Organic field-effect transistors (OFETs) have emerged as a promising technology for implantable diagnostics due to their compatibility with flexible substrates and low-temperature processing. Recent advancements focus on integrating biodegradable materials such as poly(L-lactic acid) (PLLA) and silk fibroin to address the need for environmentally benign and biocompatible electronic systems. These materials offer unique advantages, including tunable degradation rates, mechanical flexibility, and minimal immune response, making them suitable for transient medical applications.
Biodegradable OFETs leverage the semiconducting properties of organic molecules while incorporating substrates and dielectrics that dissolve or resorb after a predefined operational period. PLLA, a FDA-approved polyester, serves as a common substrate due to its controllable degradation kinetics, which can range from weeks to years depending on molecular weight and crystallinity. Silk fibroin, another biocompatible material, provides excellent film-forming capabilities and can be functionalized to modulate its dissolution profile. These materials are often combined with organic semiconductors like pentacene or polymer-based variants such as poly(3-hexylthiophene) (P3HT) to achieve the necessary charge transport properties.
The fabrication of biodegradable OFETs involves solution-based techniques, including spin-coating, inkjet printing, or vapor-phase deposition, to ensure compatibility with temperature-sensitive substrates. Critical to performance is the dielectric layer, which must balance high capacitance with biodegradability. Materials such as silk fibroin, cellulose derivatives, or cross-linked biodegradable polymers have been employed, offering dielectric constants in the range of 2–8. Device architectures often adopt a bottom-gate configuration to simplify processing, with electrodes made from biodegradable metals like magnesium or iron, or conductive polymers such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS).
Biocompatibility testing is a mandatory step before in vivo deployment. In vitro assays assess cytotoxicity, inflammatory response, and cell adhesion using standardized protocols such as ISO 10993-5. Studies involving fibroblast and macrophage cell lines have demonstrated that PLLA and silk-based OFETs exhibit minimal cytotoxicity, with cell viability typically exceeding 90% after 72 hours of exposure. Hemocompatibility tests, including hemolysis assays, confirm that these materials do not induce significant red blood cell damage, with hemolysis rates below 5%, well within the acceptable threshold for biomedical applications.
In vivo performance evaluations focus on both functionality and host response. Subcutaneous implantation in animal models reveals that biodegradable OFETs maintain stable operation for the intended duration, with negligible signal drift in sensing applications. For instance, devices designed for physiological monitoring exhibit consistent drain current modulation in response to biomarkers like glucose or lactate, with sensitivity levels comparable to non-degradable counterparts. Histological analyses post-explantation show mild fibrous encapsulation, but without severe inflammation or necrosis, confirming the materials’ benign interaction with living tissue.
Degradation kinetics are carefully engineered to match the clinical requirement. PLLA-based devices typically degrade via hydrolysis, with mass loss rates adjustable from 0.5% to 3% per week. Silk fibroin degrades enzymatically, with rates influenced by implant location and local protease activity. Accelerated degradation studies in phosphate-buffered saline (PBS) at 37°C provide preliminary data, but in vivo conditions often yield slower degradation due to reduced fluid exchange and lower enzyme concentrations.
A key challenge lies in ensuring operational stability during the degradation process. Partial dissolution of the dielectric or substrate can lead to increased leakage currents or threshold voltage shifts. Strategies such as encapsulation with slow-degrading outer layers or the use of composite materials mitigate this issue. For example, a bilayer dielectric of silk and PLLA can provide initial insulation while allowing progressive breakdown after the active lifespan.
Applications in implantable diagnostics include continuous monitoring of metabolites, neural activity recording, and drug release tracking. Biodegradable OFETs interfaced with enzymatic sensors demonstrate detection limits in the micromolar range for analytes like glucose, suitable for diabetes management. In neural interfaces, these devices record electrophysiological signals with signal-to-noise ratios exceeding 20 dB before resorption, eliminating the need for extraction surgery.
Future directions involve enhancing charge carrier mobility in biodegradable semiconductors, which currently lag behind conventional organics due to disordered film morphology. Research explores bio-derived semiconductors like indigo or melanin, which offer inherent biocompatibility and moderate mobilities around 0.1–1 cm²/V·s. Another focus is wireless power integration to enable fully biodegradable systems, using resonant inductive coupling or biodegradable antennas.
The development of biodegradable OFETs represents a convergence of materials science, electronics, and medicine, offering a pathway toward sustainable implantable devices. By addressing biocompatibility, degradation control, and electronic performance, these systems pave the way for next-generation diagnostic tools that harmonize with biological environments without leaving permanent traces.