Probiotic therapeutics represent a rapidly advancing field, with particular interest directed toward the engineering of probiotic biofilms for immune modulation and gastrointestinal (GI) health. In contrast to conventional planktonic probiotic cells, biofilm-forming strains exhibit enhanced resilience, prolonged mucosal colonization, and improved immunological interactions facilitated by their extracellular polymeric substances (EPS). These attributes confer superior therapeutic consistency and stability, thereby addressing the limitations of traditional probiotic formulations that are often characterized by transient survival and limited clinical efficacy. This review critically examines the emerging landscape of synthetic engineering of probiotic biofilms, with emphasis on their design strategies, functionalization approaches, and biomedical applications. Advances in the genetic modification of probiotics have enabled precise delivery of therapeutic molecules at mucosal sites, while encapsulation systems have been developed to shield biofilm-based therapeutics from gastrointestinal stressors. Furthermore, inactivated biofilm matrices are gaining recognition as innovative modalities for regulating host immunity, fortifying epithelial barriers, and mitigating enteric infections, offering safer alternatives to live microbial therapies. The translation of these advances into clinical practice, however, is not without challenges. Issues relating to biosafety, regulatory compliance, and ethical considerations remain critical barriers to widespread adoption. Additionally, the personalization of probiotic biofilm therapies must account for inter-individual variability in microbiome composition and host responses. Large-scale manufacturing, standardization, and quality assurance also pose significant obstacles to clinical deployment. Despite these limitations, emerging progress in precision microbiome engineering underscores the potential of synthetic probiotic biofilms as next-generation biotherapeutics, with far-reaching implications for gastrointestinal health, systemic immune regulation, and human well-being.
