Untapped Potential of Deep Eutectic Solvents for the Synthesis of Bioinspired Inorganic-Organic Materials.

Since the discovery of deep eutectic solvents (DESs) in 2003, significant progress has been made in the field, specifically advancing aspects of their preparation and physicochemical characterization. Their low-cost and unique tailored properties are reasons for their growing importance as a sustainable medium for the resource-efficient processing and synthesis of advanced materials. In this paper, the significance of these designer solvents and their beneficial features, in particular with respect to biomimetic materials chemistry, is discussed. Finally, this article explores the unrealized potential and advantageous aspects of DESs, focusing on the development of biomineralization-inspired hybrid materials. It is anticipated that this article can stimulate new concepts and advances providing a reference for breaking down the multidisciplinary borders in the field of bioinspired materials chemistry, especially at the nexus of computation and experiment, and to develop a rigorous materials-by-design paradigm.

An overview of the tribological and mechanical properties of PEEK and CFR-PEEK for use in total joint replacements.

Poly-ether-ether-ketone (PEEK) and PEEK composites are outstanding candidates for biomedical applications, such as orthopedic devices, where biocompatibility and modulus match with surrounding tissue are requisite for long-term success. The mechanical properties can be optimized by incorporating fillers such as continuous and chopped carbon fibers. While much is known about the mechanical and tribological behavior of PEEK composites, there are few articles that summarize the viability of using PEEK reinforced with carbon fibers in orthopedic implants. This paper reviews biocompatibility, tribological, and mechanical studies on PEEK and their composites with carbon fibers, notably PEEK reinforced with polyacrylonitrile (PAN)-based carbon fibers and PEEK reinforced with pitch-based carbon fibers, for application in orthopedics and total joint replacements (TJRs). The main objectives of this review are two-fold. Firstly, this paper aims to assist designers in making informed decisions on the suitability of using PEEK and PEEK composites in orthopedic applications; as it is not well understood how these materials perform on the whole in orthopedics and TJRs. Secondly, this paper aims to serve as a centralized paper in which researchers can gain information on the tribological and mechanical advancements of PEEK and PEEK composites.

A methodological framework for nanomechanical characterization of soft biomaterials and polymers.

Nanoindentation utilizes a hard indenter probe to deform the sample surface in order to measure local properties, such as indentation modulus and hardness. Initially intended for characterization of elastic and elastic-plastic materials, nanoindentation has more recently been utilized for viscoelastic solids as well as hydrated and soft biological materials. An advantage to nanoindentation is the ability to determine the nano- and microscale properties of materials with complex microstructures as well as those of limited sample dimension. Nanoindentation finds utility in the characterization of structural tissues, hydrogels, polymers and composites. Nevertheless, testing complexities such as adhesion and surface detection exist in nanoindentation of compliant viscoelastic solids and hydrated materials. These challenges require appropriate modifications in methodology and use of appropriate contact models to analyze nanoindentation data. A full discussion of protocol adjustments has yet to be assembled into a robust nanoindentation testing framework of soft biomaterials and polymers. We utilize existing nanoindentation literature and testing expertise in our laboratories to (1) address challenges and potential errors when performing indentations on soft or hydrated materials, (2) explore best practices for mitigating experimental error, and (3) develop a nanoindentation framework that serves researchers as a primer for nanoindentation testing of soft/hydrated biomaterials and polymers.

Comparison of macro-, micro- and nanomechanical properties of clinically-relevant UHMWPE formulations.

We characterized a set of eleven clinically relevant formulations of UHMWPE for total joint replacements. Although their molecular and supermolecular structure were quite similar as evidenced by IR, DSC and SAXS measurements, there were slight differences in their crystallinity (DSC crystallinity ranging from 52 to 61%), which were connected with processing conditions, such as the total radiation dose, thermal treatment and/or addition of biocompatible stabilizers. Mechanical properties were assessed at all length scales, using macroscale compression testing, non-instrumented and instrumented microindentation hardness testing (at loading forces ~500 mN), and nanoindentation hardness testing measured at both higher and lower loading (~4 mN and ~0.6 mN, respectively). In agreement with theoretical predictions, we found linear correlations between UHMWPE crystallinity and its stiffness-related properties (elastic moduli, yield stress, and hardness) at all length scales (macro-, micro- and nanoscale). Detailed statistical evaluation of our dataset showed that the accuracy and precision of the applied methods decreased in the following order: non-instrumented microindentation ≥ instrumented microindentation ≥ macromechanical properties ≥ nanoindentation measured at higher loading forces â‰« nanoindentation measured at lower loading forces. The results confirm that microindentation and nanoindentation at sufficiently high loading forces are reliable methods, suitable for UHMWPE characterization.

Nanomechanical analysis of medical grade PEEK and carbon fiber-reinforced PEEK composites.

Polyether ether ketone (PEEK) and PEEK composites are viable candidates for orthopedic implants owing to their ability for modulus match of surrounding bone tissue. The structural properties of these systems for load-bearing application in the body can be tailored by incorporating carbon fibers; to this end, polyacrylonitrile (PAN) and pitch fibers are commonly incorporated in the PEEK matrix. Mechanical property optimization for a given medical application requires consideration of carbon fiber type and volume fraction, as well as processing conditions for the composite systems. While much is known about the bulk mechanical properties of PEEK and PEEK composites, little is known about the nanomechanical properties of these systems. Insight into nanoscale behavior can offer valuable information about fiber-matrix interactions that may influence long-term integrity of these biomaterials when used in load bearing medical device applications. In this study, we utilize nanoindentation as a method to characterize mechanical behavior of clinical grade PEEK and PEEK composites. We examine PEEK formulations with pitch and PAN fibers and evaluate a range of thermal treatments known to influence polymer microstructure. We use a conospherical tip of 1.5 µm in radius and a conospherical tip of 20 µm radius to determine indentation modulus over different length scales. We correlate these findings with previous characterization on these same PEEK systems using microindentation. A novelty of this work is that we combine nanoindentation with k-means clustering to quantitatively discern the influence of heat treatment and carbon fiber type on the mechanical behavior of PEEK composites and their constituents. We demonstrate that nanoindentation is an effective characterization tool for discerning fiber-matrix interactions and measuring the mechanical behavior in response to thermal treatment and carbon fiber type in PEEK composites. Nanoindentation is shown to be a viable tool for characterizing complex biomaterials and can serve as an effective technique to guide optimization of microstructures for long-term structural applications in the body.

Relationship of Lower Lingual Arch Appliance Use and Impaction of Second Molars: A Retrospective Study.

Purpose: The purpose of this study was to determine the prevalence of permanent mandibular second molar impaction in pediatric patients treated with a lower lingual holding arch (LLHA) to maintain lower arch perimeter. Methods: In this retrospective study, 259 radiographs of nine- to 17-year-old pediatric patients were examined for permanent mandibular second molar impaction. A total of 127 patients with LLHA were compared to a control group of 132 patients who had not received LLHA. Other independent variables (sex and treatment age) were also tested for their value as predictors of impaction difficulty. For statistical analysis, the chi-square test was used. Logistic regression analysis was used to determine the statistical significance of the possible predictors of second molar impaction. Results: The mean age of the subjects was 9.2±1.7 (standard deviation) years old. The prevalence of permanent mandibular second molar impaction was 7.1 percent in patients with LLHA compared to 1.5 percent in the control group. The LLHA group had a likelihood of second molar impaction 6.53 times higher than controls after controlling for age. The relationship was significant with P-value of 0.021. Conclusions: The lower lingual holding arch is associated with an increased risk of second molar impaction in patients nine to 17 years old.

Material properties of ultra-high molecular weight polyethylene: Comparison of tension, compression, nanomechanics and microstructure across clinical formulations.

This is the first study to simultaneously measure material properties in tension, compression, nanoindentation as well as microstructure (crystallinity and lamellar level properties) across a wide variety of clinically relevant ultra-high molecular weight polyethylene (UHMWPE) formulations. Methodologies for the measurement of UHMWPE mechanical properties-namely elastic modulus, yield stress, yield strain, ultimate strength, energetic toughness, Poisson's ratio, hardness and constitutive variables-are evaluated. Engineering stress-strain behavior is compared to true stress-strain behavior for UHMWPE across a range of cross-linking and antioxidant chemistry. The tensile mechanical properties and constitutive behavior of UHMWPE are affected by resin type, antioxidant source and degree of cross-linking. Poisson's ratio is shown to be affected by resin type, antioxidant addition, and cross-linking dosage. Relationships between bulk mechanical properties from different measurement methodologies as well as microstructure are analyzed across all material formulations using Spearman rank correlation coefficients. Modulus and yield strength correlate in both tension and compression. Similarly, tensile and compressive properties including modulus and yield strength correlate strongly with crystallinity (Xc) and lamellar thickness (D). This work has broad application and provides a basis for interpreting the mechanical behavior of UHMWPE used in orthopedic implants.