Medical Implants

Medical implants are synthetic devices surgically placed inside the human body for various medical purposes, often for extended periods. They serve a range of functions, including replacing body parts such as hips or knees, delivering medications for pain relief, regulating vital functions like heart rate, and providing support to organs and tissues^[1]. These implants are not only life-saving but also life-enhancing. For instance, pacemakers and cardiac defibrillators can prevent life-threatening heart issues in high-risk patients, while others can restore mobility and improve the overall quality of life. They also have the potential to reduce healthcare costs by minimizing the need for ongoing treatments and enabling individuals to return to work sooner^[1]. However, the benefits of medical implants are not without risks, particularly related to the surgical procedure itself, which can sometimes lead to infections on the implant. Balancing the advantages and potential drawbacks, these devices continue to play a vital role in modern healthcare^[1].

Prosthetic joints

Among the users of medical implants, there is a usually overlooked group of people that we took an interest in. These are the people who went through joint replacement surgery, an orthopedic procedure in which a dysfunctional joint surface is replaced with an orthopedic prosthesis type of medical implant^[2]. Why are we interested in the lives and the situation of these patients?

Is the number of joint replacement surgeries performed in the Netherlands in 2022.^[3] In the USA in 2021, there were almost 2.4 million hip and knee surgeries performed from over 1150 institutions representing an 18.3% increase in total procedural volume compared with that in 2020. ^[4]

In Organisation for Economic Co-operation and Development countries, there has been a constant incline reported for joint replacement surgeries since 2009, due to the large rate of obesity and the aging of the population ^[5][6]. Moreover, the rise of these surgeries is expected in the following ten years - it is estimated that by 2030, the number of total knee replacements performed in the US will increase by more than 600 percent compared to 2005, while total hip replacements are expected to increase by almost 200 percent over the same time period. ^[7] Approximately 790,000 total knee replacements and over 450,000 hip replacements are performed annually in the U.S. This number continues to grow as the population ages. ^[8]

In the Netherlands, the number of orthopedic surgeries is also increasing, with an expectancy that there will be ~57,900 knee arthroplasties in 2030, a growth of 297% compared with 2005.^[9]
Reasons for needing an orthopedic surgery could be chronic diseases like arthritis, (which is a global health concern on the rise), but also sport-related injuries and aging.^[5] Any of us could, at some point in the future, require joint placement surgery.

More than 65% of all human infections are believed to be associated with biofilms ^[16]. Biofilms represent clusters of bacterial cells encased in a matrix of extracellular polymeric substances (EPS) ^[17][18]. This matrix comprises exopolysaccharides, proteins, teichoic acids, lipids, and extracellular DNA ^[16]. Biofilms form when bacteria adhere to surfaces in moist environments and begin replication. They attach to a surface through the secretion of a viscous, adhesive EPS that forms the matrix.

Biofilms can manifest on a wide array of surfaces, including metals, plastics, natural materials like rocks, medical implants, kitchen countetops, contact lenses, swimming pool walls, and even human or animal tissue. You might have encountered biofilms in your daily life without realizing it (ever noticed slime in sink pipes?). While a single microorganism can build a biofilm community, nature typically assembles biofilms from mixtures of numerous bacterial species and other microorganisms ^[19].

Biofilm infections in orthopedic practice are one of the most significant, due to bone and joint sequelae. The surfaces of commonly used othopedic components such as titanium (and its alloys), stainless steel, cobalt-chromium, various polymeric biomaterials (e.g. ceramics, hydroxyapatite, and polyethylene), and polymethylmethacrylate (PMMA) cement are all susceptible to colonization by biofilm-forming bacteria ^[16]. Acute Infections, occurring within 4-6 weeks of surgery, result from surgical exposure, making the skin susceptible to bacteria.

Late Infections, emerging 6 weeks or more after surgery, often stem from bacteria introduced from other body sites, underscoring the importance of regular follow-ups with surgeons and primary care physicians. Age-related immune weakening can facilitate late infections. Bacteria reaching hip or knee implants form biofilms, typically maturing over about 3 weeks. Eliminating mature biofilms usually requires implant removal and tissue cleansing. Early detection can preserve implants and eliminate biofilms, while research explores non-removal biofilm soltions ^[20].

Current diagnostics

Detecting infection presents challenges as symptoms vary among patients. Some experience continuous pain, swelling, drainage, or redness, while others report dull aches or persistent joint stiffness^[20]. In addition, distinguishing infection from other issues, such as aseptic loosening due to wear reactions, can be difficult. Even when bacteria are cultured in vitro from patient samples, it may not accurately reflect their in vivo growth state as bacteria can exist in both planktonic and biofilm modes. Acute infections, primarily caused by rapidly growing planktonic bacteria, are more straightforward to diagnose and treat. However, chronic subacute or indolent infections, often linked to biofilms, prove more elusive ^[21]. Occasionally, fluid or blood collection may form under the incision, creating an infection-prone environment. Surgeons may need to perform invasive drainage or wash-out procedures to prevent or treat joint infections, despite introducing potential risks ^[20].

If the infection is suspected, the surgeon typically conducts X-rays, and blood work, and may sample fluid from the affected joint implant. Blood work is a common method but lacks precise location information ^[20]. Traditional bacterial culturing detected biofilms only 30% of the time compared to 80-90% with histology and microscopy, obtained from fluid samples ^[21]. However, although the most accurate method, fluid sampling, is also the most invasive. Enhancing diagnostic methods is crucial for effective infection management, especially in cases linked to implants.

Current treatment

The treatment of biofilms poses significant challenges. Although 2-stage revision surgery can achieve up to 90% success in infection eradcation, it is a costly and hospital-intensive process ^[15]. With the growing number of joint replacement procedures, more patients will require revision surgeries, emphasizing the need for efficient treatment ^[15].

Treatment strategies for joint infections depend on the timing of detection ^[19]. Early infections (within 3 weeks of surgery/symptoms) can undergo a "washout" procedure, with intravenous antibiotics prescribed for about 6 weeks post-surgery, followed by possible long-term oral antibiotics ^[19]. In contrast, infections discovered after 3 weeks are more challenging due to biofilm formation ^[19]. The common approach is Two-stage revision surgery, involving temporarily removing all implant components and using an antibiotic cement-coated temporary implant before reinserting the final implant, which is very invasive ^[19].

The structural nature of biofilms renders them difficult to treat with antibiotics ^[22]. This could be due to the existence of slow or non-growing cells within the biofilm, the presence of bacterial subpopulations with different phenotypic levels of resistance within biofilms, overexpression of genes, and stress responses to hostile environmental conditions ^[16].

Not only are biofilms inherently resistant to antimicrobial agents (1000 times more tolerant than planktonic cells), but they are also capable of developing resistance through the exchange of resistance genes ^[23]. The urgency of antimicrobial resistance is a global phenomenon, and the shortage of novel antibiotics, as well as the logistic challenges regarding the supply of these drugs to countries all around the world, render this topic a highly relevant one ^[24].

Biofilms in implants and devices are a global concern given the difficulty of their detection and treatment. Biofilm formation on implants is specifically of interest, due to the increasingly larger number of medical procedures involving such devices ^[23]. In addition to the stress that medical establishments and professionals have to bear concerning these procedures, the formation of biofilm and the subsequent need for further interventions are only maximizing this issue.

Efforts are being made to mitigate the problem of biofilm formation on implants ^[23]. Researchers are developing new implant materials and coatings that discourage biofilm formation and enhance the body's ability to fight infections ^[23]. Additionally, improved surgical techniques, infection control protocols, and the use of antimicrobial agents are being explored to prevent and treat biofilm-related infections more effetively ^[23].

The adhesion of bacteria to the implant surface and establishment of the early biofilm has been identified as a therapeutic target to halt PJI before it has had a chance to become established ^[23]. Future directions in the prevention and treatment of biofilms in orthopedics include prosthetic antimicrobial coatings, antibiotic-coated metals, localized antibiotic delivery, and nonantibiotic biofilm targets, but not synthetic biology approaches ^[21].

We believe that now is the appropriate time to tackle this challenge as more and more attention is being paid to drug-resistant microorganclasses as well as several economic sectors, such as healthcare, agriculture, and veterinary industries^[23]. In addition to that, we were prompted to attempt to solve this problem by the current increase of interest in phage-related therapies, either as an alternative or complementary to antibiotics. These two aspects set the ideal environment for our project, in the current worldwide scenario.

Our innovative approach would offer alternative diagnostics pathways for biofilm, as well as facilitate the recovery of the patients and help medical specialists with monitoring the devices' status post-intervention.

This solution involves engineering an E. coli-based biosensor that detects the formation of biofilm and gives a light output as a signal. In add-žtion, the biosensor cells would use the M13 phagemid a helper phage duo to produce Disperisn B-fused phages that would be able to degrade the EPS lattice. The biosensor would utilize an inducible promoter that senses quorum-sensing molecules secreted by infectious E.coli during biofilm formation ^[16][17]. One such promoter is the c-di-GMP-sensing promoter design by 2022 iGEM team CUG-China. The final aspect of the biosensor setup is electronic devices paired with compatible software that translates the biochemical signals of the biological component to electronic signals, and further to visual representation through the software. In its final design, our biosensor would consist of the biological component contained in a wearable biosensor device, that patients who are at risk of developing a biofilm-related infection would use in the sensitive stages of their recovery.

Giving the medical professionals and the patients an early indication of the formation of a biofilm and additionally slowing down the biofilm formation process with Dispersion B phages would provide enough time to tackle the infection in its early stages by using antibiotics and other conventional methods. In a broader picture, we would like to design this system to be modular, so it can be adapted to the various needs of patients affected by implant-related infections. With this solution, we hope to tackle the most important aspects of the biofilm fomation issue and provide a tool that is useful both for medical specialists as well as the general public.
We have divided the development of our project into two components: biological and electronic components. For more details, visit the [engineering] and [electronic device] pages of our wiki.

The biosensor relies on its electric component to detect light emitted by two fluorescent proteins. It all starts with an optical fiber cable that sends out light, exciting the electrons in these proteins, and causing them to emit light in a specific range. Once this light is generated, it undergoes detection and amplification. To establish a wireless connection with a mobile device, an Arduino board is employed as an intermediary. This board enables seamless communication between the biosensor and the mobile device, with a mobile app in development to display the detected light intensity for users. While prioritizing human safety is the ultimate goal, the initial focus is on creating a functional prototype capable of detecting light and displaying results via the mobile app.

In terms of how the components work together, the optical fiber cable gathers emitted light and sends it to a phototransistor located outside the sensor's enclosure. The phototransistor receives this light, and as its intensity varies, it affects the current passing through it, leading to voltage changes at its output. These voltage changes are closely monitored by the Arduino board using its Analog-to-Digital Converter (ADC), accessible via pin A0. This monitoring allows the system to detect changes in light intensity, revealing whether the LEDs are emitting light or not. The visual summary of how the electronic component works is visible in Figure 3, and for more details visit the [electronic device] page.