Search for: All records

AbstractPectin is a crucial polysaccharide in plant primary cell walls. Despite its wide applications, the conformational stability of homogalacturonan pectin under different environmental conditions remains an area of ongoing investigation. To address this issue, molecular dynamics simulation is used to analyze the conformations of pectin in dry and aqueous environments. The results reveal that pectin adopts a 2-fold helical structure in dry conditions. In the presence of explicit water molecules, a 3-fold helical structure occurs. This conformational shift is driven by hydrogen bond formation. The number of hydrogen bonds increases from 0.8 to 5.1 per repeat unit of pectin in the hydrated state, with water molecules acting as key donors for hydrogen bonds. These findings provide insight into the conformations of pectin and contribute to a deeper understanding of its structural stability in various environments. Graphical abstract 

Deformation response evaluation is essential for understanding material behavior, providing insight into their suitability across many fields, such as biomechanics, materials science, and other engineering disciplines. Specialized applications in biomedical and soft materials demand miniaturization for testing under a microscope or spectroscopic stages. The current commercial machines on the market are often large, expensive, or heavy, making them difficult to use for specific needs. This hardware addresses this need by developing a cost-effective, miniature, and programmable system that can be tailored to individual lab requirements to fit multiple microscopic stages. By utilizing a bipolar stepper motor attached to a lead screw and sliding linear stage, programmed and controlled by an Arduino microcontroller, the system can apply specialized stretch under uniaxial static or cyclic loading. The developed system can be assembled for less than $100, making cost-effectiveness a central focus of this development. The device performance was validated using a variety of samples and microscope tests, with sample deformation captured in real time. The device is compatible with live imaging on microscopic stages, accommodating specialized research needs across applications. 

Cellulose and pectin are the key components of plant primary cell walls (PCWs) responsible for their dynamic growth, as they transition from a flexible structure at early stages to a rigid unit at full growth. However, a fundamental understanding of the pectin-cellulose interface and interactions within PCW and the underlying mechanics of these materials remained a subject of debate, hindering progress in bioinspired and sustainable composite designs to meet the demands of emerging fields, from flexible robotics to regenerative medicine. This study presents a multiscale investigation into the CNC-pectin interface and the influence of calcium ion-mediated cross-links, integrating molecular dynamics (MD) simulations, supported by experimental data of molecular interactions via spectroscopic studies and bulk interactions via viscosity measurements. The MD simulations revealed cross-linking mechanisms of “zipper” and “egg-box”, both being present, depending on local composite properties and ionic concentrations, with the zipper model being the dominant mechanism by almost 10 times with relative insensitivity to Ca2+, thus providing deeper insights into the long-ongoing discussion on pectin Ca2+ interactions. The zipper model is driven by the coordination of Ca2+ with deprotonated carboxyl groups (–COO–), while the egg-box model involves both carboxyl and hydroxyl groups (–OH). The confirmation via spectroscopic studies, characterized by consistent shifts in Raman peaks of the carboxylate group, indicating the rearrangement of ester and carboxyl groups of HGA, and concentration-dependent peak enhancement trends of the hydroxyl group in the FTIR study involved in the two models validated the MD outcomes. Furthermore, MD predicted viscosity aligned with bulk properties provides a basis for the future extension of the work on quantifying interface energies. Overall, the study provides fundamental knowledge on Ca2+-mediated CNC-pectin interactions, helping to resolve reported experimental discrepancies and offering design guidelines for advanced pectin-based biocomposites. 

The plant cell wall (CW) is a fiber-reinforced composite present as an interconnected unit providing plants with structural form and multifunctionality, from flexibility at the growing stage to stiffness and strength at the mature stage. This study investigates the xylem CW of sunflower stems to identify structural and compositional transitions underlying its growth demands. The study was conducted using Raman spectroscopy, scanning electron microscopy, and instrumented nanoindentation techniques on samples from four-week-old and eight-week-old. At these two growth points, both longitudinal and transverse sections are analyzed for as-cut healthy growth and after selective enzymatic treatment to target cellulose and pectin removal, the key components of growing CW. The results revealed an increase in cellulose content and crystallinity with age, indicating increased organization in CW. Single and double helical coiling, changes in wall thickness, and the presence of pitted walls, as observed via SEM, revealed the geometrical strategies adopted by CW for supporting longitudinal growth while optimizing stiffness and water transportation. Greater disruption of its structure and strength post-enzymatic treatment, especially pectin removal, was observed via the opening of helical coiling, the impact on cellulose organization, and the loss of modulus and hardness, highlighting the important role of pectin in maintaining the structure and the interdependence of pectin and cellulose components of CW. These results are presented in the context of design strategies such as directional reinforcements, spatial optimization, polymer composition balance and their interactions, which can be translated for biomimicking composite design and manufacturing for targeted performance achievement. 

While the relative abundance of plant biopolymers can vary significantly depending on the cell type and maturation, pectin and cellulose nanocrystals are among the two key biopolymers found in many plants’ primary cell walls at the early growth stage. Nanocomposites that utilize cellulose nanocrystals have gained extensive interest over the years. Limited knowledge regarding pectin and the interaction between pectin and cellulose is available because pectin was considered a non-loading-bearing component with little interaction with cellulose. However, recent developments in primary cell wall structure have shifted, and pectin is viewed as a part of the reinforcement structure. Thus, understanding the role of pectin has become relevant in creating advanced bio-composites that mimic the structure of primary cell walls. This work aims to provide fundamental information on the interaction between pectin and cellulose nanocrystals using molecular dynamics simulations. A dry interaction is modeled to replicate their status in a composite, where water is removed via processing such as freeze-drying. Interphase models consisting of two cellulose nanocrystals and a homogalacturonan pectin molecule are created to simulate the interfacial structure, including binding potential energy and hydrogen bonds. Friction and adhesion responses are predicted by moving one cellulose nanocrystal against the other. The results show that a pectin molecule increases the friction at the interphase by 14 and 8 times between CNC (200) and (110) surfaces, respectively, which is correlated to the significantly increased binding energies and interfacial hydrogen bonds, regardless of pectin’s charge density. On the other hand, the adhesion force is increased by 1.1 times with a pectin molecule between the CNC (110) surfaces. Adhesion, however, reduces to 1/5 between CNC (200) surfaces with embedded pectin, which is attributed to disrupted$$\pi$$ $\pi$-$$\pi$$ $\pi$interaction. The simulation results reveal the atomistic level interaction between pectin and cellulose nanocrystals, which is essential for designing nanocomposites using pectin and cellulose nanocrystals as main components. 

The global spread of Fall Armyworm (FAW, Spodoptera frugiperda) has posed significant challenges to crop productivity and food security, with current pest management relying heavily on synthetic pesticides. This study explores the green synthesis of neem extract and neem oil-based Azadirachtin nanopesticides using cellulose acetate (CA) as a carrier polymer, focusing on their efficacy against FAW. The objective was to assess whether CA-NEP (neem extract nanopesticides) and CA-NOL (neem oil nanopesticide) formulations were effective at FAW control with minimal ecological impact. The nanopesticides were synthesized by electrospinning at concentrations of 5 %, 10 %, 20 %, 33 %, and 50 % (w/w) and characterized using Scanning Electron Microscopy and Fourier Transform Infrared spectroscopy. Azadirachtin content was quantified using Liquid Chromatography-Mass Spectroscopy. CA-NEP and CA-NOL followed first-order, and Korsmeyer-Peppas release kinetics, respectively. Feeding bioassays showed high FAW mortality rates, with 20 %-50 % CA-NEP achieving greater than 40 % mortality in less than 3 days and 50 % CA-NEP reaching 100 % mortality by day five. The mortality rates of FAW due to feeding on CA-NOL-treated corn leaves reached 40 % after 4 and 6 days, respectively, for 50 % and 33 % CA-NOL. Placing nanopesticide fibers next to corn seeds during planting significantly reduced FAW leaf damage. The lethal dose 50 (LD50) analyses showed that 13 % CA-NEP is the optimal concentration for FAW control. Environmental safety assessments on earthworms showed no acute or chronic toxicity, indicating that the nanopesticides suit ecologically sensitive areas. Therefore, these nanopesticide formulations provide a promising, eco-friendly alternative for sustainable FAW control and management with enhanced efficacy and safety. 

The structural integrity of MXene and MXene-based materials is important across applications from sensors to energy storage. While MXene processing has received significant attention, its structural integrity for real-world applications remains challenging due to its flake-like structure. Here the mechanical response of layered MXene-polymer nanocomposites (MPC) with high MXene concentration (>70 %) and bioinspired nacre-like brick-and-mortar architecture is investigated to offer insights for MPC design and processing. An automated finite element analysis (FEA) framework is developed to analyze MPC models with randomized geometries and multiple combinations of the parameter space. Specifically, the influence of concentration, aspect ratio (AR), flake thickness, flake distribution, and interfacial strength is investigated. The results reveal property trends such as increasing elastic modulus, strength, and toughness with increasing cohesive strength and concentration for lower AR (=40, 60) but a decreasing trend at higher AR of 75. Local structural features like flake distribution, overlapping MXene lengths, and interconnected polymers in adjacent layers was found a critical determinant of performance. For example, stronger cohesive interaction showed 6X high toughness (291 226 ) compared to weaker case (50 24 ), but the large scatter highlighted the impact of microstructural features. The results are compared and validated with theoretical, computational, and experimental work. The findings provide valuable guidance for optimizing MPC design and their processing. Finally, the automation of the framework allows the design to be extended beyond the current system and chosen material combinations. 

The electrospinning method is increasingly in demand due to its capability to produce fibers in the nanometer to micrometer range, with applications in diverse fields including biomedical, filtration, energy storage, and sensing. Many of these applications demand control over fiber layout and diameter. However, a standard flat plate collector yields random fibers with limited control over diameter and density. Other viable solutions offering a higher level of control are either scarce or substantially expensive, impeding the accessibility of this vital technique. This study addresses the challenge by designing an affordable laboratory-scale electrospinning setup with interchangeable collectors, enabling the creation of targeted fibers from random, aligned, and coiled. The collectors include the standard flat plate and two additional designs, which are a rotating drum and a spinneret tip collector. The rotating drum collector has adjustable speed control to collect aligned fibers and exhibits stability even at high rotational speeds. The spinneret tip collector was designed to produce helically coiled fibers. The setup was validated by directed fiber formation using polycaprolactone (PCL), a biodegradable and FDA-approved polymer. Overall, the uniqueness of the design lies in its affordability, modifiability, and replicability using readily available materials, thus extending the reach of the electrospinning technique. 

The cell wall (CW) in plants is an anisotropic fiber-reinforced composite material made from multiple components (cellulose, hemicellulose, pectin, and lignin), with their structure and properties varying throughout the growth process to accommodate its multifunctional biological and structural needs. Revealing the architecture of plant CW and the role of its constituent and their interfaces is the key driver for this study. Here we characterized the composite-structure-mechanical response outcome of CW under component removal using enzymatic treatment, followed by instrumented indentation, optical microscopy, and Raman spectroscopy analysis to illustrate the changes. The results of the study indicate the critical role of pectin in the structure, where its breakage f1rom the cell wall leads to a maximum loss in structure and strength both for the early and later stages of plant growth. This study forms the basis of an expanded future investigation into the cell wall structure toward designing flexible fiber-reinforced composites for a broad range of applications.