Biomimetic synthesis of hydroxyapatite/bacterial cellulose nanocomposites for biomedical applications

Chitosan particles embedded bacterial nanocellulose flat membrane for hemodialysis

The development of bio-based hemodialysis membranes continues to be a challenge. Bacterial nanocellulose (BNC) membranes show potential in hemodialysis but can hardly retain beneficial proteins. Here, chitosan particles/bacterial nanocellulose (CSP/BNC) membranes were designed to efficiently remove uremic toxins and retain beneficial proteins. First, CSPs were synthesized in situ within a BNC membrane by ionic gelation following negative pressure impregnation. Subsequently, these membranes were thoroughly characterized. Compared with the BNC membrane, the pore volume and pore size of the 3 % CSP/BNC membrane decreased by 42.2 % and 32.1 %, respectively. The increased 22.2 times of Young's modulus and 88.9 % of tensile strength in the 3 % CSP/BNC membrane confirmed enhanced mechanical property. The sieving coefficient of bovine serum albumin decreased to 0.05 ± 0.03 in the 3 % CSP/BNC membrane. Moreover, the CSP/BNC membrane exhibited good hemocompatibility and cytocompatibility. The simulated dialysis results showed that the 3 % CSP/BNC membrane exhibited high clearance of urea (16.37 %/cm2) and lysozyme (3.54 %/cm2), while efficiently retaining bovine serum albumin (98.04 %/cm2). This is the first demonstration of the construction of a BNC-based hemodialysis membrane with in situ CSP formation to effectively regulate the pore properties of the membrane, making the CSP/BNC membrane a promising candidate for hemodialysis applications.

Fabrication of carboxymethyl cellulose-based thermo-sensitive hydrogels and inhibition of corneal neovascularization

Corneal neovascularization (CNV) is a common multifactorial sequela of anterior corneal segment inflammation, which could lead to visual impairment and even blindness. The main treatments available are surgical sutures and invasive drug injections, which could cause serious ocular complications. To solve this problem, a thermo-sensitive drug-loaded hydrogel with high transparency was prepared in this study, which could achieve the sustained-release of drugs without affecting normal vision. In briefly, the thermo-sensitive hydrogel (PFNOCMC) was prepared from oxidized carboxymethyl cellulose (OCMC) and aminated poloxamer 407 (PF127-NH2). The results proved the PFNOCMC hydrogels possess high transparency, suitable gel temperature and time. In the CNV model, the PFNOCMC hydrogel loading bone morphogenetic protein 4 (BMP4) showed significant inhibition of CNV, this is due to the hydrogel allowed the drug to stay longer in the target area. The animal experiments on the ocular surface were carried out, which proved the hydrogel had excellent biocompatibility, and could realize the sustained-release of loaded drugs, and had a significant inhibitory effect on the neovascularization after ocular surface surgery. In conclusion, PFNOCMC hydrogels have great potential as sustained-release drug carriers in the biomedical field and provide a new minimally invasive option for the treatment of neovascular ocular diseases.

Double-layered microneedle patch loaded with bioinspired nano-vaccine for melanoma treatment and wound healing

Malignant melanoma is a challenging problem worldwide, because the remaining tumor cells and extensive skin defects following surgical resection are difficult to treat. Biomaterial-mediated immunotherapy has emerged as a superior strategy for anti-tumor applications in recent years. Herein, a unique double-layer MNP was developed to address the problem of malignant melanoma. Hydroxyapatite (HAP) and short-chain peptides from tumor cells were self-assembled to prepare the bioinspired nano-vaccine, and then they were loaded onto the microneedle tips of methacrylated gelatin (GelMA)-based MNP. The products (dubbed HVMN) demonstrated relatively good biocompatibility and immune activity, inhibiting the proliferation and inducing apoptosis of malignant melanoma in a B16 cell-bearing model of C57BL/6 mice, and promoting skin tissue regeneration in a full thickness skin defect model of SD rats in 15 days. The putative molecular pathways were examined preliminarily. In conclusion, this research will develop a competitive microneedle patch with dual anti-tumor and pro-regenerative properties for the postoperative treatment of malignant melanoma.

Biomineralization in Three-Dimensional Scaffolds Based on Bacterial Nanocellulose for Bone Tissue Engineering: Feature Characterization and Stem Cell Differentiation

Bacterial nanocellulose (BNC) has a negative surface charge in physiological environments, which allows the adsorption of calcium ions to initiate the nucleation of different calcium phosphate phases. The aim of this study was to investigate different methods of mineralization in three-dimensional microporous bacterial nanocellulose with the intention of mimicking the composition, structure, and biomechanical properties of natural bone. To generate the 3D microporous biomaterial, porogen particles were incorporated during BNC fermentation with the Komagataeibacter medellinensis strain. Calcium phosphates (CPs) were deposited onto the BNC scaffolds in five immersion cycles, alternating between calcium and phosphate salts in their insoluble forms. Scanning electron microscopy (SEM) showed that the scaffolds had different pore sizes (between 70 and 350 µm), and their porous interconnectivity was affected by the biomineralization method and time. The crystals on the BNC surface were shown to be rod-shaped, with a calcium phosphate ratio similar to that of immature bone, increasing from 1.13 to 1.6 with increasing cycle numbers. These crystals also increased in size with an increasing number of cycles, going from 25.12 to 35.9 nm. The main mineral phase observed with X-ray diffraction was octacalcium dihydrogen hexakis phosphate (V) pentahydrate (OCP). In vitro studies showed good cellular adhesion and high cell viability (up to 95%) with all the scaffolds. The osteogenic differentiation of human bone marrow mesenchymal stem cells on the scaffolds was evaluated using bone expression markers, including alkaline phosphatase, osteocalcin, and osteopontin. In conclusion, it is possible to prepare 3D BNC scaffolds with controlled microporosity that allow osteoblast adhesion, proliferation, and differentiation.

Efficient Isolation Method for Highly Charged Phosphorylated Cellulose Nanocrystals

Phosphorylation of cellulose nanocrystals (CNCs) has remained a marginal activity despite the undisputed application potential in flame-retardant materials, sustainable high-capacity ion-exchange materials, or substrates for biomineralization among others. This is largely due to strenuous extraction methods prone to a combination of poor reproducibility, low degrees of substitution, disappointing yields, and impractical reaction sequences. Here, we demonstrate an improved methodology relying on the modification routines for phosphorylated cellulose nanofibers and hydrolysis by gaseous HCl to isolate CNCs. This allows us to overcome the aforementioned shortcomings and to reliably and reproducibly extract phosphorylated CNCs with exceptionally high surface charge (∼2000 mmol/kg) in a straightforward routine that minimizes water consumption and maximizes yields. The CNCs were characterized by NMR, ζpotential, conductometric titration, thermogravimetry, elemental analysis, wide-angle X-ray scattering, transmission electron microscopy, and atomic force microscopy.

Cellulose-based composite scaffolds for bone tissue engineering and localized drug delivery

Natural bone constitutes a complex and organized structure of organic and inorganic components with limited ability to regenerate and restore injured tissues, especially in large bone defects. To improve the reconstruction of the damaged bones, tissue engineering has been introduced as a promising alternative approach to the conventional therapeutic methods including surgical interventions using allograft and autograft implants. Bioengineered composite scaffolds consisting of multifunctional biomaterials in combination with the cells and bioactive therapeutic agents have great promise for bone repair and regeneration. Cellulose and its derivatives are renewable and biodegradable natural polymers that have shown promising potential in bone tissue engineering applications. Cellulose-based scaffolds possess numerous advantages attributed to their excellent properties of non-toxicity, biocompatibility, biodegradability, availability through renewable resources, and the low cost of preparation and processing. Furthermore, cellulose and its derivatives have been extensively used for delivering growth factors and antibiotics directly to the site of the impaired bone tissue to promote tissue repair. This review focuses on the various classifications of cellulose-based composite scaffolds utilized in localized bone drug delivery systems and bone regeneration, including cellulose-organic composites, cellulose-inorganic composites, cellulose-organic/inorganic composites. We will also highlight the physicochemical, mechanical, and biological properties of the different cellulose-based scaffolds for bone tissue engineering applications.

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Cellulose and its derivatives are renewable and biodegradable natural polymers that with great potential for bone tissue engineering.

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Cellulose-based materials can be used various therapeutics directly to the bone to achieve bone regeneration.

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Bioinks made of cellulose-based materials hold great promise to develop patient specific solutions for bone repair using 3D printing.

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Challenges associated with inaccuracies in existing preclinical models, sterilization regulatory barriers still need to be addressed before clinical translation.

Hemocompatibility of cellulose phosphate aerogel membranes with potential use in bone tissue engineering

Cellulose is an appealing material for tissue engineering. In an attempt to overcome some obstacles with cellulose II cell scaffolding materials related to insufficient biomineralization, lack of micron-size porosity, and deficiency in surface charge, respective solutions have been proposed. These included covalent phosphorylation of different cellulose materials targeting relatively low degrees of substitution (DS 0.18-0.23) and processing these cellulose derivatives into scaffolding materials by a dissolution/coagulation approach employing the hitherto rarely used TBAF/DMSO/H₂O system for cellulose dissolution. Here, we report bioactivity and preliminary hemocompatibility testing of dual-porous cellulose phosphate aerogels (contrasted with the phosphate-free reference) obtained via coagulation (water/ethanol), solvent exchange and scCO₂ drying. Deposition of hydroxyapatite from simulated body fluid (7 days of immersion) revealed good bioactivity (1.5-2.2 mg Ca²⁺ per mg scaffold). Incubation of the scCO₂-dried and rehydrated scaffolding materials in heparin anticoagulated human whole blood was conducted to study selected parameters of hemostasis (prothrombin F1+2 fragment, PF4, count of thrombocyte-leukocyte conjugates) and inflammatory response (C5a fragment, leukocyte activation marker CD11b). Adhesion of leukocytes on the surface of the incubated substrates was assessed by scanning electron and fluorescence microscopy (DAPI staining). The results suggest that phosphorylation at low DS does not increase platelet activation. However, a significant increase in platelet activation and thrombin formation was observed after a certain fraction of the negative surface charges had been compensated by Ca²⁺ ions. The combination of both phosphorylation and calcification turned out to be a potent means for controlling the inflammatory response, which was close to baseline level for some of the studied samples.

An injectable and self-healing cellulose nanofiber-reinforced alginate hydrogel for bone repair

Biomedical materials are in high demand for transplantation in cases of diseased or damaged bone tissue. Hydrogels are potential candidates for bone defect repair; however, traditional hydrogels lack the necessary strength and multiple functions. Herein, we effectively synthesized a cellulose nanofiber (CNF)-reinforced oxidized alginate (OSA)/gelatin (Gel) semi-interpenetrating network hydrogel through a facile one-step approach without a cross-linker by using the synergistic effects of dynamic imine bonds and hydrogen bonds. The OSA/Gel/CNF sample showed a notable compressive modulus (up to 361.3 KPa). The gelation time (~150 s) ensured excellent injectability. Self-healing exhibited a high efficiency of up to 92 %, which would enable minimally invasive, dynamic adjustments and personalized therapies. Furthermore, the OSA/Gel/CNF hydrogel showed excellent biomineralization (Ca/P ratio ~ 1.69) and enhanced preosteoblast cell (MC3T3-E1) viability (over 96 %), proliferation, and osteogenic differentiation. Thus, this multifunctional hydrogel has promising potential for using in the bone tissue repairs.

Microbial Synthesis of Hydroxyapatite-Nanocellulose Nanocomposites from Symbiotic Culture of Bacteria and Yeast Pellicle of Fermented Kombucha Tea

The strong need for the utilization of industrial by-products and biowaste increases as we transition towards a circular economy. On these grounds, the present research aims to explore the applicability of the Symbiotic Culture of Bacteria and Yeast (SCOBY), a by-product of a functional beverage industry, for applications in biomedicine. Herein, hydroxyapatite (HA)-coated SCOBY nanocellulose (SN) nanocomposite (SNHA) was synthesized via a novel biomimetic approach using Serratia marcescens strain by adopting two different in situ approaches. Characterization studies established the presence of functional groups corresponding to pure nanocellulose and HA. Microscopic analysis revealed SN fibers of the dimensions 30–50 nm surrounded by 10–15 nm rod-shaped HA crystals. The SNHA membranes were carbonated and harbored traces of metal ions. A deposition of nano-HA crystals as high as 30–50% was achieved. Overall, the synthesized SNHA membranes reflected increased stability, low crystalline nature and an ion-substituted structure resembling the natural bone; they are thereby suited for bone tissue engineering.

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.

Fabrication strategies and biomedical applications of three-dimensional bacterial cellulose-based scaffolds: A review

Bacterial cellulose (BC), an extracellular polysaccharide, is a versatile biopolymer due to its intrinsic physicochemical properties, broad-spectrum applications, and remarkable achievements in different fields, especially in the biomedical field. Presently, the focus of BC-related research is on the development of scaffolds containing other materials for in-vitro and in-vivo biomedical applications. To this end, prime research objectives concern the biocompatibility of BC and the development of three-dimensional (3D) BC-based scaffolds. This review summarizes the techniques used to develop 3D BC scaffolds and discusses their potential merits and limitations. In addition, we discuss the various biomedical applications of BC-based scaffolds for which the 3D BC matrix confers desired structural and conformational features. Overall, this review provides comprehensive coverage of the idea, requirements, synthetic strategies, and current and prospective applications of 3D BC scaffolds, and thus, should be useful for researchers working with polysaccharides, biopolymers, or composite materials.

The Trend of Bacterial Nanocellulose Research Published in the Science Citation Index Expanded From 2005 to 2020: A Bibliometric Analysis

To gain insight into the trend of bacterial nanocellulose research, a bibliometric analysis was performed using the Science Citation Index Expanded database from 2005 to 2020. The study concentrated on the publication's performance in terms of annual outputs and citations, mainstream journals, categories of the Web of Sciences, leading countries, prominent institutions, and trends in research. Current research priorities and future trends were analyzed after summarizing the most commonly used keywords extracted from words in the paper title analysis, authors' keyword analysis, and KeyWords Plus. The findings revealed that the annual output in the form of scholarly articles on bacterial nanocellulose research steadily increased during the first quartile of the study period, followed by a very rapid increase in the last five-years of the study. Increasing mechanical strength would remain the main future focus of bacterial nanocellulose research to create its scope in different field of applications.

The Application Status of Nanoscale Cellulose-Based Hydrogels in Tissue Engineering and Regenerative Biomedicine

As a renewable, biodegradable, and non-toxic material with moderate mechanical and thermal properties, nanocellulose-based hydrogels are receiving immense consideration for various biomedical applications. With the unique properties of excellent skeletal structure (hydrophilic functional groups) and micro-nano size (small size effect), nanocellulose can maintain the three-dimensional structure of the hydrogel to a large extent, providing mechanical strength while ensuring the moisture content. Owing to its unique features, nanocellulose-based hydrogels have made excellent progress in research and development on tissue engineering, drug carriers, wound dressings, development of synthetic organs, 3D printing, and biosensing. This review provides an overview of the synthesis of different types of nanocellulose, including cellulose nanocrystals, cellulose nanofibers, and bacterial nanocellulose, and describes their unique features. It further provides an updated knowledge of the development of nanocellulose-based functional biomaterials for various biomedical applications. Finally, it discusses the future perspective of nanocellulose-based research for its advanced biomedical applications.

One-Step Biosynthesis of Soft Magnetic Bacterial Cellulose Spheres with Localized Nanoparticle Functionalization

Actuated structures are becoming relevant in medical fields; however, they call for flexible/soft-base materials that comply with biological tissues and can be synthesized in simple fabrication steps. In this work, we extend the palette of techniques to afford soft, actuable spherical structures taking advantage of the biosynthesis process of bacterial cellulose. Bacterial cellulose spheres (BCS) with localized magnetic nanoparticles (NPs) have been biosynthesized using two different one-pot processes: in agitation and on hydrophobic surface-supported static culture, achieving core-shell or hollow spheres, respectively. Magnetic actuability is conferred by superparamagnetic iron oxide NPs (SPIONs), and their location within the structure was finely tuned with high precision. The size, structure, flexibility and magnetic response of the spheres have been characterized. In addition, the versatility of the methodology allows us to produce actuated spherical structures adding other NPs (Au and Pt) in specific locations, creating Janus structures. The combination of Pt NPs and SPIONs provides moving composite structures driven both by a magnetic field and a H₂O₂ oxidation reaction. Janus Pt/SPIONs increased by five times the directionality and movement of these structures in comparison to the controls.

Hydroxyapatite Particles from Simulated Body Fluids with Different pH and Their Effects on Mesenchymal Stem Cells

Bone-like hydroxyapatite (HAp) has been prepared by biomimetic synthesis using simulated body fluid (SBF), mimicking inorganic ion concentrations in human plasma, or 1.5SBF that has 1.5-times higher ion concentrations than SBF. In this study, the controllable preparations of HAp particles from 1.5SBF with different pH values were examined. The particles obtained as precipitates from 1.5SBF showed different morphologies and crystallinities depending on the pH of 1.5SBF. Micro-sized particles at pH 7.4 of 1.5SBF had a higher Ca/P ratio and crystallinity as compared with nano-sized particles at pH 8.0 and pH 8.4 of 1.5SBF. However, a mixture of micro-sized and nano-sized particles was obtained from pH 7.7 of 1.5SBF. When Ca²⁺ concentrations in 1.5SBF during mineralization were monitored, the concentration at pH 7.4 drastically decreased from 12 to 24 h. At higher pH, such as 8.0 and 8.4, the Ca²⁺ concentrations decreased during pH adjustment and slightly decreased even after 48 h. In this investigation at pH 7.7, the Ca²⁺ concentrations were higher than pH 8.0 and 8.4.Additionally, cytotoxicity of the obtained precipitates to mesenchymal stem cells was lower than that of synthetic HAp. Controllable preparation HAp particles from SBF has potential applications in the construction of building components of cell scaffolds.

Applications of Bacterial Cellulose as a Natural Polymer in Tissue Engineering

Choosing the material with the best regeneration potential and properties closest to that of the extracellular matrix is one of the main challenges in tissue engineering and regenerative medicine. Natural polymers, such as collagen, elastin, and cellulose, are widely used for this purpose in tissue engineering. Cellulose derived from bacteria has excellent mechanical properties, high hydrophilicity, crystallinity, and a high degree of polymerization and, therefore, can be used as scaffold/membrane for tissue engineering. In the current study, we reviewed the latest trends in the application of bacterial cellulose (BC) polymers as a scaffold in different types of tissue, including bone, vascular, skin, and cartilage. Also, we mentioned the biological and mechanical advantages and disadvantages of BC polymers. Given the data presented in this study, BC polymer could be suggested as a favorable natural polymer in the design of tissue scaffolds. Implementing novel composites that combine this polymer with other materials through modern or rapid prototyping methods can open up a great prospect in the future of tissue engineering and regenerative medicine.

Perspective Applications and Associated Challenges of Using Nanocellulose in Treating Bone-Related Diseases

Bone serves to maintain the shape of the human body due to its hard and solid nature. A loss or weakening of bone tissues, such as in case of traumatic injury, diseases (e.g., osteosarcoma), or old age, adversely affects the individuals quality of life. Although bone has the innate ability to remodel and regenerate in case of small damage or a crack, a loss of a large volume of bone in case of a traumatic injury requires the restoration of bone function by adopting different biophysical approaches and chemotherapies as well as a surgical reconstruction. Compared to the biophysical and chemotherapeutic approaches, which may cause complications and bear side effects, the surgical reconstruction involves the implantation of external materials such as ceramics, metals, and different other materials as bone substitutes. Compared to the synthetic substitutes, the use of biomaterials could be an ideal choice for bone regeneration owing to their renewability, non-toxicity, and non-immunogenicity. Among the different types of biomaterials, nanocellulose-based materials are receiving tremendous attention in the medical field during recent years, which are used for scaffolding as well as regeneration. Nanocellulose not only serves as the matrix for the deposition of bioceramics, metallic nanoparticles, polymers, and different other materials to develop bone substitutes but also serves as the drug carrier for treating osteosarcomas. This review describes the natural sources and production of nanocellulose and discusses its important properties to justify its suitability in developing scaffolds for bone and cartilage regeneration and serve as the matrix for reinforcement of different materials and as a drug carrier for treating osteosarcomas. It discusses the potential health risks, immunogenicity, and biodegradation of nanocellulose in the human body.

Coated electrospun polyamide-6/chitosan scaffold with hydroxyapatite for bone tissue engineering

Polyamide-6 (PA6) is a synthetic polymer that bears resemblance to collagen in its backbone and has excellent stability in human body fluid. Chitosan (CS) with the similar structure to that of the polysaccharides existing in the extracellular matrix (ECM), has a more suitable biodegradation rate for the formation of new-bone. Electrospun fiber have nanoscale structure, high porosity and large specific surface area, can simulate the structure and biological function of the natural ECM. To meet the requirements of mechanical properties and biocompatibility of bone tissue engineering, electrospun PA6/CS scaffolds were fabricated by electrospinning technology. The mineralized PA6/CS scaffolds were obtained through immersion in 1.5× simulated body fluid (1.5SBF), which allowed the hydroxyapatite (HA) layer to grow into the thickness range under very mild reaction conditions without the need of a prior chemical modification of the substrate surface. The results showed that electrospun PA6/CS fibrous scaffolds in the diameter range of 60-260 nm mimic the nanostructure of the ECM. The tensile strength and modulus of 10PA6/CS fibrous scaffolds reach up to 12.67 ± 2.31 MPa and 95.52 ± 6.78 MPa, respectively. After mineralization, HA particles uniformly distributed on the surface of PA6/CS fibrous scaffolds in a porous honeycomb structure, and the content of mineral was about 40%. In addition, cell culture study indicated that the mineralized PA6/CS composite scaffolds were non-cytotoxic, and had a good biocompatibility and an ability to promote MC3T3-E1 cell attachment and proliferation.

Supercritical carbon dioxide decellularization of plant material to generate 3D biocompatible scaffolds

The use of plant-based biomaterials for tissue engineering has recently generated interest as plant decellularization produces biocompatible scaffolds which can be repopulated with human cells. The predominant approach for vegetal decellularization remains serial chemical processing. However, this technique is time-consuming and requires harsh compounds which damage the resulting scaffolds. The current study presents an alternative solution using supercritical carbon dioxide (scCO2). Protocols testing various solvents were assessed and results found that scCO2 in combination with 2% peracetic acid decellularized plant material in less than 4 h, while preserving plant microarchitecture and branching vascular network. The biophysical and biochemical cues of the scCO2 decellularized spinach leaf scaffolds were then compared to chemically generated scaffolds. Data showed that the scaffolds had a similar Young's modulus, suggesting identical stiffness, and revealed that they contained the same elements, yet displayed disparate biochemical signatures as assessed by Fourier-transform infrared spectroscopy (FTIR). Finally, human fibroblast cells seeded on the spinach leaf surface were attached and alive after 14 days, demonstrating the biocompatibility of the scCO2 decellularized scaffolds. Thus, scCO2 was found to be an efficient method for plant material decellularization, scaffold structure preservation and recellularization with human cells, while performed in less time (36 h) than the standard chemical approach (170 h).

Development of composite hydrogel based on hydroxyapatite mineralization over pectin reinforced with cellulose nanocrystal

Hydrogels based on pectin and cellulose nanocrystals (CNC) were used in our study to nucleation and growth of hydroxyapatite (HAp) by the biomimetic method. In this study, we evaluated the direct impact of the different percentages of CNC on pectin hydrogel and the influence of HAp obtained through two methods. CNC were obtained from HCl hydrolysis following chemical functionalization through vinyl groups. The percentage of CNC positively induces thermal stability, mechanical properties and HAp mineralization from biomimetic using simulated body fluid (1.5 SBF). Hydrogels with 5% of CNC showed a higher amount of HAp immersed for 14 days, about 28% of HAp. The obtained hydrogels were compared with hydrogels containing 20% of HAp nanoparticles obtained by chemical precipitation. Biocompatibility of the hydrogels was evaluated by cell viability using fibroblasts (L929). In general, the hydrogels obtained through the biomimetic method show slightly larger biocompatibility compared to the hybrid hydrogels obtained from chemical precipitation.

In Situ and Ex Situ Designed Hydroxyapatite: Bacterial Cellulose Materials with Biomedical Applications

Hydroxyapatite (HAp) and bacterial cellulose (BC) composite materials represent a promising approach for tissue engineering due to their excellent biocompatibility and bioactivity. This paper presents the synthesis and characterization of two types of materials based on HAp and BC, with antibacterial properties provided by silver nanoparticles (AgNPs). The composite materials were obtained following two routes: (1) HAp was obtained in situ directly in the BC matrix containing different amounts of AgNPs by the coprecipitation method, and (2) HAp was first obtained separately using the coprecipitation method, then combined with BC containing different amounts of AgNPs by ultrasound exposure. The obtained materials were characterized by means of XRD, SEM, and FT-IR, while their antimicrobial effect was evaluated against Gram-negative bacteria (Escherichia coli), Gram-positive bacteria (Staphylococcus aureus), and yeast (Candida albicans). The results demonstrated that the obtained composite materials were characterized by a homogenous porous structure and high water absorption capacity (more than 1000% w/w). These materials also possessed low degradation rates (<5% in simulated body fluid (SBF) at 37 °C) and considerable antimicrobial effect due to silver nanoparticles (10–70 nm) embedded in the polymer matrix. These properties could be finetuned by adjusting the content of AgNPs and the synthesis route. The samples prepared using the in situ route had a wider porosity range and better homogeneity.

3D construct of hydroxyapatite/zinc oxide/palladium nanocomposite scaffold for bone tissue engineering

The purpose of this study was to produce and characterize Hydroxyapatite/Zinc Oxide/Palladium (HA/0.05 wt% ZnO/0.1 wt% Pd) nanocomposite scaffolds and study their mechanical and antibacterial properties, biocompatibility and bioactivity. The initial materials were developed using sol-gel and precipitation methods. Scaffolds were characterized using atomic absorption analysis (AA), scanning electron microcopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM), atomic force microscopy (AFM) and Brunauer-EmmeS-Teller (BET) method. Furthermore, the bioactivity of scaffolds in simulated body fluid (SBF) and the interaction of dental pulp stem cells (DPSCs) with the nanocomposite scaffolds were assessed. Our results showed that the HA/ZnO/Pd (H1), HA/ZnO/Pd coated by 0.125 g chitosan (H2) and HA/ZnO/Pd coated by 0.25 g chitosan (H3) scaffolds possess higher compressive strength and toughness and lower microhardness and density compared to the pure HA (H0) scaffolds. Immersion of samples in SBF showed the deposition of apatite on the surface of the scaffolds. The biocompatibility assay indicated lower cell proliferation on the H1, H2 and H3 in comparison to the H0. The antibacterial results obtained show a significant impact by loading Pd/ZnO on HA in the deactivation of microorganisms in vitro.

Biofilms of cellulose and hydroxyapatite composites: Alternative synthesis process

A new biofilm of cellulose coated with hydroxyapatite particles have been prepared using a simple, fast and low temperature process based on a microwave-assisted hydrothermal synthesis. The cellulose used as matrix of the biocomposite was extracted from banana stems residues. The hydroxyapatite coating was performed using calcium nitrate tetrahydrate, phosphoric acid, and 1,2-ethylenediamine dispersed in a cellulose/water solution, with posterior microwave-assisted hydrothermal synthesis, for 5 min at 140°C. The chemical, structural, thermal, and morphological properties of the composites were investigated by X-ray diffraction, infrared spectroscopy, thermogravimetry and field emission scanning electron microscopy. Results showed that the methodology was effective to produce high quality composites, with good thermal stability. Cell viability tests indicated that the cellulose/Hap films were not cytotoxic.

Bacterial Cellulose Nanocomposites: Morphology and Mechanical Properties

Bacterial cellulose (BC) is a promising material for biomedical applications due to its unique properties such as high mechanical strength and biocompatibility. This article describes the microbiological synthesis, modification, and characterization of the obtained BC-nanocomposites originating from symbiotic consortium Medusomyces gisevii. Two BC-modifications have been obtained: BC-Ag and BC-calcium phosphate (BC-Ca₃(PO₄)₂). Structure and physicochemical properties of the BC and its modifications were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and infrared Fourier spectroscopy as well as by measurements of mechanical and water holding/absorbing capacities. Topographic analysis of the surface revealed multicomponent thick fibrils (150–160 nm in diameter and about 15 µm in length) constituted by 50–60 nm nanofibrils weaved into a left-hand helix. Distinctive features of Ca-phosphate-modified BC samples were (a) the presence of 500–700 nm entanglements and (b) inclusions of Ca₃(PO₄)₂ crystals. The samples impregnated with Ag nanoparticles exhibited numerous roundish inclusions, about 110 nm in diameter. The boundaries between the organic and inorganic phases were very distinct in both cases. The Ag-modified samples also showed a prominent waving pattern in the packing of nanofibrils. The obtained BC gel films possessed water-holding capacity of about 62.35 g/g. However, the dried (to a constant mass) BC-films later exhibited a low water absorption capacity (3.82 g/g). It was found that decellularized BC samples had 2.4 times larger Young’s modulus and 2.2 times greater tensile strength as compared to dehydrated native BC films. We presume that this was caused by molecular compaction of the BC structure.

Fabrication and characterization of dextran/nanocrystalline β-tricalcium phosphate nanocomposite hydrogel scaffolds

Design of bioactive three-dimensional scaffolds to support bone tissue repair and regeneration become a key area of research in tissue engineering. Herein, porous hybrid hydrogels composed of dextran incorporated with nanocrystalline β-tricalcium phosphate (β-TCP) particles were tailor made as scaffolds for bone tissue engineering. β-TCP was successfully introduced within the dextran networks crosslinked through intermolecular ionic interactions and hydrogen bonding confirmed by FTIR spectroscopy. The effect of β-TCP content on equilibrium water uptake and swelling kinetics of composite hydrogels was investigated. It was found that the homogeneous distribution of β-TCP nanoparticles through the hydrogel matrix contributes to higher porosity and swelling capacity. In depth swelling measurements revealed that while in the early stage of swelling, water diffusion follows the Fick's law, for longer time swelling behavior of hydrogels undergo the second order kinetics. XRD measurements represented the formation of apatite layer on the surface of nanocomposite hydrogels after immersion in the SBF solution, which implies their bioactivity. Cell culture assays confirmed biocompatibility of the developed hybrid hydrogels in vitro. The obtained results converge to offer dextran/β-TCP nanocomposite hydrogels as promising scaffolds for bone regeneration applications.

Bone-Inspired Mineralization with Highly Aligned Cellulose Nanofibers as Template

Bioinspired by the aligned structure and building blocks of bone, this work mineralized the aligned bacterial cellulose (BC) through in situ mineralization using CaCl₂ and K₂HPO₄ solutions. The cellulose nanofibers were aligned by a scalable stretching process. The aligned and mineralized bacterial cellulose (AMBC) homogeneously incorporated hydroxyapatite (HAP) with a high mineral content and exhibited excellent mechanical strength. The ordered 3D structure allowed the AMBC composite to achieve a high elastic modulus and hardness and the development of a nanostructure inspired by natural bone. The AMBC composite exhibited an elastic modulus of 10.91 ± 3.26 GPa and hardness of 0.37 ± 0.18 GPa. Compared with the nonaligned mineralized bacterial cellulose (NMBC) composite with mineralized crystals of HAP randomly distributed into the BC scaffolds, the AMBC composite possessed a 210% higher elastic modulus and 95% higher hardness. The obtained AMBC composite had excellent mechanical properties by mimicking the natural structure of bone, which indicated that the organic BC aerogel with aligned nanofibers was a promising template for biomimetic mineralization.

A biocompatible bacterial cellulose/tannic acid composite with antibacterial and anti-biofilm activities for biomedical applications

Biofilm-associated infections are in a high rate of recurrence and biofilms show formidable resistance to current antibiotics, making them a growing challenge in biomedical field. In this study, a biocompatible composite was developed by incorporating tannic acid (TA) and MgCl₂ to bacterial cellulose (BC) for antimicrobial and anti-biofilm purposes. The morphology was investigated by scanning electron microscopy (SEM), and chemical structure were characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS). In vitro release profiles of tannic acid revealed that the Mg²⁺ cross-links help impede the release of TA from BC matrix, while composite BC-TA lacked Mg²⁺ ionic cross-links, thus more TA was released from the hydrogel. The BC-TA-Mg composites also displayed strong antibacterial activity against S. aureus, E. coli and P. aeruginosa. Moreover, the composites significantly reduced biofilm formation of S. aureus and P. aeruginosa after 24 h incubation by ∼80% and ∼87%, respectively. As a consequence, the BC-TA-Mg composites are a very promising material for combating biofilm-associated infections in biomedical and public health fields.

Lignocellulosic Biomass Derived Functional Materials: Synthesis and Applications in Biomedical Engineering

The pertinent issue of resources shortage arising from global climate change in the recent years has accentuated the importance of materials that are environmentally friendly. Despite the merits of current material like cellulose as the most abundant natural polysaccharide on earth, the incorporation of lignocellulosic biomass has the potential to value-add the recent development of cellulose-derivatives in drug delivery systems. Lignocellulosic biomass, with a hierarchical structure is comprised of cellulose, hemicellulose and lignin. As an excellent substrate that is renewable, biodegradable, biocompatible and chemically accessible for modified materials, lignocellulosic biomass sets forth a myriad of applications. To date, materials derived from lignocellulosic biomass have been extensively explored for new technological development and applications, such as biomedical, green electronics and energy products. In this review, chemical constituents of lignocellulosic biomass are first discussed before we critically examine the potential alternatives in the field of biomedical application. In addition, the pretreatment methods for extracting cellulose, hemicellulose and lignin from lignocellulosic biomass as well as their biological applications including drug delivery, biosensor, tissue engineering etc. are reviewed. It is anticipated there will be an increasing interest and research findings in cellulose, hemicellulose and lignin from natural resources, which help provide important directions for the development in biomedical applications.

Macroporous bacterial cellulose grafted by oligopeptides induces biomimetic mineralization via interfacial wettability

Bacterial cellulose (BC) has a role in tissue repair and regenerative medicine, which has already attracted tremendous interest from researchers, especially those working in the field of hybrid materials. Herein, we designed BC-based macroporous functional materials by dialdehyde bacterial cellulose (DBC) cross-linking with oligopeptides under mild reactive conditions. The interfacial properties of the surface modified BC were examined by biomimetic mineralization. The results showed that a macroporous structure was achieved by using oligopeptides as chemical cross-linking agents with an interconnected macroporosity ranging from 20 μm to 80 μm. Their mechanical properties were barely altered compared to the pristine BC. Their enhanced surface charges stemmed from the carboxyl groups of the oligopeptides engaging in reactions with amine and aldehyde groups. The oligopeptides cross-linked DBC showed a faster initial induction towards minerals via interfacial wettability resulting in promotion of mineralization, the hybrid materials had excellent biocompatibility relative to the pristine BC. These findings are vital to the development of other biopolymers with essential macroporous structures as well as improved interfacial wettability, which enables their possible uses in tissue repair and regenerative medicine.

Bacterial cellulose membrane functionalized with hydroxiapatite and anti-bone morphogenetic protein 2: A promising material for bone regeneration

Bone tissue engineering seeks to adequately restore functions related to physical and biological properties, aiming at a repair process similar to natural bone. The use of compatible biopolymers, such as bacterial cellulose (BC), as well as having interesting mechanical characteristics, presents a slow in vivo degradation rate, and the ability to be chemically modified. To promote better bioactivity towards BC, we synthesized an innovative BC membrane associated to hydroxyapatite (HA) and anti-bone morphogenetic protein antibody (anti-BMP-2) (BC-HA-anti-BMP-2). We present the physical-chemical, biological and toxicological characterization of BC-HA-anti-BMP-2. Presence of BC and HA components in the membranes was confirmed by SEM-EDS and FTIR assays. No toxic potential was found in MC3T3-E1 cells by cytotoxicity assays (XTT Assay and Clonogenic Survival), genotoxicity (Comet Assay) and mutagenicity (Cytokinesis-blocked micronucleus Test). The in vitro release kinetics of anti-BMP-2 antibodies detected gradually reducing antibody levels, reducing approximately 70% in 7 days and 90% in 14 days. BC-HA-anti-BMP-2 increased SPP1, BGLAP, VEGF, ALPL, RUNX2 and TNFRSF11B expression, genes involved in bone repair and also increased mineralization nodules and phosphatase alcalin (ALP) activity levels. In conclusion, we developed BC-HA-anti-BMP-2 as an innovative and promising biomaterial with interesting physical-chemical and biological properties which may be a good alternative to treatment with commercial BMP-2 protein.

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.

Mineralization of phosphorylated cellulose: crucial role of surface structure and monovalent ions for optimizing calcium content

Cellulose can be phosphorylated to produce organic matrices with highly adsorptive properties for, e.g., biocompatible materials for biomedical applications. We focus on the effects of phosphorylation of surfaces of crystalline nanocellulose and, in particular, on the competitive adsorption of mono- and divalent cations (Na+ and Ca2+) typically contained in mineralizing salt mixtures using all-atom molecular dynamics (MD) simulations. Phosphorylation was applied at 12% and 25% both in water and CaCl2 solutions. Our main result shows that Na+ and Ca2+ cations are concentrated in different interfacial layers with Na+ ions penetrating much closer to the surface. This behavior cannot be described by the Poisson-Boltzmann theory or implicit solvent simulations. Our analysis shows that the physical origin of this observation is due to a balance between the electrostatic interactions and hydration free energy associated with the ions. Adsorption levels of the different ions also respond differently to changes in the degree of phosphorylation. We show that the number of adsorbed Na+ ions per phosphate group increases whereas the number of adsorbed Ca2+ ions decreases with an increasing degree of phosphorylation (or when the number of binding sites increases). The decrease in the number of adsorbed Ca2+ ions can be explained by an increasing "charge-charge" repulsion between the Ca2+ ions attracted by the charged surface. Importantly, our results demonstrate the existence of an optimum degree of phosphorylation in terms of adsorbed Ca2+ ions and can be used as a guideline in materials design, for example, when choosing the cellulose matrix or with other similarly structured biomolecular and polymer surfaces.