Polymer and Crosslinker Content Influences Performance of Encapsulated Live Biotherapeutic Products

Introduction: Live biotherapeutic products (LBPs), or therapeutic microbes, are an emerging therapeutic modality for prevention and treatment of gastrointestinal diseases. Since LBPs are living, they are uniquely sensitive to external stresses (e.g., oxygen, acid) encountered during manufacturing, storage, and delivery. Here, we systematically evaluate how polymer and crosslinker concentration affects the performance of an encapsulated LBP toward developing a comprehensive framework for the characterization and optimization of LBP delivery systems.

Methods: We encapsulate a model LBP, Lactobacillus casei ATCC 393, in calcium chloride (CaCl₂)-crosslinked alginate beads, and evaluate how alginate and CaCl₂ concentrations influence LBP formulation performance, including: (i) encapsulation efficiency, (ii) shrinkage upon drying, (iii) survival upon lyophilization, (iv) acid resistance, (v) release, and (vi) metabolite secretion. Approaches from microbiology (e.g., colony forming unit enumeration), materials science (e.g., scanning electron microscopy), and pharmaceutical sciences (e.g., release assays) are employed.

Results: LBP-encapsulating alginate beads were systematically evaluated as a function of alginate and CaCl₂ concentrations. Specifically: (i) encapsulation efficiency of all formulations was >50%, (ii) all alginate beads shrunk (after lyophilization) and recovered (after rehydration) similarly, (iii) at 10% alginate concentration, lower CaCl₂ concentration decreased survival upon lyophilization, (iv) 10% alginate improved acid resistance, (v) sustained release was enabled by increasing alginate and CaCl₂ concentrations, and (vi) encapsulation did not impair secretion of l-lactate as compared to free LBP.

Conclusions: This research demonstrates that polymer content and crosslinking extent modulate the performance of polymer-based LBP delivery systems, motivating research into the optimization of material properties for LBP delivery systems.