Ceramic composites as matrices and scaffolds for drug delivery in tissue engineering

Osteogenic Enhancement Between Icariin and Bone Morphogenetic Protein 2: A Potential Osteogenic Compound for Bone Tissue Engineering

Icariin, a typical flavonol glycoside, is the main active component of Herba Epimedii, which was used to cure bone-related diseases in China for centuries. It has been reported that Icariin can be delivered locally by biomaterials and it has an osteogenic potential for bone tissue engineering. Biomimetic calcium phosphate (BioCaP) bone substitute is a novel drug delivery carrier system. Our study aimed to evaluate the osteogenic potential when Icariin was internally incorporated into the BioCaP granules. The BioCaP combined with Icariin and bone morphogenetic protein 2 (BMP-2) was investigated in vitro using an MC3T3-E1 cell line. We also investigated its efficacy to repair 8 mm diameter critical size bone defects in the skull of SD male rats. BioCaP was fabricated according to a well-established biomimetic mineralization process. In vitro, the effects of BioCaP alone or BioCaP with Icariin and/or BMP-2 on cell proliferation and osteogenic differentiation of MC3T3-E1 cells were systematically evaluated. In vivo, BioCaP alone or BioCaP with Icariin and/or BMP-2 were used to study the bone formation in a critical-sized bone defect created in a rat skull. Samples were retrieved for Micro-CT and histological analysis 12 weeks after surgery. The results indicated that BioCaP with or without the incorporation of Icariin had a positive effect on the osteogenic differentiation of MC3T3-E1. BioCaP with Icariin had better osteogenic efficiency, but had no influence on cell proliferation. BioCap + Icariin + BMP-2 showed better osteogenic potential compared with BioCaP with BMP-2 alone. The protein and mRNA expression of alkaline phosphatase and osteocalcin and mineralization were higher as well. In vivo, BioCaP incorporate internally with both Icariin and BMP-2 induced significantly more newly formed bone than the control group and BioCaP with either Icariin or BMP-2 did. Micro-CT analysis revealed that no significant differences were found between the bone mineral density induced by BioCaP with icariin and that induced by BioCaP with BMP-2. Therefore, co-administration of Icariin and BMP-2 was helpful for bone tissue engineering.

Bioactive Glasses and Glass-Ceramics for Healthcare Applications in Bone Regeneration and Tissue Engineering

The discovery of bioactive glasses (BGs) in the late 1960s by Larry Hench et al. was driven by the need for implant materials with an ability to bond to living tissues, which were intended to replace inert metal and plastic implants that were not well tolerated by the body. Among a number of tested compositions, the one that later became designated by the well-known trademark of 45S5 Bioglass® excelled in its ability to bond to bone and soft tissues. Bonding to living tissues was mediated through the formation of an interfacial bone-like hydroxyapatite layer when the bioglass was put in contact with biological fluids in vivo. This feature represented a remarkable milestone, and has inspired many other investigations aiming at further exploring the in vitro and in vivo performances of this and other related BG compositions. This paradigmatic example of a target-oriented research is certainly one of the most valuable contributions that one can learn from Larry Hench. Such a goal-oriented approach needs to be continuously stimulated, aiming at finding out better performing materials to overcome the limitations of the existing ones, including the 45S5 Bioglass®. Its well-known that its main limitations include: (i) the high pH environment that is created by its high sodium content could turn it cytotoxic; (ii) and the poor sintering ability makes the fabrication of porous three-dimensional (3D) scaffolds difficult. All of these relevant features strongly depend on a number of interrelated factors that need to be well compromised. The selected chemical composition strongly determines the glass structure, the biocompatibility, the degradation rate, and the ease of processing (scaffolds fabrication and sintering). This manuscript presents a first general appraisal of the scientific output in the interrelated areas of bioactive glasses and glass-ceramics, scaffolds, implant coatings, and tissue engineering. Then, it gives an overview of the critical issues that need to be considered when developing bioactive glasses for healthcare applications. The aim is to provide knowledge-based tools towards guiding young researchers in the design of new bioactive glass compositions, taking into account the desired functional properties.

Application of hydroxyapatite and its modified forms as adsorbents for water defluoridation: an insight into process synthesis

Fluorosis is a major scourge in many countries caused by prolonged consumption of drinking water with high fluoride content found in groundwater resources. Hydroxyapatite (Hap) and its composite forms are excellent biomaterials that recently gained attention as efficient adsorbents, owing to its physical and chemical nature as it can substitute both cationic and anionic complexes present in an aqueous solution in its atomic arrangement. Its biological nature, biocompatibility and biodegradability along with its chemical characteristics such as crystallinity, stability, ion adsorption capability and highly specific catalytic activity make it suitable for a variety of applications especially in water treatment for fluoride removal. This review describes various techniques for synthesis of a wide variety of biogenic, synthetic, composite and modified forms of Hap for application in water defluoridation. Hap derived from natural sources or synthesized using conventional methods, hydrothermal, sol-gel or advanced sonication-cum-precipitation technique varied in terms of its crystallinity, structure, size, etc., which affect the fluoride removal capacity. The advantage and disadvantages of various synthesis methods, process parameters and product characteristics have been compiled, which may help to identify a suitable synthesis method for a desired Hap product for potential application and future perspectives in water treatment.

3D bioactive composite scaffolds for bone tissue engineering

Bone is the second most commonly transplanted tissue worldwide, with over four million operations using bone grafts or bone substitute materials annually to treat bone defects. However, significant limitations affect current treatment options and clinical demand for bone grafts continues to rise due to conditions such as trauma, cancer, infection and arthritis. Developing bioactive three-dimensional (3D) scaffolds to support bone regeneration has therefore become a key area of focus within bone tissue engineering (BTE). A variety of materials and manufacturing methods including 3D printing have been used to create novel alternatives to traditional bone grafts. However, individual groups of materials including polymers, ceramics and hydrogels have been unable to fully replicate the properties of bone when used alone. Favourable material properties can be combined and bioactivity improved when groups of materials are used together in composite 3D scaffolds. This review will therefore consider the ideal properties of bioactive composite 3D scaffolds and examine recent use of polymers, hydrogels, metals, ceramics and bio-glasses in BTE. Scaffold fabrication methodology, mechanical performance, biocompatibility, bioactivity, and potential clinical translations will be discussed.

Potential applications of engineered nanoparticles in medicine and biology: an update

Nanotechnology advancements have led to the development of its allied fields, such as nanoparticle synthesis and their applications in the field of biomedicine. Nanotechnology driven innovations have given a hope to the patients as well as physicians in solving the complex medical problems. Nanoparticles with a size ranging from 0.2 to 100 nm are associated with an increased surface to volume ratio. Moreover, the physico-chemical and biological properties of nanoparticles can be modified depending on the applications. Different nanoparticles have been documented with a wide range of applications in various fields of medicine and biology including cancer therapy, drug delivery, tissue engineering, regenerative medicine, biomolecules detection, and also as antimicrobial agents. However, the development of stable and effective nanoparticles requires a profound knowledge on both physico-chemical features of nanomaterials and their intended applications. Further, the health risks associated with the use of engineered nanoparticles needs a serious attention.

Incorporation of microfibrillated cellulose into collagen-hydroxyapatite scaffold for bone tissue engineering

In this study, the composite of Collagen-Hydroxyapitite (COL-HA) with microfibrillated cellulose (MFC) was developed as a new bone substitute material. COL-HA was prepared by in-situ method and modified by dehydrothermal treatment. Microfibrillated cellulose (MFC), a nature polysaccharide with plenty of hydroxyl groups, was incorporated into COL-HA composites to improve the properties. The novel COL-HA-MFC scaffold with different ratios of COL-HA and MFC were fabricated by cold isostatic pressing technique and freeze-drying technology. During the forming process, a three-dimensional bone-like structure was shaped in hybrid scaffolds. The microstructural transitions of COL-HA-MFC composites were examined by Fourier transform infrared spectroscope (FTIR), Ultraviolet-visible spectrophotometer (UV), and X-ray diffraction (XRD), which indicated that HA deposited on collagen molecules and MFC bonded with COL-HA. Hydrophilicity, swelling property, mechanical property, and degradability of COL-HA-MFC composites were investigated. Biological properties, such as cytotoxicity and hemolysis, were also studied. The results showed a good swelling capacity for the scaffolds, keeping their original shapes after swelling. The compression strength and degradability of the scaffold materials could be regulated by the MFC content. The compression strength of COL-HA-MFC composite scaffords increased to 20-40 MPa, closing to that of the nature bone (1-200 MPa). The obtained scaffolds are good in biocompatibility with high level of cell growth rate (>70%) and suitable hemolysis rate (≦5%). The work might provide an efficient and alternative approach for collagen-based biomaterials with necessary properties. The COL-HA-MFC composite scaffold showed a potential application in bone tissue engineering.

Treatment of osteomyelitis defects by a vancomycin-loaded gelatin/β-tricalcium phosphate composite scaffold

OBJECTIVE

In the present study, we aimed to assess whether gelatin/β-tricalcium phosphate (β-TCP) composite porous scaffolds could be used as a local controlled release system for vancomycin. We also investigated the efficiency of the scaffolds in eliminating infections and repairing osteomyelitis defects in rabbits.

METHODS

The gelatin scaffolds containing differing amounts of of β-TCP (0%, 10%, 30% and 50%) were prepared for controlled release of vancomycin and were labelled G-TCP0, G-TCP1, G-TCP3 and G-TCP5, respectively. The Kirby-Bauer method was used to examine the release profile. Chronic osteomyelitis models of rabbits were established. After thorough debridement, the osteomyelitis defects were implanted with the scaffolds. Radiographs and histological examinations were carried out to investigate the efficiency of eliminating infections and repairing bone defects.

RESULTS

The prepared gelatin/β-TCP scaffolds exhibited a homogeneously interconnected 3D porous structure. The G-TCP0 scaffold exhibited the longest duration of vancomycin release with a release duration of eight weeks. With the increase of β-TCP contents, the release duration of the β-TCP-containing composite scaffolds was decreased. The complete release of vancomycin from the G-TCP5 scaffold was achieved within three weeks. In the treatment of osteomyelitis defects in rabbits, the G-TCP3 scaffold showed the most efficacious performance in eliminating infections and repairing bone defects.

CONCLUSIONS

The composite scaffolds could achieve local therapeutic drug levels over an extended duration. The G-TCP3 scaffold possessed the optimal porosity, interconnection and controlled release performance. Therefore, this scaffold could potentially be used in the treatment of chronic osteomyelitis defects.Cite this article: J. Zhou, X. G. Zhou, J. W. Wang, H. Zhou, J. Dong. Treatment of osteomyelitis defects by a vancomycin-loaded gelatin/β-tricalcium phosphate composite scaffold. Bone Joint Res 2018;7:46-57. DOI: 10.1302/2046-3758.71.BJR-2017-0129.R2.

Functionalized biomimetic calcium phosphates for bone tissue repair

The design and development of novel materials for biomineralized tissues is an extremely attractive field of research where calcium phosphates (CaPs)-based materials for biomedical applications play a leading role. The biological performance of these compounds can be enhanced through functionalization with biologically active ions and molecules. This review reports on some important recent achievements in creating functionalized biomimetic CaP materials for applications in the musculoskeletal field. Particular attention is focused on the modifications of these inorganic compounds with bioactive ions, growth factors and drugs, as well as on recent trends in some important CaP applications as biomaterials - namely, as bone cements, coatings of metallic implants and scaffolds for regenerative medicine.

PCL and PCL-based materials in biomedical applications

Biodegradable polymers have met with an increasing demand in medical usage over the last decades. One of such polymers is poly(ε-caprolactone) (PCL), which is a polyester that has been widely used in tissue engineering field for its availability, relatively inexpensive price and suitability for modification. Its chemical and biological properties, physicochemical state, degradability and mechanical strength can be adjusted, and therefore, it can be used under harsh mechanical, physical and chemical conditions without significant loss of its properties. Degradation time of PCL is quite long, thus it is used mainly in the replacement of hard tissues in the body where healing also takes an extended period of time. It is also used at load-bearing tissues of the body by enhancing its stiffness. However, due to its tailorability, use of PCL is not restricted to one type of tissue and it can be extended to engineering of soft tissues by decreasing its molecular weight and degradation time. This review outlines the basic properties of PCL, its composites, blends and copolymers. We report on various techniques for the production of different forms, and provide examples of medical applications such as tissue engineering and drug delivery systems covering the studies performed in the last decades.

Nano-carrier based drug delivery systems for sustained antimicrobial agent release from orthopaedic cementous material

Total joint replacement (TJR), such as hip and knee replacement, is a popular procedure worldwide. Prosthetic joint infections (PJI) after this procedure have been widely reported, where treatment of such infections is complex with high cost and prolonged hospital stay. In cemented arthroplasties, the use of antibiotic loaded bone cement (ALBC) is a standard practice for the prophylaxis and treatment of PJI. Recently, the development of bacterial resistance by pathogenic microorganisms against most commonly used antibiotics increased the interest in alternative approaches for antimicrobial delivery systems such as nanotechnology. This review summarizes the efforts made to improve the antimicrobial properties of PMMA bone cements using nanotechnology based antibiotic and non-antibiotic delivery systems to overcome drawbacks of ALBC in the prophylaxis and treatment of PJIs after hip and knee replacement.

Application of xanthan gum as polysaccharide in tissue engineering: A review

Xanthan gum is a microbial high molecular weight exo-polysaccharide produced by Xanthomonas bacteria (a Gram-negative bacteria genus that exhibits several different species) and it has widely been used as an additive in various industrial and biomedical applications such as food and food packaging, cosmetics, water-based paints, toiletries, petroleum, oil-recovery, construction and building materials, and drug delivery. Recently, it has shown great potential in issue engineering applications and a variety of modification methods have been employed to modify xanthan gum as polysaccharide for this purpose. However, xanthan gum-based biomaterials need further modification for several targeted applications due to some disadvantages (e.g., processing and mechanical performance of xanthan gum), where modified xanthan gum will be well suited for tissue engineering products. In this review, the current scenario of the use of xanthan gum for various tissue engineering applications, including its origin, structure, properties, modification, and processing for the preparation of the hydrogels and/or the scaffolds is precisely reviewed.

Therapeutic PCL scaffold for reparation of resected osteosarcoma defect

Osteosarcomas are highly malignant tumors, which develop rapid growth and local infiltration, inducing metastases that spread primarily in the lung. Treatment of these tumors is mainly based on pre- and post-operative chemotherapy and surgery of the primary tumor. Surgical resection though, generates bone defects. Reparation of these weaknesses presents formidable challenges to orthopedic surgery. Medicine regenerative grafts that act as both tumor therapy with constant local drug delivery and tissue regeneration may provide a new prospect to address this need. These implants can provide sustained drug release at the cancer area, decreasing systemic second effects such as inflammation, and a filling of the resected tissues with regenerative biomaterials. In this study microporous poly-ε-caprolactone (PCL) scaffolds have been developed for sustained local release of anti-inflammatory drug dexamethasone (DXM), used as drug model, in cancer medicine regenerative field. The microporous PCL matrix of the scaffolds supported the attachment, proliferation and osteogenic differentiation of osteoblast-like cells, while the polyelectrolyte multilayers, anchored to the inner pore surfaces, sustained locally DXM release. These microporous scaffolds demonstrate the ability to deliver DXM as a localized tumor therapy and to promote proliferation and differentiation of osteoblast-like cells in vitro.

Bone regeneration in minipigs by intrafibrillarly-mineralized collagen loaded with autologous periodontal ligament stem cells

Biomimetic intrafibrillarly-mineralized collagen (IMC) is a promising scaffold for bone regeneration because of its structural and functional similarity to natural bone. The objective of this study was to evaluate the bone regeneration potential of IMC loaded with autologous periodontal ligament stem cells (PDLSCs) in large bone defects in minipigs. A macroporous IMC with a bone-like subfibrillar nanostructure was fabricated using a biomimetic bottom-up approach. Non-healing full thickness defects were established on the cranial bone in minipigs, and IMC and hydroxyapatite (HA) scaffolds seeded with autologous PDLSCs were implanted into these defects. Computed tomographic imaging, histology staining, and atomic force microscopy were applied to evaluate to the quantity, micro/nano structures, and mechanical performance of the neo-bone after 12 weeks of implantation. Compared with HA, IMC showed superior regeneration properties characterized by the profuse deposition of new bony structures with a normal architecture and vascularization. Immunohistochemistry showed that the runt-related transcription factor 2 and transcription factor Osterix were highly expressed in the neo-bone formed by IMC. Furthermore, the nanostructure and nanomechanics of the neo-bone formed by IMC were similar to that of natural bone. This study provides strong evidence for the future clinical applications of the IMC-based bone grafts.

Trifunctional Fe3O4/CaP/Alginate Core-Shell-Corona Nanoparticles for Magnetically Guided, pH-Responsive, and Chemically Targeted Chemotherapy

Chemotherapy of bladder cancer has limited efficacy because of the short retention time of drugs in the bladder during therapy. In this research, nanoparticles (NPs) with a new core/shell/corona nanostructure have been synthesized, consisting of iron oxide (Fe₃O₄) as the core to providing magnetic properties, drug (doxorubicin) loaded calcium phosphate (CaP) as the shell for pH-responsive release, and arginylglycylaspartic acid (RGD)-containing peptide functionalized alginate as the corona for cell targeting (with the composite denoted as RGD-Fe₃O₄/CaP/Alg NPs). We have optimized the reaction conditions to obtain RGD-Fe₃O₄/CaP/Alg NPs with high biocompatibility and suitable particle size, surface functionality, and drug loading/release behavior. The results indicate that the RGD-Fe₃O₄/CaP/Alg NPs exhibit enhanced chemotherapy efficacy toward T24 bladder cancer cells, owing to successful magnetic guidance, pH-responsive release, and improved cellular uptake, which give these NPs great potential as therapeutic agents for future in vivo drug delivery systems.

pH dependent silver nanoparticles releasing titanium implant: A novel therapeutic approach to control peri-implant infection

Peri-implant infection control is crucial for implant fixation and durability. Antimicrobial administration approaches to control peri-implant infection are far from satisfactory. During bacterial infection, pH level around the peri-implant surface decreases as low as pH 5.5. This change of pH can be used as a switch to control antimicrobial drug release from the implant surface. Silver nanoparticles (AgNPs) have broad-spectrum antimicrobial properties. In this study, we aimed to design a pH-dependent AgNPs releasing titania nanotube arrays (TNT) implant for peri-implant infection control. The nanotube arrays were fabricated on the surface of titanium implant as containers; AgNPs were grafted on TNT implant surface via a low pH-sensitive acetal linker (TNT-AL-AgNPs). SEM, TEM, AFM, FTIR as well as XPS data showed that AgNPs have been successfully linked to TNT via acetal linker without affecting the physicochemical characteristics of TNT. The pH 5.5 enhanced AgNPs release from TNT-AL-AgNPs implant compared with pH 7.4. AgNPs released at pH 5.5 robustly increased antimicrobial activities against gram-positive and gram-negative bacteria compared with AgNPs released at pH 7.4. TNT-AL-AgNPs implant enhanced osteoblast proliferation, differentiation, and did not affect osteoblast morphology in vitro. In conclusion, incorporation of AgNPs in TNT via acetal linker maintained the surface characteristics of TNT. TNT-AL-AgNPs implant was biocompatible to osteoblasts and showed osteoinductive properties. AgNPs were released from TNT-AL-AgNPs implant in high dose at pH 5.5, and this release showed strong antimicrobial properties in vitro. Therefore, this novel design of low pH-triggered AgNPs releasing TNT-AL-AgNPs could be an infection-triggered antimicrobial releasing implant model to control peri-implant infection.

Controlled Release of Vanadium from a Composite Scaffold Stimulates Mesenchymal Stem Cell Osteochondrogenesis

Large bone defects often require the use of autograft, allograft, or synthetic bone graft augmentation; however, these treatments can result in delayed osseous integration. A tissue engineering strategy would be the use of a scaffold that could promote the normal fracture healing process of endochondral ossification, where an intermediate cartilage phase is later transformed to bone. This study investigated vanadyl acetylacetonate (VAC), an insulin mimetic, combined with a fibrous composite scaffold, consisting of polycaprolactone with nanoparticles of hydroxyapatite and beta-tricalcium phosphate, as a potential bone tissue engineering scaffold. The differentiation of human mesenchymal stem cells (MSCs) was evaluated on 0.05 and 0.025 wt% VAC containing composite scaffolds (VAC composites) in vitro using three different induction media: osteogenic (OS), chondrogenic (CCM), and chondrogenic/osteogenic (C/O) media, which mimics endochondral ossification. The controlled release of VAC was achieved over 28 days for the VAC composites, where approximately 30% of the VAC was released over this period. MSCs cultured on the VAC composites in C/O media had increased alkaline phosphatase activity, osteocalcin production, and collagen synthesis over the composite scaffold without VAC. In addition, gene expressions for chondrogenesis (Sox9) and hypertrophic markers (VEGF, MMP-13, and collagen X) were the highest on VAC composites. Almost a 1000-fold increase in VEGF gene expression and VEGF formation, as indicated by immunostaining, was achieved for cells cultured on VAC composites in C/O media, suggesting VAC will promote angiogenesis in vivo. These results demonstrate the potential of VAC composite scaffolds in supporting endochondral ossification as a bone tissue engineering strategy.

Fabrication and characterization of chitosan/OGP coated porous poly(ε-caprolactone) scaffold for bone tissue engineering

As one of the stimulators on bone formation, osteogenic growth peptide (OGP) improves both proliferation and differentiation of the bone cells in vitro and in vivo. The aim of this work was the preparation of three dimensional porous poly(ε-caprolactone) (PCL) scaffold with high porosity, well interpore connectivity, and then its surface was modified by using chitosan (CS)/OGP coating for application in bone regeneration. In present study, the properties of porous PCL and CS/OGP coated PCL scaffold, including the microstructure, water absorption, porosity, hydrophilicity, mechanical properties, and biocompatibility in vitro were investigated. Results showed that the PCL and CS/OGP-PCL scaffold with an interconnected network structure have a porosity of more than 91.5, 80.8%, respectively. The CS/OGP-PCL scaffold exhibited better hydrophilicity and mechanical properties than that of uncoated PCL scaffold. Moreover, the results of cell culture test showed that CS/OGP coating could stimulate the proliferation and growth of osteoblast cells on CS/OGP-PCL scaffold. These finding suggested that the surface modification could be a effective method on enhancing cell adhesion to synthetic polymer-based scaffolds in tissue engineering application and the developed porous CS/OGP-PCL scaffold should be considered as alternative biomaterials for bone regeneration.

Critical review: Injectability of calcium phosphate pastes and cements

Calcium phosphate cements (CPC) have seen clinical success in many dental and orthopaedic applications in recent years. The properties of CPC essential for clinical success are reviewed in this article, which includes properties of the set cement (e.g. bioresorbability, biocompatibility, porosity and mechanical properties) and unset cement (e.g. setting time, cohesion, flow properties and ease of delivery to the surgical site). Emphasis is on the delivery of calcium phosphate (CaP) pastes and CPC, in particular the occurrence of separation of the liquid and solid components of the pastes and cements during injection; and established methods to reduce this phase separation. In addition a review of phase separation mechanisms observed during the extrusion of other biphasic paste systems and the theoretical models used to describe these mechanisms are discussed.

STATEMENT OF SIGNIFICANCE

Occurrence of phase separation of calcium phosphate pastes and cements during injection limits their full exploitation as a bone substitute in minimally invasive surgical applications. Due to lack of theoretical understanding of the phase separation mechanism(s), optimisation of an injectable CPC that satisfies clinical requirements has proven difficult. However, phase separation of pastes during delivery has been the focus across several research fields. Therefore in addition to a review of methods to reduce phase separation of CPC and the associated constraints, a review of phase separation mechanisms observed during extrusion of other pastes and the theoretical models used to describe these mechanisms is presented. It is anticipated this review will benefit future attempts to develop injectable calcium phosphate based systems.

The use of nanoscaffolds and dendrimers in tissue engineering

To avoid tissue rejection during organ transplantation, research has focused on the use of tissue engineering to regenerate required tissues or organs for patients. The biomedical applications of hyperbranched, multivalent, structurally uniform, biocompatible dendrimers in tissue engineering include the mimicking of natural extracellular matrices (ECMs) in the 3D microenvironment. Dendrimers are unimolecular architects that can incorporate a variety of biological and/or chemical substances in a 3D architecture to actively support the scaffold microenvironment during cell growth. Here, we review the use of dendritic delivery systems in tissue engineering. We discuss the available literature, highlighting the 3D architecture and preparation of these nanoscaffolds, and also review challenges to, and advances in, the use dendrimers in tissue engineering. Advances in the manufacturing of dendritic nanoparticles and scaffold architectures have resulted in the successful incorporation of dendritic scaffolds in tissue engineering.

BMP2-coprecipitated calcium phosphate granules enhance osteoinductivity of deproteinized bovine bone, and bone formation during critical-sized bone defect healing

Most materials used clinically for filling critical-sized bone defects (CSBD), such as deproteinized bovine bone (DBB), lack osteoinductivity so that their therapeutic effects are far from satisfactory. The effect of bone morphogenic protein 2 (BMP2)-coprecipitated biomimetic calcium phosphate granules (BMP2-cop.BioCaP) on osteoinduction of DBB graft(s) during CSBD healing is still unknown. We investigated whether BMP2-cop.BioCaP affects the osteoinductivity of DBB, bone formation, and foreign body reaction during CSBD healing. DBB + BMP2-cop.BioCaP, DBB, DBB + BMP2, DBB + BioCaP, and autologous bone grafts were implanted in the CSBD of sheep. Bone formation, DBB/BioCaP degradability, foreign body reaction, and osteoinductivity of DBB were analyzed histologically and histomorphometrically at week 4 and 8. Combination of BMP2-cop.BioCaP and DBB healed CSBD as effectively as autologous bone grafts. About 95% of the BMP2-cop.BioCaP had been degraded and replaced by new bone at week 8 in the DBB + BMP2-cop.BioCaP-group. Foreign body reaction was reduced in the DBB + BMP2-cop.BioCaP-group compared to the other groups. The independent use of the BMP2-cop.BioCaP did not achieve a satisfactory bone repair. In conclusion, the BMP2-cop.BioCaP showed good degradability and biocompatibility, and enhanced osteoinductivity of DBB during CSBD healing in sheep, suggesting BMP2-cop.BioCaP as a potential osteoinducer to enhance the therapeutic effects of the graft materials in clinic.

Injectable scaffolds: Preparation and application in dental and craniofacial regeneration

Injectable scaffolds are appealing for tissue regeneration because they offer many advantages over pre-formed scaffolds. This article provides a comprehensive review of the injectable scaffolds currently being investigated for dental and craniofacial tissue regeneration. First, we provide an overview of injectable scaffolding materials, including natural, synthetic, and composite biomaterials. Next, we discuss a variety of characteristic parameters and gelation mechanisms of the injectable scaffolds. The advanced injectable scaffolding systems developed in recent years are then illustrated. Furthermore, we summarize the applications of the injectable scaffolds for the regeneration of dental and craniofacial tissues that include pulp, dentin, periodontal ligament, temporomandibular joint, and alveolar bone. Finally, our perspectives on the injectable scaffolds for dental and craniofacial tissue regeneration are offered as signposts for the future advancement of this field.

Nanohydroxyapatite Effect on the Degradation, Osteoconduction and Mechanical Properties of Polymeric Bone Tissue Engineered Scaffolds

BACKGROUND

Statistical reports show that every year around the world approximately 15 million bone fractures occur; of which up to 10% fail to heal completely and hence lead to complications of non-union healing. In the past, autografts or allografts were used as the “gold standard” of treating such defects. However, due to various limitations and risks associated with these sources of bone grafts, other avenues have been extensively investigated through which bone tissue engineering; in particular engineering of synthetic bone graft substitutes, has been recognised as a promising alternative to the traditional methods.

METHODS

A selective literature search was performed.

RESULTS

Bone tissue engineering offers unlimited supply, eliminated risk of disease transmission and relatively low cost. It could also lead to patient specific design and manufacture of implants, prosthesis and bone related devices. A potentially promising building block for a suitable scaffold is synthetic nanohydroxyapatite incorporated into synthetic polymers. Incorporation of nanohydroxyapatite into synthetic polymers has shown promising bioactivity, osteoconductivity, mechanical properties and degradation profile compared to other techniques previously considered.

CONCLUSION

Scientific research, through extensive physiochemical characterisation, in vitro and in vivo assessment has brought together the optimum characteristics of nanohydroxyapatite and various types of synthetic polymers in order to develop nanocomposites of suitable nature for bone tissue engineering. The aim of the present article is to review and update various aspects involved in incorporation of synthetic nanohydroxyapatite into synthetic polymers, in terms of their potentials to promote bone growth and regeneration in vitro, in vivo and consequently in clinical applications.

Poly(lactic acid) nanofibrous scaffolds for tissue engineering

Poly(lactic acid) (PLA) is a synthetic polyester that has shown extensive utility in tissue engineering. Synthesized either by ring opening polymerization or polycondensation, PLA hydrolytically degrades into lactic acid, a metabolic byproduct, making it suitable for medical applications. Specifically, PLA nanofibers have widened the possible uses of PLA scaffolds for regenerative medicine and drug delivery applications. The use of nanofibrous scaffolds imparts a host of desirable properties, including high surface area, biomimicry of native extracellular matrix architecture, and tuning of mechanical properties, all of which are important facets of designing scaffolds for a particular organ system. Additionally, nanofibrous PLA scaffolds hold great promise as drug delivery carriers, where fabrication parameters and drug-PLA compatibility greatly affect the drug release kinetics. In this review, we present the latest advances in the use of PLA nanofibrous scaffolds for musculoskeletal, nervous, cardiovascular, and cutaneous tissue engineering and offer perspectives on their future use.

Long-term biological performance of injectable and degradable calcium phosphate cement

Enhancing degradation of poorly degrading injectable calcium phosphate (CaP) cements (CPCs) can be achieved by adding poly(lactic-co-glycolic acid) (PLGA) microparticles, generating porosity after polymer degradation. CPC-PLGA has proven to be biodegradable, although its long-term biological performance is still unknown. Optimization of injectability could be achieved via addition of carboxymethyl cellulose (CMC). Here, we evaluated the long-term in vivo performance of CPC-PLGA with or without the lubricant CMC in comparison to the devitalized bovine bone mineral (DBBM) predicate device Bio-Oss^®. Rabbit femoral bone defects were injected with a CPC-formulation or filled with Bio-Oss^® granules. Samples were retrieved at 6 and 26 weeks. Material degradation for Bio-Oss^® was marginal, starting with 57% material remnants at implantation, 49% at 6 weeks, and 35% at 26 weeks, respectively. In contrast, CPC-PLGA and CPC-PLGA-CMC showed significant material degradation, starting with 100% material remnants at implantation, 56 and 78% at 6 weeks, and 8 and 21% at 26 weeks. Bone formation showed to be rapid for Bio-Oss^®, with 24% at 6 weeks, and a similar value (27%) at 26 weeks. Both CPC-PLGA and CPC-PLGA-CMC showed a continuous temporal increase in bone formation, with 13 and 6% at 6 weeks, and 44 and 32% at 26 weeks. This study showed that CPC-PLGA induces favorable bone responses with  >90% degradation and  >40% new bone formation after an implantation period of 26 weeks.

Hydrogel fibers encapsulating human stem cells in an injectable calcium phosphate scaffold for bone tissue engineering

Human induced pluripotent stem cells (hiPSCs), human embryonic stem cells (hESCs) and human umbilical cord mesenchymal stem cells (hUCMSCs) are exciting cell sources for use in regenerative medicine. There have been no reports on long hydrogel fibers encapsulating stem cells inside an injectable calcium phosphate cement (CPC) scaffold for bone tissue engineering. The objectives of this study were: (1) to develop a novel injectable CPC construct containing hydrogel fibers encapsulating cells for bone engineering, and (2) to investigate and compare cell viability, proliferation and osteogenic differentiation of hiPSC-MSCs, hESC-MSCs and hUCMSCs in injectable CPC. The pastes encapsulating the stem cells were fully injectable under a small injection force, and the injection did not harm the cells, compared with non-injected cells (p  >  0.1). The mechanical properties of the stem cell-CPC construct were much better than those of previous injectable polymers and hydrogels for cell delivery. The hiPSC-MSCs, hESC-MSCs and hUCMSCs in hydrogel fibers in CPC had excellent proliferation and osteogenic differentiation. All three cell types yielded high alkaline phosphatase, runt-related transcription factor, collagen I and osteocalcin expression (mean  ±  SD; n  =  6). Cell-synthesized minerals increased substantially with time (p  <  0.05), with no significant difference among the three types of cells (p  >  0.1). Mineralization by hiPSC-MSCs, hESC-MSCs and hUCMSCs in CPC at 14 d was 13-fold that at 1 d. In conclusion, all three types of cells (hiPSC-MSCs, hESC-MSCs and hUCMSCs) in a CPC scaffold showed high potential for bone tissue engineering, and the novel injectable CPC construct with cell-encapsulating hydrogel fibers is promising for enhancing bone regeneration in dental, craniofacial and orthopedic applications.

Magnesium Phosphate Cement Systems for Hard Tissue Applications: A Review

In the search for more ideal bone graft materials for clinical application, the investigation into ceramic bone cements or bone void filler is ongoing. Calcium phosphate-based materials have been widely explored and implemented for medical use in bone defect repair. Such materials are an excellent choice because the implant mimics the natural chemistry of mineralized bone matrix and in injectable cement form, can be implemented with relative ease. However, of the available calcium phosphate cements, none fully meet the ideal standard, displaying low strengths and acidic setting reactions or slow setting times, and are often very slow to resorb in vivo. The study of magnesium phosphates for bone cements is a relatively new field compared to traditional calcium phosphate bone cements. Although reports are more limited, preliminary studies have shown that magnesium phosphate cements (MPC) may be a strong alternative to calcium phosphates for certain applications. The goal of the present publication is to review the history and achievements of magnesium phosphate-based cements or bone void fillers to date, assess how these cements compare with calcium phosphate competitors and to analyze the future directions and outlook for the research, development, and clinical implementation of these cements.

Nanostructured injectable cell microcarriers for tissue regeneration

Biodegradable polymer microspheres have emerged as cell carriers for the regeneration and repair of irregularly shaped tissue defects due to their injectability, controllable biodegradability and capacity for drug incorporation and release. Notably, recent advances in nanotechnology allowed the manipulation of the physical and chemical properties of the microspheres at the nanoscale, creating nanostructured microspheres mimicking the composition and/or structure of natural extracellular matrix. These nanostructured microspheres, including nanocomposite microspheres and nanofibrous microspheres, have been employed as cell carriers for tissue regeneration. They enhance cell attachment and proliferation, promote positive cell-carrier interactions and facilitate stem cell differentiation for target tissue regeneration. This review highlights the recent advances in nanostructured microspheres that are employed as injectable, biomimetic and cell-instructive cell carriers.

Monolithic calcium phosphate/poly(lactic acid) composite versus calcium phosphate-coated poly(lactic acid) for support of osteogenic differentiation of human mesenchymal stromal cells

Calcium phosphates (CaPs), extensively used synthetic bone graft substitutes, are often combined with other materials with the aim to overcome issues related to poor mechanical properties of most CaP ceramics. Thin ceramic coatings on metallic implants and polymer-ceramic composites are examples of such hybrid materials. Both the properties of the CaP used and the method of incorporation into a hybrid structure are determinant for the bioactivity of the final construct. In the present study, a monolithic composite comprising nano-sized CaP and poly(lactic acid) (PLA) and a CaP-coated PLA were comparatively investigated for their ability to support proliferation and osteogenic differentiation of bone marrow-derived human mesenchymal stromal cells (hMSCs). Both, the PLA/CaP composite, produced using physical mixing and extrusion and CaP-coated PLA, resulting from a biomimetic coating process at near-physiological conditions, supported proliferation of hMSCs with highest rates at PLA/CaP composite. Enzymatic alkaline phosphatase activity as well as the mRNA expression of bone morphogenetic protein-2, osteopontin and osteocalcin were higher on the composite and coated polymer as compared to the PLA control, while no significant differences were observed between the two methods of combining CaP and PLA. The results of this study confirmed the importance of CaP in osteogenic differentiation while the exact properties and the method of incorporation into the hybrid material played a less prominent role.

Sol-Gel Derived Mg-Based Ceramic Scaffolds Doped with Zinc or Copper Ions: Preliminary Results on Their Synthesis, Characterization, and Biocompatibility

Glass-ceramic scaffolds containing Mg have shown recently the potential to enhance the proliferation, differentiation, and biomineralization of stem cells in vitro, property that makes them promising candidates for dental tissue regeneration. An additional property of a scaffold aimed at dental tissue regeneration is to protect the regeneration process against oral bacteria penetration. In this respect, novel bioactive scaffolds containing Mg(2+) and Cu(2+) or Zn(2+), ions known for their antimicrobial properties, were synthesized by the foam replica technique and tested regarding their bioactive response in SBF, mechanical properties, degradation, and porosity. Finally their ability to support the attachment and long-term proliferation of Dental Pulp Stem Cells (DPSCs) was also evaluated. The results showed that conversely to their bioactive response in SBF solution, Zn-doped scaffolds proved to respond adequately regarding their mechanical strength and to be efficient regarding their biological response, in comparison to Cu-doped scaffolds, which makes them promising candidates for targeted dental stem cell odontogenic differentiation and calcified dental tissue engineering.

MiR-221-inhibited adipose tissue-derived mesenchymal stem cells bioengineered in a nano-hydroxy apatite scaffold

The repair of skeletal defects is the main goal of bone tissue engineering. Recent literature highlighted various regulatory roles of microRNAs in stem cell fate determination. In addition, the role of porous hydroxyapatite/polycaprolacton (nHA/PCL) as a bioactive scaffold which enhances adipose tissue-derived mesenchymal stem cells (AT-MSCs) growth and osteogenic differentiation has been proved. The aim of the present study was to investigate the synergistic potential of both down-regulating miR-221 and nHA/PCL scaffold seeding in osteogenic potential of AT-MSCs. After isolation and characterization of AT-MSCs, the transfection of anti-miR-221 was performed into the cells using lipofectamine 2000 and the transfected cells were seeded into a synthesized nHA/PCL scaffold. The DAPI staining confirmed the presence of AT-MSCs on nHA/PCL scaffold. Quantitative expression of osteoblast marker genes, Runx2, and osteocalcin of the transfected cells in the scaffold were evaluated. Interestingly, significant upregulation of transcribed Runx2 and osteocalcin genes (P < 0.01) were observed in miR-221-inhibited nHA/PCL seeded cells. Also, alkaline phosphatase activity (ALP) was significantly higher (P < 0.01) in miR-221-inhibited AT-MSCs seeded on nHA/PCL than those seeded on nHA/PCL or transfected with anti-miR-221, individually. The results of this combination suggest a valuable method for enhancing osteogenesis in AT-MSCs. This method could be applicable for gene-cell therapy of bone defects.

Synthesis and enhanced mechanical properties of MgO substituted hydroxyapatite: a bone substitute material

Hydroxyapatite (HAp) nano-ceramic powder was synthesized successfully via microwave irradiation technique.

Nanoparticles highly loaded with gentamicin sulfate by a combination of polyhydroxylated macromonomers and ROMP for the synthesis of bioactive biomaterials

Nanoparticles highly loaded with gentamicin sulfate were synthesized by ring-opening metathesis copolymerization in a dispersion of norbornene with modified polyhydroxylated macromonomers.