## 4 Conclusions  
In this study, we have designed a mechanically robust hierarchical monolith as a cell scaffold for the immobilization and recycling batch fermentation of _P. acidilactici_ to generate \(\text{L}^{-}\)-lactic acid. First, highly ordered and tunable P(St-\(\infty\)-GMA) porous copolymers were synthesized to immobilize _P. acidilactici_ using w/o high internal phase emulsions as templates, where GMA provided anchor points for the cells to be firmly tethered to the void walls. During the fermentation of immobilized _P. acidilactici_, the open-cell structure of the polyHIPE permitted efficient substrate transfer, and the mass transfer increased along with enhanced interconnectivity of the monolith, resulting in higher \(\text{L}^{-}\)-lactic acid yield. In cyclic fermentation studies, the immobilized _P. acidilactici_ maintained produced over 92.9% of their initial relative lactic yield production after 10 cycles, exhibiting both its great cycling stability and the durability of the material structure. The polyHIPE scaffold in this work offers tremendous potential in multiple-cell co-immobilization and cascade fermentation.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/polym15081862/s1](https://www.mdpi.com/article/10.3390/polym15081862/s1)]([https://www.mdpi.com/article/10.3390/polym15081862/s1](https://www.mdpi.com/article/10.3390/polym15081862/s1)), Figure S1: FT-IR spectrum of P(St-\(\infty\)-GMA) polyHIPE; Figure S2: Water wettability of polyHIPE scaffolds of PHH-0590, PHH-2090, PHH-1075, and PHH-1080; Figure S3: Water contact angle (at 0.469 s) of PHH-1090 before (a) and after (b) immobilizing _P. acidilactici_; Figure S4: \({}^{1}\)H-NMR spectrum of \(\text{L}^{-}\)-lactic acid. The unimodal at \(\delta=2.50\) is corresponding to DMSO-d6 solvent; Figure S5: SEM image of _P. acidilactici_ immobilized PHH-1090 after 10 batches of fermentation. The inset is the corresponding PHH photographs; Figure S6: Photograph of _P. acidilactici_ immobilized PHH scaffold fermenting in a fermenter; Table S1: \(\text{L}^{-}\)-lactic acid yield by suspended _P. acidilactici_ and _P. acidilactici_ immobilized PHH-1090; Table S2: \(\text{L}^{-}\)-lactic acid yield by _P. acidilactici_ immobilized on polyHIPEs with different structure; Table S3: \(\text{L}^{-}\)-lactic acid yield enhancement using other scaffolds for cell immobilization; Table S4: \(\text{L}^{-}\)-lactic acid yield and relative lactic acid yield of suspended _P. acidilactici_.  
**Author Contributions:** [PERSON] carried out the experiments of synthesis, reactions, and measurements; [PERSON] wrote the original draft; [PERSON] and [PERSON] proposed the concept, supervised the work, and revised the manuscript. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Data Availability Statement:** Not applicable.  
**Acknowledgments:** We thank all those who participated in the study. This research was supported by the National Natural Science Foundation of China (51773059) and Shanghai Cathay Biotechnology Co., Ltd.  
**Conflicts of Interest:** The authors declare no conflict of interest.