Mechanical and compositional analysis of bone nanostructure and design for bio-inspired co-continuous composites

Pang, Siyuan

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https://hdl.handle.net/2142/117580 Copy

Description

Title

Mechanical and compositional analysis of bone nanostructure and design for bio-inspired co-continuous composites

Author(s)

Pang, Siyuan

Issue Date

2022-12-01

Director of Research (if dissertation) or Advisor (if thesis)

Jasiuk, Iwona

Doctoral Committee Chair(s)

Jasiuk, Iwona

Committee Member(s)

• Wagoner-Johnson, Amy
• Kersh , Marianna
• Elbanna , Ahmed

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Bone
• Deproteinization, Demineralization, Mineral, Age, Bio-inspired composite
• 3D printing, Geopolymer

Abstract

Bone is a biological composite material having protein and hydroxyapatite minerals as its main constituents. The unique nanostructure formation of the two phases makes bone a strong, tough, and lightweight material. This dissertation investigates the structure formed by the protein and mineral phases in bone, and the results inspire the design of bio-inspired composites with superior mechanical properties. First, we studied the structure and composition of the protein and mineral phases in bone. Deproteinization (DP) and demineralization (DM) were conducted on porcine femoral cortical bones to remove one phase and explore the composition and structure of the remaining phase. Due to the complexity and inhomogeneity of the bone structure, ensuring the complete removal of one phase is critical to studying the other phase. We investigated multiple DP and DM protocols to determine the best methods to eliminate the mineral or protein phase while preserving the other structure. Treating samples for 14 days using sodium hypochlorite with a concentration of 0.35 M in water was the most effective method for deproteinization, resulting in a high mineral-to-protein ratio, well-preserved mineral crystallinity, and minimal protein residues. The most efficient demineralization method was using hydrochloric acid, which removed most of the mineral content while preserving the protein integrity with a short treating time. In addition to the mineral-protein structure, the mineral-mineral bonding was also explored by decollagenation (DC), which removed only collagen in protein using ethylenediamine with a Soxhlet setup. Mineral aggregates were present after DC treatment, unlike the DP treatment, during which minerals were broken down into single mineral lamellae. The higher strength and toughness of DC-treated bones demonstrate that non-collagenous proteins and lipids contribute to the binding strength between mineral lamellae. A further investigation was made on the mechanical property changes of minerals collected from different ages to study bone development at its early stage. The mineral phase maintained its continuity even in a young bone at 3-week age, indicating that the continuous structure of the mineral starts at an early age. By comparing the 3-week, 4-week, 16-week, and 24-week bones, the mechanical properties of the mineral phase increased with age. This behavior was associated with a decrease in porosity and an increase in mineral content. Following the study of the bone nanostructure and its properties, a bio-inspired composite was designed by imitating the concept of the mineral-protein two-phase co-continuous structure. Geopolymer was used to represent the stiff mineral phase, and a 3D-printed polymer was used to represent the soft protein phase, with a 1:1 volume ratio. We compared the mechanical properties of the composite with single material properties by conducting compressive and 4-point bending tests. A significant improvement in the strength and energy absorption was found in the composite. The composite formed by the two phases compensated for the brittleness of the geopolymer and the softness of the polymer. The shape effect study demonstrated that structures with smaller height-to-width ratios have higher strength and elastic modulus but lower toughness. The scale effect study showed that increasing the number of unit cells at a cross-section while keeping the bulk dimension the same, strength and toughness increase, but elastic modulus does not significantly change. This work has a potential impact across numerous fields. Uncovering the bone nanostructure provides clinical benefits as it helps to improve human health and avoid potential fracture risks. Intact and pure deproteinized and demineralized bone have biomedical applications as bone scaffolds. Also, a comprehensive understanding of bone tissue provides concepts for structural design. Bio-inspired structures with excellent strength, energy absorption, and lightweight properties are of high interest to various engineering industries.

Graduation Semester

2022-12

Type of Resource

Thesis

Copyright and License Information

All rights reserved by Siyuan Pang

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