Collagen is a key extracellular matrix protein found in connective tissues. The structure and organization of collagen fibers play a crucial role in determining tissue function and how tissues respond to mechanical loads. Small leucine-rich proteoglycans (SLRPs) are well-known facilitators of collagen fibrillogenesis in connective tissues. While the role of SLRPs has been extensively documented in tissues such as tendon and skin, their functions are primarily inferred from changes observed in knockout models. Additionally, their specific roles and influences of their addition to a system, particularly in collagen gel-based materials, remain underexplored. Previous in vitro studies of SLRPs have been partly limited by the challenges associated with obtaining pure SLRPs in sufficient quantities and with appropriate glycosylation. Therefore, novel methods to reliably produce SLRPs at the required quality and scale are needed. In this study, we first evaluated the feasibility of producing recombinant decorin, biglycan, and fibromodulin using HEK293-F cells. Subsequently, we investigated the effect of SLRP supplementation on high-density collagen gels using scanning electron microscopy and assessed the impact on tensile properties. Our findings demonstrated that each SLRP uniquely influenced collagen structure at both the fibril and fiber levels, consequently modifying the tissues' mechanical response to load. Decorin, in particular, exhibited significant differences in tensile properties compared to biglycan and fibromodulin, underscoring its distinct role in promoting a structurally and mechanically robust response under tensile load.