| The treatment of bone and joint tuberculosis is always a big dilemma of clinical orthopedics. Maintaining continuous effective concentration of antituberculosis drugs in local lesion and repairing bone defects are two main therapies. Because blood circulation was damaged in the local lesion, systematic drugs could not reach the effective concentration, results in poor therapatic effect. Besides, bacterial resistance can easily produced, only rely on the systematic drugs hardly kill all of the bacteria. Postoperative debridement of infected area, bone defects with difficult-to-heal could cause the bacterial relapse. If clean infected area and spray anti-tuberculosis drugs simultaneously, although it can kill the bacteria temporarily, lacking of stable carrier release drugs which can be diluted soon, hardly block tuberculosis bacteria’s destruction on bone, severely damage effectiveness of surgery.As a reliable and effective way to maintain continuous and stable drug-release in infected area, drug delivery system has a broad application prospect of the joint tuberculosis and other chronic infectious bone disease treatment. The constantly development of bone tissue engineering technologies and carrier material brought new opportunities to treatment of joint tuberculosis.Ideal carrier scaffold material hopefully be capable to effective release anti-tuberculosis drugs on infected area and repair bone defects tuberculosis at the same time. Large-scale experimental studies show that MSN material has the significant advantages in releasing drugs as carrier materials:(1) adjustable particle size of 50-300 nm;(2) stable physical and chemical properties;(3) excellent mesoporous structure and an adjustable pore size;(4) a large surface area and pore volume;(5) an easily modified surface. Nano-hydroxyapatite(n HA) is a kind of inorganic ceramic biomaterials at nanoscale dimensions of size. As bone tissue engineering material, n HA has overcome the poor shaping, brittleness and degradation of the shortcomings of conventional hydroxyapatite. The drugs and drugs-loaded matrix particles can be dissolved or dispersed in PLGA microspheres, for the purpose of the multi-stage controlled release. Therefore, PLGA microsphere is an ideal carrier material in control release.This study focused on the longstanding problem that lacking stable drug release carrier and bone defects in the treatment of bone and joint tuberculosis. Accoring to the advantage of MSN material in carrier ability and the osteoinductive activity of n HA material, we prepared the composite microspheres carrier. The synergy in properties of composite microspheres drug release and the ability for bone defects repairing between MSN and n HA was discussed. The whole studies were divided into three parts:1. The preparation and control release properties of PLGA-MSN microspheres compositesTo prepare of a suitable anti-TB drug delivery carrier maintaining continuous effective drugs concentration. MSN-RFP and MSN-INH were respectively synthesized through a process of impregnation to improve the efficiency of drug loading. Solvent evaporation methold was applied to prepare the PLGA-MSN microspheres-loaded drugs. Their properties of sturcture and loading drugs were examined. We found that MSN carrier material loaded the RFP and INH by two ways of surface adsorption and filling mesoporous channels, and drug loading amount(MSN-RFP=38.5 ± 4.3%, MSN-INH=17.1±2.7%). PLGA is the secondary load MSN-GFP and MSN-INH for control release form, and the drug encapsulation efficiency was 75.2% and 65.3%, respectively. Release tests showed that drug-loaded PLGA-MSN composite microspheres in vitro can persist for more than 42 days. The introduction of MSN into composite microspheres can significantly improve the effectiveness of the sustained and controlled release of anti-TB drugs, to provide an experimental basis as anti-TB drug delivery carrier.2. The influence of microsphere-based composites loading with different ratios of n HA on the repair of bone defects.The aim of current study was to prepare microsphere-based composites made of n HA/PLGA at different ratios and evaluate the effects of n HA on the characteristics of the composites for tissue engineering application. Firstly, microspheres based composites made of two ratios of n HA/PLGA(n HA/PLGA =20/80 and n HA/PLGA =50/50) were prepared. Then the influences of n HA on morphology, wettability properties, mechanical strength and degradation of the n HA/PLGA composites were investigated. Secondly, the biocompatibility and osteoinductivity of the composites were evaluated and compared by co-culture with bone marrow stromal stem cells(BMSCs). The results showed that the adhesion, proliferation and osteogenic differentiation of BMSCs with n HA/PLGA(50/50) composite were better than those with n HA/PLGA(20/80) composite. Finally, we implanted the composites into femur bone defect in a rabbit model and the capacity of guiding bone regeneration and the in vivo degradation of composites were observed by micro-CT and histological examinations. At four weeks after implantation, there was no significant difference on the repair of bone defects between the two n HA/PLGA composites. However, at both eight and twelve weeks, the n HA/PLGA(20/80) composite exhibited better formation of mature bone than n HA/PLGA(50/50) composite. These results suggested that a proper concentration of n HA in the n HA/PLGA composite should be taken into account when the composite was prepared, which plays an important role in the biocompatibility, degradation rate and osteoconductivity of the composites.3. Synergistic effects of MSN and n HA in loaded PLGA microspheres on the bone regeneration and drug delivery in vivoThe objective of this study was to investigate the synergistic effect of MSN/n HA on the bone regeneration as well as its properties of drug delivery. The PLGA-MSN/n HA composite microspheres scaffold was implanted into the femur bone defect in a rabbit model, and its ability to induce bone regeneration was observed by histological examinations. Twelve weeks after implantation, the bone defects had significantly more formation of mature bone and less residual materials than in the controls. These results demonstrate that this PLGA-MSN/n HA composite, introducing both MSN and n HA into PLGA microspheres, can improve the biocompatibility and osteoinductivity of composite in vivo, and had potential application in. After introducing n HA into PLGA-MSN microspheres, the early release of drugs is more stable and the release time is longer than the control group. Therefore, PLGA-MSN/n HA composite microspheres carrier is an ideal material in bone regeneration and control release. |
PDF Full Text Request