Controlled formation of polylysinized inner pores in injectable microspheres of low molecular weight poly(lactide-co-glycolide) designed for efficient loading of therapeutic cells

Abstract

This study aimed to develop porous microspheres with a suitable porous structure and mechanical property for cell delivery using a comparatively low molecular weight (MW) poly(lactide-co-glycolide) (PLGA) having a weak mechanical strength and fast degradation rate, which could be potentially used for treatment of corneal endothelial diseases. Porous microspheres of 30 kDa PLGA with different pore sizes were prepared by varying preparation conditions, and the microspheres with mean pore diameters approximately 0.5, 1, 2 and 3 times that of a single green fluorescent protein-expressing human embryonic kidney 293 cell, used as a model cell, were chosen for cell loading study. The microspheres with an average pore diameter two times greater than that of the single cell were found to be the most appropriate for efficient cell loading in the inner pore spaces, along with demonstrating a good mechanical property, injectability and biodegradability. To maximize the cell loading amount in the microspheres, the cell adhesive property of the microspheres and cell loading conditions were optimized, leading to approximately 4.2 times increase in the cell loading amount. The porous microspheres designed using the low MW PLGA hold promise as a delivery system of corneal endothelial cells for regeneration of the corneal endothelium.

PLGA Microspheres with Alginate-Coated Large Pores for the Formulation of an Injectable Depot of Donepezil Hydrochloride

“…PLGA MS prepared using the inner aqueous phase devoid of ammonium bicarbonate exhibited few pores on their surface, whereas the MS fabricated using ammonium bicarbonate solutions showed numerous and large pores ( Figure 1). The number of pores on the surface of the MS and the pore sizes were greater when the concentration of ammonium bicarbonate in the inner aqueous phase was higher, which was consistent with the findings of previous studies [34,48,49]. The uniformity of pore structure decreased with increasing the concentration of ammonium bicarbonate in the inner aqueous phase (Figure 1).…”

“…After the degradation, the monomers are further metabolized and subsequently eliminated from the body. Our previous work also showed that most of the PLGA MS, designed for a cell delivery system, composed of PLGA of a low molecular weight (30 kDa) and an equal L/G ratio degraded within 12 weeks [34]. It was also reported that the formulation composed of PLGA of a high molecular weight (135 kDa) and an equal L/G ratio degraded more than 90% of the PLGA Morphological changes were also observed in each formulation during the in vitro release experiment (Figure 6b).…”

“…Furthermore, we assumed the elimination time of the PLGA MS formulations in the human body on the basis of our SEM observation data and previous reports [22,34,57]. It is well known that PLGA of an equal lactide (L) to glycolide (G) ratio degrades into monomers, lactic acids, and glycolic acids within 12 weeks.…”

“…PLGA MS were prepared by using a double emulsion solvent evaporation method under different conditions (Table 1) [34]. Briefly, PLGA was dissolved in dichloromethane at a concentration of 4% (w/v).…”

“…Multiple studies have been performed to fabricate the PLGA MS with large pores for delivering large substances such as therapeutic cells and peptides because of its large pore space [31][32][33]. In our previous study [34], we also designed PLGA MS for the purpose of loading therapeutic cells, which exhibited large pore sizes with a diameter greater than 15 µm. The PLGA MS with large pores designed for loading therapeutic cells is considered advantageous as it can provide more space to load the drug, thereby leading to a decrease in the amount of PLGA MS to be injected.…”