Bioceramics: from bone regeneration to cancer nanomedicine

Mediating bone regeneration by means of drug eluting implants: From passive to smart strategies

In addition to excellent biocompatibility and mechanical performance, the new generation of bone and craniofacial implants are expected to proactively contribute to the regeneration process and dynamically interact with the host tissue. To this end, integration and sustained delivery of therapeutic agents has become a rapidly expanding area. The incorporated active molecules can offer supplementary features including promoting oteoconduction and angiogenesis, impeding bacterial infection and modulating host body reaction. Major limitations of the current practices consist of low drug stability overtime, poor control of release profile and kinetics as well as complexity of finding clinically appropriate drug dosage. In consideration of the multifaceted cascade of bone regeneration process, this research is moving towards dual/multiple drug delivery, where precise control on simultaneous or sequential delivery, considering the possible synergetic interaction of the incorporated bioactive factors is of utmost importance. Herein, recent advancements in fabrication of synthetic load bearing implants equipped with various drug delivery systems are reviewed. Smart drug delivery solutions, newly developed to provide higher tempo-spatial control on the delivery of the pharmaceutical agents for targeted and stimuli responsive delivery are highlighted. The future trend of implants with bone drug delivery mechanisms and the most common challenges hindering commercialization and the bench to bedside progress of the developed technologies are covered.

Bioactive glass-based materials with hierarchical porosity for medical applications: Review of recent advances

Bioactive glasses have been traditionally used in the clinical practice to fill and restore osseous defects due to their unique ability to bond to host bone and stimulate new bone growth. In the last decade, a new set of bioactive glasses characterized by a highly ordered mesoporous texture has been developed and studied as a smart platform for the controlled release of biomolecules, in situ therapy and regenerative applications. This review points out the great potential carried by hierarchical bioactive glass scaffolds that exhibit pore scales from the meso- to the macro-range, and their impact in the broad field of tissue engineering, including the emerging applications in contact with soft tissues and diagnostics. Recent advances in the preparation methods of these multiscale constructs (e.g. mono- or multi-phase scaffolds, fibrous meshes, coated systems, porous nanospheres, and composites) are examined, along with their strengths and weaknesses. A bright future is expected for hierarchical systems based on biocompatible mesoporous materials as they can provide a unique set of functionalities, including enhanced bioactivity, local release of ions and drugs to elicit specific therapeutic effects (improved osteogenesis and angiogenesis, antibacterial properties), and implant/drug tracking, which were unthinkable when research on bioactive glasses began.

STATEMENT OF SIGNIFICANCE

The advent of mesoporous bioactive glasses led to the birth of a new class of multifunctional biomaterials that have been proposed as smart platforms for local drug release and bone regeneration. Furthermore, mesoporous materials have been recently employed in the development of hierarchical macro-mesoporous scaffolds, composites and implantable systems. This reviews summarizes the latest applications of these multiscale biomaterials in tissue engineering, including the emerging applications in contact with soft tissues and diagnostics. The preparation methods, current uses and potential of these constructs and systems are examined and critically discussed to provide a useful, up-to-date contribution to the scientists working in the field.

Ultra-small mesoporous silica nanoparticles as efficient carriers for pH responsive releases of anti-cancer drugs

Mesoporous silica has emerged as one of the most promising carriers for drug delivery systems. However, the synthesis of ultra-small mesoporous silica nanoparticles (UMSNs) and their application in drug delivery remains a significant challenge. Here, spherical UMSNs (∼25 nm) have been synthesized and tested as drug carriers. Anti-cancer drugs mitoxantrone (MX), doxorubicin (DOX) and methotrexate (MTX) have been utilized as model drugs. The pH-responsive drug delivery system can be constructed based on electrostatic interactions between carriers and drug molecules. The UMSNs could store drugs under physiological conditions and release them under acidic conditions. Different pH-responsive release profiles were obtained in phosphate buffer solutions (PBSs) at the designed pH values (from 4.0 to 7.4). MX and DOX can be used in the pH-responsive delivery system, while MTX cannot be used. Furthermore, we found that the physiological stabilities of these drug molecules in UMSNs are in a decreasing order MX > DOX > MTX, which follows the order of their isoelectric point (pI) values.

Doxorubicin loaded large-pore mesoporous hydroxyapatite coated superparamagnetic Fe3O4 nanoparticles for cancer treatment

In the present study, a series of multifunctional drug delivery systems based on mesostructured hydroxyapatite coating and superparamagnetic nanoparticles with pH-responsive characters was prepared. The structure of each new synthesized nanoscale composite was fully characterized by XRD, FTIR, TEM, VSM and BET. The results showed a good ordered mesostructure having large pores, high pore volume, high surface area, and varied super paramagnetic properties. The mesoporous hydroxyapatite coated super paramagnetic Fe3O4 nanoparticles were applied as a drug delivery carrier loaded with doxorubicin (DOX) as a model drug. The storage/release properties of the developed nonocarriers in phosphate buffer saline (PBS) were studied in two certain pHs: pH=7.4 (the human blood pH) and pH=5.5 (pH of cancer cells). The large pores in the synthesized mesoporous acted as an excellent carrier for DOX molecules with a loading efficiency of ≈93% which is much higher than that of the conventional hydroxyapatite particles. When the pH of the release medium (PBS) was changed from 7.4 to 5.5, the drug release increased significantly from 10% of the adsorbed drug to about 70%. DOX-loaded mesostructure hydroxyapatite reduced the viability of SKBR3 and T47D cells by 54.7 and 57.3%, respectively, which were very similar to 56.8 and 60.4% reduction resulted from free DOX incubation. This new drug delivery system which benefits from both super paramagnetic properties and pH-responsive performances may serve as a suitable platform for developing new biocompatible drug carriers and could have a good potential use in targeted cancer therapy.

One-step method for the preparation of poly(methyl methacrylate) modified titanium-bioactive glass three-dimensional scaffolds for bone tissue engineering

A novel three-dimensional (3D) titanium (Ti)-doping meso-macroporous bioactive glasses (BGs)/poly(methyl methacrylate) (PMMA) composite was synthesised using PMMA and EO20PO70EO20 (P123) as the macroporous and mesoporous templates, respectively. Unlike the usual calcination method, the acid steam technique was used to improve the polycondensation of Ti-BGs, and then PMMA was partially extracted via chloroform to induce the macroporous structure. Simultaneously, the residual PMMA which remained in the wall enhanced the compressive strength to 2.4 MPa (0.3 MPa for pure BGs). It is a simple and green method to prepare the macro-mesoporous Ti-BGs/PMMA. The materials showed the 3D interconnected hierarchical structure (250 and 3.4 nm), making the fast inducing-hydroxyapatite growth and the controlled drug release. Besides mentioned above, the good antimicrobial property and biocompatible of the scaffold also ensure it is further of clinical use. Herein, the fabricated materials are expected to have potential application on bone tissue regeneration.

Bioinspired trimodal macro/micro/nano-porous scaffolds loading rhBMP-2 for complete regeneration of critical size bone defect

Critical size bone defects raise great demands for efficient bone substitutes. Mimicking the hierarchical porous architecture and specific biological cues of natural bone has been considered as an effective strategy to facilitate bone regeneration. Herein, a trimodal macro/micro/nano-porous scaffold loaded with recombinant human bone morphogenetic protein-2 (rhBMP-2) was developed. With mesoporous bioactive glass (MBG) as matrix, a trimodal MBG scaffold (TMS) with enhanced compressive strength (4.28 MPa, porosity of 80%) was prepared by a "viscosity controlling" and "homogeneous particle reinforcing" multi-template process. A 7.5 nm, 3D cubic (Im3m) mesoporous structure was tailored for a "size-matched entrapment" of rhBMP-2 to achieve sustained release and preserved bioactivity. RhBMP-2-loaded TMS (TMS/rhBMP-2) induced excellent cell attachment, ingrowth and osteogenesis in vitro. Further in vivo ectopic bone formation and orthotopic rabbit radius critical size defect results indicated that compared to the rhBMP-2-loaded bimodal macro/micro- and macro/nano-porous scaffolds, TMS/rhBMP-2 exhibited appealing bone regeneration capacity. Particularly, in critical size defect, complete bone reconstruction with rapid medullary cavity reunion and sclerotin maturity was observed on TMS/rhBMP-2. On the basis of these results, TMS/rhBMP-2 developed here represents a promising bone substitute for clinical application and the concepts proposed in this study might provide new thoughts on development of future orthopedic biomaterials.

STATEMENT OF SIGNIFICANCE

Limited self-regenerating capacity of human body makes the reconstruction of critical size bone defect a significant challenge. Current bone substitutes often exhibit undesirable therapeutic efficacy due to poor osteoconductivity or low osteoinductivity. Herein, TMS/rhBMP-2, an advanced mesoporous bioactive glass (MBG) scaffold with osteoconductive trimodal macro/micro/nano-porosity and osteoinductive rhBMP-2 delivery was developed. The preparative and mechanical problems of hierarchical MBG scaffold were solved without affecting its excellent biocompatibilities, and rhBMP-2 immobilization in sizematched mesopores was first explored. Combining structural and biological cues, TMS/rhBMP-2 achieved a complete regeneration with rapid medullary cavity reunion and sclerotin maturity in rabbit radius critical size defects. The design conceptions proposed in this study might provide new thoughts on development of future orthopedic biomaterials.

Recent advances in mesoporous silica nanoparticles for antitumor therapy: our contribution

Since 2001, when our research group proposed for the first time MCM-41 as a drug release system, the scientific community has demonstrated a growing interest in mesoporous silica nanoparticles (MSNs) for their revolutionary potential in nanomedicine. Among the diverse pathologies that can be treated with MSNs, cancer has received increasing attention. MSNs can be loaded with large amounts of therapeutic cargoes and once intravenously administrated preferentially accumulate in solid tumours via the enhanced permeation and retention (EPR) effect. Herein we report the recent developments achieved by our research group as a pioneer in this field, highlighting: the design of sophisticated MSNs as stimuli-responsive drug delivery systems to release the entrapped cargo upon exposure to a given stimulus while preventing the premature release of highly cytotoxic drugs before reaching the target; transporting non-toxic prodrugs and the enzyme responsible for its conversion into cytotoxic agents into the same MSNs; improving the selectivity and cellular uptake by cancer cells by active targeting of MSNs; increasing the penetration of MSNs within the tumour mass, which is one of the major challenges in the use of NPs to treat solid tumours.

Functionalized mesoporous bioactive glass scaffolds for enhanced bone tissue regeneration

Mesoporous bioactive glass (MBG), which possesses excellent bioactivity, biocompatibility and osteoconductivity, has played an important role in bone tissue regeneration. However, it is difficult to prepare MBG scaffolds with high compressive strength for applications in bone regeneration; this difficulty has greatly hindered its development and use. To solve this problem, a simple powder processing technique has been successfully developed to fabricate a novel type of MBG scaffold (MBGS). Furthermore, amino or carboxylic groups could be successfully grafted onto MBGSs (denoted as N-MBGS and C-MBGS, respectively) through a post-grafting process. It was revealed that both MBGS and the functionalized MBGSs could significantly promote the proliferation and osteogenic differentiation of bMSCs. Due to its positively charged surface, N-MBGS presented the highest in vitro osteogenic capability of the three samples. Moreover, in vivo testing results demonstrated that N-MBGS could promote higher levels of bone regeneration compared with MBGS and C-MBGS. In addition to its surface characteristics, it is believed that the decreased degradation rate of N-MBGS plays a vital role in promoting bone regeneration. These findings indicate that MBGSs are promising materials with potential practical applications in bone regeneration, which can be successfully fabricated by combining a powder processing technique and post-grafting process.

Ca2+, pH and thermo triple-responsive mechanized Zr-based MOFs for on-command drug release in bone diseases

A new design opens up the possibility of developing smart biomaterials for bone cancer (lowered pH and hypercalcemia) therapy.

Research Perspectives on Functional Micro and Nano Scale Coatings

Research topics related to the production of nanocomposites are the most important directions of development of new semiconductor engineering, ensuring high nanocomposites obtaining useful properties in the scope of biophysical characteristics, biomedical and piezoelectric applications. We present two case studies as Hydroxyapatite are in medical applications and aluminum nitride as acoustic wave sensor. Hydroxyapatite, is the main inorganic structure of the tooth enamel and bone and is a biomaterial that is commonly used in biomedical applications that involve bone substitution, drug delivery and bone regeneration because of its excellent biocompatibility, high bioactivity and good osseoconductivity. Since the past decade. Aluminum nitride (AlN), an electrical insulating ceramic with a wide band gap of 6.3 eV, is a potentially useful dielectric material very important in fields such as optoelectronic and micro electronics.

3D-printed bioceramic scaffolds with a Fe3O4/graphene oxide nanocomposite interface for hyperthermia therapy of bone tumor cells

Magnetic scaffolds display prominent magnetothermal ability, and can effectively kill tumor cells in an alternating magnetic field and improve bone formation ability in vitro.

Smart Mesoporous Nanomaterials for Antitumor Therapy

The use of nanomaterials for the treatment of solid tumours is receiving increasing attention by the scientific community. Among them, mesoporous silica nanoparticles (MSNs) exhibit unique features that make them suitable nanocarriers to host, transport and protect drug molecules until the target is reached. It is possible to incorporate different targeting ligands to the outermost surface of MSNs to selectively drive the drugs to the tumour tissues. To prevent the premature release of the cargo entrapped in the mesopores, it is feasible to cap the pore entrances using stimuli-responsive nanogates. Therefore, upon exposure to internal (pH, enzymes, glutathione, etc.) or external (temperature, light, magnetic field, etc.) stimuli, the pore opening takes place and the release of the entrapped cargo occurs. These smart MSNs are capable of selectively reaching and accumulating at the target tissue and releasing the entrapped drug in a specific and controlled fashion, constituting a promising alternative to conventional chemotherapy, which is typically associated with undesired side effects. In this review, we overview the recent advances reported by the scientific community in developing MSNs for antitumor therapy. We highlight the possibility to design multifunctional nanosystems using different therapeutic approaches aimed at increasing the efficacy of the antitumor treatment.

Design and characterization of calcium phosphate ceramic scaffolds for bone tissue engineering

OBJECTIVES

Our goal is to review design strategies for the fabrication of calcium phosphate ceramic scaffolds (CPS), in light of their transient role in bone tissue engineering and associated requirements for effective bone regeneration.

METHODS

We examine the various design options available to meet mechanical and biological requirements of CPS and later focus on the importance of proper characterization of CPS in terms of architecture, mechanical properties and time-sensitive properties such as biodegradability. Finally, relationships between in vitro versus in vivo testing are addressed, with an attempt to highlight reliable performance predictors.

RESULTS

A combinatory design strategy should be used with CPS, taking into consideration 3D architecture, adequate surface chemistry and topography, all of which are needed to promote bone formation. CPS represent the media of choice for delivery of osteogenic factors and anti-infectives. Non-osteoblast mediated mineral deposition can confound in vitro osteogenesis testing of CPS and therefore the expression of a variety of proteins or genes including collagen type I, bone sialoprotein and osteocalcin should be confirmed in addition to increased mineral content.

CONCLUSIONS

CPS are a superior scaffold material for bone regeneration because they actively promote osteogenesis. Biodegradability of CPS via calcium and phosphate release represents a unique asset. Structural control of CPS at the macro, micro and nanoscale and their combination with cells and polymeric materials is likely to lead to significant developments in bone tissue engineering.

Biocompatible Collagen Paramagnetic Scaffold for Controlled Drug Release

A porous collagen-based hydrogel scaffold was prepared in the presence of iron oxide nanoparticles (NPs) and was characterized by means of infrared spectroscopy and scanning electron microscopy. The hybrid scaffold was then loaded with fluorescein sodium salt as a model compound. The release of the hydrosoluble species was triggered and accurately controlled by the application of an external magnetic field, as monitored by fluorescence spectroscopy. The biocompatibility of the proposed matrix was also tested by the MTT assay performed on 3T3 cells. Cell viability was only slightly reduced when the cells were incubated in the presence of the collagen-NP hydrogel, compared to controls. The economicity of the chemical protocol used to obtain the paramagnetic scaffolds as well as their biocompatibility and the safety of the external trigger needed to induce the drug release suggest the proposed collagen paramagnetic matrices for a number of applications including tissue engeneering and drug delivery.

Multifunctional hydroxyapatite and poly(D,L-lactide-co-glycolide) nanoparticles for the local delivery of cholecalciferol

Cholecalciferol, vitamin D3, plays an important role in bonemetabolism by regulating extracellular levels of calcium. Presented here is a study on the effects of the local delivery of cholecalciferol (D3) using nanoparticulate carriers composed of hydroxyapatite (HAp) and poly(D,L-lactide-co-glycolide) (PLGA). Multifunctional nanoparticulate HAp-based powders were prepared for the purpose of: (a) either fast or sustained, local delivery of cholecalciferol, and (b) the secondary, osteoconductive and defect-filling effect of the carrier itself. Two types of HAp-based powders with particles of narrowly dispersed sizes in the nano range were prepared and tested in this study: HAp nanoparticles as direct cholecalciferol delivery agents and HAp nanoparticles coated with cholecalciferol-loaded poly(D,L)-lactide-co-glycolide (HAp/D3/PLGA). Satisfying biocompatibility of particulate systems, when incubated in contact with MC3T3-E1 osteoblastic cells in vitro, was observed for HAp/D3/PLGA and pure HAp. In contrast, an extensively fast release of cholecalciferol from the system comprising HAp nanoparticles coated with cholecalciferol (HAp/D3) triggered necrosis of the osteoblastic cells in vitro. Artificial defects induced in the osteoporotic bone of the rat mandible were successfully reconstructed following implantation of cholecalciferol-coated HAp nanoparticles as well as those comprising HAp nanoparticles coated with cholecalciferol-loaded PLGA (HAp/D3/PLGA). The greatest levels of enhanced angiogenesis, vascularization, osteogenesis and bone structure differentiation were achieved upon the implementation of HAp/D3/PLGA systems.

Stimulation of osteogenesis and angiogenesis of hBMSCs by delivering Si ions and functional drug from mesoporous silica nanospheres

Multifunctional bioactive materials with the ability to stimulate osteogenesis and angiogenesis of stem cells play an important role in the regeneration of bone defects. However, how to develop such biomaterials remains a significant challenge. In this study, we prepared mesoporous silica nanospheres (MSNs) with uniform sphere size (∼90 nm) and mesopores (∼2.7 nm), which could release silicon ions (Si) to stimulate the osteogenic differentiation of human bone marrow stromal cells (hBMSCs) via activating their ALP activity, bone-related gene and protein (OCN, RUNX2 and OPN) expression. Hypoxia-inducing therapeutic drug, dimethyloxaloylglycine (DMOG), was effectively loaded in the mesopores of MSNs (D-MSNs). The sustained release of DMOG from D-MSNs could stabilize HIF-1α and further stimulated the angiogenic differentiation of hBMSCs as indicated by the enhanced VEGF secretion and protein expression. Our study revealed that D-MSNs could combine the stimulatory effect on both osteogenic and angiogenic activity of hBMSCs. The potential mechanism of D-MSN-stimulated osteogenesis and angiogenesis was further elucidated by the supplementation of cell culture medium with pure Si ions and DMOG. Considering the easy handling characteristics of nanospheres, the prepared D-MSNs may be applied in the forms of injectable spheres for minimally invasive surgery, or MSNs/polymer composite scaffolds for bone defect repair. The concept of delivering both stimulatory ions and functional drugs may offer a new strategy to construct a multifunctional biomaterial system for bone tissue regeneration.

Peptide-equipped tobacco mosaic virus templates for selective and controllable biomineral deposition

The coating of regular-shaped, readily available nanorod biotemplates with inorganic compounds has attracted increasing interest during recent years. The goal is an effective, bioinspired fabrication of fiber-reinforced composites and robust, miniaturized technical devices. Major challenges in the synthesis of applicable mineralized nanorods lie in selectivity and adjustability of the inorganic material deposited on the biological, rod-shaped backbones, with respect to thickness and surface profile of the resulting coating, as well as the avoidance of aggregation into extended superstructures. Nanotubular tobacco mosaic virus (TMV) templates have proved particularly suitable towards this goal: Their multivalent protein coating can be modified by high-surface-density conjugation of peptides, inducing and governing silica deposition from precursor solutions in vitro. In this study, TMV has been equipped with mineralization-directing peptides designed to yield silica coatings in a reliable and predictable manner via precipitation from tetraethoxysilane (TEOS) precursors. Three peptide groups were compared regarding their influence on silica polymerization: (i) two peptide variants with alternating basic and acidic residues, i.e. lysine-aspartic acid (KD) x motifs expected to act as charge-relay systems promoting TEOS hydrolysis and silica polymerization; (ii) a tetrahistidine-exposing polypeptide (CA4H4) known to induce silicification due to the positive charge of its clustered imidazole side chains; and (iii) two peptides with high ZnO binding affinity. Differential effects on the mineralization of the TMV surface were demonstrated, where a (KD) x charge-relay peptide (designed in this study) led to the most reproducible and selective silica deposition. A homogenous coating of the biotemplate and tight control of shell thickness were achieved.

3D-printed dimethyloxallyl glycine delivery scaffolds to improve angiogenesis and osteogenesis

Angiogenesis-osteogenesis coupling processes are vital in bone tissue engineering. Normal biomaterials implanted in bone defects have issues in the sufficient formation of blood vessels, especially in the central part. Single delivery of vascular endothelial growth factors (VEGF) to foci in previous studies did not show satisfactory results due to low loading doses, a short protein half-life and low efficiency. Development of a hypoxia-mimicking microenvironment for cells by local prolyl-4-hydroxylase inhibitor release, which can stabilize hypoxia-inducible factor 1α (HIF-1α) expression, is an alternative method. The aim of this study was to design a dimethyloxallyl glycine (DMOG) delivering scaffold composed of mesoporous bioactive glasses and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) polymers (MPHS scaffolds), so as to investigate whether the sustained release of DMOG promotes local angiogenesis and bone healing. The morphology and microstructure of composite scaffolds were characterized. The DMOG release patterns from scaffolds loaded with different DMOG dosages were evaluated, and the effects of DMOG delivery on human bone marrow stromal cell (hBMSC) adhesion, viability, proliferation, osteogenic differentiation and angiogenic-relative gene expressions with scaffolds were also investigated. In vivo studies were carried out to observe vascular formations and new bone ingrowth with DMOG-loaded scaffolds. The results showed that DMOG could be released in a sustained manner over 4 weeks from MPHS scaffolds and obviously enhance the angiogenesis and osteogenesis in the defects. Microfil perfusion showed a significantly increased formation of vessels in the defects with DMOG delivery. Furthermore, micro-CT imaging and fluorescence labeling indicated larger areas of bone formation for DMOG-loaded scaffolds. It is concluded that MPHS-DMOG scaffolds are promising for enhancing bone healing of osseous defects.

Silica-based mesoporous nanobiomaterials as promoter of bone regeneration process

Silica-based mesostructured nanomaterials have emerged as a full family of biomaterials with tremendous potential to address the requirements for the bone regeneration process. This review focuses on more recent advances in bone regeneration process based on silica-based mesoporous biomaterials during 2012 to January 2015. In this review, we describe application of silica-based mesoporous mesostructured nanomaterials (possessing pore sizes in the range 2-50 nm) for the bone regeneration process. We summarize the preparation methods, the effect of mesopore templates and composition on the mesopore-structure characteristics, and different forms of these materials, including particles, fibers, spheres, scaffolds, and composites. The effect of structural and textural properties of mesoporous materials on the development of new biomaterials for treatment of different bone pathologies such as infection, osteoporosis, cancer, and so forth is discussed. In addition, silica-based mesoporous bioactive glass, as a potential drug/growth factor carrier, is reviewed, which includes the composition-structure-drug delivery relationship and the functional effect on the antibacteria and tissue-stimulation properties. Also, application of different mesoporous materials on construction of 3D macroporous scaffolds for bone tissue engineering was disused. Finally, this review discusses the possibility of covalently grafting different osteoinductive agents to the silica-based mesoporous scaffold surface that act as attracting signals for bone cells to promote the bone regeneration process.

A new targeting agent for the selective drug delivery of nanocarriers for treating neuroblastoma

Novel targeting agents against neuroblastoma based on the meta-iodobenzylguanidine (MIBG) moiety were synthesized and biologically evaluated for nanocarrier vectorization. These compounds have been anchored on the surface of drug loaded mesoporous silica nanocarriers, resulting in the improved cellular uptake in tumoral cells. Neuroblastoma (NB) is the most frequent extracranial pediatric tumor. Advanced forms of the disease (metastatic and/or refractory) have a dismal prognosis despite the combination of chemotherapy, radiotherapy, surgery and bone narrow transplants. These treatments carry severe side effects and, in some cases, compromise the life of the patient. MIBG has been widely applied in the medical diagnosis of NB due to its affinity for tumor cells through the norepinephrine transporter (NET), which is expressed in 90% of NB tumors. The exclusive accumulation of MIBG in neuroblastoma has been widely studied; however, its properties have been never exploited as a targeting agent in nanocarrier drug delivery systems. Several structural analogues of MIBG have been prepared and attached on the surface of nanocarriers. Their selective internalization has been tested against human neuroblastoma cells, which show, in the best case, cellular uptake four times higher than that of the naked nanosystem. Furthermore, in vivo experiments showed preferential and selective accumulation and retention of the targeted nanosystem comparing with the naked and only PEGylated counterpart systems. This novel nanosystem could be easily applicable to all kinds of drug delivery nanocarriers, providing a universal tool for neuroblastoma chemotherapies that is superior to classical approaches through a novel nanosystem exclusively designed to target this terrible malignancy.

Monoclonal antibody-targeted fluorescein-5-isothiocyanate-labeled biomimetic nanoapatites: a promising fluorescent probe for imaging applications

Multifunctional biomimetic nanoparticles (NPs) are acquiring increasing interest as carriers in medicine and basic research since they can efficiently combine labels for subsequent tracking, moieties for specific cell targeting, and bioactive molecules, e.g., drugs. In particular, because of their easy synthesis, low cost, good biocompatibility, high resorbability, easy surface functionalization, and pH-dependent solubility, nanocrystalline apatites are promising candidates as nanocarriers. This work describes the synthesis and characterization of bioinspired apatite nanoparticles to be used as fluorescent nanocarriers targeted against the Met/hepatocyte growth factor receptor, which is considered a tumor associated cell surface marker of many cancers. To this aim the nanoparticles have been labeled with Fluorescein-5-isothiocyanate (FITC) by simple isothermal adsorption, in the absence of organic, possibly toxic, molecules, and then functionalized with a monoclonal antibody (mAb) directed against such a receptor. Direct labeling of the nanoparticles allowed tracking the moieties with spatiotemporal resolution and thus following their interaction with cells, expressing or not the targeted receptor, as well as their fate in vitro. Cytofluorometry and confocal microscopy experiments showed that the functionalized nanocarriers, which emitted a strong fluorescent signal, were rapidly and specifically internalized in cells expressing the receptor. Indeed, we found that, once inside the cells expressing the receptor, mAb-functionalized FITC nanoparticles partially dissociated in their two components, with some mAbs being recycled to the cell surface and the FITC-labeled nanoparticles remaining in the cytosol. This work thus shows that FITC-labeled nanoapatites are very promising probes for targeted cell imaging applications.

Composition and Modifications of Dental Implant Surfaces

Since Brånemark discovered the favorable effects of titanium in bone healing in 1965, titanium has emerged as the gold standard bulk material for present-time dental implantology. In the course of years researchers aimed for improvement of the implants performance in bone even at compromised implant sites and multiple factors were investigated influencing osseointegration. This review summarizes and clarifies the four factors that are currently recognized being relevant to influence the tissue-implant contact ratio: bulk materials and coatings, topography, surface energy, and biofunctionalization. The macrodesigns of bulk materials (e.g., titanium, zirconium, stainless steel, tantalum, and magnesium) provide the mechanical stability and their influence on bone cells can be additionally improved by surface treatment with various materials (calcium phosphates, strontium, bioglasses, diamond-like carbon, and diamond). Surface topography can be modified via different techniques to increase the bone-implant contact, for example, plasma-spraying, grit-blasting, acid-etching, and microarc oxidation. Surface energy (e.g., wettability and polarity) showed a strong effect on cell behavior and cell adhesion. Functionalization with bioactive molecules (via physisorption, covalent binding, or carrier systems) targets enhanced osseointegration. Despite the satisfying clinical results of presently used dental implant materials, further research on innovative implant surfaces is inevitable to pursuit perfection in soft and hard tissue performance.

Mesoporous bioactive glasses: Relevance of their porous structure compared to that of classical bioglasses

In the last decade, the development of third generation bioceramics for Bone Tissue Regeneration has experienced significant progress with the emergence of a new generation of nanostructured materials named mesoporous bioactive glasses (MBG). This new generation of materials, also known as “templated glasses”, presents chemical compositions similar to those of conventional bioactive sol–gel glasses and the added value of an ordered mesopore arrangement. This article shows an indepth comparative study of the ordered porous structures of MBGs compared to conventional glasses (melt and solgel) andhowthese properties influence the bioactivity process. Moreover, the possibility to tailor the textural and structural properties of these nanostructured materials by an exhaustive control of the different synthesis parameters is also discussed. A brief overview regarding the possibility of using these materials as controlled drug delivery systems and as starting materials for the fabrication of 3D scaffolds for bone tissue regeneration is also given.

Towards the Development of Smart 3D "gated scaffolds" for on-command delivery

A new approach towards the design of "gated scaffolds" based on the combination of capped mesoporous silica nanoparticles (MSNs) with porous biomaterials is reported. Using this approach, a 3D gelatin-based scaffold able to selectively deliver cargo in the presence of an APase enzyme is prepared and tested. This new design opens up the possibility of developing new smart biomaterials with advanced drug-delivery features.

Sol-Gel processing of silica nanoparticles and their applications

Recently, silica nanoparticles (SNPs) have drawn widespread attention due to their applications in many emerging areas because of their tailorable morphology. During the last decade, remarkable efforts have been made on the investigations for novel processing methodologies to prepare SNPs, resulting in better control of the size, shape, porosity and significant improvements in the physio-chemical properties. A number of techniques available for preparing SNPs namely, flame spray pyrolysis, chemical vapour deposition, micro-emulsion, ball milling, sol-gel etc. have resulted, a number of publications. Among these, preparation by sol-gel has been the focus of research as the synthesis is straightforward, scalable and controllable. Therefore, this review focuses on the recent progress in the field of synthesis of SNPs exhibiting ordered mesoporous structure, their distribution pattern, morphological attributes and applications. The mesoporous silica nanoparticles (MSNPs) with good dispersion, varying morphology, narrow size distribution and homogeneous porous structure have been successfully prepared using organic and inorganic templates. The soft template assisted synthesis using surfactants for obtaining desirable shapes, pores, morphology and mechanisms proposed has been reviewed. Apart from single template, double and mixed surfactants, electrolytes, polymers etc. as templates have also been intensively discussed. The influence of reaction conditions such as temperature, pH, concentration of reagents, drying techniques, solvents, precursor, aging time etc. have also been deliberated. These MSNPs are suitable for a variety of applications viz., in the drug delivery systems, high performance liquid chromatography (HPLC), biosensors, cosmetics as well as construction materials. The applications of these SNPs have also been briefly summarized.

Advances in mesoporous silica nanoparticles for targeted stimuli-responsive drug delivery

INTRODUCTION

Mesoporous silica nanoparticles (MSNPs) are one of the most promising inorganic drug delivery systems (DDSs). The design and development of tumour-targeted MSNPs with stimuli-responsive drug release capability aim at enhancing the efficiency and minimising the side effects of anti-tumour drugs for cancer therapy.

AREAS COVERED

This review provides an overview of the scientific advances in MSNPs for tumour-targeted stimuli-responsive drug delivery. The key factors that govern the passive accumulation of MSNPs within solid tumours such as size, shape and surface functionalisation are roughly described. The different active targeting strategies for the specific retention and uptake of MSNPs by tumour cells are also outlined. The approaches developed so far for the synthesis of smart MSNPs capable of releasing the trapped drugs in response to internal or external stimuli and their applications are reviewed. Critical considerations in the use of MSNPs for the treatment of cancer treatment are discussed. The future prospects and key factors concerning the clinical application of MSNPs are considered throughout the manuscript.

EXPERT OPINION

MSNPs are promising nanocarriers to efficiently transport and site-specifically deliver highly toxic drugs, such as chemotherapeutic agents for cancer treatment. However, there are certain issues that should be overcome to improve the suitability of MSNPs for clinical applications. Increasing the penetration capability of MSNPs within tumour tissues, providing them of appropriate colloidal stability in physiological fluids and ensuring that their active targeting capability and stimuli-responsive performance are preserved in complex biological media are of foremost significance. Few in vivo evaluation tests of MSNPs have been reported and much research effort into this field is mandatory to be able to move from bench to bedside.

3D-printed magnetic Fe3O4/MBG/PCL composite scaffolds with multifunctionality of bone regeneration, local anticancer drug delivery and hyperthermia

In this study, three-dimensional (3D) magnetic Fe₃O₄ nanoparticles containing mesoporous bioactive glass/polycaprolactone (Fe₃O₄/MBG/PCL) composite scaffolds have been fabricated by the 3D-printing technique. The physiochemical properties, in vitro bioactivity, anticancer drug delivery, mechanical strength, magnetic heating ability and cell response of Fe₃O₄/MBG/PCL scaffolds were systematically investigated. The results showed that Fe₃O₄/MBG/PCL scaffolds had uniform macropores of 400 μm, high porosity of 60% and excellent compressive strength of 13-16 MPa. The incorporation of magnetic Fe₃O₄ nanoparticles into MBG/PCL scaffolds did not influence their apatite mineralization ability but endowed excellent magnetic heating ability and significantly stimulated proliferation, alkaline phosphatase (ALP) activity, osteogenesis-related gene expression (RUNX2, OCN, BSP, BMP-2 and Col-1) and extra-cellular matrix (ECM) mineralization of human bone marrow-derived mesenchymal stem cells (h-BMSCs). Moreover, using doxorubicin (DOX) as a model anticancer drug, Fe₃O₄/MBG/PCL scaffolds exhibited a sustained drug release for use in local drug delivery therapy. Therefore, the 3D-printed Fe₃O₄/MBG/PCL scaffolds showed the potential multifunctionality of enhanced osteogenic activity, local anticancer drug delivery and magnetic hyperthermia.

Direct Manufacture of Hydroxyapatite Scaffolds Using Blue Laser

The study deals with the direct manufacturing of hydroxyapatite scaffolds using selective polymerization of the slurry liquid phase. The bovine hydroxyapatite has great similarity with the human bone structure, making it able for a direct connection with the bone tissues. This study aims to obtain scaffolds using a new technique of rapid prototyping, obtained by polymerization of acrylic resin (liquid phase of slurry) by ultraviolet light present in a range of the band spectrum emitted by the blue laser light. Sub-micrometer hydroxyapatite was obtained by the calcination and grinding of bovine bone in a vibratory mill. Mixtures of hydroxyapatite and resin were prototyped in three-dimensional pieces and sintered afterword and subjected to blue laser emission path directed in a CNC equipment. Grounded particles obtained in the grinding vibratory mill, with equivalent diameter of 0.35 microns, were reactive enough to compensate the low green densification bellow 50 vol%. Polymerization tests realized indicated that the incidence of the laser with fluency of 170 mW.s/mm2promoted the curing of the 0.5 mm diameter pieces in depth about 0.5 mm, which allowed the prototyping of the scaffolds with sufficient mechanical strength for handling.

Novel chitosan hydrogel formed by ethylene glycol chitosan, 1,6-diisocyanatohexan and polyethylene glycol-400 for tissue engineering scaffold: in vitro and in vivo evaluation

Traditional chitosan hydrogels were prepared by chemical or physical crosslinker, and both of the two kinds of hydrogels have their merits and demerits. In this study, researchers attempted to prepare one kind of chitosan hydrogel by slightly crosslinker, which could combine the advantages of the two kinds of hydrogels. In this experiment, the crosslinker was formed by a reaction between the isocyanate group of 1,6-diisocyanatohexan and the hydroxyl group of polyethylene glycol-400 (PEG-400), then the crosslinker reacted with the amidine and the hydroxyl group of ethylene glycol chitosan to form the network structure. Physical properties of the hydrogel were tested by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and biodegradation. Biocompatibility was assessed by cell implantation in vitro and the scaffold was used as a cartilage tissue engineering scaffold to repair a defect in rabbit knee joints in vivo. FTIR results show the formation of a covalent bond during thickening of the ethylene glycol chitosan. SEM and degradation experiments showed that the ethylene glycol chitosan hydrogel is a 3-D, porous, and degradable scaffold. The hydrogel contained 2% ethylene glycol chitosan and 10 μl crosslinker was selected for the biocompatibility experiment in vitro and in vivo. After chondrocytes were cultured in the ethylene glycol chitosan hydrogel scaffold for 1 week cells exhibited clustered growth and had generated extracellular matrix on the scaffold in vitro. The results in vivo showed that hydrogel-chondrocytes promoted the repair of defect in rabbits. Based on these results, it could be concluded that ethylene glycol chitosan hydrogel is a scaffold with excellent physicochemical properties and it is a promising tissue engineering scaffold.

Bioceramics in ophthalmology

The benefits of ceramics in biomedical applications have been universally appreciated as they exhibit an extraordinarily broad set of physico-chemical, mechanical and biological properties which can be properly tailored by acting on their composition, porosity and surface texture to increase their versatility and suitability for targeted healthcare applications. Bioceramics have traditionally been used for the repair of hard tissues, such as bone and teeth, mainly due to their suitable strength for load-bearing applications, wear resistance (especially alumina, zirconia and composites thereof) and, in some cases, bone-bonding ability (calcium orthophosphates and bioactive glasses). Bioceramics have been also applied in other medical areas, like ophthalmic surgery; although their use in such a context has been scientifically documented since the late 1700s, the potential and importance of ceramic ocular implants still seem to be underestimated and an exhaustive, critical assessment is currently lacking in the relevant literature. The present review aims to fill this gap by giving a comprehensive picture of the ceramic-based materials and implants that are currently used in ophthalmology and pointing out the strengths and weaknesses of the existing devices. A prospect for future research is also provided, highlighting the potential of new, smart bioceramics able to carry specific added values which could have a significant impact on the treatment of ocular diseases.

Parathyroid hormone-related protein (107-111) improves the bone regeneration potential of gelatin-glutaraldehyde biopolymer-coated hydroxyapatite

Biopolymer-coated nanocrystalline hydroxyapatite (HA) made as macroporous foams which are degradable and flexible are promising candidates as orthopaedic implants. The C-terminal (107-111) epitope of parathyroid hormone-related protein (PTHrP) exhibits osteogenic properties. The main aim of this study was to evaluate whether PTHrP (107-111) loading into gelatin-glutaraldehyde biopolymer-coated HA (HAGlu) scaffolds would produce an optimal biomaterial for tissue engineering applications. HAGlu scaffolds with and without PTHrP (107-111) were implanted into a cavitary defect performed in both distal tibial metaphysis of adult rats. Animals were sacrificed after 4 weeks for histological, microcomputerized tomography and gene expression analysis of the callus. At this time, bone healing occurred only in the presence of PTHrP (107-111)-containing HAGlu implant, related to an increase in bone volume/tissue volume and trabecular thickness, cortical thickness and gene expression of osteocalcin and vascular cell adhesion molecule 1, but a decreased gene expression of Wnt inhibitors, SOST and dickkopf homolog 1. The autonomous osteogenic effect of the PTHrP (107-111)-loaded HAGlu scaffolds was confirmed in mouse and human osteoblastic cell cultures. Our findings demonstrate the advantage of loading PTHrP (107-111) into degradable HAGlu scaffolds for achieving an optimal biomaterial that is promising for low load bearing clinical applications.

Chitosan-based scaffolds for bone tissue engineering

Bone defects requiring grafts to promote healing are frequently occurring and costly problems in health care. Chitosan, a biodegradable, naturally occurring polymer, has drawn considerable attention in recent years as scaffolding material in tissue engineering and regenerative medicine. Chitosan is especially attractive as a bone scaffold material because it supports the attachment and proliferation of osteoblast cells as well as formation of mineralized bone matrix. In this review, we discuss the fundamentals of bone tissue engineering and the unique properties of chitosan as a scaffolding material to treat bone defects for hard tissue regeneration. We present the common methods for fabrication and characterization of chitosan scaffolds, and discuss the influence of material preparation and addition of polymeric or ceramic components or biomolecules on chitosan scaffold properties such as mechanical strength, structural integrity, and functional bone regeneration. Finally, we highlight recent advances in development of chitosan-based scaffolds with enhanced bone regeneration capability.