Abstract
Objective and Impact Statement. Real-time monitoring of the temperatures of regional tissue microenvironments can serve as the diagnostic basis for treating various health conditions and diseases. Introduction. Traditional thermal sensors allow measurements at surfaces or at near-surface regions of the skin or of certain body cavities. Evaluations at depth require implanted devices connected to external readout electronics via physical interfaces that lead to risks for infection and movement constraints for the patient. Also, surgical extraction procedures after a period of need can introduce additional risks and costs. Methods. Here, we report a wireless, bioresorbable class of temperature sensor that exploits multilayer photonic cavities, for continuous optical measurements of regional, deep-tissue microenvironments over a timeframe of interest followed by complete clearance via natural body processes. Results. The designs decouple the influence of detection angle from temperature on the reflection spectra, to enable high accuracy in sensing, as supported by in vitro experiments and optical simulations. Studies with devices implanted into subcutaneous tissues of both awake, freely moving and asleep animal models illustrate the applicability of this technology for in vivo measurements. Conclusion. The results demonstrate the use of bioresorbable materials in advanced photonic structures with unique capabilities in tracking of thermal signatures of tissue microenvironments, with potential relevance to human healthcare.
Highlights
The local temperatures of tissue microenvironments can serve as simple, yet important, diagnostic metrics relevant to a wide range of diseases and disorders [1,2,3,4,5,6], including those associated with chronic inflammation, traumatic injury, immunological irregularities, infections, and transplant rejection processes
Temperature is useful in these and other contexts because of the essential role that thermoregulatory processes play in maintaining normal cellular functions through a homeostatic balance between energy production and dissipation coordinated through metabolic mechanisms, local tissue perfusion, and hemodynamics [7,8,9]
Abnormalities in absolute values and/or temporal patterns of regional tissue temperatures can arise from certain immune responses and metabolic adjustments
Summary
The local temperatures of tissue microenvironments can serve as simple, yet important, diagnostic metrics relevant to a wide range of diseases and disorders [1,2,3,4,5,6], including those associated with chronic inflammation, traumatic injury, immunological irregularities, infections, and transplant rejection processes. Abnormalities in absolute values and/or temporal patterns of regional tissue temperatures can arise from certain immune responses and metabolic adjustments These signatures can provide early signs of critical illness, to allow for proactive treatments and intervention [10]. Precise and continuous measurements of temperatures at regions deep inside the body, by contrast, require invasive probes and/or disruptive surgical interventions, with potential for adverse effects, including immune responses and pain/discomfort [15]. Such strategies rely on permanent devices with wired connections for readout, when many scenarios demand wireless operation and/or temporary monitoring for time periods that match natural biological processes such as wound healing. Studies of the dissolution of the constituent materials and their biodistribution through various internal organs highlight processes by which these optical devices undergo bioresorption
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