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With societal, industrial, and clinical progress continuously reaching greater heights, the crucial need for enhanced materials with versatile properties is ever increasing to help this growth. As such, polymer nanocomposites (PNCs) have been heavily researched, becoming redefined as their own class of materials, focusing on fundamental structure/property relationships, manufacturing techniques, and commercial applications, due to their remarkable properties and application versatility. Through countless nanoparticle and polymer matrix variations, PNCs can be finely-tuned to exhibit a multitude of unique characteristics. Utilizing this concept, the research laid out in the combined chapters of this dissertation sought to produce various PNCs embedded with cellulose nanocrystals/nanofibrils (CNCs/CNFs) and magnetic nanoparticles (MNPs) to obtain uniquely tunable properties to further progress the biomaterials field for biomedical applications. Initially, CNCs were extracted from the otherwise useless agricultural waste product of spent coffee grounds through phosphoric acid hydrolysis, and analyzed using multiple physical and chemical characterization techniques. In particular, a few crucial properties determined were aspect ratio of 12 ± 3, crystallinity of 74.2%, surface charge density of 48.4 ± 6.2 mmol/kg cellulose, and the ability to successfully reinforce PNCs, comparing well to other literature data and common commercial CNCs. Following extraction, CNCs/CNFs, as well as MNPs, were incorporated into various polymer matrices, including poly(ethylene glycol) diacrylate, sodium alginate, gelatin, and polyurethane, among others. Through solution casting and 3D bioprinting fabrication methods, as well as composition manipulation, CNCs/CNFs were able to reach ideal percolating networks within the PNCs for maximum mechanical reinforcement with minimal hindrance of the polymer matrix’s natural properties. The various PNC hydrogel scaffolds successfully demonstrated tunability of their nanostructural, mechanical, hydration, and biodegradation properties, utilizing the benefits of manipulated composition, crosslinking density, and nanofiller orientation to increase versatility for tissue engineering constructs. Additionally, MNP incorporation was shown to successfully produce inductive heating responses to promote topographical shape memory effects, while invoking minute thermal dissipation into surrounding environments to reduce thermal shock to seeded biological components. The success of this work makes strides to overcome a few crucial disadvantages of current PNC biomaterial hydrogels, specifically their inability to regenerate biomimetic native tissues during wound healing.