(Nanowerk Spotlight) The complex process of wound healing has long challenged medical professionals seeking to monitor recovery accurately and non-invasively. Traditional methods of assessing wound status often rely on visual inspection or periodic sampling, providing only intermittent glimpses into the healing process. These limitations have spurred research into advanced biosensors capable of continuous, real-time monitoring of wound conditions.
One key indicator of wound healing is the pH level of the wound environment. During normal healing, the pH typically shifts from slightly alkaline immediately after injury to slightly acidic as healing progresses. Deviations from this pattern can signal complications such as infections or delayed healing. Recent years have seen the development of various bioelectronic pH sensors, but most have taken the form of external patches or bandages, limiting their use to superficial wounds.
Advancements in flexible electronics and nanomaterials have recently opened new possibilities for creating miniaturized, implantable sensors. These technologies enable the development of electronics that can conform to the body’s contours and withstand its dynamic environment. Simultaneously, progress in electrochemical sensing techniques has improved the accuracy and stability of pH measurements in biological fluids.
Building on these developments, a team of researchers in Korea has now introduced an innovative approach that combines the functionality of a pH sensor with a standard medical suture. This integration addresses a critical need in wound care by enabling direct, continuous monitoring of pH levels within deeper tissues, where traditional sensors cannot reach.
a) Illustration of the wound monitoring system based on the pH-sensing suture, showing the suture directly applied to the wound site and connected to a wireless readout module for monitoring local pH levels by measuring its Open Circuit Potential. b) Design of the pH-sensing suture, comprising a core supporting suture thread, a PANI-coated working fiber electrode, and an Ag/AgCl-coated reference fiber electrode. (click on image to enlarge)
The pH-sensing suture consists of two main components: a polyaniline (PANI)-coated working electrode and a silver/silver chloride (Ag/AgCl) reference electrode. These electrodes wind helically around a core thread made from standard medical suture material. A thin layer of biocompatible polymer then coats the entire assembly, leaving only the sensing portion exposed.
The sensor operates based on the electrochemical properties of PANI, which alters its molecular structure in response to surrounding pH levels. This change modifies the electrical potential between the working and reference electrodes, allowing pH determination by measuring the voltage difference between them.
A key innovation in the design is the use of gold nanoparticles (AuNPs) embedded in a flexible, biocompatible polymer matrix to create the base electrodes. This composite structure provides both high electrical conductivity and mechanical flexibility, enabling the suture to maintain its sensing capabilities even when subjected to bending and stretching during and after the suturing process.
Extensive testing characterized the performance of the pH-sensing suture. It demonstrated a sensitivity of 58.9 millivolts per pH unit, closely matching theoretical predictions. The sensor showed minimal measurement discrepancies when cycling between different pH levels, maintained stability over time, and exhibited excellent selectivity for hydrogen ions in the presence of other common ions found in wound environments.
Crucially, the pH-sensing suture retained its performance even after undergoing 10 000 cycles of intense bending, simulating the mechanical stresses it might encounter in real-world use. The team also verified that the suture’s surface friction was comparable to or lower than that of standard medical sutures, ensuring it would not cause additional tissue damage during insertion.
To demonstrate practical applicability, the researchers conducted in vivo experiments using mouse models. They created both normal incision wounds and a chronic wound model mimicking atopic dermatitis. The pH-sensing suture closed these wounds, and a custom-designed wireless readout module collected its readings over several days.
In the normal incision model, the suture successfully tracked the expected pattern of pH change during healing. The pH initially increased to about 6.8, then gradually returned to the normal range of 5.4-5.8 over approximately one week. In the chronic wound model, the pH remained elevated at around 7.7 for a longer period, consistent with delayed healing and prolonged inflammation. The researchers also showed that treatment with an anti-inflammatory medication accelerated the normalization of pH in the chronic wound model, demonstrating the potential of the pH-sensing suture for monitoring treatment efficacy.
The team thoroughly evaluated the biocompatibility of the pH-sensing suture through in vitro studies with multiple cell types, including human skin fibroblasts and stem cells. These tests showed no significant cytotoxicity or inhibition of cell growth, indicating that the suture is safe for use in living tissues.
While the pH-sensing suture represents a significant advance in wound monitoring technology, further development is needed before clinical use. One limitation is that the current version is not biodegradable, necessitating a second procedure for removal after use. Future research will focus on developing a fully biodegradable version that the body can absorb once its monitoring function is complete.
Another area for improvement is enhancing the suture’s mechanical properties to facilitate its use in standard surgical procedures. The researchers plan to optimize the design and materials to increase its flexibility and ease of handling during suturing and knot-tying.
The potential applications of this technology extend beyond wound monitoring. Similar sensor-integrated sutures could measure other important biomarkers, such as glucose levels or specific proteins associated with infection or inflammation. This could lead to a new generation of “smart” surgical materials that provide real-time feedback on tissue health and healing progress.
The development of the pH-sensing suture represents a convergence of multiple technological advances in materials science, flexible electronics, and biosensors. By integrating these technologies into a familiar and widely used medical device – the surgical suture – the researchers have created a tool that could significantly improve post-surgical care and chronic wound management.
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