Preparation And Application Of Ropivacaine Loaded Microspheres

Local Anesthetics,Ropivacaine,are widely used in postoperative analgesia,local nerve block in surgical and the therapy of chronic pain.Due to its short half-time,a single injection of ropivacaine just provides a nerve block lasting only 3-4 hours,making it difficult to achieve desirable analgesia effect.To meet the long-time analgesia requirement,multiple methods such as frequent inj ection,catheter implantation in vivo or patient controlled analgesia(PCA)device have been applied in clinical The wide-spread use of these approaches has been hampered by poor patient compliance,the lack of portability and the risks of infection.Nowadays,a lot of work have focused on the development of ropivacaine loaded microspheres.Nevertheless,there are still several issues to be solved,such as particle size with broad distribution,low drug loading efficiency,undesirable release behavior.In order to overcome these key problems,we proposed to combine O/W emulsion method with novel premix membrane emulsification technique.After the optimization of fabrication procedure,ropivacaine loaded microspheres with narrow size distribution,high drug loading efficiency and an ideal constant release behavior have been obtained.This work is divided into four parts:The first part focused on the difficulty of preparing ropivacaine loaded microspheres with uniform size.Premix membrane emulsification technique combine with O/W emulsion method were developed.After the optimization of tran-membrane pressure,tran-membrane cycles,PLGA concentration,PLGA molecule weight,pH value of external water phase,primary emulsion preparation and solidification method,we obtained ropivacaine loaded microsphere with a narrow size distribution,a high drug loading efficiency and an ideal constant release behavior.Based on the above optimization,the influences caused by solidification method(ambient pressure and negative pressure)were investigated.It was found that high burst release and low encapsulation efficiency was achieved in ambient pressure condition Because ropivacaine gradually aggregate into a crystal which might easily leak out from droplets,that would result in lower drug loading efficiency.As for in vitro release profile,the leaked drug crystal on the surface of the ASE microspheres could not easily be washed away completely,which led to strong initial burst release.With respect to NSE-MS,ropivacaine existed in amorphous state was difficult to escape and inclined to uniformly disperse inside polymer matrix,which led to a higher drug loading efficiency and constant release rate.The effect of terminal group of PLGA(OH,COOH,COOR)were systematically investigated.It was found that the encapsulation efficiency of ropivacaine loaded microsphere prepared by COOH-PLGA was higher than that of OH-PLGA and COOR-PLGA.Meanwhile,the initial burst of ropivacaine loaded microsphere prepared by COOH-PLGA was lower than that of OH-PLGA and COOR-PLGA.The reasons for the distinction in adsorption force between different terminal group of PLGA and ropivacaine were analyzed from the microscopic level by using QCM-D and AFM.Furthermore,the combination ability of molecule reaction activation center is analyzed by density functional theory and frontier molecule orbital theory.The pharmacodynamic of the optimized ropivacaine loaded microspheres were evaluated through the nerve block model SD rats and the local infiltration model of guinea pigs.It was found that ropivacaine loaded microspheres exhibited the good sustained release effect in terms of both intensity and duration of anesthetic effect.Additional,in vitro cytotoxicity and histological evaluation proved that ropivacaine loaded microspheres did not cause nerve damage and local tissue inflammation.Biochemical analysis results demonstrated the cardiotoxicity was reduced by encapsulation ropivacaine into microspheres because a steady release behavior in vivo.In this research,the ropivacaine loaded microsphere with high drug loading efficiency,narrow size distribution and prolonged local analgesic effect were obtained by premix membrane emulsification technique combined with O/W emulsion method.By optimizing the preparation process parameters,investigating the effect and mechanism of different solidification methods as well as different terminal group of PLGA,it provides a theoretical direction for encapsulating soluble small molecular drug.