Osteogenic and antimicrobial nanoparticulate calcium phosphate and poly-(D,L-lactide-co-glycolide) powders for the treatment of osteomyelitis

Targeted Clindamycin Delivery Systems: Promising Options for Preventing and Treating Bacterial Infections Using Biomaterials

Targeted therapy represents a real opportunity to improve the health and lives of patients. Developments in this field are confirmed by the fact that the global market for drug carriers was worth nearly $40 million in 2022. For this reason, materials engineering and the development of new drug carrier compositions for targeted therapy has become a key area of research in pharmaceutical drug delivery in recent years. Ceramics, polymers, and metals, as well as composites, are of great interest, as when they are appropriately processed or combined with each other, it is possible to obtain biomaterials for hard tissues, soft tissues, and skin applications. After appropriate modification, these materials can release the drug directly at the site requiring a therapeutic effect. This brief literature review characterizes routes of drug delivery into the body and discusses biomaterials from different groups, options for their modification with clindamycin, an antibiotic used for infections caused by aerobic and anaerobic Gram-positive bacteria, and different methods for the final processing of carriers. Examples of coating materials for skin wound healing, acne therapy, and bone tissue fillers are given. Furthermore, the reasons why the use of antibiotic therapy is crucial for a smooth and successful recovery and the risks of bacterial infections are explained. It was demonstrated that there is no single proven delivery scheme, and that the drug can be successfully released from different carriers depending on the destination.

Calcium Phosphate Delivery Systems for Regeneration and Biomineralization of Mineralized Tissues of the Craniofacial Complex

Calcium phosphate (CaP)-based materials have been extensively used for mineralized tissues in the craniofacial complex. Owing to their excellent biocompatibility, biodegradability, and inherent osteoconductive nature, their use as delivery systems for drugs and bioactive factors has several advantages. Of the three mineralized tissues in the craniofacial complex (bone, dentin, and enamel), only bone and dentin have some regenerative properties that can diminish due to disease and severe injuries. Therefore, targeting these regenerative tissues with CaP delivery systems carrying relevant drugs, morphogenic factors, and ions is imperative to improve tissue health in the mineralized tissue engineering field. In this review, the use of CaP-based microparticles, nanoparticles, and polymer-induced liquid precursor (PILPs) amorphous CaP nanodroplets for delivery to craniofacial bone and dentin are discussed. The use of these various form factors to obtain either a high local concentration of cargo at the macroscale and/or to deliver cargos precisely to nanoscale structures is also described. Finally, perspectives on the field using these CaP materials and next steps for the future delivery to the craniofacial complex are presented.

Polymeric Nanotechnologies for the Treatment of Periodontitis: A Chronological Review

Periodontitis is a chronic infectious and inflammatory disease of periodontal tissues estimated to affect 70 - 80 % of all adults. At the same time, periodontium, the site of periodontal pathologies, is an extraordinarily complex plexus of soft and hard tissues, the regeneration of which using even the most advanced forms of tissue engineering continues to be a challenge. Nanotechnologies, meanwhile, have provided exquisite tools for producing biomaterials and pharmaceutical formulations capable of elevating the efficacies of standard pharmacotherapies and surgical approaches to whole new levels. A bibliographic analysis provided here demonstrates a continuously increasing research output of studies on the use of nanotechnologies in the management of periodontal disease, even when they are normalized to the total output of studies on periodontitis. The great majority of biomaterials used to tackle periodontitis, including those that pioneered this interesting field, have been polymeric. In this article, a chronological review of polymeric nanotechnologies for the treatment of periodontitis is provided, focusing on the major conceptual innovations since the late 1990s, when the first nanostructures for the treatment of periodontal diseases were fabricated. In the opening sections, the etiology and pathogenesis of periodontitis and the anatomical and histological characteristics of the periodontium are being described, along with the general clinical manifestations of the disease and the standard means of its therapy. The most prospective chemistries in the design of polymers for these applications are also elaborated. It is concluded that the amount of innovation in this field is on the rise, despite the fact that most studies are focused on the refinement of already established paradigms in tissue engineering rather than on the development of revolutionary new concepts.

When Nothing Turns Itself Inside out and Becomes Something: Coating Poly (Lactic-Co-Glycolic Acid) Spheres with Hydroxyapatite Nanoparticles vs. the Other Way Around

To stabilize drugs physisorbed on the surface of hydroxyapatite (HAp) nanoparticles and prevent burst release, these nanoparticles are commonly coated with polymers. Bioactive HAp, however, becomes shielded from the surface of such core/shell entities, which partially defeats the purpose of using it. The goal of this study was to assess the biological and pharmacokinetic effects of inverting this classical core/shell structure by coating poly(lactic-co-glycolic acid) (PLGA) spheres with HAp nanoparticles. The HAp shell did not hinder the release of vancomycin; rather, it increased the release rate to a minor degree, compared to that from undecorated PLGA spheres. The decoration of PLGA spheres with HAp induced lesser mineral deposition and lesser upregulation of osteogenic markers compared to those induced by the composite particles where HAp nanoparticles were embedded inside the PLGA spheres. This was explained by homeostatic mechanisms governing the cell metabolism, which ensure than the sensation of a product of this metabolism in the cell interior or exterior is met with the reduction in the metabolic activity. The antagonistic relationship between proliferation and bone production was demonstrated by the higher proliferation rate of cells challenged with HAp-coated PLGA spheres than of those treated with PLGA-coated HAp. It is concluded that the overwhelmingly positive response of tissues to HAp-coated biomaterials for bone replacement is unlikely to be due to the direct induction of new bone growth in osteoblasts adhering to the HAp coating. Rather, these positive effects are consequential to more elementary aspects of cell attachment, mechanotransduction, and growth at the site of contact between the HAp-coated material and the tissue.

Osteomyelitis: Focus on Conventional Treatments and Innovative Drug Delivery Systems

Osteomyelitis is a bone marrow infection which generally involves cortical plates and which may occur after bone trauma, orthopedic/maxillofacial surgery or after vascular insufficiency episodes. It mostly affects people from the Third World Countries, the elderly and patients affected by systemic diseases e.g. autoimmune disorders, AIDS, osteoporosis and microvascular disease. The highest percentage of osteomyelitis cases (almost 75%) is caused by Staphylococcus spp., and in particular by Staphylococcus aureus (more than 50%). The ideal classification and the diagnosis of osteomyelitis are two important tools which help the physicians to choose the best therapeutic strategies. Currently, common therapies provide an extensive debridement in association with intravenous administration of antibiotics (penicillin or clindamycin, vancomycin and fluoroquinolones among all for resistant microorganisms), to avoid the formation of sequestra. However, conventional therapeutic approach involves several drawbacks like low concentration of antibiotics in the infected site, leading to resistance and adverse effects due to the intravenous administration. For these reasons, in the last years several studies have been focused on the development of drug delivery systems such as cements, beads, scaffolds and ceramics made of hydroxyapatite (HA), calcium phosphate (CaP) and β-tricalcium phosphate (β-TCP) which demonstrated to be biocompatible, poorly toxic and capable to allow osteointegration and a prolonged drug release. The aim of this review is to provide a focus on current therapies and latest developed drug delivery systems with particular attention on those based on CaP and its derivatives, hoping that this work could allow further direction in the field of osteomyelitis.

Bone Diseases: Current Approach and Future Perspectives in Drug Delivery Systems for Bone Targeted Therapeutics

Bone diseases include a wide group of skeletal-related disorders that cause mobility limitations and mortality. In some cases, e.g., in osteosarcoma (OS) and metastatic bone cancer, current treatments are not fully effective, mainly due to low patient compliance and to adverse side effects. To overcome these drawbacks, nanotechnology is currently under study as a potential strategy allowing specific drug release kinetics and enhancing bone regeneration. Polymers, ceramics, semiconductors, metals, and self-assembled molecular complexes are some of the most used nanoscale materials, although in most cases their surface properties need to be tuned by chemical or physical reactions. Among all, scaffolds, nanoparticles (NPs), cements, and hydrogels exhibit more advantages than drawbacks when compared to other nanosystems and are therefore the object of several studies. The aim of this review is to provide information about the current therapies of different bone diseases focusing the attention on new discoveries in the field of targeted delivery systems. The authors hope that this paper could help to pursue further directions about bone targeted nanosystems and their application for bone diseases and bone regeneration.

Multifunctional Coatings and Nanotopographies: Toward Cell Instructive and Antibacterial Implants

In biomaterials science, it is nowadays well accepted that improving the biointegration of dental and orthopedic implants with surrounding tissues is a major goal. However, implant surfaces that support osteointegration may also favor colonization of bacterial cells. Infection of biomaterials and subsequent biofilm formation can have devastating effects and reduce patient quality of life, representing an emerging concern in healthcare. Conversely, efforts toward inhibiting bacterial colonization may impair biomaterial-tissue integration. Therefore, to improve the long-term success of medical implants, biomaterial surfaces should ideally discourage the attachment of bacteria without affecting eukaryotic cell functions. However, most current strategies seldom investigate a combined goal. This work reviews recent strategies of surface modification to simultaneously address implant biointegration while mitigating bacterial infections. To this end, two emerging solutions are considered, multifunctional chemical coatings and nanotopographical features.

Calcium Phosphate Nanoparticles as Intrinsic Inorganic Antimicrobials: The Antibacterial Effect

Cheap and simple to make, calcium phosphate (CP), thanks to its unusual functional pleiotropy, belongs to the new wave of abundant and naturally accessible nanomaterials applicable as a means to various technological ends. It is used in a number of industries, including the biomedical, but its intrinsic antibacterial activity in the nanoparticle form has not been sufficiently explored to date. In this study, we report on this intrinsic antibacterial effect exhibited by two distinct CP phases: an amorphous CP (ACP) and hydroxyapatite (HAp). The effect is prominent against a number of regular bacterial species, including Staphylococcus aureus, Staphylococcus epidermis, Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa, but also their multidrug-resistant (MDR) analogues. Although ACP and HAp displayed similar levels of activity against Gram-negative organisms, ACP proved to be more effective against the Gram-positive ones, with respect to which HAp was mostly inert, yet this trend became reversed for the MDR strains. In addition to the intrinsic antimicrobial effect of CP nanoparticles, we have also observed a synergistic effect between the nanoparticles and certain antibiotics. Both forms of CP were engaged in a synergistic relationship with a variety of concomitantly delivered antibiotics, including ampicillin, kanamycin, oxacillin, vancomycin, minocycline, erythromycin, linezolid, and clindamycin, and enabled even antibiotics completely ineffective against particular bacterial strains to significantly suppress their growth. This relationship was complex; depending on a particular CP phase, bacterial strain and antibiotic, the antibacterial activity (i) intensified proportionally to the nanoparticle concentration, (ii) plateaued immediately after the introduction of nanoparticles in minute amounts, or (iii) exhibited concentration-dependent minima due to stress-induced biofilm formation. These findings present grounds for the further optimization of CP properties and maximization of this intriguing effect, which could in the long run make this material comparable in activity to the inorganics of choice for this application, including silver, copper, or zinc oxide, while retaining its superb safety profile and positive eukaryotic versus prokaryotic cell selectivity.

Bone biomaterials and interactions with stem cells

Bone biomaterials play a vital role in bone repair by providing the necessary substrate for cell adhesion, proliferation, and differentiation and by modulating cell activity and function. In past decades, extensive efforts have been devoted to developing bone biomaterials with a focus on the following issues: (1) developing ideal biomaterials with a combination of suitable biological and mechanical properties; (2) constructing a cell microenvironment with pores ranging in size from nanoscale to submicro- and microscale; and (3) inducing the oriented differentiation of stem cells for artificial-to-biological transformation. Here we present a comprehensive review of the state of the art of bone biomaterials and their interactions with stem cells. Typical bone biomaterials that have been developed, including bioactive ceramics, biodegradable polymers, and biodegradable metals, are reviewed, with an emphasis on their characteristics and applications. The necessary porous structure of bone biomaterials for the cell microenvironment is discussed, along with the corresponding fabrication methods. Additionally, the promising seed stem cells for bone repair are summarized, and their interaction mechanisms with bone biomaterials are discussed in detail. Special attention has been paid to the signaling pathways involved in the focal adhesion and osteogenic differentiation of stem cells on bone biomaterials. Finally, achievements regarding bone biomaterials are summarized, and future research directions are proposed.

Nanomedicine for safe healing of bone trauma: Opportunities and challenges

Historically, high-energy extremity injuries resulting in significant soft-tissue trauma and bone loss were often deemed unsalvageable and treated with primary amputation. With improved soft-tissue coverage and nerve repair techniques, these injuries now present new challenges in limb-salvage surgery. High-energy extremity trauma is pre-disposed to delayed or unpredictable bony healing and high rates of infection, depending on the integrity of the soft-tissue envelope. Furthermore, orthopedic trauma surgeons are often faced with the challenge of stabilizing and repairing large bony defects while promoting an optimal environment to prevent infection and aid bony healing. During the last decade, nanomedicine has demonstrated substantial potential in addressing the two major issues intrinsic to orthopedic traumas (i.e., high infection risk and low bony reconstruction) through combatting bacterial infection and accelerating/increasing the effectiveness of the bone-healing process. This review presents an overview and discusses recent challenges and opportunities to address major orthopedic trauma through nanomedical approaches.

Population Effects of Calcium Phosphate Nanoparticles in Drosophila melanogaster: The Effects of Phase Composition, Crystallinity, and the Pathway of Formation

Unpredictable biological response due to the finest nanostructural variations is one of the hallmarks of nanoparticles. Because of this erratic behavior of nanoparticles in living systems, thorough analyses of biosafety must precede the analyses of the pharmacotherapeutic efficacy and simple animal models are ideal for such purposes. Drosophila melanogaster, the common fruit fly, is an animal model capable of giving a fast, high-throughput response as to the safety and efficacy of drug delivery carriers and other pharmacological agents, while minimizing the suffering imposed onto animals in more complex in vivo models. Here we studied the effects on the viability and fertility of D. melanogaster due to variations in phase composition, crystallinity, and the pathway of formation of four different calcium phosphate (CP) nanopowders consumed orally. To minimize the effect of other nanostructural variables, CP nanopowders were made to possess highly similar particle sizes and morphologies. The composition of CP affected the fecundity of flies, but so did crystallinity and the pathway of formation. Both the total number of eclosed viable flies and pupae in populations challenged with hydroxyapatite (HAP) greatly exceeded those in control populations. Viability was adversely affected by the only pyrophosphate tested (CPP) and by the metastable and the most active of all CP nanopowders analyzed: the amorphous CP (ACP). The pupation peak was delayed and the viable fly to-pupa ratio increased in all the CP-challenged populations. F1 CPP population, whose viability was most adversely affected by the CP consumption, when crossed, produced the largest number of F2 progeny under regular conditions, possibly pointing to stress as a positive evolutionary drive. The positive effect of HAP on fertility of fruit flies may be due to its slow absorption and the activation of calmodulin during the transit of oocytes through the reproductive tract of fertilized females. Exerted in the prepupation stage, the effect of CP is thus traceable beyond the instar larval stage and to the oogenesis stage of the Drosophila lifecycle.

An injectable hydroxyapatite/poly(lactide-co-glycolide) composite reinforced by micro/nano-hybrid poly(glycolide) fibers for bone repair

Porous nanocomposite of hydroxyapatite/poly(lactide-co-glycolide) (HA/PLGA) is conventionally used in bone tissue engineering but seldom in load-bearing orthopedic applications due to poor mechanical property. This study aimed to fabricate an injectable ternary composite by incorporating different contents of poly(glycolide) (PGA) fibers (0, 30, 50 and 70wt%) into the nanocomposite HA/PLGA matrix as reinforcing fillers for bone tissue repair. The fibers were obtained from melt-spinning and fiber diameter ranged from 70nm to 191μm. The injectability, mechanical strength, solidification rate and cytotoxicity of injectable composites were characterized. All composites achieved the acceptable injectability under an injection force of 100N. The mechanical properties of composites were gradually enhanced by increasing PGA fiber contents. The compression strength of composite with 70wt% content of PGA fibers was up to 31.1MPa, which was four times stronger than that of composite without PGA fibers. In the solidification rate analysis, the compression strength of composites with 50 or 70wt% PGA fibers in immersion time of only 45min was similar to that of composite without fibers in immersion time of 4-5h. The MTT test showed that exceeding 70% cells could survive in the fourfold dilution of extract, and its cytotoxicity focused on the first 4h after immersing. This study have revealed that the PGA fiber-reinforced HA/PLGA composite is a promising candidate for orthopedic applications.

Sustainable Release of Vancomycin from Silk Fibroin Nanoparticles for Treating Severe Bone Infection in Rat Tibia Osteomyelitis Model

The successful treatment of bone infections is a major challenge in the field of orthopedics. There are some common methods for treating bone infections, including systemic antibiotic administration, local nondegradable drug vehicles, and surgical debridement, and each of these approaches has advantages and disadvantages. In the present study, the antibiotic vancomycin (VANCO) was loaded in silk fibroin nanoparticles (SFNPs) and the complexes were then entrapped in silk scaffolds to form sustained drug delivery systems. The release kinetics of VANCO from SFNPs alone and when the SFNPs were entrapped in silk scaffolds were assessed at two different pH values, 4.5 and 7.4, that affected the release profiles of VANCO. Disk diffusion tests performed with pathogens causing osteomyelitis methicillin-resistant Staphylococcus aureus (MRSA) showed antibacterial activity of the released drug at two different pH values. Additionally, injection of 8 × 10⁶ CFU MRSA in rat's tibia induced severe osteomyelitis disease. Radiographic and histopathological analyses were performed to evaluate the effectiveness of treatment after 6 weeks. The VANCO-loaded silk fibroin nanoparticles entrapped in scaffolds reduced bone infections at the defected site with better outcomes than the other treatment groups. In conclusion, the delivery system with good biocompatibility and sustained release properties would be appropriate for further study in the context of osteomyelitis disease.

Is there a relationship between solubility and resorbability of different calcium phosphate phases in vitro?

BACKGROUND

Does chemistry govern biology or it is the other way around - that is a broad connotation of the question that this study attempted to answer.

METHOD

Comparison was made between the solubility and osteoclastic resorbability of four fundamentally different monophasic calcium phosphate (CP) powders with monodisperse particle size distributions: alkaline hydroxyapatite (HAP), acidic monetite (DCP), β-calcium pyrophosphate (CPP), and amorphous CP (ACP). Results With the exception of CPP, the difference in solubility between different CP phases became neither mitigated nor reversed, but augmented in the resorptive osteoclastic milieu. Thus, DCP, a phase with the highest solubility, was also resorbed more intensely than any other CP phase, whereas HAP, a phase with the lowest solubility, was resorbed least. CPP becomes retained inside the cells for the longest period of time, indicating hindered digestion of only this particular type of CP. Osteoclastogenesis was mildly hindered in the presence of HAP, ACP and DCP, but not in the presence of CPP. The most viable CP powder with respect to the mitochondrial succinic dehydrogenase activity was the one present in natural biological bone tissues: HAP.

CONCLUSION

Chemistry in this case does have a direct effect on biology. Biology neither overrides nor reverses the chemical propensities of inorganics with which it interacts, but rather augments and takes a direct advantage of them.

SIGNIFICANCE

These findings set the fundamental basis for designing the chemical makeup of CP and other biosoluble components of tissue engineering constructs for their most optimal resorption and tissue regeneration response.

Multifunctional coatings to simultaneously promote osseointegration and prevent infection of orthopaedic implants

The two leading causes of failure for joint arthroplasty prostheses are aseptic loosening and periprosthetic joint infection. With the number of primary and revision joint replacement surgeries on the rise, strategies to mitigate these failure modes have become increasingly important. Much of the recent work in this field has focused on the design of coatings either to prevent infection while ignoring bone mineralization or vice versa, to promote osseointegration while ignoring microbial susceptibility. However, both coating functions are required to achieve long-term success of the implant; therefore, these two modalities must be evaluated in parallel during the development of new orthopaedic coating strategies. In this review, we discuss recent progress and future directions for the design of multifunctional orthopaedic coatings that can inhibit microbial cells while still promoting osseointegration.

Mesenchymal stem cell proliferation and mineralization but not osteogenic differentiation are strongly affected by extracellular pH

Osteomyelitis is a serious complication in oral and maxillofacial surgery affecting bone healing. Bone remodeling is not only controlled by cellular components but also by ionic and molecular composition of the extracellular fluids in which calcium phosphate salts are precipitated in a pH dependent manner.

OBJECTIVE

To determine the effect of pH on self-renewal, osteogenic differentiation and matrix mineralization of mesenchymal stem cells (MSCs).

METHODS

We selected three different pH values; acidic (6.3, 6.7), physiological (7.0-8.0) and severe alkaline (8.5). MSCs were cultured at different pH ranges, cell viability measured by WST-1, apoptosis detected by JC-1, senescence was analyzed by β-galactosidase whereas mineralization was detected by Alizarin Red and osteogenic differentiation analyzed by Real-time PCR.

RESULTS

Self-renewal was affected by pH as well as matrix mineralization in which pH other than physiologic inhibited the deposition of extracellular matrix but did not affect MSCs differentiation as osteoblast markers were upregulated. The expression of osteocalcin and alkaline phosphatase activity was upregulated whereas osteopontin was downregulated under acidic pH.

CONCLUSION

pH affected MSCs self-renewal and mineralization without influencing osteogenic differentiation. Thus, future therapies, based on shifting acid-base balance toward the alkaline direction might be beneficial for prevention or treatment of osteomyelitis.

Organic Nanomaterials and Their Applications in the Treatment of Oral Diseases

There is a growing interest in the development of organic nanomaterials for biomedical applications. An increasing number of studies focus on the uses of nanomaterials with organic structure for regeneration of bone, cartilage, skin or dental tissues. Solid evidence has been found for several advantages of using natural or synthetic organic nanostructures in a wide variety of dental fields, from implantology, endodontics, and periodontics, to regenerative dentistry and wound healing. Most of the research is concentrated on nanoforms of chitosan, silk fibroin, synthetic polymers or their combinations, but new nanocomposites are constantly being developed. The present work reviews in detail current research on organic nanoparticles and their potential applications in the dental field.

Synthesis, Properties, and In Vitro Hydrolytic Degradation of Poly(d,l-lactide-co-glycolide-co-ε-caprolactone)

Random copolymers of poly(d,l-lactide-co-glycolide-co-ε-caprolactone) (PLGC) were synthesized by the ring-opening polymerization of d,l-lactide (DLLA), glycolide (GA), andε-caprolactone (CL). The effects of CL on the copolymers were evaluated to prepare suitable copolymers with controlled properties. Our results showed that the CL content significantly influenced the thermal and mechanical properties of the copolymers and that the CL content in compositions could be altered to control properties of random copolymers. The in vitro hydrolytic degradation of the resulting implants showed that the degradation rate of PLGC was lower than that of PLGA, which could markedly reduce acidic degradation products. Finally, we demonstrated that higher CL contents in compositions slowed degradation rates.

When 1+1>2: Nanostructured composites for hard tissue engineering applications

Multicomponent, synergistic and multifunctional nanostructures have taken over the spotlight in the realm of biomedical nanotechnologies. The most prospective materials for bone regeneration today are almost exclusively composites comprising two or more components that compensate for the shortcomings of each one of them alone. This is quite natural in view of the fact that all hard tissues in the human body, except perhaps the tooth enamel, are composite nanostructures. This review article highlights some of the most prospective breakthroughs made in this research direction, with the hard tissues in main focus being those comprising bone, tooth cementum, dentin and enamel. The major obstacles to creating collagen/apatite composites modeled after the structure of bone are mentioned, including the immunogenicity of xenogeneic collagen and continuously failing attempts to replicate the biomineralization process in vitro. Composites comprising a polymeric component and calcium phosphate are discussed in light of their ability to emulate the soft/hard composite structure of bone. Hard tissue engineering composites created using hard material components other than calcium phosphates, including silica, metals and several types of nanotubes, are also discoursed on, alongside additional components deliverable using these materials, such as cells, growth factors, peptides, antibiotics, antiresorptive and anabolic agents, pharmacokinetic conjugates and various cell-specific targeting moieties. It is concluded that a variety of hard tissue structures in the body necessitates a similar variety of biomaterials for their regeneration. The ongoing development of nanocomposites for bone restoration will result in smart, theranostic materials, capable of acting therapeutically in direct feedback with the outcome of in situ disease monitoring at the cellular and subcellular scales. Progress in this research direction is expected to take us to the next generation of biomaterials, designed with the purpose of fulfilling Daedalus' dream - not restoring the tissues, but rather augmenting them.

Chitosan-PLGA polymer blends as coatings for hydroxyapatite nanoparticles and their effect on antimicrobial properties, osteoconductivity and regeneration of osseous tissues

Composite biomaterials comprising nanostructured hydroxyapatite (HAp) have an enormous potential for natural bone tissue reparation, filling and augmentation. Chitosan (Ch) as a naturally derived polymer has many physicochemical and biological properties that make it an attractive material for use in bone tissue engineering. On the other hand, poly-D,L-lactide-co-glycolide (PLGA) is a synthetic polymer with a long history of use in sustained drug delivery and tissue engineering. However, while chitosan can disrupt the cell membrane integrity and may induce blood thrombosis, PLGA releases acidic byproducts that may cause tissue inflammation and interfere with the healing process. One of the strategies to improve the biocompatibility of Ch and PLGA is to combine them with compounds that exhibit complementary properties. In this study we present the synthesis and characterization, as well as in vitro and in vivo analyses of a nanoparticulate form of HAp coated with two different polymeric systems: (a) Ch and (b) a Ch-PLGA polymer blend. Solvent/non-solvent precipitation and freeze-drying were used for synthesis and processing, respectively, whereas thermogravimetry coupled with mass spectrometry was used for phase identification purposes in the coating process. HAp/Ch composite particles exhibited the highest antimicrobial activity against all four microbial strains tested in this work, but after the reconstruction of the bone defect they also caused inflammatory reactions in the newly formed tissue where the defect had lain. Coating HAp with a polymeric blend composed of Ch and PLGA led to a decrease in the reactivity and antimicrobial activity of the composite particles, but also to an increase in the quality of the newly formed bone tissue in the reconstructed defect area.

Nanoparticulate platforms for targeting bone infections: meeting a major therapeutic challenge

Bone infections are devastating complications in orthopedics due to biofilm formation. Treatment requires high antibiotic doses, which may lead to systemic toxicity thus limiting the drug therapeutic effectiveness. In this context, nanoparticles are well-known controlled release drug carriers that are able to modulate release rate, versatile in terms of administration routes and may be used as local delivery systems. Regarding bone infections, although nanoparticles are a promising strategy for overcoming biofilm tolerance, there are clearly technical, safety, regulatory and clinical challenges that need to be overcome before such nanomedicines may be translated into clinical use. In this paper, we present a critical overview on the high expectations against the real potential of the nanotechnological approaches to bone infection treatment.

Effects of fluoridation of porcine hydroxyapatite on osteoblastic activity of human MG63 cells

Biological hydroxyapatite, derived from animal bones, is the most widely used bone substitute in orthopedic and dental treatments. Fluorine is the trace element involved in bone remodeling and has been confirmed to promote osteogenesis when administered at the appropriate dose. To take advantage of this knowledge, fluorinated porcine hydroxyapatite (FPHA) incorporating increasing levels of fluoride was derived from cancellous porcine bone through straightforward chemical and thermal treatments. Physiochemical characteristics, including crystalline phases, functional groups and dissolution behavior, were investigated on this novel FPHA. Human osteoblast-like MG63 cells were cultured on the FPHA to examine cell attachment, cytoskeleton, proliferation and osteoblastic differentiation for in vitro cellular evaluation. Results suggest that fluoride ions released from the FPHA play a significant role in stimulating osteoblastic activity in vitro, and appropriate level of fluoridation (1.5 to 3.1 atomic percents of fluorine) for the FPHA could be selected with high potential for use as a bone substitute.

Design and development of intraocular polymeric implant systems for long-term controlled-release of clindamycin phosphate for toxoplasmic retinochoroiditis

BACKGROUND

The release of the anti-toxoplasmosis drug, clindamycin phosphate, from intraocular implants of the biodegradable polymers poly (D, L-lactic acid) (PLA) and poly (D, L-lactide-co-glycolide) (PLGA) has been studied in vitro.

MATERIALS AND METHODS

The preparation of the implants was performed by a melt-extrusion method. The developed extrudates were characterized and compared in in-vitro release profiles for elucidating the drug release mechanism. The formulations containing up to 40% w/w of drug were prepared. Release data in phosphate buffer (pH 7.4) were analyzed by high performance liquid chromatography. The release kinetics were fitted to the zero-order, Higuchi's square-root, first order and the Korsmeyer-Peppas empirical equations for the estimation of various parameters of the drug release curves. Degradation of implants was also investigated morphologically with time (Scanning Electron Microscopy).

RESULTS

It was observed that, the release profiles for the formulations exhibit a typical biphasic profile for bulk-eroding systems, characterized by a first phase of burst release (in first 24 hrs), followed by a phase of slower release. The duration of the secondary phase was found to be proportional to the molecular weight and monomer ratio of copolymers and also polymer-to-drug ratios. It was confirmed that Higuchi and first-order kinetics were the predominant release mechanisms than zero order kinetic. The Korsmeyer-Peppas exponent (n) ranged between 0.10 and 0.96. This value, confirmed fickian as the dominant mechanism for PLA formulations (n ≤ 0.45) and the anomalous mechanism, for PLGAs (0.45 < n < 0.90).

CONCLUSION

The implant of PLA (I.V. 0.2) containing 20% w/w of clindamycin, was identified as the optimum formulation in providing continuous efficient in-vitro release of clindamycin for about 5 weeks.

Nanostructured platforms for the sustained and local delivery of antibiotics in the treatment of osteomyelitis

This article provides a critical view of the current state of the development of nanoparticulate and other solid-state carriers for the local delivery of antibiotics in the treatment of osteomyelitis. Mentioned are the downsides of traditional means for treating bone infection, which involve systemic administration of antibiotics and surgical debridement, along with the rather imperfect local delivery options currently available in the clinic. Envisaged are more sophisticated carriers for the local and sustained delivery of antimicrobials, including bioresorbable polymeric, collagenous, liquid crystalline, and bioglass- and nanotube-based carriers, as well as those composed of calcium phosphate, the mineral component of bone and teeth. A special emphasis is placed on composite multifunctional antibiotic carriers of a nanoparticulate nature and on their ability to induce osteogenesis of hard tissues demineralized due to disease. An ideal carrier of this type would prevent the long-term, repetitive, and systemic administration of antibiotics and either minimize or completely eliminate the need for surgical debridement of necrotic tissue. Potential problems faced by even hypothetically "perfect" antibiotic delivery vehicles are mentioned too, including (i) intracellular bacterial colonies involved in recurrent, chronic osteomyelitis; (ii) the need for mechanical and release properties to be adjusted to the area of surgical placement; (iii) different environments in which in vitro and in vivo testings are carried out; (iv) unpredictable synergies between drug delivery system components; and (v) experimental sensitivity issues entailing the increasing subtlety of the design of nanoplatforms for the controlled delivery of therapeutics.

Nanoparticulate drug delivery platforms for advancing bone infection therapies

INTRODUCTION

The ongoing surge of resistance of bacterial pathogens to antibiotic therapies and the consistently aging median member of the human race signal an impending increase in the incidence of chronic bone infection. Nanotechnological platforms for local and sustained delivery of therapeutics hold the greatest potential for providing minimally invasive and maximally regenerative therapies for this rare but persistent condition.

AREAS COVERED

Shortcomings of the clinically available treatment options, including poly(methyl methacrylate) beads and calcium sulfate cements, are discussed and their transcending using calcium-phosphate/polymeric nanoparticulate composites is foreseen. Bone is a composite wherein the weakness of each component alone is compensated for by the strength of its complement and an ideal bone substitute should be fundamentally the same.

EXPERT OPINION

Discrepancy between in vitro and in vivo bioactivity assessments is highlighted, alongside the inherent imperfectness of the former. Challenges entailing the cross-disciplinary nature of engineering a new generation of drug delivery vehicles are delineated and it is concluded that the future for the nanoparticulate therapeutic carriers belongs to multifunctional, synergistic and theranostic composites capable of simultaneously targeting, monitoring and treating internal organismic disturbances in a smart, feedback fashion and in direct response to the demands of the local environment.

Regenerative nanomedicine: current perspectives and future directions

Nanotechnology has considerably accelerated the growth of regenerative medicine in recent years. Application of nanotechnology in regenerative medicine has revolutionized the designing of grafts and scaffolds which has resulted in new grafts/scaffold systems having significantly enhanced cellular and tissue regenerative properties. Since the cell–cell and cell-matrix interaction in biological systems takes place at the nanoscale level, the application of nanotechnology gives an edge in modifying the cellular function and/or matrix function in a more desired way to mimic the native tissue/organ. In this review, we focus on the nanotechnology-based recent advances and trends in regenerative medicine and discussed under individual organ systems including bone, cartilage, nerve, skin, teeth, myocardium, liver and eye. Recent studies that are related to the design of various types of nanostructured scaffolds and incorporation of nanomaterials into the matrices are reported. We have also documented reports where these materials and matrices have been compared for their better biocompatibility and efficacy in supporting the damaged tissue. In addition to the recent developments, future directions and possible challenges in translating the findings from bench to bedside are outlined.

Simultaneous bactericidal and osteogenic effect of nanoparticulate calcium phosphate powders loaded with clindamycin on osteoblasts infected with Staphylococcus aureus

Staphylococcus aureus internalized by bone cells and shielded from the immune system provides a reservoir of bacteria in recurring osteomyelitis. Its targeting by the antibiotic therapy may thus be more relevant for treating chronic bone infection than eliminating only the pathogens colonizing the bone matrix. Assessed was the combined osteogenic and antibacterial effect of clindamycin-loaded calcium phosphate nanoparticles of different monophasic compositions on co-cultures comprising osteoblasts infected with S. aureus. Antibiotic-carrying particles were internalized by osteoblasts and minimized the concentration of intracellular bacteria. In vitro treatments of the infected cells, however, could not prevent cell necrosis due to the formation of toxic byproducts of the degradation of the bacterium. Antibiotic-loaded particles had a positive morphological effect on osteoblasts per se, without reducing their viability, alongside stimulating the upregulation of expression of different bone growth markers in infected osteoblasts to a higher degree than achieved during the treatment with antibiotic only.

In vitro analysis of nanoparticulate hydroxyapatite/chitosan composites as potential drug delivery platforms for the sustained release of antibiotics in the treatment of osteomyelitis

Nanoparticulate composites of hydroxyapatite (HAp) and chitosan were synthesized by ultrasound-assisted sequential precipitation and characterized for their microstructure at the atomic scale, surface charge, drug release properties, and combined antibacterial and osteogenic response. Crystallinity of HAp nanoparticles was reduced because of the interference of the surface layers of chitosan with the dissolution/reprecipitation-mediated recrystallization mechanism that conditions the transition from the as-precipitated amorphous calcium phosphate phase to the most thermodynamically stable one--HAp. Embedment of 5-10 nm sized, narrowly dispersed HAp nanoparticles within the polymeric matrix mitigated the burst release of the small molecule model drug, fluorescein, bound to HAp by physisorption, and promoted sustained-release kinetics throughout the 3 weeks of release time. The addition of chitosan to the particulate drug carrier formulation, however, reduced the antibacterial efficacy against S aureus. Excellent cell spreading and proliferation of osteoblastic MC3T3-E1 cells evidenced on microscopic conglomerates of HAp nanoparticles in vitro also markedly diminished on HAp/chitosan composites. Mitochondrial dehydrogenase activity exhibited normal values only for HAp/chitosan particle concentrations of up to 2 mg/cm(2) and significantly dropped, by about 50%, at higher particle concentrations (4 and 8 mg/cm(2)). The gene expression of osteocalcin, a mineralization inductor, and the transcription factor Runx2 was downregulated in cells incubated in the presence of 3 mg/cm(2) HAp/chitosan composite particles, whereas the expression of osteopontin, a potent mineralization inhibitor, was upregulated, further demonstrating the partially unfavorable osteoblastic cell response to the given particles. The peak in the expression of osteogenic markers paralleling the osteoblastic differentiation was also delayed most for the cell population incubated with HAp/chitosan particles. Overall, the positive effect of chitosan coating on the drug elution profile of HAp nanoparticles as carriers for the controlled delivery of antibiotics in the treatment of osteomyelitis was compensated for by the lower bacteriostatic efficiency and the comparatively unviable cell response to the composite material, especially at higher dosages.