Fabrication of dicalcium phosphate dihydrate-coated β-TCP granules and evaluation of their osteoconductivity using experimental rats

A novel two-step conversion from DCPD-coated β-TCP to low crystallinity β-TCP porous scaffolds via combination between dry heating and hydrothermal methods: Effects on pre-osteoblast cell responses

This study presents a novel two-step process to fabricate low crystallinity (LC) β-tricalcium phosphate (β-TCP) porous scaffolds and evaluates their implications for pre-osteoblast cell responses. The novelty of this study lies in the two-step conversion of dicalcium phosphate dihydrate (DCPD) -coated β-TCP porous scaffold into LC β-TCP porous scaffolds through a combination of dry heating and hydrothermal conditions at 200°C. The obtained LC β-TCP porous scaffolds were characterised using a Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Fourier-Transform Infrared (FTIR), porosity, and compressive strength analysis confirmed the successful fabrication of LC β-TCP scaffolds. Besides, in vitro tests using pre-osteoblast MC3T3-E1 cells were conducted to investigate the cell responses toward LC β-TCP porous scaffolds. The results revealed that the LC β-TCP porous scaffolds were successfully fabricated by converting the DCPD-coated β-TCP into the dicalcium phosphate anhydrous (DCPA) coated β-TCP, followed by a hydrothermal process in a 0.1 mol/L calcium chloride (CaCl2) aqueous solution at 200°C for 24 hours to obtain LC of pure β-TCP scaffold. Moreover, in vitro cell study indicated that the cell density and proliferation surrounding the surface of the LC β-TCP porous scaffold were greater than DCPD-coated β-TCP porous scaffolds. The findings from this study are expected to significantly impact bioceramic technology by enhancing cell responses.

TyroFill-Titanium Implant Constructs for the Coordinated Repair of Rabbit Mandible and Tooth Defects

Currently used methods to repair craniomaxillofacial (CMF) bone and tooth defects require a multi-staged surgical approach for bone repair followed by dental implant placement. Our previously published results demonstrated significant bioengineered bone formation using human dental pulp stem cell (hDPSC)-seeded tyrosine-derived polycarbonate scaffolds (E1001(1K)-bTCP). Here, we improved upon this approach using a modified TyroFill (E1001(1K)/dicalcium phosphate dihydrate (DCPD)) scaffold-supported titanium dental implant model for simultaneous bone-dental implant repair. TyroFill scaffolds containing an embedded titanium implant, with (n = 3 each time point) or without (n = 2 each time point) seeded hDPCs and Human Umbilical Vein Endothelial Cells (HUVECs), were cultured in vitro. Each implant was then implanted into a 10 mm full-thickness critical-sized defect prepared on a rabbit mandibulee. After 1 and 3 months, replicate constructs were harvested and analyzed using Micro-CT histological and IHC analyses. Our results showed significant new bone formation surrounding the titanium implants in cell-seeded TyroFill constructs. This study indicates the potential utility of hDPSC/HUVEC-seeded TyroFill scaffolds for coordinated CMF bone-dental implant repair.

A review on in vitro/in vivo response of additively manufactured Ti-6Al-4V alloy

Bone replacement using porous and solid metallic implants, such as Ti-alloy implants, is regarded as one of the most practical therapeutic approaches in biomedical engineering. The bone is a complex tissue with various mechanical properties based on the site of action. Patient-specific Ti-6Al-4V constructs may address the key needs in bone treatment for having customized implants that mimic the complex structure of the natural tissue and diminish the risk of implant failure. This review focuses on the most promising methods of fabricating such patient-specific Ti-6Al-4V implants using additive manufacturing (AM) with a specific emphasis on the popular subcategory, which is powder bed fusion (PBF). Characteristics of the ideal implant to promote optimized tissue-implant interactions, as well as physical, mechanical/chemical treatments and modifications will be discussed. Accordingly, such investigations will be classified into 3B-based approaches (Biofunctionality, Bioactivity, and Biostability), which mainly govern native body response and ultimately the success in implantation.

Influence of pH and ion components in the liquid phase on the setting reaction of carbonate apatite granules

Carbonate apatite (CO₃Ap) is an inorganic component of bone and replaces by natural bone after implantation into the bone defect. Because of this unique characteristic, CO₃Ap granules have been used in the dental field. However, washing out of granules from the bone defect area is an issue. The aim of this study was to set CO₃Ap granules by mixing CO₃Ap granules with acidic phosphate solutions and evaluate the influence of the pH and ion components of the solutions. When Na⁺ was the counter ion, the amount of precipitated dicalcium phosphate dihydrate (DCPD) was small and the setting ability disappeared with increasing pH of the solutions. Alternatively, when the counter ion was Ca²⁺, the amount of precipitated DCPD was high and the setting ability was observed even at high pH. These results suggest the presence of Ca²⁺ in the acidic phosphate solution is a key for fabricating CO₃Ap granular cement.

Improvement of mechanical properties of zein porous scaffold by quenching/electrospun fiber reinforcement

As a novel bone substitute material, zein-based scaffolds (ZS) should have suitable mechanical properties and porosity. ZS has shown good compressive properties matching cancellous bone, but there is still a demand to improve its mechanical properties, especially tensile and bending properties without adding plasticizers. The present study explored two simple and environment-friendly factors for this purpose: fiber reinforcement and quenching. Addition of electrospun zein fibers enhanced all mechanical properties significantly including compressive, tensile, and bending moduli; compressive and bending strengths of ZS with both higher (70-80%) and lower (50-60%) porosities, no matter whether heating treated or not treated. Especially, all these parameters were further enhanced significantly by addition of heating treated fibers. AFM provided evidence that high temperature modification could significantly alter the micro-elastic properties of zein electrospun fibers, i.e., increased stiffness of fibers. Quenching treatment also enhanced compressive, tensile, and bending strengths significantly. Finally, quenching treated ZS were implanted into critical-sized bone defects (15 mm) of the rabbit model to compare the repair efficacy with a commercial β-tricalcium phosphate product. The results demonstrated that there were no remarkable differences in bone reconstructions between these two materials.

Biodegradable materials for bone defect repair

Compared with non-degradable materials, biodegradable biomaterials play an increasingly important role in the repairing of severe bone defects, and have attracted extensive attention from researchers. In the treatment of bone defects, scaffolds made of biodegradable materials can provide a crawling bridge for new bone tissue in the gap and a platform for cells and growth factors to play a physiological role, which will eventually be degraded and absorbed in the body and be replaced by the new bone tissue. Traditional biodegradable materials include polymers, ceramics and metals, which have been used in bone defect repairing for many years. Although these materials have more or fewer shortcomings, they are still the cornerstone of our development of a new generation of degradable materials. With the rapid development of modern science and technology, in the twenty-first century, more and more kinds of new biodegradable materials emerge in endlessly, such as new intelligent micro-nano materials and cell-based products. At the same time, there are many new fabrication technologies of improving biodegradable materials, such as modular fabrication, 3D and 4D printing, interface reinforcement and nanotechnology. This review will introduce various kinds of biodegradable materials commonly used in bone defect repairing, especially the newly emerging materials and their fabrication technology in recent years, and look forward to the future research direction, hoping to provide researchers in the field with some inspiration and reference.

Calcium phosphate enriched synthetic tyrosine-derived polycarbonate - dicalcium phosphate dihydrate polymer scaffolds for enhanced bone regeneration

Optimal repair of large craniomaxillofacial (CMF) defects caused by trauma or disease requires the development of new, synthetic osteoconductive materials in combination with cell-based therapies, to overcome the limitations of traditionally used bone graft substitutes. In this study, tyrosine-derived polycarbonate, E1001(1k) scaffolds were fabricated to incorporate the osteoinductive coating, Dicalcium phosphate dihydrate (DCPD). The biocompatibility of E1001(1k)-DCPD, E1001(1k)-βTCP and E1001(1k) scaffolds was compared using in vitro culture with human dental pulp stem cells (hDPSCs). We found that the DCPD coating was converted to carbonated hydroxyapatite over time in in vitro culture in Osteogenic Media, while the βTCP did not. hDPSCs exhibited slow initial attachment and proliferation on DCPD E1001(1k) scaffolds, but subsequently improved over time in culture, and promoted osteogenic differentiation. To the best of our knowledge, this study highlights for the first time the effects of Osteogenic Media on phase changes of DCPD, and on DCPD scaffold cytocompatibility with hDPSCs. DCPD showed similar hDPSC biocompatibility and osteoconductivity as compared to βTCP, and osteogenic differentiation of seeded hDPSCs. These studies suggest that E1001(1k)-DCPD scaffolds are a superior tool for craniofacial bone regeneration and provide the foundation for future in vivo testing.

Bone regeneration using β-tricalcium phosphate (β-TCP) block with interconnected pores made by setting reaction of β-TCP granules

We fabricated an interconnected dual porous β-tricalcium phosphate (β-TCP) block via a setting reaction of β-TCP granules. This β-TCP block was unique because it exhibits a fully interconnected macroporous structure with micropores in the walls surrounding macropores and a roughened surface. The porosity and diametral tensile strength of the resulting product were 58.1 ± 1.7% and 1.4 ± 0.2 MPa, respectively. Rabbit distal femur bone defects were reconstructed using the porous β-TCP block and the efficacy of the porous β-TCP block as an artificial bone substitute was evaluated histomorphometrically. For a dense β-TCP control, 4 weeks following implantation, only 0.2 ± 0.1% of the β-TCP was resorbed, and the amount of newly formed bone was limited (0.1 ± 0.1%), whereas when the defect was reconstructed with porous β-TCP, 9.2 ± 3.1% was resorbed, and the amount of new bone was 18.9 ± 5.5%. This represents an approximately 50-fold enhancement in resorption and a 200-fold increase in bone formation for our porous β-TCP block. Therefore, interconnected dual porous β-TCP made via β-TCP granule setting has good potential as an artificial bone substitute.

Characterization of Sol-Gel Derived Calcium Hydroxyapatite Coatings Fabricated on Patterned Rough Stainless Steel Surface

Sol-gel derived calcium hydroxyapatite (Ca10(PO4)6(OH)2; CHA) thin films were deposited on stainless steel substrates with transverse and longitudinal patterned roughness employing a spin-coating technique. Each layer in the preparation of CHA multilayers was separately annealed at 850 °C in air. Fabricated CHA coatings were placed in simulated body fluid (SBF) for 2, 3, and 4 weeks and investigated after withdrawal. For the evaluation of obtained and treated with SBF coatings, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray diffraction (XRD) analysis, Raman spectroscopy, XPS spectroscopy, scanning electron microscopy (SEM) analysis, and contact angle measurements were used. The tribological properties of the CHA coatings were also investigated in this study.

Dual therapeutic cobalt-incorporated bioceramics accelerate bone tissue regeneration

Bone grafting on defects caused by trauma or tumor stimulates bone regeneration, a complex process requiring highly orchestrated cell-signal interactions. Bone vascular growth is coupled with osteogenesis, but less is known about the interplay between angiogenesis and osteogenesis. Understanding this relationship is relevant to improved bone regeneration. Here, tricalcium phosphate (TCP) scaffolds doped with varying concentration of cobalt (Co-TCP) were designed to investigate the dosage effect of vascularization on bone formation. The surface structure, phase composition, mechanical features, and chemical composition were investigated. Co doping improved the mechanical properties of TCP. Co-TCP, particularly 2% and 5% Co-TCP, boosted cell viability of bone marrow stromal cells (BMSCs). The 2% Co-TCP promoted alkaline phosphatase activity, matrix mineralization, and expression of osteogenic genes in BMSCs in vitro. However, excessive Co doping decreased TCP-induced osteogenesis. Meanwhile, Co-TCP dose-dependently favored the growth and migration of human umbilical vein endothelial cells (HUVECs), and the expression of vascular endothelial growth factor (VEGF). The 2% Co-TCP significantly shrank the defect area in rat alveolar bone compared with TCP. Smaller bone volume and more abundant blood vessels were observed for 5% Co-TCP compared with 2% Co-TCP. The CD31 immunostaining in the 5% Co-TCP group was more intense than the other two groups, indicating of the increment of endothelium cells. Besides, 5% Co-TCP led to mild inflammatory response in bone defect area. Overall, TCP doped appropriately with Co has positive effect on osteogenesis, while excessive Co suppressed osteoblast differentiation and bone formation. These data indicate that vascularization within a proper range promotes osteogenesis, which may be a design consideration for bone grafts.

A Multimaterial Scaffold With Tunable Properties: Toward Bone Tissue Repair

Polyetheretherketone (PEEK)/β-tricalcium phosphate (β-TCP) scaffolds are expected to be able to combine the excellent mechanical strength of PEEK and the good bioactivity and biodegradability of β-TCP. While PEEK acts as a closed membrane in which β-TCP is completely wrapped after the melting/solidifying processing, the PEEK membrane degrades very little, hence the scaffolds cannot display bioactivity and biodegradability. The strategy reported here is to blend a biodegradable polymer with PEEK and β-TCP to fabricate multi-material scaffolds via selective laser sintering (SLS). The biodegradable polymer first degrades and leaves caverns on the closed membrane, and then the wrapped β-TCP is exposed to body fluid. In this study, poly(l-lactide) (PLLA) is adopted as the biodegradable polymer. The results show that large numbers of caverns form on the membrane with the degradation of PLLA, enabling direct contact between β-TCP and body fluid, and allowing for their ion-exchange. As a consequence, the scaffolds display the bioactivity, biodegradability and cytocompatibility. Moreover, bone defect repair studies reveal that new bone tissues grow from the margin towards the center of the scaffolds from the histological analysis. The bone defect region is completely connected to the host bone end after 8 weeks of implantation.

Biomaterial Property Effects on Platelets and Macrophages: An in Vitro Study

The purpose of this study was to evaluate the effects of surface properties of bone implants coated with hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) on platelets and macrophages upon implant installation and compare them to grit-blasted Ti and Thermanox used as a control. Surface properties were characterized using scanning electron microscopy, profilometry, crystallography, Fourier transform infrared spectroscopy, and coating stability. For platelets, platelet adherence and morphology were assessed. For macrophages, morphology, proliferation, and polarization were evaluated. Surface characterization showed similar roughness of ∼2.5 μm for grit-blasted Ti discs, both with and without coating. Coating stability assessment showed substantial dissolution of HA and β-TCP coatings. Platelet adherence was significantly higher for grit-blasted Ti, Ti-HA, and Ti-β-TCP coatings compared to that of cell culture control Thermanox. Macrophage cultures revealed a decreased proliferation on both HA and β-TCP coated discs compared to both Thermanox and grit-blasted Ti. In contrast, secretion of pro-inflammatory cytokine TNF-α and anti-inflammatory cytokine TGF-β were marginal for grit-blasted Ti and Thermanox, while a coating-dependent increased secretion of pro- and anti-inflammatory cytokines was observed for HA and β-TCP coatings. The results demonstrated a significantly upregulated pro-inflammatory and anti-inflammatory cytokine secretion and marker gene expression of macrophages on HA and β-TCP coatings. Furthermore, HA induced an earlier M1 macrophage polarization but more M2 phenotype potency than β-TCP. In conclusion, our data showed that material surface affects the behaviors of first cell types attached to implants. Due to the demonstrated crucial roles of platelets and macrophages in bone healing and implant integration, this information will greatly aid the design of metallic implants for a higher rate of success in patients.

Fabrication of self-setting β-tricalcium phosphate granular cement

Bone defect reconstruction would be greatly improved if β-tricalcium phosphate (β-TCP) granules had the ability to self-set without sacrificing their osteoconductivity potential. This study aimed to identify a method to permit β-TCP self-setting whilst maintaining good osteoconductivity. When mixed with acidic calcium phosphate solution, β-TCP granules were found to readily set, forming a fully interconnected porous structure. On mixing, dicalcium phosphate dihydrate crystals formed on the surface of β-TCP granules, bridging the granules and resulting in the setting reaction. The setting time of the β-TCP granular cement (β-TCP GC) was approximately 1 min and its mechanical strength, in terms of diametral tensile strength, was approximately 0.8 MPa. The β-TCP GC and β-TCP granules both showed the same level of osteoconductivity within rat calvaria bone defects. At 2 and 4 weeks post-implantation, new bone formation was comparable between the two β-TCP based bone substitutes. We conclude that β-TCP GC has excellent potential for use as a cement in bone defect reconstruction. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 800-807, 2018.