The promise of cell therapy for repair and restoration of damaged tissues or organs relies on administration of large dose of cells whose healing benefits are still limited and sometimes irreproducible due to uncontrollable cell loss and death at lesion sites. Using a large amount of therapeutic cells increases the costs for cell processing and the risks of side effects. Optimal cell delivery strategies are therefore in urgent need to enhance the specificity, efficacy, and reproducibility of cell therapy leading to minimized cell dosage and side effects. Here, we addressed this unmet need by developing injectable 3D microscale cellular niches (microniches) based on biodegradable gelatin microcryogels (GMs). The microniches are constituted by in vitro priming human adipose-derived mesenchymal stem cells (hMSCs) seeded within GMs resulting in tissue-like ensembles with enriched extracellular matrices and enhanced cell-cell interactions. The primed 3D microniches facilitated cell protection from mechanical insults during injection and in vivo cell retention, survival, and ultimate therapeutic functions in treatment of critical limb ischemia (CLI) in mouse models compared with free cell-based therapy. In particular, 3D microniche-based therapy with 105 hMSCs realized better ischemic limb salvage than treatment with 106 freeinjected hMSCs, the minimum dosage with therapeutic effects for treating CLI in literature. To the best of our knowledge, this is the first convincing demonstration of injectable and primed cell delivery strategy realizing superior therapeutic efficacy for treating CLI with the lowest cell dosage in mouse models. This study offers a widely applicable cell delivery platform technology to boost the healing power of cell regenerative therapy.

Purpose Different amendments have diverse adsorption capacity for heavy metals. The objectives of this study were to evaluate adsorption efficiency of different kinds of amendments for heavy metals and to provide theoretical guidance for alleviation of heavy metals. Materials and methods The indoor oscillating experiments were carried out to investigate the adsorption efficiency of five amendments (i.e., lime, illite ilerite, ground phosphate rock, chitin, and corn straw charcoal) for adsorption capacity of heavy metals (i.e., Zn, Pb, and Cd). Results and discussion The adsorption efficiency of lime for Zn and Cd was 99.64% and 99.99% followed by chitin with adsorption efficiency of 74.94% and 81.63% respectively. The adsorption efficiency of amendments for Pb, Zn, and Cd was increased gradually with adsorption time. The adsorption efficiency has gradually reached a stable stage after certain time. In addition to adsorption of Pb by corn straw charcoal, the other four materials (i.e., lime, illite ilerite, ground phosphate rock, and chitin) have reached equilibrium when pH value was 3. The adsorption efficiency of lime (1%) for Zn was highest (99.98%). The adsorption efficiency of other materials for Pb was enhanced with increase in dosage except for chitin; however, the unit adsorption capacity was not decreased. Conclusions It is concluded that adsorption efficiency of lime and chitin for heavy metals such as Zn, Pb, and Cd was more than illite ilerite, ground phosphate rock, and corn straw charcoal, which can be considered as an active sorption materials.