Intrinsic Osteoinductivity of Porous Titanium Scaffold for Bone Tissue Engineering

Photobiomodulation Therapy Improves Repair of Bone Defects Filled by Inorganic Bone Matrix and Fibrin Heterologous Biopolymer

Biomaterials are used extensively in graft procedures to correct bone defects, interacting with the body without causing adverse reactions. The aim of this pre-clinical study was to analyze the effects of photobiomodulation therapy (PBM) with the use of a low-level laser in the repair process of bone defects filled with inorganic matrix (IM) associated with heterologous fibrin biopolymer (FB). A circular osteotomy of 4 mm in the left tibia was performed in 30 Wistar male adult rats who were randomly divided into three groups: G1 = IM + PBM, G2 = IM + FB and G3 = IM + FB + PBM. PBM was applied at the time of the experimental surgery and three times a week, on alternate days, until euthanasia, with 830 nm wavelength, in two points of the operated site. Five animals from each group were euthanized 14 and 42 days after surgery. In the histomorphometric analysis, the percentage of neoformed bone tissue in G3 (28.4% ± 2.3%) was higher in relation to G1 (24.1% ± 2.91%) and G2 (22.2% ± 3.11%) at 14 days and at 42 days, the percentage in G3 (35.1% ± 2.55%) was also higher in relation to G1 (30.1% ± 2.9%) and G2 (31.8% ± 3.12%). In the analysis of the birefringence of collagen fibers, G3 showed a predominance of birefringence between greenish-yellow in the neoformed bone tissue after 42 days, differing from the other groups with a greater presence of red-orange fibers. Immunohistochemically, in all experimental groups, it was possible to observe immunostaining for osteocalcin (OCN) near the bone surface of the margins of the surgical defect and tartrate-resistant acid phosphatase (TRAP) bordering the newly formed bone tissue. Therefore, laser photobiomodulation therapy contributed to improving the bone repair process in tibial defects filled with bovine biomaterial associated with fibrin biopolymer derived from snake venom.

Poly-ε-Caprolactone 3D-Printed Porous Scaffold in a Femoral Condyle Defect Model Induces Early Osteo-Regeneration

Large bone reconstruction following trauma poses significant challenges for reconstructive surgeons, leading to a healthcare burden for health systems, long-term pain for patients, and complex disorders such as infections that are difficult to resolve. The use of bone substitutes is suboptimal for substantial bone loss, as they induce localized atrophy and are generally weak, and unable to support load. A combination of strong polycaprolactone (PCL)-based scaffolds, with an average channel size of 330 µm, enriched with 20% w/w of hydroxyapatite (HA), β-tricalcium phosphate (TCP), or Bioglass 45S5 (Bioglass), has been developed and tested for bone regeneration in a critical-size ovine femoral condyle defect model. After 6 weeks, tissue ingrowth was analyzed using X-ray computed tomography (XCT), Backscattered Electron Microscopy (BSE), and histomorphometry. At this point, all materials promoted new bone formation. Histological analysis showed no statistical difference among the different biomaterials (p > 0.05), but PCL-Bioglass scaffolds enhanced bone formation in the center of the scaffold more than the other types of materials. These materials show potential to promote bone regeneration in critical-sized defects on load-bearing sites.

Forged to heal: The role of metallic cellular solids in bone tissue engineering

Metallic cellular solids, made of biocompatible alloys like titanium, stainless steel, or cobalt-chromium, have gained attention for their mechanical strength, reliability, and biocompatibility. These three-dimensional structures provide support and aid tissue regeneration in orthopedic implants, cardiovascular stents, and other tissue engineering cellular solids. The design and material chemistry of metallic cellular solids play crucial roles in their performance: factors such as porosity, pore size, and surface roughness influence nutrient transport, cell attachment, and mechanical stability, while their microstructure imparts strength, durability and flexibility. Various techniques, including additive manufacturing and conventional fabrication methods, are utilized for producing metallic biomedical cellular solids, each offering distinct advantages and drawbacks that must be considered for optimal design and manufacturing. The combination of mechanical properties and biocompatibility makes metallic cellular solids superior to their ceramic and polymeric counterparts in most load bearing applications, in particular under cyclic fatigue conditions, and more in general in application that require long term reliability. Although challenges remain, such as reducing the production times and the associated costs or increasing the array of available materials, metallic cellular solids showed excellent long-term reliability, with high survival rates even in long term follow-ups.

Investigations into the effects of scaffold microstructure on slow-release system with bioactive factors for bone repair

In recent years, bone tissue engineering (BTE) has played an essential role in the repair of bone tissue defects. Although bioactive factors as one component of BTE have great potential to effectively promote cell differentiation and bone regeneration, they are usually not used alone due to their short effective half-lives, high concentrations, etc. The release rate of bioactive factors could be controlled by loading them into scaffolds, and the scaffold microstructure has been shown to significantly influence release rates of bioactive factors. Therefore, this review attempted to investigate how the scaffold microstructure affected the release rate of bioactive factors, in which the variables included pore size, pore shape and porosity. The loading nature and the releasing mechanism of bioactive factors were also summarized. The main conclusions were achieved as follows: i) The pore shapes in the scaffold may have had no apparent effect on the release of bioactive factors but significantly affected mechanical properties of the scaffolds; ii) The pore size of about 400 μm in the scaffold may be more conducive to controlling the release of bioactive factors to promote bone formation; iii) The porosity of scaffolds may be positively correlated with the release rate, and the porosity of 70%-80% may be better to control the release rate. This review indicates that a slow-release system with proper scaffold microstructure control could be a tremendous inspiration for developing new treatment strategies for bone disease. It is anticipated to eventually be developed into clinical applications to tackle treatment-related issues effectively.

High porosity 3D printed titanium mesh allows better bone regeneration

BACKGROUND

Most patients with insufficient bone mass suffer from severe horizontal or vertical bone defects in oral implant surgery. The purpose of this study was to compare the bone regeneration effects of titanium meshes with different porosity in the treatment of bone defects.

METHODS

Nine beagle dogs were equally divided into three groups based on execution time. Three months after the extraction of the first to fourth premolars of the mandible, three bone defects were randomly made in the mandible. Bone particles and three kinds of three-dimensional (3D) printed titanium nets with different porosities (low porosity group (LP), 55%; medium porosity group (MP), 62%; and high porosity group (HP), 68%) were replanted in situ. The beagles were killed 4, 8, and 12 weeks after surgery. Formalin-fixed specimens were embedded in acrylic resin. The specimens were stained with micro-CT, basic fuchsin staining, and toluidine blue staining.

RESULTS

Micro-CT analysis showed that the trabecular thickness, trabecular number, and bone volume fraction of the HP group were higher than those of the other two groups. Moreover, the trabecular separation of the HP group decreased slightly and was lower than that of the MP and LP groups. Histological staining analysis showed that the trabecular number in the HP group was higher than in the other two groups at 8 and 12 weeks, and the bone volume fraction of the HP was higher than that in the other two groups at 12 weeks. Moreover, the trabecular thickness of the MP was higher than that of the LP group at 12 weeks and the trabecular separation was lower in the HP group at 4 and 8 weeks. The differences were statistically significant (p < 0.05).

CONCLUSION

A 3D printed titanium mesh with HP in a certain range may have more advantages than a titanium mesh with LP in repairing large bone defects.

Mechanical Characteristics and Bioactivity of Nanocomposite Hydroxyapatite/Collagen Coated Titanium for Bone Tissue Engineering

In the present study, we have analyzed the mechanical characteristics and bioactivity of titanium coating with hydroxyapatite/bovine collagen. Hydroxyapatite (HAp) was synthesized from a Pinctada maxima shell and has a stoichiometry (Ca/P) of 1.72 and a crystallinity of 92%, suitable for coating materials according to ISO and Food and Drug Administration (FDA) standards. Titanium (Ti) substrate coatings were fabricated at HAp concentrations of 1% (Ti/HAp-1) and 3% (Ti/HAp-3) and a bovine collagen concentration of 1% (Ti/HAp/Coll) by the electrophoresis deposition (EPD) method. The compressive strength of Ti/HAp-1 and Ti/HAp-3 was 87.28 and 86.19 MPa, respectively, and it increased significantly regarding the control/uncoated Ti (46.71 MPa). Furthermore, the Ti/HAp-coll (69.33 MPa) has lower compressive strength due to collagen substitution (1%). The bioactivity of Ti substrates after the immersion into simulated body fluids (SBF) for 3-10 days showed a high apatite growth (Ca²⁺ and PO43-), according to XRD, FTIR, and SEM-EDS results, significantly on the Ti/HAp-coll.

Nanohydroxyapatite-Protein Interface in Composite Sintered Scaffold Influences Bone Regeneration in Rabbit Ulnar Segmental Defect

The healing physiology of bone repair and remodeling that occurs after normal fracture is well orchestrated. However, it fails in complex clinical conditions and hence requires augmentation by grafts. In this study, composite nanohydroxyapatite (nHA), poly(hydroxybutyrate) (PHB) and poly(ɛ-caprolactone) (PCL) constituted microspheres sintered three-dimensional scaffold were evaluated in rabbit ulnar segmental defect. A composite scaffold using PHB-PCL-nHA microspheres was developed with protein interface by solvent/non-solvent sintering to provide multiple cues such as biocomposition, cancellous bone equivalent meso-micro multi-scale porosity, and compressive strength. In vitro DNA quantification and alkaline phosphatase (ALP) assays revealed that the protein interfaced composite scaffolds supported osteoblast proliferation and mineralization significantly higher than scaffolds without protein and TCPS (p < 0.05). Scanning electron micrographs of osteoblasts cultured scaffolds demonstrated cell-matrix interaction, cell spreading, colonization and filopodial extension across the porous voids. Cylindrical scaffolds (5 × 10 mm) were implanted following segmental defect (10 mm) in rabbit ulnar bone and compared with untreated control. Radiography (4, 8 and 12 weeks) and µ-computed tomography (12 weeks) analysis showed directional bone tissue formation by bridging defective site in both scaffolds with and without protein interface. Whereas, undesired sclerotic-like tissue formation was observed in control groups from 8 weeks. Histology by hot Stevenel's blue and van Gieson's picrofuchsin staining has confirmed enhanced bone maturation in scaffold groups while presence of osteoids was observed in control after 12 weeks. Thus, the developed composite matrices exhibits osteoinductive, osteoconductive properties and demonstrates its bone regenerative potential owing to its compositional, micro & macro structural and mechanical properties. Graphical abstract.

In vivo evaluation of additively manufactured multi-layered scaffold for the repair of large osteochondral defects

The repair of osteochondral defects is one of the major clinical challenges in orthopaedics. Well-established osteochondral tissue engineering methods have shown promising results for the early treatment of small defects. However, less success has been achieved for the regeneration of large defects, which is mainly due to the mechanical environment of the joint and the heterogeneous nature of the tissue. In this study, we developed a multi-layered osteochondral scaffold to match the heterogeneous nature of osteochondral tissue by harnessing additive manufacturing technologies and combining the established art laser sintering and material extrusion techniques. The developed scaffold is based on a titanium and polylactic acid matrix-reinforced collagen “sandwich” composite system. The microstructure and mechanical properties of the scaffold were examined, and its safety and efficacy in the repair of large osteochondral defects were tested in an ovine condyle model. The 12-week in vivo evaluation period revealed extensive and significantly higher bone in-growth in the multi-layered scaffold compared with the collagen–HAp scaffold, and the achieved stable mechanical fixation provided strong support to the healing of the overlying cartilage, as demonstrated by hyaline-like cartilage formation. The histological examination showed that the regenerated cartilage in the multi-layer scaffold group was superior to that formed in the control group. Chondrogenic genes such as aggrecan and collagen-II were upregulated in the scaffold and were higher than those in the control group. The findings showed the safety and efficacy of the cell-free “translation-ready” osteochondral scaffold, which has the potential to be used in a one-step surgical procedure for the treatment of large osteochondral defects.

On-Growth and In-Growth Osseointegration Enhancement in PM Porous Ti-Scaffolds by Two Different Bioactivation Strategies: Alkali Thermochemical Treatment and RGD Peptide Coating

A lack of primary stability and osteointegration in metallic implants may result in implant loosening and failure. Adding porosity to metallic implants reduces the stress shielding effect and improves implant performance, allowing the surrounding bone tissue to grow into the scaffold. However, a bioactive surface is needed to stimulate implant osteointegration and improve mechanical stability. In this study, porous titanium implants were produced via powder sintering to create different porous diameters and open interconnectivity. Two strategies were used to generate a bioactive surface on the metallic foams: (1) an inorganic alkali thermochemical treatment, (2) grafting a cell adhesive tripeptide (RGD). RGD peptides exhibit an affinity for integrins expressed by osteoblasts, and have been reported to improve osteoblast adhesion, whereas the thermochemical treatment is known to improve titanium implant osseointegration upon implantation. Bioactivated scaffolds and control samples were implanted into the tibiae of rabbits to analyze the effect of these two strategies in vivo regarding bone tissue regeneration through interconnected porosity. Histomorphometric evaluation was performed at 4 and 12 weeks after implantation. Bone-to-implant contact (BIC) and bone in-growth and on-growth were evaluated in different regions of interest (ROIs) inside and outside the implant. The results of this study show that after a long-term postoperative period, the RGD-coated samples presented higher quantification values of quantified newly formed bone tissue in the implant's outer area. However, the total analyzed bone in-growth was observed to be slightly greater in the scaffolds treated with alkali thermochemical treatment. These results suggest that both strategies contribute to enhancing porous metallic implant stability and osteointegration, and a combination of both strategies might be worth pursuing.

Histological Processing of CAD/CAM Titanium Scaffold after Long-Term Failure in Cranioplasty

Cranioplasty is a frequently performed procedure after craniectomy and includes several techniques with different materials. Due to high overall complication rates, alloplastic implants are removed in many cases. Lack of implant material osseointegration is often assumed as a reason for failure, but no study has proven this in cranioplasty. This study histologically evaluates the osteointegration of a computer-aided design and computer-aided manufacturing (CAD/CAM) titanium scaffold with an open mesh structure used for cranioplasty. A CAD/CAM titanium scaffold was removed due to late soft tissue complications 7.6 years after cranioplasty. The histological analyses involved the preparation of non-decalcified slices from the scaffold’s inner and outer sides as well as a light-microscopic evaluation, including the quantification of the bone that had formed over the years. Within the scaffold pores, vital connective tissue with both blood vessels and nerves was found. Exclusive bone formation only occurred at the edges of the implant, covering 0.21% of the skin-facing outer surface area. The inner scaffold surface, facing towards the brain, did not show any mineralization at all. Although conventional alloplastic materials for cranioplasty reduce surgery time and provide good esthetic results while mechanically protecting the underlying structures, a lack of adequate stimuli could explain the limited bone formation found. CAD/CAM porous titanium scaffolds alone insufficiently osseointegrate in such large bone defects of the skull. Future research should investigate alternative routes that enable long-term osteointegration in order to reduce complication rates after cranioplasty. Opportunities could be found in mechano-biologically optimized scaffolds, material modifications, surface coatings, or other routes to sustain bone formation.

Osteoconductive Effect of a Nanocomposite Membrane Treated with UV Radiation

Modulation of the bio-regenerative characteristics of materials is an indispensable requirement in tissue engineering. Particularly, in bone tissue engineering, the promotion of the osteoconductive phenomenon determines the elemental property of a material be used therapeutically. In addition to the chemical qualities of the constituent materials, the three-dimensional surface structure plays a fundamental role that various methods are expected to modulate in a number of ways, one most promising of which is the use of different types of radiation. In the present manuscript, we demonstrate in a calvarial defect model, that treatment with ultraviolet irradiation allows modification of the osteoconductive characteristics in a biomaterial formed by gelatin and chitosan, together with the inclusion of hydroxyapatite and titanium oxide nanoparticles.

Comprehensive Review on Design and Manufacturing of Bio-scaffolds for Bone Reconstruction

Bio-scaffolds are synthetic entities widely employed in bone and soft-tissue regeneration applications. These bio-scaffolds are applied to the defect site to provide support and favor cell attachment and growth, thereby enhancing the regeneration of the defective site. The progressive research in bio-scaffold fabrication has led to identification of biocompatible and mechanically stable materials. The difficulties in obtaining grafts and expenditure incurred in the transplantation procedures have also been overcome by the implantation of bio-scaffolds. Drugs, cells, growth factors, and biomolecules can be embedded with bio-scaffolds to provide localized treatments. The right choice of materials and fabrication approaches can help in developing bio-scaffolds with required properties. This review mostly focuses on the available materials and bio-scaffold techniques for bone and soft-tissue regeneration application. The first part of this review gives insight into the various classes of biomaterials involved in bio-scaffold fabrication followed by design and simulation techniques. The latter discusses the various additive, subtractive, hybrid, and other improved techniques involved in the development of bio-scaffolds for bone regeneration applications. Techniques involving multimaterial printing and multidimensional printing have also been briefly discussed.

Bilayered scaffold with 3D printed stiff subchondral bony compartment to provide constant mechanical support for long-term cartilage regeneration

BACKGROUND/OBJECTIVE

We seek to figure out the effect of stable and powerful mechanical microenvironment provided by Ti alloy as a part of subchondral bone scaffold on long-term cartilage regeneration.Methods: we developed a bilayered osteochondral scaffold based on the assumption that a stiff subchondral bony compartment would provide stable mechanical support for cartilage regeneration and enhance subchondral bone regeneration. The subchondral bony compartment was prepared from 3D printed Ti alloy, and the cartilage compartment was created from a freeze-dried collagen sponge, which was reinforced by poly-lactic-co-glycolic acid (PLGA).

RESULTS

In vitro evaluations confirmed the biocompatibility of the scaffold materials, while in vivo evaluations demonstrated that the mechanical support provided by 3D printed Ti alloy layer plays an important role in the long-term regeneration of cartilage by accelerating osteochondral formation and its integration with the adjacent host tissue in osteochondral defect model at rabbit femoral trochlea after 24 weeks.

CONCLUSION

Mechanical support provided by 3D printing Ti alloy promotes cartilage regeneration by promoting subchondral bone regeneration and providing mechanical support platform for cartilage synergistically.

TRANSLATIONAL POTENTIAL STATEMENT

The raw materials used in our double-layer osteochondral scaffolds are all FDA approved materials for clinical use. 3D printed titanium alloy scaffolds can promote bone regeneration and provide mechanical support for cartilage regeneration, which is very suitable for clinical scenes of osteochondral defects. In fact, we are conducting clinical trials based on our scaffolds. We believe that in the near future, the scaffold we designed and developed can be formally applied in clinical practice.

Lateral pterygoid muscle enthesis reconstruction in total temporomandibular joint replacement: An animal experiment with radiological correlation

A novel total temporomandibular joint replacement (TMJR) was developed with CADskills BV (Ghent, Belgium), aiming to achieve reinsertion of the (LPM) onto a scaffold in the implant. In order to investigate the possibility of reinsertion of the LPM, an animal experiment was conducted. An in vivo sheep experiment was conducted, which involved implanting sheep with a TMJR. Clinical parameters were recorded regularly and computed tomography (CT) scan images of two randomly selected sheep per scan were made at 1, 3, and 6 months. After 9.5 months, the sheep were euthanized, and CT scans of all animals were performed in order to evaluate the LPM's enthesis. A total of 13 sheep were implanted with a TMJR. One sheep was used as a sham. Radiographs revealed four outcome types of enthesis reconstruction. In four sheep, there was no reconstruction between the implant and the LPM. In three sheep, there was a purely soft tissue connection of 0.5-0.9 mm (average 0.7 mm) between the ostectomized bony LPM insertion and the implant's lattice structure. A combination of partial bony and partial soft tissue enthesis attachment (0.3-0.5 mm, average 0.4 mm) was found in three sheep. A bony ingrowth of the enthesis into the scaffold occurred in two sheep. A secondary bony connection between the mandible and the insertion of the LPM was found in 10 of 13 sheep. Four fossa components were found to be displaced, yet TMJ function remained in these ewes. The heterotopic ossification that was seen may be a confounding factor in these results. This in vivo experiment showed promising results for improving the current approach to TMJR with the possibility of restoring the laterotrusive function. The fossa displacement was considered to be due to insufficient fixation and predominant laterotrusive force not allowing for proper osseointegration. Further optimization of the reattachment technique, scaffold position and surface area should be done, as well as trials in humans to evaluate the effect of proper revalidation.

The Effect of Electrophoretic Deposition Parameters on the Microstructure and Adhesion of Zein Coatings to Titanium Substrates

Zein coatings were obtained by electrophoretic deposition (EPD) on commercially pure titanium substrates in an as-received state and after various chemical treatments. The properties of the zein solution, zeta potential and conductivity, at varying pH values were investigated. It was found that the zein content and the ratio of water to ethanol of the solution used for EPD, as well as the process voltage value and time, significantly influence the morphology of coatings. The deposits obtained from the solution containing 150 g/L and 200 g/L of zein and 10 vol % of water and 90 vol % of ethanol, about 4-5 μm thick, were dense and homogeneous. The effect of chemical treatment of the Ti substrate surface prior to EPD on coating adhesion to the substrate was determined. The coatings showed the highest adhesion to the as-received and anodized substrates due to the presence of a thick TiO2 layer on their surfaces and the presence of specific surface features. Coated titanium substrates showed slightly lower electrochemical corrosion resistance than the uncoated one in Ringer's solution. The coatings showed a well-developed surface topography compared to the as-received substrate, and they demonstrated hydrophilic nature. The present results provide new insights for the further development of zein-based composite coatings for biomedical engineering applications.

Osteochondral scaffolds for early treatment of cartilage defects in osteoarthritic joints: from bench to clinic

Osteoarthritis is a degenerative joint disease, typified by the loss in the quality of cartilage and bone at the interface of a synovial joint, resulting in pain, stiffness and reduced mobility. The current surgical treatment for advanced stages of the disease is joint replacement, where the non-surgical therapeutic options or less invasive surgical treatments are no longer effective. These are major surgical procedures which have a substantial impact on patients' quality of life and lifetime risk of requiring revision surgery. Treatments using regenerative methods such as tissue engineering methods have been established and are promising for the early treatment of cartilage degeneration in osteoarthritis joints. In this approach, 3-dimensional scaffolds (with or without cells) are employed to provide support for tissue growth. However, none of the currently available tissue engineering and regenerative medicine products promotes satisfactory durable regeneration of large cartilage defects. Herein, we discuss the current regenerative treatment options for cartilage and osteochondral (cartilage and underlying subchondral bone) defects in the articulating joints. We further identify the main hurdles in osteochondral scaffold development for achieving satisfactory and durable regeneration of osteochondral tissues. The evolution of the osteochondral scaffolds - from monophasic to multiphasic constructs - is overviewed and the osteochondral scaffolds that have progressed to clinical trials are examined with respect to their clinical performances and their potential impact on the clinical practices. Development of an osteochondral scaffold which bridges the gap between small defect treatment and joint replacement is still a grand challenge. Such scaffold could be used for early treatment of cartilage and osteochondral defects at early stage of osteoarthritis and could either negate or delay the need for joint replacements.

Osteogenic potential of human adipose derived stem cells (hASCs) seeded on titanium trabecular spinal cages

Spine degenerative conditions are becoming increasingly prevalent, affecting about 5.7% of the population in Europe, resulting in a significant reduction of life's quality. Up to now, many materials have been used in manufacturing cage implants, used as graft substitutes, to achieve immediate and long-term spinal fixation. Particularly, titanium and its alloys are emerging as valuable candidates to develop new types of cages. The aim of this in vitro study was to evaluate the adhesion, proliferation and osteogenic differentiation of adipose derived mesenchymal stem cells (ASCs) seeded on trabecular titanium cages. ASCs adhered, proliferated and produced an abundant extracellular matrix during the 3 weeks of culture. In the presence of osteogenic medium, ASCs differentiated into osteoblast-like cells: the expression of typical bone genes, as well as the alkaline phosphatase activity, was statistically higher than in controls. Furthermore, the dispersive spectrometry microanalysis showed a marked increase of calcium level in cells grown in osteogenic medium. Plus, our preliminary data about osteoinduction suggest that this titanium implant has the potential to induce the ASCs to produce a secretome able to trigger a shift in the ASCs phenotype, possibly towards the osteogenic differentiation, as illustrated by the qRT-PCR and ALP biochemical assay results. The trabecular porous organization of these cages is rather similar to the cancellous bone structure, thus allowing the bone matrix to colonize it efficiently; for these reasons we can conclude that the architecture of this cage may play a role in modulating the osteoinductive capabilities of the implant, thus encouraging its engagement in in vivo studies for the treatment of spinal deformities and diseases.

Human Mesenchymal Stem Cell Derived Exosomes Enhance Cell-Free Bone Regeneration by Altering Their miRNAs Profiles

Implantation of stem cells for tissue regeneration faces significant challenges such as immune rejection and teratoma formation. Cell-free tissue regeneration thus has a potential to avoid these problems. Stem cell derived exosomes do not cause immune rejection or generate malignant tumors. Here, exosomes that can induce osteogenic differentiation of human mesenchymal stem cells (hMSCs) are identified and used to decorate 3D-printed titanium alloy scaffolds to achieve cell-free bone regeneration. Specifically, the exosomes secreted by hMSCs osteogenically pre-differentiated for different times are used to induce the osteogenesis of hMSCs. It is discovered that pre-differentiation for 10 and 15 days leads to the production of osteogenic exosomes. The purified exosomes are then loaded into the scaffolds. It is found that the cell-free exosome-coated scaffolds regenerate bone tissue as efficiently as hMSC-seeded exosome-free scaffolds within 12 weeks. RNA-sequencing suggests that the osteogenic exosomes induce the osteogenic differentiation by using their cargos, including upregulated osteogenic miRNAs (Hsa-miR-146a-5p, Hsa-miR-503-5p, Hsa-miR-483-3p, and Hsa-miR-129-5p) or downregulated anti-osteogenic miRNAs (Hsa-miR-32-5p, Hsa-miR-133a-3p, and Hsa-miR-204-5p), to activate the PI3K/Akt and MAPK signaling pathways. Consequently, identification of osteogenic exosomes secreted by pre-differentiated stem cells and the use of them to replace stem cells represent a novel cell-free bone regeneration strategy.

Electrochemical Deposition of Nanostructured Hydroxyapatite Coating on Titanium with Enhanced Early Stage Osteogenic Activity and Osseointegration

Purpose

The aim of research is to fabricate nanostructured hydroxyapatite (HA) coatings on the titanium via electrochemical deposition (ED). Additionally, the biological properties of the ED-produced HA (EDHA) coatings with a plate-like nanostructure were evaluated in vitro and in vivo by undertaking comparisons with those prepared by acid/alkali (AA) treatment and by plasma spray-produced HA (PSHA) nanotopography-free coatings.

Materials and Methods

Nanoplate-like HA coatings were prepared through ED, and nanotopography-free PSHA coatings were fabricated. The surface morphology, phase composition, roughness, and wettability of these samples were investigated. Furthermore, the growth, proliferation, and osteogenic differentiation of MC3T3-E1 cells cultured on each sample were evaluated via in vitro experiments. Histological assessment and push-out tests for the bone–implant interface were performed to explore the effect of the EDHA coatings on the interfacial osseointegration in vivo.

Results

XRD analysis showed that the strongest intensity for the EDHA coatings was at the (002) plane rather than at the regular (211) plane. Relatively higher surface roughness and greater wettability were observed for the EDHA coatings. Cellular experiments revealed that the plate-like nanostructured EDHA coatings not only possessed an ability, similar to that of PSHA coatings, to promote the adhesion and proliferation of MC3T3-E1 cells but also demonstrated significantly enhanced early or intermediate markers of osteogenic differentiation. Significant osseointegration enhancement in the early stage of implantation period and great bonding strength were observed at the interface of bone and EDHA samples. In comparison, relatively weak osseointegration and bonding strength of the bone–implant interface were observed for the AA treatment.

Conclusion

The biological performance of the plate-like nanostructured EDHA coating, which was comparable with that of the PSHA, improves early-stage osteogenic differentiation and osseointegration abilities and has great potential for enhancing the initial stability and long-term survival of uncemented or 3D porous titanium implants.

Development of Polymeric Nanocomposite (Xyloglucan-co-Methacrylic Acid/Hydroxyapatite/SiO2) Scaffold for Bone Tissue Engineering Applications-In-Vitro Antibacterial, Cytotoxicity and Cell Culture Evaluation

Advancement and innovation in bone regeneration, specifically polymeric composite scaffolds, are of high significance for the treatment of bone defects. Xyloglucan (XG) is a polysaccharide biopolymer having a wide variety of regenerative tissue therapeutic applications due to its biocompatibility, in-vitro degradation and cytocompatibility. Current research is focused on the fabrication of polymeric bioactive scaffolds by freeze drying method for nanocomposite materials. The nanocomposite materials have been synthesized from free radical polymerization using n-SiO₂ and n-HAp XG and Methacrylic acid (MAAc). Functional group analysis, crystallinity and surface morphology were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) techniques, respectively. These bioactive polymeric scaffolds presented interconnected and well-organized porous morphology, controlled precisely by substantial ratios of n-SiO₂. The swelling analysis was also performed in different media at varying temperatures (27, 37 and 47 °C) and the mechanical behavior of the dried scaffolds is also investigated. Antibacterial activities of these scaffolds were conducted against pathogenic gram-positive and gram-negative bacteria. Besides, the biological behavior of these scaffolds was evaluated by the Neutral Red dye assay against the MC3T3-E1 cell line. The scaffolds showed interesting properties for bone tissue engineering, including porosity with substantial mechanical strength, biodegradability, biocompatibility and cytocompatibility behavior. The reported polymeric bioactive scaffolds can be aspirant biomaterials for bone tissue engineering to regenerate defecated bone.

Osteogenesis and bone remodeling: A focus on growth factors and bioactive peptides

Bone is one of the most frequently transplanted tissues. The bone structure and its physiological function and stem cells biology were known to be closely related to each other for many years. Bone is considered a home to the well-known systems of postnatal mesenchymal stem cells (MSCs). These bone resident MSCs provide a range of growth factors (GF) and cytokines to support cell growth following injury. These GFs include a group of proteins and peptides produced by different cells which are regulators of important cell functions such as division, migration, and differentiation. GF signaling controls the formation and development of the MSCs condensation and plays a critical role in regulating osteogenesis, chondrogenesis, and bone/mineral homeostasis. Thus, a combination of both MSCs and GFs receives high expectations in regenerative medicine, particularly in bone repair applications. It is known that the delivery of exogenous GFs to the non-union bone fracture site remarkably improves healing results. Here we present updated information on bone tissue engineering with a specific focus on GF characteristics and their application in cellular functions and tissue healing. Moreover, the interrelation of GFs with the damaged bone microenvironment and their mechanistic functions are discussed.

Synthesis of Silver-Coated Bioactive Nanocomposite Scaffolds Based on Grafted Beta-Glucan/Hydroxyapatite via Freeze-Drying Method: Anti-Microbial and Biocompatibility Evaluation for Bone Tissue Engineering

Advancement and development in bone tissue engineering, particularly that of composite scaffolds, are of great importance for bone tissue engineering. We have synthesized polymeric matrix using biopolymer (β-glucan), acrylic acid, and nano-hydroxyapatite through free radical polymerization method. Bioactive nanocomposite scaffolds (BNSs) were fabricated using the freeze-drying method and Ag was coated by the dip-coating method. The scaffolds have been characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction analysis (XRD) to investigate their functional groups, surface morphology, and phase analysis, respectively. The pore size and porosity of all BNS samples were found to be dependent on silver concentration. Mechanical testing of all BNS samples have substantial compressive strength in dry form that is closer to cancellous bone. The samples of BNS showed substantial antibacterial effect against DH5 alpha E. coli. The biological studies conducted using the MC3T3-E1 cell line via neutral red dye assay on the scaffolds have found to be biocompatible and non-cytotoxic. These bioactive scaffolds can bring numerous applications for bone tissue repairs and regenerations.

Arabinoxylan-co-AA/HAp/TiO2 nanocomposite scaffold a potential material for bone tissue engineering: An in vitro study

Arabinoxylan (AX) is a natural biological macromolecule with several potential biomedical applications. In this research, AX, nano-hydroxyapatite (n-HAp) and titanium dioxide (TiO₂) based polymeric nanocomposite scaffolds were fabricated by the freeze-drying method. The physicochemical characterizations of these polymeric nanocomposite scaffolds were performed for surface morphology, porosity, swelling, biodegradability, mechanical, and biological properties. The scaffolds exhibited good porosity and rough surface morphology, which were efficiently controlled by TiO₂ concentrations. MC3T3-E1 cells were employed to conduct the biocompatibility of these scaffolds. Scaffolds showed unique biocompatibility in vitro and was favorable for cell attachment and growth. PNS3 proved more biocompatible, showed interconnected porosity and substantial mechanical strength compared to PNS1, PNS2 and PNS4. Furthermore, it has also showed more affinity to cells and cell growth. The results illustrated that the bioactive nanocomposite scaffold has the potential to find applications in the tissue engineering field.

Porous Tantalum and Titanium in Orthopedics: A Review

Porous metal is metal with special porous structures, which can offer high biocompatibility and low Young's modulus to satisfy the need for orthopedic applications. Titanium and tantalum are the most widely used porous metals in orthopedics due to their excellent biomechanical properties and biocompatibility. Porous titanium and tantalum have been studied and applied for a long history until now. Here in this review, various manufacturing methods of titanium and tantalum porous metals are introduced. Application of these porous metals in different parts of the body are summarized, and strengths and weaknesses of these porous metal implants in clinical practice are discussed frankly for future improvement from the viewpoint of orthopedic surgeons. Then according to the requirements from clinics, progress in research for clinical use is illustrated in four aspects. Various creative designs of microporous and functionally gradient structure, surface modification, and functional compound systems of porous metal are exhibited as reference for future research. Finally, the directions of orthopedic porous metal development were proposed from the clinical view based on the rapid progress of additive manufacturing. Controllable design of both macroscopic anatomical bionic shape and microscopic functional bionic gradient porous metal, which could meet the rigorous mechanical demand of bone reconstruction, should be developed as the focus. The modification of a porous metal surface and construction of a functional porous metal compound system, empowering stronger cell proliferation and antimicrobial and antineoplastic property to the porous metal implant, also should be taken into consideration.

Surface properties and bioactivity of TiO2 nanotube array prepared by two-step anodic oxidation for biomedical applications

A highly ordered TiO₂ nanotube array has been prepared on a commercial pure titanium substrate in a hydrofluoric (HF) electrolyte using a DC power source through two-step anodic oxidation. The morphology, composition, wettability and surface energy of the nanotube array have been characterized by using a field-emission scanning electron microscope (FE-SEM), a transmission electron microscope (JEM-2010) with energy-dispersive X-ray spectrometer EDX (INCA OXFORD), X-ray diffraction method, an atomic force microscope (AFM), an optical contact angle measuring device and the Owens method with two liquids. The electrochemical behaviours of anodic oxidation films with different structures have been investigated in Sodium Lactate Ringer's Injection at 37±1°C by potentiodynamic polarization curve and electrochemical impedance spectroscopy. The formation mechanism of the nanotube array and the advantages of two-step oxidation have been discussed according to the experimental observation and the characterized results. Meanwhile, the structural changes of nanotubes are analysed according to the results of impedance spectroscopy. Cytotoxicity testing and cell adhesion and proliferation have been studied in order to evaluate the bioactivity of the nanotube array film. The diameters of nanotubes are in the range of 120-140 nm. The nanotube surface shows better wettability and higher surface energy compared to the bare substrate. The nanotube surface exhibits a wide passivation range and good corrosion resistance. The growth of the nanotube array is the result of the combined action of the anodization and field-assisted dissolution. The nanotube array by two-step oxidation becomes more regular and orderly. Moreover, the nanotube array surface is non-toxic and favourable to cell adhesion and proliferation. Such nanotube array films are expected to have significant biomedical applications.

Role of the Complement System in the Response to Orthopedic Biomaterials

Various synthetic biomaterials are used to replace lost or damaged bone tissue that, more or less successfully, osseointegrate into the bone environment. Almost all biomaterials used in orthopedic medicine activate the host-immune system to a certain degree. The complement system, which is a crucial arm of innate immunity, is rapidly activated by an implanted foreign material into the human body, and it is intensely studied regarding blood-contacting medical devices. In contrast, much less is known regarding the role of the complement system in response to implanted bone biomaterials. However, given the increasing knowledge of the complement regulation of bone homeostasis, regeneration, and inflammation, complement involvement in the immune response following biomaterial implantation into bone appears very likely. Moreover, bone cells can produce complement factors and are target cells of activated complement. Therefore, new bone formation or bone resorption around the implant area might be greatly influenced by the complement system. This review aims to summarize the current knowledge on biomaterial-mediated complement activation, with a focus on materials primarily used in orthopedic medicine. In addition, methods to modify the interactions between the complement system and bone biomaterials are discussed, which might favor osseointegration and improve the functionality of the device.

Two Different Strategies to Enhance Osseointegration in Porous Titanium: Inorganic Thermo-Chemical Treatment Versus Organic Coating by Peptide Adsorption

In this study, highly-interconnected porous titanium implants were produced by powder sintering with different porous diameters and open interconnectivity. The actual foams were produced using high cost technologies: Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), and spark plasma sintering, and the porosity and/or interconnection was not optimized. The aim was to generate a bioactive surface on foams using two different strategies, based on inorganic thermo-chemical treatment and organic coating by peptide adsorption, to enhance osseointegration. Porosity was produced using NaCl as a space holder and polyethyleneglicol as a binder phase. Static and fatigue tests were performed in order to determine mechanical behaviors. Surface bioactivation was performed using a thermo-chemical treatment or by chemical adsorption with peptides. Osteoblast-like cells were cultured and cytotoxicity was measured. Bioactivated scaffolds and a control were implanted in the tibiae of rabbits. Histomorphometric evaluation was performed at 4 weeks after implantation. Interconnected porosity was 53% with an average diameter of 210 µm and an elastic modulus of around 1 GPa with good mechanical properties. The samples presented cell survival values close to 100% of viability. Newly formed bone was observed inside macropores, through interconnected porosity, and on the implant surface. Successful bone colonization of inner structure (40%) suggested good osteoconductive capability of the implant. Bioactivated foams showed better results than non-treated ones, suggesting both bioactivation strategies induce osteointegration capability.

Biomineralization improves mechanical and osteogenic properties of multilayer-modified PLGA porous scaffolds

Poly-(lactide-co-glycolide acid) (PLGA) has been widely investigated as scaffold material for bone tissue engineering owing to its biosafety, biodegradability, and biocompatibility. However, the bioinert surface of PLGA may fail in regulating cellular behavior and directing osteointegration between the scaffold and the host tissue. In this article, oxidized chondroitin sulfate (oCS) and type I collagen (Col I) were assembled onto PLGA surface via layer by layer technique (LbL) as an adhesive coating for the attachment of inorganic minerals. The multilayer-modified PLGA scaffold was mineralized in vitro to ensure the deposition of nanohydroxyapatite (nHAP). It was found that nHAP crystals were more uniformly and firmly attached on the multilayer-modified PLGA as compared with the pure PLGA scaffold, which remarkably improved PLGA surface and mechanical properties. Additionally, in vitro biocompatibility of PLGA scaffold, in terms of bone mesenchymal stem cells (BMSCs) attachment, spreading and proliferation was greatly enhanced by nHAP coating and multilayer deposition. Furthermore, the fabricated composite scaffold also shows the ability to promote the osteogenic differentiation of BMSCs through the up-regulation of osteogenic marker genes. Thus, this novel biomimetic composite scaffold might achieve a desirable therapeutic result for bone tissue regeneration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2714-2725, 2018.

Bone tissue engineering via growth factor delivery: from scaffolds to complex matrices

In recent years, bone tissue engineering has emerged as a promising solution to the limitations of current gold standard treatment options for bone related-disorders such as bone grafts. Bone tissue engineering provides a scaffold design that mimics the extracellular matrix, providing an architecture that guides the natural bone regeneration process. During this period, a new generation of bone tissue engineering scaffolds has been designed and characterized that explores the incorporation of signaling molecules in order to enhance cell recruitment and ingress into the scaffold, as well as osteogenic differentiation and angiogenesis, each of which is crucial to successful bone regeneration. Here, we outline and critically analyze key characteristics of successful bone tissue engineering scaffolds. We also explore candidate materials used to fabricate these scaffolds. Different growth factors involved in the highly coordinated process of bone repair are discussed, and the key requirements of a growth factor delivery system are described. Finally, we concentrate on an analysis of scaffold-based growth factor delivery strategies found in the recent literature. In particular, the incorporation of two-phase systems consisting of growth factor-loaded nanoparticles embedded into scaffolds shows great promise, both by providing sustained release over a therapeutically relevant timeframe and the potential to sequentially deliver multiple growth factors.

Osteochondral tissue repair in osteoarthritic joints: clinical challenges and opportunities in tissue engineering

Osteoarthritis (OA), identified as one of the priorities for the Bone and Joint Decade, is one of the most prevalent joint diseases, which causes pain and disability of joints in the adult population. Secondary OA usually stems from repetitive overloading to the osteochondral (OC) unit, which could result in cartilage damage and changes in the subchondral bone, leading to mechanical instability of the joint and loss of joint function. Tissue engineering approaches have emerged for the repair of cartilage defects and damages to the subchondral bone in the early stages of OA and have shown potential in restoring the joint’s function. In this approach, the use of three-dimensional scaffolds (with or without cells) provides support for tissue growth. Commercially available OC scaffolds have been studied in OA patients for repair and regeneration of OC defects. However, none of these scaffolds has shown satisfactory clinical results. This article reviews the OC tissue structure and the design, manufacturing and performance of current OC scaffolds in treatment of OA. The findings demonstrate the importance of biological and biomechanical fixations of OC scaffolds to the host tissue in achieving an improved cartilage fill and a hyaline-like tissue formation. Achieving a strong and stable subchondral bone support that helps the regeneration of overlying cartilage seems to be still a grand challenge for the early treatment of OA.