In vitro-in vivo characterization of gentamicin bone implants

Overview of strategies to improve the antibacterial property of dental implants

The increasing number of peri-implant diseases and the unsatisfactory results of conventional treatment are causing great concern to patients and medical staff. The effective removal of plaque which is one of the key causes of peri-implant disease from the surface of implants has become one of the main problems to be solved urgently in the field of peri-implant disease prevention and treatment. In recent years, with the advancement of materials science and pharmacology, a lot of research has been conducted to enhance the implant antimicrobial properties, including the addition of antimicrobial coatings on the implant surface, the adjustment of implant surface topography, and the development of new implant materials, and significant progress has been made in various aspects. Antimicrobial materials have shown promising applications in the prevention of peri-implant diseases, but meanwhile, there are some shortcomings, which leads to the lack of clinical widespread use of antimicrobial materials. This paper summarizes the research on antimicrobial materials applied to implants in recent years and presents an outlook on the future development.

Material Extrusion Based Fabrication of Surgical Implant Template and Accuracy Analysis

An implant template with great precision is significantly critical for clinical application. Currently, the application of an immediate implant remains limited by the deviations between the planned and actual achieved positions and long periods required for preparation of implant templates. Material Extrusion (MEX), as one kind of 3D printing method, is well known for its low cost and easy operation. However, the accuracy of the implant template printed by MEX has not been fully researched. To investigate the accuracy and feasibility of in vitro computer-guided surgery assisted with a MEX printed template, unidentified plaster samples missing a maxillary molar are digitalized. Mimics software (Materialise, Leuven, Belgium) is used for preoperative design. Surgical templates are fabricated by a MEX 3D printer (Lingtong III, Beijing SHINO, Beijing, China). Postoperative CBCT data are obtained after surgical template placement. The differences in positions of X, Y, Z, and dXYZ as well as angulations between the placed and the designed template are measured on labiolingual and mesiodistal planes. The deviations of the planned and the actual outcome in each dimension are observed and analyzed. Data from different samples indicate that the mean deviation of the angle measures approximately 3.640°. For position deviation, the maximum deviation is found in the z-direction and the mean deviation is about 0.365 ± 0.136 mm. The mean deviation of space Euclidean distance dXYZ is approximately 0.537 ± 0.123 mm. Implant templates fabricated by MEX present a relatively high accuracy for tooth-supported guide implantation.

Modulating antibiotic release from reservoirs in 3D-printed orthopedic devices to treat periprosthetic joint infection

Periprosthetic joint infection is a costly debilitating affliction following total joint arthroplasty. Despite a relatively low incidence rate, periprosthetic joint infection is an increasing problem due to a substantial increase in arthroplasty surgeries over time. The current treatment is replacing the primary implant with a temporary bone cement spacer that releases antibiotics over time. However, the spacer is mechanically weak with an ineffective antibiotic release. Alternatively, three-dimensional (3D)-printed reservoirs in high-strength devices have the potential to release antibiotics long term in a controlled manner. In this study, 3D-printed reservoirs were loaded with calcium sulfate embedded with gentamicin. In vitro antibiotic release is tuned by varying reservoir parameters, such as channel length, diameter, and quantity. In addition, a straightforward computational model effectively predicts antibiotic release curves to rapidly design devices with a preferred release profile. Overall, this study highlights a novel approach to potentially develop high-strength joint implants with the long-term effective release of antibiotics to treat the periprosthetic joint infection.

Release mechanisms and applications of drug delivery systems for extended-release

INTRODUCTION

Drug delivery systems with extended-release profiles are ideal in improving patient compliance with enhanced efficacy. To develop devices capable of a prolonged delivery kinetics, it is crucial to understand the various underlying mechanisms contributing to extended drug release and the impact thereof on modulating the long-term performance of such systems in a practical application environment.

AREAS COVERED

This review article intends to provide a comprehensive summary of release mechanisms in extended-release drug delivery systems, particularly polymer-based systems; however, other material types will also be mentioned. Selected current research in the delivery of small molecule drugs and macromolecules is highlighted. Emphasis is placed on the combined impact of different release mechanisms and drug properties on the long-term release kinetics in vitro and in vivo.

EXPERT OPINION

The development of drug delivery systems over an extended duration is promising but also challenging when considering the numerous interrelated delivery-related parameters. Achieving a well-controlled extended drug release requires advanced techniques to minimize burst release and lag phase, a better understanding of the dynamic interrelationship between drug properties and release profiles over time, and a thorough elucidation of the impact of multiple in vivo conditions to methodically evaluate the eventual clinical efficacy.

A comprehensive review of biodegradable synthetic polymer-ceramic composites and their manufacture for biomedical applications

The application of various materials in biomedical procedures has recently experienced rapid growth. One area that is currently receiving significant attention from the scientific community is the treatment of a number of different types of bone-related diseases and disorders by using biodegradable polymer-ceramic composites. Biomaterials, the most common materials used to repair or replace damaged parts of the human body, can be categorized into three major groups: metals, ceramics, and polymers. Composites can be manufactured by combining two or more materials to achieve enhanced biocompatibility and biomechanical properties for specific applications. Biomaterials must display suitable properties for their applications, about strength, durability, and biological influence. Metals and their alloys such as titanium, stainless steel, and cobalt-based alloys have been widely investigated for implant-device applications because of their excellent mechanical properties. However, these materials may also manifest biological issues such as toxicity, poor tissue adhesion and stress shielding effect due to their high elastic modulus. To mitigate these issues, hydroxyapatite (HA) coatings have been used on metals because their chemical composition is similar to that of bone and teeth. Recently, a wide range of synthetic polymers such as poly (l-lactic acid) and poly (l-lactide-co-glycolide) have been studied for different biomedical applications, owing to their promising biocompatibility and biodegradability. This article gives an overview of synthetic polymer-ceramic composites with a particular emphasis on calcium phosphate group and their potential applications in tissue engineering. It is hoped that synthetic polymer-ceramic composites such as PLLA/HA and PCL/HA will provide advantages such as eliminating the stress shielding effect and the consequent need for revision surgery.

Recent developments in drug eluting devices with tailored interfacial properties

Drug eluting devices have greatly evolved during past years to become fundamental products of great marketing importance in the biomedical field. There is currently a large diversity of highly specialized devices for specific applications, making the development of these devices an exciting field of research. The replacement of the former bare metal devices by devices loaded with drugs allowed the sustained and controlled release of drugs, to achieve the desired local therapeutic concentration of drug. The newer devices have been "engineered" with surfaces containing micro- and nanoscale features in a well-controlled manner, that have shown to significantly affect cellular and subcellular function of various biological systems. For example, the topography can be structured to form an antifouling surface mimicking the defense mechanisms found in nature, like the skin of the shark. In the case of bone implants, well-controlled nanostructured interfaces can promote osteoblast differentiation and matrix production, and enhance short-term and long-term osteointegration. In any case, the goal of current research is to design implants that induce controlled, guided, and rapid healing. This article reviews recent trends in the development of drug eluting devices, as well as recent developments on the micro/nanotechnology scales, and their future challenges. For this purpose medical devices have been divided according to the different systems of the body they are focused to: orthopedic devices, breathing stents, gastrointestinal and urinary systems, devices for cardiovascular diseases, neuronal implants, and wound dressings.

Calcium Phosphate Bioceramics: A Review of Their History, Structure, Properties, Coating Technologies and Biomedical Applications

Calcium phosphate (CaP) bioceramics are widely used in the field of bone regeneration, both in orthopedics and in dentistry, due to their good biocompatibility, osseointegration and osteoconduction. The aim of this article is to review the history, structure, properties and clinical applications of these materials, whether they are in the form of bone cements, paste, scaffolds, or coatings. Major analytical techniques for characterization of CaPs, in vitro and in vivo tests, and the requirements of the US Food and Drug Administration (FDA) and international standards from CaP coatings on orthopedic and dental endosseous implants, are also summarized, along with the possible effect of sterilization on these materials. CaP coating technologies are summarized, with a focus on electrochemical processes. Theories on the formation of transient precursor phases in biomineralization, the dissolution and reprecipitation as bone of CaPs are discussed. A wide variety of CaPs are presented, from the individual phases to nano-CaP, biphasic and triphasic CaP formulations, composite CaP coatings and cements, functionally graded materials (FGMs), and antibacterial CaPs. We conclude by foreseeing the future of CaPs.

Poly (lactic acid)-based biomaterials for orthopaedic regenerative engineering

Regenerative engineering converges tissue engineering, advanced materials science, stem cell science, and developmental biology to regenerate complex tissues such as whole limbs. Regenerative engineering scaffolds provide mechanical support and nanoscale control over architecture, topography, and biochemical cues to influence cellular outcome. In this regard, poly (lactic acid) (PLA)-based biomaterials may be considered as a gold standard for many orthopaedic regenerative engineering applications because of their versatility in fabrication, biodegradability, and compatibility with biomolecules and cells. Here we discuss recent developments in PLA-based biomaterials with respect to processability and current applications in the clinical and research settings for bone, ligament, meniscus, and cartilage regeneration.

Nanofibers used for delivery of antimicrobial agents

Nanotechnology has gained an increased interest in several different areas of biotechnology including the drug delivery via nanofibers. Self-assembly, phase separation and electrospinning can all be used to successfully generate nanofibers with sizes well within the range of those of the fibers present in the native extracellular matrix (50-500 nm). In this article, the authors introduced the most popular applications of nanofibers related to the delivery of antimicrobial agents for infectious diseases. To date, only a few in-vivo studies are available at present to demonstrate its clinical potential; most of the studies are of exploratory nature and rely mostly on in-vitro experiments. Therefore, further advancement in the production and clinical performance of drug-loaded nanofibrous matrices seems necessary.

In vivo quantification of gentamicin released from an implant coating

Drug-releasing implants are gaining increasing interest. The present study reports a detailed physicochemical analysis of a polymeric coating based on poly(D,L-lactide) and the incorporated gentamicin combined with an in vitro and in vivo study of the gentamicin release. Differential scanning calorimeter, Fourier transform infrared spectroscopy, gel permeation chromatography and high-performance liquid chromatography showed no effect of the gamma sterilisation on the coating components or an interaction of the polymer and the gentamicin. Microbiological analysis revealed an inhibition of bacterial growth on the implant surface. For the in vivo study, gentamicin-coated wires were implanted into the tibiae of rats and harvested at different time points up to day 42. To monitor the release in vivo, gentamicin was quantified in serum, bone, endosteum, kidney, and on the explanted wires. Gentamicin was detectable over a time period of 42 days in the endosteum, up to seven days in the kidney, up to 4 h in the bone and at the end of the experiment on one of eight wires. The locally released gentamicin caused no histological changes of the kidney. Microbiologically active concentrations of released gentamicin were found in the endosteum up to 4 h after implantation. The combination of different methods supports the individual results, where quantification is complemented by visualisation or antimicrobial activity. This work demonstrates that the coating procedure results in no substantial alteration of the incorporated drug and that the in vitro burst release occurs also in vivo.

Optimization of recombinant human platelet-derived growth factor-BB encapsulated in Poly (lactic-co-glycolic acid) microspheres for applications in wound healing

Growth factors play multiple and critical roles in wound repair processes. Platelet-derived growth factor (PDGF) is a potent growth factor that is particularly important in the early inflammatory phase of wound healing. In order to extend the half-life of PDGF, polymeric encapsulation is used. In the current study, Poly (lactic-co-glycolic acid) (PLGA) microspheres containing recombinant human (rh) PDGF-BB were prepared to prolong the effectiveness of this growth factor. PLGA microspheres were optimized using a modified w/o/w-double-emulsion/solvent evaporation method by changing the processing conditions of stirring speed and emulsifier (polyvinyl alcohol) concentration. Microspheres prepared using the optimized method released rhPDGF-BB for up to three weeks. An in vitro migration assay showed a significant decrease in the wound area in cells treated with rhPDGF-BB microspheres compared to control cells. These findings demonstrate the potential of rhPDGF-BB encapsulated in microspheres to enhance wound healing.

Marine structure derived calcium phosphate-polymer biocomposites for local antibiotic delivery

Hydrothermally converted coralline hydroxyapatite (HAp) particles loaded with medically active substances were used to develop polylactic acid (PLA) thin film composites for slow drug delivery systems. The effects of HAp particles within PLA matrix on the gentamicin (GM) release and release kinetics were studied. The gentamicin release kinetics seemed to follow Power law Korsmeyer Peppas model with mainly diffusional process with a number of different drug transport mechanisms. Statistical analysis shows very significant difference on the release of gentamicin between GM containing PLA (PLAGM) and GM containing HAp microspheres within PLA matrix (PLAHApGM) devices, which PLAHApGM displays lower release rates. The use of HAp particles improved drug stabilization and higher drug encapsulation efficiency of the carrier. HAp is also the source of Ca²⁺ for the regeneration and repair of diseased bone tissue. The release profiles, exhibited a steady state release rate with significant antimicrobial activity against Staphylococcus aureus (S. aureus) (SH1000) even at high concentration of bacteria. The devices also indicated significant ability to control the growth of bacterial even after four weeks of drug release. Clinical release profiles can be easily tuned from drug-HAp physicochemical interactions and degradation kinetics of polymer matrix. The developed systems could be applied to prevent microbial adhesion to medical implant surfaces and to treat infections mainly caused by S. aureus in surgery.

Vancomycin containing PLLA/β-TCP controls experimental osteomyelitis in vivo

Background

Implant-related osteomyelitis (IRO) is recently controlled with local antibiotic delivery systems to overcome conventional therapy disadvantages. In vivo evaluation of such systems is however too little.

Questions/purposes

We asked whether vancomycin (V)-containing poly-l-lactic acid/β-tricalcium phosphate (PLLA/β-TCP) composites control experimental IRO and promote bone healing in vivo.

Methods

Fifty-six rats were distributed to five groups in this longitudinal controlled study. Experimental IRO was established at tibiae by injecting methicillin-resistant Staphylococcus aureus (MRSA) suspensions with titanium particles in 32 rats. Vancomycin-free PLLA/β-TCP composites were implanted into the normal and infected tibiae, whereas V-PLLA/β-TCP composites and coated (C)-V-PLLA/β-TCP composites were implanted into IRO sites. Sham-operated tibiae established the control group. Radiological and histological scores were quantified with microbiological findings on weeks 1 and 6.

Results

IRO is resolved in the CV- and the V-PLLA/β-TCP groups but not in the PLLA/β-TCP group. MRSA was not isolated in the CV- and the V-PLLA/β-TCP groups at all times whereas the bacteria were present in the PLLA/β-TCP group. Radiological signs secondary to infection are improved from 10.9 ± 0.9 to 3.0 ± 0.3 in the V-PLLA/β-TCP group but remained constant in the PLLA/β-TCP group. Histology scores are improved from 24.7 ± 6.5 to 17.6 ± 4.8 and from 27.6 ± 7.9 to 32.4 ± 8.9 in the CV-PLLA/β-TCP and the V-PLLA/β-TCP groups, respectively. New bone was formed in all the PLLA/β-TCP group at weeks 1 and 6.

Conclusions

CV- and V-PLLA/β-TCP composites controlled experimental IRO and promoted bone healing.

Clinical relevance

CV- and V-PLLA/β-TCP composites have the potential of controlling experimental IRO and promoting bone healing.

Gentamicin release from biodegradable poly-l-lactide based composites for novel intramedullary nails

One of the major problems in orthopedic surgery is infection associated with implantation. The treatment is a very difficult and long-term process. A solution to this issue can be the use of implants which additionally constitute an antibiotic carrier preventing the development of an infection. Prototypes of biodegradable intramedullary nails made of three different composites with a poly(L-lactide) matrix were designed. The nails served as gentamicin sulfate (GS) carrier - an antibiotic commonly used in the treatment of osteomyelitis. The matrix was reinforced with carbon fibers (CF), alginate fibers (Alg) and magnesium alloy wires (Mg), as well as modified with bioactive particles of tricalcium phosphate (TCP) in various systems. In this way, novel, multi-phase and multifunctional degradable intramedullary nails were obtained. The tests demonstrated strong dependence between the type of the modifying phase introduced into the composite, and the rate of drug release. Introduction of gentamicin into the nail structure strengthened and prolonged antibacterial activity of the nails.

Antibiotic-loaded chitosan hydrogel with superior dual functions: antibacterial efficacy and osteoblastic cell responses

It is critical for the clinical success to take the biological function into consideration when integrating the antibacterial function into the implanted biomaterials. To this aim, we prepared gentamycin sulfate (GS)-loaded carboxymethyl-chitosan (CM-chitosan) hydrogel cross-linked by genipin. The prepared hydrogels not only achieved superb inhibition on bacteria growth and biofilm formation of Staphylococcus aureus but also significantly enhanced the adhesion, proliferation, and differentiation of MC3T3-E1 cells. The observed dual functions were likely based on the intrinsic property of the positive charged chitosan-based hydrogel, which could be modified to selectively disrupt the bacteria wall/membrane and promote cell adhesion and proliferation, as suggested by the membrane permeability study. The genipin concentration played an important role in controlling the degradation time of the chitosan hydrogel and the MC3T3-E1 cell responses. The loading of GS not only significantly increased the antibacterial efficiency but also was beneficial for the osteoblastic cell responses. Overall, the biocompatibility of the prepared chitosan-GS hydrogel could be tuned with both the genipin and GS concentrations, which control the available positive charged sites of chitosan. The results demonstrated that chitosan-GS hydrogel is an effective and simple approach to achieving combined antibacterial efficacy and excellent osteoblastic cell responses, which has great potential in orthopedic applications.

Controlled release of gentamicin from gelatin/genipin reinforced beta-tricalcium phosphate scaffold for the treatment of osteomyelitis

Infection of the bone (osteomyelitis) remains one of the most challenging problems in the field of orthopedic surgery. The limitations of systemic antibiotics administration include undesired side effects, systemic toxicity, patient discomfort, and development of bacterial resistance. In this study, we developed a bactericidal gentamicin-doped beta-tricalcium phosphate (TCP) scaffold reinforced with a gelatin/genipin hydrogel (G-TCP). Our data showed that the gentamicin-doped G-TCP had a much longer drug releasing period, while the gentamicin was completely released from pure TCP cements (B-TCP) within one day. In addition, the release profile of G-TCP exhibited an initial burst followed by a zero-order release. One standard strain, Staphylococcus aureus (S. aureus, ATCC25923) was selected to evaluate the antibacterial activity and therapeutic effect of this scaffold. G-TCP significantly inhibited growth of S. aureus both in vitro and in vivo. In a rat osteomyelitis model, osteomyelitis could be totally cured after implantation of G-TCP for three weeks. We propose that the gelatin/genipin-gentamicin TCP scaffold represents one of the promising gentamicin releasing bone scaffolds in treating osteomyelitis.

In vitro study of vancomycin release and osteoblast-like cell growth on structured calcium phosphate-collagen

A drug delivery vehicle consisting of spherical calcium phosphate-collagen particles covered by flower-like (SFCaPCol) blossoms composed of nanorod building blocks and their cellular response is studied. The spherical structure was achieved by a combination of sonication and freeze-drying. The SFCaPCol blossoms have a high surface area of approximately 280 m(2) g(-1). The blossom-like formation having a high surface area allows a drug loading efficiency of 77.82%. The release profile for one drug, vancomycin (VCM), shows long term sustained release in simulated body fluid (SBF), in a phosphate buffer saline (PBS, pH 7.4) solution and in culture media over 2 weeks with a cumulative release ~53%, 75% and 50%, respectively, over the first 7 days. The biocompatibility of the VCM-loaded SFCaPCol scaffold was determined by in vitro cell adhesion and proliferation tests of rat osteoblast-like UMR-106 cells. MTT tests indicated that UMR-106 cells were viable after exposure to the VCM loaded SFCaPCol, meaning that the scaffold (the flower-like blossoms) did not impair the cell's viability. The density of cells on the substrate was seen to increase with increasing cultured time.

Local drug delivery to the bone by drug-releasing implants: perspectives of nano-engineered titania nanotube arrays

Titania nanotube (TNT) arrays fabricated by electrochemical anodization of titanium are currently one of the most attractive nanomaterials due to their remarkable properties. In this review, we highlight recent research activities that are focused on the application of the TNT arrays for local drug delivery, specifically for addressing problems associated with orthopedic implants. The advantages of drug-releasing implants based on TNT arrays for local delivery of therapeutics in bone related to these challenging problems including inflammation, infection and osseointegration are discussed. An overview of recent research to advance the drug-releasing performance of TNT arrays and the potential of their future applications and development are presented.

A platelet derived growth factor delivery system for bone regeneration

platelet derived growth factor (PDGF) was formulated in a calcium phosphate/biodegradable polymer system for local and controlled delivery to enhance bone regeneration. Implants with a porosity of 67 %, composed of hydroxyapatite, PLGA microspheres and Pluronic(®), were obtained by compression. An increase in porosity with time was expected due to Pluronic(®) dissolution and PLGA microsphere degradation. In vivo PDGF release and tissue distribution were monitored after system implantation into femurs of rabbits using (125)I-PDGF. Most of the PDGF was released within approximately 5 days and remained located around the implantation site with negligible systemic exposure. Compared with the reference groups, an important enhancement of bone regeneration was found with doses of 600 and 1,200 ng of PDGF, although no histological differences were observed between the two doses. In conclusion, the elaborated system exhibited good biocompatibility and offered a physiologically relevant PDGF profile that enhances bone formation compared to the non-treated bone defect.

In vivo osteogenic response to different ratios of BMP-2 and VEGF released from a biodegradable porous system

Bone regeneration and vascularization with porous PLGA scaffolds loaded with VEGF (0.35 and 1.75 μg) and BMP-2 (3.5 and 17.5 μg), incorporated in PLGA microspheres, or the combination of either dose of BMP-2 with the low dose of VEGF were investigated in an intramedullary femur defect in rabbits. The system was designed to control growth factor (GF) release and maintain the GFs localized within the defect. An incomplete release was observed in vitro whereas in vivo VEGF and BMP-2 were totally delivered during 3 and 4 weeks, respectively. A weak synergistic effect of the dual delivery of VEGF and BMP-2 (high dose) was found by 4 weeks. However, the absence of an apparent synergistic long-term effect (12 weeks) of the combination over BMP-2 alone suggests that more work has to be done to optimize VEGF dose, sequential presentation, and the ratio of the two GFs to obtain a beneficial bone repair response.

Blood compatibility of iron-doped nanosize hydroxyapatite and its drug release

Nanosize hydroxyapatite (nHAp) doped with varying levels of Fe(3+) (Fe-nHAp of average size 75 nm) was synthesized by hydrothermal and microwave techniques. The samples were characterized for physiochemical properties by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), inductively coupled plasma optical emission spectrometer (ICP-OES), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), mechanical and dielectric properties. The biological properties like hemocompatibility, antibacterial efficacy, in vitro bioactivity and the cell proliferation of the samples were determined. XRD pattern of the samples were of single phase hydroxyapatite. As the content of Fe(3+) increased, the crystallite size as well as crystallinity decreased along with a morphological change from spherulites to rods. The dielectric constants and Vickers hardness were enhanced on Fe(3+) doping. The VSM studies revealed that the saturation magnetization (M(s)) and retentivity (M(r)) were found to increase for Fe-nHAp. nHAp impregnated with an antibiotic as a new system for drug delivery in the treatment of chronic osteomyelitis was also attempted. The in vitro drug release with an antibiotic amoxicillin and anticancer drug 5-fluorouracil showed sustained release for the lowest concentration of Fe(3+), while with an increase in the content; there was a rapid release of the drug. The hemolytic assay of Fe(3+) doped samples revealed high blood compatibility (<5% hemolysis). The antibacterial activities of the antibiotic impregnated materials were tested against a culture of E. coli, S. epidermidis and S. aureus by agar diffusion test. The in vitro bioactivity test using simulated body fluid (SBF) showed better bone bonding ability by the formation of an apatite layer on the doped samples. The growth of the apatite layer on the samples surface has been confirmed by EDS analysis. The proliferative potential of MG63 cells by MTT assay confirmed the noncytotoxicity of the samples.

Effect of triple growth factor controlled delivery by a brushite-PLGA system on a bone defect

Bone regeneration is a complex process that involves multiple cell types, growth factors (GFs) and cytokines. A synergistic contribution of various GFs and a crosstalk between their signalling pathways was suggested as determinative for the overall osteogenic outcome. The purpose of this work was to develop a brushite-PLGA system, which controls the release rate of the integrated growth factors (GFs) to enhance bone formation. The brushite cement implants were prepared by mixing a phosphate solid phase with an acid liquid phase. PDGF (250 ng) and TGF-β1 (100 ng) were incorporated into the liquid phase. PLGA microsphere-encapsulated VEGF (350 ng) was pre-blended with the solid phase. VEGF, PDGF and TGF-β1 release kinetics and tissue distributions were determined using iodinated ((125)I) GFs. In vivo results showed that PDGF and TGF-β1 were delivered more rapidly from these systems implanted in an intramedullary defect in rabbit femurs than VEGF. The three GFs released from the brushite-PLGA system remained located around the implantation site (5 cm) with negligible systemic exposure. Bone peak concentrations of approximately 4 ng/g and 1.5 ng/g of PDGF and TGF-β1, respectively were achieved on day 3. Thereafter, PDGF and TGF-β1 concentrations stayed above 1 ng/g during the first week. The scaffolds also provided a VEGF peak concentration of nearly 6 ng/g on day 7 and a local concentration of approximately 1.5 ng/g during at least 4 weeks. Four weeks post implantation bone formation was considerably enhanced with the brushite-PLGA system loaded with each of the three GFs separately as well as with the combination of PDGF and VEGF. The addition of TGF-β1 did not further improve the outcome. In conclusion, the herein presented brushite-PLGA system effectively controlled the release kinetics and localisation of the three GFs within the defect site resulting in markedly enhanced bone regeneration.

Material-related effects of BMP-2 delivery systems on bone regeneration

Material-related effects of a brushite and a PLGA controlled release system loaded with two distinct doses of bone morphogenetic protein-2 (BMP-2) (3.5 and 17.5 μg), pre-encapsulated in poly(lactic-co-glycolic acid) (PLGA), were investigated in an intramedullary femur defect model in rabbits. The systems were characterized in vitro and in vivo over 12 weeks in terms of morphology, release kinetics, porosity, molecular weight, and composition using scanning electron microscopy, mercury porosimetry, radioactivity counting, X-ray diffractometry, differential scanning calorimetry, and gel permeation chromatography. During the experimental period the investigated systems underwent significant changes in vitro as well as in vivo. It should be stressed that the two in vitro release patterns were similar, however in vivo parallel profiles were observed with a higher burst effect for BMP-2 in the PLGA system. The PLGA system degraded and disintegrated significantly faster than the brushite system, which suffered slowly progressing external erosion and, additionally, material resorption by osteoclasts in vivo. The consequences of this were reflected in the degree of bone regeneration. Although a sustained delivery of BMP-2 was achieved with both systems, the brushite construct, independent of the loaded growth factor dose, failed to consistently induce defect repair, a result attributed to its slow resorption rate. In contrast, the PLGA system resulted in complete regeneration with mature trabecular bone formation 8 weeks after implantation.

Drug-eluting Ti wires with titania nanotube arrays for bone fixation and reduced bone infection

Current bone fixation technology which uses stainless steel wires known as Kirschner wires for fracture fixing often causes infection and reduced skeletal load resulting in implant failure. Creating new wires with drug-eluting properties to locally deliver drugs is an appealing approach to address some of these problems. This study presents the use of titanium [Ti] wires with titania nanotube [TNT] arrays formed with a drug delivery capability to design alternative bone fixation tools for orthopaedic applications. A titania layer with an array of nanotube structures was synthesised on the surface of a Ti wire by electrochemical anodisation and loaded with antibiotic (gentamicin) used as a model of bone anti-bacterial drug. Successful fabrication of TNT structures with pore diameters of approximately 170 nm and length of 70 μm is demonstrated for the first time in the form of wires. The drug release characteristics of TNT-Ti wires were evaluated, showing a two-phase release, with a burst release (37%) and a slow release with zero-order kinetics over 11 days. These results confirmed our system's ability to be applied as a drug-eluting tool for orthopaedic applications. The established biocompatibility of TNT structures, closer modulus of elasticity to natural bones and possible inclusion of desired drugs, proteins or growth factors make this system a promising alternative to replace conventional bone implants to prevent bone infection and to be used for targeted treatment of bone cancer, osteomyelitis and other orthopaedic diseases.

Thermal and ultrasonic influence in the formation of nanometer scale hydroxyapatite bio-ceramic

Hydroxyapatite (HAP) is a widely used biocompatible ceramic in many biomedical applications and devices. Currently nanometer-scale forms of HAP are being intensely investigated due to their close similarity to the inorganic mineral component of the natural bone matrix. In this study nano-HAP was prepared via a wet precipitation method using Ca(NO₃)₂ and KH₂PO₄ as the main reactants and NH₄OH as the precipitator under ultrasonic irradiation. The Ca/P ratio was set at 1.67 and the pH was maintained at 9 during the synthesis process. The influence of the thermal treatment was investigated by using two thermal treatment processes to produce ultrafine nano-HAP powders. In the first heat treatment, a conventional radiant tube furnace was used to produce nano-particles with an average size of approximately 30 nm in diameter, while the second thermal treatment used a microwave-based technique to produce particles with an average diameter of 36 nm. The crystalline structure and morphology of all nanoparticle powders produced were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). Both thermal techniques effectively produced ultrafine powders with similar crystalline structure, morphology and particle sizes.

Development of 3D wet-spun polymeric scaffolds loaded with antimicrobial agents for bone engineering

Three-dimensional wet-spun microfibrous meshes of a star poly(∈-caprolactone) were developed as potential scaffolds endowed with antimicrobial activity. The in vitro release kinetics of the meshes, under physiological conditions, was initially fast and then a sustained release for more than one month was observed. Cell cultures of a murine pre-osteoblast cell line showed good cell viability and adhesion on the wet-spun star poly(∈-caprolactone) fiber scaffolds. These promising results indicate a potential application of the developed meshes as engineered bone scaffolds with antimicrobial activity.

A new concept of gentamicin loaded HAP/TCP bone substitute for prophylactic action: in vivo pharmacokinetic study

Despite systemic prophylaxis, infection rates after orthopedic surgery can reach more than 1%. A new HAP/TCP bone substitute loaded with 125 mg of gentamicin was designed for prophylactic use. Its aim was to enhance the efficacy of systemic prophylactic treatments by increasing the local antibiotic concentration. The release rate of gentamicin from the bone substitute was investigated after implantation in the femoral condyle of five sheep. In order to investigate the local and systemic gentamicin concentrations, synovial fluids and blood samples were assessed over a 5-day period. The mean gentamicin concentration peak in blood was 4.2 μg/ml and the mean local concentration in synovial fluids during the first 8 h was 305 μg/ml. After 48 h, the concentrations in blood and synovial fluids were less than 0.5 μg/ml. No remaining gentamicin was detected in bone substitutes explanted after 8 days of implantation. The gentamicin release rate from the bone substitutes assessed corresponds to the recommendations for the prophylactic use of antibiotics: high local concentration but limited in time (less than 48 h) not to select antibiotic-resistant bacterial strains. Our results indicated that this implant should be an effective prophylactic tool in orthopedic surgery in combination with systemic prophylaxis.

Calcium Phosphate Bone Cements Including Sugar Surfactants: Part Two-Injectability, Adhesive Properties and Biocompatibility

Addition of sugar surfactants, sucrose fatty acid esters and alkylpolyglucosides to a calcium phosphate cement, designed for bone reconstruction, is described. Thanks to their adsorption at the surface of the calcium phosphate particles, the sugar surfactants allowed a full injectability and brought a very good workability. Injectability was measured by monitoring force-distance curves. With some of the selected sugar surfactants adhesive properties of the cement pastes were also observed, which were measured by tack tests. Finally, some properties related to biological applications are described, including gentamicine release and osteoblast viability experiments. The whole study demonstrates that addition of these mild surfactants improved several properties of the calcium phosphate cement, without impairing function.

Recent progress in inorganic and composite coatings with bactericidal capability for orthopaedic applications

This review covers the most recent developments of inorganic and organic-inorganic composite coatings for orthopedic implants, providing the interface with living tissue and with potential for drug delivery to combat infections. Conventional systemic delivery of drugs is an inefficient procedure that may cause toxicity and may require a patient's hospitalization for monitoring. Local delivery of antibiotics and other bioactive molecules maximizes their effect where they are required, reduces potential systemic toxicity and increases timeliness and cost efficiency. In addition, local delivery has broad applications in combating infection-related diseases. Polymeric coatings may present some disadvantages. These disadvantages include limited chemical stability, local inflammatory reactions, uncontrolled drug-release kinetics, late thrombosis and restenosis. As a result, embedding of bioactive compounds and biomolecules within inorganic coatings (bioceramics, bioactive glasses) is attracting significant attention. Recently nanoceramics have attracted interest because surface nanostructuring allows for improved cellular adhesion, enhances osteoblast proliferation and differentiation, and increases biomineralization. Organic-inorganic composite coatings, which combine biopolymers and bioactive ceramics that mimick bone structure to induce biomineralization, with the addition of biomolecules, represent alternative systems and ideal materials for "smart" implants. In this review, emphasis is placed on materials and processing techniques developed to advance the therapeutic use of biomolecules-eluting coatings, based on nanostructured ceramics. One part of this report is dedicated to inorganic and composite coatings with antibacterial functionality.

FROM THE CLINICAL EDITOR

Inorganic and composite nanotechnology-based coating methods have recently been developed for orthopedic applications, with the main goal to provide bactericide and other enhanced properties, which may result in reduced need for pharmaceutical interventions and overall more cost effective orthopedic procedures. This review discusses key aspects of the above developments.

Vancomycin release from poly(D,L-lactic acid) spray-coated hydroxyapatite fibers

The influence of the poly(D,L-lactic acid) (PDLLA) coating thickness on the in vitro vancomycin release from a hydroxyapatite (HA) carrier was studied. Microporous HA fibers with a porosity of 51 v% and an average pore diameter of 1.0 μm were fabricated by a diffusion-induced phase separation technique. They were loaded with 38 mg vancomycin hydrochloride (VH)/gHA, and their cylindrical shape enabled the application of the spray coating technique for the deposition of uniform PDLLA coating thicknesses, varying from 6.5 μm to 28 μm. The resulting in vitro VH release varied from a complete release within 14 days for 6.5 μm coatings to a release of 23% after 28 days for 28 μm coatings. It was clear that the VH release rate from a HA fiber can be adjusted by varying the PDLLA coating thickness. Microbiological tests of these fibers against a methicillin-resistant Staphylococcus aureus (MRSA) isolate pointed to the importance of the initial burst release and confirmed that the released antibiotics had the potential to interfere with S. aureus biofilm formation.

Covalent coating of hydroxyapatite by keratin stabilizes gentamicin release

A novel hybrid hydroxyapatite (HAP) matrix, covalently coated with rarely applied, hardly degradable keratin and effectively modified by gentamicin immobilized in mixed-type mode (via interactions of diverse strength), was created. This hybrid showed a remarkably high drug immobilization yield and the most sustainable antibiotic release among all tested composites. It was also able to inhibit bacterial growth, both in surrounding liquid and on matrix surface, much longer (for at least 121 days of experiment) than analogous gelatin-modified and nonmodified matrices. Gentamicin-keratin-coated-HAP granules were nontoxic to human osteoblasts and enabled their proliferation with a rate similar as noncoated HAP. Presence of keratin on HAP granules seemed to slightly enhance the osteoblast proliferation. The results indicate that newly created HAP hybrid with covalently immobilized keratin and gentamicin--nontoxic and osteoblast-friendly--is a promising biomaterial of significantly prolonged antibacterial activity.

Synthesis and characterisation of nanohydroxyapatite using an ultrasound assisted method

Nanostructured hydroxyapatite (HAP) was prepared by a wet precipitation method using Ca(NO(3)) and KH(2)PO(4) as the main material and NH(3) as the precipitator under ultrasonic irradiation. The Ca/P ratio was set at 1.67 and the pH maintained at a minimum of 9. The temperature conditions and ultrasound influences were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FT-IR). The results showed that Nano-HAP can be obtained by this method and the particles were achieved to around 30 nm.