Hardystonite improves biocompatibility and strength of electrospun polycaprolactone nanofibers over hydroxyapatite: A comparative study

The aim of this study was to compare physico-chemical and biological properties of hydroxyapatite (HA) and hardystonite (HS) based composite scaffolds. Hardystonite (Ca₂ZnSi₂O₇) powders were synthesized by a sol–gel method while polycaprolactone–hardystonite (PCL–HS) and polycaprolactone–hydroxyapatite (PCL–HA) were fabricated in nanofibrous form by electrospinning. The physico-chemical and biological properties such as tensile strength, cell proliferation, cell infiltration and alkaline phosphatase activity were determined on both kinds of scaffolds. We found that PCL–HS scaffolds had better mechanical strength compared to PCL–HA scaffolds. Addition of HA and HS particles to PCL did not show any inhibitory effect on blood biocompatibility of scaffolds when assessed by hemolysis assay. The in vitro cellular behavior was evaluated by growing murine adipose-tissue-derived stem cells (mE-ASCs) over the scaffolds. Enhanced cell proliferation and improved cellular infiltrations on PCL–HS scaffolds were observed when compared to HA containing scaffolds. PCL–HS scaffolds exhibited a significant increase in alkaline phosphatase (ALP) activity and better mineralization of the matrix in comparison to PCL–HA scaffolds. These results clearly demonstrate the stimulatory role of Zn and Si present in HS based composite scaffolds, suggesting their potential application for bone tissue engineering.     

Fabrication and characterization of novel hydroxyapatite/porous carbon composite scaffolds

Novel hydroxyapatite (HA)/porous carbon composite scaffolds were prepared by applying sonoelectrodeposition and a subsequent hydrothermal treatment to previous carbonized phenolic resin coated polyurethane sponges. The interconnected pore network and morphology of HA/porous carbon composite scaffolds were determined by scanning electron microscope (SEM), and the whole surface of porous carbons were evenly coated with the deposited HA layer which was confirmed by EDS and XRD. The porosity (83.5 ± 0.3%) and the bulk density (0.297 ± 0.009 g·cm⁻³) of HA/porous carbon scaffolds were detected by the Archimedes method. The compressive and flexural strength of the scaffolds is 1.187 ± 0.064 MPa and 0.607 ± 0.268 MPa, respectively. Compared with the polymeric surface of 24-well cell culture plates, these novel scaffolds significantly promote the proliferation of human osteoblast-like MG-63 cells, indicating that this novel HA/porous carbon composite scaffold could be used for in vitro 3D culture of osteoblasts.     

Control of morphological properties of porous biodegradable scaffolds processed by supercritical CO2 foaming

A low cost supercritical CO₂ foaming rig with a novel design has been used to prepare fully interconnected and highly porous biodegradable scaffolds with controllable pore size and structure that can promote cancellous bone regeneration. Porous polymer scaffolds have been produced by plasticising the polymer with high pressure CO₂ and by the formation of a porous structure following the escape of CO₂ from the polymer. Although, control over pore size and structure has been previously reported as difficult with this process, the current study shows that control is possible. The effects of processing parameters such as CO₂ saturation pressure, time and temperature and depressurisation rate on the morphological properties, namely porosity, pore interconnectivity, pore size and wall thickness- of the scaffolds have been investigated. Poly(d,l)lactic acid was used as the biodegradable polymer. The surfaces and internal morphologies of the poly(d,l)lactic acid scaffolds were examined using optical microscope and micro computed tomography. Preosteoblast human bone cells were seeded on the porous scaffolds in vitro to assess cell attachment and viability. The scaffolds showed a good support for cell attachment, and maintained cell viability throughout 7 days in culture. This study demonstrated that the morphology of the porous structure can be controlled by varying the foaming conditions, allowing the porous scaffolds to be used in various tissue engineering applications.     

Trabecular-like Ti-6Al-4V scaffolds for orthopedic: fabrication by selective laser melting and in vitro biocompatibility

Porous metal scaffolds play an important role in the orthopedic field, due to their wide applications in prostheses implantation. Some previous studies showed that the scaffolds with trabecular bone structure reconstructed via computed tomography had satisfactory biocompatibility. However, the reverse modeling scaffolds were inflexible for customized design. Therefore, a top-down designing biomimetic bone scaffold with favorable mechanical performances and cytocompatibility is urgently demanded for orthopedic implants. An emerging additive manufacturing technique, selective laser melting, was employed to fabricate the trabecular-like porous Ti-6Al-4 V scaffolds with varying irregularities (0.05-0.5) and porosities (48.83%–74.28%) designed through a novel Voronoi-Tessellation based method. Micro-computed tomography and scanning electron microscopy were used to characterize the scaffolds’ morphology. Quasi-static compression tests were performed to evaluate the scaffolds’ mechanical properties. The MG63 cells culture in vitro experiments, including adhesion, proliferation, and differentiation, were conducted to study the cytocompatibility of scaffolds. Compressive tests of scaffolds revealed an apparent elastic modulus range of 1.93–5.24 GPa and an ultimate strength ranging within 44.9–237.5 MPa, which were influenced by irregularity and porosity, and improved by heat treatment. Furthermore, the in vitro assay suggested that the original surface of the SLM-fabricated scaffolds was favorable for osteoblasts adhesion and migration because of micro scale pores and ravines. The trabecular-like porous scaffolds with full irregularity and higher porosity exhibited enhanced cells proliferation and osteoblast differentiation at earlier time, due to their preferable combination of small and large pores with various shapes. This study suggested that selective laser melting-derived Ti-6Al-4 V scaffold with the trabecular-like porous structure designed through Voronoi-Tessellation method, favorable mechanical performance, and good cytocompatibility was a potential biomaterial for orthopedic implants.     

Characterization and enhancement of chondrogenesis in porous hyaluronic acid-modified scaffolds made of PLGA(75/25) blended with PEI-grafted PLGA(50/50)

Hyaluronic acid (HA) improves the quality of microfracture-mediated cartilage regeneration by recruiting bone marrow mesenchymal stem cells (BMSCs) and chondrocytes. An HA-enriched scaffold was investigated to enhance chondrogenesis by BMSCs and chondrocytes in articular cartilage tissue engineering with the microfracture technique. Pre-fabricated porous PGP2/1 [poly(d,l-lactic acid-co-glycolic acid)(75/25) blended with polyethylenimine-grafted-poly(d,l-lactic acid-co-glycolic acid)(50/50) in a 2:1 ratio] scaffolds with 72.7% porosity and a 200–400-μm pore size were generated via the gas foaming/salt leaching method. HA-modified porous PGP2/1 (HA-PGP) scaffolds were used as the HA-enriched microenvironment. The mRNA levels of chondrogenic marker genes (SOX-9, aggrecan and type II collagen) were quantified using real-time polymerase chain reaction (PCR). Sulfated glycosaminoglycan (sGAG) deposition was detected by Alcian blue staining and dimethylmethylene blue (DMMB) assays. The expression of the chondrogenic genes type II collagen and aggrecan was significantly elevated in chondrocytes and BMSCs grown on HA-PGP scaffolds after seven days of culturing. BMSCs cultured in HA-PGP scaffolds showed increased sGAG content after four weeks of culturing. These results demonstrate that HA-PGP scaffolds provide a microenvironment that induces chondrogenesis by chondrocytes and BMSCs, which may be beneficial for regenerating cartilage-like tissue in vivo with the microfracture technique.     

Low-temperature fabrication of macroporous scaffolds through foaming and hydration of tricalcium silicate paste and their bioactivity

A low-temperature fabrication method for highly porous bioactive scaffolds was developed. The two-step method involved the foaming of tricalcium silicate cement paste and hydration to form calcium silicate hydrate and calcium hydroxide. Scaffolds with a combination of interconnected macro- and micro-sized pores were fabricated by making use of the decomposition of a hydrogen peroxide (H₂O₂) solution that acted as a foaming agent and through the hydration of tricalcium silicate cement. It was found possible to control the porosity and pore sizes by adjusting the concentration of the H₂O₂ solution. The in vitro bioactivity of the highly porous scaffolds was investigated by immersion in simulated body fluid (SBF) for 7 days. Hydroxyapatite (HAp) was formed on the surface of the scaffolds. Their bioactivity could be expected to be as good as that of tricalcium silicate cement, making the material competent for the bone tissue engineering application.     

Influence of preparation method on hydroxyapatite porous scaffolds

Hydroxyapatite (HA) is extensively used in medical applications as an artificial bone because of its similarity to the natural components of human bones and for its excellent biocompatibility. The porous structure of HA ceramics is more generally used as a scaffold. Many techniques, which are performed under fluid system, have been applied to fabricate HA porous scaffolds. In this work, polymeric sponge technique was employed in the preparation of HA slurry appropriated for porous ceramic fabrication. Effort for strength improvement was made on porous HA ceramic in several aspects. The effect of HA/water, binder/plasticizer ratios and dispersant content on the rheological properties of HA suspension in combination with the addition of SiC and SiO₂ on the compressive strength of porous bodies were investigated and discussed.     

Highly porous titanium (Ti) scaffolds with bioactive microporous hydroxyapatite/TiO2 hybrid coating layer

Highly porous Ti scaffolds with a bioactive microporous hydroxyapatite (HA)/TiO₂ hybrid coating layer were fabricated using the sponge replication process and micro-arc oxidation (MAO) treatment to produce the porous Ti scaffold and hybrid coating layer, respectively. In particular, the morphology and chemical composition of the hybrid coating layer were controlled by carrying out the MAO treatment in electrolyte solutions containing various concentrations of HA, ranging from 0 to 30 wt.%. The fabricated sample showed high porosity of approximately 70 vol.% with interconnected pores and reasonably high compressive strength of 18 ± 0.3 MPa. Furthermore, the surfaces could be coated successfully with a bioactive microporous HA/TiO₂ hybrid layer. The amount of HA particles in the hybrid coating layer increased with increasing HA content in the electrolyte solution, while preserving the microporous morphology. This hybrid coating improved the osteoblastic activity of the porous Ti scaffolds significantly.     

Preparation and characterization of bimodal porous poly(γ-benzyl-L-glutamate) scaffolds for bone tissue engineering

An ideal scaffold in bone tissue-engineering strategy should provide biomimetic extracellular matrix-like architecture and biological properties. Poly(γ-benzyl-L-glutamate) (PBLG) has been a popular model polypeptide for various potential biomedical applications due to its good biocompatibility and biodegradability. This study developed novel bimodal porous PBLG polypeptide scaffolds via a combination of biotemplating method and in situ ring-opening polymerization of γ-benzyl-L-gIutamate N-carboxyanhydride (BLG-NCA). The PBLG scaffolds were characterized by proton nuclear magnetic resonance spectroscopy, X-ray diffraction, differential scanning calorimetry, scanning electron microscope (SEM) and mechanical test. The results showed that the semi-crystalline PBLG scaffolds exhibited an anisotropic porous structure composed of honeycomb-like channels (100–200 μm in diameter) and micropores (5–20 μm), with a very high porosity of 97.4 ± 1.6%. The compressive modulus and glass transition temperature were 402.8 ± 20.6 kPa and 20.2 °C, respectively. The in vitro biocompatibility evaluation with MC3T3-E1 cells using SEM, fluorescent staining and MTT assay revealed that the PBLG scaffolds had good biocompatibility and favored cell attachment, spread and proliferation. Therefore, the bimodal porous polypeptide scaffolds are promising for bone tissue engineering.     

Effect of TiO2 nanoparticle loading on Poly(l-lactic acid) porous scaffolds fabricated by TIPS

Porous nanocomposite scaffolds of poly(l-lactic acid) (PLA), loaded with TiO₂ nanoparticles, were prepared by thermally induced phase-separation (TIPS). The preparation procedure induced crystalline polymer structures (with degree of crystallinity up to 51%) with no evidence of residual solvent, as confirmed by thermal analysis. Scaffold porosity, distribution of the nanofiller and shape of the pores were investigated by X-ray micro computed tomography (μ-CT) and scanning electron microscopy (SEM). The produced scaffolds with porosity of 86 ± 2% have interconnected open tubular pores with diameter and length in the ranges 40–80 μm and 200–400 μm respectively. The inorganic TiO₂ nano-additive is well dispersed in the scaffold walls, with only a small fraction of micrometric aggregates observable. All investigated polymer scaffolds display similar compressive moduli (between 2.1 and 2.8 MPa). Thermogravimetry (TGA), wide angle X-ray diffraction (XRD) and SEM analyses run on scaffolds subjected to in vitro mineralization tests showed that PLA scaffolds loaded with TiO₂ develop an amount of hydroxyapatite four times higher than that of plain PLA, thus assessing that titania nanoparticles confer improved bioactivity to the scaffolds.     

Hydroxyapatite porous scaffold engineered with biological polymer hybrid coating for antibiotic Vancomycin release

The purpose of this study is to improve hydroxyapatite (HA) porous scaffolds via coating with biological polymer-HA hybrids for use as wound healing and tissue regeneration. Highly porous HA scaffolds, fabricated by a polyurethane foam reticulate method, were coated with hybrid coating solution, consisting of poly(-caprolactone) (PCL), HA powders, and the antibiotic Vancomycin. The PCL to HA ratio was fixed at 1.5 and the drug amounts were varied [drug/(PCL + HA) = 0.02 and 0.04]. For the purpose of comparison, bare HA scaffold without the hybrid coating layer was also loaded with Vancomycin via an immersion-adsorption method. The hybrid coating structure and morphology were observed with Fourier transformed infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The effects of the hybrid coating on the compressive mechanical properties and the in vitro drug release of the scaffolds were investigated in comparison with bare HA scaffold. The PCL-HA hybrid coating altered the scaffold pore structure slightly, resulting in thicker stems and reduced porosity. With the hybrid coating, the HA scaffold responded to an applied compressive stress more effectively without showing a brittle failure. This was attributed to the shielding and covering of the framework surface by the coating layer. The encapsulated drugs within the coated scaffold was released in a highly sustained manner as compared to the rapid release of drugs directly adsorbed on the pure HA scaffold. These findings suggest that the coated HA scaffolds expand their applicability in hard tissue regeneration and wound healing substitutes delivering bioactive molecules.     

Effect of nanosilica addition on the physicomechanical properties,pore morphology,and phase transformation of freeze cast hydroxyapatite scaffolds

Freeze casting technique is a simple and effective method for the fabrication of porous ceramic structures. The objective of this work is to study the production and characterization of hydroxyapatite/nanosilica (HA/nSiO₂) scaffolds fabricated through this method. In the experimental procedure, the solidified samples were prepared by slurries containing different concentration of HA and nSiO₂ followed by sintering procedure at 1200 and 1350 °C. The phase composition, microstructure, and compressive strength of the scaffolds were characterized by X-ray diffraction, scanning electron microscopy, and mechanical strength test. It was found that the porosity of the scaffolds was in the range of 30–86.5 % and the value of compressive strengths lied between 0.16 and 71.96 MPa which were influenced by nSiO₂ content, cooling rate, and sintering temperature. With respect to porosity, pore size, and compressive strength, the scaffolds with 5 % nSiO₂, the cooling rate of 1 °C/min and the sintering temperature of 1350 °C showed preferable results for bone tissue engineering applications.     

Thermal shock resistance of the porous Al2O3/ZrO2 ceramics prepared by gelcasting

Porous Al₂O₃/ZrO₂ ceramics with porosity varying from 6% to 50% were fabricated by gelcasting using polystyrene (PS) as pore-forming agent. The effects of sintering temperature on porosity, strength as well as pore size were investigated. The flexural strength of these porous ceramics at room temperature significantly decreases as the porosity increases. Thermal shock resistance of these ceramics was improved by increasing the porosity. Both the critical difference temperature (ΔT_c) and residual strength of high porosity ceramics were higher than those of low porosity ceramics. These improvements can be attributed to the pores in the specimens which relax the thermal shock stress and arrest the propagation of microcracks effectively, which is confirmed by XRD analysis of specimens which encountered different thermal shock temperature difference.     

Porous nanocellulose gels and foams: Breakthrough status in the development of scaffolds for tissue engineering

We report on the latest scientific advances related to the use of porous foams and gels prepared with cellulose nanofibrils (CNF) and nanocrystals (CNC) as well as bacterial nanocellulose (BNC) – collectively nanocelluloses – as biomedical materials for application in tissue regeneration. Interest in such applications stems from the lightweight and strong structures that can be efficiently produced from these nanocelluloses. Dried nanocellulose foams and gels, including xerogels, cryogels, and aerogels have been synthesized effortlessly using green, scalable, and cost-effective techniques. Methods to control structural features (e.g., porosity, morphology, and mechanical performance) and biological interactions (e.g., biocompatibility and biodegradability) are discussed in light of specific tissues of interest. The state-of-the-art in the field of nanocellulose-based scaffolds for tissue engineering is presented, covering physicochemical and biological properties relevant to these porous systems that promise groundbreaking advances. Specifically, these materials show excellent performance for in vitro cell culturing and in vivo implantation. We report on recent efforts related to BNC scaffolds used in animal and human implants, which furthermore support the viability of CNF- and CNC-based scaffolds in next-generation biomedical materials.     

Highly porous gelatin–silica hybrid scaffolds with textured surfaces using new direct foaming/freezing technique

Highly porous gelatin–silica hybrid scaffolds with high porosity, large pores and large interconnections, as well as tailored surface textures were produced using a newly developed direct foaming/freezing. Two different types of precursors as the silica source, 3-glycidoxyproyltrimethoxysilane (denoted as “GS”) and sol–gel derived silica (denoted as “SS”), were used for producing the porous GLA–GS and GLA–GS–SS hybrid scaffolds. In this method, air bubbles could be vigorously incorporated into the GLA–GS and GLA–GS–SS mixtures and then stabilized by rapid freezing of the foamed mixtures at −70 °C. Both the porous GLA–GS and GLA–GS–SS hybrid scaffolds produced herein had a highly porous structure (porosity > 90 vol%, pore size = 200–500 μm, interconnection size = 100–200 μm) with a uniform distribution of the silica phase in the gelatin matrix. In addition, surface textures with a rugged morphology could be created after immersion of the porous GLA–GS and GLA–GS–SS hybrid scaffolds in ethanol at −20 °C for 24 h. The porous GLA–GS and GLA–GS–SS hybrid scaffolds showed much higher mechanical properties than the porous GLA scaffold, while preserving excellent in vitro biocompatibility, demonstrating potential application as the bone scaffold.     

Poly(ε-caprolactone)/nano fluoridated hydroxyapatite scaffolds for bone tissue engineering: in vitro degradation and biocompatibility study

In this study, biodegradation and biocompatibility of novel poly(ε-caparolactone)/nano fluoridated hydroxyapatite (PCL–FHA) scaffolds were investigated. The FHA nanopowders were prepared via mechanical alloying method and had a chemical composition of Ca₁₀ (PO₄)₆OH_2–x F _x (where x values were selected equal to 0.5 and 2.0). In order to fabricate PCL–FHA scaffolds, 10, 20, 30 and 40 wt% of the FHA were added to the PCL. The PCL–FHA scaffolds were produced by the solvent casting/particulate leaching using sodium chloride particles (with diameters of 300–500 μm) as the porogen. The phase structure, microstructure and morphology of the scaffolds were evaluated using X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy techniques. Porosity of the scaffolds was measured using the Archimedes’ Principle. In vitro degradation of PCL–FHA scaffolds was studied by incubating the samples in phosphate buffered saline at 37°C and pH 7.4 for 30 days. Moreover, biocompatibility was evaluated by MTT assay after seeding and culture of osteoblast-like cells on the scaffolds. Results showed that the osteoblast-like cells attached to and proliferated on PCL–FHA and increasing the porosity of the scaffolds increased the cell viability. Also, degradation rate of scaffolds were increased with increasing the fluorine content in scaffolds composition.     

Fabrication of highly porous titanium (Ti) scaffolds with two interlaced periodic pores

This paper reports a novel type of porous titanium (Ti) scaffolds with two interlaced periodic pores that were produced by coating the surfaces of a dual-channeled hydroxyapatite (HA) scaffold, as a supporting framework, with a titanium hydride (TiH₂) slurry followed by heat-treatment at 1200 °C for 3 h in a vacuum to convert TiH₂ to Ti metal. This method allowed the porous Ti scaffolds to mimic the original pore structure of the dual-channeled HA scaffold in a tightly controlled manner. It was observed that the Ti layer was strongly adhered to the HA layer, owing to the diffusion of P ions into the Ti layer. The fabricated sample showed a high compressive strength of 6.0 ± 0.77 MPa and a porosity of 78 vol.% due to its unique pore structure, as well as perfect interconnections between the pores.     

Biodegradable poly(lactic acid)/hydroxyl apatite 3D porous scaffolds using high-pressure molding and salt leaching

Scaffolds comprising poly(lactic acid) (PLA) and hydroxyl apatite (HA) were fabricated by combination of the high-pressure compression-molding plus salt-leaching techniques. The optimized HA content was determined in terms of the pore morphology, porosity, storage modulus, degradation behavior, hydrophilicity as well as the cell growth ability of the scaffolds. At HA content of 20 wt%, the scaffolds exhibited an interconnected open pore structure with the high porosity of 82.2 %. More importantly, the storage modulus of PLA/HA scaffolds (87.6 MPa) achieved almost three times higher compared with pure PLA scaffolds, while under low-pressure condition, the increase of modulus caused by HA does not reach 150 %. The obvious contrast indicated that HA and high pressure had a synergistic effect on enhancing mechanical properties of porous scaffolds. It was truly interesting that the hydrophilicity of PLA/HA scaffolds was significantly improved by alkaline hydrolysis treatment, which eventually led to the excellent cellular biocompatibility of the scaffolds, as revealed from the morphology and spreading of the cells cultured in our scaffolds. On the whole, the resultant PLA/HA scaffolds are well-suited candidates for the design of tailor-made matrices in tissue engineering.     

Preparation and comparative characterization of keratin–chitosan and keratin–gelatin composite scaffolds for tissue engineering applications

We report fabrication of three dimensional scaffolds with well interconnected matrix of high porosity using keratin, chitosan and gelatin for tissue engineering and other biomedical applications. Scaffolds were fabricated using porous Keratin–Gelatin (KG), Keratin–Chitosan (KC) composites. The morphology of both KG and KC was investigated using SEM. The scaffolds showed high porosity with interconnected pores in the range of 20–100 μm. They were further tested by FTIR, DSC, CD, tensile strength measurement, water uptake and swelling behavior. In vitro cell adhesion and cell proliferation tests were carried out to study the biocompatibility behavior and their application as an artificial skin substitute. Both KG and KC composite scaffolds showed similar properties and patterns for cell proliferation. Due to rapid degradation of gelatin in KG, we found that it has limited application as compared to KC scaffold. We conclude that KC scaffold owing to its slow degradation and antibacterial properties would be a better substrate for tissue engineering and other biomedical application.