The Preparation Of Mesoporous Hydroxyapatite/Chitosan Composite Biomaterials Loaded With Vancomycin And Basic Research Application In Orthopaedics

The treatment of acute and chronic orthopaedic infection is difficult,time consuming and expensive. Despite the availability of a myriad ofantibiotics and marked advances in surgical treatment, the long-termrecurrence rateremains alarming at a rate of20%to30%. Absence ofantibiotics labelled exclusively for osteomyelitic conditions leave thechoice of therapy to the preferences and experience of the attendingphysicians. Very high concentrations of antibiotics are required at thetarget site but could hardly be attained by conventional routes of drugadministration without provoking serious side effects. Hence,conventional therapy hampers clinicians in striking a balance betweenefficacy and safety in deciding an optimal treatment strategy forosteomyelitic patients. Moreover, patients bear unfulfilled therapeuticoutcomes, development of adverse drug effects and huge healthcare bills. Local drug delivery systems placed in the affected area, release druglocally for prolonged periods and at concentrations generally higher thanthose achieved by conventional drug delivery strategies.So far, a largenumber of systems have been employed as various drug delivery systems,such as biodegradable polymers hydroxyapatite,calcium phosphatecement xerogels, hydrogels, and mesoporous silica. Recently mesoporousmaterials is chemistry and material field research hotspot, and they havegained enhanced interest with particular attention as drug storage andrelease carrier due to their large unique surface area and hole volume,uniform and adjustable pore canal, easily modified surface features forsite specific delivery. Due to these advantages, mesoporous materialsshow a broad application prospect in chemitry, biological medicine,chemical catalysis, nanometer materials and so on.The drug deliverysystems using mesoporous materials as drug carriers have been reported.Due to the bioactivity, biocompatibility,stability, nontoxic properties,hydroxyapatite with porous surface structure and–OH groups may serveas an ideal candidate drug carrier for the delivery of a variety ofpharmaceutical molecules, and especially mesoporous HA have broader pore canal space and adsorption performance than nano HA. Thus, thedesign and development of mesoporous HA might be able to reach thisgoal. Chitosan as a high molecular bioactive polymer has satisfactorybiocompatibility and biodegradation, and itself can improve survival rateof the osteoblast and promote the osteoblast differentiation and Matrixmineralization.Its surface hydrophilicity is beneficial to celldifferentiation and adhesion.So HA and CS two kinds of materials wereformed composite materials and may fully exrt their advantage. HA wasscattered among chitosan matrix and formed composite obtained goodosteoinduction and osteoconduction. Moreover, biological space ofdissolving chitosan is helpful to tissue reconstruction and then isconductive to drug releasing.Mesoporous hydroxyapatite/chitosan composite have beensuccessfully prepared and synthesized using a freeze-drying method, andthen characterized by Scanning Electron Microscope, X-ray diffractionand IR. Results showed that mesoporous HA/CS presented higher surfacearea and porosity. The effect of mesoporous HA/CS on early adhesion,proliferation and differentiation of osteoblast cells in vitro was measured.. MTT cytotoxicity test and cell adhesion test show that the materials havegood biocompatibility and make cell viability and proliferation. In vitrotesting using osteoblast-like cells showed that on the surfaces of cells areable to adhere, proliferate, and migrate through the pores. These cellsmaintained similar expression levels of osteoblastic-associated markersnamely collagen type I (COL-1), alkaline phosphatase(ALP). Histologicanalysis and radiological analysis in vivo also prove that HA/CS canrepair bone defect as a new kind of bone grafting material. Thisexperiment In vivo evaluated local tissue vancomycin concentrations byHigh Performance Liquid Chromatography Tandem mass spectrometry(HPLC-TS) and antibacterial activity against methicillin-resistantStaphylococcus aureus (MRSA) using a muscular rabbit model.Moreover, the number of viable MRSA on HA/CS was significantly morethan seen on mesoporous HA/CS. We can conclude that the mesoporousHA/CS loaded with vancomycin represents a promising candidate forbone regeneration as a drug delivery. This experiment evaluated localtissue vancomycin concentrations and antibacterial activity againstmethicillin-resistant Staphylococcus aureus (MRSA) using a muscular rabbit model. Mesoporous HA/CS loaded with vancomycin samples wereimplanted into the muscular pockets of the rabbit extremity. The resultsrevealed that local tissue vancomycin concentrations of mesoporousHA/CS was higher than it of HA/CS at different time(3d,7d,14d,28d)anddifferent distance site(1cm,2cm). Antibacterial assays indicate thatmesoporous HA/CS loaded with vancomycin have the effect of on growthof organisms and keep the diameter of inhibition zone until it disappearedfor20d. Moreover, the number of viable MRSA on HA/CS wassignificantly more than seen on mesoporous HA/CS. These resultsdemonstrated that mesoporous HA/CS could enhance the drug loadingamount and releasing amount in vivo and offer good ability to killMRSA.In the present investigation, a novel and rational approach was madeto combine antibiotic drugs with HA/CS scaffold matrix, which candeliver the drug locally and in a sustained fashion. Nano-HA scaffoldshave been studied in detail to cure osteomyelitis in animal model.Mesoporous HA/CS presented a higher surface area and porosity whencompared with conventional micro-structured HA. BMP-2, Collagen-1 gene expression of osteoblastic associated markers also presented a highexpression. MTT assay and Cell adhesion assay showed that Mesoporoushydroxyapatite/chitosan provided a more adequate environment for celladhesion and migration and possessed good biocompatibility, improvingcell response. Because the VCM molecules can be adsorbed onto outersurface and inner area of mesoporous materials, it is suitable forcontrolled release as a drug carrier. This study provides novel andimportant information on the in vivo and in vitro effects of HA/CS loadedwith VCM, and suggests that this mesoporous materials releases VCMfor a long time after implantation and disinfects against MRSA, andsatisfies the demand as a drug delivery system.