Preparation and characterization of 3D hydroxyapatite/collagen scaffolds and its application in bone regeneration with bone morphogenetic protein-2

Desirable bone engineering materials should have a conducive three-dimensional (3D) structure and bioactive mediators for guided bone regeneration. In the present study, hydroxyapatite (HA)/collagen (Col) scaffolds were prepared by an optimized freeze-drying process. The porosity, moisture content, and mechanical properties of the composite have been investigated. The micro-morphology and structure were analyzed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM), confirmed that self-cross-linked HA/Col was evenly distributed and formed a 3D porous scaffold. The physicochemical/mechanical characterization was carried out by Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). Morphological observation and CCK-8 assay of co-culture cells indicated that HA/Col scaffolds were biocompatible. Then HA/Col scaffolds coupled with recombinant human bone morphogenetic proteins 2 (rhBMP-2) were implanted in the mandibular critical size defect in rats, and histological staining was used to evaluate the bone reconstruction. The result showed that HA/Col coupled with rhBMP-2 could significantly improve the formation of new bone and angiogenesis within the scaffolds as well as the proliferation and differentiation of osteoblasts. Thanks to the encouraging osteogenesis effects, the well-defined 3D scaffolds (HA/Col) cooperating with bioactive agents (rhBMP-2) are expected to be a promising candidate for bone tissue engineering applied to regenerative medicine.

An Extracellular Matrix-like Surface for Zn Alloy to Enhance Bone Regeneration

Zn-based alloys are promising biodegradable implants for bone defect repair due to their good mechanical performance and degradability. However, local Zn²⁺ released from Zn-based implants can seriously affect adhering cell behaviors as well as new bone formation on implant surfaces. To address this issue, we have fabricated a bone-mimetic extracellular matrix (ECM)-like surface on Zn-1Ca implants using a hybrid process of anodization, hydrothermal treatment (HT), and fluorous-curing. The ECM-like surface consisted of Zn₂SiO₄ nanorods layered with collagen I (Col-I). The Zn₂SiO₄ nanorods were hemicrystallized and transformed by the reaction of Zn(OH)₂ and SiO₄^4- during the HT. The Zn₂SiO₄ nanorods effectively protected the substrate from corrosion; the Col-I layer decreased the degradation of Zn₂SiO₄ nanorods and further reduced Zn²⁺ release into the medium. This ECM-like surface generated a microenvironment with appropriate Zn²⁺ levels, nanorod-like topography, and Col-I. It significantly improved adhesion, proliferation, and differentiation of osteoblasts on implant surfaces and vascularization of endothelial cells in the extract medium. The in vivo results are in good agreement with in vitro tests, with the ECM-like surface significantly enhancing new bone formation and bone-implant contact compared to the bare implant surface. Overall, this bone-mimetic ECM-like material of Col-I layered Zn₂SiO₄ nanorods is a promising scaffold that promotes the bone regeneration of Zn-based implants.

Medical applications of biopolymer nanofibers

A wide array of biomedical applications, extending from the fabrication of implant materials to targeted drug delivery, can be attributed to polymers. The utilization of chemical monomers to form polymers, such as polypropylene, polystyrene, and polyethylene, can provide high mechanical stability to them and they can be utilized for diverse electronic or thermal applications. However, certain chemical-based synthetic polymers are toxic to humans, animals, plants, and microbial cells. Thus, biopolymers have been introduced as an alternative to make them utilizable for biomedical applications. Even though biopolymers possess beneficial biomedical applications, they are not stable in biological fluids and exhibit toxicity in certain cases. Recent advances in nanotechnology have expanded its applicational significance in various domains, especially in the evolution of biopolymers to transform them into nanoparticles for numerous biomedical applications. In particular, biopolymers are fabricated as nanofibers to enhance their biological properties and to be utilized for exclusive biomedical applications. The aim of this review is to present an overview of various biopolymer nanofibers and their distinct synthesis approaches. In addition, the medical applications of biopolymer nanofibers, including antimicrobial agents, drug delivery systems, biosensor production, tissue engineering, and implant fabrication, are also discussed.

Coral-inspired environmental durability aerogels for micron-size plastic particles removal in the aquatic environment

Removing microplastics (MPs) from water has been a huge challenge due to their inherent features including small size and high stability. In this research, inspired by the active adsorption and passive adhesion mechanisms of corals to MPs, a new strategy to fabricate polydopamine enhanced magnetic chitosan (PDA-MCS) aerogels was developed with a target to match the surface properties of MPs, achieving high MPs removal efficiency. PDA-MCS aerogels were highly efficient in adsorbing polyethylene terephthalate (PET) microplastics in water at pH values of 6-9, with a removal efficiency of up to 91.6%. Even after three recycles, PDA-MCS aerogels still displayed comparatively high removal efficiency (83.4%). Kinetic and isothermal experiments showed that the adsorption process was the result of electrostatic interactions and physical adhesion between aerogels and microplastics. Moreover, PDA-MCS aerogels maintained high removal efficiency under simulated environmental conditions, and the removal efficiency of PET, polyethylene (PE) and polystyrene (PS) microplastics in waters reached 97.3%, 94.6%, and 92.3%, respectively. Therefore, high-efficiency environmentally durable aerogels adsorbent materials have the potential for the removal of MPs from the aquatic environment.

Multifunctional Biosensors Made with Self-Healable Silk Fibroin Imitating Skin

We report on robust silk fibroin (SF) gels fabricated by incorporating cellulose nanocrystals (SF/CNC) as a "tough" unit and photopolymerization of acrylamide as an "elastic" segment. The addition of CNC affects the refolding process of SF molecules controlled by nucleation via templating, resulting in a stable mesoscopic structure. The gel shows robust mechanical stability (88.8% of initial stress after 1000 compression cycles) and excellent adhesion to various materials. The connected gel can recover its ionic conductivity within 20 s and be stretched to a maximum strain of 498% after healing for 10 h with an efficiency of 95.2%. This multifunctional gel sensor can sensitively detect different toxic gases and small-scale and large-scale human motions in real-time. Its sensitivity is calculated as GF = 3.84 at 0-200% strain. Especially, the gel with 5 wt % thermochromic pigments as a visual temperature indicator can quickly reflect abnormal human body temperature according to the color change. Therefore, the strategy shows potential applications in flexible electrodes, biomimetic sensors, and visual biosensors.

Collagen-based biomaterials for biomedical applications

Collagen is an insoluble fibrous protein that composes the extracellular matrix in animals. Although collagen has been used as a biomaterial since 1881, the properties and the complex structure of collagen are still extensive study subjects worldwide. In this article, several topics of importance for understanding collagen research are reviewed starting from its historical milestones, followed by the description of the collagen superfamily and its complex structures, with a focus on type I collagen. Subsequently, some of the superior properties of collagen-based biomaterials, such as biocompatibility, biodegradability, mechanical properties, and cell activities, are pinpointed. These properties make collagen applicable in biomedicine, such as wound healing, tissue engineering, surface coating of medical devices, and skin supplementation. Moreover, some antimicrobial strategies and the general host tissue responses regarding collagen as a biomaterial are presented. Finally, the current status and clinical application of the three-dimensional (3D) printing techniques for the fabrication of collagen-based scaffolds and the reconstruction of the human heart's constituents, such as capillary structures or even the entire organ, are discussed. Besides, an overall outlook for the future of this unique biomaterial is provided.

A review on native well-preserved chitin nanofibrils for materials of high mechanical performance

Novel chitin nanofibrils (ChNF) demonstrate excellent mechanical properties due to a long and extended polymer conformation. The current study highlights the importance of preserving ChNFs for stronger nanomaterials. Various chitin sources - crab, lobster, shrimp, squid pen, mushrooms, and insects have been reviewed. We have discussed preparation protocols and the physical properties of ChNF and presented the mechanical performance of nanomaterials. ChNF close to the native state uses fewer chemicals for treatment and shows a higher molar mass, degree of acetylation, crystallinity index, micrometer length, and a smaller diameter (3 nm), making them cheap, eco-friendly, and competitive to cellulose or synthetic fibrils. A highly acetylated or partially deacetylated ChNF forms a stable colloidal suspension, and it is possible to prepare from it strong films, hydrogels, aerogels, foams, polymer matrix nanocomposites, and microfibers. Moreover, it is possible to regenerate, functionalize, or cross-link the ChNFs to improve nanomaterials' mechanical performance. The preparation protocols remain the key to these achievements. However, the chemical techniques are not friendly ecologically and may hydrolytically degrade the chitin. The biological processes using enzymes or microorganisms are much better but still inefficient. Besides, the processing time limits the rapid preparation of the fibrils in the long-term perspective.

Dual Functionalized Injectable Hybrid Extracellular Matrix Hydrogel for Burn Wounds

Low strength and rapid biodegradability of acellular dermal matrix (ADM) restrict its wider clinical application as a rapid cell delivery platform in situ for management of burn wounds. Herein, the extracted ADM was modified by a dual cross-linking approach with ionic crosslinking using chitosan and covalent cross-linking using an iodine-modified 2,5-dihydro-2,5-dimethoxy-furan cross-linker, termed as CsADM-Cl. In addition, inherent growth factors and cytokines were found to be preserved in CsADM-Cl, irrespective of ionic/covalent crosslinking. CsADM-Cl demonstrated improvement in post crosslinking stiffness with a decreased biodegradation rate. This hybrid crosslinked hydrogel supported adhesion, proliferation, and migration of human foreskin-derived fibroblasts and keratinocytes. Also, the angiogenic potential of CsADM-Cl was manifested by chick chorioallantoic membrane assay. CsADM-Cl showed excellent antibacterial activity against Escherichia coli and Staphylococcus aureus. Moreover, CsADM-Cl treated full thickness burn wounds and demonstrated rapid healing marked with superior angiogenesis, well-defined dermal-epidermal junctions, mature basket weave collagen deposition, and development of more pronounced secondary appendages. Altogether, the bioactive CsADM-Cl hydrogel established significant clinical potential to support wound healing as an apt injectable antibacterial matrix to encounter unmet challenges concerning critical burn wounds.

Novel bone-mimetic nanohydroxyapatite/collagen porous scaffolds biomimetically mineralized from surface silanized mesoporous nanobioglass/collagen hybrid scaffold: Physicochemical, mechanical and in vivo evaluations

Bone-mimetic scaffolds are receiving much interest as such scaffolds exhibit excellent biocompatibility and very close mimic to bone structure and composition. Here, novel bone-mimetic nanohydroxyapatite (nHA)/collagen (Col) porous scaffolds (nHA/Col) were prepared from surface silanized mesoporous nanobioglass (NBG)/Col hybrid scaffold by biomimetic mineralization. Surface silanized mesoporous NBG was prepared by ultrasound-assisted sol-gel method and post treatment with 3-aminopropyltriethylsilane (APTS). The surface silanized mesoporous NBG was characterized by transmission electron microscopy (TEM), transmission electron microscopy-selected area electron diffraction (TEM-SAED) and X-ray photoelectron spectroscopy (XPS). The physicochemical/mechanical characterizations of the scaffolds included scanning electron microscopy (SEM) and TEM imaging of micro/nanostructure, energy dispersive X-ray (EDX) analysis of chemical composition, TEM-SAED and X-ray diffraction/Attenuated total Reflectance-Fourier Infrared spectroscopy (XRD/ATR-FTIR) analyses of amorphous-to-crystalline transformations, thermogravimetric/differential scanning calorimetric (TGA/DSC) analyses of thermal behaviour , porosity and dynamic mechanical analyses. The presence of NBG in collagen fibrillar network enabled progressive growth of HA nanocrystals and generation of a novel bone-mimetic hybrid structures while preserving the highly porous structure of collagen scaffold. The crystallinity, crystallite size and crystal morphology of the grown HA nanocrystals were controllable by regulation of the mineralization time. Furthermore, the osteogenic properties of the non-mineralized (NBG/Col) and mineralized (nHA/Col) hybrid porous scaffolds were examined in vivo using critical-sized calvarial bone defect model in rat. Histological and micro-computed tomography (Micro-CT) analyses after 6 weeks of implantation revealed that the mineralized scaffolds possess excellent in vivo osteogenic potential compared to the non-mineralized one. Collectively, by using surface silanized mesoporous NBG hybridization with collagen fibrillar network, we successfully introduced a new approach for developing novel bone-mimetic nanohydroxyapatite/collagen hybrid scaffolds that possess significant potential for bone tissue regeneration.