Challenges in the characterization of plasma-processed three-dimensional polymeric scaffolds for biomedical applications

Using 1,8-cineole plasma with both pulsed and continuous depositions to modify commercially available wound dressing materials

The current clinical standards for infected chronic wounds are oral and topical antibiotics. These strategies are problematic because antibiotic resistance can occur with prolonged use. As an alternative to clinical methods, essential oils show promise in preventing bacterial growth. Specifically, 1,8-cineole-an active component in eucalyptus oil-exhibits antifungal, anti-inflammatory, and antibacterial properties. Applying 1,8-cineole directly onto a wound is challenging, however, due to its volatile nature. To combat this issue, plasma-enhanced chemical vapor deposition (PECVD) has been established as a method to deposit a stable 1,8-cineole-derived film on model surfaces (e.g., glass and electrospun polystyrene nanofibers). The current study represents an extension of previous work, where both pulsed and continuous 1,8-cineole plasmas were used to deposit a 1,8-cineole-derived film on two commercially available wound dressings. Three surface analyses were conducted to characterize the plasma-modified dressings. First, water contact angle goniometry data demonstrated a decrease in hydrofiber wettability after treatment. Through scanning electron spectroscopy, the surface morphology of both materials did not change upon treatment. When comparing pulsed and continuous treatments, deconvolution of high-resolution C1s x-ray photoelectron spectra showed no differences in functional group retention. Importantly, the chemical compositions of treated wound dressings were different compared to untreated materials. Overall, this work seeks to elucidate how different PECVD parameters affect the surface properties of wound dressings. Understanding these parameters represents a key step toward developing alternative chronic wound therapies.

Nanomaze Lure: Pheromone Sandwich in Graphene Oxide Interlayers for Sustainable Targeted Pest Control

The indiscriminate use of pesticides leads to irreparable damage to the ecosystem, which motivates for sustainable alternatives like pheromone-assisted pest management. The tomato pinworm Tuta absoluta is a major threat to tomato cultivation. Moreover, its green management technology uses a pheromone trap that has a short field life. To overcome this problem, a pheromone composite with graphene oxide (GO) and amine-modified graphene oxide (AGO) that can extend the diffusion path has been developed. The composite stimulates an effective electrophysiological response in the antenna, which results in trapping of a significantly higher number of insects as compared to the commercial septa, thus qualifying it for field evaluation. Compared to AGO, the GO composite has pheromones assembled into a multilayer, which increases the pheromone diffusion path. This in turn resulted in the extension of the pheromone life that proportionally increased the pest trapped. This technique will be beneficial to farmers as they have longer field efficacy to keep the pest damage low in an environmentally friendly manner.

Plasma-Assisted Deposition of Magnesium-Containing Coatings on Porous Scaffolds for Bone Tissue Engineering

Magnesium plays a pivotal role in the formation, growth, and repair of bone tissue; therefore, magnesium-based materials can be considered promising candidates for bone tissue engineering. This study aims to functionalize the surfaces of three-dimensional (3D) porous poly-ε caprolactone (PCL) scaffolds with magnesium-containing coatings using cold plasma-assisted deposition processes. For this purpose, the radiofrequency (RF) sputtering of a magnesium oxide target was carried out in a low-pressure plasma reactor using argon, water vapor, hydrogen, or mixtures of argon with one of the latter two options as the feed. Plasma processes produced significant differences in the chemical composition and wettability of the treated PCL samples, which are tightly related to the gas feed composition, as shown by X-ray photoelectron spectroscopy (XPS) and water contact angle (WCA) analyses. Cytocompatibility assays performed with Saos-2 osteoblast cells showed that deposited magnesium-containing thin films favor cell proliferation and adhesion on 3D scaffold surfaces, as well as cell colonization inside them. These films appear to be very promising for bone tissue regeneration.

Plasma Fabrication and SERS Functionality of Gold Crowned Silicon Submicrometer Pillars

Sequential plasma processes combined with specific lithographic methods allow for the fabrication of advanced material structures. In the present work, we used self-assembled colloidal monolayers as lithographic structures for the conformation of ordered Si submicrometer pillars by reactive ion etching. We explored different discharge conditions to optimize the Si pillar geometry. Selected structures were further decorated with gold by conventional sputtering, prior to colloidal monolayer lift-off. The resulting structures consist of a gold crown, that is, a cylindrical coating on the edge of the Si pillar and a cavity on top. We analysed the Au structures in terms of electronic properties by using X-ray absorption spectroscopy (XAS) prior to and after post-processing with thermal annealing at 300 °C and/or interaction with a gold etchant solution (KI). The angular dependent analysis of the plasmonic properties was studied with Fourier transformed UV-vis measurements. Certain conditions were selected to perform a surface enhanced Raman spectroscopy (SERS) evaluation of these platforms with two model dyes, prior to confirming the potential interest for a well-resolved analysis of filtered blood plasma.

Improving Internal Cell Colonization of Porous Scaffolds with Chemical Gradients Produced by Plasma Assisted Approaches

Cell colonization of the surrounding environment is a very significant process in both physiological and pathological events. In order to understand the tissue regeneration process and thereby provide guidance principles for designing new biomaterials, it is of paramount importance to study the cell colonization in the presence of physical, chemical, and biological cues. Flat "gradient" materials are generally used with this purpose. Three dimensional gradient scaffolds mimicking more precisely the situation in vivo are somewhat more complex to fabricate and characterize. Scaffolds for Tissue Engineering (TE) made of hydrophobic synthetic polymers do not allow good cell colonization: far from their periphery, in fact, internal cell colonization is usually low. In this research poly-ε caprolactone (PCL) scaffolds have been "decorated" with chemical gradients both on top and along their thickness by means of cold plasma processes, in order to improve cell colonization of their core. Plasma treatments with a mixture of argon and oxygen (Ar/O₂), as well as plasma deposition of differently cross-linked poly(ethylene oxide) (PEO)-like coatings, have been performed. This study establishes that cross-linked PEO-like domains interspaced with native PCL ones deposited only on top of the scaffold (i.e., coating that penetrates less than 300 μm inside the scaffold) are more effective in promoting cell colonization across the scaffolds than the other tested materials including superhydrophilic samples and that ones produced by tested double step approaches. Last but not least, one result of this research is that, in the case of plasma coatings with low deposition rates and porous materials with a low pore interconnectivity, it is possible to improve penetration of low pressure plasma active species inside the scaffold's core thorough a pretreatment of the porous materials (i.e., penetration up to 4500 mm far from topside).

Modification of a commercial thromboelastography instrument to measure coagulation dynamics with three-dimensional biomaterials

Three-dimensional synthetic constructs with complex geometries have immense potential for use in a multitude of blood-contacting applications. Understanding coagulation phenomena is arguably the most critical aspect for applications involving synthetic biomaterials; however, real-time evaluation of the clot formation while interfacing with these materials is difficult to achieve in a reproducible and robust manner. Here, work representing first steps toward addressing this deficit is presented, wherein modified consumables for a clinical instrument (a Thromboelastograph(®)) have been fabricated. Thromboelastography (TEG) measures viscoelastic properties throughout clot formation and therefore provides clinically relevant coagulation measurements in real time (i.e., kinetics and strength of clot formation). Through our modification, TEG consumables can readily accommodate three-dimensional materials (e.g., those for regenerative tissue applications). The authors performed proof-of-concept experiments using polymer scaffolds with a range of surface properties and demonstrated that variations in surface properties resulted in differences in blood plasma coagulation dynamics. For example, the maximum rate of thrombus generation ranged from 22.2 ± 2.2 (dyn/cm(2))/s for fluorocarbon coated scaffolds to 8.7 ± 1.0 (dyn/cm(2))/s for nitrogen-containing scaffolds. Through this work, the ability to make real-time coagulation activity measurements during constant coagulation factor interface with biomedically relevant materials is demonstrated.

Superelastic, superabsorbent and 3D nanofiber-assembled scaffold for tissue engineering

Fabrication of 3D scaffold to mimic the nanofibrous structure of the nature extracellular matrix (ECM) with appropriate mechanical properties and excellent biocompatibility, remain an important technical challenge in tissue engineering. The present study reports the strategy to fabricate a 3D nanofibrous scaffold with similar structure to collagen in ECM by combining electrospinning and freeze-drying technique. With the technique reported here, a nanofibrous structure scaffold with hydrophilic and superabsorbent properties can be readily prepared by Gelatin and Polylactic acid (PLA). In wet state the scaffold also shows a super-elastic property, which could bear a compressive strain as high as 80% and recovers its original shape afterwards. Moreover, after 6 days of culture, L-929 cells grow, proliferate and infiltrated into the scaffold. The results suggest that this 3D nanofibrous scaffold would be promising for varied field of tissue engineering application.

Conformal encapsulation of three-dimensional, bioresorbable polymeric scaffolds using plasma-enhanced chemical vapor deposition

Bioresorbable polymers such as poly(ε-caprolactone) (PCL) have a multitude of potential biomaterial applications such as controlled-release drug delivery and regenerative tissue engineering. For such biological applications, the fabrication of porous three-dimensional bioresorbable materials with tunable surface chemistry is critical to maximize their surface-to-volume ratio, mimic the extracellular matrix, and increase drug-loading capacity. Here, two different fluorocarbon (FC) precursors (octofluoropropane (C3F8) and hexafluoropropylene oxide (HFPO)) were used to deposit FC films on PCL scaffolds using plasma-enhanced chemical vapor deposition (PECVD). These two coating systems were chosen with the intent of modifying the scaffold surfaces to be bio-nonreactive while maintaining desirable bulk properties of the scaffold. X-ray photoelectron spectroscopy showed high-CF2 content films were deposited on both the exterior and interior of PCL scaffolds and that deposition behavior is PECVD system specific. Scanning electron microscopy data confirmed that FC film deposition yielded conformal rather than blanket coatings as the porous scaffold structure was maintained after plasma treatment. Treated scaffolds seeded with human dermal fibroblasts (HDF) demonstrate that the cells do not attach after 72 h and that the scaffolds are noncytotoxic to HDF. This work demonstrates conformal FC coatings can be deposited on 3D polymeric scaffolds using PECVD to fabricate 3D bio-nonreactive materials.