The use of design, specifically collaborative design in social entrepreneurial initiatives, is still ill-defined. Social entrepreneurship ecosystems comprise multiple actors that negotiate resources and information to generate social impact. The negotiation of these resources and information is supported by utilising boundary objects that act as mediators of further collaboration among different social worlds or communities of practices. This paper aims to unveil the collaborative design practices that social entrepreneurs utilise to negotiate resources and information with other ecosystem actors. This paper describes the early stages of a Chilean social enterprise participating in an incubation programme through a longitudinal qualitative study. The empirical data collected through semi-structured interviews shows how this organisation negotiate their business idea and their proposals with the business incubator and their beneficiary communities. The findings show that the organisation's business model and collaborative workshops acted as negotiating boundary artefacts that enabled collaboration with the business incubator and communities. This analysis allows eliciting the role that collaborative design practices play in creating these artefacts to align different interests of the ecosystem actors and generate social impact.