SURFI

Caraua Fibers

In August 2014, Dr. Drelich visited the Military Institute of Engineering (MIE) in Rio de Janeiro (Brazil) and established a research collaboration with this institute in the area of natural fibers and composite materials. At that time he started to to write a review paper with collaborators from Brazil as well as Turkey. This review has been just published in the Polymer Reviews journal and is entitled “Re-emerging field of lignocellulosic fiber – polymer composites and ionizing radiation technology in their formulation“.

Natural cellulose-based fibers offer low cost, low density composite reinforcement with good strength and stiffness. Because of their annual renewability and biodegradability, natural fibers have materialized as environmentally-friendly alternatives to synthetic fibers in the last two decades. They are replacing synthetic materials in some traditional composites in industrial manufacturing sectors such as automotive, construction, furniture, and other consumer goods. In this work, the use of lignocellulosic fibers in green materials engineering, particularly their application as polymeric composite reinforcement and surface treatment via ionizing radiation, are reviewed. Because these cellulose-based materials are intrinsically hydrophilic, they require surface modification to improve their affinity for hydrophobic polymeric matrices, which enhances the strength, durability, and service lifetime of the resulting lignocellulosic fiber-polymer composites. In spite of a long history of using chemical methods in the modification of material surfaces, including the surface of lignocellulosic fibers, recent research leans instead towards application of ionizing radiation. Ionizing radiation methods are considered superior to chemical methods, as they are viewed as clean, energy saving, and environmentally friendly. Recent applications of controlled ionizing radiation doses in the formulation of natural fiber – reinforced polymeric composites resulted in products with enhanced fiber-polymer interfacial bonding without affecting the inner structure of lignocellulosic fibers. These applications are critically reviewed in this contribution.

Biodegradable Stent

Metallic stents are commonly used to promote revascularization and maintain patency of plaqued or damaged arteries following balloon angioplasty. To mitigate the long-term side effects associated with corrosion-resistant stents (i.e. chronic inflammation and late stage thrombosis), a new generation of so-called “bioabsorbable” stents is currently being developed. The bioabsorbable coronary stents will corrode and be absorbed by the artery after completing their task as vascular scaffolding. Research spanning the last two decades has focused on biodegradable polymeric, iron-based, and magnesium-based stent materials. The inherent mechanical and surface properties of metals make them more attractive stent material candidates than their polymeric counterparts. Unfortunately, iron produces a voluminous, retained oxide product in the arterial wall, whereas magnesium and its alloys corrode too rapidly. A third class of metallic bioabsorbable materials that are based on zinc has been introduced in the last few years. As summarized in this contribution, this new zinc-based class of materials demonstrates the potential for an absorbable metallic stent with the mechanical and biodegradation characteristics required for optimal stent performance. They appear to be free of flaws that limit the application of iron- and magnesium-based alloys, and polymers. In the new review article entitled “Biodegradable Metals for Cardiovascular Stents: from Clinical Concerns to Recent Zn-Alloys” published in Advanced Healthcare Materials, we compare bioabsorbable materials and summarize progress towards bioabsorbable stents. We emphasize on current understanding of physiological and biological benefits of zinc and its biocompatibility. Finally, our review provides an outlook on challenges in designing zinc-based stents of optimal mechanical properties and biodegradation rate.

Sugarcane Fibers in Armor

The residue obtained from sugarcane juice extraction, in sugar and ethanol production, is known as bagasse. At the industrial mill, bagasse is either incinerated for steam and power generation or discarded as a waste. The incorporation of bagasse waste into polymeric composites for ballistic resistant materials is presented in our new publication entitled “Sugarcane Bagasse Waste in Composites for Multilayered Armor” published in the European Polymer Journal. This is the result of our continuing collaboration with Prof. Sergio N. Monteiro from the Institute of Military in Rio de Janeiro, Brazil. In this study, plates of epoxy composites reinforced with either raw bagasse or extracted bagasse fibers were characterized. The 30 vol% bagasse composites were selectedused as a second layer, backing a front ceramic, in multilayered armors against 7.62 mm ammunition. Ballistic performance of composites was compared to Kevlar™ plates used in commercial multilayered armor systems. Results of ballistic tests indicated that multilayered armors with Kevlar™ and bagasse fiber composites satisfied the National Institute of Justice (NIJ) norm, and displayed similar depths of indentation (19 – 21 mm) in a clay witness. By contrast, the armor with raw bagasse composite demonstrated worse performance, with nearly two times deeper indentations, some of which exceeded the NIJ limit. Economical analysis revealed that armor with bagasse fiber composite is nearly 180% less expensive than a corresponding armor with Kevlar™. Therefore, it is shown for the first time that composites reinforced with fibers extracted from sugarcane bagasse (a large scale worldwide generated waste) could replace Kevlar™ in multilayered armor systems making them cheaper and more sustainable.

Human Aortic Endothelial Cells on Zn

Zinc (Zn) and its alloys have been introduced by our team as a new class of biodegradable metals with potential application for making biodegradable vascular stents. Although our previous feasibility in vivo study suggested biocompatibility of Zn –based implants in vascular environments, a thorough understanding of how Zn and its ions affect surrounding cells was lacking. In our comparative study published in the ACS Biomaterials Science and Engineering journal in the article entitled “In Vitro Cytotoxicity, Adhesion, and Proliferation of Human Vascular Cells Exposed to Zinc,” three vascular cell types were used including human endothelial cells (HAEC), human aortic smooth muscle cells (AoSMC), and human dermal fibroblasts (hDF), to advance understanding of Zn-cell interactions. Aqueous cytotoxicity using a Zn ion insult assay resulted in LD50 values of 50 μM for hDF, 70 μM for AoSMC, and 265 μM for HAEC. Direct cell contact with the metallic Zn surface resulted initially in cell attachment, but was quickly followed by cell death. After modification of the Zn surface using a layer of gelatin—intended to mimic a protein layer seen in vivo—the cells were able to attach and proliferate on the Zn surface. Further experiments demonstrated a Zn dose-dependent effect on cell spreading and migration, suggesting that both adhesion and cell mobility may be hindered by free Zn ions.
This publication is the result of our collaboration with Prof. Feng Zhao’s team of the Department of Biomedical Engineering, and this work was led by Dr. Emily Shearier who graduated with her PhD degree in December 2015.