Abstract
In this study, a bio-inspired hybrid material is investigated by in situ X-ray scattering experiments in combination with mechanical tensile testing. The material is composed of nanometer-sized spherical magnesium fluoride particles which are linked via material-specific peptide-poly(ethylene glycol) (PEG) conjugates to a semi-crystalline poly(ethylene oxide) (PEO) matrix. Mechanically relevant changes in crystal size and orientation in the PEO matrix are followed by wide angle X-ray scattering during the application of tensile stress. The amorphous phase of PEO is stabilized by the surface-engineered MgF2 nanoparticles, leading to increased Young´s modulus and tensile strength. Furthermore, small angle X-ray scattering experiments allowed the identification of a layer on the MgF2 particle surfaces, which increases in thickness with the conjugate amount and leads to suppression of the agglomeration of MgF2 nanoparticles. In conclusion, the use of selected peptide-PEG conjugates tailored to link MgF2 particles to a PEO matrix successfully mimics the biological principle of interface polymers and suggests new directions for material fabrication for bio-applications.
Highlights
Inorganic fillers are widely used in synthetic polymers as well as in natural hybrid materials to enhance their mechanical performance
In situ wide angle X-ray scattering (WAXS) experiments combining X-ray scattering and mechanical tensile testing allowed a detailed analysis of the relationship between structure and mechanical properties of the hybrid material by examining the crystallite size and deformation of the crystallites during applied tensile stress of the matrix material poly(ethylene oxide) (PEO)
For calculating the true layer thickness (δ) of the conjugate layer coating the MgF2 particles the following equation was used to relate the differences of the electron densities of MgF2 with ρ (r) = 0.91 e−1/Å3, ρ (r) = 0.38 e−1/Å3 for PEO (Glatter et al, 1994) and ρ (r) = 0.45 e−1/Å3 for the conjugate by using the biomolecular scattering length density calculator
Summary
Inorganic fillers are widely used in synthetic polymers as well as in natural hybrid materials to enhance their mechanical performance. Biological hybrid materials, made of inorganic nanoparticles embedded in an organic matrix, are of great interest for material scientists in terms of their mechanical performance (Studart, 2012; Wegst et al, 2015). Bio-inspired hybrid materials with defined structuring of the material constituents across various length scales as well as precisely defined internal material interfaces exhibit advanced material properties (Bonderer et al, 2008; Munch et al, 2008; Studart, 2012; Wegst et al, 2015). Bone is probably one of the most prominent examples of hierarchically structured hybrid materials with well-dispersed inorganic hydroxyapatite particles in a collagen matrix and tailored internal interfaces between these constituents (Fratzl et al, 2004b).
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