Bedabibhas Mohanty

Characterizing and Identifying Incipient Carious Lesions in Dental Enamel Using Micro-Raman Spectroscopy

Early detection of dental caries is vital if improved patient outcomes are to be achieved by reversal of the demineralization process. Current techniques used by dentists for identifying carious lesions are effective in identifying more advanced lesions, but do not have sufficient sensitivity and specificity to detect them at the earliest stages. This study focused on characterizing the growth of incipient carious lesions in vitro using micro-Raman spectroscopy. The incipient carious lesions were grown on the buccal faces of human molars by controlled exposure to lactic acid. Lesions were cross-sectioned to expose the subsurface body of the lesion and then examined using micro-Raman spectroscopy. The intensity of the phosphate peaks in the Raman spectra was found to differ significantly between healthy enamel and the demineralized region of the lesions. The sensitivity of the phosphate peaks to the degree of demineralization was observed by taking a series of spectra over the cross section of the lesions. This revealed that the body of the lesion is highly demineralized, but in a narrow surface region (up to 10 µm) there is little demineralization. All the phosphate peaks were found to be sensitive to the degree of demineralization; however, changes in the intensity of the pronounced phosphate peak at 961 cm–1 offer the most promise for identifying lesions. The results indicate that micro-Raman spectroscopy has both the sensitivity and selectivity to identify incipient carious lesions, but the presence of a surface layer with a relatively high mineral content could complicate the analysis.

Influence of backbone chain length and functional groups of organic modifiers on crystallinity and nanomechanical properties of intercalated clay-polycaprolactam nanocomposites

In this paper, we report the influence of chain length of organic modifier on the crystallinity and nanomechanical properties of polymer clay nanocomposites (PCNs) using modifiers of three different chain lengths while maintaining the same functional groups. We also report the influence of change in functional group on the properties, while maintaining the same backbone and length. The clay and polymer used are the same in all cases. The PCNs have been synthesised with these modifiers, and their crystallinity and nanomechanical properties have been evaluated to assess the influence of backbone chain-length and functional groups. Our study reveals that backbone chain length of organic modifier has significant effect on the structure, crystallinity and nanomechanical properties of PCNs. Further it is observed that end functional group of organic modifier also has significant effect on the crystallinity and nanomechanical properties of PCN. However, the change in backbone chain-length of organic modifier plays a more critical role on the crystallinity and nanomechanical properties of PCNs.

Biomimetic Lessons Learnt from Nacre

Nacre, the inner iridescent layer of molluscan shells has been investigated for many decades due to its exceptional mechanical properties, tremendous structural redundancy and complex hierarchical structure that spans nanometer to millimeter length scale. This chapter gives an overview of past and current literature on advancements in evolution of understanding of the hierarchical microstructure of nacre, the molecular makeup of mineral and organic components, as well as recent efforts on biomimicking this structure for a variety of applications. In addition, we will also describe multiscale modeling efforts in simulating the mechanical response of this material. Modeling efforts in literature include fracture mechanics based continuum theories to molecular dynamics studies on mineralprotein interactions in nacre. The goal of this chapter would be to give the reader an in depth understanding of the existing knowledge on architecture of nacre and the structure property relationships therein. Lessons from nature to accomplish optimized mechanical response, structural redundancy and fracture toughness will be illustrated for this important material system. Also described are efforts in literature on mimicking the structure of nacre.

Mechanical Properties of Biomimetic Composites for Bone Tissue Engineering

A biomimetic process involving in situ mineralization of hydroxyapatite (HAP) is used to design new composite biomaterials for bone tissue engineering. Surface and bulk properties of HAP composites have been studied for hydroxyapatite mineralized in absence (ex situ) of polyacrylic acid (PAAc) and in presence (in situ) of PAAc. XRD studies show existence of structural disorder within in situ HAP. It has been observed that PAAc increases the rate of crystallization. FTIR studies indicate calcium deficiency in structure of both in situ and ex situ HAP. PAAc provides favorable sites for nucleation of HAP. During crystallization of HAP, PAAc dissociates to form carboxylate ion, which binds to HAP. Porous and solid composites of in situ and ex situ HAP with polycaprolactone (PCL) in 50:50 ratio have been made to evaluate their applicability as bone scaffold. Mechanical tests on solid samples indicate ex situ HAP/PCL composites have higher elastic modulus (1.16 GPa) than in situ HAP/PCL composites (0.82 GPa). However, in case of porous composites, in situ HAP/PCL composites are found to have higher elastic modulus (29.5 MPa) than ex situ HAP/PCL composites (10.4 MPa). Nanoindentation tests were also performed at different loads to evaluate mechanical properties of the composites. In situ HAP mineralized using non-degradable polymers has thus been shown to improve mechanical response in porous composites.

Biopolymer Polyelectrolyte Complex – Hydroxyapatite Composites for Bone Tissue Engineering

The excellent biocompatibility, biofunctionality, and non-antigenic property make chitosan an ideal material for tissue regeneration. In addition to that its hydrophilic surface promotes cell adhesion, proliferation, and differentiation, and evokes a minimal foreign body reaction on implantation. In spite of these favorable properties, the inadequate mechanical strength and loosening of structural integrity under wet conditions, limit its application for bone tissue engineering. To improve the suitability of chitosan for bone tissue engineering, we have biomimetically synthesized composites of chitosan, polygalacturonic acid and hydroxyapatite. Polygalacturonic acid (PgA) is biocompatible, biodegradable and electrostatically complementary to chitosan. The strong interactions between negatively charged carboxylate groups of PgA and positively charged amino groups of chitosan lead to complex formation. This biopolymer complex provides improved mechanical strength and better structural integrity under wet condition. In this study, we have investigated the applicability of chitosan-PgA-hydroxyapatite composites for bone tissue engineering.