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.

The COVID-19 and Taste Lab: A Mini Course-Based Undergraduate Research Experience on Taste Differences and COVID-19 Susceptibility.

Traditional course-based undergraduate research experiences (CUREs) are common approaches to expose students to authentic laboratory practices. Traditional CUREs typically take up most of or an entire semester, require a laboratory section or may be a standalone lab course, and require significant financial and time commitments by the institution and instructors. As such, CUREs are harder to implement at institutions with fewer resources. Here, we developed a mini-CURE, which are typically shorter in duration, called the COVID-19 and Taste Lab (CT-LAB). The CT-LAB requires significantly fewer resources ($0.05/student) and time commitment (two class periods) than traditional CUREs. CT-LAB centers around the biological relationship between COVID-19 susceptibility and taste status (non-taster, taster, and supertaster) as well as potential implications for public policy behavior. Students participated in a class-wide study where they examined if taste status was related to COVID-19 susceptibility. They found that non-tasters had a higher likelihood of testing positive previously for COVID-19 compared to tasters and supertasters. To assess student outcomes of this CURE, students completed a pre- and post-test assessment including a content test, STEM identity survey, taste test, COVID-19 history test, and a modified CURE survey. Content test scores improved while STEM identity and attitudes about science were unchanged. A direct comparison to a repository of traditional CUREs shows that the CT-LAB produced comparable benefits to traditional CUREs primarily in skills that were particularly relevant for the CT-LAB. This work suggests that mini-CUREs, even as brief as two class periods, could be a way to improve student outcomes.

Evaluating hydrophobic recovery of N2 and H2O(g) plasma modified silk fibroin films aged at ambient and elevated temperatures.

Silk fibroin is a naturally derived polymer with great potential for biomedical use due to its strength, lack of immune response, and ability to biodegrade. The relatively hydrophobic nature of silk, however, can cause challenges with cell adhesion in vivo. Therefore, modification must be performed to improve the surface hydrophilicity, enhancing silk utility in the biomedical space. Low-temperature plasma (LTP) treatment is an established method for polymer modification and has the benefits of being a solvent-free, adaptable process. N2 and H2O(g) LTP treatments are both well-documented as strategies to enhance polar functional groups on a polymer's surface. However, many polymers tend to revert to their original hydrophobic state upon aging, reversing the effects of LTP modification. The hydrophobic recovery of N2 and H2O(g) LTP-modified silk has not been previously studied but has important implications for the uses and longevity of silk substrates in biomedical contexts. The goal of this study was to systematically evaluate the hydrophobic recovery of N2 and H2O(g) LTP-treated silk films. Films were LTP-modified using optimized plasma parameters (applied power, pressure, treatment time) and aged under both ambient and elevated temperature conditions up to 6 weeks after the initial treatment. Silk film surface properties were evaluated immediately after treatment and throughout the aging process using both water contact angle goniometry and x-ray photoelectron spectroscopy. LTP-treated silk films demonstrated a significant decrease in hydrophobicity compared to the untreated controls. Remarkably, both N2 and H2O(g) LTP modifications resulted in surfaces that retained hydrophilic properties over the 6 week aging period. Our findings represent a departure from what has been previously demonstrated in most LTP-modified synthetic polymers, suggesting that the secondary structure of silk fibroin plays a critical role in resisting hydrophobic recovery.

Utilizing Radio Frequency Plasma Treatment to Modify Polymeric Materials for Biomedical Applications.

Studies that utilize radio frequency plasma modification as a strategy to tune the surface properties of polymeric constructs with the goal of enhancing their use as biomedical devices have grown considerably in number over the past decade. In this Review, we present the importance of plasma surface treatment to biomedical applications, including tissue engineering and wound healing. First, we introduce several key polymeric materials of interest for use as biomaterials, including those that are naturally derived and synthetic. We, then, provide an overview of possible outcomes of plasma modification, such as surface activation, etching, and deposition of a thin film, all of which can be used to alter the surface properties of a given polymer. Following this discussion, we review the methods used to characterize plasma-treated polymer surface properties, as well as the techniques used to evaluate their interactions with biological species of interest such as mammalian cells, bacteria, and blood components. To close, we provide a perspective on future outlooks of this exciting and rapidly evolving field.

Towards Non-stick Silk: Tuning the Hydrophobicity of Silk Fibroin Protein.

Silk fibroin protein is a biomaterial with excellent biocompatibility and low immunogenicity. These properties have catapulted the material as a leader for extensive use in stents, catheters, and wound dressings. Modulation of hydrophobicity of silk fibroin protein to further expand the scope and utility however has been elusive. We report that installing perfluorocarbon chains on the surface of silk fibroin transforms this water-soluble protein into a remarkably hydrophobic polymer that can be solvent-cast. A clear relationship emerged between fluorine content of the modified silk and film hydrophobicity. Water contact angles of the most decorated silk fibroin protein exceeded that of Teflon®. We further show that water uptake in prefabricated silk bars is dramatically reduced, extending their lifetimes, and maintaining mechanical integrity. These results highlight the power of chemistry under moderate conditions to install unnatural groups onto the silk fibroin surface and will enable further exploration into applications of this versatile biomaterial.

Silk-Based Therapeutics Targeting Pseudomonas aeruginosa.

Pseudomonas aeruginosa (P. aeruginosa) infections may lead to severe damage of the cornea, mucosa, and skin. The highly aggressive nature of P. aeruginosa and the rise in multi-drug resistance, particularly in nosocomial settings, lead to an increased risk for permanent tissue damage and potentially death. Thus, a growing need exists to develop alternative treatments to reduce both the occurrence of bacterial infection and biofilm development, as well as pathological progression post-infection. Silk derived from Bombyx mori silkworms serves as a unique biomaterial that is biocompatible with low immunogenicity and high versatility, and thereby ideal for stabilizing therapeutics. In this study, we assessed the cytotoxicity of P. aeruginosa on human corneal stromal stem cells and two mucosal cell lines (Caco-2 and HT29-MTX). To determine whether antibiotic-immobilized scaffolds can serve as alternative therapeutics to free, diffuse forms, we developed novel gentamicin-conjugated silk films as functional scaffolds and compared antimicrobial effects and free gentamicin. The advantages of generating a surface coating with a covalently-bound antibiotic may reduce potential side-effects associated with free gentamicin, as well as limit the diffusion of the drug. Our results suggest that gentamicin conjugated to native silk and carboxyl-enriched silk inhibits P. aeruginosa growth. Development of stabilized antibiotic treatments with surface toxicity selective against bacteria may serve as an alternative approach to treat active infections, as well as potential prophylactic use as coatings in high-risk cases, such as post-surgical complications or prolonged hospitalization.

Conductive Silk-Based Composites Using Biobased Carbon Materials.

There is great interest in developing conductive biomaterials for the manufacturing of sensors or flexible electronics with applications in healthcare, tracking human motion, or in situ strain measurements. These biomaterials aim to overcome the mismatch in mechanical properties at the interface between typical rigid semiconductor sensors and soft, often uneven biological surfaces or tissues for in vivo and ex vivo applications. Here, the use of biobased carbons to fabricate conductive, highly stretchable, flexible, and biocompatible silk-based composite biomaterials is demonstrated. Biobased carbons are synthesized via hydrothermal processing, an aqueous thermochemical method that converts biomass into a carbonaceous material that can be applied upon activation as conductive filler in composite biomaterials. Experimental synthesis and full-atomistic molecular dynamics modeling are combined to synthesize and characterize these conductive composite biomaterials, made entirely from renewable sources and with promising applications in fields like biomedicine, energy, and electronics.

Time of flight secondary ion mass spectrometry-A method to evaluate plasma-modified three-dimensional scaffold chemistry.

Biopolymers are used extensively in the manufacture of porous scaffolds for a variety of biological applications. The surfaces of these scaffolds are often modified to encourage specific interactions such as surface modification of scaffolds to prevent fouling or to promote a cell supportive environment for tissue engineering implants. However, few techniques can effectively characterize the uniformity of surface modifications in a porous scaffold. By filling the scaffold pores through polymer embedding, followed by analysis with imaging time-of-flight secondary ion mass spectrometry (ToF-SIMS), the distribution and composition of surface chemical species though complex porous scaffolds can be characterized. This method is demonstrated on poly(caprolactone) scaffolds modified with a low-fouling plasma-deposited coating from octafluoropropane via plasma enhanced chemical vapor deposition. A gradient distribution of CF+/CF3+ is observed for scaffolds plasma treated for 5 min, whereas a 20 min treatment results in more uniform distribution of the surface modification throughout the entire scaffold. The authors expect this approach to be widely applicable for ToF-SIMS analysis of scaffolds modified by multiple plasma processing techniques as well as alternative surface modification approaches.

Solvent-Free Strategy To Encapsulate Degradable, Implantable Metals in Silk Fibroin.

Implantable electronics hold enormous clinical potential for diagnosis and treatment of neurodegenerative and cardiac diseases and abnormalities. Transient devices are attractive alternatives to conventional silicon electrodes, as they can provide short-term electrical stimulation/recording followed by complete device degradation, mitigating the need for removal surgeries. Packaging transient metals is inherently challenging as they degrade upon contact with aqueous conditions. Development of new transient metal packaging strategies is a critical step toward transient device development. In this fundamental work, a solvent-free compression molding approach to encapsulate magnesium, a resorbable metal, in silk fibroin protein is reported. Silk fibroin was selected because of its processing versatility, desirable mechanical properties, compatibility with biological environments, and controllable degradation behavior in aqueous environments. The silk/magnesium composites were fabricated via compression molding, followed by water annealing to modify the secondary structure of the silk protein matrix to tune physical properties. Transient composite properties as a function of water annealing time are presented, which elucidate synergies between silk physical properties and degradation kinetics of the encapsulated magnesium, information useful in the design of multifunctional, transient metal-based constructs.

Plasma-modified nitric oxide-releasing polymer films exhibit time-delayed 8-log reduction in growth of bacteria.

Tygon(®) and other poly(vinyl chloride)-derived polymers are frequently used for tubing in blood transfusions, hemodialysis, and other extracorporeal circuit applications. These materials, however, tend to promote bacterial proliferation which contributes to the high risk of infection associated with device use. Antibacterial agents, such as nitric oxide donors, can be incorporated into these materials to eliminate bacteria before they can proliferate. The release of the antimicrobial agent from the device, however, is challenging to control and sustain on timescales relevant to blood transport procedures. Surface modification techniques can be employed to address challenges with controlled drug release. Here, surface modification using H2O (v) plasma is explored as a potential method to improve the biocompatibility of biomedical polymers, namely, to tune the nitric oxide-releasing capabilities from Tygon films. Film properties are evaluated pre- and post-treatment by contact angle goniometry, x-ray photoelectron spectroscopy, and optical profilometry. H2O (v) plasma treatment significantly enhances the wettability of the nitric-oxide releasing films, doubles film oxygen content, and maintains surface roughness. Using the kill rate method, the authors determine both treated and untreated films cause an 8 log reduction in the population of both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. Notably, however, H2O (v) plasma treatment delays the kill rate of treated films by 24 h, yet antibacterial efficacy is not diminished. Results of nitric oxide release, measured via chemiluminescent detection, are also reported and correlated to the observed kill rate behavior. Overall, the observed delay in biocidal agent release caused by our treatment indicates that plasma surface modification is an important route toward achieving controlled drug release from polymeric biomedical devices.

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.

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.