AVS 70 Session BI2-MoM: Functional Materials

Naturally-derived polymers are the fastest-growing biomaterials because they are non-immunogenic and are able to recapitulate a range of biological tissues through bulk mechanical property tuning. This remarkable materials class includes silk, collagen and cellulose, all of which have high potential for use as tissue engineering implants, biosensors, and drug delivery devices. One drawback is that naturally-derived polymers are bioinert, exhibiting non-specific interactions with proteins, cells, bacteria, enzymes, and other biological species. Another possible drawback in some applications includes fixed degradation kinetics which may not match the rate required for a given application. Plasma-enhanced chemical vapor deposition (PECVD) is a useful strategy to address both drawbacks, providing a chemically customizable coating that can control interfacial interactions while also modulating degradation.

Large-scale detection of and active response to changing conditions at interfaces is a promising pathway to facilitating the long-term growth and stability of the biotic component of biotic/abiotic living materials. In Nature, one method of both detecting and actively responding to environmental changes is by using vascular networks as intermediaries that transport signals and materials from one location to another. In this work, we explore various methods of embedding vascular networks into abiotic polymeric matrices that use widely available fused filament deposition model (FDM) 3D printing. We test each method for the efficacy of diffusion to and from the interface, as well as how well it can be used in both hydrophobic and hydrophilic abiotic polymers. Our goal is to create detection-and/or-response systems to support the growth of biotic systems located at abiotic polymer interfaces in a low-cost, easily scalable manner, paving the way for the creation of durable and adaptable biotic/abiotic living materials.

Polylactic acid (PLA) and chitosan (CS) are biopolymers with vast potential in the biomedical field. Their biodegradability and non-toxicity in vivo makes them useful as tissue engineering scaffolds. The slower degradability of PLA is suitable for slower-healing bone tissues, while the faster degradability of CS is suitable for faster-healing soft tissues. Nevertheless, both polymers are inherently hydrophobic, which would potentially restrict the cell adhesion desirable for tissue engineering applications. There is some evidence that hydrophilic surfaces are preferable for cell adhesion and growth. Previous studies display the promise of utilizing radio-frequency nitrogen plasma treatment in increasing the surface hydrophilicity of PLA and CS. In addition, nitrogen plasma treatment polymers have been shown to exhibit improved surface cell adhesion properties. Many plasma treated polymers, including PLA and CS exhibit a phenomenon known as hydrophobic recovery, where the polymers partially retain their original hydrophobic properties with age. Hydrophilicity loss in treated PLA and CS is detrimental, especially in applications that require cell adhesion. Methods of preventing this phenomenon in PLA and CS are widely unexplored.

This work explored the impact of various aging conditions (storage in vacuum, cold temperature, and air) on the surface hydrophilicity of nitrogen-plasma-treated PLA and CS following treatment. Films were prepared as model substrates using the solvent-casting method. The films were treated in a RF plasma reactor under optimized parameters (power, pressure, and treatment time). After treatment, the films were aged in the different aging environments for two weeks. Throughout the aging period, multiple surface analyses were conducted on samples exposed to the various preservation environments, including untreated samples as controls. Surface wettability analysis utilizing water contact angle goniometry displayed that vacuum aged samples possess the least hydrophobic recovery in comparison to the other aging conditions. Additionally, surface chemical composition was examined using x-ray photoelectron spectroscopy. Expanding these treatment preservation methods to PLA and CS has potential to positively impact their use as scaffolds in the biomedical field.

Superhydrophobic surfaces offer effective resistance against the adhesion of biomolecules like bacteria and proteins. This property holds promise for their application in medical devices, aiming to mitigate complications such as infections and thrombosis. Hierarchical roughness plays a pivotal role in enhancing superhydrophobicity by providing multiple scales of surface features, which collectively contribute to increased water repellency and reduced adhesion of biomolecules. Traditional fabrication of topographical roughness requires specific substrates or solvent-based processing, which could raise concerns regarding biotoxicity. We constructed topographical roughness using an initiated chemical vapor deposition (iCVD) method that is applicable independent of substrate material and geometry. We studied how the processing parameters affect the formed surface topography and the bio-adhesion properties. In addition, surfaces with hierarchical roughness were created by varying the vapor deposition parameters in situ. The hierarchically roughened surface demonstrated superhydrophobicity, with more than 80% reduction in the adhered bacteria and a 98.8% decrease in the surface fibrin clotting, as compared with the homogeneously rough surface. This iCVD technique presents a novel avenue for attaining superhydrophobicity on medical devices to reduce device-related adverse events.

Hemorrhage is one of the main causes of preventable civilian death and on the battlefield. According to a report by the USAMRDC in 2022, nearly 50% of combat deaths have been due to exsanguinating hemorrhage. Of those, about half could have been saved if timely, appropriate care had been available. This underscores the need to develop appropriate FDA-approved hemostatic treatments. While external wound injury can be treated mostly by visual inspection, internal hemorrhages are often much more intractable. The need to treat trauma wounds requires an immediate solution that can be applied by individual soldiers in the field swiftly and efficiently. In our current study, we report a silicone-based hemostatic bandage system that is both antibacterial and self-expanding. The two-component hemostatic system chemically reacts in situ to form a stretchable foam that generates autogenous pressure on the wound to control bleeding. It can be easily administered with a dual-syringe device, and when the components interact on delivery, hydrogen peroxide decomposition is catalyzed by silver oxide, releasing oxygen to expand the siloxane matrix into a rigid ‘foam’ within seconds. This foam or sponge then acts as a 'tamponade' arresting further bleeding. The adhesive properties of the foam render them optimal for wound-dressing applications and the presence of silver oxide imparts antibacterial effects against both Gram-positive and Gram-negative strains of bacteria. Optimization of the constituents allows control over system temperature and porosity. Support data include studies on rheology, adhesion, and in-vitro assays. To further assess the efficacy of the foam, a unique mannequin system capable of simulating a deep abdominal wound has been employed. The objective of this novel hemostatic agent is to provide the injured party with a means to rapidly stagnate or arrest bleeding from external and internal wounds in a manner superior to those currently available. This unique formulation presents an easy and economical approach to a hemostatic bandage system with spontaneous self-expanding properties, capable of remaining functional in inclement weather conditions.