Deformation processes in poly(ethylene terephthalate) fibers

Effect of the flame-retardant 3-hydroxyphenylphosphinyl-propanoic acid on the mechanical, thermal, and flammability properties of poly(ethylene terephthalate) nanofiber mats

The structure, thermal stability, and mechanical properties of electrospun nanofiber mats obtained from poly(ethylene terephthalate) (PET) solutions in trifluoroacetic acid/dichloromethane were evaluated. The electrospun PET nanofibers were characterized by means of attenuated total reflection Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, limiting oxygen index, and tensile testing. PET-3-hydroxyphenylphosphinyl-propanoic acid (HPP) copolymer was used as the flame-retardant (FR) agent to improve the thermal stability and flammability of the nanofiber mats. HPP is a commercial FR for polyesters which was studied from the viewpoint of chemical reactivity and reaction mechanism. To enhance the tensile strength of the nanofiber mats, the nanofibers were collected on high-speed rotating drum. The results showed that the nanofibers were oriented, and their strength was enhanced by increasing the velocity of the collector. The average diameter of electrospun nanofibers was in the range of 110–240 nm, decreasing with the increasing drum speed. Also the mean pore size of the mats decreased significantly with increasing orientation of the nanofibers. The results showed that HPP improved the flame retardancy of PET.

Raman spectroscopy of biomedical polyethylenes

With the development of three-dimensional Raman algorithms for local mapping of oxidation and plastic strain, and the ability to resolve molecular orientation patterns with microscopic spatial resolution, there is an opportunity to re-examine many of the foundations on which our understanding of biomedical grade ultra-high molecular weight polyethylenes (UHMWPEs) are based. By implementing polarized Raman spectroscopy into an automatized tool with an improved precision in non-destructively resolving Euler angles, oxidation levels, and microscopic strain, we become capable to make accurate and traceable measurements of the in vitro and in vivo tribological responses of a variety of commercially available UHMWPE bearings for artificial hip and knee joints. In this paper, we first review the foundations and the main algorithms for Raman analyses of oxidation and strain of biomedical polyethylene. Then, we critically re-examine a large body of Raman data previously collected on different polyethylene joint components after in vitro testing or in vivo service, in order to shed new light on an area of particular importance to joint orthopedics: the microscopic nature of UHMWPE surface degradation in the human body. A complex scenario of physical chemistry appears from the Raman analyses, which highlights the importance of molecular-scale phenomena besides mere microstructural changes. The availability of the Raman microscopic probe for visualizing oxidation patterns unveiled striking findings related to the chemical contribution to wear degradation: chain-breaking and subsequent formation of carboxylic acid sites preferentially occur in correspondence of third-phase regions, and they are triggered by emission of dehydroxylated oxygen from ceramic oxide counterparts. These findings profoundly differ from more popular (and simplistic) notions of mechanistic tribology adopted in analyzing joint simulator data. Statement of Significance This review was dedicated to the theoretical and experimental evaluation of the commercially available biomedical polyethylene samples by Raman spectroscopy with regard to their molecular textures, oxidative patterns, and plastic strain at the microscopic level in the three dimensions of the Euclidean space. The main achievements could be listed, as follow: (i) visualization of molecular patterns at the surface of UHMWPE bearings operating against metallic components; (ii) differentiation between wear and creep deformation in retrievals; (iii) non-destructive mapping of oxidative patterns; and, (iv) the clarification of chemical interactions between oxide/non-oxide ceramic heads and advanced UHMWPE liners.

In situ Raman spectroscopic study of Al-infiltrated spider dragline silk under tensile deformation

Natural materials consisting of protein structures impregnated with a tiny amount of metals often exhibit impressive mechanical behavior, which represents a new design paradigm for the development of biomimetic materials. Here, we produced Al-infiltrated silks by applying a modified Al2O3 atomic layer deposition process to the dragline silk of the Nephila pilipes spider, which showed unusual mechanical properties. The deformation behavior of the molecular structure of the Al-infiltrated silk was investigated by performing in situ Raman spectroscopy, where Raman shifts were measured concurrently with macroscopic mechanical deformations. For identifying the role of the infiltrated Al atoms, the study was performed in parallel with untreated silk, and the results were compared. Our experimental results revealed that superior mechanical properties of the Al-infiltrated silk are likely to be caused by the alterations of the sizes of the β-sheet crystals and their distribution.

Effects of treatment protocols and subcutaneous implantation on bovine pericardium: a Raman spectroscopy study

Using Raman microspectroscopy, we have studied mineral deposition on bovine pericardia, fixed according to three different protocols and either implanted subcutaneously or not implanted (controls). A lightly carbonated apatitic phosphate mineral, similar to that found in bone tissue, was deposited on the surface of a glutaraldehyde-fixed, implanted pericardium. Implanted pericardia fixed in glutaraldehyde followed by treatment in either an 80% ethanol or a 5% octanol/40% ethanol solution did not mineralize on implantation. Collagen secondary structure changes were observed on glutaraldehyde fixation by monitoring the center of gravity of the amide I envelope. It is proposed that the decrease in the amide I center of gravity frequency for the glutaraldehyde-fixed tissue compared to the nonfixed tissue is due to an increase in nonreducible collagen cross-links (1660 cm(-1)) and a decrease in reducible cross-links (1690 cm(-1)). The amide I center of gravity in the glutaraldehyde/ethanol-fixed pericardium was higher than the glutaraldehyde-fixed tissue center of gravity. This increase in center of gravity could possibly be due to a decrease in hydrogen bonding within the collagen fibrils following the ethanol pretreatment. In addition, we found a secondary structure change to the pericardial collagen after implantation: an increase in the frequency of the center of gravity of amide I is indicative of an increase in cross-links.

Strength and structure of spiders' silks

Spider silks are composite materials with often complex microstructures. They are spun from liquid crystalline dope using a complicated spinning mechanism which gives the animal considerable control. The material properties of finished silk are modified by the effects of water and other solvents, and spiders make use of this to produce fibres with specific qualities. The surprising sophistication of spider silks and spinning technologies makes it imperative for us to understand both material and manufacturing in nature before embarking on the commercialization of biotechnologically modified silk dope.