Preparation and properties of nano-hydroxyapatite/chitosan/carboxymethyl cellulose composite scaffold

Sulfonic acid functionalized cellulose-derived (nano)materials: Synthesis and application

The preparation/application of heterogeneous (nano)materials from natural resources has currently become increasingly fascinating for researchers. Cellulose is the most abundant renewable polysaccharide on earth. The unique physicochemical, structural, biological, and environmental properties of this natural biopolymer have led to its increased application in many fields. The more desirable features of cellulose-based (nano)materials such as biodegradability, renewability, biocompatibility, cost-effectiveness, simplicity of preparation, environmentally friendly nature, and widespread range of applications have converted them into promising compounds in medicine, catalysis, biofuel cells, and water/wastewater treatment processes. Functionalized cellulose-based (nano)materials containing sulfonic acid groups may prove to be one of the most promising sustainable bio(nano)materials of modern times in the field of cellulose science and (nano)technology owing to their intrinsic features, high crystallinity, high specific surface area, abundance, reactivity, and recyclability. In this review, the developments in the application of sulfonated cellulose-based (nano)materials containing sulfonic acid (-SO3H) groups in catalysis, water purification, biological/biomedical, environmental, and fuel cell applications have been reported. This review provides an overview of the methods used to chemically modify cellulose and/or cellulose derivatives in different forms, including nanocrystals, hydrogels, films/membranes, and (nano)composites/blends by introducing sulfonate groups on the cellulose backbone, focusing on diverse sulfonating agents utilized and substitution regioselectivity, and highlights their potential applications in different industries for the generation of alternative energies and products.

Incorporating mesoporous SiO2-HA particles into chitosan/hydroxyapatite scaffolds: A comprehensive evaluation of bioactivity and biocompatibility

In this work, composite scaffolds with various composition ratios of chitosan (CS), hydroxyapatite (HA), and mesoporous SiO2 particles co-synthesized with hydroxyapatite (SiO2-HA) were fabricated via the freeze-drying method for bone tissue engineering applications. Morphological studies showed that adding mesoporous particles resulted in a structure with a more uniformly porous geometry, subsequently leading to reduced biodegradation rates and water absorption in the scaffolds. The bioactivity results showed the introduction of mesoporous particles notably enhanced the coverage of the scaffold surface with apatite films. Moreover, biocompatibility assessments using sarcoma osteogenic cell line (SAOS-2) highlighted mesoporous particles' positive impact on cell adhesion and growth. The fluorescence images showed spindle-shaped cells with a greater number and normal cell nuclei for the scaffolds containing mesoporous SiO2-HA particles. The MTT cytotoxicity results indicated that the scaffolds containing mesoporous particles showed approximately 25 % higher cell survival more than single chitosan-based ones. What is more, the mesoporous-containing scaffolds occurred to have the best alkaline phosphatase test (ALP) activity among all scaffolds. It is important to add that CS/HA/mesoporous SiO2-HA scaffolds including SAOS-2 cells showed no sign of either early or late apoptosis. These findings affirm the potential of CS/HA/mesoporous SiO2-HA scaffolds as promising implants for bone tissue engineering.

Fabrication of nano-biocomposite for the removal of Eriochrome Black T and malachite green from aqueous solution: isotherm and kinetic studies

The increasing generation of toxic dye wastewater from various enterprises continues to be a serious public health issue and happens to be of environmental concern, posing a significant challenge to existing conventional water treatment facilities. Malachite green (MG) and Eriochrome Black T (EBT) are extremely hazardous and carcinogenic substances; hence it is crucial to remove them from water bodies. A well-known cleaner, more economical, and environmentally friendly treatment method is adsorption. The kind of adsorbent material employed determines how well the treatment procedure works. A physiologically compatible nanocomposite adsorbent (HAP@CT@MNP) was fabricated from laboratory synthesized hydroxyapatite (HAP) and magnetite (MNP) for its application in the wastewater remediation process. The ability of the fabricated nanocomposite to remove the harmful dyes EBT and MG from a simulated wastewater was evaluated. The impact of operational parameters including pH, adsorbate concentration, adsorbent dose, contact time, and temperature was examined to gauge the maximum adsorption capacity of the developed nanocomposite. The optimum pH for the eradication of EBT and MG were found to be 3 and 7.4, respectively. The maximum capacity evaluated was 222 mg/g and 500 mg/g at room temperature and at contact time of 50 and 40 min respectively. The binding of either EBT or MG followed the monolayer Langmuir model and kinetic studies revealed the suitability of pseudo-second-order model. Studies using spectroscopy and isotherm modeling showed that the main mechanism controlling the adsorption of EBT and MG onto HAP@CT@MNP is physisorption. The efficacy of the adsorbent to be reused with 8% loss in its efficiency reveals the economic viability of HAP@CT@MNP. The current work showed that a biocompatible nanocomposite could be successfully fabricated and used as an enhanced adsorbent for the quick and effective removal of the toxic dyes EBT and MG from wastewater.

Fabrication, Properties, and Biomedical Applications of Calcium-Containing Cellulose-Based Composites

Calcium-containing cellulose-based composites possess the advantages of high mechanical strength, excellent osteoconductivity, biocompatibility, biodegradation, and bioactivity, which represent a promising application system in the biomedical field. Calcium-containing cellulose-based composites have become the hotspot of study of various biomedical fields. In this mini-review article, the synthesis of calcium-containing cellulose-based composites is summarized via a variety of methods such as the biomimetic mineralization method, microwave method, co-precipitation method, hydrothermal method, freeze-drying method, mechanochemical reaction method, and ultrasound method. The development on the fabrication, properties, and applications of calcium-containing cellulose-based composites is highlighted. The as-existed problems and future developments of cellulose-based composites are provided. It is expected that calcium-containing cellulose-based composites are the ideal candidate for biomedical application.

Zinc substituted hydroxyapatite/silk fiber/methylcellulose nanocomposite for bone tissue engineering applications

Fibrous bio-composite based on silk fiber (SF), methylcellulose (MC) and zinc substituted hydroxyapatite (Zn_xCa_5-x (PO₄)₃(OH) (x = 0.1, 0.2, 0.5 and 1.0)) were obtained with the use of electrospinning (E-Spin) method. XRD, FTIR, SEM-EDAX, swelling, porosity and mechanical properties of the composites were analyzed. The elongation at break (%) (20.97-317.20 %) and tensile strength (29.85-110.92 MPa) of nanocomposites was increased with an increase in the wt% of Zn-HAP in SF/MC. An increase in the zone of inhibition with an increase in the wt% of Zn-HAP into the SF/MC was observed against E. coli (34 ± 0.33 to 47 ± 1.15), S. aureus (28 ± 0.24 to 38 ± 1.32) and C. albicans (24 ± 0.36 to 39 ± 2.36). The in-vitro biomineralization study using SBF (simulated body fluid) showed apatite layer formation on the nano-composite. In addition, the optimized (20 wt % of Zn₁.₀Ca_4.0(PO₄)₃(OH)/SF/MC) nano-composite showed good cell viability against human bone osteosarcoma (MG-63) cells.

Multifunctional Hemostatic PVA/Chitosan Sponges Loaded with Hydroxyapatite and Ciprofloxacin

The present study describes the development of multifunctional hemostatic sponges to control bleeding. Chitosan (Ch) and poly(vinyl alcohol) (PVA) were selected as the basic polymeric matrix [Ch/PVA] for sponges. Glycerol and citric acid were used as crosslinkers [Ch/PVA/G(Cl)] to enhance the mechanical properties of the developed sponges. Ciprofloxacin (AB) was added to the developed sponge to impart antibacterial activity. Hydroxyapatite (HA) was also added, which would make the sponge suitable for bone surgery. Among the developed sponges, the Ch/PVA/G(Cl)-HA-AB sponge demonstrated enhanced cell viability, mechanical properties, and strong antimicrobial effect against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus, in addition to platelet aggregation activity. The addition of ciprofloxacin and hydroxyapatite promotes a unique synergistic effect of antimicrobial activity and hemostasis. Thus, the present study introduces Ch/PVA/G(Cl)-HA-AB, a multifunctional hemostatic sponge that would be suitable for bone surgical applications.

Bioinspired TiO2/Chitosan/HA Coatings on Ti Surfaces: Biomedical Improvement by Intermediate Hierarchical Films

The most common reasons for hard-tissue implant failure are structural loosening and prosthetic infections. Hence, to fix the first problem, different bioinspired coatings were applied to the titanium alloy surfaces in this study, including dual acid-etched, anodic TiO2 nanotubes array (TNTs), anodic hierarchical titanium oxide, micro- and nanostructured hydroxyapatite (HA) layers, and HA/chitosan (HA/CS) nanocomposite coating. XRD and FTIR analysis demonstrated that the in situ HA/chitosan nanocomposite formed successfully. The MTT assay showed that all samples had excellent cell viability, with cell proliferation rates ranging from 120-150% after 10 days. The hierarchical coating demonstrated superhydrophilicity (θ ≈ 0°) and increased the wettability of the metallic Ti surface by more than 120%. The friction coefficient of all fabricated surfaces was within the range of natural bone's mechanical behavior. The intermediate hierarchical oxide layer increased the adhesion strength of the HA/chitosan coating by more than 60%. The Hierarchical middle oxide layer caused the mechanical stability of HA/CS during the 1000 m of friction test. The microhardness of HA/CS (22.5 HV) and micro-HA (25.5 HV) coatings was comparable to that of human bone. An intermediate hierarchical oxide-based mechanism for improving adhesion strength in HA/CS coatings was presented.

Preparation and applications of chitosan and cellulose composite materials

Chitosan is a natural fiber, chemically cellulose-like biopolymer, which is processed from chitin. Its use as a natural polymer is getting more attention because it is non-toxic, renewable, and biocompatible. However, its poor mechanical and thermal strength, particle size, and surface area restrict its industrial use. Consequently, to improve these properties, cellulose and/or inorganic nanoparticles have been used. This review discusses the recent progress of chitosan and cellulose composite materials, their preparation, and their applications in different industrial sectors. It also discusses the modification of chitosan and cellulose composite materials to allow their use on a large scale. Finally, the recent development of chitosan composite materials for drug delivery, food packaging, protective coatings, and wastewater treatment are discussed. The challenges and perspectives for future research are also considered. This review suggests that chitosan and cellulose nano-composite are promising, low-cost products for environmental remediation involving a simple production process.

Xanthan-gelatin and xanthan-gelatin-keratin wound dressings for local delivery of Vitamin C

Recently, functional dressings that can protect the wound area from dehydration and bacterial infection and support healing have gained importance in place of passive dressings. This study aimed to develop temporary and regenerative xanthan/gelatin (XGH) and keratin/xanthan/gelatin hydrogels (KXGHs) that have high absorption capacity and applicability as a wound dressing that can provide local delivery of Vitamin C (VC). Firstly, xanthan/gelatin hydrogels were produced by crosslinking with different glycerol concentrations and characterized to determine the hydrogel composition. According to their weight ratios, xanthan, gelatin, and glycerol hydrogels are named. If their weight ratio is 1:1:2 (w/w/w), the group name is selected as X1:GEL1:GLY2. X1:GEL1:GLY2 hydrogel was selected for biocompatibility, mechanical property, water vapor transmission rate (WVTR), and porosity. The addition of keratin to X1:GEL1:GLY2 improved L929 fibroblasts viability and increased protein release. Water vapor transmission of XGHs and KXGHs was between 3059.09 ± 126 and 4523 ± 133 g m^-2 d^-1; therefore, they can be suitable for granulating, low to moderate exudate wounds. XGH and KXGHs loaded with VC had higher water uptake, making it more convenient for exudate wounds. VC was released for 100 h, and VC containing XGHs and KXGHs increased the collagen synthesis of L929 fibroblasts. All of the hydrogels (XGH, KXGH, and VC-KXGHs) inhibited the bacteria transmission. In conclusion, our results suggest that VC-XGH and VC-KXGH can be candidates for temporary wound dressing materials for skin wounds.

Biomimetic Mechanically Strong One-Dimensional Hydroxyapatite/Poly(d,l-lactide) Composite Inducing Formation of Anisotropic Collagen Matrix

Natural bone is a complex composite, consisting predominantly of collagen and hydroxyapatite (HA), which form a highly organized, hierarchical structure from the nano- to the macroscale. Because of its biphasic, anisotropic, ultrafine structural design, bone tissue possesses excellent mechanical properties. Herein, inspired by the composition and microstructure of natural bone, a biphasic composite consisting of highly aligned strontium/copper-doped one-dimensional hydroxyapatite (Sr/Cu-doped 1D HA) and poly(d,l-lactide) (PDLA) was developed. The presence and alignment of Sr/Cu-doped 1D HA crystals resulted in mechanical reinforcement of the polymer matrix, including compressive and tensile strength and modulus, fracture toughness, swelling resistance, and long-term structural stability. The compressive strength, tensile strength, and Young's modulus of the biomimetic composite were comparable to that of cortical bone. Biologically, the biomimetic composite showed a sustained release of the incorporated Sr and Cu ions, facilitated mineral deposition from simulated body fluid, and supported attachment, proliferation, and alkaline phosphatase activity of human mesenchymal stromal cells (hMSCs). Moreover, the highly aligned Sr/Cu-doped 1D HA crystals in the 3D porous scaffolds induced the alignment of hMSCs and secretion of an anisotropic collagen fiber matrix in 3D. The biomimetic Sr/Cu-doped 1D HA/PDLA composite presented here contributes to the current efforts aiming at the design and development of load-bearing bioactive synthetic bone graft substitutes. Moreover, the biomimetic composite may serve as a 3D platform for studying cell-extracellular matrix interactions in bone tissue.

Recent Developments of Carboxymethyl Cellulose

Carboxymethyl cellulose (CMC) is one of the most promising cellulose derivatives. Due to its characteristic surface properties, mechanical strength, tunable hydrophilicity, viscous properties, availability and abundance of raw materials, low-cost synthesis process, and likewise many contrasting aspects, it is now widely used in various advanced application fields, for example, food, paper, textile, and pharmaceutical industries, biomedical engineering, wastewater treatment, energy production, and storage energy production, and storage and so on. Many research articles have been reported on CMC, depending on their sources and application fields. Thus, a comprehensive and well-organized review is in great demand that can provide an up-to-date and in-depth review on CMC. Herein, this review aims to provide compact information of the synthesis to the advanced applications of this material in various fields. Finally, this article covers the insights of future CMC research that could guide researchers working in this prominent field.

3D printing of robust and biocompatible poly(ethylene glycol)diacrylate/nano-hydroxyapatite composites via continuous liquid interface production

Three-dimensional (3D) printing technology with satisfactory speed and accuracy has been a powerful force in biomaterial processing. Early studies on 3D printing of biomaterials mainly focused on their biocompatibility and cellular viability while rarely attempted to produce robust specimens. Nonetheless, the biomedical applications of polymers can be severely limited by their inherently weak mechanical properties particularly in bone tissue engineering. In this study, continuous liquid interface production (CLIP) is applied to construct 3D objects of nano-hydroxyapatite (n-HA) filled polymeric biomaterials with complex architectures. Notably, the bioactive and osteoconductive n-HA endows the 3D prints of poly(ethyleneglycol)diacrylate (PEGDA) composites with a high compression strength of 6.5 ± 1.4 MPa, about 342% improvement over neat PEGDA. This work demonstrates the first successful attempt on CLIP 3D printing of n-HA nanocomposites, providing a feasible, cost-effective and patient-specific solution to various fields in the biomedical industry.

Complex interior and surface modified alginate reinforced reduced graphene oxide-hydroxyapatite hybrids: Removal of toxic azo dyes from the aqueous solution

In this study, alginate reinforced reduced graphene oxide@hydroxyapatite (rGO@HAP-Alg) hybrids have been fabricated via co-precipitation technique. The developed adsorbent was effectively utilized for the removal of Reactive Blue 4 (RB4), Indigo Carmine (IC) and Acid Blue 158 (AB158) azo dyes from aqueous solution, and found to have the adsorption efficiency of 45.56, 47.16 and 48.26 mg/g, respectively. The thermodynamic parameters demonstrated the endothermic and spontaneous nature of the adsorption process. The adsorption system was pH-dependent and showed maximum dye removal at pH 6-7, which was indicative of the electrostatic interactions, surface complexation and the hydrogen bonding mechanisms involved between the adsorbate and adsorbent during the adsorption process. Furthermore, the renewability studies demonstrated the reusability and stability of rGO@HAP-Alg hybrids up to five successive cycles. This study delivers a promising strategy for removing dye molecules and extends the potential application of rGO@HAP-Alg hybrids to treat practical dye contaminated water/wastewater.

Hydroxyapatite Nanoparticles Fortified Xanthan Gum-Chitosan Based Polyelectrolyte Complex Scaffolds for Supporting the Osteo-Friendly Environment

Nanoparticle-reinforced polymer-based scaffolding matrices as artificial bone-implant materials are potential suitors for bone regenerative medicine as they simulate the native bone. In the present work, a series of bioinspired, osteoconductive tricomposite scaffolds made up of nano-hydroxyapatite (NHA) embedded xanthan gum-chitosan (XAN-CHI) polyelectrolyte complex (PEC) are explored for their bone-regeneration potential. The Fourier transform infrared spectroscopy studies confirmed complex formation between XAN and CHI and showed strong interactions between the NHA and PEC matrix. The X-ray diffraction studies indicated regulation of the nanocomposite (NC) scaffold crystallinity by the physical cues of the PEC matrix. Further results exhibited that the XAN-CHI/NHA5 scaffold, with a 50/50 (polymer/NHA) ratio, has optimized porous structure, appropriate compressive properties, and sufficient swelling ability with slower degradation rates, which are far better than those of CHI/NHA and other XAN-CHI/NHA NC scaffolds. The simulated body fluid studies showed XAN-CHI/NHA5 generated apatite-like surface structures of a Ca/P ratio ∼1.66. Also, the in vitro cell-material interaction studies with MG-63 cells revealed that relative to the CHI/NHA NC scaffold, the cellular viability, attachment, and proliferation were better on XAN-CHI/NHA scaffold surfaces, with XAN-CHI/NHA5 specimens exhibiting an effective increment in cell spreading capacity compared to XAN-CHI/NHA4 and XAN-CHI/NHA6 specimens. The presence of an osteo-friendly environment is also indicated by enhanced alkaline phosphatase expression and protein adsorption ability. The higher expression of extracellular matrix proteins, such as osteocalcin and osteopontin, finally validated the induction of differentiation of MG-63 cells by tricomposite scaffolds. In summary, this study demonstrates that the formation of PEC between XAN and CHI and incorporation of NHA in XAN-CHI PEC developed tricomposite scaffolds with robust potential for use in bone regeneration applications.

Study of Mechanical and Thermal Properties in Nano-Hydroxyapatite/Chitosan/Carboxymethyl Cellulose Nanocomposite-Based Scaffold for Bone Tissue Engineering: The Roles of Carboxymethyl Cellulose

Synthetic scaffolding for bone tissue engineering (BTE) has been widely utilized. The scaffold for BTE requires sufficient porosity as a template for bone cell development and growth so that it can be used in the treatment of bone defects and fractures. Nevertheless, the porosity significantly influences the compressive strength of the scaffold. Hence, controlling the porosity is a pivotal role to obtain a proper scaffold for practical BTE application. Herein, we fabricated the nanocomposite-based scaffold utilizing nano-hydroxyapatite (n-HA). The scaffold was prepared in combination with chitosan (Ch) and carboxymethyl cellulose (CMC). The ratios of n-HA, Ch, and CMC used were 40:60:0, 40:55:5, 40:50:10, 40:45:15, and 40:40:20, respectively. By controlling the Ch and CMC composition, we can tune the porosity of the nanocomposite. We found that the interpolation of the CMC prevails, as a crosslinker reinforces the nanocomposite. In addition, the binding to Ch enhanced the compressive strength of the scaffold. Thermal characteristics revealed the coefficient of thermal expansion decreases with increasing CMC content. The nanocomposite does not expand at 25–75 °C, which is suitable for human body temperature. Therefore, this nanocomposite-based scaffold is feasible for BTE application.

Development of hybrid scaffold: Bioactive glass nanoparticles/chitosan for tissue engineering applications

Bone tissue engineering is gaining popularity as an alternative method for the treatment of osseous defects. A number of biodegradable polymers have been explored for tissue engineering purposes. A new family of biodegradable polymer/bioactive glass composite materials has been designed to be used in bone regeneration approaches. In this work, a hybrid scaffold of chitosan (CH) and bioactive glass nanoparticles (BGN) was prepared by the freeze-gelation method. This method has been studied by adjusting the concentration of acetic acid; this process can influence the structure properties of the scaffold. In this work, several BGN/CH composites have been prepared by varying the proportion of BGN in the hybrid scaffold (20, 40, 60, and 80%). Brunauer-Emmett-Teller results showed the increased surface area and porosity volume of our composite with decreasing BGN proportion. BGN/CH hybrid scaffold was characterized by using physicochemical techniques. Obtained results showed a macroporous morphology of the scaffold with a pore size of about 200 μm, and a homogeneous distribution of the BGN in the CH matrix. X-ray diffraction study confirmed the amorphous state of the BGN/CH hybrid scaffold. Interaction between CH and BGNs in the composite was confirmed. The in vitro assays showed adequate degradation properties, which is essential for the potential replacement by the new tissue. The in vitro bioactivity studies confirmed the formation of an apatite layer on the surface of the hybrid scaffold, which results in a direct bone bonding of the implant. These results indicate that BGN/CH hybrid scaffold developed is a potential candidate for bone tissue engineering.

Functionalized cellulose to remove surfactants from cosmetic products in wastewater

A flocculant composed of paper mulberry dicarboxylic cellulose (PM-DCC) made from using paper mulberry (Broussonetia kazinoki Siebold and Zucc.) has been developed to reduce the amount of inorganic coagulants needed to remove surfactants in wastewater. The characteristics of PM and soda pulp were determined according to the degree of polymerization, α-cellulose, lignin, free sugar, and extract contents. FTIR, XRD, the aldehyde content, the carboxyl content and coagulant-flocculation experiments were conducted to confirm the properties of PM-DCC and paper mulberry dialdehyde cellulose (PM-DAC). A dramatic removal efficiency (95.62 %) was revealed when 0.3 % PM-DCC was added into a linear alkylbenzene sulfonate (LAS) solution with 1% FeCl₃·6H₂O at pH 2. This means that PM-DCC contributes to both a lower amount of inorganic coagulant needed and a reduction of water pollution by an ecofriendly method.

Biomimetic hydroxyapatite/silkfibre/methylcellulose composites for bone tissue engineering applications

Hydroxyapatite (HAP)/silk fibre (SF)/methylcellulose (MC) composites were developed by an electrospinning (E-Spin) method.

dos Santos BF, A. Tavares A, Maciel MA, Lucena BDM, L. Fook MV, de L. Silva SM. The Impact of the Ionic Cross-Linking Mode on the Physical and In Vitro Dexamethasone Release Properties of Chitosan/Hydroxyapatite Beads

In this study, the effect of the ionic cross-linking mode on the ability to control physical properties and in vitro release behavior of the dexamethasone (DEX) drug from chitosan (CS) and chitosan/hydroxyapatite (CS/HA) beads was investigated. CS solutions without and with HA and DEX were dripped into two coagulation solutions, prepared with a non-toxic ionic crosslinker (sodium tripolyphosphate, TPP) and distilled water, one at pH = 9.0 and other at pH = 6.0. Optical microscopy (OM) and scanning electron microscopy (SEM) results showed changes on the surface topology of the beads, with a reduction of roughness for beads prepared at pH = 6.0 and an increase for the one prepared at pH = 9.0. The diameter and sphericity of the beads prepared at pH = 6.0 proved more uniform and had a larger pore size with a good interconnectivity framework. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) suggested a higher crosslinking degree for beads prepared at pH = 6.0, corroborated by X-ray diffraction profiles (XRD) analysis that indicated a decrease in the crystalline structure for such beads. In in vitro drug release data, all beads presented a sustained release during the studied period (24 h). The drug release rate was affected by the pH of the coagulation solution used in the preparation of the beads. The in vitro kinetics of the release process was of the Peppas-Sahlin model, controlled by both diffusion and relaxation of polymer chains or swelling (anomalous transport mechanism). Our results suggest that DEX-loaded CS/HA beads, crosslinked in TPP coagulation solution at pH = 9.0, led to a decrease in the DEX release rate and prolonged the release period. Thus, this composition might have prospective as a functional material for bone and cartilage tissue engineering.

Thyroxine-loaded chitosan/carboxymethyl cellulose/hydroxyapatite hydrogels enhance angiogenesis in in-ovo experiments

Angiogenesis is one of the most important processes in repair and regeneration of many tissues and organs. Blood vessel formation also play a major role in repair of dental tissue(s) after ailments like periodontitis. Here we report the preparation of chitosan/carboxymethyl cellulose/hydroxyapatite based hydrogels, loaded with variable concentrations of thyroxin i.e., 0.1 μg/ml, 0.5 μg/ml and 1 μg/ml. Scanning electron microcopy images (SEM) showed all hydrogels were found to be porous and solution absorption study exhibited high swelling potential in aqueous media. FTIR spectra confirmed that the used materials did not change their chemical identity in synthesized hydrogels. The synthesized hydrogels demonstrated good bending, folding, rolling and stretching abilities. The hydrogels were tested in chick chorioallantoic membrane (CAM) assay to investigate their angiogenic potential. Hydrogel containing 0.1 μg/ml of thyroxine showed maximum neovascularization. For cytotoxicity analyses, preosteoblast cells (MC3T3-E1) were seeded on these hydrogels and materials were found to be non-toxic. These hydrogels with pro-angiogenic activity possess great potential to be used for periodontal regeneration.

Fabrication of regular macro-mesoporous reduced graphene aerogel beads with ultra-high mechanical property for efficient bilirubin adsorption

Three-dimensional graphene materials have been widely studied in many fields for their role as potential absorbent, especially for bilirubin adsorption. In this study, we developed a simple method to prepare reduced graphene aerogel beads as hemoperfusion materials for fast bilirubin adsorption. The graphene oxide (GO) aerogel beads were produced by self-assembly of GO nanosheet that cross-linked by Ca²⁺ previously in a coagulation bath, then it was reduced by ascorbic acid and lyophilized to yield the reduced graphene aerogel beads. The beads had a regular macroscopic spherical structure with a diameter of about 1.3-2 mm, where the macroporosity was about 10 μm and the mesoporosity was about 12 nm. The macro-mesoporous structure also gave the reduced graphene aerogel beads ultra-high mechanical strengths and high specific surface area, which were both important for hemoperfusion materials. Moreover, the fixed-bed column adsorption revealed that the reduced graphene aerogel beads manifested excellent bilirubin adsorption (649.512 mg/g) with a rapid adsorption equilibrium time (1.5 h) under the optimized conditions. Even in the bilirubin-enriched blood, the adsorption capacity of the beads could reach 367.14 mg/g. Furthermore, the aerogel beads had a low hemolysis ratio and improved anticoagulant property showing good blood compatibility. Hence, the spherical reduced graphene aerogel beads with millimeter-level size presented a good potential for clinical applications in hemoperfusion therapy.

A comparative study on agarose acetate and PDLLA scaffold for rabbit femur defect regeneration

The development of degradable polymer scaffolds is a key issue in bone regeneration. Poly(D, L-lactide) (PDLLA) and its derivatives have usually been applied to the construction of degradable scaffolds, but these scaffolds had problems with acidic degradation products and quick loss of mechanic strength during the later degradation, which usually led to scaffold collapse and cavity formation because of the slower rate of bone regeneration. In the present paper, a polysaccharide derivative, agarose acetate (AGA), was synthesized and a novel porous AGA scaffold was successfully developed through a salt-leaching process. The AGA scaffold had over 90% porosity without swelling in water, and compared to collapse and acidic products of PDLLA scaffold during degradation, the AGA scaffold maintained a stable morphology and a nearly neutral pH value over 18 months' degradation in PBS. A bone mesenchymal stem cells (BMSCs) adhesion and proliferation experiment showed that more cells adhered to the AGA scaffold than to the PDLLA scaffold. A subcutaneous implant test showed that the AGA scaffold slowly degraded and did not cause an inflammatory response surrounding the implantation lesion site. AGA scaffold was implanted into femur defects in New Zealand white rabbits to test its in vivo performance. Results indicated that the AGA scaffold accelerated the process of bone regeneration compared to the PDLLA group and, with time, new bone was formed from the margin toward the center of the scaffolds, and the scaffold left in place retained its porous structure without collapsing. Meanwhile, the AGA scaffold showed a low degradation rate and kept its shape during the in vivo degradation compared to the PDLLA scaffold. This performance could have the benefit of integrated regenerative bone being formed instead of cavities due to the quickly degraded scaffold disappearing. These results demonstrate that the AGA scaffold has significant potential in bone regeneration applications.

Bioactive diatomite and POSS silica cage reinforced chitosan/Na-carboxymethyl cellulose polyelectrolyte scaffolds for hard tissue regeneration

Recently, natural polymers are reinforced with silica particles for hard tissue engineering applications to induce bone regeneration. In this study, as two novel bioactive agents, effects of diatomite and polyhedral oligomeric silsesquioxanes (POSS) on chitosan (CS)/Na-carboxymethylcellulose (Na-CMC) polymer blend scaffolds are examined. In addition, the effect of silica reinforcements was compared with Si-substituted nano-hydroxyapatite (Si-Hap) particles. The morphology, physical and chemical structures of the scaffolds were characterized with SEM, liquid displacement, FT-IR, mechanical analysis, swelling and degradation studies. The particle size and the crystal structure of diatomite, POSS and Si-Hap particles were determined with DLS and XRD analyses. In vitro studies were performed to figure out the cytotoxicity, proliferation, ALP activity, osteocalcin production and biomineralization to demonstrate the promising use of natural silica particles in bone regeneration. Freeze-dried scaffolds showed 190-307 μm pore size range and 61-70% porosity. Both inorganic reinforcements increased the mechanical strength, enhanced the water uptake capacity and fastened the degradation rate. The nanocomposite scaffolds did not show any cytotoxic effect and enhanced the surface mineralization in osteogenic medium. Thus, diatomite and POSS cage structures can be potential reinforcements for nanocomposite design in hard tissue engineering applications.

Biomimetic composite scaffold from an in situ hydroxyapatite coating on cellulose nanocrystals

A novel nanocomposite scaffold was developed by homogeneous deposition of hydroxyapatite (HAP) on a cellulose nanocrystals (CNCs) matrix suspended in a simulated body fluid (SBF). By adjusting the pH of the SBF, the HAP content in the nanocomposite could be controlled between 15 wt% and 47 wt%. Physical and chemical characteristics of the nanocomposites were analyzed by SEM, FTIR, XRD, SAED, and TEM, which confirmed the successful incorporation of HAP onto the CNCs. The nanocomposites were then freeze-casted into porous scaffolds by different solidification technologies (i.e., directional freezing (DF), plunging in liquid N₂ (PL) or in a −20 °C freezer (FZ)) followed by lyophilization. Compression testing of the HAP/CNCs foams indicated that DF caused significant improvement in mechanical properties due to the specific orientation and anisotropic porous structure compared to conventional freezing methods such as PL and FZ. Moreover, the scaffold with high HAP content exhibited improved mechanical and thermal properties, which holds potential for application in bone tissue engineering.

A novel nanocomposite scaffold was developed by homogeneous deposition of hydroxyapatite (HAP) on a cellulose nanocrystal (CNCs) matrix suspended in a simulated body fluid (SBF).

Novel Hierarchical Nitrogen-Doped Multiwalled Carbon Nanotubes/Cellulose/Nanohydroxyapatite Nanocomposite As an Osteoinductive Scaffold for Enhancing Bone Regeneration

Nanomaterials based on hybrid scaffolds have shown a high potential to promote osteointegration and bone regeneration. In this study, a novel nanocomposite scaffold was synthesized via a cross-linking/hydrothermal/freeze-drying method, resulting in layer-by-layer structures with functional and structural properties mimicking the natural bone. The hierarchical structures of the scaffold were reinforced with nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs), cellulose, and nanohydroxyapatite. The N-MWCNT/Cel/nHA scaffolds were characterized and evaluated in terms of structure, morphology, biocompatibility, cellular responses, and bone repair efficiency in vivo. The resulting scaffolds showed that incorporation of 1 wt % N-MWCNTs into the hybrid scaffold with micropores (∼5 μm) significantly improved its mechanical properties, although the surface morphology of the scaffold tended to be rough and porous. Importantly, the resulting scaffolds supported in vitro cellular attachment, proliferation, viability, and mineralization of bone mesenchymal stem cells (BMSCs). On the other hand, incorporation of N-MWCNTs into the scaffold induced preferential differentiation of BMSCs to osteogenic lineage accompanied by increased alkaline phosphatase activity and expression of key osteogenic genes. Furthermore, 12 weeks after implantation, the 1%N-MWCNT/Cel/nHA porous scaffolds successfully cicatrized a distal femoral condyle critical size defect in rabbit without obvious inflammatory responses, as indicated by the results of the Micro-CT and histological analyses. In vitro and in vivo experiments confirmed that the scaffolds not only improved the interface bonding with bone tissue but also accelerated the new bone formation and regeneration by up-regulating signaling molecules that are involved in cell proliferation and differentiation. These results indicated that the novel N-MWCNT/Cel/nHA scaffold is an efficient platform for osteogenesis research and bone regeneration medicine.

Mesenchymal stem cells associated with chitosan scaffolds loaded with rosuvastatin to improve wound healing

In this study we explored the role of rosuvastatin calcium in skin regeneration as statins play important role in the field of tissue engineering. Chitosan hydrochloride was crosslinked with different weight ratios of collagen, β-glycerolphosphate and carboxymethyl cellulose to produce scaffolds by lyophilization technique. Subsequently, the fabricated scaffolds were examined for their morphology, water absorption capacity, water retention, friability and in-vitro drug release as well as in-vivo studies. The results revealed porous 3-D structured scaffolds with maximum water absorption values-ranging between 396 and 2993%. Scaffolds containing carboxymethyl cellulose revealed highest water absorption-values. In-vitro drug release results showed gradual drug release for 60 h with mean dissolution time-values (MDT) between 13 and 21 h. Combination of chitosan, collagen, carboxymethyl cellulose in weight ratio of 40:30:30, respectively achieved gradual disintegration of the scaffold in a simulating medium to an open wound after 4 days. This selected scaffold loaded with rosuvastatin revealed increase proliferation of human dermal fibroblasts compared to placebo scaffold. After 30 days of implantation of selected medicated scaffold loaded with/without mesenchymal stem cells and placebo scaffolds to induced wounds in Albino rats, enhanced skin regeneration and absence of scar formation for drug loaded scaffolds were observed. The histopathological study showed the advantage of stem cells-loaded scaffolds through the normal redistribution of collagen in the epidermal layer. In conclusion, rosuvastatin calcium and stem cells loaded in the tested scaffolds proved their potential effect in enhancing skin healing and regeneration.

Chitosan microparticles based polyelectrolyte complex scaffolds for bone tissue engineering in vitro and effect of calcium phosphate

Chitosan microparticles were mixed with chitosan and carboxymethyl cellulose solution to achieve a good binding between the microparticles. Three different compositions of scaffolds were made by varying the calcium phosphate (CaP) amount: 0%, 10%, and 20%. Potassium chloride was used as salt, to make pores inside the scaffolds after leaching out when immersed in phosphate buffer saline (PBS). Compressive strength and compressive modulus of both non-porous (before leaching out), and porous (after leaching out) scaffolds were measured according to the ASTM standards. The highest compressive strength of 27 MPa was reported on 10% CaP scaffolds while 20% CaP scaffolds showed the lowest. The increasing CaP content reduces the compressive strength of the scaffolds. The highest wet state compressive strength was reported on 0% CaP scaffolds with 0.36 MPs and 0.40 MPa at day 1 and day 3 respectively. In vitro cell culture studies showed good cell adhesion and cell proliferation on 10% CaP scaffolds.

Fabrication and biocompatibility of agarose acetate nanofibrous membrane by electrospinning

In the present paper, agarose acetate (AGA) nanofibrous membranes containing different weight percentages of β-tricalcium phosphate (β-TCP) were successfully developed through electrospinning. The fibers in the nanofibrous membranes had a rough surface due to the β-TCP particles which were uniformly dispersed within or on the surface of AGA fibers. Rat-bone marrow-derived mesenchymal stem cells (rBMSCs) were cultured on the AGA based nanofibrous membranes while showed a good adhesion and proliferation. It was found that more rBMSCs were differentiated to osteoblast-like cells on the β-TCP containing nanofibrous membranes compared with the single AGA membrane, and more alkaline phosphatase (ALP) and mineralized matrix could be detected when rBMSCs were cultured on the β-TCP containing nanofibrous membranes. The nanofibrous membranes were implanted into Sprague-Dawley (SD) rats for biocompatibility test. Gross examination and histological analysis of the AGA based nanofibrous membranes results showed that there was less inflammatory response. All of experimental results suggested that the AGA based nanofibrous membranes had the great potential application in bone tissue engineering.

Enhanced chondrogenic differentiation of human mesenchymal stems cells on citric acid-modified chitosan hydrogel for tracheal cartilage regeneration applications

Congenital tracheal stenosis in infants and children is a worldwide clinical problem. Tissue engineering is a promising method for correcting long segmental tracheal defects. Nonetheless, the lack of desirable scaffolds always limits the development and applications of tissue engineering in clinical practice. In this study, a citric-acid-functionalized chitosan (CC) hydrogel was fabricated by a freeze–thaw method. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) confirmed that citric acid was successfully attached to the chitosan hydrogel. Scanning electron microscopy (SEM) images and compression tests showed that the CC hydrogel had an interconnected porous structure and better wet mechanical properties. Using morphological and proliferation analyses, cell biocompatibility of the CC hydrogel was shown by culturing human mesenchymal stem cells (hMSCs) on it. Specific expression of cartilage-related markers was analyzed by real-time polymerase chain reaction and western blotting. The expression of chondrocytic markers was strongly upregulated in the culture on the CC hydrogel. Hematoxylin and eosin staining revealed that the cells had the characteristic shape of chondrocytes and clustered into the CC hydrogel. Both Alcian blue staining and a sulfated glycosaminoglycan (sGAG) assay indicated that the CC hydrogel promoted the expression of glycosaminoglycans (GAGs). In a nutshell, these results suggested that the CC hydrogel enhanced chondrogenic differentiation of hMSCs. Thus, the newly developed CC hydrogel may be a promising tissue-engineered scaffold for tracheal cartilage regeneration.

A novel citric acid functionalized chitosan hydrogel for tracheal cartilage regeneration applications.

Metal and polymer-mediated synthesis of porous crystalline hydroxyapatite nanocomposites for environmental remediation

This study was focused on the preparation of metal and polymer-mediated porous crystalline hydroxyapatite (HAp) nanocomposites for environmental applications. Four different nano HAp systems were synthesized, namely, microwave irradiated HAp (M1), Zn doped HAp (M2), Mg-doped HAp (M3) and sodium alginate incorporated HAp (M4), and characterized using X-ray diffraction (XRD), Fourier transform infra-red spectroscopy, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, nuclear magnetic resonance (NMR), X-ray fluorescence, thermogravimetric analysis and Brunauer-Emmett-Teller (BET) analyses. Systems M1-M4 showed morphologies similar to coral shapes, polymer-like interconnected structures, sponges and feathery mycelium assemblies. Using XRD, selected area electron diffraction patterns and 1H and 31P CP/MAS solid-state NMR studies, crystallinity variation was observed from highest to lowest in the order of M4 > M1 > M3 > M2. Surface area estimates using BET isotherm reflected the highest surface area for M3, and M1 > M2 > M4. Four systems of M1-M4 were used as potential adsorbent materials for the removal of metal containing azo dye from aqueous system. Adsorption data were correlated to Freundlich and Langmuir isotherm models. According to the results, the highest capacity of 212.8 mg g-1 was exhibited by M4 having mycelium like morphology with alginate groups. This study highlights the possibility of developing HAp nanocomposites for the effective removal of dye contaminants in the environment.

Modulating cell response on cellulose surfaces; tunable attachment and scaffold mechanics

Combining surface chemical modification of cellulose to introduce positively charged trimethylammonium groups by reaction with glycidyltrimethylammonium chloride (GTMAC) allowed for direct attachment of mammalian MG-63 cells, without addition of protein modifiers, or ligands. Very small increases in the surface charge resulted in significant increases in cell attachment: at a degree of substitution (DS) of only 1.4%, MG-63 cell attachment was > 90% compared to tissue culture plastic, whereas minimal attachment occurred on unmodified cellulose. Cell attachment plateaued above DS of ca. 1.85% reflecting a similar trend in surface charge, as determined from ζ-potential measurements and capacitance coupling (electric force microscopy). Cellulose film stiffness was modulated by cross linking with glyoxal (0.3-2.6% degree of crosslinking) to produce a range of materials with surface shear moduli from 76 to 448 kPa (measured using atomic force microscopy). Cell morphology on these materials could be regulated by tuning the stiffness of the scaffolds. Thus, we report tailored functionalised biomaterials based on cationic cellulose that can be tuned through surface reaction and glyoxal crosslinkin+g, to influence the attachment and morphology of cells. These scaffolds are the first steps towards materials designed to support cells and to regulate cell morphology on implanted biomaterials using only scaffold and cells, i.e. without added adhesion promoters.