) structures that can template mineral location by recruiting calcium cations from an ion-rich mineralization solution. Poly(acrylic acid) (PAA) is used as the NCP analogue to understand the role of polyelectrolytes in scaffold mineralization. We demonstrate that the addition of PAA in the mineralization solution suppresses the development of extrafibrillar minerals as well as slows down the accumulation and development of mineral phases within NFSKs. We probe the mechanism behind this effect by monitoring the free calcium ion concentration, investigating the PAA molecular weight effect, and conducting mineralization in membrane-partitioned solutions. Our results suggest the 2-fold effect of PAA as a solution stabilizer and physical barrier on the NFSK surface. This work could shed light on the understanding of the NCP effect in biomineralization.

Electrospun poly(ε-caprolactone) nanofiber shish kebabs mimic mineralized bony surface features.

Electrospinning of nanofiber is of growing interest especially in bone tissue engineering because of its similar fibrous properties to the extracellular matrix. To this end, we have fabricated polycaprolactone (PCL) nanofiber shish kebab (NFSK) templates. The novelty of this work is the ability to control the mineral orientation and spatial location on the nanofiber, mimicking natural collagen fibers. However, NFSK templates have properties that need to be investigated in terms of cellular response including fiber alignment and crystallization. In this study, MC3T3 E1 preosteoblast cells were seeded onto the templates to determine the effect of both fiber orientation and kebab size on the cell metabolic activity. PCL was electrospun to form aligned and randomly oriented nanofibers, which were then crystallized in a PCL solution in pentyl acetate for 15 and 60 min, resulting in the formation of homopolymer PCL NFSK templates. We evaluated the cell proliferation and alkaline phosphatase activity of MC3T3 E1 cells after 3, 7, and 14 days in coculture. Aligned nanofiber and polymer crystallization both significantly increased the cell proliferation and alkaline phosphatase activity at each time point. The aligned nanofibers and polymer crystallization resulted in the highest metabolic activities of the cells compared to the randomly oriented fibers and noncrystallized controls. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1141-1149, 2019.

Structure and Morphology of Poly(vinylidene fluoride) Nanoscrolls.

To date the scrolled morphology of γ-phase poly(vinylidene fluoride) (PVDF) has been witnessed via high temperature melt crystallization of crystalline thin films and through imaging of chemical etched PVDF bulk films. Here we show the first growth and characterization of free-standing γ-phase PVDF scrolls via solution crystallization. Scanning electron microscopy, transmission electron microscopy, and atomic force microscopy have been used to characterize and to further understand the fundamental preferred crystalline habit of the γ-phase of PVDF.

Hierarchically ordered polymer nanofiber shish kebabs as a bone scaffold material.

The ideal bone scaffold harnesses the body's ability to regenerate bone in critical size defects. A potential strategy to design the ideal bone scaffold is to mimic the natural structure of bone at the molecular level. The orientation and spatial distribution of nanocrystals in the organic matrix are two important and distinctive structural characteristics associated with natural bone. There has yet to be a synthetic system or scaffold that is able to control both the spatial distribution and orientation of the hydroxyapatite crystalline structure. To mimic the unique hybrid structure of natural bone using synthetic materials, there have been a number of reported approaches to control the mineral nanocrystal orientation on synthetic scaffolds. However, the spatial distribution of minerals is challenging to reproduce in a biomimetic manner. Herein we report using block copolymer-decorated polymer nanofibers to achieve biomineralized fibrils with precise control of both mineral crystal orientation and spatial distribution. We show that the crystallization of poly(caprolactone)-b-poly(acrylic acid) block copolymer on poly(caprolactone) nanofibers resulted in a unique shish kebab structure that significantly enhances the mechanical properties of the nanofibers, and is cytocompatible to L-929 mouse fibroblast cells. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1786-1798, 2017.