We are developing a synthetic bacterial-based bioelectrochemical device for wound protecting and healing applications. Namely, we aim to create a self-powered, autonomous, and closed-loop system that detects and treats bacterial infection caused by Pseudomonas aeruginosa. We will also explore a new therapeutic treatment against P. aeruginosa with curcumin, a naturally-occurring compound found in turmeric known to exhibit many antibacterial and anti-inflammatory properties ¹.

An important hallmark of P. aeruginosa infection is the presence of pyocyanin (PYO), a redox-active quorum sensing and signaling molecule ². We will utilize the inherent redox activity of PYO to “turn on” our electrochemical circuit. Escherichia Coli (E.coli) expressing an engineered glucose dehydrogenase (GDH) can utilize PYO as its electron acceptor to oxidize glucose. Only when PYO is present, GDH is able to oxidize glucose and reduce PYO. In our fuel cell design, GDH will oxidize glucose, leading to reduction of PYO on the anode. Followingly, oxygen will be reduced on the cathode, generating electrical power. The fuel cell will be combined with a charge pump circuit and stored in a capacitor. When the capacitor reaches a certain threshold voltage, the capacitor will discharge and power a Bluetooth Low Energy (BLE) wireless transmission system to notify the user that PYO has been detected, indicative of P. aeruginosa infection ³.

The oxidation of glucose by GDH will also produce gluconic acid, decreasing the environmental pH. In this initial study, we will employ a pH-sensitive hydrogel that contains curcumin to act as an antibacterial agent that treats the wound site. Curcumin is a natural compound found in turmeric which has exhibited many antibacterial and anti-inflammatory properties ¹. The pH sensitive hydrogel will release curcumin via the pH decrease triggered by the detection of PYO, and will act as the delivery mechanism for effective curcumin treatment.

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen bacteria, meaning it primarily affects individuals with compromised immune systems or those who have underlying medical conditions. P. aeruginosa can cause a wide range of infections in the body, including the respiratory tract, urinary tract, wounds, and bloodstream.

P. aeruginosa infections are commonly found in healthcare settings such as hospitals and long-term care facilities where it can colonize medical devices such as catheters and ventilators, and spread between patients, leading to healthcare-associated infections. Ill patients in healthcare settings on ventilators or who have wounds or burns are particularly susceptible due to their body being in a state of recovery in an environment where P. aeruginosa can spread between people through contact by contaminated hands, equipment, and surfaces. For many such high-risk patients, P. aeruginosa can cause life-threatening complications, including pneumonia, sepsis, and necrotizing fasciitis. P. aeruginosa infections can be severe and difficult to treat due to the bacterium's intrinsic resistance to many antibiotics and its ability to develop acquired resistance through genetic mutations. As a result, P. aeruginosa infections are associated with higher rates of treatment failure and increased mortality compared to other bacterial infections.

Current detection methods for wound treatment take between 24-48 hours through use of swap samples and plate cultures. During this time, the infection has already begun to grow and form a biofilm, increasing the difficulty to eradicate the infection. Therefore, rapid and accurate detection systems are crucial in combating these virulent infections.

P. aerguinosa is a bacterium known for its high propensity to develop resistance against antibiotics, which is especially problematic when considering that P. aerguinosa is an opportunistic bacterium that causes infections in burn wounds and immunocompromised patients ⁴. Since P. aeruginosa develops resistance to antibiotics relatively quickly, and immunocompromised patients are likely to be on other antibiotics intended to treat a different bacterium, P. aerguinosa may develop resistances to these antibiotics as well. Therefore, novel treatments are needed to treat this bacterium—ideally those which have a low inherent propensity for bacteria to develop resistance against them.

Curcumin has many beneficial biological effects both directly accelerating wound healing through decreasing inflammation and increasing neovascularization, and indirectly accelerating wound healing via its antimicrobial effects ⁵.

In humans, curcumin can bind to nuclear factor kappa B, a transcription factor. This results in the inhibition of the production of markers of inflammation, including interleukins 1,8 and tumor necrosis factor-1 ⁵. educed inflammation accelerates wound healing. Curcumin can further reduce inflammation by binding to prostaglandin-endoperoxide synthase 2, reducing prostaglandin synthesis—prostaglandins are a paracrine hormone that stimulate inflammation ⁵.

Specifically with P. aeruginosa, curcumin can bind to many targets the bacterium uses in the quorum sensing process, which is required for biofilm formation. Curcumin results in a thinner biofilm and inhibits extracellular polymer secretion required for biofilms. It is important to note in physiological conditions, curcumin will autoxidize further into various compounds that have antimicrobial properties. ⁶. Furthermore, curcumin inhibits components of the bacterial DNA repair system by binding with bacterial proteins needed for cell survival. For example, curcumin has been shown to inhibit filamentous temperature-sensitive protein Z, bacterial RNA, and sortaseA, required for cell motility and division, protein synthesis, and cellular adhesion respectively ⁶. Lastly, curcumin can also insert in the bacterial cell membrane similar to cholesterol, causing cell membrane weakening, thinning, and increased permeability, including to other antibiotics ⁶.

Table adapted from ⁶.

Our project idea arose from early team discussions about “smart bandages.” Smart bandages were designed to improve on traditional bandages in healing, longevity, and anti-infection properties. We were interested in smart bandages’ variety of applications and the recent advancements in the field ⁷. We particularly found interest in two capabilities of Smart Bandages: sensing and antibiotic release. Smart bandage sensing of different factors associated with wound healing could be monitored both rapidly, for urgent wounds, and over time, for chronic wounds, which greatly improves wound management ⁸. Sensing capabilities of Smart Bandages have evolved to detect biomarkers related to infection of the wound site ⁹. Ongoing research has also focused on developing bandages which are able to release antibiotics or antimicrobials directly to the wound ⁹. We aimed to combine these preexisting ideas in the field and develop a device which would not only detect the presence of an infection, but also provide treatment for that infection in a closed-loop system. This symbiotic bioelectrical response is highlighted through our use of a novel enzymatic fuel cell ¹⁰. Hydrogels, which are networks of polymers engorged with water ¹¹, were selected as the structure which the system would reside in because of their ability to house bacteria, which has been thoroughly described in a variety of papers ^{12, 13},

Through our investigation of Smart Bandages, we encountered research on antibiotic resistant bacteria and their related biomarker. Specifically, we investigated P. aeruginosa, an opportunistic bacterium which is typically considered to be nosocomial. As stated previously, P. aeruginosa produces pyocyanin (PYO), a redox-active secondary metabolite important in the quorum sensing system that the bacteria useless to regulate virulence through the formation of reactive oxygen species.

Previous research groups have exploited the redox activity of PYO to sense the presence of P. aeruginosa by developing electrochemical sensors ^{14, 15}. Our group was inspired by research in the Sode Lab to combine these ideas into one project: a device that can both sense and treat P. aeruginosa infection.Their previous work reported on BioCapacitors, systems capable of providing power to electrical devices through enzyme fuel cells ³. We intend to use PYO as the “fuel” for our BioCapacitor, leading to downstream processes which alert patients of infection as well as releasing an antimicrobial compound.