Hydroxyapatite-coated carboxymethyl chitosan scaffolds for promoting osteoblast and stem cell differentiation

Characterization of nano-hydroxyapatite incorporated carboxymethyl chitosan composite on human dental pulp stem cells

AIM

To compare the odontogenic differentiation potential of a composite scaffold (CSHA) comprising of nano-hydroxyapatite (nHAp) and carboxymethyl chitosan (CMC) with Biodentine on human dental pulp stem cells (hDPSCs).

METHODOLOGY

A CSHA scaffold was prepared through an ultrasonication route by adding nHAp and CMC (1:5 w/w) in water medium followed by freeze-drying. Physicochemical characterization was achieved using scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared spectroscopy. In-vitro bioactivity and pH assessments were done by soaking in simulated body fluid (SBF) for 28 days. The angiogenic and odontogenic differentiation abilities were assessed by expression of vascular endothelial growth factor (VEGF) and Dentine sialophosphoprotein (DSPP) markers on cultured hDPSCs by flow cytometry and RT-qPCR at 7, 14 and 21 days. Cell viability/proliferation and biomineralization abilities of CSHA were compared with Biodentine by MTT assay, alkaline phosphatase (ALP) activity, Alizarin Red Staining (ARS) and osteopontin (OPN) expression on hDPSCs following 7 and 14 days. Data were statistically analysed with Kruskal Wallis and Friedman tests as well as one way anova followed by appropriate post hoc tests (p < .05).

RESULTS

Characterization experiments revealed a porous microstructure of CSHA with pore diameter ranging between 60 and 200 μm and 1.67 Ca/P molar ratio along with the characteristic functional groups of both HAp and CMC. CSHA displayed bioactivity in SBF by forming apatite-like crystals and maintained a consistent pH value of 7.70 during 28 days' in vitro studies. CSHA significantly upregulated VEGF and DSPP levels on hDPSCs on day 21 compared with day 7 (p < .05). Further, CSHA supported cell viability/proliferation over 14 days like Biodentine with no statistical differences (p > .05). However, CSHA exhibited increased ALP and ARS activity with an intense OPN staining compared with Biodentine after 14 days (p < .05).

CONCLUSION

The results highlighted the odontogenic differentiation and biomineralization abilities of CSHA on hDPSCs with significant VEGF and DSPP gene upregulations. Further, CSHA exhibited enhanced mineralization activity than Biodentine, as evidenced by increased ALP, ARS and OPN activity on day 14. The nHAp-CMC scaffold has the potential to act as an effective pulp capping agent; however, this needs to be further validated through in-vivo animal studies.

Recent advances in carboxymethyl chitosan-based materials for biomedical applications

Chitosan (CS) and its derivatives have been applied extensively in the biomedical field owing to advantageous characteristics including biodegradability, biocompatibility, antibacterial activity and adhesive properties. The low solubility of CS at physiological pH limits its use in systems requiring higher dissolving ability and a suitable drug release rate. Besides, CS can result in fast drug release because of its high swelling degree and rapid water absorption in aqueous media. As a water-soluble derivative of CS, carboxymethyl chitosan (CMC) has certain improved properties, rendering it a more suitable candidate for wound healing, drug delivery and tissue engineering applications. This review will focus on the antibacterial, anticancer and antitumor, antioxidant and antifungal bioactivities of CMC and the most recently described applications of CMC in wound healing, drug delivery, tissue engineering, bioimaging and cosmetics.

Effects of Micro-Arc Oxidation Discharge Parameters on Formation and Biomedical Properties of Hydroxyapatite-Containing Flower-like Structure Coatings

The micro-arc oxidation (MAO) process was used to prepare hydroxyapatite-containing flower-like structure coatings on commercially pure titanium substrates with various values of the applied voltage (330, 390, 450 V), applied current (0.4, 0.5, 0.6 A), and duration time (1, 3, 5 min). It was found that the surface morphology of the coatings was determined primarily by the applied voltage. A voltage of 330 V yielded a flower-like/plate-like structure, while voltages of 390 V and 450 V produced a flower-like structure and a porous morphology, respectively. The applied current and duration time mainly affected the coating formation speed and petal size of the flower-like structures, respectively. The coatings prepared using voltages of 330 V and 390 V (0.6 A, 5 min) both contained Ti, TiO₂-A (anatase), TiO₂-R (rutile), DCPD (CaHPO₄·2H₂O, calcium hydrogen phosphate), and hydroxyapatite (HA). However, the latter coating contained less DCPD and had a higher HA/DCPD ratio and a Ca/P ratio closer to the ideal value of HA. The coating prepared with a voltage of 450 V consisted mainly of Ti, TiO₂-A, TiO₂-R, and CaTiO₃. For the coatings prepared with a voltage of 390 V, the flower-like structures consisted mainly of HA-containing compounds. DCPD plate-like structures were observed either between the HA-containing flower-like structures (330 V samples) or within the flower-like structures themselves (390 V samples). The coating surfaces with flower-like/plate-like or flower-like structures had a greater roughness, which increased their hydrophilicity and resulted in superior bioactivity (SBF immersion) and biocompatibility (MG-63 cell culture). The optimal biomedical performance was found in the 390 V coating due to its flower-like structure and high HA/DCPD ratio.

Strategies to improve bioactive and antibacterial properties of polyetheretherketone (PEEK) for use as orthopedic implants

Polyetheretherketone (PEEK) has gradually become the mainstream material for preparing orthopedic implants due to its similar elastic modulus to human bone, high strength, excellent wear resistance, radiolucency, and biocompatibility. Since the 1990s, PEEK has increasingly been used in orthopedics. Yet, the widespread application of PEEK is limited by its bio-inertness, hydrophobicity, and susceptibility to microbial infections. Further enhancing the osteogenic properties of PEEK-based implants remains a difficult task. This article reviews some modification methods of PEEK in the last five years, including surface modification of PEEK or incorporating materials into the PEEK matrix. For surface modification, PEEK can be modified by chemical treatment, physical treatment, or surface coating with bioactive substances. For PEEK composite material, adding bioactive filler into PEEK through the melting blending method or 3D printing technology can increase the biological activity of PEEK. In addition, some modification methods such as sulfonation treatment of PEEK or grafting antibacterial substances on PEEK can enhance the antibacterial performance of PEEK. These strategies aim to improve the bioactive and antibacterial properties of the modified PEEK. The researchers believe that these modifications could provide valuable guidance on the future design of PEEK orthopedic implants.

Composite Coatings for Osteoblast Growth Attachment Fabricated by Matrix-Assisted Pulsed Laser Evaporation

The bioactive and biocompatible properties of hydroxyapatite (HAp) promote the osseointegration process. HAp is widely used in biomedical applications, especially in orthopedics, as well as a coating material for metallic implants. We obtained composite coatings based on HAp, chitosan (CS), and FGF2 by a matrix-assisted pulsed laser evaporation (MAPLE) technique. The coatings were physico-chemically investigated by means of X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Infrared Microscopy (IRM), and Scanning Electron Microscopy (SEM). Further, biological investigations were performed. The MAPLE-composite coatings were tested in vitro on the MC3T3-E1 cell line in order to endorse cell attachment and growth without toxic effects and to promote pre-osteoblast differentiation towards the osteogenic lineage. These coatings can be considered suitable for bone tissue engineering applications that lack toxicity and promotes cell adhesion and proliferation while also sustaining the differentiation of pre-osteoblasts towards mature bone cells.

Retention of Intrafibrillar Minerals Improves Resin-Dentin Bond Durability

The concept of extrafibrillar demineralization involves selective removal of apatite crystallites from the extrafibrillar spaces of mineralized dentin without disturbing the intrafibrillar minerals within collagen. This helps avoiding activation of endogenous proteases and enables air-drying of partially demineralized dentin without causing collapse of completely demineralized collagen matrix that adversely affects resin infiltration. The objective of the present study was to evaluate the potential of quaternized carboxymethyl chitosan (QCMC)-based extrafibrillar demineralization in improving resin-dentin bond durability. Isothermal titration calorimetry indicated that QCMC synthesized by quaternization of O-carboxymethyl chitosan had moderate affinity for Ca²⁺ (binding constant: 8.9 × 10⁴ M^-1). Wet and dry bonding with the QCMC-based demineralization produced tensile bond strengths equivalent to the phosphoric acid (H₃PO₄)-based etch-and-rinse technique. Those bond strengths were maintained after thermocycling. Amide I and PO₄^3- mappings of QCMC-conditioned dentin were performed with atomic force microscope-infrared spectroscopy (AFM-IR). Whereas H₃PO₄-etched dentin exhibited an extensive reduction in PO₄^3- signals corresponding to apatite depletion, QCMC-conditioned dentin showed scattered dark areas and bright PO₄^3- streak signals. The latter were consistent with areas identified as collagen fibrils in the amide I mapping and were suggestive of the presence of intrafibrillar minerals in QCMC-conditioned dentin. Young's modulus mapping of QCMC-demineralized dentin obtained by AFM-based amplitude modulation-frequency modulation recorded moduli that were the same order of magnitude as those in mineralized dentin and at least 1 order higher than H₃PO₄-etched dentin. In situ zymography of the gelatinolytic activity within hybrid layers created with QCMC conditioning revealed extremely low signals before and after thermocycling, compared with H₃PO₄-etched dentin for both wet and dry bonding. Confocal laser scanning microscopy identified the antibacterial potential of QCMC against Streptococcus mutans and Enterococcus faecalis biofilms. Taken together, the QCMC-based demineralization retains intrafibrillar minerals, preserves the elastic modulus of collagen fibrils, reduces endogenous proteolytic activity, and inhibits bacteria biofilms to extend dentin bond durability.

Chemical Immobilization of Carboxymethyl Chitosan on Polycaprolactone Nanofibers as Osteochondral Scaffolds

Carboxymethyl chitosan (CMC) as a bio-based osteochondral inductive material was chemically immobilized on the surface of polycaprolactone (PCL) nanofibers to fabricate scaffolds for osteochondral tissue engineering applications. The chemical immobilization process included the aminolysis of ester bonds and bonding of the primary amines with glutaraldehyde as a coupling agent. The SEM and FTIR results confirmed the successfulness of the CMC immobilization. The fabricated scaffolds presented cell viabilities of > 82% and supported the attachment and proliferation of the human bone marrow mesenchymal stem cells (hBM-MSCs). The CMC-immobilized scaffolds concentration dependently induced the diverse osteochondral differentiation pathways for the hBM-MSCs without using any external differential agents. According to the Alcian Blue and Alizarin Red staining and immunocytochemistry results, scaffolds with a higher content of CMC presented more chondro-inductivity and less osteoinductivity. Thus, the CMC-immobilized scaffolds can be employed as great potential candidates for osteochondral tissue engineering applications.

Effectiveness of bio-dispersant in homogenizing hydroxyapatite for proliferation and differentiation of osteoblast

Hydroxyapatite (HA), an inorganic compound, plays an essential role in the proliferation and differentiation of bone cells. Using cellulose nanocrystals (CNCs) as green dispersants to improve homogenization of HA is promising in the fabrication of nanocomposite scaffolds with biocompatibility for bone tissue engineering. The HA/CNC (HC) nanoparticle suspension was incorporated in polyvinyl alcohol (PVA)-based scaffold to investigate the physical and chemical properties. The PVA/HC composites demonstrated high porous structure and swelling ability for cell attachment and a 3-fold improvement in compressive modulus compared with free HC scaffold. Moreover, the presence of HC nanoparticles has promoted the proliferation and mineralization of pre-osteoblast. Our findings could provide an effective strategy by using bio-dispersants to incorporate mineral elements into synthetic polymers for the fabrication of functional tissue engineering scaffolds.

Chitosan-Based Biomimetically Mineralized Composite Materials in Human Hard Tissue Repair

Chitosan is a natural, biodegradable cationic polysaccharide, which has a similar chemical structure and similar biological behaviors to the components of the extracellular matrix in the biomineralization process of teeth or bone. Its excellent biocompatibility, biodegradability, and polyelectrolyte action make it a suitable organic template, which, combined with biomimetic mineralization technology, can be used to develop organic-inorganic composite materials for hard tissue repair. In recent years, various chitosan-based biomimetic organic-inorganic composite materials have been applied in the field of bone tissue engineering and enamel or dentin biomimetic repair in different forms (hydrogels, fibers, porous scaffolds, microspheres, etc.), and the inorganic components of the composites are usually biogenic minerals, such as hydroxyapatite, other calcium phosphate phases, or silica. These composites have good mechanical properties, biocompatibility, bioactivity, osteogenic potential, and other biological properties and are thus considered as promising novel materials for repairing the defects of hard tissue. This review is mainly focused on the properties and preparations of biomimetically mineralized composite materials using chitosan as an organic template, and the current application of various chitosan-based biomimetically mineralized composite materials in bone tissue engineering and dental hard tissue repair is summarized.

Chitosan-coated hydroxyapatite and drug-loaded polytrimethylene carbonate/polylactic acid scaffold for enhancing bone regeneration

Biocompatible polymers and drug-delivery scaffolds have driven development in bone regeneration. In this study, we fabricated a chitosan (CS)-coated polytrimethylene carbonate (PTMC)/polylactic acid (PLLA)/oleic acid-modified hydroxyapatite (OA-HA)/vancomycin hydrochloride (VH) microsphere scaffold for drug release with excellent biocompatibility. The incorporation of PLLA, OA-HA, and VH into PTMC microspheres not only slowed the biodegradability of the scaffold but also enhanced its mechanical properties and surface properties. Moreover, the CS coating stimulated extensive adhesion of osteoblasts before OA-HA incorporation, which facilitated the controlled release of OA-HA. The scaffolds were characterized via scanning electron microscopy, in vitro comprehensive performance testing, cell culturing, and microcomputer tomography scanning. The results indicated that the surface of the composite microsphere scaffold was suitable for osteoblast adhesion. Additionally, the release of OA-HA stimulated osteogenic proliferation. Our findings suggest that the CS-PTMC/PLLA/OA-HA/VH microsphere scaffold is promising for bone tissue engineering applications.

The Injectable Woven Bone-Like Hydrogel to Perform Alveolar Ridge Preservation With Adapted Remodeling Performance After Tooth Extraction

Grafting bone substitute is paramount to prevent the alveolar ridge resorption after tooth extraction and facilitate the subsequent implant treatment. An ideal bone substitute should acquire the excellent osteogenic property, more importantly, possess the suitable remodeling rate in balance with bone formation and desirable clinical manageability. However, none of bone substitute is simultaneously characterized by these features, and currently, the limited remodeling property leads to the excessive waiting time before implantation. Enlightened by woven bone, the transitional tissue that is able to induce osteogenesis during bone healing could be easily remodeled within a short period and depend on the favorable injectability of hydrogel, an injectable woven bone-like hydrogel (IWBLH) was constructed in this study to address the above problems. To mimic the component and hierarchical structure of woven bone, amorphous calcium phosphate (ACP) and mineralized collagen fibril were synthesized and compounded with alginate to form IWBLHs with various ratio. Screened by physiochemical characterization and in vitro biological assays, an optimal IWBLH was selected and further explored in rat model of tooth extraction. Compared with the most widely used bone substitute, we showed that IWBLH could be easily handled to fully fill the tooth socket, perform a comparable function to prevent the alveolar bone resorption, and completely remodeled within 4 weeks. This IWBLH stands as a promising candidate for alveolar ridge preservation (ARP) in future.

Preparation of BMP-2/chitosan/hydroxyapatite antibacterial bio-composite coatings on titanium surfaces for bone tissue engineering

In this paper, petaling hydroxyapatite (HA)/TiO₂ composite coatings were firstly prepared on titanium (Ti) surface by one-step micro-arc oxidation (MAO), and then pure chitosan (CS) and bone morphogenic protein-2 (BMP-2)-encapsulated CS coatings were respectively loaded on the HA/TiO₂ surfaces by dip-coating method to endow Ti with good antibacterial and biological properties. The bonding strength between coatings was studied by scratch method. The degradability of CS, BMP-2 release behavior, bioactivity, biocompatibility and antibacterial activity of the obtained (BMP-2)/CS/HA/TiO₂ coatings were examined by in vitro tests. The results showed that, the thicker the HA layer, the larger the loaded BMP-2 and CS amount, resulting in better bonding strength between coatings, antibacterial activity and biocompatibility. In addition, with the increase of CS concentration, more CS was loaded on HA coatings, which benefited the increase of CS degrading amount, the prolonged CS degradation time and BMP-2 release time, resulting in improved antibacterial and biological property. All CS/HA/TiO₂ coatings accelerated cell adhesion, spreading and proliferation, and promoted HA formation in simulated body fluids (SBF). After loading BMP-2 in CS, the BMP-2 can significantly improve cell adhesion, spreading and proliferation, and the loaded amount can also be controlled by the concentration of BMP-2 solution. The present study indicates that, by controlling the thickness of HA layers and concentrations of CS and BMP-2 solutions, the Ti implant material with excellent biological and antibacterial properties can be achieved.

Heat-curing polylactide for bone implants: Preparation and investigation on properties relevant to degradation

Several processes have been used to produce polylactide for bone replacement. The challenge remains, however, to produce these devices by a simpler and more economical process. In this study, a method of combining powder and liquid parts was introduced. Star-shaped polylactides with molecular weights ranging from 3 to 16 kg/mol were synthesized and blended with a linear polylactide (Mw = 188 kg/mol) using the technique of emulsion solvent evaporation. The blends in a form of spherical powder were characterized by scanning electron microscopy, gel permeation chromatography, and particle size analysis. The heat-curing polylactide was fabricated by mixing the powder with triethylene glycol dimethacrylate, molded, and then heated in a hot water bath to solidify. The effects of powder composition in terms of amount and molecular weight of the star-shaped polylactide on mechanical properties were investigated. The results showed an increase in flexural strength with increase in the amount of star-shaped polylactide. The powder comprised star-shaped polylactide having the molecular weight of 10,770 g/mol, not less than 80wt%, offered the fabricated heat-curing polylactide with high strength ranging from 95 to 100 MPa. This formulation was further incorporated with hydroxyapatite to improve biocompatibility and subjected to degradation at 37°C. Mechanical test and weight loss determination together with biological test were conducted at certain times during degradation of the materials. Both materials with and without hydroxyapatite showed mechanical stability upon degradation for at least 6 months, but the one with hydroxyapatite revealed significantly better bioactivity at the end of 1-year follow-up study, making it the most promising material for bone implants.

Construction and in vivo/in vitro evaluation of a nanoporous ion-responsive targeted drug delivery system for recombinant human interferon α-2b delivery

Background

Like most protein macromolecular drugs, the half-life of rhIFNɑ-2b is short, with a low drug utilization rate, and the preparation and release conditions significantly affect its stability.

Methods

A nanoporous ion-responsive targeted drug delivery system (PIRTDDS) was designed to improve drug availability of rhIFNα-2b and target it to the lung passively with sustained release. Chitosan rhIFNα-2b carboxymethyl nanoporous microspheres (CS-rhIFNα-2b-CCPM) were prepared by the column method. Here, an electrostatic self-assembly technique was undertaken to improve and sustain rhIFNα-2b release rate.

Results

The size distribution of the microspheres was 5~15 μm, and the microspheres contained nanopores 300~400 nm in diameter. The in vitro release results showed that rhIFNα-2b and CCPM were mainly bound by ionic bonds. After self-assembling, the release mechanism was transformed into being membrane diffusion. The accumulative release amount for 24 hrs was 83.89%. Results from circular dichrogram and SDS-PAGE electrophoresis showed that there was no significant change in the secondary structure and purity of rhIFNα-2b. Results from inhibition rate experiments for A549 cell proliferation showed that the antitumor activity of CS-rhIFNα-2b-CCPM for 24 hrs retained 91.98% of the stock solution, which proved that the drug-loaded nanoporous microspheres maintained good drug activity. In vivo pharmacokinetic experimental results showed that the drugs in CS-rhIFNα-2b-CCPM can still be detected in vivo after 24 hrs, equivalent to the stock solution at 6 hrs, which indicated that CS-rhIFNα-2b-CCPM had a certain sustained-release effect in vivo. The results of in vivo tissue distribution showed that CS-rhIFNα-2b-CCPM was mainly concentrated in the lungs of mice (1.85 times the stock solution). The pharmacodynamics results showed that CS-rhIFNα-2b-CCPM had an obvious antitumor effect, and the tumor inhibition efficiency was 29.2%.

Conclusion

The results suggested a novel sustained-release formulation with higher drug availability and better lung targeting from CS-rhIFNα-2b-CCPM compared to the reference (the stock solution of rhIFNα-2b), and, thus, should be further studied.

Antitumor evaluation of carboxymethyl chitosan based norcantharidin conjugates against gastric cancer as novel polymer therapeutics

Novel polymer-drug conjugates (CNC) were prepared from carboxymethyl chitosan (CMCS) and norcantharidin (NCTD) via amidation reaction and characterized by FTIR and ¹H NMR spectroscopy. The aim of this study was to elucidate the antitumor efficacy of CNC on gastric cancer and the possible underlying mechanisms. The CNC conjugates possessed significant inhibitory effects on the proliferation of SGC-7901 cells and suppressed the migration as well as tube formation of HUVECs. Besides, Hoechst 33258 staining and Annexin V-FITC/PI detection suggested that the conjugates were more effective in triggering apoptosis of SGC-7901 cells compared with free NCTD. Moreover, CNC remarkably reduced systemic toxicity and enhanced the antitumor efficacy in vivo with a tumor suppression rate of 59.57% against SGC-7901 gastric tumor in BALB/c nude mice. Further investigation about the underlying mechanisms indicated that CNC could upregulate expressions of TNF-α and Bax, and downregulate expressions of VEGF, Bcl-2, MMP-2 and MMP-9, thereby inhibiting tumor metastasis and inducing apoptosis in vivo. Overall, our results demonstrated that CNC might be a promising and feasible polymer therapeutics for gastrointestinal tumor therapy.

Cross-linked cellulose nanocrystal aerogels as viable bone tissue scaffolds

Chemically cross-linked cellulose nanocrystal (CNC) aerogels possess many properties beneficial for bone tissue scaffolding applications. CNCs were extracted using sulfuric acid or phosphoric acid, to produce CNCs with sulfate and phosphate half-ester surface groups, respectively. Hydrazone cross-linked aerogels fabricated from the two types of CNCs were investigated using scanning electron microscopy, X-ray micro-computed tomography, X-ray photoelectron spectroscopy, nitrogen sorption isotherms, and compression testing. CNC aerogels were evaluatedin vitrowith osteoblast-like Saos-2 cells and showed an increase in cell metabolism up to 7 days while alkaline phosphatase assays revealed that cells maintained their phenotype. All aerogels demonstrated hydroxyapatite growth over 14 days while submerged in simulated body fluid solution with a 0.1 M CaCl₂ pre-treatment. Sulfated CNC aerogels slightly outperformed phosphated CNC aerogels in terms of compressive strength and long-term stability in liquid environments, and were implanted into the calvarian bone of adult male Long Evans rats. Compared to controls at 3 and 12 week time points, sulfated CNC aerogels showed increased bone volume fraction of 33% and 50%, respectively, compared to controls, and evidence of osteoconductivity. These results demonstrate that cross-linked CNC aerogels are flexible, porous and effectively facilitate bone growth after they are implanted in bone defects. STATEMENT OF SIGNIFICANCE: Due to the potential complications associated with autografts, there is a need for synthetic bone tissue scaffolds. Here, we report a new naturally-based aerogel material for bone regeneration made solely from chemically cross-linked cellulose nanocrystals (CNC). These highly porous CNC aerogels were shown to promote the proliferation of bone-like cells and support the growth of hydroxyapatite on their surface in vitro. The first in vivo study on these materials was conducted in rats and showed their osteconductive properties and an increase in bone volume up to 50% compared to sham sites. This study demonstrates the potential of using functionalized cellulose nanocrystals as the basis for aerogel scaffolds for bone tissue engineering.

Rat sciatic nerve regeneration across a 10-mm defect bridged by a chitin/CM-chitosan artificial nerve graft

Chitosan as a natural bioactive biopolymer has been commonly employed in guidance conduit for repairing peripheral nerve injury, due to its excellent properties of low toxicity, antibacterial properties, high biocompatibility and biodegradability. In this study, chitin and CM-chitosan were prepared from pharmaceutical grade chitosan. Moreover, a novel composite chitosan-based nerve graft comprising microporous chitin-based conduit and internal CM-chitosan fiber was constructed and applied to bridge sciatic nerve across a 10-mm defect in SD rats. The chitin/CM-chitosan artificial nerve graft could promote the proliferation of rat Schwann cells (RSC96) with good cell biocompatibility. After implantation, the artificial nerve graft showed slow degradation. No apparent toxicity was observed, and tissue inflammation was very slight after implantation, indicating favorable bio-safety of the nerve graft. Furthermore, the chitin/CM-chitosan artificial nerve graft could effectively promote restoration of damaged neurons with similar effect compared to the autograft. In conclusion, the composite biodegradable chitin/CM-chitosan nerve grafts possessed favorable biocompatibility and good potential in repairing peripheral nervous injury.

Osteoblast responses to injectable bone substitutes of kappa-carrageenan and nano hydroxyapatite

The combination of kappa-carrageenan (κ-CG) and hydroxyapatite (HA) to generate a bone substitute material has been underexplored to date. Carrageenans (CGs) have remarkable characteristics such as biocompatibility, hydrophilicity, and structural similarities with natural glycosaminoglycans (GAGs), and they have demonstrated the ability to stimulate cellular adhesion and proliferation. Hydroxyapatite nanoparticles have been one of the most investigated materials for bone regeneration due to their excellent biocompatibility, bioactivity and osteoconductivity. In particular, this study presents an approach for the preparation of new bioactive composites of κ-CG/nHA for numerous bone regeneration applications. We performed a set of in vitro experiments to evaluate the influence of the bone substitutes on human osteoblasts. Cell culture studies indicated that all samples tested were cytocompatible. Relative to control substrates, cellular attachment and proliferation were better on all the scaffold surfaces that were tested. The S2 and S3 samples, those permeated by 1.5 and 2.5 wt% of CG, respectively, exhibited an enhancement in cell spreading capacity compared to the S1 test materials which were comprised of 1 wt% of CG. Excellent osteoblast viability and adhesion were observed for each of the tested materials. Additionally, the bone substitutes developed for this study presented a distinct osteoconductive environment. Data supporting this claim were derived from alkaline phosphatase (ALP) and calcium deposition analyses, which indicated that, compared to the control species, ALP expression and calcium deposition were both improved on test κ-CG/nHA surfaces. In summary, the injectable bone substitute developed here demonstrated great potential for numerous bone regeneration applications, and thus, should be studied further. STATEMENT OF SIGNIFICANCE: The novelty of this work lies in the determination of the in vitro cytocompatibility behavior of carrageenan and hydroxyapatite composite materials used as injectable bone substitutes. This injectable biomaterial can fill in geometric complex defects, and it displays bioactivity as well as high bone regeneration capacity. In this study, we evaluated the behaviors of osteoblast cells in contact with the scaffolds, including cellular adhesion and proliferation, cellular metabolism, and mineralization on the fabricated injectable bone substitutes. The results show than the carrageenan and hydroxyapatite substitutes provided a biomaterial with a great capacity for promoting cellular growth, adhesion, and proliferation, as well as contributing an osteoinductive environment for osteoblast differentiation and osteogenesis.

Evaluation of cytotoxicity and antimicrobial activity of an injectable bone substitute of carrageenan and nano hydroxyapatite

A successful post-surgical implant is associated with accelerated recovery periods, involving the efficient regeneration of lost or non-viable tissue and a reduction in microbial growth. Alternatively, the long-term success of an implant is guided by the selection of an engineered biomimetic material that is biocompatible, non-biodegradable, and stable at the site of implantation, without invoking any non-essential or undesirable biological responses. The potential for developing an injectable bone substitute (IBS) was investigated here. In particular, carrageenan (CG) and nano-hydroxyapatite (nHA) injectable composites were fabricated by chemical cross-linking, and the in vitro behavior of mammalian cells and bacteria on the IBS surface structures were evaluated. Formulations consisting of 1%, 1.5%, and 2.5% CG and 60% nHA by weight were then evaluated for their interactions with human osteoblasts (or bone forming cells). MTS viability testing indicated that osteoblast adhesion and viability on the IBS were excellent and uniform among various formulation types. Bacteria assays were also performed to assess antimicrobial functions on the CG/nHA composite against both Gram-negative and Gram-positive strains. A higher CG content, as found in some samples, correlated with improved Pseudomonas aeruginosa growth inhibition, although other bacteria strains appeared unaffected by the IBS. In summary, this study highlights CG/nHA composites as innovative biomaterials that should be further studied for reduced bacteria activity and promoted osteoblast responses which was achieved without using pharmaceutical drugs. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 2984-2993, 2018.

Composite scaffolds loaded with bone mesenchymal stem cells promote the repair of radial bone defects in rabbit model

This study aimed to investigate the efficacy of three-dimensional scaffolds of silk fibroin/chitosan/nano-hydroxyapatite (SF/CS/nHA) and bone marrow derived mesenchymal stem cells (BMSCs) on the repair of long segmental bone defects in rabbits. BMSCs were cultured with SF/CS/nHA in vitro, and cell proliferation, alkaline phosphatase activity and Ca2+ content were examined. A 15mm segmental defect in the radius was generated in 12 New Zealand White rabbits, which were divided randomly into three groups (n=4): experimental group with SF/CS/nHA scaffold of induced BMSCs; control group with SF/CS/nHA scaffold; and blank group without any materials. Postoperatively at 12 weeks, osteogenesis effect and the degradation and absorption of SF/CS/nHA were evaluated by X-ray, hematoxylin eosin staining, and scanning electron microscopy. In vitro, SF/CS/nHA scaffolds exhibited good biocompatibility and no toxicity. SF/CS/nHA promoted adhesion, growth, and calcium nodule formation of BMSCs compared to control (P<0.05). In vivo, we observed gradual new bone formation and bone defect gradually recovered at 12 weeks in experimental and control group, but more new bone was formed in experimental group (P<0.05). In blank group, limited bone formation was observed and bone defect was obvious. In conclusion, SF/CS/nHA scaffolds loaded with BMSCs achieve high efficacy to repair segmental defect in the radius.

Application of silk fibroin/chitosan/nano-hydroxyapatite composite scaffold in the repair of rabbit radial bone defect

Silk fibroin (SF), chitosan (CS) and nano-hydroxyapatite (nHA) possess excellent biocompatibility, thus, these were used to construct a SF/CS/nHA composite scaffold. Previously published results identified that this material exhibited satisfactory physical and chemical properties, and therefore qualified as a repair material in bone tissue engineering. The aim of the present study was to investigate the capacity and mechanism of this composite scaffold in repairing bone defects. In total, 45 New Zealand white rabbits were used to model defect in the right radial bone. A radial bone defect was induced, and rabbits were divided into the following treatment groups (n=15 in each): Group A, in which the SF/CS/nHA scaffold was implanted; group B, in which the SF/CS scaffold was implanted; and group C, in which rabbits did not receive subsequent treatment. X-ray scanning, specimen observation and histopathological examination were implemented at 1, 2, 3 and 4 months after modeling, in order to evaluate the osteogenic capacity and mechanism. At 1 month after modeling, the bone density shadow in the X-ray scan was darker in group A as compared with that in group B. Observation of the pathological specimens indicated that normal bone tissues partially replaced the scaffold. At 2 months, the bone density shadow of group A was similar to normal bone tissues, and normal tissue began to replace the scaffold. At 3-4 months after modeling, the X-ray scan and histopathological observation indicated that the normal bone tissues completely replaced the scaffold in group A, with an unobstructed marrow cavity. However, the bone mass of group B was lower in comparison with that of group A. The bone defect induced in group C was filled with fibrous connective tissues. Therefore, it was concluded that the SF/CS/nHA composite scaffold may be a promising material for bone tissue engineering.

Physico-mechanical and morphological features of zirconia substituted hydroxyapatite nano crystals

Zirconia doped Hydroxyapatite (HAP) nanocrystals [Ca₁₀(PO₄)_6−x(ZrO₂)_x(OH)₂]; (0 ≤ x ≤ 1 step 0.2) were synthesized using simple low cost facile method. The crystalline phases were examined by X-ray diffraction (XRD). The crystallinity percentage decreased with increasing zirconia content for the as-synthesized samples. The existence of zirconia as secondary phase on the grain boundaries; as observed from scanning electron micrographs (FESEM); resulted in negative values of microstrain. The crystallite size was computed and the results showed that it increased with increasing annealing temperature. Thermo-gravimetric analysis (TGA) assured the thermal stability of the nano crystals over the temperature from room up to 1200 °C depending on the zirconia content. The corrosion rate was found to decrease around 25 times with increasing zirconia content from x = 0.0 to 1.0. Microhardness displayed both compositional and temperature dependence. For the sample (x = 0.6), annealed at 1200 °C, the former increased up to 1.2 times its original value (x = 0.0).

Reducing Escherichia coli growth on a composite biomaterial by a surface immobilized antimicrobial peptide

A new composite bioceramic consisting of calcium aluminum oxide (CaAlO) and hydroxyapatite (HA) was functionalized with the synthetic antimicrobial peptide Inverso-CysHHC10. CaAlO is a bioceramic that can be mold cast easily and quickly at room temperature. Improved functionality was previously achieved through surface reactions. Here, composites containing 0-5% HA (by mass) were prepared and the elastic modulus and modulus of rupture were mechanically similar to non-load bearing bone. The addition of hydroxyapatite resulted in increased osteoblast attachment (>180%) and proliferation (>140%) on all composites compared to 100% CaAlO. Antimicrobial peptide (AMP) immobilization was achieved using an interfacial alkene-thiol click reaction. The linked AMP persisted on the composite (>99.6% after 24h) and retained its activity against Escherichia coli based on N-phenylnaphthylamine uptake and bacterial turbidity tests. Overall, this simple scaffold system improves osteoblast activity and reduces bacterial activity.

Reactive electrospinning of composite nanofibers of carboxymethyl chitosan cross-linked by alginate dialdehyde with the aid of polyethylene oxide

We have prepared carboxymethyl chitosan-alginate dialdehyde (CMCS-ADA) nanofibers via a reactive electrospinning process with the aid of polyethylene oxide (PEO). The presence of PEO delayed the gelation of CMCS and ADA, thus providing ease of use to adjust the mixing of CMCS-PEO and ADA-PEO blended solution. The mixed solution can be adjusted to come out from the needle before the gel formation or when the gel was just about to form. Defect-free CMCS-ADA-PEO nanofibers with average diameters ranging from 100nm to 900nm were obtained using water as a solvent. The in situ cross-linked CMCS-ADA nanofibers were then obtained following the extraction of water-soluble PEO. After immersion in phosphate-buffered saline (PBS) at a pH of 7.4 for up to 15days, the as-spun CMCS-ADA-PEO composite nanofibers maintained structural integrity, confirming the success of the crosslinking. The PEO-extracted CMCS-ADA nanofibers promoted the adhesion, proliferation and alkaline phosphatase activity of bone marrow stromal cells.

Fabrication of Gelatin/PCL Electrospun Fiber Mat with Bone Powder and the Study of Its Biocompatibility

Fabricating ideal scaffolds for bone tissue engineering is a great challenge to researchers. To better mimic the mineral component and the microstructure of natural bone, several kinds of materials were adopted in our study, namely gelatin, polycaprolactone (PCL), nanohydroxyapatite (nHA), and bone powder. Three types of scaffolds were fabricated using electrospinning; gelatin/PCL, gelatin/PCL/nHA, and gelatin/PCL/bone powder. Scaffolds were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. Then, Adipose-derived Stem Cells (ADSCs) were seeded on these scaffolds to study cell morphology, cell viability, and proliferation. Through this study, we found that nHA and bone powder can be successfully united in gelatin/PCL fibers. When compared with gelatin/PCL and gelatin/PCL/nHA, the gelatin/PCL/bone powder scaffolds could provide a better environment to increase ADSCs' growth, adhesion, and proliferation. Thus, we think that gelatin/PCL/bone powder has good biocompatibility, and, when compared with nHA, bone powder may be more effective in bone tissue engineering due to the bioactive factors contained in it.

A carboxymethyl chitosan and peptide-decorated polyetheretherketone ternary biocomposite with enhanced antibacterial activity and osseointegration as orthopedic/dental implants

Carbon fiber-reinforced polyetheretherketone (CFRPEEK) possesses biomechanical properties such as elastic modulus similar to human bones and is becoming a dominant alternative to replace the traditional metallic implants. The defective osseointegration and bacterial infection risk of CFRPEEK, however, impede its clinical adoption. In the current study, a newly-developed carbon fiber-reinforced polyetheretherketone/nanohydroxyapatite (CFRPEEK/n-HA) ternary biocomposite was functionalized by covalently grafting carboxymethyl chitosan (CMC) followed by the decoration of a bone-forming peptide (BFP) assisted via the polydopamine tag strategy. Antibacterial test with Staphylococcus aureus (S. aureus) indicated that the CMC and peptide-conjugated substrates (pep-CMC-CFRPEEK/n-HA) significantly suppressed bacterial adhesion. In vitro cell attachment/growth, spreading assay, alkaline phosphatase activity, real-time PCR analysis, osteogenesis-related protein expression and calcium mineral deposition all disclosed greatly accelerated adhesion, proliferation and osteo-differentiation of human mesenchymal stem cells (hMSCs) on the pep-CMC-CFRPEEK/n-HA biocomposite due to the additive effect of the CMC polysaccharide and the small osteoinductive peptide. More importantly, in vivo evaluation of the beagle tibia model by means of micro-CT, histological analysis, SEM observation and fluorescent labeling confirmed the remarkably boosted bioactivity and osteointegration. The CFRPEEK/n-HA ternary composite with the dual functions of bacterial adhesion reduction and osteointegration promotion holds great potential as a bioactive implant material in orthopedic/dental applications based on this scheme.

Structural properties of scaffolds: Crucial parameters towards stem cells differentiation

Tissue engineering is a multidisciplinary field that applies the principles of engineering and life-sciences for regeneration of damaged tissues. Stem cells have attracted much interest in tissue engineering as a cell source due to their ability to proliferate in an undifferentiated state for prolonged time and capability of differentiating to different cell types after induction. Scaffolds play an important role in tissue engineering as a substrate that can mimic the native extracellular matrix and the properties of scaffolds have been shown to affect the cell behavior such as the cell attachment, proliferation and differentiation. Here, we focus on the recent reports that investigated the various aspects of scaffolds including the materials used for scaffold fabrication, surface modification of scaffolds, topography and mechanical properties of scaffolds towards stem cells differentiation effect. We will present a more detailed overview on the effect of mechanical properties of scaffolds on stem cells fate.

In vitro culture and directed osteogenic differentiation of human pluripotent stem cells on peptides-decorated two-dimensional microenvironment

Human pluripotent stem cells (hPSCs) are a promising cell source with pluripotency and capacity to differentiate into all human somatic cell types. Designing simple and safe biomaterials with an innate ability to induce osteoblastic lineage from hPSCs is desirable to realize their clinical adoption in bone regenerative medicine. To address the issue, here we developed a fully defined synthetic peptides-decorated two-dimensional (2D) microenvironment via polydopamine (pDA) chemistry and subsequent carboxymethyl chitosan (CMC) grafting to enhance the culture and osteogenic potential of hPSCs in vitro. The hPSCs including human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs) were successfully cultured on the peptides-decorated surface without Matrigel and ECM protein coating and underwent promoted osteogenic differentiation in vitro, determined from the alkaline phosphate (ALP) activity, gene expression, and protein production as well as calcium deposit amount. It was found that directed osteogenic differentiation of hPSCs was achieved through a peptides-decorated niche. This chemically defined and safe 2D microenvironment, which facilitates proliferation and osteo-differentiation of hPSCs, not only helps to accelerate the translational perspectives of hPSCs but also provides tissue-specific functions such as directing stem cell differentiation commitment, having great potential in bone tissue engineering and opening new avenues for bone regenerative medicine.