Hydrogels,three-dimensional hydrophilic polymer networks,are appealing candidate materials for studying the cellular microenvironment as their substantial water content helps to better mimic soft tissue.However,hydrogels can lack mechanical stifness,strength,and toughness.Composite hydrogel systems have been shown to improve upon mechanical properties compared to their singlecomponent counterparts.Poly(ethylene glycol)dimethacrylate(PEGDMA)and alginate are polymers that have been used to form hydrogels for biological applications.Singlecomponent and composite PEGDMA and alginate systems were fabricated with a range of total polymer concentrations.Bulk gels were mechanically characterized using spherical indentation testing and a viscoelastic analysis framework.An increase in shear modulus with increasing polymer concentration was demonstrated for all systems.Alginate hydrogels were shown to have a smaller viscoelastic ratio than the PEGDMA gels,indicating more extensive relaxation over time.Composite alginate and PEGDMA hydrogels exhibited a combination of the mechanical properties of the constituents,as well as a qualitative increase in toughness.Additionally,multiple hydrogel systems were produced that had similar shear moduli,but diferent viscoelastic behaviors.Accurate measurement of the mechanical properties of hydrogels is necessary in order to determine what parameters are key in modeling the cellular microenvironment. Hydrogels, three-dimensional hydrophilic polymer networks, are appealing candidate candidates materials for studying the cellular microenvironment as their substantial water content helps to mimic soft tissue. Still, hydrogels can lack mechanical stifness, strength, and toughness .Composite hydrogel systems have been shown to improve upon mechanical properties compared to their singlecomponent counterparts.Poly (ethylene glycol) dimethacrylate (PEGDMA) and alginate are polymers that have been used to form hydrogels for biological applications. Singlecomponent and composite PEGDMA and alginate systems were fabricated with a range of total number of polymer concentrations . Bullk gels were mechanical characterized using spherical indentation testing and a viscoelastic analysis framework. An increase in shear modulus with increasing polymer concentration was demonstrated for all systems. Alginate hydrogels were shown to have a smaller viscoelastic ratio than the PEGDMA gels, indicating more extensive relaxation over time. Composite alginate and PEGDMA hydrogels exhibited a combination of the mechanical properties of the constituents, as well as a qualitative increase in toughness. Additionally, multiple hydrogel systems were produced similar had shear moduli, but diferent viscoelastic behaviors. Accurate measurement of the mechanical properties of hydrogels is necessary in order to determine what parameters are key in modeling the cellular microenvironment.