Hydroxyethyl Chitosan-Reinforced Polyvinyl Alcohol/Biphasic Calcium Phosphate Hydrogels for Bone Regeneration

Current trend on preparation, characterization and biomedical applications of natural polysaccharide-based nanomaterial reinforcement hydrogels: A review

The tunable properties of hydrogels have led to their widespread use in various biomedical applications such as wound treatment, drug delivery, contact lenses, tissue engineering and 3D bioprinting. Among these applications, natural polysaccharide-based hydrogels, which are fabricated from materials like agarose, alginate, chitosan, hyaluronic acid, cellulose, pectin and chondroitin sulfate, stand out as preferred choices due to their biocompatibility and advantageous fabrication characteristics. Despite the inherent biocompatibility, polysaccharide-based hydrogels on their own tend to be weak in physiochemical and mechanical properties. Therefore, further reinforcement in the hydrogel is necessary to enhance its suitability for specific applications, ensuring optimal performance in diverse settings. Integrating nanomaterials into hydrogels has proven effective in improving the overall network and performance of the hydrogel. This approach also addresses the limitations associated with pure hydrogels. Next, an overview of recent trends in the fabrication and applications of hydrogels was presented. The characterization of hydrogels was further discussed, focusing specifically on the reinforcement achieved with various hydrogel materials used so far. Finally, a few challenges associated with hydrogels by using polysaccharide-based nanomaterial were also presented.

Chitosan hydrogels enriched with bioactive phloroglucinol for controlled drug diffusion and potential wound healing

We report a facile strategy to prepare chitosan (CS) hydrogels that eliminates the need for chemical crosslinking for advanced biomedical therapies. This approach gives controlled properties to the hydrogels by incorporating a natural bioactive phenolic compound, phloroglucinol (PG), into their microstructure. The adsorption of PG onto CS chains enhanced the hydrogels' antioxidant activity by up to 25 % and resulted in a denser, more entangled structure, reducing the pore size by 59 μm while maintaining porosity above 94 %. This allowed us to finely adjust pore size and swelling capacity. These structural properties make these hydrogels well-suited for wound healing dressings, promoting fibroblast proliferation and exhibiting excellent hemocompatibility. Furthermore, to ensure the versatility of these hydrogels, herein, we demonstrate their potential as drug delivery systems, particularly for dermal infections. The drug release can be controlled by a combination of drug diffusion through the swollen hydrogel and relaxation of the CS chains. In summary, our hydrogels leverage the synergistic effects of CS's antibacterial and antifungal properties with PG's antimicrobial and anti-inflammatory attributes, positioning them as promising candidates for biomedical and pharmaceutical applications, more specifically in advanced wound healing therapies with local drug delivery.

Injecting hope: chitosan hydrogels as bone regeneration innovators

Spontaneous bone regeneration encounters substantial restrictions in cases of bone defects, demanding external intervention to improve the repair and regeneration procedure. The field of bone tissue engineering (BTE), which embraces a range of disciplines, offers compelling replacements for conventional strategies like autografts, allografts, and xenografts. Among the diverse scaffolding materials utilized in BTE applications, hydrogels have demonstrated great promise as templates for the regeneration of bone owing to their resemblance to the innate extracellular matrix. In spite of the advancement of several biomaterials, chitosan (CS), a natural biopolymer, has garnered significant attention in recent years as a beneficial graft material for producing injectable hydrogels. Injectable hydrogels based on CS formulations provide numerous advantages, including their capacity to absorb and preserve a significant amount of water, their minimally invasive character, the existence of porous structures, and their capability to adapt accurately to irregular defects. Moreover, combining CS with other naturally derived or synthetic polymers and bioactive materials has displayed its effectiveness as a feasible substitute for traditional grafts. We aim to spotlight the composition, production, and physicochemical characteristics and practical utilization of CS-based injectable hydrogels, explicitly focusing on their potential implementations in bone regeneration. We consider this review a fundamental resource and a source of inspiration for future research attempts to pioneer the next era of tissue-engineering scaffold materials.

Construction methods and biomedical applications of PVA-based hydrogels

Polyvinyl alcohol (PVA) hydrogel is favored by researchers due to its good biocompatibility, high mechanical strength, low friction coefficient, and suitable water content. The widely distributed hydroxyl side chains on the PVA molecule allow the hydrogels to be branched with various functional groups. By improving the synthesis method and changing the hydrogel structure, PVA-based hydrogels can obtain excellent cytocompatibility, flexibility, electrical conductivity, viscoelasticity, and antimicrobial properties, representing a good candidate for articular cartilage restoration, electronic skin, wound dressing, and other fields. This review introduces various preparation methods of PVA-based hydrogels and their wide applications in the biomedical field.

Bioactive and biomimetic 3D scaffolds for bone tissue engineering using graphitic carbon nitride as a sustainable visible light photoinitiator

Graphitic carbon nitride (g-C3N4) is explored as a novel sustainable visible light photoinitiator for the preparation of biomimetic 3D hydrogel scaffolds comprising gelatin methacrylamide (GelMA) and dopamine methacrylamide for use in tissue engineering. The initiator efficiency was assessed by comparing the swelling behavior and the stability of photopolymerized hydrogels prepared with GelMA of different degrees of functionalization and different comonomer compositions. Bioactive composite hydrogels with a 50 wt% nanohydroxyapatite (nHAp) content, to closely mimic the actual bone composition, were successfully obtained by the introduction of nHAp in the prepolymer solutions followed by photopolymerization. The composite hydrogels demonstrated enhanced mechanical properties and excellent stability in PBS verifying the preparation of robust 3D scaffolds for use in cancellous or pre-calcified bone tissue engineering applications. The in vitro cell response of the composite scaffolds exhibited high cell viability and enhanced differentiation of pre-osteoblasts to mature osteoblasts, demonstrating their osteogenic potential. This work establishes, for the first time, the excellent properties of g-C3N4 as a sustainable, visible light initiator, fully satisfying the principles of green chemistry, for the preparation of robust and biologically relevant hydrogels, and proposes a new approach to overcome the main challenges of conventional photoinitiators in cell scaffold fabrication, such as photobleaching, high cost and non-scalable synthesis employing toxic organic precursors and solvents.

Tri-Component Hydrogel as Template for Nanocrystalline Hydroxyapatite Deposition Using Alternate Soaking Method for Bone Tissue Engineering Applications

Composite hydrogels containing apatite-like particles can act as scaffolds for osteoblast proliferation, with applications in bone tissue engineering. In this respect, porous biocompatible hydrogels were obtained from chitosan, oxidized pullulan, and PVA in different ratios. The stability of the hydrogels was ensured both by covalent bonds between aldehyde groups of oxidized pullulan and free amino groups of chitosan, and by physical bonds formed during freeze-thaw cycles and lyophilization. The deposition of calcium phosphates was performed by alternate soaking of the porous hydrogels into solutions with calcium and phosphate ions, assuring a basic pH required for hydroxyapatite formation. The mineralized hydrogels were characterized using FTIR spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis, showing that inorganic particles containing between 80 and 92% hydroxyapatite were deposited in a high amount on the pore walls of the polymeric matrix. The composition of the organic matrix influenced the crystallization of calcium phosphates and the mechanical properties of the composite hydrogels. In vitro biological tests showed that mineralized hydrogels support the proliferation of MG-63 osteoblast-like cells to a greater extent compared to pristine hydrogels.

Synthesis, physicochemical characteristics, cytocompatibility, and antibacterial properties of iron-doped biphasic calcium phosphate nanoparticles with incorporation of silver

The application of biphasic calcium phosphate (BCP) in tissue engineering and regenerative medicine has been widely explored due to its extensively documented multi-functionality. The present study attempts to synthesize a new type of BCP nanoparticles, characterised with favourable cytocompatibility and antibacterial properties via modifications in their structure, functionality and assemblage, using dopants. In this regard, this study initially synthesized iron-doped BCP (FB) nanoparticles with silver subsequently incorporated into FB nanoparticles to create a nanostructured composite (FBAg). The FB and FBAgnanoparticles were then characterized using Fourier transform infrared spectroscopy, x-ray diffraction, ultraviolet-visible spectroscopy, and x-ray photoelectron spectroscopy. The results showed that silver was present in the FBAgnanoparticles, with a positive correlation observed between increasing AgNO3concentrations and increasing shape irregularity and reduced particle size distribution. Additionally, cell culture tests revealed that both FB and FBAgnanoparticles were compatible with bone marrow-derived mesenchymal stem cells (hBMSCs). The antibacterial activity of the FBAgnanoparticles was also tested using Gram-negativeE. coliand Gram-positiveS. aureus, and was found to be effective against both bacteria. The inhibition rates of FBAgnanoparticles againstE. coliandS. aureuswere 33.78 ± 1.69-59.03 ± 2.95%, and 68.48 ± 4.11-89.09 ± 5.35%, respectively. These findings suggest that the FBAgnanoparticles have potential use in future biomedical applications.

Fabrication of ACP-CCS-PVA composite membrane for a potential application in guided bone regeneration

The barrier membranes of guided bone regeneration (GBR) have been widely used in clinical medicine to repair bone defects. However, the unmatched mechanical strength, unsuitable degradation rates, and insufficient regeneration potential limit the application of the current barrier membranes. Here, amorphous calcium phosphate-carboxylated chitosan-polyvinyl alcohol (ACP-CCS-PVA) composite membranes are fabricated by freeze-thaw cycles, in which the ATP-stabilized ACP nanoparticles are uniformly distributed throughout the membranes. The mechanical performance and osteogenic properties are significantly improved by the ACP incorporated into the CCS-PVA system, but excess ACP would suppress cell proliferation and osteogenic differentiation. Our work highlights the pivotal role of ACP in GBR and provides insight into the need for biomaterial fabrication to balance mechanical strength and mineral content.

Protein Adsorption, Calcium-Binding Ability, and Biocompatibility of Silver Nanoparticle-Loaded Polyvinyl Alcohol (PVA) Hydrogels Using Bone Marrow-Derived Mesenchymal Stem Cells

Several approaches have evolved to facilitate the exploration of hydrogel systems in biomedical research. In this sense, poly(vinyl alcohol) (PVA) has been widely used in hydrogel (HG) fabrication for several therapeutic applications. The biological properties of PVA hydrogels (PVA-HGs) are highly dependent on their interaction with protein receptors and extracellular matrix (mainly calcium) deposition, for which there is not enough evidence from existing research yet. Thus, for the first time, the functional properties, like protein and mineral interactions, related to the proliferation of mesenchymal stem cells (MSCs) by silver nanoparticle (AgNP)-loaded PVA hydrogels (AgNPs-PVA-HGs) were investigated in the present study. The UV absorption spectrum and TEM microscopic results showed a maximum absorbance of synthesized AgNPs at 409 nm, with an average particle size of 14.5 ± 2.5 nm, respectively. The functional properties, such as the calcium-binding and the protein adsorption of PVA-HG, were accelerated by incorporating AgNPs; however, the swelling properties of the HGs were reduced by AgNPs, which might be due to the masking of the free functional groups (hydroxyl groups of PVA) by AgNPs. SEM images showed the presence of AgNPs with a more porous structure in the HGs. The proliferative effect of MSCs increased over culture time from day 1 to day 7, and the cell proliferative effect was upregulated by HGs with more pronounced AgNPs-PVA-HG. In addition, both HGs did not produce any significant cytotoxicity in the MSCs. The histological (bright light and H&E staining) and fluorescence microscopic images showed the presence of a cytoskeleton and the fibrillar structure of the MSCs, and the cells adhered more firmly to all HGs. More fibrillar bipolar and dense fibrillar structures were seen in the day 1 and day 7 cultures, respectively. Interestingly, the MSCs cultured on AgNPs-PVA-HG produced extracellular matrix deposition on day 7. Accordingly, the present results proved the biocompatibility of AgNPs-PVA-HG as a suitable system for culturing mammalian stem cells for regenerative tissue applications.

Application of polyvinyl alcohol/chitosan copolymer hydrogels in biomedicine: A review

Hydrogels is a hydrophilic, cross-linked polymer of three-dimensional network structures. The application of hydrogels prepared from a single polymer in the biomedical field has many drawbacks. The functional blend of polyvinyl alcohol and chitosan allows hydrogels to have better and more desirable properties than those produced from a single polymer, which is a good biomaterial for development and design. In this paper, we have reviewed the progress in the application of polyvinyl alcohol/chitosan composite hydrogels in various medical fields, the different cross-linking agents and cross-linking methods, and the research progress in the optimization of composite hydrogels for their subsequent wide range of biomedical applications.

Flaxseed mucilage/calcium phosphate composites as bioactive material for bone tissue regeneration

Biocompatible polymers are attractive material for the manufacturing of surgical implants which break down in vivo without the necessity for a consequent operation for removal. Elaboration of composite biomaterials scaffolds as artificial bone graft materials remains a major task in bioengineering. Flaxseed mucilage was used as bioactive polysaccharide for preparing composite scaffolds made of calcium phosphate embedded in mucilage matrix. Calcium chloride was mixed with mucilage followed by the addition of phosphate precursor to stimulate the in situ formation of calcium phosphate. The obtained scaffolds mucilage/calcium phosphate at different pHs (5 and 8) were characterized using FTIR, XRD, TGA, SEM/EDX and TEM. The results showed the formation of two phases: mucilage/dicalcium phosphate dihydrate (MU/brushite) and mucilage/hydroxyapatite (MU/HA). MTT test was applied to evaluate viability of MC3T3-E1 osteoblasts cells, and the formed hybrids at various pH conditions were classified as non-cytotoxic. These findings establish the potential of developed composite to be used as bone graft substitute materials.

Modification and Functionalization of Polymers for Targeting to Bone Cancer and Bone Regeneration

Bone is one of the most complex, inaccessible body structures, responsible for calcium storage and haematopoiesis. The second highest cause of death across the world is cancer. Amongst all the types of cancers, bone cancer treatment modalities are limited due to the structural complexity and inaccessibility of bones. The worldwide incidence of bone diseases and bone defects due to cancer, infection, trauma, age-related bone degeneration is increasing. Currently different conventional therapies are available for bone cancer such as chemotherapy, surgery and radiotherapy, but they have several disadvantages associated with them. Nanomedicine is being extensively researched as viable therapeutics to mitigate drug resistance in cancer therapy and promote bone regeneration. Several natural polymers such as chitosan, dextran, alginate, hyaluronic acid, and synthetic polymers like polyglycolic acid, poly(lactic-co-glycolic acid), polycaprolactone are investigated for their application in nanomedicine for bone cancer treatment and bone regeneration. Nanocarriers have shown promising results in preclinical experimental studies. However, they still face a major drawback of inadequate targetability. The paper summarizes the status of research and the progress made so far in modifications and functionalization of natural polymers for improving their site specificity and targeting for effective treatment of bone cancer and enhancing bone regeneration.

Enzymatically crosslinked hydrogel based on tyramine modified gelatin and sialylated chitosan

The enzymatically crosslinked hydrogel could replicate the cellular microenvironment for biomedical applications. In the present study, to improve the cytocompatibility of chitosan (CS), sialic acid (SA) was introduced to CS to synthesize sialylated CS (CS-SA), and the tyramine (TA) was grafted to gelatin (G) to obtain TA modified gelatin (G-TA). The successful synthesis of CS-SA and G-TA was confirmed using¹H NMR and UV-Vis absorption spectra. The interpenetrating polymer networks G-TA/CS-SA (GC) hydrogel was then fabricated via blending G-TA and CS-SA solutions and crosslinked using horseradish peroxidase. The storage modulus (G') of the fabricated GC hydrogels with different ratios of G-TA/CS-SA greatly varied during the formation and strain of hydrogels. With the increase of CS-SA concentration from 0% to 2%, the storage modulus of GC hydrogels was also observed to decrease from 1500 Pa to 101 Pa; the water uptake capacity of GC hydrogels increased from 1000% to 4500%. Additionally, the cell counting kit-8 and fluorescent images demonstrated the excellent cytocompatibility of GC hydrogels after culturing with NIH 3T3 cells. The obtained results indicated that the fabricated GC hydrogels might have potential in biomedical fields, such as wound dressing.

Hybrid gum tragacanth/sodium alginate hydrogel reinforced with silver nanotriangles for bacterial biofilm inhibition

Biomaterial associated bacterial infections are indomitable to treatment due to the rise in antibiotic resistant strains, thereby triggering the need for new antibacterial agents. Herein, composite bactericidal hydrogels were formulated by incorporating silver nanotriangles (AgNTs) inside a hybrid polymer network of Gum Tragacanth/Sodium Alginate (GT/SA) hydrogels. Physico-chemical examination revealed robust mechanical strength, appreciable porosity and desirable in vitro enzymatic biodegradation of composite hydrogels. The antibacterial activity of AgNT-hydrogel was tested against planktonic and biofilm-forming Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacteria. For all the strains, AgNT-hydrogel showed a dose-dependent decrease in bacterial growth. The addition of AgNT-hydrogels (40-80 mg ml^-1) caused 87% inhibition of planktonic biomass and up to 74% reduction in biofilm formation. Overall, this study proposes a promising approach for designing antibacterial composite hydrogels to mitigate various forms of bacterial infection.

Chitosan as Bone Scaffold for Craniofacial Bone Regeneration: A Systematic Review

Background: The reconstruction of bone defect in the face and head is indispensable yet one of the most challenging procedure to date. Chitosan has emerged as a promising low-cost natural biopolymer for the bone scaffold as an alternative to surgery. This study aims to review the effectiveness of chitosan as a bone scaffold for craniofacial bone regeneration. Methods: This systematic review used Google Scholar and PubMed as database sources. Study selection using PRISMA diagram and Boolean operator to specify the study search. The quality assessment of the study used a checklist from Joanna Briggs Institute for experimental study. Result: We included 18 experimental studies, both in vivo and in vitro study—the in vivo study used animal subjects such as mice, goats and rabbits. The studies mostly used chitosan combined with other biomaterials such as demineralized bone matrix (DBM), genipin (GP), sodium alginate (SA), resveratrol (Res), polycaprolactone (PCL) and collagen, growth factor and stem cells such as bone morphogenic protein-2 (BMP-2), dental pulp stem cell (DPSC), and human umbilical cord mesenchymal stem cells (hUCMSC). Conclusion: Chitosan is a natural polymer with promising osteoconductive, osteoinductive and osteo-integrative effects in bone regeneration. Chitosan utilization for bone scaffolds combined with other biomaterials, growth factors, or stem cells gives better bone regeneration results than chitosan alone.

A Critical Review of Additive Manufacturing Techniques and Associated Biomaterials Used in Bone Tissue Engineering

With the ability to fabricate complex structures while meeting individual needs, additive manufacturing (AM) offers unprecedented opportunities for bone tissue engineering in the biomedical field. However, traditional metal implants have many adverse effects due to their poor integration with host tissues, and therefore new material implants with porous structures are gradually being developed that are suitable for clinical medical applications. From the perspectives of additive manufacturing technology and materials, this article discusses a suitable manufacturing process for ideal materials for biological bone tissue engineering. It begins with a review of the methods and applicable materials in existing additive manufacturing technologies and their applications in biomedicine, introducing the advantages and disadvantages of various AM technologies. The properties of materials including metals and polymers, commonly used AM technologies, recent developments, and their applications in bone tissue engineering are discussed in detail and summarized. In addition, the main challenges for different metallic and polymer materials, such as biodegradability, anisotropy, growth factors to promote the osteogenic capacity, and enhancement of mechanical properties are also introduced. Finally, the development prospects for AM technologies and biomaterials in bone tissue engineering are considered.

High-performance bilayer composites for the replacement of osteochondral defects

Two novel bilayer constructs for the repair of osteochondral defects were developed from nanofibers and ceramic particles embedded into PVA matrices, exhibiting multiple promising properties similar to those of corresponding natural tissues.

Bio-Inspired Hydrogels via 3D Bioprinting

Many soft tissues of the human body such as cartilages, muscles, and ligaments are mainly composed of biological hydrogels possessing excellent mechanical properties and delicate structures. Nowadays, bio-inspired hydrogels have been intensively explored due to their promising potential applications in tissue engineering. However, the traditional manufacturing technology is challenging to produce the bio-inspired hydrogels, and the typical biological composite topologies of bio-inspired hydrogels are accessible completed using 3D bioprinting at micrometer resolution. In this chapter, the 3D bioprinting techniques used for the fabrication of bio-inspired hydrogels were summarized, and the materials used were outlined. This chapter also focuses on the applications of bio-inspired hydrogels fabricated using available 3D bioprinting technologies. The development of 3D bioprinting techniques in the future would bring us closer to the fabrication capabilities of living organisms, which would be widely used in biomedical applications.

Bone Grafts and Substitutes in Dentistry: A Review of Current Trends and Developments

After tooth loss, bone resorption is irreversible, leaving the area without adequate bone volume for successful implant treatment. Bone grafting is the only solution to reverse dental bone loss and is a well-accepted procedure required in one in every four dental implants. Research and development in materials, design and fabrication technologies have expanded over the years to achieve successful and long-lasting dental implants for tooth substitution. This review will critically present the various dental bone graft and substitute materials that have been used to achieve a successful dental implant. The article also reviews the properties of dental bone grafts and various dental bone substitutes that have been studied or are currently available commercially. The various classifications of bone grafts and substitutes, including natural and synthetic materials, are critically presented, and available commercial products in each category are discussed. Different bone substitute materials, including metals, ceramics, polymers, or their combinations, and their chemical, physical, and biocompatibility properties are explored. Limitations of the available materials are presented, and areas which require further research and development are highlighted. Tissue engineering hybrid constructions with enhanced bone regeneration ability, such as cell-based or growth factor-based bone substitutes, are discussed as an emerging area of development.

Three-Dimensional Printing of Hydroxyapatite Composites for Biomedical Application

Hydroxyapatite (HA) and HA-based nanocomposites have been recognized as ideal biomaterials in hard tissue engineering because of their compositional similarity to bioapatite. However, the traditional HA-based nanocomposites fabrication techniques still limit the utilization of HA in bone, cartilage, dental, applications, and other fields. In recent years, three-dimensional (3D) printing has been shown to provide a fast, precise, controllable, and scalable fabrication approach for the synthesis of HA-based scaffolds. This review therefore explores available 3D printing technologies for the preparation of porous HA-based nanocomposites. In the present review, different 3D printed HA-based scaffolds composited with natural polymers and/or synthetic polymers are discussed. Furthermore, the desired properties of HA-based composites via 3D printing such as porosity, mechanical properties, biodegradability, and antibacterial properties are extensively explored. Lastly, the applications and the next generation of HA-based nanocomposites for tissue engineering are discussed.

Recent progress in preparation and applications of chitosan/calcium phosphate composite materials

Studying the development of unique materials from sustainable and renewable resources has gained increasing concern due to the depletion of fossil resources. Chitosan and its derivatives have been considered as versatile candidates for preparing attractive materials. The fabrication of chitosan/calcium phosphate composite compounds has received much attention for the development of numerous promising products in different fields. In this short review, recent preparation strategies for chitosan/calcium phosphate composites such as freeze casting, vacuum-assisted filtration, and biomimetic mineralization were discussed. The review presented their advances for diverse applications such as bone tissue engineering implants, drug delivery, wound healing, dental caries, as well adsorption of organic and heavy metals from polluted water. The challenges and future perspectives for the application of chitosan/calcium phosphate materials in biomedical and environmental applications were also involved in this review article.

Advances in Growth Factor Delivery for Bone Tissue Engineering

Shortcomings related to the treatment of bone diseases and consequent tissue regeneration such as transplants have been addressed to some extent by tissue engineering and regenerative medicine. Tissue engineering has promoted structures that can simulate the extracellular matrix and are capable of guiding natural bone repair using signaling molecules to promote osteoinduction and angiogenesis essential in the formation of new bone tissues. Although recent studies on developing novel growth factor delivery systems for bone repair have attracted great attention, taking into account the complexity of the extracellular matrix, scaffolding and growth factors should not be explored independently. Consequently, systems that combine both concepts have great potential to promote the effectiveness of bone regeneration methods. In this review, recent developments in bone regeneration that simultaneously consider scaffolding and growth factors are covered in detail. The main emphasis in this overview is on delivery strategies that employ polymer-based scaffolds for spatiotemporal-controlled delivery of both single and multiple growth factors in bone-regeneration approaches. From clinical applications to creating alternative structural materials, bone tissue engineering has been advancing constantly, and it is relevant to regularly update related topics.

Fish Collagen: Extraction, Characterization, and Applications for Biomaterials Engineering

The utilization of marine-based collagen is growing fast due to its unique properties in comparison with mammalian-based collagen such as no risk of transmitting diseases, a lack of religious constraints, a cost-effective process, low molecular weight, biocompatibility, and its easy absorption by the human body. This article presents an overview of the recent studies from 2014 to 2020 conducted on collagen extraction from marine-based materials, in particular fish by-products. The fish collagen structure, extraction methods, characterization, and biomedical applications are presented. More specifically, acetic acid and deep eutectic solvent (DES) extraction methods for marine collagen isolation are described and compared. In addition, the effect of the extraction parameters (temperature, acid concentration, extraction time, solid-to-liquid ratio) on the yield of collagen is investigated. Moreover, biomaterials engineering and therapeutic applications of marine collagen have been summarized.

Nanostructured selenium-doped biphasic calcium phosphate with in situ incorporation of silver for antibacterial applications

Selenium-doped nanostructure has been considered as an attractive approach to enhance the antibacterial activity of calcium phosphate (CaP) materials in diverse medical applications. In this study, the selenium-doped biphasic calcium phosphate nanoparticles (SeB-NPs) were first synthesized. Then, silver was in situ incorporated into SeB-NPs to obtain nanostructured composite nanoparticles (AgSeB-NPs). Both SeB-NPs and AgSeB-NPs were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis), X-ray photoelectron spectroscopy (XPS), and Raman spectra. The results confirmed that the SeO32- was doped at the PO43- position and silver nanoparticles were deposited on the surface of SeB-NPs. Next, Transmission Electron Microscopy (TEM) analysis displayed that the prepared AgSeB-NPs had a needle-cluster-like morphology. CCK-8 analysis revealed SeB-NPs and AgSeB-NPs had good cytocompatibility with osteoblasts. The antibacterial activity of the prepared AgSeB-NPs was confirmed by using Gram-negative E. coli and Gram-positive S. aureus. The above results manifested the significance of the final AgSeB-NPs for biomedical applications.

Polyvinyl Alcohol/Sodium Alginate Hydrogels Incorporated with Silver Nanoclusters via Green Tea Extract for Antibacterial Applications

Silver-based nanoparticles and biomaterials have extensive biomedical applications owing to their unique antimicrobial properties. Thus, green and facile synthesis of such materials is highly desirable. This study reports an antibacterial hydrogel based on polyvinyl alcohol/sodium alginate network with the incorporation of silver nanoparticles (AgNPs), which is greenly synthesized by reductive metabolites obtained from the leaves of green tea. The 'flower-shape' AgNPs were acquired, it formed a mono-disperse system with a distinct uniform interparticle separation. The average size of AgNPs varied from 129.5 to 243.6 nm, which could be regulated by using different volumes of the green tea extract. Zeta potentials of the AgNPs were from -39.3 mV to -20.3 mV, indicating the moderate stability of the particles in water. In the next stage, the antibacterial polyvinyl alcohol/sodium alginate hydrogels were fabricated by incorporating prepared AgNPs. Scanning Electron Microscopy (SEM) images showed that the porous structure was obtained, and Energy Dispersive X-Ray (EDX) analysis confirmed that the AgNPs were uniformly dispersed in the polymer network. The hydrogels exhibited superior water absorption properties, which were characterized by a high swelling ratio (500-900%) and fast equilibrium. The hydrogels also exhibited good antimicrobial activity in assays with Gram-positive bacteria Escherichia coli and Gram-negative bacteria Staphylococcus aureus. To sum up, a process for the green preparation of antibacterial hydrogels based on AgNPs derived from tea leaves as a conveniently available cheap local agricultural product was established.