Modern bioelectronic devices increasingly demand materials that can integrate seamlessly with the body’s soft, dynamic, and hydrated tissues. Conventional electronics, built from rigid and dry components, often fail to form stable or biocompatible interfaces, limiting their long-term performance and safety. This mismatch has driven the development of multifunctional biomaterials, particularly hydrogels and skin-mimetic polymers that offer tissue-like mechanical properties, improved conformity, and biointegration. Meanwhile, the rising need for sustainability and accessibility in healthcare technologies calls for biomaterials that are not only functional, but also scalable, affordable, and environmentally responsible. This thesis explores a spectrum of biomaterial strategies to address these dual imperatives: achieving biological performance while advancing material sustainability. I begin by developing viscoelastic hydrogels from husk-derived polysaccharides, offering a sustainable and scalable alternative to synthetic interfaces. These hydrogels are applied as skin-conforming interfacial layers for both epidermal and epicardial ECG recording, where they significantly enhance signal quality and mechanical coupling. To extend their utility, I reinforce the hydrogel matrix with chitosan, yielding a composite dressing that promotes keratinocyte migration, modulates inflammation, and accelerates wound healing in vivo. Bridging from material design to systems integration, I introduce a synthetic kangaroo care system engineered from soft silicone materials and multisensory components to replicate the physiological and emotional benefits of parent-infant skin contact in the NICU. This work emphasizes the potential of soft material systems in human-centered therapeutic design. To frame the broader context of tissue-biomaterial integration, I provide a technical and conceptual review of tissue-like bioelectronics for neural interfacing, discussing current material challenges and emerging strategies, from self-healing systems to organoid-integrated electronics. Lastly, through collaborative efforts, I explore two directions that expand the thesis’ scope: a granular hydrogel system capable of penetrating confined biological environments for therapeutic delivery, and a sustainable microfabrication platform using cellulose substrates, salt-assisted carbonization, and chemomechanical delamination. These projects point toward a future where biomedical interfaces are not only functionally sophisticated but also environmentally and economically viable. Together, these investigations advance the vision of biointegrated devices that are both biologically gentle and materially responsible, laying the groundwork for medical technologies that are as sustainable as they are effective.