Implantable Sensors for Post‐Surgical Monitoring of Vascular Complications

For surgeries involving vessel anastomosis, it is critical to ensure fluent blood flow and to monitor the occurrence of vascular complications. However, the current clinical methods are ineffective in achieving direct, continuous, and accurate monitoring. At present, implantable sensors are widely used and explored in various biomedical applications, including cardiovascular disease, neurological disorders, cancer treatment, and health monitoring. They can be easily placed during surgical procedures and offer irreplaceable advantages including directness, continuity, and higher accuracy of monitoring. Based on this, the types of implantable sensors for vascular monitoring are reviewed, and some preclinical research advances which are expected to provide promising methods for post‐surgical vascular complications are discussed. In the end, the future perspectives of the research of implantable sensors for post‐surgical monitoring are put forward. It is believed that implantable sensors hold great promise in clinical translation, providing physicians with more accurate, continuous, and real‐time monitoring results, helping to improve surgical success and patient outcomes.


Introduction
Vessel anastomosis is a surgical technique often applied in cardiovascular surgery, vascular surgery, organ transplantation, and reconstructive surgery, and early detection of vascular complications is crucial to prevent further adverse outcomes.However, DOI: 10.1002/adsr.202200095more desirable methods of monitoring remain the goal to pursue.In reconstructive surgery, the current methods commonly used in the clinic include interval measurements of clinical examination, application of external Doppler evaluation, or near-infrared spectroscopy. [1]he clinical examination includes observation of color change and tissue turgor, measurement of tissue temperature, capillary refill, and pinprick test through the surface of transplanted tissue. [2]Like clinical examination, external Doppler evaluation or near-infrared spectroscopy is also performed through the body surface.Although these approaches can be performed non-invasively, they do not allow for direct assessment of vessels and are not suitable when the tissue is buried deeply and invisible from the outside. [3,4]For allogeneic solid organ transplantation, vascular complications such as stenosis and thrombosis are important causes of graft failure which are often serious and can lead to the death of the patient. [5,6]Despite the seriousness of the consequences, monitoring is often more difficult because the surgical site is often deep and ideal methods are currently lacking. [7]In the treatment of cardiovascular or vascular disease, early stenosis, reduced blood flow, and thrombus are common after surgical bypass surgery or removal of plaque from diseased vessels. [8]he difficulty of detecting the surgical site is also a challenge in clinical practice.
Therefore, to realize the continuous monitoring of deep vascular complications after surgery, the application of implantable sensors is promising. [9][12][13] However, they often require cables to be connected to bedside devices with a high false positive rate, and the removal process may cause damage to the vessels. [3]The vessels are usually fragile after surgery and can be easily affected by the surrounding environment; so, it is also very important to reduce the local interference of monitoring devices to avoid additional complications and reduction of reliability of monitoring.This places a higher demand on the application of implantable sensors.
Those implanted sensors can be classified into wired and wireless sensors depending on whether they use physical wires to interface with external technology. [14]Implantable wireless sensors need to transmit data wirelessly, and power needs to be supplied in a completely different way. [15]For data transmission, the weakening phenomenon of wireless signals in biological tissues and the security problems in vivo need to be paid attention to.The data transmission methods include Bluetooth protocol, LAN, and other network protocols. [16,17]According to the way of supplying power, there are active and passive devices.The former includes power systems, either with built-in batteries or powered wirelessly.The latter does not contain batteries and is powered externally. [16]Wireless power supply techniques include inductive coupling, radio frequency, mid-field, ultrasonic, magnetoelectric, and optical methods. [15]The application of implantable wireless sensors can help to avoid complications resulting from wire penetration from the body, can reduce patient discomfort and inconvenience of movement, can reduce the impact of wire connection on measurement accuracy, is more suitable for patients in the perioperative period, and helps to achieve continuous monitoring after discharge, which has irreplaceable advantages and is the trend of future development. [18]n summary, for post-surgical vascular complication monitoring, the challenges we face include: 1) the goals of reducing the size of the implanted part, reducing the impact on the vessels and surrounding tissues, ensuring early mobilization of patients, improving long-term biocompatibility, and extending the service life need to be pursued and balanced.2) Due to the unique nature of these patients and the effects of the surgery itself, the design of sensors and the wireless technology needs to be considered accordingly, including the attenuation of the signal and the damage to the human body caused by the transmission.3) Considering the severity of post-surgical complications, the importance of timely management, additional complications, and increased costs caused by unnecessary reoperation, it is important to reduce the false-positive and false-negative rates and to improve the reliability and timeliness of communications.4) For different diseases and surgeries, there may be differences in the need for service life, the indicators suitable for monitoring, and so on, but improving the scope of application is still the goal to be pursued.5) The impact of sterilization needs to be considered.
This paper reviews the progress of research on implantable sensors for post-surgical monitoring of vascular complications.First, we summarize the types of implantable sensors used for this purpose.We then describe the progress of the studies according to different monitoring strategies and select several preclinical studies that we consider to be promisin.Last, we provide an outlook for future research.

Classifications and Sensing Mechanism of Implantable Sensors for Monitoring
A sensor node typically includes a sensing unit, a processing unit, a communication unit, and a power supply. [19]Here, the classification is done mainly by the type of measured parameters.

Mechanical Sensors
The flow of blood in the arteries under physiological conditions varies cyclically with the intermittent diastole of the heart, causing changes in blood flow velocity, vessel diameter, blood flow, and so on. [20]The occurrence of vascular complications is detected by the changes in these parameters afterward.[23] The proximity of these types of sensors to the blood vessel allows them to recognize the change in mechanical signal and subsequently convert changes in resistance, capacitance, or induced charge under pressure or strain into an electrical signal output. [24,25]

Optical Sensors
Optical sensors generally refer to devices that convert changes in light into electronic signals.[28] The monitoring method based on the optical principle has been widely used in the clinic. [29]Nearinfrared spectroscopy can detect tissues by measuring the scattering and absorption of near-infrared light.It has been widely used to monitor tissue oxygen saturation through the skin. [30]Compared with implantable Doppler probes, it can identify occlusion earlier and more reliably. [31]In addition, it has been proven to be cost-effective. [1,32]However, due to the limitation of penetration depth, the monitoring of deep tissue cannot be realized.The laser Doppler flowmeter uses a laser beam to detect the velocity of capillary blood flow by measuring the frequency shift of the reflected light invasively or noninvasively. [33,34]Optical sensors can also be combined with oxygen sensing film to create optical oxygen sensors for monitoring tissue oxygenation. [35]

Thermal Sensors
Thermal sensors are used to measure temperature in space, and the sensing elements of thermal sensors used for tissue temperature measurement in vivo include devices such as thermocouples, resistance temperature detectors, thermistors, and semiconductor temperature sensors. [36,37]Blood perfusion in the transplanted tissue affects the temperature as well as the thermal reactivity of the tissue; therefore, thermal sensors can be used to indirectly monitor vascular complications. [38]Considering the penetration capability, the use of implantable microvascular blood flow probes allows for a more accurate estimation of tissue perfusion compared to non-invasive devices. [39]

Ultrasound Sensors
Ultrasonography is an ultrasound-based diagnostic technique that allows the visualization of tissues through the reflection effect of sound waves, where the Doppler mode has been widely used in clinical settings for the examination of blood vessels, where the direction and relative velocity of blood movement relative to the probe is assessed through the Doppler effect; and thus, information on the velocity and frequency of blood flow is obtained. [33,34,40]For transducers based on ultrasound technology, the ultrasound transducer is the central part, and usually, a piezoelectric transducer is used to generate acoustic waves, which are subsequently converted into electrical signals after receiving echoes. [40]igure 1.Biodegradable and flexible arterial-pulse sensor for the wireless monitoring of blood flow.Reproduced with permission. [43]Copyright 2019, Springer Nature America.a) Illustration of the sensor with an exposed view of the bilayer coil structure for wireless data transmission and the cuff-type pulse sensor wrapped around the artery.b) The two inductors that are in series with a fixed capacitor correspond to the top and bottom Mg coils, and the PLLA insulation layer, respectively.c) Equivalent electrical circuit.d) Sensing concept.

Other Types of Sensors
Oxygen partial pressure can be measured not only by optical sensors but also by electrochemical means, such as Licox PtO 2 probes and other Clark-type electrodes, which have been applied in clinical practice, which are based on the current generated by the electrochemical reduction of oxygen. [13,35,41,42]Microdialysis allows real-time monitoring of metabolite concentrations, such as glucose and lactate, in transplanted tissues by chemical methods. [12]The concentration of these metabolites can reflect the metabolic status of the tissue and thus determine the status of the transplanted tissue.

Using Capacitive Sensors
Bao et al. reported a biodegradable pressure sensor for real-time monitoring of arterial blood flow that can be wrapped outside arteries of different diameters and does not need to be removed after use (Figure 1). [43]Based on fringe-field capacitor technology, arterial blood flow was measured by contact or non-contact mode.Due to the changes of arterial diameter with blood flow pulsation, capacitance changes and is measured by the capacitive sensor, resulting in a change in the resonant frequency of the inductance-capacitance-resistance (LCR) circuit, which is coupled inductively to an external reader coil for wireless monitoring through the skin without a battery.The sensor can be easily wrapped around arteries less than 1 mm in diameter.The sensor was subsequently implanted in rats for up to 12 weeks and verified to have good biocompatibility. [44]Follow-up studies have further demonstrated that this proposed wireless capacitive sensor system can detect arterial conditions at least 20 cm upstream and downstream of the sensor and can remain stable for up to 3 weeks in vivo, longer than the use time of the Cook-Swartz Probe. [8]The investigators also noted that future studies will need to extend the duration of the study and overcome the limitations of implantation depth.

Using Piezoresistive Sensors
Chong et al. prepared a thin flexible pulsation sensor (FPS) with a wireless data readout. [45]In this case, carbon black nanoparticles were dispersed in polydimethylsiloxane (PDMS) to form a piezoresistive sensor layer; then, they were encapsulated within structural PDMS layers and connected to stainless steel interconnect leads.The sensor was used as a strain-sensitive biomaterial with a strain range greater than 50% and a modulus of elasticity less than 500 kPa that allowed it to be effectively wrapped around a vessel or synthetic graft intraoperatively to maintain long-term monitoring, which could be studied in vitro for more than 100 cardiac cycles showing linear output to pulsation flows and pressures.Subsequently, investigators also implemented the integration of the sensor with a flexible wireless transmitter, both encapsulated by a PDMS, allowing real-time data reading. [46]nother study proposed a flexible strain sensor that directly measures the circumferential strain caused by changes in blood flow rate in blood vessels (Figure 2). [47]The sensor consists of PDMS and multi-walled carbon nanotubes (MWCNT) that can be overlaid on the curved surface of the soft tubes.Through theoretical model analysis and in vitro simulations, it was verified that the developed sensors can accurately detect the changes in flow; the sensitivity and detection limits were 0.55% min L −1 and 0.4 L −1 min.

Using Piezoelectric Sensors
Vascular replacement is common in the surgical treatment of a series of cardiovascular and vascular diseases, but failures can still occur. [48]Early identification of graft failure is important as there can be no obvious precursor symptoms.An in vivo and in vitro experiment on a self-monitoring venous graft system was reported by Neville et al. [49] The system includs a prosthetic graft composed of expanded polytetrafluoroethylene (ePTFE), a wire-less and microchip sensor unit integrated into the outer surface of the lumen, and a remote processor.In vitro, studies were conducted in a pulsatile circulatory flow system, and the degree and location of stricture could be well recognized in the range of 50-80% stenosis degree.A 30-day in vivo experiment in a sheep carotid artery model verified that remote transmission and collection of signals could be achieved after implantation without adverse effects on tissue healing.The above results suggest that the sensor system is capable of continuously monitoring hemodynamic parameters that reflect graft function via wireless data transmission and allow for stenosis determination.
Li et al. proposed in situ-polarized ferroelectric artificial arteries by electric field-assisted 3D printing for battery-free real-time blood pressure sensing and occlusion monitoring (Figure 3). [50]onsisting of ferroelectric potassium niobate particles embedded within a ferroelectric polyvinylidene difluoride (PVDF) polymer matrix, they can be rapidly polarized and shaped during the printing process with excellent piezoelectric properties (bulk-scale d 33 > 12 pC N −1 ), which become the basis for the application of the piezoelectric effect for self-powering and information acquisition.The artificial arteries with sinusoidal structure have a mechanical modulus close to that of blood vessels and can sensitively sense subtle changes in vasomotion in the human blood pressure range (0.306 mV mmHg −1 , R 2 > 0.99), allowing the identification of lower degrees of obstruction by changes in the voltage profile, while the amplitude of the voltage increases significantly in occlusions of 40% and above, which in turn can be used for early identification of blockage to prevent graft failure.D'Ambrogio et al. designed a novel biocompatible piezoelectric composite for the self-monitoring of smart vascular grafts. [51]The piezoelectric composite made of sodium niobate (NanbO 3 ) microfibers (MF) embedded in a PDMS matrix can be integrated into grafts for monitoring blood pressure and identifying thrombus-related abnormalities and enable wireless power and data transmission through resonant inductive coupling.The study points out that the low elastic modulus matrix provides a balance of piezoelectric sensitivity and tensile properties.The composite is coupled with a inductive coil where changes in resonant frequency due to pressure shift can be detected by the analyzer; thus, enabling early identification of vascular occlusion.The results show that the composite developed in this study has a sensitivity of more than 0.5 V Pa −1 m −2 ) with a minimum detectable pressure of ≈0.15 mmHg and can be used to identify occlusions of less than 25% in degree.The limitation of the above two studies is that both have not yet been examined in vivo.

Using Frictional Electrical Sensors
The application of bioabsorbable devices can avoid secondary surgery and is getting more attention in the research of implantable sensors.A bioresorbable frictional electrical sensor (BTS), which can be implanted in vivo and can identify vascular occlusion events successfully in large animals based on the frictional initiation effect, was reported to convert the biomechanical signal of vascular changes with the diastole and systole phase into an electrical signal (Figure 4). [52]The main part of the sensor is based on a frictional electrode layer constructed of polylactic acid-(4% chitosan) (PLA/C) and magnesium, with stable output performance under mechanical stimulation (2 V), good sensitivity (11 mV mmHg −1 ), linearity (R 2 = 99.3%), and good durability to remain stable at 450 000 cycles, as well as antimicrobial properties.The service life after implantation is 5 days, and in vitro, tests have verified that complete degradation can be achieved in an average of 84 days.The limitations are the short service life and the fact that it still requires magnesium wires to be threaded out of the body for data transmission and does not achieve full wireless implantability.

Using Ultrasound Sensors
Implantable Doppler probes, represented by the Cook-Swartz Doppler Probe, have been widely used in clinical practice for monitoring post-anastomotic vessels, including free flap grafts and organ transplants. [10,11]The Cook-Swartz Doppler Probe, introduced by Swartz and colleagues in 1988, uses a silicone 1.0 mm Doppler probe secured to an expanded Teflon cuff using silicone and placed around an arterial or venous anastomosis, allowing direct real-time monitoring of blood flow, the application of which has been widely reported in the literature. [1,53]Although it has been widely used and proven to be accurate, effective, and cost-efficient to reduce surgical failure rates, limitations include the limitation of patient activity that prevents long-term use, the risk of vascular injury, the potential for increased false-positive rates due to the learning curve, and the difficulty of early identification of venous occlusion. [3,32,54]However, due to the limitations of size and lifetime, there is a lack of ideal wireless implantable ultrasound sensors that have the potential to outperform traditional implantable probes for post-surgical monitoring, and the application of technologies such as wireless power transmission is expected to be a solution to the problem. [3,55]In a study, the size can be reduced to approximately 18.0 cm 3 , but it still falls short of the ideal level and has a short lifetime limited by the built-in battery. [54]igure 4.A bioresorbable dynamic pressure sensor for cardiovascular postoperative care.Reproduced with permission. [52]Copyright 2021, Wiley.

By Monitoring the Tissue Oxygenation
For both organ transplantation and reconstructive surgery, the immediate effect and serious consequence of post-surgical vas-cular complications is graft ischemia, and the detection of tissue oxygenation is the key to responding to this situation early.The near-infrared spectroscopy currently used in clinical practice is limited by the depth of penetration. [1]onmezoglu et al. developed a wireless ultrasound-powered implantable luminescent oxygen sensor for continuous real-time oxygen measurement at centimeter depth (Figure 5). [35]The Figure 5. Monitoring deep-tissue oxygenation with a millimeter-scale ultrasonic implant.Reproduced with permission. [35]Copyright 2021, Springer Nature America.a) Schematic of the system as demonstrated in this paper for local tissue O 2 monitoring in sheep.b) An expanded view of the wireless sensor platform, including a lead zirconate titanate (PZT) piezocrystal and a luminescence sensor, consisting of a LED, a 3D-printed LED holder, an O 2 -sensing film, an optical filter, and an IC.c) An expanded cross-sectional view of the O 2 sensor.use of ultrasound for power anddata transmission increases the transmission depth with lower attenuation in soft tissues compared to electromagnetic waves.The implant is placed in the muscle or deep tissue and includes a piezoelectric ceramic attached to a luminescence sensor consisting of a LED, an O 2sensing film, an optical filter, and a piezoelectric crystal used for ultrasound-based energy collection and bi-directional communication, with the energy input passing through an external ultrasonic transceiver.The sensor is based on the principle of phase luminometry, which measures the phase shift between the excitation and emission light to determine the luminous lifetime.The key structure is the O 2 -sensing film, which consists of PDMS containing silica particles with surface-adsorbed ruthenium dyes, where the excited ruthenium dyes undergo collisional quenching with O 2 molecules reducing the luminescence intensity and lifetime, which in turn reflects the oxygen partial pressure.In vitro experiments suggest that the system has a resolution of < 5.8 mmHg Hz −1/2 in the physiologically relevant O 2 range (0-100 mmHg).Wireless operation with 10-cm depth is examined in isolated porcine tissue, and implantation beneath the biceps femoris muscle of sheep proves the accurate reflection of muscle oxygen partial pressure levels at centimeter depths.In vivo experiments with anesthetized sheep models were applied for further demonstration.The advantages of the system include a weight of only ≈17.4 mg and a volume of only ≈4.5 mm 3 , with an average power consumption of <150 W and high resolution achieved by compact integration of the sensor components and custom integrated circuits.This system also has the advantage that it can be sterilized by ethylene oxide without loss of function.
In 2022, Guo et al. reported a wireless implantable nearinfrared spectroscopic probe for the continuous monitoring of oxygen saturation in flaps and organ grafts to overcome the limitations of the current technologies for tissue oxygenation. [7]The implanted portion of the system is an injectable probe consisting of a pair of microscale inorganic light-emitting diodes and photodetectors, bioresorbable barbs along the edges, and a thin parylene encapsulation layer.Then, it is connected to a small batterypowered module using Bluetooth low energy (BLE) protocols through the skin.The device's sub-millimeter form with bioresorbable barbs enables minimal invasiveness , self-anchoring, and safe extraction in deep tissue.In addition, the oxygen saturation can be measured without assumed optical parameters.The in vivo experiments in muscle flaps and kidneys in live porcine models prove the feasibility, reliability, and reproducibility of monitoring in deep tissue.

By Monitoring the Microvascular Flow
Transdermal temperature monitoring of grafted tissue has long been a routine post-surgical tool, with temperature measurement at intervals being part of the clinical examination, and continuous transcutaneous temperature monitoring can be performed with simple devices.However, it does not apply to buried tissue.To address this issue, implantable thermal sensors can be used to measure microvascular flow to directly monitor vascular complications.Lu et al. proposed a submillimeter-scale, multi-node thermal probe for measuring tissue microcirculation by measuring microvascular blood flow, which can be used for graft monitoring (Figure 6). [56,57]The sensing device implanted in the tissue consists of a resistive heater and four thermistors which are attached to a small BLE data communication module and a battery adhered to the skin.Due to the small size (≈2 mm wide × 1 mm thick) and the thin and narrow shape, the sensitivity is improved, and the measurement error is 0.06 °C.The application of multiple sensing nodes can further reduce the error in flow measurement by least-squares fitting.Besides, the tiny size facilitates easy and minimally invasive implantation into various types of tissues without contacting the vasculature, and biodegradable barbs can be used for fixation for up to 9 days, with subsequent simple removal.The probe was tested in a porcine muscle flap model with arterial and venous occlusion and a kidney model and demonstrated that microvascular flow velocities in flaps and organ grafts for transplantation could be reliably monitored with high robustness to changes in tissue temperature.Table 1 summarizes all the studies mentioned above.

Summary and Outlook
In summary, implantable sensors have promising applications in post-surgical vascular repair and blood flow monitoring.Compared with non-implantable devices, implantable sensors have irreplaceable advantages for the detection of deep tissues.
Depending on the patient's condition, the type of disease and surgery, the location and size of operated blood vessels,the monitoring methods and requirements also differ.For both strategies of direct and indirect monitoring of blood vessels, there may not be a clear conclusion about which approach is superior.For vascular replacement, complications may occur without significant premonitory symptoms for a long time after surgery without proper indicators for indirect monitoring.For organ transplantation and reconstructive surgery, the relative fragility of operated Monitoring microvascular flow rates in skin flaps and organ grafts for transplantation [56, 57]   blood vessels in the early period presents a further challenge for direct contact.Therefore, sensors based on various technologies and strategies may all hold great potential.However, it would be better if the scope of the application could be extended by enriching the indicators that can be monitored, extending the service life, improving long-term biocompatibility, and so on. [58]here are also different advantages and challenges in terms of leaving the implanted portion in situ to degrade or not degrade, or removal by subsequent surgery.The in situ presence of the sensor avoids additional operations but increases the difficulty of designing and constructing and requires further improvements in wireless technology to address current limitations.For sensors to be removed, they often require wires through the skin but can help reduce the impact on surrounding tissues in the body and circumvent some of the limitations of wireless technology.However, reducing disturbances such as mechanical irritation is a common goal.
Here are some other issues that deserve our attention.The service life of designed sensors is still limited and not available for long-term monitoring yet.The need for at-home monitoring after discharge also needs to be considered which places greater demands on strategies for power and data transmission.Besides, some studies have not yet considered how sterilization or disinfection is performed before in vivo application and the impact of this process on the structure and function of the sensor, which is important for application in vivo. [59]e believe that in the future, more flexible, miniaturized, biocompatible, and fully implantable wireless sensors with longer service life will be further developed and receive more attention.After further examination of cost-effectiveness, long-term reliability, and safety compared with existing modalities as well as the gold standard, the implantable sensors will realize their full po-tential for the monitoring of post-surgical vascular complications in the clinic.

Figure 2 .
Figure 2. Measurement of pulsating flow using a self-attachable flexible strain sensor based on adhesive PDMS and CNT.Reproduced under terms of the CC-BY license [47] Copyright 2022, The Arthors, published by MDPI.a) A schematic of adhesive PDMS (a−PDMS)/CNT strain sensor.b) Fabrication process of the sensor implementing the CNT spray deposition.c) Schematic of the fluid−flow measurement system consisting of a motor pump to flow the fluid, digital multimeter to measure the resistance, fluid reservoir, and tube.d) Photograph of aPDMS/CNT strain sensor rolled on the silicone tube with a fluid flow.

Figure 3 .
Figure 3. Multifunctional artificial artery from direct 3D printing with built-in ferroelectricity and tissue-matching modulus for real-time sensing and occlusion monitoring.Reproduced with permission.[50]Copyright 2020, Wiley.a) Schematic illustration of the piezoelectric effect in artificial artery in response to blood pressure.b) Voltage response of the artery as a function of pressure change.c) Linear fitting of peak-to-peak voltage and pressure change.Data are expressed as mean ± SD (n = 3).
Figure 4.A bioresorbable dynamic pressure sensor for cardiovascular postoperative care.Reproduced with permission. [52]Copyright 2021, Wiley.a) Illustration of the BTS.b) Structure of the BTS.c) Principle of the BTS based on contact electrification and electrostatic induction.d) Relationship between the mass ratio of the BTS and degradation time.e) Schematic of in vivo experimental electrical characterization and physiological signal monitoring.

Figure 6 .
Figure 6.Implantable, wireless, self-fixing thermal sensors for continuous measurements of microvascular blood flow in flaps and organ grafts.Reproduced with permission. [56]Copyright 2022, Elsevier.a) Schematic illustration of the microvascular flow measurement system.b) Sensing components in a flow probe.c) Exploded view schematic illustration of a flow probe.d) Schematic illustration of the complete flow sensor, showing an exploded view of the BLE module.e) Schematic block diagram of the circuits of the BLE module.f) Hooking mechanism associated with the biodegradable barbs.

Binfan
Zhao is now pursuing a doctorate at the Department of Plastic and Reconstructive Surgery at Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine.Her research interests focus on functional biomaterials promoting skin tissue regeneration.Loy Eid is now pursuing a master's degree at the Department of Plastic and Reconstructive Surgery at Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine.Her research interests focus on skin aging and tissue regeneration.Yuguang Zhang is the Chief Surgeon and professor of the Department of Plastic and Reconstructive Surgery at Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine.His current research is focused on medical-engineering cross-study on adipose-derived stem cells, promotion of vascularization of ischemic skin tissue, and treatment of pathological scarring.Xiaoming Sun gets a doctorate in Plastic Surgery from Shanghai Jiao Tong University School of Medicine.He is working at the Department of Plastic and Reconstructive Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine.His current research is focused on adipose-derived stem cells promoting the vascularization of ischemic skin tissue, microenvironmental regulation of adipose-derived stem cells, and functional biomaterials promoting skin tissue regeneration.

Table 1 .
Summary of reported implantable sensors for post-surgical monitoring of vascular complications.