Biodegradable semiconductor materials represent a transformative advancement in transient medical implants, particularly for post-surgical monitoring. These materials dissolve harmlessly in the body after fulfilling their function, eliminating the need for secondary extraction surgeries. Key candidates include silicon, zinc oxide (ZnO), and organic semiconductors, each offering unique dissolution profiles, biocompatibility, and electronic performance. Their integration into medical devices enables real-time physiological monitoring, drug delivery feedback, and tissue regeneration tracking without long-term foreign body risks.

Silicon, a cornerstone of conventional electronics, has been engineered into biodegradable forms through nanostructuring. Silicon’s dissolution in aqueous environments occurs via hydrolysis, forming silicic acid, a benign byproduct excreted through urine. The dissolution rate depends on crystallinity, porosity, and surface chemistry. For instance, mesoporous silicon nanowires dissolve within weeks under physiological conditions, while dense silicon films may take months. Studies show that 100 nm-thick silicon membranes dissolve completely in phosphate-buffered saline (PBS) at 37°C within 25 days. The rate accelerates in vivo due to enzymatic activity and dynamic fluid flow. Toxicity assessments confirm that silicon degradation products exhibit no cytotoxic or inflammatory effects at clinically relevant concentrations.

Zinc oxide is another promising material due to its biocompatibility and tunable dissolution. ZnO dissolves via hydrolysis into zinc ions and hydroxide, both metabolically regulated in the body. Zinc is an essential trace element involved in enzymatic processes, reducing toxicity concerns. Dissolution kinetics are pH-dependent; faster degradation occurs in acidic environments (e.g., inflamed tissues) compared to neutral pH. Thin-film ZnO dissolves within 10–30 days in physiological saline, making it suitable for short-term implants. In vivo studies demonstrate that ZnO-based sensors maintain functionality for 2–3 weeks before resorption, with no adverse tissue reactions. The material’s wide bandgap (3.37 eV) also enables UV-selective optoelectronics for light-activated drug release systems.

Organic semiconductors, such as poly(lactic-co-glycolic acid) (PLGA)-encapsulated conjugated polymers, offer programmable degradation via ester hydrolysis. PLGA’s degradation rate is adjustable by varying the lactide-to-glycolide ratio; higher glycolide content accelerates dissolution. These materials are ideal for ultra-short-term applications (e.g., 5–10 days) and exhibit excellent mechanical flexibility, conforming to dynamic tissues. However, their lower charge carrier mobility limits complex circuitry integration compared to inorganic alternatives.

Applications in post-surgical monitoring leverage these materials’ transient nature. Biodegradable pressure sensors, fabricated from silicon nanomembranes, monitor intracranial or intraorgan pressure after surgery. A representative device with a 5 µm-thick silicon membrane operates for 14 days before dissolving, transmitting data wirelessly via inductive coupling. Similarly, ZnO-based strain gauges track tissue contraction during wound healing, dissolving once mechanical stability is achieved. Electrochemical sensors for pH, glucose, or electrolytes use ZnO or silicon electrodes, providing real-time metabolic data without retrieval procedures.

Drug delivery feedback systems integrate biodegradable semiconductors to optimize therapy. A silicon-based device with embedded ZnO transistors can detect local drug concentrations and adjust release rates via resistive heating of PLGA matrices. The entire system degrades after the therapeutic cycle, minimizing foreign body reactions. In cardiac applications, transient pacemakers made of silicon and magnesium conductors provide temporary rhythm support post-surgery, dissolving harmlessly after myocardial recovery.

Toxicity management is critical for clinical translation. Silicon and ZnO degradation products must remain below thresholds established by regulatory agencies. For silicon, daily silicic acid excretion in humans averages 20–50 mg, far exceeding implant-derived amounts. Zinc ions from ZnO implants typically release <10 mg/day, well within the recommended dietary allowance (8–11 mg/day). Organic semiconductors must avoid toxic oligomers; FDA-approved PLGA formulations mitigate this risk. Histopathological evaluations in animal models show minimal fibrosis or immune response around dissolving devices.

Challenges remain in optimizing dissolution uniformity and electronic stability. Variations in local pH, temperature, or mechanical stress can accelerate or retard degradation unpredictably. Encapsulation strategies, such as silk fibroin coatings, provide temporal control by delaying fluid penetration. Power supply is another hurdle; biodegradable batteries using magnesium anodes and iron cathodes offer limited energy density. Wireless power transfer or piezoelectric energy harvesting are alternatives for prolonged operation.

Future directions include multi-functional materials combining sensing, actuation, and drug release. Heterostructures of silicon and ZnO could enable graded dissolution, where one layer degrades faster than another to stagger functionality. Machine learning models are being explored to predict dissolution kinetics based on implant geometry and patient-specific factors. Another frontier is bioresorbable neural interfaces for transient neuromodulation, where organic semiconductors with low impedance are critical.

In summary, biodegradable semiconductors like silicon and ZnO are redefining transient medical implants by merging advanced electronics with bioresorbability. Their dissolution kinetics, low toxicity, and versatile applications in post-surgical monitoring address unmet needs in patient care. As material designs evolve, these technologies will enable safer, more adaptive implants that disappear once their task is complete.