Sequential release kinetics of two (gentamicin and BMP-2) or three (gentamicin, IGF-I and BMP-2) substances from a one-component polymeric coating on implants

Optimizing Delivery of Therapeutic Growth Factors for Bone and Cartilage Regeneration

Bone- and cartilage-related diseases, such as osteoporosis and osteoarthritis, affect millions of people worldwide, impairing their quality of life and increasing mortality. Osteoporosis significantly increases the bone fracture risk of the spine, hip, and wrist. For successful fracture treatment and to facilitate proper healing in the most complicated cases, one of the most promising methods is to deliver a therapeutic protein to accelerate bone regeneration. Similarly, in the setting of osteoarthritis, where degraded cartilage does not regenerate, therapeutic proteins hold great promise to promote new cartilage formation. For both osteoporosis and osteoarthritis treatments, targeted delivery of therapeutic growth factors, with the aid of hydrogels, to bone and cartilage is a key to advance the field of regenerative medicine. In this review article, we propose five important aspects of therapeutic growth factor delivery for bone and cartilage regeneration: (1) protection of protein growth factors from physical and enzymatic degradation, (2) targeted growth factor delivery, (3) controlling GF release kinetics, (4) long-term stability of regenerated tissues, and (5) osteoimmunomodulatory effects of therapeutic growth factors and carriers/scaffolds.

Sequential release of vascular endothelial growth factor-A and bone morphogenetic protein-2 from osteogenic scaffolds assembled by PLGA microcapsules: A preliminary study in vitro

Bone regeneration is a complex process sequentially regulated by multiple cytokines at different stages. Vascular endothelial growth factor-A (VEGF-A) and bone morphogenetic protein-2 (BMP-2) are the two most important factors involved in this process, and the combination of the two can achieve better bone regeneration by coupling angiogenesis and osteogenesis. In this study, poly(lactic-co-glycolic acid) (PLGA) microspheres with core-shell structure (microcapsules) encapsulating VEGF-A or BMP-2 were prepared by coaxial channel injection and continuous fluid technology. The sequential release of two cytokines by microcapsules with different PLGA molecular weight and shell thickness and its performance in vitro were explored. It was demonstrated that the molecular weight of PLGA significantly affected the degradation and release kinetics of microcapsules, while the thickness of the shell can regulate the release in a finer level. VEGF-A encapsulated microcapsules with low molecular weight can induce vascular endothelial cells to form lumens structures in vitro at an early stage. And BMP-2 encapsulated microcapsules could promote osteogenic differentiation, but the effect could be delayed when the microcapsules were prepared with PLGA of 150 kDa. In conclusion, the core-shell PLGA microcapsules in this study can sequentially release VEGF-A and BMP-2 at different stages to simulate natural bone repair.

Preparation and Synergistic Effect of Biomimetic Poly(lactic acid)/Graphene Oxide Composite Scaffolds Loaded with Dual Drugs

To promote the bone repair ability of drug-loaded scaffolds, poly(lactic acid) (PLA)/graphene oxide (GO)/Salvianolic acid B (Sal-B)/aspirin (ASA) dual drug-loaded biomimetic composite scaffolds were prepared. The results showed that the addition of these two drugs delayed the gel formation of the composite system, but a biomimetic nanofiber structure could still be obtained by extending the gel time. The addition of Sal-B increased the hydrophilicity of the scaffold, while an increase in ASA reduced the porosity. Dual drug-loaded scaffolds had good haemocompatibility and synergically promoted the proliferation of MC3T3-E1 cells and enhanced alkaline phosphatase activity. Sustained-release experiments of the two drugs showed that the presence of ASA slowed the cumulative release of Sal-B, while Sal-B promoted the release of ASA. Kinetic modeling showed that the release of both drugs conforms to the Korsmeyer-Peppas model, but Sal-B conforms to the Fick diffusion mechanism and ASA follows Fick diffusion and carrier swelling/dissolution.

Methods of Topical Administration of Drugs and Biological Active Substances for Dental Implants-A Narrative Review

Dental implants are, nowadays, established surgical devices for the restoration of lost teeth. Considered as an alternative for traditional prosthetic appliances, dental implants surpass them in reliability and patient feedback. Local drug delivery around the implants promotes osseointegration and reduces peri-implantitis. However, there are currently no methods of a multiple, precise topical administration of drugs to the implant area. Engineering coatings on the implants, drug application on carriers during implantation, or gingival pockets do not meet all requirements of dental surgeons. Therefore, there is a need to create porous implants and other medical devices that will allow a multiple drug delivery at a controlled dose and release profile without traumatic treatment. Due to the growing demand for the use of biologically active agents to support dental implant treatment at its various stages (implant placement, long-term use of dental superstructures, treatment of the peri-implant conditions) and due to the proven effectiveness of the topical application of pharmacological biologically active agents to the implant area, the authors would like to present a review and show the methods and devices that can be used by clinicians for local drug administration to facilitate dental implant treatment. Our review concludes that there is a need for research in the field of inventions such as new medical devices or implants with gradient solid-porous structures. These devices, in the future, will enable to perform repeatable, controllable, atraumatic, and repeatable injections of active factors that may affect the improvement of osteointegration and the longer survival of implants, as well as the treatment of peri-implantitis.

ELISA- and Activity Assay-Based Quantification of BMP-2 Released In Vitro Can Be Biased by Solubility in "Physiological" Buffers and an Interfering Effect of Chitosan

Chitosan nanogel-coated polycaprolactone (PCL) fiber mat-based implant prototypes with tailored release of bone morphogenic protein 2 (BMP-2) are a promising approach to achieve implant-mediated bone regeneration. In order to ensure reliable in vitro release results, the robustness of a commercially available ELISA for E. coli-derived BMP-2 and the parallel determination of BMP-2 recovery using a quantitative biological activity assay were investigated within a common release setup, with special reference to solubility and matrix effects. Without bovine serum albumin and Tween 20 as solubilizing additives to release media buffed at physiological pH, BMP-2 recoveries after release were notably reduced. In contrast, the addition of chitosan to release samples caused an excessive recovery. A possible explanation for these effects is the reversible aggregation tendency of BMP-2, which might be influenced by an interaction with chitosan. The interfering effects highlighted in this study are of great importance for bio-assay-based BMP-2 quantification, especially in the context of pharmaceutical release experiments.

New Insight into the Mechanism of Drug Release from Poly(d,l-lactide) Film by Electron Paramagnetic Resonance

A novel approach based on convolution of the electron paramagnetic resonance (EPR) spectra was used for quantitative study of the release kinetics of paramagnetic dopants from poly(d,l-lactide) films. A non-monotonic dependence of the release rate on time was reliably recorded. The release regularities were compared with the dynamics of polymer structure changes determined by EPR, SEM, and optic microscopy. The data obtained allow for the conclusion that the main factor governing dopant release is the formation of pores connected with the surface. In contrast, the contribution of the dopant diffusion through the polymer matrix is negligible. The dopant release can be divided into two phases: release through surface pores, which are partially closed with time, and release through pores initially formed inside the polymer matrix due to autocatalytic hydrolysis of the polymer and gradually connected to the surface of the sample. For some time, these processes co-occur. The mathematical model of the release kinetics based on pore formation is presented, describing the kinetics of release of various dopants from the polymer films of different thicknesses.

In vitro characterization of osteoblast cells on polyelectrolyte multilayers containing detonation nanodiamonds

Nanoparticle-enhanced coatings of bone implants are a promising method to facilitate sustainable wound healing, leading to an increase in patient well-being. This article describes the in vitro characterization of osteoblast cells interacting with polyelectrolyte multilayers, which contain detonation nanodiamonds (NDs), as a novel class of carbon-based coating material, which presents a unique combination of photoluminescence and drug-binding properties. The cationic polyelectrolyte, namely polydiallyldimethylammonium chloride (PDDA), has been used to immobilize NDs on silica glass. The height of ND-PDDA multilayers varies from a minimum of 10 nm for one bilayer to a maximum of 90 nm for five bilayers of NDs and PDDA. Human fetal osteoblasts (hFOBs) cultured on ND-PDDA multilayers show a large number of focal adhesions, which were studied via quantitative fluorescence imaging analysis. The influence of the surface roughness on the filopodia formation was assessed via scanning electron microscopy and atomic force microscopy. The nano-rough surface of five bilayers constrained the filopodia formation. The hFOBs grown on NDs tend to show not only a similar cell morphology compared to cells cultured on extracellular matrix protein-coated silica glass substrates, but also increased cell viability by about 40%. The high biocompatibility of the ND-PDDA multilayers, indicated via high cell proliferation and sound cell adhesion, shows their potential for biomedical applications such as drug-eluting coatings and biomaterials in general.

Antimicrobial Prosthetic Surfaces in the Oral Cavity-A Perspective on Creative Approaches

Replacement of missing teeth is an essential component of comprehensive dental care for patients suffering of edentulism. A popular option is implant-supported restorations. However, implant surfaces can become colonized with polymicrobial biofilms containing Candida species that may compromise peri-implant health. To prevent this, implant components may be treated with a variety of coatings to create surfaces that either repel the attachment of viable microorganisms or kill microorganisms on contact. These coatings may consist of nanoparticles of pure elements (more commonly silver, copper, and zinc), sanitizing agents and disinfectants (quaternary ammonium ions and chlorhexidine), antibiotics (cefalotin, vancomycin, and gentamicin), or antimicrobial peptides (AMPs). AMPs in bioactive coatings have a number of advantages. They elicit a protective action against pathogens, inhibit the formation of biofilms, are less toxic to host tissues, and do not prompt inflammatory responses. Furthermore, many of these coatings may involve unique delivery systems to direct their antimicrobial capacity against pathogens, but not commensals. Coatings may also contain multiple antimicrobial substances to widen antimicrobial activity across multiple microbial species. Here, we compiled relevant information about a variety of creative approaches used to generate antimicrobial prosthetic surfaces in the oral cavity with the purpose of facilitating implant integration and peri-implant tissue health.

Varying the sustained release of BMP-2 from chitosan nanogel-functionalized polycaprolactone fiber mats by different polycaprolactone surface modifications

Polycaprolactone (PCL) fiber mats with different surface modifications were functionalized with a chitosan nanogel coating to attach the growth factor human bone morphogenetic protein 2 (BMP-2). Three different hydrophilic surface modifications were compared with regard to the binding and in vitro release of BMP-2. The type of surface modification and the specific surface area derived from the fiber thickness had an important influence on the degree of protein loading. Coating the PCL fibers with polydopamine resulted in the binding of the largest BMP-2 quantity per surface area. However, most of the binding was irreversible over the investigated period of time, causing a low release in vitro. PCL fiber mats with a chitosan-graft-PCL coating and an additional alginate layer, as well as PCL fiber mats with an air plasma surface modification boundless BMP-2, but the immobilized protein could almost completely be released. With polydopamine and plasma modifications as well as with unmodified PCL, high amounts of BMP-2 could also be attached directly to the surface. Integration of BMP-2 into the chitosan nanogel functionalization considerably increased binding on all hydrophilized surfaces and resulted in a sustained release with an initial burst release of BMP-2 without detectable loss of bioactivity in vitro.

Burst Release of Antibiotics Combined with Long-Term Release of Silver Targeting Implant-Associated Infections: Design, Characterization and in vitro Evaluation of Novel Implant Hybrid Surface

Implant-associated infections represent a serious risk in human medicine and can lead to complications, revisions and in worst cases, amputations. To target these risks, the objective was to design a hybrid implant surface that allows a local burst release of antibiotics combined with long-term antimicrobial activity based on silver. The efficacy should be generated with simultaneous in vitro cytocompatibility. The investigations were performed on titanium K-wires and plates and gentamicin was selected as an illustrative antibiotic. A gentamicin depot (max 553 µg/cm2) was created on the surface using laser structuring. The antibiotic was released within 15 min in phosphate buffered saline (PBS) or agar medium. Metallic silver particles (4 µg/cm2) in a titanium dioxide layer were deposited using plasma vapor deposition (PVD). About 16% of the silver was released within 28 days in the agar medium. The local efficacy of the incorporated silver was demonstrated in a direct contact assay with a reduction of more than 99.99% (Escherichia coli). The local efficacy of the hybrid surface was confirmed in a zone of inhibition (ZOI) assay using Staphylococcus cohnii. The biocompatibility of the hybrid surface was proven using fibroblasts and osteoblasts as cell systems. The hybrid surface design seems to be promising as treatment of implant-associated infections, considering the achieved amount and release behavior of the active ingredients (gentamicin, silver). The generated in vitro results (efficacy, biocompatibility) proofed the concept. Further in vivo studies will be necessary translate the hybrid surface towards clinical applied research.

Is NO the Answer? The Nitric Oxide Pathway Can Support Bone Morphogenetic Protein 2 Mediated Signaling

The growth factor bone morphogenetic protein 2 (BMP2) plays an important role in bone development and repair. Despite the positive effects of BMP2 in fracture healing, its use is associated with negative side effects and poor cost effectiveness, partly due to the large amounts of BMP2 applied. Therefore, reduction of BMP2 amounts while maintaining efficacy is of clinical importance. As nitric oxide (NO) signaling plays a role in bone fracture healing and an association with the BMP2 pathway has been indicated, this study aimed to investigate the relationship of BMP2 and NO pathways and whether NO can enhance BMP2-induced signaling and osteogenic abilities in vitro. To achieve this, the stable BMP reporter cell line C2C12BRELuc was used to quantify BMP signaling, and alkaline phosphatase (ALP) activity and gene expression were used to quantify osteogenic potency. C2C12BRELuc cells were treated with recombinant BMP2 in combination with NO donors and substrate (Deta NONOate, SNAP & L-Arginine), NOS inhibitor (LNAME), soluble guanylyl cyclase (sGC) inhibitor (LY83583) and activator (YC-1), BMP type-I receptor inhibitor (LDN-193189), or protein kinase A (PKA) inhibitor (H89). It was found that the NOS enzyme, direct NO application, and sGC enhanced BMP2 signaling and improved BMP2 induced osteogenic activity. The application of a PKA inhibitor demonstrated that BMP2 signaling is enhanced by the NO pathway via PKA, underlining the capability of BMP2 in activating the NO pathway. Collectively, this study proves the ability of the NO pathway to enhance BMP2 signaling.

Scaffold-mediated sequential drug/gene delivery to promote nerve regeneration and remyelination following traumatic nerve injuries

Neural tissue regeneration following traumatic injuries is often subpar. As a result, the field of neural tissue engineering has evolved to find therapeutic interventions and has seen promising outcomes. However, robust nerve and myelin regeneration remain elusive. One possible reason may be the fact that tissue regeneration often follows a complex sequence of events in a temporally-controlled manner. Although several other fields of tissue engineering have begun to recognise the importance of delivering two or more biomolecules sequentially for more complete tissue regeneration, such serial delivery of biomolecules in neural tissue engineering remains limited. This review aims to highlight the need for sequential delivery to enhance nerve regeneration and remyelination after traumatic injuries in the central nervous system, using spinal cord injuries as an example. In addition, possible methods to attain temporally-controlled drug/gene delivery are also discussed for effective neural tissue regeneration.

Surface Immobilization of TiO2 Nanotubes with Bone Morphogenetic Protein-2 Synergistically Enhances Initial Preosteoblast Adhesion and Osseointegration

Although titanium (Ti) alloys have been widely used as implant materials, the bioinertness of pristine Ti impairs their bioactivity and early osseointegration. In the present work, we prepared TiO₂ nanotubes (TNT) layer on the titanium (Ti) surface by anodic oxidation. The anodized surface was functionalized with human bone morphogenetic protein-2 coating to form the hBMP-2/TNT surface. The release behavior of hBMP-2 on the hBMP-2/TNT surface displayed a controlled and sustained pattern, compared to that on the hBMP-2/Ti surface, which showed a rapid release. In vitro cellular activity tests demonstrated that both TNT and hBMP-2/Ti surfaces, particularly the hBMP-2/TNT surface, enhanced adhesion, proliferation, and differentiation of osteoblast cells. Increased cell adhesion, improved cytoskeleton organization, and immunofluorescence staining of vinculin were observed on the modified surfaces. The TNT, hBMP-2/Ti, and hBMP-2/TNT surfaces, especially the hBMP-2/TNT surface, further displayed an upregulated gene expression of adhesion and osteogenic markers vinculin, collagen type 1, osteopontin, and osteocalcin, compared to the pristine Ti surface. In vivo experiments using a rat model demonstrated that the TNT and hBMP-2/Ti surfaces, in particular the hBMP-2/TNT surface, improved osseointegration and showed a superior bone bonding ability compared to Ti. Our study revealed a synergistic role played by TiO₂ nanotubes nanotopography and hBMP-2 in promoting initial osteoblast adhesion, proliferation, differentiation, and osseointegration, thus suggesting a promising method for better modifying the implant surface.

Healing in peri-implant gap with BMP-2 and systemic bisphosphonate is dependent on BMP-2 dose-A canine study

The bone-implant interface of cementless orthopedic implants can be described as a series of uneven sized gaps with discontinuous areas of direct bone-implant contact. Bridging these voids and crevices by addition of an anabolic stimulus to increase new bone formation can potentially improve osseointegration of implants. Bone morphogenetic protein 2 (BMP-2) stimulates osteoblast formation to increase new bone formation but also indirectly stimulates osteoclast activity. In this experiment, we investigate the hypothesis that osseointegration, defined as mechanical push-out and histomorphometry, depends on the dose of BMP-2 when delivered as an anabolic agent with systemic administration of the anti-resorptive agent zoledronate to curb an increase in osteoclast activity. Four porous coated titanium implants (one with each of three doses of surface-applied BMP-2 (15 µg; 60 µg; 240 µg) and untreated) surrounded by a 0.75 mm empty gap, were inserted into the distal femurs of each of twelve canines. Zoledronate IV (0.1 mg/kg) was administered 10 days into the observation period of 4 weeks. Bone-implant specimens were evaluated by mechanical push-out test and histomorphometry. The 15 µg implants had the best fixation on all mechanical parameters and largest surface area covered with new bone compared to the untreated, 60 and 240 µg implants, as well as the highest volume of new bone in the implant gap compared to 60 and 240 µg implants. The results in a canine implant model demonstrated that a narrow range of BMP-2 doses have opposite effects in bridging an empty peri-implant gap with bone, when combined with systemic zoledronate. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1406-1414, 2018.

Dose-Dependent Resorption of Allograft by rhBMP-2 Uncompensated by New Bone Formation-A Canine Study With Implants and Zoledronate

BACKGROUND

Impacted bone allograft is used to restore lost bone in total joint arthroplasties. Bone morphogenetic proteins (BMPs) can induce new bone formation to improve allograft incorporation, but they simultaneously invoke a seemingly dose-dependent allograft resorption mediated by osteoclasts. Bisphosphonates effectively inhibit osteoclast activity. Predicting allograft resorption when augmented with bone morphogenetic protein 2 (BMP-2), we intended to investigate whether a balanced bone metabolism was achievable within a range of BMP-2 doses with systemic zoledronate treatment.

METHODS

Implants were coated with 1 of 3 BMP-2 doses (15 μg, 60 μg, and 240 μg) or left untreated. Implants were surrounded by a 2.5-mm gap filled with impacted morselized allograft. Each of the 12 dogs included received 1 of each implant (15 μg, 60 μg, 240 μg, and untreated), 2 in each proximal humerus. During the 4-week observation period, zoledronate intravenous (0.1 mg/kg) was administered to all animals 10 days after surgery as anticatabolic treatment. Implant osseointegration was evaluated by histomorphometry and mechanical push-out tests.

RESULTS

Untreated implants had the best mechanical fixation and superior retention of allograft as compared to any of the BMP-2 implants. Both mechanical implant fixation and retention of allograft decreased significantly with BMP-2 dose increments. Surprisingly, there was no difference among the treatment groups in the amount of new bone.

CONCLUSION

The use of BMP-2 to augment impaction-grafted implants cannot be recommended even when combined with systemic zoledronate.

The effect of two different crosslinkers on in vitro characteristics of ciprofloxacin-loaded chitosan implants

The objective of this study was to determine and evaluate a controlled release implant of ciprofloxacin using bovine hydroxyapatite (BHA)-chitosan composite and glutaraldehyde or genipin as crosslinking agents. Ciprofloxacin implants were prepared using BHA, chitosan, ciprofloxacin at 30:60:10 and using three different concentrations of glutaraldehyde or genipin (0.3, 0.5, or 0.7%) as crosslinkers. Implants were formed as mini-tablet with 4.0 mm diameter weighing 100 mg using compression method. Further, the prepared ciprofloxacin implants were characterized for porosity, density, water absorption capacity, swelling, degradation, compressive strength, compatibility (Fourier transforms-infrared spectroscopy (FT-IR)), morphology (scanning electron microscope (SEM)), X-ray diffraction (X-RD), and in vitro drug release. The addition of glutaraldehyde or genipin as crosslinkers in ciprofloxacin implant showed controlled release profile of ciprofloxacin over a time period of 30 days. SEM photomicrograph revealed low porosity of the implant after crosslinking with glutaraldehyde or genipin. The FTIR study confirmed the formation of covalent imine bonds between chitosan and glutaraldehyde. Moreover, the addition of glutaraldehyde or genipin as crosslinkers caused a decrease in the mechanical strength of the implant. Increased concentration of glutaraldehyde or genipin reduced the crystallinity of BHA and chitosan, which were confirmed by X-RD studies. The results obtained from this study indicated that glutaraldehyde or genipin had the potential effect to retard ciprofloxacin release from BHA-chitosan-ciprofloxacin implant for 30 days.

Biomaterials for Craniofacial Bone Regeneration

Functional reconstruction of craniofacial defects is a major clinical challenge in craniofacial sciences. The advent of biomaterials is a potential alternative to standard autologous/allogenic grafting procedures to achieve clinically successful bone regeneration. This article discusses various classes of biomaterials currently used in craniofacial reconstruction. Also reviewed are clinical applications of biomaterials as delivery agents for sustained release of stem cells, genes, and growth factors. Recent promising advancements in 3D printing and bioprinting techniques that seem to be promising for future clinical treatments for craniofacial reconstruction are covered. Relevant topics in the bone regeneration literature exemplifying the potential of biomaterials to repair bone defects are highlighted.

Drug release from core-shell PVA/silk fibroin nanoparticles fabricated by one-step electrospraying

Silk fibroin (SF), a FDA-approved natural protein, is renowned for its great biocompatibility, biodegradability, and mechanical properties. SF-based nanoparticles provide new options for drug delivery with their tunable drug loading and release properties. To take advantage of the features of carrier polymers, we present a one-step electrospraying method that combines SF, polyvinyl alcohol (PVA) and therapeutic drugs without an emulsion process. A distinct core-shell structure was obtained with the PVA core and silk shell after the system was properly set up. The model drug, doxorubicin, was encapsulated in the core with a greater than 90% drug encapsulation efficiency. Controllable drug release profiles were achieved by alternating the PVA/SF ratio. Although the initial burst release of the drug was minimized by the SF coating, a large number of drug molecules remained entrapped by the carrier polymers. To promote and trigger drug release on demand, low intensity focused ultrasound (US) was applied. The US was especially advantageous for accelerating the drug diffusion and release. The apoptotic activity of MDA-MB-231 cells incubated with drug-loaded nanoparticles was found to increase with time. In addition, we also observed PVA/SF nanoparticles that could elicit a drug release in response to pH.

A short artificial antimicrobial peptide shows potential to prevent or treat bone infections

Infection of bone is a severe complication due to the variety of bacteria causing it, their resistance against classical antibiotics, the formation of a biofilm and the difficulty to eradicate it. Antimicrobial peptides (AMPs) are naturally occurring peptides and promising candidates for treatment of joint infections. This study aimed to analyze the effect of short artificial peptides derived from an optimized library regarding (1) antimicrobial effect on different bacterial species, (2) efficacy on biofilms, and (3) effect on osteoblast‑like cells. Culturing the AMP-modifications with Escherichia coli, Enterococcus faecalis, Pseudomonas aeruginosa, Staphylococcus aureus (including clinical isolates of MRSA and MSSA) and Staphylococcus epidermidis identified one candidate that was most effective against all bacteria. This AMP was also able to reduce biofilm as demonstrated by FISH and microcalorimetry. Osteoblast viability and differentiation were not negatively affected by the AMP. A cation concentration comparable to that physiologically occurring in blood had almost no negative effect on AMP activity and even with 10% serum bacterial growth was inhibited. Bacteria internalized into osteoblasts were reduced by the AMP. Taken together the results demonstrate a high antimicrobial activity of the AMP even against bacteria incorporated in a biofilm or internalized into cells without harming human osteoblasts.

A systems biology approach to studying the molecular mechanisms of osteoblastic differentiation under cytokine combination treatment

Recent studies revealed that sequential release of bone morphogenetic protein 2 and insulin-like growth factor 1 plays an important role in osteogenic process, suggesting that cytokines bone morphogenetic protein 2 and insulin-like growth factor 1 function in a time-dependent manner. However, the specific molecular mechanisms underlying these observations remained elusive, impeding the elaborate manipulation of cytokine sequential delivery in tissue repair. The aim of this study was to identify the key relevant pathways and processes regulating bone morphogenetic protein 2/insulin-like growth factor 1-mediated osteoblastic differentiation. Based on the microarray and proteomics data, and differentiation/growth status of mouse bone marrow stromal cells, we constructed a multiscale systems model to simulate the bone marrow stromal cells lineage commitment and bone morphogenetic protein 2 and insulin-like growth factor 1-regulated signaling dynamics. The accuracy of our model was validated using a set of independent experimental data. Our study reveals that, treatment of bone marrow stromal cells with bone morphogenetic protein 2 prior to insulin-like growth factor 1 led to the activation of transcription factor Runx2 through TAK1-p38 MAPK and SMAD1/5 signaling pathways and initiated the lineage commitment of bone marrow stromal cells. Delivery of insulin-like growth factor 1 four days after bone morphogenetic protein 2 treatment optimally activated transcription factors osterix and β-catenin through ERK and AKT pathways, which are critical to preosteoblast maturity. Our systems biology approach is expected to provide technical and scientific support in optimizing therapeutic scheme to improve osteogenesis/bone regeneration and other essential biological processes.

Transparent TiO2 nanotubes on zirconia for biomedical applications

Depositing anodised titanium on ZrO₂ substrate improves the bioactivity of the ZrO₂ substrate in terms of enhanced cell viability, cell attachment and cell elongation.

Strategies for delivering bone morphogenetic protein for bone healing

Bone morphogenetic proteins (BMPs) are the most significant growth factors that belong to the Transforming Growth Factor Beta (TGF-β) super-family. Though more than twenty members of this family have been identified so far in humans, Food and Drug Administration (FDA) approved two growth factors: BMP-2 and BMP-7 for treatments of spinal fusion and long-bone fractures with collagen carriers. Currently BMPs are clinically used in spinal fusion, oral and maxillofacial surgery and also in the repair of long bone defects. The efficiency of BMPs depends a lot on the selection of suitable carriers. At present, different types of carrier materials are used: natural and synthetic polymers, calcium phosphate and ceramic-polymer composite materials. Number of research articles has been published on the minute intricacies of the loading process and release kinetics of BMPs. Despite the significant evidence of its potential for bone healing demonstrated in animal models, future clinical investigations are needed to define dose, scaffold and route of administration. The efficacy and application of BMPs in various levels with a proper carrier and dose is yet to be established. The present article collates various aspects of success and limitation and identifies the prospects and challenges associated with the use of BMPs in orthopaedic surgery.

Extracellular Matrix (ECM) Multilayer Membrane as a Sustained Releasing Growth Factor Delivery System for rhTGF-β3 in Articular Cartilage Repair

Recombinant human transforming growth factor beta-3 (rhTGF-β₃) is a key regulator of chondrogenesis in stem cells and cartilage formation. We have developed a novel drug delivery system that continuously releases rhTGF-β₃ using a multilayered extracellular matrix (ECM) membrane. We hypothesize that the sustained release of rhTGF-β₃ could activate stem cells and result in enhanced repair of cartilage defects. The properties and efficacy of the ECM multilayer-based delivery system (EMLDS) are investigated using rhTGF-β₃ as a candidate drug. The bioactivity of the released rhTGF-ß3 was evaluated through chondrogenic differentiation of mesenchymal stem cells (MSCs) using western blot and circular dichroism (CD) analyses in vitro. The cartilage reparability was evaluated through implanting EMLDS with endogenous and exogenous MSC in both in vivo and ex vivo models, respectively. In the results, the sustained release of rhTGF-ß3 was clearly observed over a prolonged period of time in vitro and the released rhTGF-β₃ maintained its structural stability and biological activity. Successful cartilage repair was also demonstrated when rabbit MSCs were treated with rhTGF-β3-loaded EMLDS ((+) rhTGF-β3 EMLDS) in an in vivo model and when rabbit chondrocytes and MSCs were treated in ex vivo models. Therefore, the multilayer ECM membrane could be a useful drug delivery system for cartilage repair.

Biomaterials with Antibacterial and Osteoinductive Properties to Repair Infected Bone Defects

The repair of infected bone defects is still challenging in the fields of orthopedics, oral implantology and maxillofacial surgery. In these cases, the self-healing capacity of bone tissue can be significantly compromised by the large size of bone defects and the potential/active bacterial activity. Infected bone defects are conventionally treated by a systemic/local administration of antibiotics to control infection and a subsequent implantation of bone grafts, such as autografts and allografts. However, these treatment options are time-consuming and usually yield less optimal efficacy. To approach these problems, novel biomaterials with both antibacterial and osteoinductive properties have been developed. The antibacterial property can be conferred by antibiotics and other novel antibacterial biomaterials, such as silver nanoparticles. Bone morphogenetic proteins are used to functionalize the biomaterials with a potent osteoinductive property. By manipulating the carrying modes and release kinetics, these biomaterials are optimized to maximize their antibacterial and osteoinductive functions with minimized cytotoxicity. The findings, in the past decade, have shown a very promising application potential of the novel biomaterials with the dual functions in treating infected bone defects. In this review, we will summarize the current knowledge of novel biomaterials with both antibacterial and osteoinductive properties.

Influence of implant properties and local delivery systems on the outcome in operative fracture care

Fracture fixation devices are implanted into a growing number of patients each year. This may be attributed to an increase in the popularity of operative fracture care and the development of ever more sophisticated implants, which may be used in even the most difficult clinical cases. Furthermore, as the general population ages, fragility fractures become more frequent. With the increase in number of surgical interventions, the absolute number of complications of these surgical treatments will inevitably rise. Implant-related infection and compromised fracture healing remain the most challenging and prevalent complications in operative fracture care. Any strategy that can help to reduce these complications will not only lead to a faster and more complete resumption of activities, but will also help to reduce the socio-economic impact. In this review we describe the influence of implant design and material choice on complication rates in trauma patients. Furthermore, we discuss the importance of local delivery systems, such as implant coatings and bone cement, and how these systems may have an impact on the prevalence, prevention and treatment outcome of these complications.

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.

Importance of dual delivery systems for bone tissue engineering

Bone formation is a complex process that requires concerted function of multiple growth factors. For this, it is essential to design a delivery system with the ability to load multiple growth factors in order to mimic the natural microenvironment for bone tissue formation. However, the short half-lives of growth factors, their relatively large size, slow tissue penetration, and high toxicity suggest that conventional routes of administration are unlikely to be effective. Therefore, it seems that using multiple bioactive factors in different delivery systems can develop new strategies for improving bone tissue regeneration. Combination of these factors along with biomaterials that permit tunable release profiles would help to achieve truly spatiotemporal regulation during delivery. This review summarizes the various dual-control release systems that are used for bone tissue engineering.

BMPs in bone regeneration: Less is more effective, a paradigm-shift

Worldwide, the clinical application of BMP2 (bone morphogenetic protein 2) has helped an increasing number of patients achieve bone regeneration in a clinical area lacking simple solutions for difficult bone healing situations. In this review, the historical aspects and current critical clinical issues are summarized and positioned against new research findings on efficacy and function of BMP2. Knowledge concerning how the dose of this growth factor as well as its interaction with mechanical loading influences the efficacy of bone regeneration, might open possible future strategies in cases where bony bridging is unachievable so far. In conclusion, it is apparent that there is a substantial need for continued basic research to unravel the details of its function and the underlying signaling pathways involved, to make BMP2 even more relevant and safe in daily clinical use, even though this growth factor has been known for more than 125 years.

Microparticle entrapment for drug release from porous-surfaced bone implants

Metallic bone implants face interfacial concerns, such as infection and insufficient bone formation. Combination of drug-loaded microparticles with the implant surface is a promising approach to reducing the concerns. The present study reports a simple method for this purpose. Drug-loaded chitosan and alginate microparticles were separately prepared by emulsion methods. Dry microparticles were introduced into porous titanium (Ti) coatings on Ti discs, and induced to agglomerate in pores by wetting with water. Agglomerates were stably entrapped in the pores: 77-82% retained in the coating after immersion in a water bath for 7 d. Discs carrying drug-loaded microparticles showed a rapid release within 6 h and a subsequent slow release up to 1 d. After coculture with Staphylococcus epidermidis for 24 h, the discs formed inhibition zones, confirming antibacterial properties. These suggest that the microparticle entrapment-based method is a promising method for reducing some of the bone-implant interfacial concerns.

Antibacterial activity of chitosan nanofiber meshes with liposomes immobilized releasing gentamicin

Chitsan (Ch) nanofiber mesh (NFM) is a material with natural characteristics favoring its use in human wound dressing. The present work proposes a gentamicin-loaded liposome immobilized at the surface of Ch NFMs to promote its antibacterial activity. To achieve this purpose, Ch NFMs were functionalized with thiol groups, and gentamicin-loaded liposomes were covalently immobilized by the reaction of the SH groups with maleimide. The maximum concentration of SH groups (55.52±11.19nmolcm(-2)) was obtained at pH 7. A fluorescent dye was covalently bound to the SH groups present at the surface of electrospun Ch NFMs. Their spatial distribution was uniform throughout the NFMs when analyzed by fluorescence microscopy. Gentamicin was successfully encapsulated into the liposomes with an efficiency of 17%. Gentamicin-loaded liposomes were uniformly distributed at the surface of the Ch NFMs and the drug release kinetic showed a sustained release of gentamicin during 16h, achieving a steady state at 24h. The in vitro susceptibility tests confirmed that the gentamicin released from the liposomes immobilized at the surface of electrospun Ch NFM has bactericidal activity against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus. The results show that the developed system has promising performance for wound dressing applications, avoiding infections caused by these common pathogens.

Longitudinal analysis of osteogenic and angiogenic signaling factors in healing models mimicking atrophic and hypertrophic non-unions in rats

Impaired bone healing can have devastating consequences for the patient. Clinically relevant animal models are necessary to understand the pathology of impaired bone healing. In this study, two impaired healing models, a hypertrophic and an atrophic non-union, were compared to physiological bone healing in rats. The aim was to provide detailed information about differences in gene expression, vascularization and histology during the healing process. The change from a closed fracture (healing control group) to an open osteotomy (hypertrophy group) led to prolonged healing with reduced mineralized bridging after 42 days. RT-PCR data revealed higher gene expression of most tested osteogenic and angiogenic factors in the hypertrophy group at day 14. After 42 days a significant reduction of gene expression was seen for Bmp4 and Bambi in this group. The inhibition of angiogenesis by Fumagillin (atrophy group) decreased the formation of new blood vessels and led to a non-healing situation with diminished chondrogenesis. RT-PCR results showed an attempt towards overcoming the early perturbance by significant up regulation of the angiogenic regulators Vegfa, Angiopoietin 2 and Fgf1 at day 7 and a further continuous increase of Fgf1, -2 and Angiopoietin 2 over time. However µCT angiograms showed incomplete recovery after 42 days. Furthermore, lower expression values were detected for the Bmps at day 14 and 21. The Bmp antagonists Dan and Twsg1 tended to be higher expressed in the atrophy group at day 42. In conclusion, the investigated animal models are suitable models to mimic human fracture healing complications and can be used for longitudinal studies. Analyzing osteogenic and angiogenic signaling patterns, clear changes in expression were identified between these three healing models, revealing the importance of a coordinated interplay of different factors to allow successful bone healing.

Biomimetic approaches in bone tissue engineering: Integrating biological and physicomechanical strategies

The development of responsive biomaterials capable of demonstrating modulated function in response to dynamic physiological and mechanical changes in vivo remains an important challenge in bone tissue engineering. To achieve long-term repair and good clinical outcomes, biologically responsive approaches that focus on repair and reconstitution of tissue structure and function through drug release, receptor recognition, environmental responsiveness and tuned biodegradability are required. Traditional orthopedic materials lack biomimicry, and mismatches in tissue morphology, or chemical and mechanical properties ultimately accelerate device failure. Multiple stimuli have been proposed as principal contributors or mediators of cell activity and bone tissue formation, including physical (substrate topography, stiffness, shear stress and electrical forces) and biochemical factors (growth factors, genes or proteins). However, optimal solutions to bone regeneration remain elusive. This review will focus on biological and physicomechanical considerations currently being explored in bone tissue engineering.

How does the pathophysiological context influence delivery of bone growth factors?

"Orthobiologics" represents an important category of therapeutics for the regeneration of bone defects caused by injuries or diseases, and bone growth factors are a particularly rapidly growing sub-category. Clinical application of bone growth factors has accelerated in the last two decades with the introduction of BMPs into clinical bone repair. Optimal use of growth factor-mediated treatments heavily relies on controlled delivery, which can substantially influence the local growth factor dose, release kinetics, and biological activity. The characteristics of the surrounding environment, or "context", during delivery can dictate growth factor loading efficiency, release and biological activity. This review discusses the influence of the surrounding environment on therapeutic delivery of bone growth factors. We specifically focus on pathophysiological components, including soluble components and cells, and how they can actively influence the therapeutic delivery and perhaps efficacy of bone growth factors.

BMP-functionalised coatings to promote osteogenesis for orthopaedic implants

The loss of bone integrity can significantly compromise the aesthetics and mobility of patients and can be treated using orthopaedic implants. Over the past decades; various orthopaedic implants; such as allografts; xenografts and synthetic materials; have been developed and widely used in clinical practice. However; most of these materials lack intrinsic osteoinductivity and thus cannot induce bone formation. Consequently; osteoinductive functionalisation of orthopaedic implants is needed to promote local osteogenesis and implant osteointegration. For this purpose; bone morphogenetic protein (BMP)-functionalised coatings have proven to be a simple and effective strategy. In this review; we summarise the current knowledge and recent advances regardingBMP-functionalised coatings for orthopaedic implants.

Composite chitosan and calcium sulfate scaffold for dual delivery of vancomycin and recombinant human bone morphogenetic protein-2

A biodegradable, composite bone graft, composed of chitosan microspheres embedded in calcium sulfate, was evaluated in vitro for point-of-care loading and delivery of antibiotics and growth factors to prevent infection and stimulate healing in large bone injuries. Microspheres were loaded with rhBMP-2 or vancomycin prior to mixing into calcium sulfate loaded with vancomycin. Composites were evaluated for set time, drug release kinetics, and bacteriostatic/bactericidal activity of released vancomycin, induction of ALP expression by released rhBMP-2, and interaction of drugs on cells. Results showed the composite set in under 36 min and released vancomycin levels that were bactericidal to S. aureus (>MIC 8-16 μg/mL) for 18 days. Composites exhibited a 1 day-delayed release, followed by a continuous release of rhBMP-2 over 6 weeks; ranging from 0.06 to 1.49 ng/mL, and showed a dose dependent release based on initial loading. Released rhBMP-2 levels were, however, too low to induce detectable levels of ALP in W20-17 cells, due to the affinity of rhBMP-2 for calcium-based materials. With stimulating amounts of rhBMP-2 (>50 ng/mL), the ALP response from W-20-17 cells was inhibited when exposed to high vancomycin levels (1,800-3,600 μg/mL). This dual-delivery system is an attractive alternative to single delivery or preloaded systems for bone regeneration since it can simultaneously fight infection and deliver a potent growth factor. Additionally, this composite can accommodate a wide range of therapeutics and thus be customizable for specific patient needs, however, the potential interactive effects of multiple agents must be investigated to ensure that functional activity is not altered.

Stimulation of bone healing by sustained bone morphogenetic protein 2 (BMP-2) delivery

The aim of the study was to investigate the effect of a sustained release of bone morphogenetic protein2 (BMP-2) incorporated in a polymeric implant coating on bone healing. In vitro analysis revealed a sustained, but incomplete BMP-2 release until Day 42. For the in vivo study, the rat tibia osteotomy was stabilized either with control or BMP-2 coated wires, and the healing progress was followed by micro computed tomography (μCT), biomechanical testing and histology at Days 10, 28, 42 and 84. MicroCT showed an accelerated formation of mineralized callus, as well as remodeling and an increase of mineralized/total callus volume (p = 0.021) at Day 42 in the BMP-2 group compared to the control. Histology revealed an increased callus mineralization at Days 42 and 84 (p = 0.006) with reduced cartilage at Day 84 (p = 0.004) in the BMP-2 group. Biomechanical stiffness was significantly higher in the BMP-2 group (p = 0.045) at Day 42. In summary, bone healing was enhanced after sustained BMP-2 application compared to the control. Using the same drug delivery system, but a burst release of BMP-2, a previous published study showed a similar positive effect on bone healing. Distinct differences in the healing outcome might be explained due to the different BMP release kinetics and dosages. However, further studies are necessary to adapt the optimal release profiles to physiological mechanisms.

Prevention of infection in external fixator pin sites

Infection in external fixator pins is known to be a significant problem, with incidences between 3% and 80% reported in the literature. An infection occurs when planktonic bacteria adhere to external fixator pins and subsequently produce a biofilm which protects the bacteria from host defences. The most commonly implicated organisms are Staphylococcus aureus and Staphylococcus epidermidis. Once an infection occurs, treatment is difficult. Systemic antibiotics have limited benefits and considerable side-effects. The only definitive management is removal of the pin. This review will consider the current and potential future strategies for reducing pin site infection. Techniques to prevent infection must prevent bacterial adhesion, allow good osteointegration and have a low toxicity. Current areas of interest reviewed are titanium-copper alloys, nanosilver coatings, nitric oxide coatings, chitosan coatings, chlorhexidine and iodine, hydroxyapatite and antibiotic coatings. At present there is no consensus on the prevention of pin site infection, and there is a paucity of randomized controlled trials on which to draw a conclusion. Whilst a number of these strategies have potential future use, many of the above strategies need further studies in animal models to ensure no cytotoxicity and prevention of osteointegration. Following this, well-designed randomized controlled clinical trials are required to give future ways to prevent external fixator pin site infections.

Recent developments of functional scaffolds for craniomaxillofacial bone tissue engineering applications

Autogenous bone grafting remains a gold standard for the reconstruction critical-sized bone defects in the craniomaxillofacial region. Nevertheless, this graft procedure has several disadvantages such as restricted availability, donor-site morbidity, and limitations in regard to fully restoring the complicated three-dimensional structures in the craniomaxillofacial bone. The ultimate goal of craniomaxillofacial bone reconstruction is the regeneration of the physiological bone that simultaneously fulfills both morphological and functional restorations. Developments of tissue engineering in the last two decades have brought such a goal closer to reality. In bone tissue engineering, the scaffolds are fundamental, elemental and mesenchymal stem cells/osteoprogenitor cells and bioactive factors. A variety of scaffolds have been developed and used as spacemakers, biodegradable bone substitutes for transplanting to the new bone, matrices of drug delivery system, or supporting structures enhancing adhesion, proliferation, and matrix production of seeded cells according to the circumstances of the bone defects. However, scaffolds to be clinically completely satisfied have not been developed yet. Development of more functional scaffolds is required to be applied widely to cranio-maxillofacial bone defects. This paper reviews recent trends of scaffolds for crania-maxillofacial bone tissue engineering, including our studies.