Using Small-Angle Scattering Techniques to Understand Mechanical Properties of Biopolymer-Based Biomaterials

Abstract

The design and engineering of innovative biopolymer-based biomaterials for a variety of biomedical applications should be based on the understanding of the relationship between their nanoscale structure and mechanical properties. Down the road, such understanding could be fundamental to tune the properties of engineered tissues, extracellular matrices for cell delivery and proliferation/differentiation, etc. In this tutorial review, we attempt to show in what way biomaterial structural data can help to understand the bulk material properties. We begin with some background on common types of biopolymers used in biomaterials research, discuss some typical mechanical testing techniques and then review how others in the field of biomaterials have utilized small-angle scattering for material characterization. Detailed examples are then used to show the full range of possible characterization techniques available for biopolymer-based biomaterials. Future developments in the area of material characterization by small-angle scattering will undoubtedly facilitate the use of structural data to control the kinetics of assembly and final properties of prospective biomaterials.

Fig. 1

Pictorial presentation of small-angle scattering in the case of the particles of different size. 2θ₁ and 2θ₂ are the angles between incident and scattered waves from two particles, λ is a wavelength of incident radiation and is a path difference between two waves scattered from two arbitrary points within a particle. Since the scattering is elastic, the wavelength of the scattered radiation is unchanged and also equals to λ. Red dashed arrows show the direction of the scattered radiation to the detector.

Fig. 2

Dynamic rheological characterization of heterochiral and homochiral peptide pairs. Homochiral pairs lead to higher G′ values at 48 h of gelation. Blue: (L⁺L⁻); Orange: (D⁺D⁻); Green: (L⁺D⁻); Red: (D⁺L⁻). Reprinted with permission from ref. 109. Copyright 2012 American Chemical Society.

Fig. 3

SAXS monitoring of the gelation process. Left and right columns show the time evolution of the 2D average cross-section of the peptide fibers. Red: (D⁺L⁻); Green: (L⁺D⁻); Orange: (D⁺D⁻); Blue: (L⁺L⁻). Reprinted with permission from ref. 109. Copyright 2012 American Chemical Society.

Fig. 4

Pictorial presentation of the 3D slice of the hydrogels under study showing the cross sections of the individual fibers interconnected with flat, “lappet-like” webs shown in gray. Reconstruction from the 2D cross-shape restored from SANS data with the low Q_min values (∼0.003–0.005 Å⁻¹): (A) for the heterochiral hydrogel pair (L⁺D⁻) and (D⁺L⁻). and (B) for the homochiral hydrogel pair: (L⁺L⁻) and (D⁺D⁻). (C) shows a pictorial cartoon illustrating the schematic fibrous network organization. Reprinted with permission from ref. . Reprinted with permission from ref. 109. Copyright 2012 American Chemical Society.

Fig. 5

Dynamic oscillatory rheological characterization of peptide, polysaccharide and composite materials. The graphs in red are the time (top) and strain (bottom) sweep for the chitosan+alginate (CA) network. The graphs in purple are the time (top) and strain (bottom) sweep for the peptide (P) hydrogel. The graphs in black are the time (top) and strain (bottom) sweep for the chitosan+alginate+peptide (CAP) network. G = (G′+G″)^½. Reprinted with permission from ref. 61. Copyright 2011 Wiley Periodicals, Inc.

Fig. 6

Pictorial description of the 2D shapes of a fiber cross-section in polysaccharide and composite peptide-polysaccharide networks. The addition of chondroitin D to CA (chitosan + alginate, red) leads to much bigger and thicker fiber CAD (CA + chondroitin, green); while the addition of the peptides P (L⁺ + L⁻, purple) to the above polysaccharide networks with the formation of CAP (CA + P, black) or CADP (CAD + P, blue) completely disrupts the structures of polysaccharides and results in the fibers with the cross-section very similar to the pure peptide network P. Reprinted with permission from ref. 61. Copyright 2011 Wiley Periodicals, Inc.