Foam Replication Technique Research Articles

Preparation, Characterization, and Drug Delivery of Hexagonal Boron Nitride-Borate Bioactive Glass Biomimetic Scaffolds for Bone Tissue Engineering

In this study, biomimetic borate-based bioactive glass scaffolds containing hexagonal boron nitride hBN nanoparticles (0.1, 0.2, 0.5, 1, and 2% by weight) were manufactured with the polymer foam replication technique to be used in hard tissue engineering and drug delivery applications. To create three-dimensional cylindrical-shaped scaffolds, polyurethane foams were used as templates and covered using a suspension of glass and hBN powder mixture. Then, a heat treatment was applied at 570 °C in an air atmosphere to remove the polymer foam from the structure and to sinter the glass structures. The structural, morphological, and mechanical properties of the fabricated composites were examined in detail. The in vitro bioactivity of the prepared composites was tested in simulated body fluid, and the release behavior of gentamicin sulfate and 5-fluorouracil from glass scaffolds were analyzed separately as a function of time. The cytotoxicity was investigated using osteoblastic MC3T3-E1 cells. The findings indicated that the hBN nanoparticles, up to a certain concentration in the glass matrix, improved the mechanical strength of the glass scaffolds, which mimic the cancellous bone. Additionally, the inclusion of hBN nanoparticles enhanced the in vitro hydroxyapatite-forming ability of bioactive glass composites. The presence of hBN nanoparticles accelerated the drug release rates of the system. It was concluded that bioactive glass/hBN composite scaffolds mimicking native bone tissue could be used for bone tissue repair and regeneration applications.

LZS bioactive glass-ceramic scaffolds: Colloidal processing, foam replication technique and mechanical properties to bone tissue engineering

Scaffolds are used in bone replacement because present biocompatibility, three-dimensional structure, and high porosity. However, despite the efforts, there are still significant barriers to the development of reliable, synthetic scaffolds to repair large defects is one of the challenges of regenerative medicine. Therefore, innovative solutions are needed better to meet the requirements of a minimally invasive approach while providing adequate vascularity and strength and mechanical reliability. In this sense, the obtainment of a material that satisfies all these requirements is very important. This work aims to evaluate the mechanical properties of glass-ceramic scaffolds of the LZS (Li2O–ZrO2–SiO2) system produced by the replica method. For this, detailed colloidal processing was carried out to identify the solids content, amount of dispersant, and the binder most suitable to produce scaffolds. Finally, the mechanical reliability of the most suitable composition was evaluated by Weibull statistics. Suspensions containing 47 vol% of LZS relative to glass and 0.2 wt % of dispersant were used. In addition, dispersion times and the amount of binder were adjusted. Scaffolds of bioactive glass-ceramics were obtained at 900 °C, replicating polyurethane foams. Then they were morphologically, structurally, and mechanically characterized. The obtained bioactive glass-ceramic scaffolds presented porosity up to 83%, compressive strengths comparable to those of trabecular bone, up to 1.3 MPa, in addition to pore size >300 μm, desirable to favor biological interests destined to the regeneration and formation of bone tissue, demonstrating the possibility of its use as a material for bone replacement or filling. The Weibull modulus found for the glass-ceramic scaffolds produced is 4.18: within the expected range of mechanical reliability for application in bone regeneration.

Influence of ternary divalent cations (Mg2+, Co2+, Sr2+) substitution on the physicochemical, mechanical and biological properties of carbonated hydroxyapatite scaffolds

Substitution of ionic either anion or cation in a controlled amount into carbonated hydroxyapatite (CHA) structure is one of the efficient and safest ways in enhancing the properties of the materials. However, most of the works studied only focused on the physical and mechanical properties of single ionic substitution. For the first time, the influence of simultaneous ternary substitutions of divalent cations into porous CHA scaffolds on the physicochemical, mechanical, degradative, and in vitro biological properties is investigated in the present study. Three different compositions of porous scaffolds with binary and ternary divalent cations, namely, pure CHA (S11), CoSr CHA (S21), and MgCoSr CHA (S31) were fabricated using a polyurethane (PU) foam replication technique. Despite a small amount of Mg2+, Co2+, and Sr2+ being added, these divalent cations had successfully substituted into the Ca2+ site and remained as single-phase B-type CHA. The produced scaffolds demonstrated open, interconnected, and uniform pores. Interestingly, simultaneous ternary divalent cation substitution into CHA structure had successfully enhanced the compressive strength of the sintered scaffolds and also promoted better cell attachment and activities than the binary doped- and pure CHA scaffolds. It is important to note that choosing the right divalent cation can be the determining factor in tuning the physicochemical, mechanical, and biological properties of CHA scaffolds.

Additive Manufacturing of Carbon Nanotube Reinforced Bioactive Glass Scaffolds for Bone Tissue Engineering

Abstract Scaffolds play an essential role in bone healing by providing temporary structural support to the native bone tissue and by hosting bone cells. To this end, several biomaterials and manufacturing methods have been proposed. Among the biomaterials, bio-active glasses have attractive properties as a scaffold material for bone repair. Simultaneously, additive manufacturing (AM) techniques have attracted significant attention owing to their capability of fabricating complex and patient-specific scaffolds. Accordingly, borosilicate bio-active glass (BG-B30) has been used to fabricate the scaffolds using an extrusion-based AM devices in this study. Pluronic F-127 was used as an ink carrier that showed suitable shear thinning behavior for fabrication. The pure BG-B30 scaffold had a compressive strength of 23.30 MPa and was reinforced further with functionalized multiwalled carbon nanotube (MWCNT-COOH) to reduce its brittleness and enhance its compressive strength. When compared to the conventional polymer foam replication technique, the combination of MWCNT-COOH reinforcement and AM resulted in an enhancement of the compressive strength by ∼646% (1.05 MPa to 35.84 MPa). Further, structural analysis using microcomputed tomography revealed that the scaffolds fabricated using AM had better control over strut size and pore size in addition to better network connectivity. Finally, in vitro experiments demonstrated its bio-active behavior by the formation of hydroxyapatite, and the cellular studies revealed good cell viability and osteogenesis initiation. These results are promising for the fabrication of patient-specific CNT-reinforced bio-active glass porous scaffolds for bone tissue engineering applications.

Effectiveness of various sintering aids on the densification and in vitro properties of carbonated hydroxyapatite porous scaffolds produced by foam replication technique

Synthetic carbonated hydroxyapatite (CHA) ceramics are considered as future materials for bone substitutes due to their good bioactivity, biocompatibility and similarity to the inorganic mineralized phase of bone. However, limited thermal stability of CHA-based materials due to carbonate content at elevated temperature remains a critical challenge particularly in producing three-dimensional (3D) porous scaffolds. To address the aforementioned limitation, this paper presents a new approach by incorporating several types of sintering aids, namely Mg(OH)2, Ca(OH)2, NaOH, KOH and K2CO3 into the CHA slurry composition to identify the most effective aid in producing 3D CHA scaffolds in terms of architecture, mechanical and biological properties. This approach focused on physico-chemical, mechanical and biological characteristics that can be helpful in designing scaffolds for bone tissue engineering. Five compositions of scaffolds with different sintering aid were prepared by replication technique, sintered at 800 °C and eventually cooled down in wet CO2 atmosphere. Scaffolds prepared with K2CO3 (CHAKC) as sintering aid exhibited optimum interconnected pores with densified struts and the highest compressive strength. Biologically, CHAKC provides the most favorable environment in supporting apatite formation as well as encouraging better cell attachment and activities. Our findings highlight that the use of K2CO3 had effectively enhanced the architecture and compressive strength of the CHA scaffolds without any toxicity evidence.

Synthesis and Characterisation of Bioactive Glass 13-93 Scaffolds for Bone Tissue Regeneration

A modified sol-gel method was used in the current work to prepare a 13-93 bioactive glass powder, which was selected for the therapeutic actions of its constituent parts. In particular bioactive glass 13-93 can chemically bond with host tissue and induce osteogenesis. The produced gel was calcined at a temperature of 600 °C, while particle size analysis and x-ray diffraction were performed after the preparation of the glass powder. Porous bioactive glass 13-93 scaffolds were synthesised using the polymer foam replication technique that uses polyurethane sponges as a template. Sintering at 700 °C was then performed for one hour to the produce the required structures. After sintering, the microstructure was examined by scanning electron microscope (SEM) and Fourier transform infrared analysis (FTIR). The x-ray diffraction (XRD) results were also examined. The average particle size of bioactive glass 13-93 thus produced was about 2.978 μm, and XRD pattern analysis showed that the porous scaffolds were amorphous. The microstructure of the 13 – 93 glass scaffolds contained interconnected cellular pores and a dense network of bioactive glass, allowing scaffolds with porosity between 80 and 83% to be obtained. An in vitro bioactivity test was performed on the scaffolds by soaking them in a solution of simulated body fluid (SBF). The subsequent SEM images confirmed the bioactivity of the prepared scaffolds based on the formation of obvious and dense hydroxyapatite particles on the surface after 7 days of immersion in SBF. It was thus concluded that bioactive glass scaffold prepared in this work via the polymer foam replication technique has the potential to be used in several future applications.

Effect of TiO2 doping on degradation rate, microstructure and strength of borate bioactive glass scaffolds.

A titanium-containing borate glass series based on the system (52-X) B2O3-12CaO-6P2O5-14Na2O-16ZnO-XTiO2 with X varying from 0, 5 and 15 mol% of TiO2 incorporated, identified as BRT0, BRT1 and BRT3, respectively, were used in this study. Scaffolds (pore sizes, 165-230 μm and porosity, 53.51-69.51%) were prepared using a polymer foam replication technique. BRT3 scaffolds exhibited higher compressive strength (7.16 ± 0.22 MPa) when compared to BRT0 (6.02 ± 0.47 MPa) and BRT1 (5.65 ± 0.28 MPa) scaffolds with lower, or no, TiO2 content. The solubility of the scaffolds decreased as the TiO2 content increased up to 15 mol% when samples of each scaffold were immersed in DI water and the pH of all these extracts went up from 7.0 to 8.5 in 30 days. The cumulative ion release from the scaffolds showed significant difference with respect to TiO2 content; addition of 5 mol% TiO2 at the expense of borate (B2O3) decreased the ion release remarkably. Furthermore, it was found that for all three scaffolds, cumulative ion release increased with incubation time. The results indicate that the degradation rates and compressive strengths of borate bioactive glass scaffolds could be controlled by varying the amount of TiO2 incorporated, confirming their potential as scaffolds in TKA and rTKA.

Easy manufacturing of 3D ceramic scaffolds by the foam replica technique combined with sol-gel or ceramic slurry

A material, whose composition was based on the SiO 2 –CaO–P 2 O 5 system, was used to prepare 3D porous ceramic scaffolds made by the foam replication technique linking the sol-gel route or ceramic slurry in barbotine suspension processes. With an appropriate heat treatment, it was possible to obtain a 3D-scaffold containing two crystalline phases or more, and a controlled nano-to microscale microstructure. The obtained scaffolds presented an interconnected and well-defined porous structure. Its pore size was 0.060–600 μm. It had a rough pore wall that could potentially benefit ingrowth and cell adhesion. In terms of hydroxycarbonate apatite formation in simulated body fluid (SBF), the 3D scaffolds’ bioactivity was confirmed after 3 and 14 days of immersion in SBF. This clearly confirms that these new scaffolds are suitable for bone regeneration applications. Processing technology allows 3D scaffolds to be adapted with particular microstructures to increase/decrease their in vitro behavior.

Compressive Strength Enhancement of Carbon Nanotube Reinforced 13-93B1 Bioactive Glass Scaffolds.

45S5 Bioglass® has been used quite extensively in the form of particulate as synthetic bone graft. However, 45S5 glass has certain limitations such as difficulty in sintering and slow and partial conversion to hydroxy carbonated apatite. In pursuit of overcoming these limitations, bioactive glasses (13-93B1) containing increased amount of B₂O₃ by partial replacement of SiO₂ have been prepared using sol-gel technique in this study. Since bioactive glasses are brittle in nature, therefore, they are unsuitable for load bearing sites. Consequently, 3D porous scaffolds by reinforcement with varying weight percent of carbon nanotubes (CNTs) have been fabricated in this work by physical mixing and polymer foam replication technique. Compared with pure 13-93B1 bioactive glasses, addition of 0.2 weight percent of CNT resulted in maximum increase in compressive strength from 1.80 MPa to 5.84 MPa (a 224% increase) and elastic modulus from 102 MPa to 269.4 MPa (a 164% increase), respectively. Bioactivity of these scaffolds was confirmed in vitro using simulated body fluid test for 28 days. The compressive strength post-SBF studies were within the range of compressive strength of trabecular bone. These results show potential of fabricating a 3D porous scaffold with sufficient strength and biocompatibility using CNT-1393B1 bioactive glasses.

Bioactive glass based scaffolds coated with gelatin for the sustained release of icariin

Gelatin-coated, 3D sponge-like scaffolds based on 45S5 bioactive glass were produced using the foam replication technique. Compressive strength tests of gelatin-coated samples compared to uncoated scaffolds showed significant strengthening and toughening effects of the gelatin coating with compressive strength values in the range of cortical bone. Additionally, the crosslinked gelatin network (using either caffeic acid or N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride (EDC)/N-hxdroxysuccinimide (NHS) as crosslinking agent) was shown to be a suitable candidate for the sustained release of the bioactive molecule icariin. Concerning bioactivity of the produced scaffolds, characterization by FTIR and SEM indicated the formation of hydroxyapatite (HA) in all samples after immersion in simulated body fluid (SBF) for 14 days, highlighting the favorable combination of mechanical robustness, bioactivity and drug delivery capability of this new type of scaffolds.

Fabrication and characterization of strontium-doped borate-based bioactive glass scaffolds for bone tissue engineering

Boron is an essential element for bone health, but its cytotoxicity depends on its concentration. In the present study, borate-based 13-93B2 glass scaffolds doped with varying amounts of strontium (0-9 mol.% Sr) with a porosity of 80% and pore size of 200–500 μm were prepared by a polymer foam replication technique. The effect of strontium content on the structure and bioactive properties of scaffolds were investigated by FTIR, XRD, ICP and MTT test. The results showed that the appearance of strontium in the glass has no obvious effect on the structure. The as-made scaffolds were amorphous and had a compressive strength of 11 MPa. The scaffolds in vitro bioactivity was observed by the conversion of the glass surface to a nanostructured hydroxyapatite layer in SBF. The increase of strontium concentration in borate-based glass accelerated the release of Si4+, Ca2+ ions, and significantly reduced the release of B3+ ions in some extent. The results indicated that borate-based bioactive glass doped with particular proportion of Sr suppressed the rapid release of boron and the cytotoxicity of glass scaffolds was minimized at least. This strontium-doped borate-based bioactive glass could be a potential scaffold material for bone tissue engineering.

Electrically conductive borate-based bioactive glass scaffolds for bone tissue engineering applications.

In this study, electrically conductive, borate-based, porous 13-93B3 bioactive glass composite scaffolds were prepared using a polymer foam replication technique. For this purpose, a slurry containing 40 vol% glass particles and 0-10 wt% graphene nanoplatelets was prepared by dispersing the particles in ethanol in the presence of ethyl cellulose. Composite scaffolds were subjected to a controlled heat treatment, in air atmosphere, to decompose the foam and sinter the glass particles into a dense network. It was found that the applied heat treatment did not influence the structure of graphene in the glass network. Graphene additions did not negatively affect the mechanical properties and enhanced the electrical conductivity of the glass scaffolds. In X-ray diffraction analysis, the crystalline peak corresponding to hydroxyapatite was observed in all the samples suggesting that all of the samples were bioactive after 30 days of immersion in simulated body fluid. However, Fourier transform infrared spectroscopy analysis and scanning electron microscope observations revealed that hydroxyapatite formation rate decreased with increasing graphene concentration especially for samples treated in simulated body fluid for shorter times. Based on the cytotoxicity assay findings, the MC3T3-E1 cell growth was significantly inhibited by the scaffolds containing higher amount of graphene compared to bare glass scaffolds. Best performance was obtained for 5 wt% graphene which yielded an enhancement of electrical conductivity with moderate cellular response and invitro hydroxyapatite forming ability. The study revealed that the electrically conductive 13-93B3 graphene scaffolds are promising candidates for bone tissue engineering applications.

Angiogenic potential of boron-containing bioactive glasses: in vitro study

Boron-containing bioactive glasses (BGs) are being extensively researched for the treatment and regeneration of bone defects because of their osteostimulatory and neovascularization potential. In this study, we report the effects of the ionic dissolution products (IDPs) of different boron-doped, borosilicate, and borate BG scaffolds on mouse bone marrow stromal cells in vitro, using an angiogenesis assay. Five different BG scaffolds of the system SiO2–Na2O–K2O–MgO–CaO–P2O5–B2O3 (with varying amounts of SiO2 and B2O3) were fabricated by the foam replication technique. Bone marrow stromal cells were cultivated in contact with the IDPs of the boron-containing BG scaffolds at different concentrations for 48 h. The expression and secretion of vascular endothelial growth factor (VEGF) from the cultured cells was measured quantitatively using the VEGF ELISA Kit. Cell viability and cell morphology were determined using WST-8 assay and H&E staining, respectively. The cellular response was found to be dependent on boron content and the B release profile from the glasses corresponded to the positive or negative biological activity of the BGs.

<i>In Vitro</i> Bioactivity of Macroporous Calcium Phosphate Scaffold for Biomedical Application

In this study, the effects of macroporous calcium phosphate (MCP) scaffold on bioactivity as an in-vitro model has been investigated. MCP scaffold was prepared using foam replication technique by combination of ceramic and polyurethane (PU). MCP was examined by scanning electron microscope (SEM) and X-ray diffractometer (XRD) to confirm its microstructure and phase composition respectively. Bioactivity in simulated body fluid (SBF) was characterized by apatite mineralisation on MCP scaffold surface, pH, calcium (Ca2+) and phosphate (PO43-) ion dissolution and compressive strength using universal testing machine (UTM). Experimental results showed the formation of apatite around the MCP scaffold after 30 days in SBF. pH value was gradually decreased up to 7 days and constant until 30 days. Dissolution of Ca2+ and PO43- ion in SBF due to the occurrence of MCP degradation, hence the compressive strength are gradually decreased gradually in line with immersion period. This material may be promising for biomedical application.

In vivo evaluation of cerium, gallium and vanadium-doped borate-based bioactive glass scaffolds using rat subcutaneous implantation model

The main objective of this study was to evaluate the cerium, gallium and vanadium-containing bioactive borate glass scaffolds for soft tissue applications and determine the potential toxicity of these scaffolds on the adjacent tissues. The effects of the cerium, gallium and vanadium substitution on the soft tissue ingrowth and angiogenesis in porous borate based bioactive glass scaffolds were investigated using rat subcutaneous implantation model. For this purpose, bioactive borate glass powders containing therapeutic ions were prepared by melt-cast method and subsequently scaffolds were fabricated using polymer foam replication technique. The scaffolds were implanted subcutaneously for 4 weeks in Sprague Dawley rats. Bare borate glass scaffolds with the same microstructure were used as the control. Histology was used to evaluate tissue ingrowth and blood vessel formation in the implants. Additionally, the antibacterial activities of cerium, gallium and vanadium containing porous bioactive glass scaffolds were investigated in vitro by a zone inhibition method. Results revealed that addition of cerium ions to the borate glass network caused an increase in blood vessel formation. On the other hand, a decrease was obtained in angiogenesis in gallium and vanadium-containing glasses. All of the scaffolds prepared in the study did not show any antibacterial activity towards Escherichia coli and Staphylococcusaureus.

Facile production of porous bioactive glass scaffolds by the foam replica technique combined with sol–gel/electrophoretic deposition

3D porous bioactive glass (BG) scaffolds were fabricated by the foam replication technique combining sol–gel and electrophoretic deposition (EPD) processes. A special EPD set-up was built to optimize the scaffolds fabrication, which results in the rapid production of BG-based scaffolds in comparison to the traditional time-consuming foam replication technique normally used for the same kind of BG scaffolds. The influences of parameters related to the BG sol (aging time) as well as to the electrically driven process (deposition voltage) were studied and discussed in terms of the final scaffolds microstructure. Bioactivity of the samples, in terms of hydroxycarbonate apatite (HCA) formation in simulated body fluid (SBF), was determined after 1 day of immersion in SBF, confirming the suitability of the new scaffolds for bone regeneration applications.

PHYSICAL PROPERTIES CHARACTERIZATION OF POROUS CALCIUM PHOSPHATE SCAFFOLD FOR BONE TISSUE ENGINEERING

The porous calcium phosphate scaffold is used to repair bone defect. Cracked during pyrolysis process is the main problem of the porous calcium phosphate due to the low mechanical strength and high brittleness. This lead to reduce efficiency of the scaffold for cells proliferation. The aim of this work is to improve the mechanical properties of these ceramic scaffolds. Green body was produced using foam replication technique. The polyurethane foam with dimension of (20 x 10 x20) mm was immersed in slurry of apatite powder and poly vinyl alcohol (PVA). To obtain porous scaffolds, the green body was treated under various sintering temperature i.e. 1150°C, 1250°C and 1300°C for 3 hours, followed by dipping in PDLLA solution and dried at room temperature for 24 hours. The specimen was analysed under X-ray diffraction, SEM and compressive strength. The X-ray diffraction spectrum shows the presence of Ca10(PO4)6OH2 phases in the sintered scaffold. The formation of rod-like apatite was observed through SEM. The compressive strength was increased with increasing sintered temperature. It has a potential to be used as tissue engineering for low-load bearing application.

Macro-porous Ti2AlC MAX-phase ceramics by the foam replication method

This paper describes the fabrication of porous Ti2AlC MAX-phase ceramics using the foam replication technique. The influence of heat-treatment cycle and sintering time on phase composition, microstructure and type of defect is discussed. Compression testing indicates that strength is related to defects that are introduced during the foam replication stage, as observed by optical and electron microscopy. The manufacturing process is adapted by employing additional coating stages to produce electrically conductive macro-porous ceramics with a range of strengths (0.2–6.3MPa) and macrostructures. Such materials are of interest for use as a high surface area electrode for harsh environments or microbial fuel cells.

Investigating the Vascularization of Tissue-Engineered Bone Constructs Using Dental Pulp Cells and 45S5 Bioglass® Scaffolds.

Identification of a suitable cell source combined with an appropriate 3D scaffold is an essential prerequisite for successful engineering of skeletal tissues. Both osteogenesis and angiogenesis are key processes for bone regeneration. This study investigated the vascularization potential of a novel combination of human dental pulp stromal cells (HDPSCs) with 45S5 Bioglass® scaffolds for tissue-engineered mineral constructs in vivo and in vitro. 45S5 Bioglass scaffolds were produced by the foam replication technique with the standard composition of 45 wt% SiO2, 24.5 wt% Na2O, 24.5 wt% CaO, and 6 wt% P2O5. HDPSCs were cultured in monolayers and on porous 45S5 Bioglass scaffolds under angiogenic and osteogenic conditions for 2–4 weeks. HDPSCs expressed endothelial gene markers (CD34, CD31/PECAM1, and VEGFR2) under both conditions in the monolayer. A combination of HDPSCs with 45S5 Bioglass enhanced the expression of these gene markers. Positive immunostaining for CD31/PECAM1 and VEGFR2 and negative staining for CD34 supported the gene expression data, while histology revealed evidence of endothelial cell-like morphology within the constructs. More organized tubular structures, resembling microvessels, were seen in the constructs after 8 weeks of implantation in vivo. In conclusion, this study suggests that the combination of HDPSCs with 45S5 Bioglass scaffolds offers a promising strategy for regenerating vascularized bone grafts.

Production of Porous Scaffolds from Bioglass 45S5-derived Glasses

Bioglass 45S5 has been successfully implemented in clinical applications, because of its capability of developing a strong bond with the bone tissue. However, its low mechanical strength does not allow applying it in places that support load. In addition to the high reactivity, an important requirement for its application is that the material must have a high porosity with pore sizes greater than 100 microns, one of the key features tissue engineering materials. In a previous work, glass compositions derived from Bioglass 45S5 were designed by means of natural minerals such as feldspar and quartz. Besides, leucite was developed as a reinforcing phase after thermal treatment, getting good bioactivity results. The objective of this study is to evaluate the possibility of producing porous scaffolds from such glasses. The foam replication technique is used to manufacture the scaffolds. Thermal evolutions of glasses are studied, so as to choose the best heat treatment schedule for the production of porous scaffolds. Textural characteristics are evaluated.