Development and evaluation of cross-linked collagen-hydroxyapatite scaffolds for tissue engineering

Biomimetic Apatite/Natural Polymer Composite Granules as Multifunctional Dental Tissue Regenerative Material

This study presents a comprehensive evaluation of novel composite biomaterials designed for dental applications, aiming to potentially address the prevalent challenge of dental and periodontal tissue loss. The composites consisted of biomimetic hydroxyapatite (mHA) enriched with Mg2+, CO32-, and Zn2+ ions, type I collagen, alginate, and, additionally, chitosan and sericin. The granules were loaded with ibuprofen sodium salt. The investigation encompassed a morphology characterization, a porosity analysis, a chemical structure assessment, and an examination of the swelling behavior, drug release kinetics (ibuprofen), and release profiles of zinc and magnesium ions. The granules exhibited irregular surfaces with an enhanced homogeneity in the chitosan-coated granules and well-developed mesoporous structures. The FT-IR spectra confirmed the presence of ibuprofen sodium, despite overlapping bands for the polymers. The granules demonstrated a high water-absorption capacity, with delayed swelling observed in the chitosan-coated granules. Ibuprofen displayed burst-release profiles, especially in the G1 and G3 samples. In the case of the chitosan-coated granules (G2 and G4), lower amounts of ibuprofen were released. In turn, there was a significant difference in the released amount of magnesium and zinc ions from the granules, which was most likely caused by their different location in the hydroxyapatite crystals. The cytotoxicity assays confirmed the non-cytotoxic behavior of the biomaterial. These findings suggest the potential applicability of these biomaterials in dental scenarios, emphasizing their multifunctional and biocompatible nature.

Enhanced bone regeneration by low-intensity pulsed ultrasound and lipid microbubbles on PLGA/TCP 3D-printed scaffolds

BACKGROUND

To investigate the effect of low-intensity pulsed ultrasound (LIPUS) combined with lipid microbubbles on the proliferation and bone regeneration of bone marrow mesenchymal stem cells (BMSCs) in poly (lactic-glycolic acid copolymer) (PLGA)/α-tricalcium phosphate (TCP) 3D-printed scaffolds.

METHODS

BMSCs were irradiated with different LIPUS parameters and microbubble concentrations, and the best acoustic excitation parameters were selected. The expression of type I collagen and the activity of alkaline phosphatase were detected. Alizarin red staining was used to evaluate the calcium salt production during osteogenic differentiation.

RESULTS

BMSCs proliferation was the most significant under the condition of 0.5% (v/v) lipid microbubble concentration, 2.0 MHz frequency, 0.3 W/cm² sound intensity and 20% duty cycle. After 14 days, the type I collagen expression and alkaline phosphatase activity in the scaffold increased significantly compared to those in the control group, and alizarin red staining showed more calcium salt production during osteogenic differentiation. After 21 days, scanning electron microscopy experiments showed that osteogenesis was obvious in the PLGA/TCP scaffolds.

CONCLUSION

LIPUS combined with lipid microbubbles on PLGA/TCP scaffolds can promote BMSCs growth and bone differentiation, which is expected to provide a new and effective method for the treatment of bone regeneration in tissue engineering.

Polymeric Nanocomposite Hydrogel Scaffolds in Craniofacial Bone Regeneration: A Comprehensive Review

Nanocomposite biomaterials combine a biopolymeric matrix structure with nanoscale fillers. These bioactive and easily resorbable nanocomposites have been broadly divided into three groups, namely natural, synthetic or composite, based on the polymeric origin. Preparing such nanocomposite structures in the form of hydrogels can create a three-dimensional natural hydrophilic atmosphere pivotal for cell survival and new tissue formation. Thus, hydrogel-based cell distribution and drug administration have evolved as possible options for bone tissue engineering and regeneration. In this context, nanogels or nanohydrogels, created by cross-linking three-dimensional polymer networks, either physically or chemically, with high biocompatibility and mechanical properties were introduced as promising drug delivery systems. The present review highlights the potential of hydrogels and nanopolymers in the field of craniofacial tissue engineering and bone regeneration.

A New, Biomimetic Collagen-Apatite Wound-Healing Composite with a Potential Regenerative and Anti-Hemorrhagic Effect in Dental Surgery

The aim of this work was to obtain and characterize composite biomaterials containing two components, namely carbonated hydroxyapatite, which was substituted with Mg²⁺ and Zn²⁺ ions, and natural polymer-collagen protein. The following two different types of collagen were used: lyophilized powder of telocollagen from bovine Achilles tendon and atelocollagen solution from bovine dermis. The obtained 3D materials were used as potential matrices for the targeted delivery of tranexamic acid for potential use in wound healing after tooth extractions. Tranexamic acid (TXA) was introduced into composites by two different methods. The physicochemical analyses of the obtained composites included Fourier-transform infrared spectroscopy (FT-IR), inductively coupled plasma-optical emission spectroscopy (ICP-OES), transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (PXRD), release kinetics tests, swelling test, and cytotoxicity assays. The studies showed that the proposed synthetic methods yielded biomaterials with favorable physicochemical properties, as well as the expected release profile of the drug and ions from the matrices.

Chemical Bonding of Biomolecules to the Surface of Nano-Hydroxyapatite to Enhance Its Bioactivity

Hydroxyapatite (HA) is a significant constituent of bones or teeth and is widely used as an artificial bone graft. It is often used to replace the lost bones or in reconstructing alveolar bones before dental implantation. HA with biological functions finds its importance in orthopedic surgery and dentistry to increase the local concentration of calcium ions, which activate the growth and differentiation of mesenchymal stem cells (MSC). To make relevant use of HA in bone transplantation, the surfaces of orthopedic and dental implants are frequently coated with nanosized hydroxyapatite (nHA), but its low dispersibility and tendency to form aggregates, the purpose of the surface modification of bone implants is defeated. To overcome these drawbacks and to improve the histocompatibility of bone implants or to use nHA in therapeutic applications of implants in the treatment of bone diseases, various studies suggested the attachment of biomolecules (growth factors) or drugs through chemical bonding at the surface of nHA. The growth factors or drugs bonded physically at the surface of nHA are mostly unstable and burst released immediately. Therefore, reported studies suggested that the surface of nHA needs to be modified through the chemical bonding of biologically active molecules at the surface of bone implants such as proteins, peptides, or naturally occurring polysaccharides to prevent the aggregation of nHA and to get homogenous dispersion of nHA in solution. The role of irradiation in producing bioactive and antibacterial nHA through morphological variations in surfaces of nHA is also summarized by considering internal structures and the formation of reactive oxygen species on irradiation. This mini-review aims to highlight the importance of small molecules such as proteins, peptides, drugs, and photocatalysts in surface property modification of nHA to achieve stable, bioactive, and antibacterial nHA to act as artificial bone implants (scaffolds) in combination with biodegradable polymers.

Influence of Biomimetically Mineralized Collagen Scaffolds on Bone Cell Proliferation and Immune Activation

Collagen, as the main component of connective tissue, is frequently used in various tissue engineering applications. In this study, porous sponge-like collagen scaffolds were prepared by freeze-drying and were then mineralized in a simulated body fluid. The mechanical stability was similar in both types of scaffolds, but the mineralized scaffolds (MCS) contained significantly more calcium, magnesium and phosphorus than the unmineralized scaffolds (UCS). Although the MCS contained a lower percentage (~32.5%) of pores suitable for cell ingrowth (113–357 μm in diameter) than the UCS (~70%), the number of human-osteoblast-like MG-63 cells on days 1, 3 and 7 after seeding was higher on MCS than on UCS, and the cells penetrated deeper into the MCS. The cell growth in extracts prepared by eluting the scaffolds for 7 days in a cell culture medium was also markedly higher in the MCS extracts, as indicated by real-time monitoring in the sensory xCELLigence system for 7 days. From this point of view, MCS are more promising for bone tissue engineering than UCS. However, MCS evoked a more pronounced inflammatory response than UCS, as indicated by the production of tumor necrosis factor-alpha (TNF-α) in macrophage-like RAW 264.7 cells in cultures on these scaffolds.

Injectable chitosan/collagen hydrogels nano-engineered with functionalized single wall carbon nanotubes for minimally invasive applications in bone

Mechanical robustness is an essential consideration in the development of hydrogel platforms for bone regeneration, and despite significant advances in the field of injectable hydrogels, many fail in this regard. Inspired by the mechanical properties of carboxylated single wall carbon nanotubes (COOH-SWCNTs) and the biological advantages of natural polymers, COOH-SWCNTs were integrated into chitosan and collagen to formulate mechanically robust, injectable and thermoresponsive hydrogels with interconnected molecular structure for load-bearing applications. This study presents a complete characterisation of the structural and biological properties, and mechanism of gelation of these novel formulated hydrogels. Results demonstrate that β-glycerophosphate (β-GP) and temperature play important roles in attaining gelation at physiological conditions, and the integration with COOH-SWCNTs significantly changed the structural morphology of the hydrogels to a more porous and aligned network. This led to a crystalline structure and significantly increased the mechanical strength of the hydrogels from kPa to MPa, which is closer to the mechanical strength of the bone. Moreover, increased osteoblast proliferation and rapid adsorption of hydroxyapatite on the surface of the hydrogels indicates increased bioactivity with addition of COOH-SWCNTs. Therefore, these nano-engineered hydrogels are expected to have wide utility in the area of bone tissue engineering and regenerative medicine.

Mesenchymal stem cell spheroids incorporated with collagen and black phosphorus promote osteogenesis of biodegradable hydrogels

Mesenchymal stem cell (MSC)-spheroids have sparked significant interest in bone tissue engineering due to their resemblance to natural bone tissue, especially in terms of cell-cell and cell-extracellular matrix interactions. Many biomaterials or biomolecules have been incorporated into MSC-spheroids to enhance their osteogenic abilities. In this respect, we assessed the osteogenic responses of MSC spheroids leveraged through the unique combination of collagen and black phosphorus (BP). The MSC spheroids were successfully constructed with 6 μg/mL collagen and/or a concentration gradient (0 μg/mL, 4 μg/mL, 8 μg/mL, and 16 μg/mL) of BP and were evaluated for MSC viability and their osteogenic differentiation over a time period of 14 days. Improved MSC viability and osteogenic ability were observed for the spheroids with collagen and BP at the concentration of 4 μg/mL and 8 μg/mL. Next, blank spheroids (Control) or the optimized MSC spheroids with 6 μg/mL collagen and 4 μg/mL BP (Col+BP4) were further encapsulated into two types of hydrogel scaffolds: porous oligo[poly(ethylene glycol) fumarate] (OPF) hydrogel and hydroxyapatite-collagen I scaffold (HE-COL). The osteogenic abilities of these four groups were evaluated after 14 and 21 days of osteogenic induction. The MSC spheroids incorporated with collagen and BP implanted into OPF porous hydrogel (Col+BP/OPF) elicited a higher expression of Runx2, osteopontin, and alkaline phosphatase than blank spheroids implanted into OPF porous hydrogel (Control/OPF). Enhanced osteogenesis was also observed in the Col+BP/HE-COL group as compared to Control/HE-COL. Taken together, the results from this study showed the perspectives of collagen and BP incorporated MSC spheroids for the development of injectable cellular therapies for bone regeneration.

Biologically Inspired Collagen/Apatite Composite Biomaterials for Potential Use in Bone Tissue Regeneration-A Review

Type I collagen and nanocrystalline-substituted hydroxyapatite are the major components of a natural composite—bone tissue. Both of these materials also play a significant role in orthopedic surgery and implantology; however, their separate uses are limited; apatite is quite fragile, while collagen’s mechanical strength is very poor. Therefore, in biomaterial engineering, a combination of collagen and hydroxyapatite is used, which provides good mechanical properties with high biocompatibility and osteoinduction. In addition, the porous structure of the composites enables their use not only as bone defect fillers, but also as a drug release system providing controlled release of drugs directly to the bone. This feature makes biomimetic collagen–apatite composites a subject of research in many scientific centers. The review focuses on summarizing studies on biological activity, tested in vitro and in vivo.

Biomimetic polyvinyl alcohol/type II collagen hydrogels for cartilage tissue engineering

Type II collagen (Col-II) is one of the important organic components of the cartilage extracellular matrix (ECM). Such natural material is known for its good biocompatibility, but it could not provide a good supporting environment for seed cells due to its rapid degradation and poor strength. In the present work, different contents of Col-II were incorporated into porous polyvinyl alcohol (PVA) to fabricate porous PVA/Col-II composite hydrogels for cartilage tissue engineering. The results illustrate that, after incorporation of Col-II, the elasticity modulus of the composite hydrogels firstly increases, and then decreases (under moisture state). The elasticity modulus of PVA/Col-II (at the ratio of 1:1) hydrogels reaches 11 ± 1.7 KPa, about two-fold higher than pure PVA hydrogels (4.9 ± 0.6 KPa). Meanwhile, all hydrogels exhibit relatively high water content (> 95%) and porosity (> 75%). The degradation analysis indicates that Col-II incorporation induce a high degradation ratio of the composite hydrogels. Cell culture results show PVA/Col-II hydrogels have no negative effects on cells viability and proliferation. The PVA/Col-II hydrogels may possess a potential application in the field of articular cartilage tissue engineering and regeneration.

Recent trends in the application of widely used natural and synthetic polymer nanocomposites in bone tissue regeneration

The goal of a biomaterial is to support the bone tissue regeneration process at the defect site and eventually degrade in situ and get replaced with the newly generated bone tissue. Nanocomposite biomaterials are a relatively new class of materials that incorporate a biopolymeric and biodegradable matrix structure with bioactive and easily resorbable fillers which are nano-sized. This article is a review of a few polymeric nanocomposite biomaterials which are potential candidates for bone tissue regeneration. These nanocomposites have been broadly classified into two groups viz. natural and synthetic polymer based. Natural polymer-based nanocomposites include materials fabricated through reinforcement of nanoparticles and/or nanofibers in a natural polymer matrix. Several widely used natural biopolymers, such as chitosan (CS), collagen (Col), cellulose, silk fibroin (SF), alginate, and fucoidan, have been reviewed regarding their present investigation on the incorporation of nanomaterial, biocompatibility, and tissue regeneration. Synthetic polymer-based nanocomposites that have been covered in this review include polycaprolactone (PCL), poly (lactic-co-glycolic) acid (PLGA), polyethylene glycol (PEG), poly (lactic acid) (PLA), and polyurethane (PU) based nanocomposites. An array of nanofillers, such as nano hydroxyapatite (nHA), nano zirconia (nZr), nano silica (nSi), silver nano particles (AgNPs), nano titanium dioxide (nTiO₂), graphene oxide (GO), that is used widely across the bone tissue regeneration research platform are included in this review with respect to their incorporation into a natural and/or synthetic polymer matrix. The influence of nanofillers on cell viability, both in vitro and in vivo, along with cytocompatibility and new tissue generation has been encompassed in this review. Moreover, nanocomposite material characterization using some commonly used analytical techniques, such as electron microscopy, spectroscopy, diffraction patterns etc., has been highlighted in this review. Biomaterial physical properties, such as pore size, porosity, particle size, and mechanical strength which strongly influences cell attachment, proliferation, and subsequent tissue growth has been covered in this review. This review has been sculptured around a case by case basis of current research that is being undertaken in the field of bone regeneration engineering. The nanofillers induced into the polymeric matrix render important properties, such as large surface area, improved mechanical strength as well as stability, improved cell adhesion, proliferation, and cell differentiation. The selection of nanocomposites is thus crucial in the analysis of viable treatment strategies for bone tissue regeneration for specific bone defects such as craniofacial defects. The effects of growth factor incorporation on the nanocomposite for controlling new bone generation are also important during the biomaterial design phase.

Three-dimensional (3D) printed scaffold and material selection for bone repair

Critical-sized bone defect repair remains a substantial challenge in clinical settings and requires bone grafts or bone substitute materials. However, existing biomaterials often do not meet the clinical requirements of structural support, osteoinductive property, and controllable biodegradability. To treat large-scale bone defects, the development of three-dimensional (3D) porous scaffolds has received considerable focus within bone engineering. A variety of biomaterials and manufacturing methods, including 3D printing, have emerged to fabricate patient-specific bioactive scaffolds that possess controlled micro-architectures for bridging bone defects in complex configurations. During the last decade, with the development of the 3D printing industry, a large number of tissue-engineered scaffolds have been created for preclinical and clinical applications using novel materials and innovative technologies. Thus, this review provides a brief overview of current progress in existing biomaterials and tissue engineering scaffolds prepared by 3D printing technologies, with an emphasis on the material selection, scaffold design optimization, and their preclinical and clinical applications in the repair of critical-sized bone defects. Furthermore, it will elaborate on the current limitations and potential future prospects of 3D printing technology. STATEMENT OF SIGNIFICANCE: 3D printing has emerged as a critical fabrication process for bone engineering due to its ability to control bulk geometry and internal structure of tissue scaffolds. The advancement of bioprinting methods and compatible ink materials for bone engineering have been a major focus to develop optimal 3D scaffolds for bone defect repair. Achieving a successful balance of cellular function, cellular viability, and mechanical integrity under load-bearing conditions is critical. Hybridization of natural and synthetic polymer-based materials is a promising approach to create novel tissue engineered scaffolds that combines the advantages of both materials and meets various requirements, including biological activity, mechanical strength, easy fabrication and controllable degradation. 3D printing is linked to the future of bone grafts to create on-demand patient-specific scaffolds.

3D porous collagen/functionalized multiwalled carbon nanotube/chitosan/hydroxyapatite composite scaffolds for bone tissue engineering

In this study, we describe new collagen/functionalized multiwalled carbon nanotube/chitosan/hydroxyapatite (Col/f-MWCNT/CS/HA) composite scaffolds which were fabricated by freezing (-40 °C at 0.9 °C/min) and lyophilization (48 h, 0 °C and 200 mtorr). The compressive stresses (from 523 to 1112 kPa), swelling (from 513.9 ± 27 to 481.05 ± 25%), porosity (from 98 ± 0.15 to 95.7 ± 0.1%), contact angle (from 87.8 to 76.7°) properties examined before and after biomineralization for comparison 3D porous Col, CS, Col/f-MWCNT and Col/f-MWCNT/CS scaffolds. Biomineralization was performed by biomimetic method in concentrated SBF (10 × SBF, at 37 °C and 6.5 pH). XRD, SEM, EDS, FTIR, TGA, Optical microscopy and BET results showed that compared to Col, CS and Col/f-MWCNT scaffolds, Col/f-MWCNT/CS scaffolds had higher in vitro bioactivity, large surface area (11.746 m²/g) and a good pore volume (0.026 cc/g), interconnected porous microstructure (with 20-350 μm pore size) and incorporates the advantageous properties of both Col, f-MWCNT, CS and HA. Finally, the methyl thiazolyl tetrazolium (MTT) assay was performed to evaluate scaffolds cytotoxicity which showed that Col/f-MWCNT/CS scaffolds have the best biocompatibility.

Fabrication of a three dimensional spongy scaffold using human Wharton's jelly derived extra cellular matrix for wound healing

The Wharton's jelly (WJ) contains significant amounts of extracellular matrix (ECM) components and rich source of endogenous growth factors. In this study, we designed a new biomimetic spongy scaffold from decellularized WJ-derived ECM and used it as a skin substitute. Histological analysis and biochemical assays showed that bio-active molecules preserved in the fabricated scaffolds and that the scaffolds have highly interconnected porous structure. Cytotoxicity and mechanical evaluation of the scaffold indicated that it is non-toxic and has appropriate mechanical properties. MTT assay, SEM and histological analysis of human fibroblast, seeded on the scaffolds, confirmed cellular viability, attachment, penetration and proliferation. The effectiveness of WJ-derived scaffolds in the regeneration of full-thickness wound was assessed through an in vivo experiment. Our results demonstrated that the scaffolds were well integrated into the mouse tissue and absorbed the exudates after one week. Unlike the controls, in WJ group there were not only complete wound closing and disappearance of the scab, but also complete reepithelialization, newly generated epidermal layers and appendages after 12days of implantation. Taken together, our results indicate that WJ-derived scaffolds are able to improve attachment, penetration and growth of the fibroblast cells and speed up the healing processes, which would offer a proper skin graft for wound healing.

Capturing relevant extracellular matrices for investigating cell migration

Much progress in understanding cell migration has been determined by using classic two-dimensional (2D) tissue culture platforms. However, increasingly, it is appreciated that certain properties of cell migration in vivo are not represented by strictly 2D assays. There is much interest in creating relevant three-dimensional (3D) culture environments and engineered platforms to better represent features of the extracellular matrix and stromal microenvironment that are not captured in 2D platforms. Important to this goal is a solid understanding of the features of the extracellular matrix—composition, stiffness, topography, and alignment—in different tissues and disease states and the development of means to capture these features