A Review on Polymers for Biomedical Applications on Hard and Soft Tissues and Prosthetic Limbs.

In the past decades, there has been a significant increase in the use of polymers for biomedical applications. The global medical polymer market size was valued at USD 19.92 billion in 2022 and is expected to grow at a CAGR of 8.0% from 2023 to 2030 despite some limitations, such as cost (financial limitation), strength compared to metal plates for bone fracture, design optimization and incorporation of reinforcement. Recently, this increase has been more pronounced due to important advances in synthesis and modification techniques for the design of novel biomaterials and their behavior in vitro and in vivo. Also, modern medicine allows the use of less invasive surgeries and faster surgical sutures. Besides their use in the human body, polymer biomedical materials must have desired physical, chemical, biological, biomechanical, and degradation properties. This review summarizes the use of polymers for biomedical applications, mainly focusing on hard and soft tissues, prosthetic limbs, dental applications, and bone fracture repair. The main properties, gaps, and trends are discussed.

Effect of the Graphene Quantum Dot Content on the Thermal, Dynamic-Mechanical, and Morphological Properties of Epoxy Resin.

Different amounts of graphene quantum dots (CQDs) (0, 1, 2.5, and 5 wt%) were incorporated into an epoxy matrix. The thermal conductivity, density, morphology, and dynamic mechanical thermal (DMTA) properties were reused from the study of Seibert et al.. The Pearson plot showed a high correlation between mass loading, thermal conductivity, and thermal diffusivity. A poorer correlation with density and heat capacity was observed. At lower CQD concentrations (0.1 wt%), the fracture surface showed to be more heterogeneous, while at higher amounts (2.5 and 5 wt%), a more homogeneous surface was observed. The storage modulus values did not change with the CQD amount. But the extension of the glassy plateau increased with higher CQD contents, with an increase of ~40 °C for the 5 wt% compared to the 2.5 wt% and almost twice compared to the neat epoxy. This result is attributed to the intrinsic characteristics of the filler. Additionally, lower energy dissipation and a higher glass transition temperature were observed with the CQD amount. The novelty and importance are related to the fact that for more rigid matrices (corroborated with the literature), the mechanical properties did not change, because the polymer bridging mechanism was not present, in spite of the excellent CQD dispersion as well as the filler amount. On the other hand, thermal conductivity is directly related to particle size and dispersion.

Artificial Neural Networks for Pyrolysis, Thermal Analysis, and Thermokinetic Studies: The Status Quo.

Artificial neural networks (ANNs) are a method of machine learning (ML) that is now widely used in physics, chemistry, and material science. ANN can learn from data to identify nonlinear trends and give accurate predictions. ML methods, and ANNs in particular, have already demonstrated their worth in solving various chemical engineering problems, but applications in pyrolysis, thermal analysis, and, especially, thermokinetic studies are still in an initiatory stage. The present article gives a critical overview and summary of the available literature on applying ANNs in the field of pyrolysis, thermal analysis, and thermokinetic studies. More than 100 papers from these research areas are surveyed. Some approaches from the broad field of chemical engineering are discussed as the venues for possible transfer to the field of pyrolysis and thermal analysis studies in general. It is stressed that the current thermokinetic applications of ANNs are yet to evolve significantly to reach the capabilities of the existing isoconversional and model-fitting methods.

Recent studies on modified cellulose/nanocellulose epoxy composites: A systematic review.

Cellulose and its derivatives are widely explored for films and thickening of pharmaceutical solutions, in paints, as reinforcement in composites, among others. This versatility is due to advantages such as renewability, low cost, and environmental friendliness. When used in polymer composites, due to the hydrophilic character of the cellulose, surface chemical modification is highly recommended to improve its compatibility with the polymeric matrix. Hence, this paper presents a systematic review of chemically modified cellulose/epoxy resin composites focusing on the last five years. The investigation followed the PRISMA protocol that delivers a meticulous summary of all available primary research in response to a research question. After including/excluding steps, thirty-six studies were included in the review. The results were presented focusing on thermal, mechanical and dynamic-mechanical properties of the composites. In brief, this methodology helped identifying the main gaps in knowledge in that field.

Effect of chemical treatment of pineapple crown fiber in the production, chemical composition, crystalline structure, thermal stability and thermal degradation kinetic properties of cellulosic materials.

Recently, the growing environmental concerns and economic demands have driven the need to develop effective solutions for the treatment of vegetal fibers to be used as renewable source for various industrial applications. The present study aimed to explore pineapple crown fibers (PCs) as an alternative source of cellulose. The three treatments (alcohol-insoluble residue (AIR), alkaline (AT), and organosolv) evaluated promoted chemical and morphological changes to the PCs. Fresh and treated PCs were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), thermogravimetric analysis (TG), and chemical composition. The XRD results showed that the Cellulose-I allomorph was not altered during extraction, and that the crystallinity index of the fibers treated with AT, first bleaching step, second bleaching step, and the second bleaching step followed by KOH treatment (2B_KOH) increased to 77.8; 83.2; 83.5 and 86% when compared with fresh PC (62.3%). Results from the thermal analysis revealed that thermal stability increased for the isolated cellulose, and the maximum degradation for (2B_KOH) is 350 °C. Chemical composition results showed a decrease in the content of hemicellulose, lignin and other soluble materials after alkaline treatment, suggesting high-quality 2B_KOH with 74.6% of cellulose. SEM revealed changes in the morphological structure on fibers. Alkaline treatment followed by H2O2 bleaching is an excellent alternative for the removal of non-cellulosic material and facilitates the isolation of cellulose. These results suggested that there is a potential to isolate cellulose from PC via the sequence of treatment of a methodology by chlorite-free.

The influence of silane surface modification on microcrystalline cellulose characteristics.

Microcrystalline cellulose (MCC) can be a reinforcement in composites, especially after surface modification. In this paper, MCC was modified using 3-aminopropyltriethoxysilane (APTES) in the following ratios (MCC/APTES): 1:3, 1:4, 1:5, 1:10). The MCC morphologies did not change with the treatment even though the distribution of APTES over the MCC surface varied. FTIR analysis showed MCC and APTES characteristic peaks for all samples. The crystallinity index (CI) decreased with the APTES ratio. The non-isothermal kinetic degradation by thermogravimetric analysis in different heating rates was studiedin order to evaluate the kinetic triplet: activation energy Ea, exponential factor (A), and reaction order (f(α)). The Ea dependence on conversion degree was not affected, but two degradation steps were observed for all samples. Ratios up to 1:4 suggested two consecutive autocatalytic degradation mechanisms. The 1:5 and 1:10 ratios caused a change in the most probable degradation mechanism for nucleation followed by autocatalytic degradation mechanism.