Bone tissue engineering: recent advances and challenges

Effects of Propolis Impregnation on Polylactic Acid (PLA) Scaffolds Loaded with Wollastonite Particles against Staphylococcus aureus, Staphylococcus epidermidis, and Their Coculture for Potential Medical Devices

Several diseases and injuries cause irreversible damage to bone tissues, which may require partial or total regeneration or replacement. Tissue engineering suggests developing substitutes that may contribute to the repair or regeneration process by using three-dimensional lattices (scaffolds) to create functional bone tissues. Herein, scaffolds comprising polylactic acid and wollastonite particles enriched with propolis extracts from the Arauca region of Colombia were developed as gyroid triply periodic minimal surfaces using fused deposition modeling. The propolis extracts exhibited antibacterial activity against Staphylococcus aureus (ATCC 25175) and Staphylococcus epidermidis (ATCC 12228), which cause osteomyelitis. The scaffolds were characterized using scanning electron microscopy, Fourier-transform infrared spectroscopy, differential scanning calorimetry, contact angle, swelling, and degradation. Their mechanical properties were assessed using static and dynamic tests. Cell viability/proliferation assay was conducted using hDP-MSC cultures, while their bactericidal properties against monospecies cultures (S. aureus and S. epidermidis) and cocultures were evaluated. The wollastonite particles did not affect the physical, mechanical, or thermal properties of the scaffolds. The contact angle results showed that there were no substantial differences in the hydrophobicity between scaffolds with and without particles. Scaffolds containing wollastonite particles suffered less degradation than those produced using PLA alone. A representative result of the cyclic tests at F_max = 450 N showed that the maximum strain reached after 8000 cycles is well below the yield strain (i.e., <7.5%), thereby indicating that even under these stringent conditions, these scaffolds will be able to work properly. The scaffolds impregnated with propolis showed a lower % of cell viability using hDP-MSCs on the 3rd day, but these values increased on the 7th day. These scaffolds exhibited antibacterial activity against the monospecies cultures of S. aureus and S. epidermidis and their cocultures. The samples without propolis loads did not show inhibition halos, whereas those loaded with EEP exhibited halos of 17.42 ± 0.2 mm against S. aureus and 12.9 ± 0.5 mm against S. epidermidis. These results made the scaffolds possible bone substitutes that exert control over species with a proliferative capacity for the biofilm-formation processes required for typical severe infectious processes.

Regenerative engineering of long bones using the small molecule forskolin

Bone grafting procedures have become increasingly common in the United States, with approximately 500,000 cases occurring each year at a societal cost exceeding $2.4 billion. Recombinant human bone morphogenetic proteins (rhBMPs) are therapeutic agents that have been widely used by orthopedic surgeons to stimulate bone tissue formation alone and when paired with biomaterials. However, significant limitations such as immunogenicity, high production cost, and ectopic bone growth from these therapies remain. Therefore, efforts have been made to discover and repurpose osteoinductive small-molecule therapeutics to promote bone regeneration. Previously, we have demonstrated that a single-dose treatment with the small-molecule forskolin for just 24 h induces osteogenic differentiation of rabbit bone marrow-derived stem cells in vitro, while mitigating adverse side effects attributed with prolonged small-molecule treatment schemes. In this study, we engineered a composite fibrin-PLGA [poly(lactide-co-glycolide)]-sintered microsphere scaffold for the localized, short-term delivery of the osteoinductive small molecule, forskolin. In vitro characterization studies showed that forskolin released out of the fibrin gel within the first 24 h and retained its bioactivity toward osteogenic differentiation of bone marrow-derived stem cells. The forskolin-loaded fibrin-PLGA scaffold was also able to guide bone formation in a 3-mo rabbit radial critical-sized defect model comparable to recombinant human bone morphogenetic protein-2 (rhBMP-2) treatment, as demonstrated through histological and mechanical evaluation, with minimal systemic off-target side effects. Together, these results demonstrate the successful application of an innovative small-molecule treatment approach within long bone critical-sized defects.

Biometric and gonadosomatic indices and chemical constituents of edible tissues and exoskeletons of Callinectes amnicola and their potential for reuse in the circular economy paradigm

The study investigates some biological indices and chemical compositions of Callinectes amnicola and their potential for reuse in the context of the circular economy paradigm. The total of 322 mixed-sex C. amnicola collected over a period of six months was examined. The morphometric and meristic characteristics were estimated for biometric assessment. The gonads were obtained from the female crabs for gonadosomatic indices. The shell was obtained using the hand removal technique by detaching it from the crab body. The edible and shell portions were processed separately and subjected to chemical analysis. Our findings showed that females had the highest sex ratio across the six months. The slope values (b) for both sexes exhibited negative allometric growth across all months since the slope values obtained were less than 3 (b < 3). The values obtained for Fulton's condition factor (K) of crabs in all examined months were greater than 1. The edible portion had the highest moisture level at 62.57 ± 2.16% and varied significantly (P < 0.05). The high amount of total ash obtained in the shell sample showed that ash is the main mineral present in crab shells and showed a significant difference (P < 0.05). The shell sample had the highest concentrations of Na and CaCO₃. Based on the findings of this study, it was observed that the shell waste contains some essential and transitional minerals (Ca, CaCO₃, Na, and Mg) and can be utilized as catalysts in several local and industrial applications, such as pigments, adsorbents, therapeutics, livestock feeds, biomedical industries, liming, fertilization, and so on. Proper valorization of this shell waste should be encouraged rather than discarding it.

Effects of ATP on the Physicochemical Properties and Cytocompatibility of Calcium Sulfate/Calcium Citrate Composite Cement

Adenosine triphosphate (ATP), acting as a source of energy, has effects on cellular activities, such as adhesion, proliferation, and differentiation. In this study, ATP-loaded calcium sulfate hemihydrate/calcium citrate tetrahydrate cement (ATP/CSH/CCT) was successfully prepared for the first time. The effect of different contents of ATP on the structure and physicochemical properties of ATP/CSH/CCT was also studied in detail. The results indicated that incorporating ATP into the cement did not significantly alter their structures. However, the addition ratio of ATP directly impacted the mechanical properties and in vitro degradation properties of the composite bone cement. The compressive strength of ATP/CSH/CCT gradually decreased with an increasing ATP content. The degradation rate of ATP/CSH/CCT did not significantly change at low concentrations of ATP, but it increased with a higher ATP content. The composite cement induced the deposition of a Ca-P layer in a phosphate buffer solution (PBS, pH = 7.4). Additionally, the release of ATP from the composite cement was controlled. The ATP was controlled releasing at the 0.5% and 1% ATP in cement by the diffusion of ATP and the degradation of the cement, whereas it was controlled by the diffusion process merely at the 0.1% ATP in cement. Furthermore, ATP/CSH/CCT demonstrated good cytoactivity with the addition of ATP and is expected to be used for the repair and regeneration of bone tissue.

Recent Advancements in Electrospun Chitin and Chitosan Nanofibers for Bone Tissue Engineering Applications

Treatment of large segmental bone loss caused by fractures, osteomyelitis, and non-union results in expenses of around USD 300,000 per case. Moreover, the worst-case scenario results in amputation in 10% to 14.5% of cases. Biomaterials, cells, and regulatory elements are employed in bone tissue engineering (BTE) to create biosynthetic bone grafts with effective functionalization that can aid in the restoration of such fractured bones, preventing amputation and alleviating expenses. Chitin (CT) and chitosan (CS) are two of the most prevalent natural biopolymers utilized in the fields of biomaterials and BTE. To offer the structural and biochemical cues for augmenting bone formation, CT and CS can be employed alone or in combination with other biomaterials in the form of nanofibers (NFs). When compared with several fabrication methods available to produce scaffolds, electrospinning is regarded as superior since it enables the development of nanostructured scaffolds utilizing biopolymers. Electrospun nanofibers (ENFs) offer unique characteristics, including morphological resemblance to the extracellular matrix, high surface-area-to-volume ratio, permeability, porosity, and stability. This review elaborates on the recent strategies employed utilizing CT and CS ENFs and their biocomposites in BTE. We also summarize their implementation in supporting and delivering an osteogenic response to treat critical bone defects and their perspectives on rejuvenation. The CT- and CS-based ENF composite biomaterials show promise as potential constructions for bone tissue creation.

Poly(3-hydroxybutyrate) (PHB) and Polycaprolactone (PCL) Based Blends for Tissue Engineering and Bone Medical Applications Processed by FDM 3D Printing

In the presented work, poly(3-hydroxybutyrate)-PHB-based composite blends for bone medical applications and tissue engineering are prepared and characterized. PHB used for the work was in two cases commercial and, in one case, was extracted by the chloroform-free route. PHB was then blended with poly(lactic acid) (PLA) or polycaprolactone (PCL) and plasticized by oligomeric adipate ester (Syncroflex, SN). Tricalcium phosphate (TCP) particles were used as a bioactive filler. Prepared polymer blends were processed into the form of 3D printing filaments. The samples for all the tests performed were prepared by FDM 3D printing or compression molding. Differential scanning calorimetry was conducted to evaluate the thermal properties, followed by optimization of printing temperature by temperature tower test and determination of warping coefficient. Tensile test, three-point flexural test, and compression test were performed to study the mechanical properties of materials. Optical contact angle measurement was conducted to determine the surface properties of these blends and their influence on cell adhesion. Cytotoxicity measurement of prepared blends was conducted to find out whether the prepared materials were non-cytotoxic. The best temperatures for 3D printing were 195/190, 195/175, and 195/165 °C for PHB-soap/PLA-SN, PHB/PCL-SN, and PHB/PCL-SN-TCP, respectively. Their mechanical properties (strengths ~40 MPa, moduli ~2.5 GPa) were comparable with human trabecular bone. The calculated surface energies of all blends were ~40 mN/m. Unfortunately, only two out of three materials were proven to be non-cytotoxic (both PHB/PCL blends).

Polyvinylpyrrolidone Nanofibers Incorporating Mesoporous Bioactive Glass for Bone Tissue Engineering

Composite biomaterials that combine osteoconductive and osteoinductive properties are a promising approach for bone tissue engineering (BTE) since they stimulate osteogenesis while mimicking extracellular matrix (ECM) morphology. In this context, the aim of the present research was to produce polyvinylpyrrolidone (PVP) nanofibers containing mesoporous bioactive glass (MBG) 80S15 nanoparticles. These composite materials were produced by the electrospinning technique. Design of experiments (DOE) was used to estimate the optimal electrospinning parameters to reduce average fiber diameter. The polymeric matrices were thermally crosslinked under different conditions, and the fibers' morphology was studied using scanning electron microscopy (SEM). Evaluation of the mechanical properties of nanofibrous mats revealed a dependence on thermal crosslinking parameters and on the presence of MBG 80S15 particles inside the polymeric fibers. Degradation tests indicated that the presence of MBG led to a faster degradation of nanofibrous mats and to a higher swelling capacity. The assessment of in vitro bioactivity in simulated body fluid (SBF) was performed using MBG pellets and PVP/MBG (1:1) composites to assess if the bioactive properties of MBG 80S15 were kept when it was incorporated into PVP nanofibers. FTIR and XRD analysis along with SEM-EDS results indicated that a hydroxy-carbonate apatite (HCA) layer formed on the surface of MBG pellets and nanofibrous webs after soaking in SBF over different time periods. In general, the materials revealed no cytotoxic effects on the Saos-2 cell line. The overall results for the materials produced show the potential of the composites to be used in BTE.

The Clinical Use of Osteobiologic and Metallic Biomaterials in Orthopedic Surgery: The Present and the Future

As the area and range of surgical treatments in the orthopedic field have expanded, the development of biomaterials used for these treatments has also advanced. Biomaterials have osteobiologic properties, including osteogenicity, osteoconduction, and osteoinduction. Natural polymers, synthetic polymers, ceramics, and allograft-based substitutes can all be classified as biomaterials. Metallic implants are first-generation biomaterials that continue to be used and are constantly evolving. Metallic implants can be made from pure metals, such as cobalt, nickel, iron, or titanium, or from alloys, such as stainless steel, cobalt-based alloys, or titanium-based alloys. This review describes the fundamental characteristics of metals and biomaterials used in the orthopedic field and new developments in nanotechnology and 3D-printing technology. This overview discusses the biomaterials that clinicians commonly use. A complementary relationship between doctors and biomaterial scientists is likely to be necessary in the future.

New Challenges and Prospective Applications of Three-Dimensional Bioactive Polymeric Hydrogels in Oral and Craniofacial Tissue Engineering: A Narrative Review

Regenerative medicine, and dentistry offers enormous potential for enhancing treatment results and has been fueled by bioengineering breakthroughs over the previous few decades. Bioengineered tissues and constructing functional structures capable of healing, maintaining, and regenerating damaged tissues and organs have had a broad influence on medicine and dentistry. Approaches for combining bioinspired materials, cells, and therapeutic chemicals are critical in stimulating tissue regeneration or as medicinal systems. Because of its capacity to maintain an unique 3D form, offer physical stability for the cells in produced tissues, and replicate the native tissues, hydrogels have been utilized as one of the most frequent tissue engineering scaffolds during the last twenty years. Hydrogels' high water content can provide an excellent conditions for cell viability as well as an architecture that mimics real tissues, bone, and cartilage. Hydrogels have been used to enable cell immobilization and growth factor application. This paper summarizes the features, structure, synthesis and production methods, uses, new challenges, and future prospects of bioactive polymeric hydrogels in dental and osseous tissue engineering of clinical, exploring, systematical and scientific applications.

Influence of Crosslinking Methods on Biomimetically Mineralized Collagen Matrices for Bone-like Biomaterials

To assist in bone defect repair, ideal bone regeneration scaffolds should exhibit good osteoconductivity and osteoinductivity, but for load-bearing applications, they should also have mechanical properties that emulate those of native bone. The use of biomimetic processing methods for the mineralization of collagen fibrils has resulted in interpenetrating composites that mimic the nanostructure of native bone; however, closely matching the mechanical properties of bone on a larger scale is something that is still yet to be achieved. In this study, four different collagen crosslinking methods (EDC-NHS, quercetin, methacrylated collagen, and riboflavin) are compared and combined with biomimetic mineralization via the polymer-induced liquid-precursor (PILP) process, to obtain bone-like collagen-hydroxyapatite composites. Densified fibrillar collagen scaffolds were fabricated, crosslinked, and biomimetically mineralized using the PILP process, and the effect of each crosslinking method on the degree of mineralization, tensile strength, and modulus of the mineralized scaffolds were analyzed and compared. Improved modulus and tensile strength values were obtained using EDC-NHS and riboflavin crosslinking methods, while quercetin and methacrylated collagen resulted in little to no increase in mechanical properties. Decreased mineral contents appear to be necessary for retaining tensile strength, suggesting that mineral content should be kept below a percolation threshold to optimize properties of these interpenetrating nanocomposites. This work supports the premise that a combination of collagen crosslinking and biomimetic mineralization methods may provide solutions for fabricating robust bone-like composites on a larger scale.

Structural Mechanical Properties of 3D Printing Biomimetic Bone Replacement Materials

One of the primary challenges in developing bone substitutes is to create scaffolds with mechanical properties that closely mimic those of regenerated tissue. Scaffolds that mimic the structure of natural cancellous bone are believed to have better environmental adaptability. In this study, we used the porosity and thickness of pig cancellous bone as biomimetic design parameters, and porosity and structural shape as differential indicators, to design a biomimetic bone beam scaffold. The mechanical properties of the designed bone beam model were tested using the finite element method (FEM). PCL/β-TCP porous scaffolds were prepared using the FDM method, and their mechanical properties were tested. The FEM simulation results were compared and validated, and the effects of porosity and pore shape on the mechanical properties were analyzed. The results of this study indicate that the PCL/β-TCP scaffold, prepared using FDM 3D printing technology for cancellous bone tissue engineering, has excellent integrity and stability. Predicting the structural stability using FEM is effective. The triangle pore structure has the most stability in both simulations and tests, followed by the rectangle and honeycomb shapes, and the diamond structure has the worst stability. Therefore, adjusting the porosity and pore shape can change the mechanical properties of the composite scaffold to meet the mechanical requirements of customized tissue engineering.

Graphite nanopowder incorporated xanthan gum scaffold for effective bone tissue regeneration purposes with improved biomineralization

In the current work, biomaterial composed of Xanthan gum and Diethylene glycol dimethacrylate with impregnation of graphite nanopowder filler in their matrices was fabricated successfully for their potential usage in the engineering of bone defects. Various physicochemical properties associated with the biomaterial were characterized using FTIR, XRD, TGA, SEM etc. The biomaterial rheological studies imparted the better notable properties associated with the inclusion of graphite nanopowder. The biomaterial synthesized exhibited a controlled drug release. Adhesion and proliferation of different secondary cell lines do not generate ROS on the current biomaterial and thus show its biocompatibility and non-toxic nature. The synthesized biomaterial's osteogenic potential on SaOS-2 cells was supported by increased ALP activity, enhanced differentiation and biomineralization under osteoinductive circumstances. The current biomaterial demonstrates that in addition to the drug-delivery applications, it can also be a cost-effective substrate for cellular activities and has all the necessary properties to be considered as a promising alternative material suitable for repairing and restoring bone tissues. We propose that this biomaterial may have commercial importance in the biomedical field.

Preclinical Evaluation of Bioactive Scaffolds for the Treatment of Mandibular Critical-Sized Bone Defects: A Systematic Review

This systematic review evaluated current in vivo research on regenerating critical-sized mandibular defects and discussed methodologies for mandibular bone tissue engineering. Out of the 3650 articles initially retrieved, 88 studies were included, and all studies that used a scaffold reported increased bone formation compared to negative controls. Combining scaffolds with growth factors and mesenchymal stem cells improved bone formation and healing. Bone morphogenic proteins were widely used and promoted significant bone formation compared to controls. However, discrepancies between studies exist due to the various methodologies and outcome measures used. The use of scaffolds with bioactive molecules and/or progenitor cells enhances success in mandibular bone engineering. Scaffold-based mandibular bone tissue engineering could be introduced into clinical practice due to its proven safety, convenience, and cost-effectiveness.

Engineering of an Osteoinductive and Growth Factor-Free Injectable Bone-Like Microgel for Bone Regeneration

Bone autografts remain the gold standard for bone grafting surgeries despite having increased donor site morbidity and limited availability. Bone morphogenetic protein-loaded grafts represent another successful commercial alternative. However, the therapeutic use of recombinant growth factors has been associated with significant adverse clinical outcomes. This highlights the need to develop biomaterials that closely approximate the structure and composition of bone autografts, which are inherently osteoinductive and biologically active with embedded living cells, without the need for added supplements. Here, injectable growth factor-free bone-like tissue constructs are developed, that closely approximate the cellular, structural, and chemical composition of bone autografts. It is demonstrated that these micro-constructs are inherently osteogenic, and demonstrate the ability to stimulate mineralized tissue formation and regenerate bone in critical-sized defects in-vivo. Furthermore, the mechanisms that allow human mesenchymal stem cells (hMSCs) to be highly osteogenic in these constructs, despite the lack of osteoinductive supplements, are assessed, whereby Yes activated protein (YAP) nuclear localization and adenosine signaling appear to regulate osteogenic cell differentiation. The findings represent a step toward a new class of minimally invasive, injectable, and inherently osteoinductive scaffolds, which are regenerative by virtue of their ability to mimic the tissue cellular and extracellular microenvironment, thus showing promise for clinical applications in regenerative engineering.

Stem cell-derived exosomes in bone healing: focusing on their role in angiogenesis

Fractures in bone, a tissue critical in protecting other organs, affect patients' quality of life and have a heavy economic burden on societies. Based on regenerative medicine and bone tissue engineering approaches, stem cells have become a promising and attractive strategy for repairing bone fractures via differentiation into bone-forming cells and production of favorable mediators. Recent evidence suggests that stem cell-derived exosomes could mediate the therapeutic effects of their counterpart cells and provide a cell-free therapeutic strategy in bone repair. Since bone is a highly vascularized tissue, coupling angiogenesis and osteogenesis is critical in bone fracture healing; thus, developing therapeutic strategies to promote angiogenesis will facilitate bone regeneration and healing. To this end, stem cell-derived exosomes with angiogenic potency have been developed to improve fracture healing. This review summarizes the effects of stem cell-derived exosomes on the repair of bone tissue, focusing on the angiogenesis process.

Lignin-enriched tricalcium phosphate/sodium alginate 3D scaffolds for application in bone tissue regeneration

The bone is a connective, vascularized, and mineralized tissue that confers protection to organs, and participates in the support and locomotion of the human body, maintenance of homeostasis, as well as in hematopoiesis. However, throughout the lifetime, bone defects may arise due to traumas (mechanical fractures), diseases, and/or aging, which when too extensive compromise the ability of the bone to self-regenerate. To surpass such clinical situation, different therapeutic approaches have been pursued. Rapid prototyping techniques using composite materials (consisting of ceramics and polymers) have been used to produce customized 3D structures with osteoinductive and osteoconductive properties. In order to reinforce the mechanical and osteogenic properties of these 3D structures, herein, a new 3D scaffold was produced through the layer-by-layer deposition of a tricalcium phosphate (TCP), sodium alginate (SA), and lignin (LG) mixture using the Fab@Home 3D-Plotter. Three different TCP/LG/SA formulations, LG/SA ratio 1:3, 1:2, or 1:1, were produced and subsequently evaluated to determine their suitability for bone regeneration. The physicochemical assays demonstrated that the LG inclusion improved the mechanical resistance of the scaffolds, particularly in the 1:2 ratio, since a 15 % increase in the mechanical strength was observed. Moreover, all TCP/LG/SA formulations showed an enhanced wettability and maintained their capacity to promote the osteoblasts' adhesion and proliferation as well as their bioactivity (formation of hydroxyapatite crystals). Such results support the LG inclusion and application in the development of 3D scaffolds aimed for bone regeneration.

Mineralization of Bone Extracellular Matrix-like Scaffolds Fabricated as Silk Sericin-Functionalized Dense Collagen–Fibrin Hybrid Hydrogels

The design of hydrogels that combine both the biochemical cues needed to direct seeded cellular functions and mineralization to provide the structural and mechanical properties approaching those of mineralized native bone extracellular matrix (ECM) represents a significant challenge in bone tissue engineering. While fibrous hydrogels constituting of collagen or fibrin (and their hybrids) can be considered as scaffolds that mimic to some degree native bone ECM, their insufficient mechanical properties limit their application. In the present study, an automated gel aspiration–ejection (automated GAE) method was used to generate collagen–fibrin hybrid gel scaffolds with micro-architectures and mechanical properties approaching those of native bone ECM. Moreover, the functionalization of these hybrid scaffolds with negatively charged silk sericin accelerated their mineralization under acellular conditions in simulated body fluid and modulated the proliferation and osteoblastic differentiation of seeded MC3T3-E1 pre-osteoblastic cells. In the latter case, alkaline phosphatase activity measurements indicated that the hybrid gel scaffolds with seeded cells showed accelerated osteoblastic differentiation, which in turn led to increased matrix mineralization. In summary, the design of dense collagen–fibrin hybrid gels through an automated GAE process can provide a route to tailoring specific biochemical and mechanical properties to different types of bone ECM-like scaffolds, and can provide a model to better understand cell–matrix interactions in vitro for bioengineering purposes.

Water-soluble PEG segmented mannose-based macromolecules: Synthesis and their biocompatibility

The macromolecular architectures, namely mannose-based methacrylate acetyl-mannopyranoside and PEG block copolymers (AB type copolymer [PEG-b-PMAM], poly(ethyleneglycol)-b-poly(methacryl-2,3,4,6-tetra-O-acetyl-D-mannopyranoside and ABA type copolymer [PMAM-b-PEG-b-PMAM], poly(methacryl-2,3,4,6-tetra-O-acetyl-D-mannopyranoside-b-poly(ethyleneglycol)-b-poly(methacryl-2,3,4,6-tetra-O-acetyl-D-mannopyranoside) were synthesized by atom transfer radical polymerization (ATRP) method that were deacetylated to generate the corresponding water-soluble and biocompatible glycopolymer macromolecules. The molecular weight of acetyl and deacetylate macromolecules was in the range of 7083-9499 and 4659-6026, as determined by GPC and proton NMR spectra. The 5 % decomposition temperatures for acetylated methacrylate macromolecules (218-299 °C) were higher than the corresponding water-soluble macromolecules (204-248 °C). The conjugation of poly(methacryl-2,3,4,6-tetra-O-acetyl-D-mannopyranoside (PMAM) segment with the PEG block decreased the glass transition (Tg) value, and the water-soluble macromolecules displayed Tg in the range of 92-95 °C. The biocompatibility of the synthesized water-soluble mannose-based macromolecules was determined using Human Bone Derived Cells (HBDC) culture with the TCP (Tissue culture plastic) template as control. Using three different concentrations of the synthesized glycopolymers, HBDC's were cultured for 1, 3, and 7 days. The effect of mannomethacrylate macromolecules on mitochondrial activity of HBDC's was estimated using colorimetry that showed the conversion of MTS [3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium-bromide] to formazan (MTS assay). ABA type diblock copolymer architecture exhibited increased absorbance values of 3 and 7 day cultures at 1-100 M concentrations, with the highest values observed at a concentration of 1 M for day 3 cultures. The design of these novel mannose-based macromolecules is important for improving cell proliferation, cell adhesion, and osteointegration efficiency.

PCL and DMSO2 Composites for Bio-Scaffold Materials

Polycaprolactone (PCL) has been one of the most popular biomaterials in tissue engineering due to its relatively low melting temperature, excellent thermal stability, and cost-effectiveness. However, its low cell attraction, low elastic modulus, and long-term degradation time have limited its application in a wide range of scaffold studies. Dimethyl sulfone (DMSO₂) is a stable and non-hazardous organosulfur compound with low viscosity and high surface tension. PCL and DMSO₂ composites may overcome the limitations of PCL as a biomaterial and tailor the properties of biocomposites. In this study, PCL and DMSO₂ composites were investigated as a new bio-scaffold material to increase hydrophilicity and mechanical properties and tailor degradation properties in vitro. PCL and DMSO₂ were physically mixed with 10, 20, and 30 wt% of DMSO₂ to evaluate thermal, hydrophilicity, mechanical, and degradation properties of the composites. The water contact angle of the composites for hydrophilicity decreased by 15.5% compared to pure PCL. The experimental results showed that the mechanical and degradation properties of PCL and DMSO₂ were better than those of pure PCL, and the properties can be tuned by regulating DMSO2 concentration in the PCL matrix. The elastic modulus of the composite with 30 wt% of DMSO2 showed 532 MPa, and its degradation time was 18 times faster than that of PCL.

Scaffold Using Chitosan, Agarose, Cellulose, Dextran and Protein for Tissue Engineering-A Review

Biological macromolecules like polysaccharides/proteins/glycoproteins have been widely used in the field of tissue engineering due to their ability to mimic the extracellular matrix of tissue. In addition to this, these macromolecules are found to have higher biocompatibility and no/lesser toxicity when compared to synthetic polymers. In recent years, scaffolds made up of proteins, polysaccharides, or glycoproteins have been highly used due to their tensile strength, biodegradability, and flexibility. This review is about the fabrication methods and applications of scaffolds made using various biological macromolecules, including polysaccharides like chitosan, agarose, cellulose, and dextran and proteins like soy proteins, zein proteins, etc. Biopolymer-based nanocomposite production and its application and limitations are also discussed in this review. This review also emphasizes the importance of using natural polymers rather than synthetic ones for developing scaffolds, as natural polymers have unique properties, like high biocompatibility, biodegradability, accessibility, stability, absence of toxicity, and low cost.

Fabrication of Porous Tantalum with Low Elastic Modulus and Tunable Pore Size for Bone Repair

Porous tantalum (Ta) is a potential bone substitute due to its excellent biocompatibility and desirable mechanical properties. In this work, a series of porous Ta materials with interconnected micropores and varying pore sizes from 23 to 210 μm were fabricated using spark plasma sintering. The porous structure was formed by thermal decomposition of ammonium bicarbonate powder premixed in the Ta powder. The pore size and porosity were controlled by the categorized particle size of ammonium bicarbonate. The porous Ta has elastic moduli in the range of 2.1-3.2 GPa and compressive yield strength in the range of 23-34 MPa, which are close to those of human bone. In vitro, as-fabricated porous Ta demonstrates excellent biocompatibility by supporting adhesion and proliferation of preosteoblasts. In vivo studies also validate its bone repair capability after implantation in a rat femur defect model. The study demonstrates a facile strategy to fabricate porous Ta with controllable pore size for bone repair.

Physiologic Response Evaluation of Human Foetal Osteoblast Cells within Engineered 3D-Printed Polylactic Acid Scaffolds

Large bone defect treatments have always been one of the important challenges in clinical practice and created a huge demand for more efficacious regenerative approaches. The bone tissue engineering (BTE) approach offered a new alternative to conventional bone grafts, addressing all clinical needs. Over the past years, BTE research is focused on the study and realisation of new biomaterials, including 3D-printed supports to improve mechanical, structural and biological properties. Among these, polylactic acid (PLA) scaffolds have been considered the most promising biomaterials due to their good biocompatibility, non-toxic biodegradability and bioresorbability. In this work, we evaluated the physiological response of human foetal osteoblast cells (hFOB), in terms of cell proliferation and osteogenic differentiation, within oxygen plasma treated 3D-printed PLA scaffolds, obtained by fused deposition modelling (FDM). A mechanical simulation to predict their behaviour to traction, flexural or torque solicitations was performed. We found that: 1. hFOB cells adhere and grow on scaffold surfaces; 2. hFOB grown on oxygen plasma treated PLA scaffolds (PLA_PT) show an improvement of cell adhesion and proliferation, compared to not-plasma treated scaffolds (PLA_NT); 3. Over time, hFOB penetrate along strands, differentiate, and form a fibrous matrix, tissue-like; 4. 3D-printed PLA scaffolds have good mechanical behaviour in each analysed configuration. These findings suggest that 3D-printed PLA scaffolds could represent promising biomaterials for medical implantable devices in the orthopaedic field.

Mangiferin-Enriched Mn-Hydroxyapatite Coupled with β-TCP Scaffolds Simultaneously Exhibit Osteogenicity and Anti-Bacterial Efficacy

Biphasic calcium phosphate (BCP) containing β-tricalcium phosphate and manganese (Mn)-substituted hydroxyapatite (HAP) was synthesized. Biomedical scaffolds were prepared using this synthesized powder on a sacrificial polyurethane sponge template after the incorporation of mangiferin (MAN). Mn was substituted at a concentration of 5% and 10% in HAP to examine the efficacy of Mn at various concentrations. The phase analysis of the as-formed BCP scaffold was carried out by X-ray diffraction analysis, while the qualitative observation of morphology and the osteoblast cell differentiation were carried out by scanning electron microscopy and confocal laser scanning microscopy techniques. Gene expressions of osteocalcin, collagen 1, and RUNX2 were carried out using qRT-PCR analyses. Significantly higher (p < 0.05) levels of ALP activity were observed with extended osteoblast induction on the mangiferin-incorporated BCP scaffolds. After characterization of the specimens, it was found that the scaffolds with 10% Mn-incorporated BCP with mangiferin showed better osteogenicity and simultaneously the same scaffolds exhibited higher anti-bacterial properties as observed from the bacterial viability test. This study was carried out to evaluate the efficacy of Mn and MAN in BCP for osteogenicity and antibacterial action.

Bacterial Inhibition and Osteogenic Potentials of Sr/Zn Co-Doped Nano-Hydroxyapatite-PLGA Composite Scaffold for Bone Tissue Engineering Applications

Bacterial infection associated with bone grafts is one of the major challenges that can lead to implant failure. Treatment of these infections is a costly endeavor; therefore, an ideal bone scaffold should merge both biocompatibility and antibacterial activity. Antibiotic-impregnated scaffolds may prevent bacterial colonization but exacerbate the global antibiotic resistance problem. Recent approaches combined scaffolds with metal ions that have antimicrobial properties. In our study, a unique strontium/zinc (Sr/Zn) co-doped nanohydroxyapatite (nHAp) and Poly (lactic-co-glycolic acid) -(PLGA) composite scaffold was fabricated using a chemical precipitation method with different ratios of Sr/Zn ions (1%, 2.5%, and 4%). The scaffolds’ antibacterial activity against Staphylococcus aureus were evaluated by counting bacterial colony-forming unit (CFU) numbers after direct contact with the scaffolds. The results showed a dose-dependent reduction in CFU numbers as the Zn concentration increased, with 4% Zn showing the best antibacterial properties of all the Zn-containing scaffolds. PLGA incorporation in Sr/Zn-nHAp did not affect the Zn antibacterial activity and the 4% Sr/Zn-nHAp-PLGA scaffold showed a 99.7% bacterial growth inhibition. MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cell viability assay showed that Sr/Zn co-doping supported osteoblast cell proliferation with no apparent cytotoxicity and the highest doping percentage in the 4% Sr/Zn-nHAp-PLGA was found to be ideal for cell growth. In conclusion, these findings demonstrate the potential for a 4% Sr/Zn-nHAp-PLGA scaffold with enhanced antibacterial activity and cytocompatibility as a suitable candidate for bone regeneration.

Incorporation of strontium-containing bioactive particles into PEOT/PBT electrospun scaffolds for bone tissue regeneration

The combination of biomaterials and bioactive particles has shown to be a successful strategy to fabricate electrospun scaffolds for bone tissue engineering. Among the range of bioactive particles, hydroxyapatite and mesoporous bioactive glasses (MBGs) have been widely used for their osteoconductive and osteoinductive properties. Yet, the comparison between the chemical and mechanical characteristics as well as the biological performances of these particle-containing scaffolds have been characterized to a limited extent. In this work, we fabricated PEOT/PBT-based composite scaffolds incorporating either nanohydroxyapatite (nHA), strontium-containing nanohydroxyapatite (nHA_Sr) or MBGs doped with strontium ions up to 15 wt./vol% and 12,5 wt./vol% for nHA and MBG, respectively. The composite scaffolds presented a homogeneous particle distribution. Morphological, chemical and mechanical analysis revealed that the introduction of particles into the electrospun meshes caused a decrease in the fiber diameter and mechanical properties, yet maintaining the hydrophilic nature of the scaffolds. The Sr²⁺ release profile differed according to the considered system, observing a 35-day slowly decreasing release from strontium-containing nHA scaffolds, whereas MBG-based scaffolds showed a strong burst release in the first week. In vitro, culture of human bone marrow-derived mesenchymal stromal cells (hMSCs) on composite scaffolds demonstrated excellent cell adhesion and proliferation. In maintenance and osteogenic media, all composite scaffolds showed high mineralization as well as expression of Col I and OCN compared to PEOT/PBT scaffolds, suggesting their ability to boost bone formation even without osteogenic factors. The presence of strontium led to an increase in collagen secretion and matrix mineralization in osteogenic medium, while gene expression analysis showed that hMSCs cultured on nHA-based scaffolds had a higher expression of OCN, ALP and RUNX2 compared to cells cultured on nHA_Sr scaffolds in osteogenic medium. Yet, cells cultured on MBGs-based scaffolds showed a higher gene expression of COL1, ALP, RUNX2 and BMP2 in osteogenic medium compared to nHA-based scaffolds, which is hypothesized to lead to high osteoinductivity in long term cultures.

SAXS imaging reveals optimized osseointegration properties of bioengineered oriented 3D-PLGA/aCaP scaffolds in a critical size bone defect model

Healing large bone defects remains challenging in orthopedic surgery and is often associated with poor outcomes and complications. A major issue with bioengineered constructs is achieving a continuous interface between host bone and graft to enhance biological processes and mechanical stability. In this study, we have developed a new bioengineering strategy to produce oriented biocompatible 3D PLGA/aCaP nanocomposites with enhanced osseointegration. Decellularized scaffolds -containing only extracellular matrix- or scaffolds seeded with adipose-derived mesenchymal stromal cells were tested in a mouse model for critical size bone defects. In parallel to micro-CT analysis, SAXS tensor tomography and 2D scanning SAXS were employed to determine the 3D arrangement and nanostructure within the critical-sized bone. Both newly developed scaffold types, seeded with cells or decellularized, showed high osseointegration, higher bone quality, increased alignment of collagen fibers and optimal alignment and size of hydroxyapatite minerals.

Sustained delivery of a heterodimer bone morphogenetic protein-2/7 via a collagen hydroxyapatite scaffold accelerates and improves critical femoral defect healing

Despite the glimmer of hope provided by the discovery and commercialization of bone morphogenetic protein-2 (BMP-2) as a bone graft substitute, side effects related to the use of supraphysiological doses have hindered its clinical usage. In this study, we compared the osteoinductive potential of BMP-2 homodimer with a heterodimer of BMP-2/7, both delivered via a collagen-hydroxyapatite (CHA) scaffold delivery system, with the aim to reduce the overall therapeutic BMP doses and the associated side-effects. We first show that the incorporation of hydroxyapatite in collagen-based BMP delivery systems is pivotal for achieving efficient BMP sequestration and controlled release. Using an ectopic implantation model, we then showed that the CHA+BMP-2/7 was more osteoinductive than CHA+BMP-2. Further evaluation of the molecular mechanisms responsible for this increased osteoinductivity at an early stage in the regeneration process indicated that the CHA+BMP-2/7 enhanced progenitor cell homing at the implantation site, upregulated the key transcriptomic determinants of bone formation, and increased the production of bone extracellular matrix components. Using fluorescently labelled BMP-2/7 and BMP-2, we demonstrated that the CHA scaffold provided a long-term delivery of both molecules for at least 20 days. Finally, using a rat femoral defect model, we showed that an ultra-low dose (0.5 µg) of BMP-2/7 accelerated fracture healing and performed at a level comparable to 20-times higher BMP-2 dose. Our results indicate that the sustained delivery of BMP-2/7 via a CHA scaffold could bring us a step closer in the quest for the use of physiological growth factor doses in fracture healing. STATEMENT OF SIGNIFICANCE: • Incorporation of hydroxyapatite (HA) in a collagen scaffold dramatically improves bone morphogenic protein (BMP) sequestration via biophysical interactions with BMP, thereby providing more controlled BMP release compared with pristine collagen. • We then investigate the molecular mechanisms responsible for increased osteoinductive potential of a heterodimer BMP-2/7 with is clinically used counterpart, the BMP-2 homodimer. • The superior osteoinductive properties of BMP-2/7 are a consequence of its direct positive effect on progenitor cell homing at the implantation site, which consequently leads to upregulation of cartilage and bone related genes and biochemical markers. • An ultra-low dose of BMP-2/7 delivered via a collagen-HA (CHA) scaffold leads to accelerated healing of a critical femoral defect in rats while a 20-times higher BMP-2 dose was required to achieve comparable results.

An overview of translational research in bone graft biomaterials

Natural bone healing is often inadequate to treat fractures with critical size bone defects and massive bone loss. Immediate surgical interventions through bone grafts have been found to be essential on such occasions. Naturally harvested bone grafts, although are the preferred choice of the surgeons; they suffer from serious clinical limitations, including disease transmission, donor site morbidity, limited supply of graft etc. Synthetic bone grafts, on the other hand, offer a more clinically appealing approach to decode the pathways of bone repair through use of tissue engineered biomaterials. This article critically retrospects the translational research on various engineered biomaterials towards bringing transformative changes in orthopaedic healthcare. The first section of the article discusses about composition and ultrastructure of bone along with the global perspectives on statistical escalation of bone fracture surgeries requiring use of bone grafts. The next section reviews the types, benefits and challenges of various natural and synthetic bone grafts. An overview of clinically relevant biomaterials from traditionally used metallic, bioceramic, and biopolymeric biomaterials to new generation composites have been summarised. Finally, this narrative review concludes with the discussion on the emerging trends and future perspectives of the promising bone grafts.

Effect of Pore Characteristics and Alkali Treatment on the Physicochemical and Biological Properties of a 3D-Printed Polycaprolactone Bone Scaffold

Polycaprolactone scaffolds were designed and 3D-printed with different pore shapes (cube and triangle) and sizes (500 and 700 μm) and modified with alkaline hydrolysis of different ratios (1, 3, and 5 M). In total, 16 designs were evaluated for their physical, mechanical, and biological properties. The present study mainly focused on the pore size, porosity, pore shapes, surface modification, biomineralization, mechanical properties, and biological characteristics that might influence bone ingrowth in 3D-printed biodegradable scaffolds. The results showed that the surface roughness in treated scaffolds increased compared to untreated polycaprolactone scaffolds (R _a = 2.3-10.5 nm and R _q = 17- 76 nm), but the structural integrity declined with an increase in the NaOH concentration especially in the scaffolds with small pores and a triangle shape. Overall, the treated polycaprolactone scaffolds particularly with the triangle shape and smaller pore size provided superior performance in mechanical strength similar to that of cancellous bone. Additionally, the in vitro study showed that cell viability increased in the polycaprolactone scaffolds with cubic pore shapes and small pore sizes, whereas mineralization was enhanced in the designs with larger pore sizes. Based on the results obtained, this study demonstrated that the 3D-printed modified polycaprolactone scaffolds exhibit a favorable mechanical property, biomineralization, and better biological properties; therefore, they can be applied in bone tissue engineering.

Metatarsal bone model production using 3D printing and comparison of material properties with results obtained from CT-based modeling and real bone

Using a real bone is very important to find correct results for the biomechanical studies. However, it is very difficult to find the real bone and sometimes artificial bone models can be preferred instead of real bone. The aim of this study is to obtain an easy-to-manufacture, easy-to-customize and inexpensive method the artificial first metatarsal bone model that is similar material properties with the real bone. 3D printer technology was used to produce the artificial bone model. First metatarsal bone was modeled using MIMICS software to produce and determined the mechanical properties. The bone mechanical properties were calculated via MIMICS software using computer tomography images. 3D bone models were produced in different infill density and infill pattern to determine the real bone mechanical properties using 3D printer. The infill density of the bone model was adjusted as 20%, 40%, and 60%. Five different infill pattern types were used as grid, cubic, triangle, trihexagon, and gyroid. The produced models were subjected to torsional test and the elasticity modulus of all models were obtained. The results of the elasticity modulus of all produced (artificial) and modeled (calculated) bone were compared and the optimum bone model was obtained. The optimum infill density and infill pattern was determined as 40% and trihexagon, respectively.

Autologous Tooth Graft: Innovative Biomaterial for Bone Regeneration. Tooth Transformer® and the Role of Microbiota in Regenerative Dentistry. A Systematic Review

Different biomaterials, from synthetic products to autologous or heterologous grafts, have been suggested for the preservation and regeneration of bone. The aim of this study is to evaluate the effectiveness of autologous tooth as a grafting material and examine the properties of this material and its interactions with bone metabolism. PubMed, Scopus, Cochrane Library, and Web of Science were searched to find articles addressing our topic published from 1 January 2012 up to 22 November 2022, and a total of 1516 studies were identified. Eighteen papers in all were considered in this review for qualitative analysis. Demineralized dentin can be used as a graft material, since it shows high cell compatibility and promotes rapid bone regeneration by striking an ideal balance between bone resorption and production; it also has several benefits, such as quick recovery times, high-quality newly formed bone, low costs, no risk of disease transmission, the ability to be performed as an outpatient procedure, and no donor-related postoperative complications. Demineralization is a crucial step in the tooth treatment process, which includes cleaning, grinding, and demineralization. Since the presence of hydroxyapatite crystals prevents the release of growth factors, demineralization is essential for effective regenerative surgery. Even though the relationship between the bone system and dysbiosis has not yet been fully explored, this study highlights an association between bone and gut microbes. The creation of additional scientific studies to build upon and enhance the findings of this study should be a future objective of scientific research.

Structural parameters of nanoparticles affecting their toxicity for biomedical applications: a review

Rapidly growing interest in using nanoparticles (NPs) for biomedical applications has increased concerns about their safety and toxicity. In comparison with bulk materials, NPs are more chemically active and toxic due to the greater surface area and small size. Understanding the NPs' mechanism of toxicity, together with the factors influencing their behavior in biological environments, can help researchers to design NPs with reduced side effects and improved performance. After overviewing the classification and properties of NPs, this review article discusses their biomedical applications in molecular imaging and cell therapy, gene transfer, tissue engineering, targeted drug delivery, Anti-SARS-CoV-2 vaccines, cancer treatment, wound healing, and anti-bacterial applications. There are different mechanisms of toxicity of NPs, and their toxicity and behaviors depend on various factors, which are elaborated on in this article. More specifically, the mechanism of toxicity and their interactions with living components are discussed by considering the impact of different physiochemical parameters such as size, shape, structure, agglomeration state, surface charge, wettability, dose, and substance type. The toxicity of polymeric, silica-based, carbon-based, and metallic-based NPs (including plasmonic alloy NPs) have been considered separately.

Interaction of Ceramic Implant Materials with Immune System

The immuno-compatibility of implant materials is a key issue for both initial and long-term implant integration. Ceramic implants have several advantages that make them highly promising for long-term medical solutions. These beneficial characteristics include such things as the material availability, possibility to manufacture various shapes and surface structures, osteo-inductivity and osteo-conductivity, low level of corrosion and general biocompatibility. The immuno-compatibility of an implant essentially depends on the interaction with local resident immune cells and, first of all, macrophages. However, in the case of ceramics, these interactions are insufficiently understood and require intensive experimental examinations. Our review summarizes the state of the art in variants of ceramic implants: mechanical properties, different chemical modifications of the basic material, surface structures and modifications, implant shapes and porosity. We collected the available information about the interaction of ceramics with the immune system and highlighted the studies that reported ceramic-specific local or systemic effects on the immune system. We disclosed the gaps in knowledge and outlined the perspectives for the identification to ceramic-specific interactions with the immune system using advanced quantitative technologies. We discussed the approaches for ceramic implant modification and pointed out the need for data integration using mathematic modelling of the multiple ceramic implant characteristics and their contribution for long-term implant bio- and immuno-compatibility.

Antibacterial Activity and Cell Viability of Biomimetic Magnesian Calcite Coatings on Biodegradable Mg

Mg is a material of choice for biodegradable implants. The main challenge for using Mg in temporary implants is to provide protective surfaces that mitigate its rapid degradation in biological fluids and also confer sufficient cytocompatibility and bacterial resistance to Mg-coated surfaces. Even though carbonate mineralization is the most important source of biominerals, such as the skeletons and shells of many marine organisms, there has been little success in the controlled growth of carbonate layers by synthetic processes. We present here the formation mechanism, antibacterial activity, and cell viability of magnesian calcite biomimetic coatings grown on biodegradable Mg via a green, one-step route. Cell compatibility assessment showed cell viability higher than 80% after 72 h using fibroblast cells (NCTC, clone L929) and higher than 60% after 72 h using human osteoblast-like cells (SaOS-2); the cells displayed a normal appearance and a density similar to the control sample. Antimicrobial potential evaluation against both Gram-positive (Staphylococcus aureus (ATCC 25923)) and Gram-negative (Pseudomonas aeruginosa (ATCC 27853)) strains demonstrated that the coated samples significantly inhibited bacterial adhesion and biofilm formation compared to the untreated control. Calcite coatings grown on biodegradable Mg by a single coating process showed the necessary properties of cell compatibility and bacterial resistance for application in surface-modified Mg biomaterials for temporary implants.

Cellular metabolism: a link connecting cellular behaviour with the physiochemical properties of biomaterials for bone tissue engineering

Biomaterial properties, such as surface roughness, morphology, stiffness, conductivity, and chemistry, significantly influence a cell's ability to sense and adhere to its surface and regulate cell functioning. Understanding how biomaterial properties govern changes in cellular function is one of the fundamental goals of tissue engineering. Still, no generalized rule is established to predict cellular processes (adhesion, spreading, growth and differentiation) on biomaterial surfaces. A few studies have highlighted that cells sense biomaterial properties at multiple length scales and regulate various intracellular biochemical processes like cytoskeleton organization, gene regulation, and receptor expression to influence cell function. However, recent studies have found cellular metabolism as another critical aspect of cellular processes that regulate cell behavior, co-relating metabolism to cellular functions like adhesion, proliferation, and differentiation. Now researchers have started to uncover previously overlooked factors on how biomaterial properties govern changes in cellular functions mediated through metabolism. This review highlights how different physiochemical properties of scaffolds designed from different biomaterials influence cell metabolism. The review also discusses the role of metabolism change in cellular functions and cell behavior in the context of bone tissue engineering. It also emphasizes the importance of cell metabolism as a missing link between the cellular behavior and physicochemical properties of scaffolds and serves as a guiding principle for designing scaffolds for tissue engineering.

Recent Trends in Hydroxyapatite Supplementation for Osteoregenerative Purposes

Bone regeneration has gained attention in the biomedical field, which has led to the development of materials and synthesis methods meant to improve osseointegration and cellular bone activity. The properties of hydroxyapatite, a type of calcium phosphate, have been researched to determine its advantages for bone tissue engineering, particularly its biocompatibility and ability to interact with bone cells. Recently, the advantages of utilizing nanomolecules of hydroxyapatite, combined with various substances, in order to enhance and combine their characteristics, have been reported in the literature. This review will outline the cellular and molecular roles of hydroxypatite, its interactions with bone cells, and its nano-combinations with various ions and natural products and their effects on bone growth, development, and bone repair.

Protocol for Cell Colonization and Comprehensive Monitoring of Osteogenic Differentiation in 3D Scaffolds Using Biochemical Assays and Multiphoton Imaging

The goal of bone tissue engineering is to build artificial bone tissue with properties that closely resemble human bone and thereby support the optimal integration of the constructs (biografts) into the body. The development of tissues in 3D scaffolds includes several complex steps that need to be optimized and monitored. In particular, cell-material interaction during seeding, cell proliferation and cell differentiation within the scaffold pores play a key role. In this work, we seeded two types of 3D-printed scaffolds with pre-osteoblastic MC3T3-E1 cells, proliferated and differentiated the cells, before testing and adapting different assays and imaging methods to monitor these processes. Alpha-TCP/HA (α-TCP with low calcium hydroxyapatite) and baghdadite (Ca₃ZrSi₂O₉) scaffolds were used, which had comparable porosity (~50%) and pore sizes (~300-400 µm). Cell adhesion to both scaffolds showed ~95% seeding efficiency. Cell proliferation tests provided characteristic progression curves over time and increased values for α-TCP/HA. Transmitted light imaging displayed a homogeneous population of scaffold pores and allowed us to track their opening state for the supply of the inner scaffold regions by diffusion. Fluorescence labeling enabled us to image the arrangement and morphology of the cells within the pores. During three weeks of osteogenesis, ALP activity increased sharply in both scaffolds, but was again markedly increased in α-TCP/HA scaffolds. Multiphoton SHG and autofluorescence imaging were used to investigate the distribution, morphology, and arrangement of cells; collagen-I fiber networks; and hydroxyapatite crystals. The collagen-I networks became denser and more structured during osteogenic differentiation and appeared comparable in both scaffolds. However, imaging of the HA crystals showed a different morphology between the two scaffolds and appeared to arrange in the α-TCP/HA scaffolds along collagen-I fibers. ALP activity and SHG imaging indicated a pronounced osteo-inductive effect of baghdadite. This study describes a series of methods, in particular multiphoton imaging and complementary biochemical assays, to validly measure and track the development of bone tissue in 3D scaffolds. The results contribute to the understanding of cell colonization, growth, and differentiation, emphasizing the importance of optimal media supply of the inner scaffold regions.

Hyaluronic acid hydrogels support to generate integrated bone formation through endochondral ossification in vivo using mesenchymal stem cells

Engineered cartilage tissue from differentiated mesenchymal stem cells (MSCs) can generate bone in vivo through endochondral ossification (ECO). This ECO-mediated approach has the potential to circumvent the severe problems associated with conventional MSC-based bone tissue engineering techniques that lack mechanisms to induce angiogenesis. Hyaluronic acid (HA) is a key component in the cartilage extracellular matrix. However, the ECO-supporting properties of HA remain largely unclear. This study aimed to compare the ability of HA and collagen hydrogels to support in vitro differentiation of MSC-based hypertrophic cartilage tissues and to promote endochondral bone formation in vivo. Following the chondrogenic and hypertrophic differentiation in vitro, both HA and collagen constructs accumulated sulfated glycosaminoglycan (sGAG) and type 1, type II, and type X collagen. However, HA hydrogels exhibited a more uniform distribution of sGAG, type 1 collagen, type X collagen, and osteocalcin proteins; in addition, the cells embedded in the hydrogels had more rounded cell morphologies than those in the collagen constructs. At week 5 of in vitro culture, two to three constructs were implanted into a subcutaneous pocket in nude mice and harvested after 4 and 8 weeks. Both HA and collagen constructs promoted endochondral bone formation with vascularization and bone marrow development; however, the HA constructs fused to form integrated bone tissues and the bone marrow developed along the space between the two adhered grafts in all implanted pockets (n = 5). In the collagen constructs, the integration was observed in 40% of the pockets (n = 5). Microcomputer CT analysis revealed that the bone volume of HA constructs was larger than that of collagen constructs. In conclusion, compared to collagen hydrogels, HA hydrogels had superior potential to generate integrated bone with vascularization and bone marrow development. This study provides valuable insights for applying ECO-mediated bone tissue engineering approaches for the repair of critical-sized bone defects.

A Novel Construct of Coral Granules-Poly-L-Lactic Acid Nanomembrane Sandwich Double Stem Cell Sheet Transplantation as Regenerative Therapy of Bone Defect Model

OBJECTIVES

We examined the use of a new approach in nanotechnology and stem cell research as regenerative therapy for bone tissue defects.

MATERIALS AND METHODS

We compared in vitro osteogenic potential of human Wharton jelly mesenchymal stem cells using coral granules and poly-L-lactic acid nanofiber according to proliferation (by cck-8 kit) and osteogenes (runt-related transcription factor 2, alkaline phosphatase, osteonectin) by quantitative reverse transcription-polymerase chain reaction, alkaline phosphatase assay, calcium measurement, and assessment of mineralization by Alizarin red and von Kossa staining. To overcome the limitations of natural coral, we made a modification by packaging the coral granules-human Wharton jelly mesenchymal stem cells by nanomembrane-human Wharton jelly mesenchymal stem cells to form sandwich double cell sheets and compared this hole with other holes (one was filled by human Wharton jelly mesenchymal stem cell suspension, and the other was filled by coral granules saturated with preinduced mesenchymal stem cells) by radiological and histopathological studies for repairing the bone gap.

RESULTS

Collagen-coated poly-L-lactic acid showed higher mRNA levels for all osteogenes (P < .001), higher alkaline phosphatase and calcium content (P < .001), and greater stainability. Our in vivo experiment showed that the holes implanted with sandwich double cell sheet-poly-L-lactic acid coral were completely filled mature compact bone. The holes implanted with human Wharton jelly mesenchymal stem cells alone were filled with immature compact bone. Holes implanted with coral granules-human Wharton jelly mesenchymal stem cells were filled with condensed connective tissue.

CONCLUSIONS

Poly-L-lactic acid nanofiber has greater osteogenic differentiating effect than the coral granules. The new approach of sDCS-PLLA-coral construct proved success for bone regeneration and repairing the bone gap and this may improve the design of tissue constructs for bone tissue regenerative therapy.

Bone regeneration in osteoporosis: opportunities and challenges

Osteoporosis is a bone disorder characterised by low bone mineral density, reduced bone strength, increased bone fragility, and impaired mineralisation of bones causing an increased risk of bone fracture. Several therapies are available for treating osteoporosis which include bisphosphonates, anti-resorptive agents, oestrogen modulators, etc. These therapies primarily focus on decreasing bone resorption and do not assist in bone regeneration or offering permanent curative solutions. Additionally, these therapies are associated with severe adverse events like thromboembolism, increased risk of stroke, and hypocalcaemia. To overcome these limitations, bone regenerative pathways and approaches are now considered to manage osteoporosis. The bone regenerative pathways involved in bone regeneration include wingless-related integration site/β-catenin signalling pathway, notch signalling pathway, calcium signalling, etc. The various regenerative approaches which possess potential to heal and replace the bone defect site include scaffolds, cements, cell therapy, and other alternative medicines. The review focuses on describing the challenges and opportunities in bone regeneration for osteoporosis.

The controlled release, bioactivity and osteogenic gene expression of Quercetin-loaded gelatin/tragacanth/ nano-hydroxyapatite bone tissue engineering scaffold

In this study, a Gelatin/Tragacanth/Nano-hydroxyapatite scaffold was fabricated via freeze-drying method. A highly porous scaffold with an average pore diameter of 142 µm and porosity of 86% was found by the micro-computed tomography. The mean compressive strength of the scaffold was about 1.5 MPa, a value in the range of the spongy bone. The scaffold lost 10 wt.% of its initial weight after 28 days soaking in PBS that shows a fair degradation rate for a bone tissue engineering scaffold. Apatite formation ability of the scaffold was confirmed via scanning electron microscopy, X-ray diffraction and Fourier transforming infrared spectroscopy, after 28 days soaking in simulated body fluid. The scaffold was able to deliver 93% of the loaded drug, Quercetin, during 120 h in phosphate-buffered solution, in a sustainable manner. The MTT assay using human bone mesenchymal stem cells showed 84% cell viability of the Quercetin-loaded scaffold. The expression of the osteogenic genes including Col I, Runx-2, BGLAP (gene of osteocalcin), bFGF, SP7 (gene of osterix) and SPP1 (gene of osteopontin) were all upregulated when Quercetin was loaded on the scaffold, which indicates the synergetic effect of the drug and the scaffold.

A Comprehensive Review on Silk Fibroin as a Persuasive Biomaterial for Bone Tissue Engineering

Bone tissue engineering (BTE) utilizes a special mix of scaffolds, cells, and bioactive factors to regulate the microenvironment of bone regeneration and form a three-dimensional bone simulation structure to regenerate bone tissue. Silk fibroin (SF) is perhaps the most encouraging material for BTE given its tunable mechanical properties, controllable biodegradability, and excellent biocompatibility. Numerous studies have confirmed the significance of SF for stimulating bone formation. In this review, we start by introducing the structure and characteristics of SF. After that, the immunological mechanism of SF for osteogenesis is summarized, and various forms of SF biomaterials and the latest development prospects of SF in BTE are emphatically introduced. Biomaterials based on SF have great potential in bone tissue engineering, and this review will serve as a resource for future design and research.

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and amino-functionalized nanodiamond bionanocomposites for bone tissue defect repair

Injection-molded nanocomposites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) with 6 % of 3-hydroxyvalerate (HV) and amino-nanodiamonds (nD-A) were produced and characterized to investigate the effect of functionalized nanodiamonds on mechanical and biological behavior to bone replacement application. To prepare mixtures of PHBHV and nD-A in different concentrations, nD-A was dispersed in chloroform by sonication with 40 % of amplitude. Three specimens were characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (DRX), differential scanning calorimetry (DSC), 3-point flexural tests, dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). FTIR and TGA evidenced the existence of interactions between the nD-A and PHBHV. The crystallinity degree of PHBHV slightly reduced (~9 %) in nanocomposites and the morphology of the crystals changed. Nanocomposites achieved satisfactory dispersion and distribution of nD-A for low concentrations. Elastic modulus (E) increased from 1.96 ± 0.20 (PHBHV) to 2.59 ± 0.19 GPa (PHBHV/1.0%nD-A) (30 %). Despite the relatively limited dispersion, PHBHV/2.0 % nD-A had the best combination of E, strength, and maximum deformation. It had the highest glass transition temperature (43.1 vs 40.3 °C of PHBHV) and the best adhesion coefficient and reinforcement effectiveness. PHBHV-nD-A did not induce toxicity in 7 days and allowed cell fixation and expansion. These bionanocomposites should be considered for supplementary studies for bone tissue engineering.

Influence of porosity on osteogenesis, bone growth and osteointegration in trabecular tantalum scaffolds fabricated by additive manufacturing

Porous tantalum implants are a class of materials commonly used in clinical practice to repair bone defects. However, the cumbersome and problematic preparation procedure have limited their widespread application. Additive manufacturing has revolutionized the design and process of orthopedic implants, but the pore architecture feature of porous tantalum scaffolds prepared from additive materials for optimal osseointegration are unclear, particularly the influence of porosity. We prepared trabecular bone-mimicking tantalum scaffolds with three different porosities (60%, 70% and 80%) using the laser powder bed fusing technique to examine and compare the effects of adhesion, proliferation and osteogenic differentiation capacity of rat mesenchymal stem cells on the scaffolds in vitro. The in vivo bone ingrowth and osseointegration effects of each scaffold were analyzed in a rat femoral bone defect model. Three porous tantalum scaffolds were successfully prepared and characterized. In vitro studies showed that scaffolds with 70% and 80% porosity had a better ability to osteogenic proliferation and differentiation than scaffolds with 60% porosity. In vivo studies further confirmed that tantalum scaffolds with the 70% and 80% porosity had a better ability for bone ingrowh than the scaffold with 60% porosity. As for osseointegration, more bone was bound to the material in the scaffold with 70% porosity, suggesting that the 3D printed trabecular tantalum scaffold with 70% porosity could be the optimal choice for subsequent implant design, which we will further confirm in a large animal preclinical model for better clinical use.

Magnetic Hydroxyapatite Composite Nanoparticles for Augmented Differentiation of MC3T3-E1 Cells for Bone Tissue Engineering

Progressive aging harms bone tissue structure and function and, thus, requires effective therapies focusing on permanent tissue regeneration rather than partial cure, beginning with regenerative medicine. Due to advances in tissue engineering, stimulating osteogenesis with biomimetic nanoparticles to create a regenerative niche has gained attention for its efficacy and cost-effectiveness. In particular, hydroxyapatite (HAP, Ca₁₀(PO₄)₆(OH)₂) has gained significant interest in orthopedic applications as a major inorganic mineral of native bone. Recently, magnetic nanoparticles (MNPs) have also been noted for their multifunctional potential for hyperthermia, MRI contrast agents, drug delivery, and mechanosensitive receptor manipulation to induce cell differentiation, etc. Thus, the present study synthesizes HAP-decorated MNPs (MHAP NPs) via the wet chemical co-precipitation method. Synthesized MHAP NPs were evaluated against the preosteoblast MC3T3-E1 cells towards concentration-dependent cytotoxicity, proliferation, morphology staining, ROS generation, and osteogenic differentiation. The result evidenced that MHAP NPs concentration up to 10 µg/mL was non-toxic even with the time-dependent proliferation studies. As nanoparticle concentration increased, FACS apoptosis assay and ROS data showed a significant rise in apoptosis and ROS generation. The MC3T3-E1 cells cocultured with 5 µg/mL MHAP NPs showed significant osteogenic differentiation potential. Thus, MHAP NPs synthesized with simple wet chemistry could be employed in bone regenerative therapy.