Preparation And Mechanisms Study Of Vancomycin-PDLLA Loaded Plates And -HA Loaded Plates

BackgroundAs the report of AO in 2006 suggests,those patients with opened fractures are known to be at higher risk of infection ranged from 3~40% (the rate of infection in closed fractures is 1.5%). Up to 60% of open fractures are contaminated with bacteria at the time of injury . In wartime firearm injuries, serious tissue damage and pollution allow great quantities of bacteria to survive in the area (0.5 cm) around the wound. The infection rate of bone and soft tissue ranged from 25% to 40%, and even followed by adequate wound debridement. Maurer et al reported the rate of infection in open tibia fractures increased to greater than 30% when internal fixation was used. For instance, implant-associated infections account for nearly 50% of the estimated 2 million nosocomial infections in the United States per year. In Britain, the loss was 7-11 million pounds per year. Meanwhile, the infection raised the expense of patients and increased the suffering of the human body and psychology of patients. Infection can even have such severe consequences as death. Therefore, it would be clinically advantageous to develop an internal fixation that possesses anti-infection properties to prevent and cure implant infections.During the past thirty years, a drug-delivery system was gradually developed on the basis of a series of original, fine biocompatibility inorganic material and organ-polymers. This system had a broad application perspective in the treatment directions of opened fracture, osteomyelitis and bone defects due to infection. Vancomycin (VCM) belongs to glycopeptide antibiotics. It has broad antimicrobial spectrum, covering most bacteria commonly involved in Gram-positive bacteria. Now it is the one of the top choice to cure severe infection which caused by MRSA or MRSE. And it is considered the one of the antibiotics for local application. Poly(D,L)-lactic acid (PDLLA) has excellent features with respect to implant-coating including high mechanical stability, good osteoinductive potential, biodegradability and excellent biocompatibility in vivo. The PDLLA coating is degraded by hydrolysis 3-6 months after implantation. The products of degradation are metabolized in the citric acid cycle. Otherwise, HA has excellent features with respect to implant-coating including biodegradability and excellent biocompatibility too. Because of these above mentioned reasons, PDLLA and HA can be used in orthopedic internal fixation. It is possible that the risk of infection can be reduced by developing an antiseptic surface coating for medical implants.ObjectiveWith PDLLA as a carrier, PDLLA coatings carrying VCM were prepared on the surface of titanium alloy plate substrates using solvent-casting technology. Meanwhile, HA coatings which carrying Vancomycin were prepared on the surface of titanium plate substrate using simulated body fluid technology with the HA as a carrier. Through vivo and vitro test, VCM-PDLLA loaded plates and VCM-HA loaded plates were expected to have dual effects of prophylaxis and cure infection in local and had a characteristic of fine therapeutic measure for opened fracture and firearm wound .MethodsPart 1Experiment 1: VCM-PDLLA loaded plates were prepared by solvent casting technology. To observe the coating of VCM-PDLLA loaded plates by SEM. The drug release profile of the plates were measured by immersing plates into 20ml PBS and measuring the content of VCM in different phase. The bacteriostatic activity to Staphylococcus aureus of the plates were evaluated by put the plates into Mueller-Hinton (MH) agar Petri dishes and the inhibition zones forming around the discs were measured in different phase.Experiment 2: To consult the biological evaluation of medical devices, the biocompatibility of VCM-PDLLA loaded plates were investigated by pryogen test, hemolytic test, cytotoxic test, et al.Part 2VCM-HA loaded plates were prepared using simulated body fluid technology. VCM-HA loaded plates were detected by the test method of SEM, EDX and FT-IR. The bacteriostatic activity to Staphylococcus aureus of the plates were evaluated by put the plates into MH agar Petri dishes and the inhibition zones forming around the discs were measured in different phase.Part 3VCM-PDLLA loaded plates were inserted in model of rabits that the middle tibia were fracture and were stained with 1×106CFU/ml S. aureus. In different phase, WBC, CRP, ESR, et al were measured to evaluate the anti-infection effect of the plates.Results1. VCM-PDLLA loaded plates were obtained. Plates showed a sustained in vitro drug release character in the experiment, in which VCM released from the plate was sustained over 20 days. The in vitro inhibition of Staphylococcus aureus showed that the plates had an inhibitory effect on Staphylococcus aureus, and the antibacterial activity was maintained for at least 15 days. There were no toxicity for the VCM-PDLLA loaded plates, and the plates had good biocompatibility .2. VCM-HA loaded coatings were prepared on the plates. The test of SEM, EDX and FT-IR indicated that the smooth and uniform coating was formed on the surface of the plates. The test of bacteriostasis indicated that obvious inhibition zone was appeared around the plate and it showed that VCM was successfully loaded on the coating. But in the next day the inhibition zone quickly contracted and in 3d the inhibition zone vanished. The result showed it could not achive the valid inhibitive concentration through the explosive release of the first day. According this, we think it may be related to various factor such as the preparative technique and determined to cancel the next study of VCM-HA loaded plates.3. VCM-PDLLA loaded plates could effective cut down the content of WBC, ESR and CRP of the model of rabits that the middle tibia were fracture and were stained with S.aureus, and could affect the body temperature, but could not affect the body weight in different phase. X-ray, pathologic examine and bacterial culture showed the plates could effective cut down the infection rate of the model.Conclusion1. VCM-PDLLA loaded plates showed a sustained in vitro drug release character, and the plates had an stabile inhibitory effect on S.aureus in vivo. There was a good biocompatibility for the plates. The plates were effective at inhibiting infection in an model of rabits that the middle tibia were fracture and were stained with S. aureus.2. VCM-HA loaded plates carried Vancomycin effectively and kept their bacteriostatic activity, but only sustained 24h.