Devendra K. Dubey

Role of Molecular Level Interfacial Forces in Hard Biomaterial Mechanics: A Review

Biological materials have evolved over millions of years and are often found as complex composites with superior properties compared to their relatively weak original constituents. Hard biomaterials such as nacre, bone, and dentin have intrigued researchers for decades for their high stiffness and toughness, multifunctionality, and self-healing capabilities. Challenges lie in identifying nature’s mechanisms behind imparting such properties and her pathways in fabricating these composites. The route frequently acquired by nature is embedding submicron- or nano-sized mineral particles in protein matrix in a well-organized hierarchical arrangement. The key here is the formation of large amount of precisely and carefully designed organic–inorganic interfaces and synergy of mechanisms acting over multiple scales to distribute loads and damage, dissipate energy, and resist change in properties owing to events such as cracking. An important aspect to focus on is the chemo-mechanics of the organic–inorganic interfaces and its correlation with overall mechanical behavior of materials. This review focuses on presenting an overview of the past work and currently ongoing work done on this aspect. Analyses focuses on understanding role played by the interfacial mechanics on overall mechanical strength of hard biomaterials. Specific attention is given to synergy between experiments and modeling at the nanoscale to understand the hard biomaterial biomechanics.

Effect of osteogenesis imperfecta mutations in tropocollagen molecule on strength of biomimetic tropocollagen-hydroxyapatite nanocomposites

Osteogenesis Imperfecta (OI) is a genetic disorder that affects cellular synthesis of Type-I collagen fibrils and causes extreme bone fragility. This study reports the effects of OI mutations in Tropocollagen (TC) molecules on strength of model Tropocollagen-Hydroxyapatite biomaterials with two different mineral [hydroxyapatite (HAP)] distributions using three dimensional atomistic simulations. Results show that the effect of TC mutations on the strength of TC-HAP biomaterials is insignificant. Instead, change in mineral distribution showed significant impact on the overall strength of TC-HAP biomaterials. Study suggests that TC mutations manifest themselves by changing the mineral distribution during hydroxyapatite growth and nucleation period.

Effect of changes in tropocollagen residue sequence and hydroxyapatite mineral texture on the strength of ideal nanoscale tropocollagen-hydroxyapatite biomaterials

Changes in mineral texture (e.g. hydroxyapatite (HAP) or aragonite) and polypeptide (e.g. tropocollagen (TC)) residue sequence are characteristic features of a disease known as osteogenesis imperfecta (OI). In OI, different possibilities of changes in polypeptide residue sequence as well as changes in polypeptide helix replacement (e.g. 3 α1 chains instead of 2 α1 and 1 α2 chain in OI murine) exist. The cross section of the HAP crystals could be needle like or plate like. Such texture and residue sequence related changes can significantly affect the material strength at the nanoscale. In this work, a mechanistic understanding of such factors in determining strength of nanoscale TC–HAP biomaterials is presented using three dimensional molecular dynamics (MD) simulations. Analyses point out that the peak interfacial strength for failure is the highest for supercells with plate shaped HAP crystals. TC molecules with higher number of side chain functional groups impart higher strength to the TC–HAP biomaterials at the nanoscale. Overall, HAP crystal shape variation, the direction of applied loading with respect to the relative TC–HAP orientation, and the number of side chain functional groups in TC molecules are the factor that affect TC–HAP biomaterial strength in a significant manner.

Spectroscopic Experiments: A Review of Raman Spectroscopy of Biological Systems

Raman spectroscopy is fast emerging as an important characterization tool for biological systems. Raman spectroscopy has proven to be a powerful and versatile characterization tool used for determining chemical composition of material systems such as nanoscale semiconductor devices or biological systems. One major advantage of Raman spectroscopy in the case of biological molecules is that water gives very weak, uncomplicated Raman signal. Biological systems are essentially wet systems; hence, Raman spectrum of a biological system can be easily obtained by filtering the water’s Raman signal. Another advantage of Raman spectroscopy in the case of biological molecules is the ability of Raman spectroscopy to analyze in vivo samples. This aspect gives this technique an edge over other methods such as infrared (IR) spectroscopy which requires elaborate signal preparation for excitation and complex instrumentation for signal processing after the excitation. This chapter focuses on presenting information on advancements made regarding the Raman spectroscopy of algae.

Multiscaling for Molecular Models: Investigating Interface Thermomechanics

One of the most important aspects of understanding the influence of interfaces on natural material properties is the knowledge of how stress transfer occurs across the organic–inorganic interfaces. The multicomponent hierarchical structure of biomaterials results in organic–inorganic interfaces appearing at different length scales, i.e., between the basic components at the nanoscale, between the mineralized fibrils at the microscale, and between the layers of the multilayered structures at micro- or macroscale. For a given peak tensile strength of a given material, which position of total strength is attributed to interface strength? What is the contribution of interface sliding in time-dependent deformation observed in a simple tension test of a given material sample? This chapter focuses on addressing such questions using molecular simulations.

Multiscaling for Molecular Models to Predict Lab Scale Sample Properties: A Review of Phenomenological Models

One of the defining features of biological materials is that they are highly hierarchical with different structures at different length scales. Often they are complex nanocomposites of soft fibrous polymeric phase and hard mineral phase. For instance, bone has up to seven levels of hierarchy and nacre shows up to six levels of hierarchal structure. In spite of complex hierarchical structures, the smallest building blocks in such biological materials are at the nanometer length scale. The extent of interfacial interaction and the interfacial arrangement are important determinants of the structure–function property relationship of biomaterials and influence the mechanical strength substantially. Challenges lie in identifying nature’s mechanisms behind imparting such properties and its pathways in fabricating and optimizing these composites. The key here is the formation of large amount of precisely and carefully designed organic–inorganic interfaces and synergy of mechanisms acting over multiple scales to distribute loads and damage, dissipate energy, and resist change in properties owing to damages such as cracking. This chapter presents a brief overview of the role of interfacial structural design and interfacial forces in imparting superior mechanical performance to hard biological materials. Focus is on understanding the underlying engineering principles of nature’s materials for use in biomedical engineering and biomaterial development.

Molecular Modeling: A Review of Nanomechanics Based on Molecular Modeling

Nature’s design and engineering of biological material systems have always intrigued researchers for their extraordinary properties and structure–property–function relationships. One aspect of biomaterials science and engineering is to understand the underlying mechanisms, design, and fabrication pathways of such biological materials, which will have benefit in multiple disciplines such as prosthetic implants, regenerative medicine, self-healing materials, novel high-strength biomimetic materials, and bioenergy applications. The focus of this review is on the chemo-mechanics of the organic–inorganic interfaces and its correlation with overall mechanical behavior. This understanding is vital for selecting appropriate constituents, their size scales and their relative arrangements, which in turn is governed by the functional requirements of the composite materials.

Nanomechanics Experiments: A Microscopic Study of Mechanical Property Scale Dependence and Microstructure of Crustacean Thin Films as Biomimetic Materials

Most recent studies on the natural material include shrimp exoskeleton, crab exoskeletons, lobsters, ganoid scale of an ancient fish, toucan beak, and seashells such as nacre and mollusk. Studies focusing on biomimetic materials include development of biomimetic scaffolds for tissue growth and fabrication of tissues from biocompatible, biodegradable polymers, development of the honeycomb plates with design from beetle forewings to eliminate problems of edge sealing, molding process by thoroughly investigating beetle forewing to be able to mimic its design for better sandwich panel structures, and development of high-performance functional nanocomposites from graphene sheets with enhanced thermal conductivity and mechanical stiffness. In the present chapter, basic design principles of the crustaceans and deformation mechanisms responsible for higher strength, stiffness, and toughness are highlighted.

An atomistic investigation into the molecular effects of osteogenesis imperfecta like genetic mutations on biomaterial strength

Osteogenesis imperfecta (OI) is a genetic disease marked by extreme bone fragility and is associated with mutations in tropocollagen (TC) molecule and changes in hydroxyapatite (HAP) mineral texture. Mutations in TC can manifest in both ways, substitution of polypeptide chains and point mutations of residues. This study presents a mechanistic view on the effects of OI mutations in TC on strength of model TC-HAP biomaterials with two different mineral distributions using three dimensional atomistic simulations. Analysis points out that substitution of residue sequences with higher number of side chain functional groups impart higher strength to the TC-HAP biomaterials. Results show that the effect of TC point mutations on the strength of TC-HAP biomaterials is insignificant. Instead, change in mineral distribution showed significant impact on the overall strength of TC-HAP biomaterials. Overall, study suggests that TC mutations manifest themselves by altering the mineral distribution during hydroxyapatite ...