Genipin‐crosslinked gelatin microspheres as a drug carrier for intramuscular administration: In vitro and in vivo studies

Abstract

Gelatin microspheres have been widely evaluated as a drug carrier. Nevertheless, gelatin dissolves rather rapidly in aqueous environments, making the use of the polymer difficult for the production of long-term delivery systems. This adverse aspect requires the use of a crosslinking agent in forming nonsoluble networks in microspheres. However, the use of crosslinking agents such as formaldehyde and glutaraldehyde can lead to toxic side effects owing to residual crosslinkers. In an attempt to overcome this problem, a naturally occurring crosslinking agent (genipin) was used to crosslink gelatin microspheres as a biodegradable drug-delivery system for intramuscular administration. Glutaraldehyde was used as a control. In the in vitro study, the morphology, dynamic swelling, and antienzymatic degradation of test microspheres were evaluated. In the in vivo study, the biocompatibility and degradability of test microspheres were implanted in the skeletal muscle of a rat model via intramuscular injection. The results obtained in the study suggested that crosslinking of gelatin microspheres with glutaraldehyde or genipin may produce distinct crosslinking structures. The water transport mechanism in both the glutaraldehyde- and genipin-crosslinked gelatin microspheres exhibit anomalous behavior ranging from Fickian to Case-II extremes. The increase of the swelling diameter for the genipin-crosslinked microspheres was significantly less than that observed for the glutaraldehyde-crosslinked microspheres. In the animal study, it was found that the degree in inflammatory reaction for tissues implanted with the genipin-crosslinked microspheres was significantly less than that implanted with the glutaraldehyde-crosslinked microspheres. Additionally, the degradation rate of the genipin-crosslinked microspheres was significantly slower than their glutaraldehyde-crosslinked counterparts. These results indicated that the genipin-crosslinked gelatin microspheres may be used as a long-acting drug carrier for intramuscular administration.

Calcium Phosphate Cement with BMP-2-loaded Gelatin Microspheres Enhances Bone Healing in Osteoporosis: A Pilot Study

“…At the end of our test period, the However, there were no differences in the mineralization rates among the (D) rhBMP-2/CPC, (E) rhBMP-2/GM/CPC, and (F) untreated groups at 140 days (Double fluorescent labeling; original magnification, 9100). cumulative rhBMP-2 release was only approximately 38% when GMs had almost completely degraded [10,12] because part of the rhBMP-2 interacted with CPC after delivery from the microspheres and was released very slowly via diffusion [5,24,25]. In our model, the defect did not heal spontaneously after 140 days, which is similar to results reported for an ovine model [23].…”

“…The mean amount of rhBMP-2 release from our rhBMP-2/GM/CPC was 38% after 28 days, and greater than the mean of 15% to 33% of rhBMP-2/PLGA/CPC reported previously [4,25]. Greater rhBMP-2 release in our composite also resulted from the faster degradation of the GM (4 weeks) compared with PLGA (8-12 weeks) [7,10,12,27]. Release of rhBMP-2/GM/CPC was characterized by an initial burst release followed by a period of sustained release, as reported previously [5].…”

“…Sustained release of BMPs can accelerate bone healing in osteoporosis [3,23]. GMs have been widely used as a controlledrelease carrier of growth factors with good biocompatibility and degradability [12,33]. Thus, we asked whether (1) controlled release of rhBMP-2 could be improved in a composite bone substitute with rhBMP-2-loaded GMs and CPC and (2) osteoporotic bone healing could be accelerated by increasing factors released from the composite bone substitute.…”

“…We prepared GMs using an emulsification-solvent extraction with some modifications [10,12]. Briefly, type B gelatin (1.5 g, 225 Bloom; Sigma-Aldrich Corporation, St Louis, MO, USA) was dissolved in 10 mL phosphatebuffered saline (PBS, pH 7.4) at 50°C.…”

“…GMs are biodegradable, biocompatible, and can be crosslinked to increase their thermal and mechanical stability under physiologic conditions [33]. Degradation properties of GMs can be adjusted by varying the cross-linking agent concentration and reaction period [12,33]. Gelatinenriched CPC also shows strengthened mechanical properties and enhances the bioactivity of osteoblasts [1,2].…”