Implantable bioelectronics are rapidly advancing towards multifunctional platforms capable of real-time monitoring and therapeutic intervention. However, designing implants with stable, long-term integration with soft, dynamic biological tissues, especially under strain or movement, is still challenging. Here we introduce a stretchable, strain-insensitive, wet-tissue-adhesive elastomer–hydrogel biphasic platform for cross-functional bioelectronics, enabling simultaneous physical sensing, chemical monitoring and neural modulation in vivo. This platform, termed ElHyX, features a molecularly integrated elastomer–hydrogel architecture, functionalized with conductive fillers to achieve mechanical compliance, robust electrical performance and strong tissue adhesion without the need for sutures or additional surface treatments. Using direct ink writing, we fabricated customizable ElHyX-based devices for in vivo electrocardiogram monitoring, glucose sensing and nerve stimulation. A closed-loop system for diabetic management in rats was also developed, where real-time biosignal detection autonomously triggered neuromodulation to regulate blood glucose levels. Overall, our findings establish ElHyX as a versatile, scalable platform for next-generation bioelectronics, capable of continuous physicochemical monitoring and autonomous therapeutic intervention in complex biological environments.