The fabrication of nano-hydroxyapatite on PLGA and PLGA/collagen nanofibrous composite scaffolds and their effects in osteoblastic behavior for bone tissue engineering

Electrospun Polylactic Acid Based Nanofibers for Biomedical Applications

Electrospinning technique has excellent advantages such as tunable functionality, thin fibers with large surface areas, ease of processing and good physical properties. Electrospinning provides wide usage area with these advantages in biomedical applications. Polylactic acid (PLA) is a biodegradable and biocompatible polymer, so it can be used in various biomedical applications. PLA can be easily electrospun from solution by using different kinds of conventional solvents. Electrospun PLA based nanofibers are used in many biomedical applications such as drug delivery, scaffold for tissue engineering, dressings for wound healing, dental applications etc. This review focuses on electrospun PLA based nanofibers used in biomedical applications in recent years. Future perspectives of electrospun PLA based fibers are also discussed in the last part.

Starch-Hydroxyapatite Composite Bone Scaffold Fabrication Utilizing a Slurry Extrusion-Based Solid Freeform Fabricator

Significant efforts have been made to treat bone disorders through the development of composite scaffolds utilizing calcium phosphate (CaP) through additive manufacturing techniques. However, the incorporation of natural polymers with CaP during 3D printing is difficult and remains a formidable challenge in bone and tissue engineering applications. The objective of this study is to understand the use of a natural polymer binder system in ceramic composite scaffolds using a ceramic slurry-based solid freeform fabricator (SFF). This was achieved through the utilization of naturally sourced gelatinized starch with hydroxyapatite (HA) ceramic in order to obtain high mechanical strength and enhanced biological properties of the green part without the need for cross-linking or post processing. The parametric effects of solids loading, polycaprolactone (PCL) polymer addition, and designed porosity on starch-HA composite scaffolds were assessed through mechanical strength, microstructure, and in vitro biocompatibility utilizing human osteoblast cells. It was hypothesized that starch incorporation would improve the mechanical strength of the scaffolds and increase proliferation of osteoblast cells in vitro. Starch loading was shown to improve mechanical strength from 4.07 ± 0.66 MPa to 10.35 ± 1.10 MPa, more closely resembling the mechanical strength of cancellous bone. Based on these results, a reinforcing mechanism of gelatinized starch based on interparticle and apatite crystal interlocking is proposed. Morphological characterization utilizing FESEM and MTT cell viability assay showed enhanced osteoblast cell proliferation in the presence of starch and PCL. Overall, the utilization of starch as a natural binder system in SFF scaffolds was found to improve both green strength and in vitro biocompatibility.

Settable polymer/ceramic composite bone grafts stabilize weight-bearing tibial plateau slot defects and integrate with host bone in an ovine model

Bone fractures at weight-bearing sites are challenging to treat due to the difficulty in maintaining articular congruency. An ideal biomaterial for fracture repair near articulating joints sets rapidly after implantation, stabilizes the fracture with minimal rigid implants, stimulates new bone formation, and remodels at a rate that maintains osseous integrity. Consequently, the design of biomaterials that mechanically stabilize fractures while remodeling to form new bone is an unmet challenge in bone tissue engineering. In this study, we investigated remodeling of resorbable bone cements in a stringent model of mechanically loaded tibial plateau defects in sheep. Nanocrystalline hydroxyapatite-poly(ester urethane) (nHA-PEUR) hybrid polymers were augmented with either ceramic granules (85% β-tricalcium phosphate/15% hydroxyapatite, CG) or a blend of CG and bioactive glass (BG) particles to form a settable bone cement. The initial compressive strength and fatigue properties of the cements were comparable to those of non-resorbable poly(methyl methacrylate) bone cement. In animals that tolerated the initial few weeks of early weight-bearing, CG/nHA-PEUR cements mechanically stabilized the tibial plateau defects and remodeled to form new bone at 16 weeks. In contrast, cements incorporating BG particles resorbed with fibrous tissue filling the defect. Furthermore, CG/nHA-PEUR cements remodeled significantly faster at the full weight-bearing tibial plateau site compared to the mechanically protected femoral condyle site in the same animal. These findings are the first to report a settable bone cement that remodels to form new bone while providing mechanical stability in a stringent large animal model of weight-bearing bone defects near an articulating joint.

Nanostructure coated AZ31 magnesium cylindrical mesh cage for potential long bone segmental defect repair applications

This current study is aimed towards the fabrication of AZ31 magnesium cylindrical mesh cage implant with circular holes for orthopedic applications. This mesh cage is coated with nanocomposite material containing polycaprolactone (PCL), pluronic F127 and nano hydroxyapatite (nHA) by electrospinning process. Morphology and composition were analyzed by various characterization techniques. Controlled degradation and weight loss of the nanocomposite coated samples in 28 days were observed when compared with uncoated samples in SBF (simulated body fluid). The nanocomposite coated material was not cytotoxic to MG63 osteosarcoma cells. The cell viability, morphology, ALP activity, calcium mineralization and collagen deposition were also better on this when compared to uncoated. Smooth and randomly deposited nanofibers on the mesh cage was observed and the contact angle indicated that the surface is hydrophilic with (initial contact angle of 55 ± 1° and after 10 s 0°) when compared to PCL (99°) coated surface. 2-5 fold higher mRNA expression levels of osteogenic genes namely ALP, BMP2, COL1 and RUNX2 was observed with nanocomposite coated scaffolds than uncoated and PCL coated samples in 14 days. These results indicate the potential use of the nanocomposite coated AZ31 cylindrical mesh cage for segmental bone defect repair and can be used as a degradable implant for orthopedic applications.

Bone Regeneration Using Adipose-Derived Stem Cells in Injectable Thermo-Gelling Hydrogel Scaffold Containing Platelet-Rich Plasma and Biphasic Calcium Phosphate

For bone regeneration, a biocompatible thermo-gelling hydrogel, hyaluronic acid-g-chitosan-g-poly(N-isopropylacrylamide) (HA-CPN) was used as a three-dimensional organic gel matrix for entrapping rabbit adipose-derived stem cells (rASCs). Biphasic calcium phosphate (BCP) ceramic microparticles were embedded within the gel matrix as a mineralized bone matrix, which was further fortified with platelet-rich plasma (PRP) with osteo-inductive properties. In vitro culture of rASCs in HA-CPN and HA-CPN/PRP/BCP was compared for cell proliferation and osteogenic differentiation. Overall, HA-CPN/PRP/BCP was a better injectable cell carrier for osteogenesis of rASCs with increased cell proliferation rate and alkaline phosphatase activity, enhanced calcium deposition and mineralization of extracellular matrix, and up-regulated expression of genetic markers of osteogenesis. By implanting HA-CPN/PRP/BCP/rASCs constructs in rabbit critical size calvarial bone defects, new bone formation at the defect site was successfully demonstrated from computed tomography, and histological and immunohistochemical analysis. Taken together, by combining PRP and BCP as the osteo-inductive and osteo-conductive factor with HA-CPN, we successfully demonstrated the thermo-gelling composite hydrogel scaffold could promote the osteogenesis of rASCs for bone tissue engineering applications.

Effect of hydroxyapatite fillers on the mechanical properties and osteogenesis capacity of bio-based polyurethane composite scaffolds

A newly designed hydroxyapatite-polyurethane (HA-PU) composite scaffold was prepared by polymerizing glyceride of castor oil (GCO) with isophorone diisocyanate (IPDI) and HA as fillers. The aim of this study was to determine the effect of HA fillers on the mechanical properties and osteogenesis capacity of the composite scaffolds. The physical and biological properties of the scaffold were evaluated by SEM observation, mechanical testing, cell culture and animal experiments. The results showed that HA fillers enhanced the mechanical properties of PU composite scaffolds such as compressive strength and elastic modulus. The mechanical properties of the scaffolds were seen to increase with increase in HA loading. The compressive strength of composite scaffold with 0 wt%, 20 wt%, 40 wt% of HA was 0.6 ± 0.1 MPa, 2.1 ± 0.1 MPa, and 4.6 ± 0.3 MPa, respectively. In vitro biodegradation studies of scaffolds were carried out. The results showed that all of the scaffolds were susceptible to cholesterol esterase (CE) -catalyzed degradation. HA-PU composite scaffolds exhibited a high affinity to osteoblastic cells and were good template for cell growth and proliferation. When implanted in bone defects of rats, PU scaffolds incorporated HA were biocompatible with the tissue host and had no immune rejection. Moreover, the higher the loading of HA in the composite scaffold, the better chances of osteogenesis. It confirmed that the prepared HA-PU composite scaffolds can be promising candidate for bone repair and bone tissue engineering.

A Review on Properties of Natural and Synthetic Based Electrospun Fibrous Materials for Bone Tissue Engineering

Bone tissue engineering is an interdisciplinary field where the principles of engineering are applied on bone-related biochemical reactions. Scaffolds, cells, growth factors, and their interrelation in microenvironment are the major concerns in bone tissue engineering. Among many alternatives, electrospinning is a promising and versatile technique that is used to fabricate polymer fibrous scaffolds for bone tissue engineering applications. Copolymerization and polymer blending is a promising strategic way in purpose of getting synergistic and additive effect achieved from either polymer. In this review, we summarize the basic chemistry of bone, principle of electrospinning, and polymers that are used in bone tissue engineering. Particular attention will be given on biomechanical properties and biological activities of these electrospun fibers. This review will cover the fundamental basis of cell adhesion, differentiation, and proliferation of the electrospun fibers in bone tissue scaffolds. In the last section, we offer the current development and future perspectives on the use of electrospun mats in bone tissue engineering.

Controlled degradability of PCL-ZnO nanofibrous scaffolds for bone tissue engineering and their antibacterial activity

Up to date, tissue regeneration of large bone defects is a clinical challenge under exhaustive study. Nowadays, the most common clinical solutions concerning bone regeneration involve systems based on human or bovine tissues, which suffer from drawbacks like antigenicity, complex processing, low osteoinductivity, rapid resorption and minimal acceleration of tissue regeneration. This work thus addresses the development of nanofibrous synthetic scaffolds of polycaprolactone (PCL) - a long-term degradation polyester - compounded with hydroxyapatite (HA) and variable concentrations of ZnO as alternative solutions for accelerated bone tissue regeneration in applications requiring mid- and long-term resorption. In vitro cell response of human fetal osteoblasts as well as antibacterial activity against Staphylococcus aureus of PCL:HA:ZnO and PCL:ZnO scaffolds were here evaluated. Furthermore, the effect of ZnO nanostructures at different concentrations on in vitro degradation of PCL electrospun scaffolds was analyzed. The results proved that higher concentrations ZnO may induce early mineralization, as indicated by high alkaline phosphatase activity levels, cell proliferation assays and positive Alizarin-Red-S-stained calcium deposits. Moreover, all PCL:ZnO scaffolds particularly showed antibacterial activity against S. aureus which may be attributed to release of Zn²⁺ ions. Additionally, results here obtained showed a variable PCL degradation rate as a function of ZnO concentration. Therefore, this work suggests that our PCL:ZnO scaffolds may be promising and competitive short-, mid- and long-term resorption systems against current clinical solutions for bone tissue regeneration.

Incorporation of silica nanoparticles to PLGA electrospun fibers for osteogenic differentiation of human osteoblast-like cells

The development of bone tissue engineering scaffolds still remains a challenging field, although various biomaterials have been developed for this purpose. Electrospinning is a promising approach to fabricate nanofibers with an interconnected porous structure, which can support cell adhesion, guide cell proliferation and regulate cell differentiation. The aim of this study is to fabricate composite fibers composed of poly(lactic-co-glycolic acid) (PLGA) and silica nanoparticles (NPs) via electrospinning and investigate the effect of PLGA/SiO2 composite fibers on the cellular response of osteoblast-like cells (SaOS-2 cells). SEM and EDX analysis showed that silica NPs were homogenously dispersed in the composite fibers. The mechanical behavior of the fibers showed that silica NPs acted as reinforcements at concentrations of 2.5 and 5 mg/ml. The incorporation of silica NPs led to enhancement of cell attachment and spreading on PLGA/SiO2 composite fibers. SaOS-2 cells cultured on PLGA/SiO2 composite fibers exhibited increased alkaline phosphatase activity, collagen secretion and bone nodules formation. The bone nodules formation of SaOS-2 cells increased along with the amount of incorporated silica NPs. The present findings indicate that PLGA/SiO2 composite fibers can stimulate osteogenic differentiation of SaOS-2 cells and may be a promising candidate scaffold for bone tissue engineering.

Gelatin/Nanohyroxyapatite Cryogel Embedded Poly(lactic-co-glycolic Acid)/Nanohydroxyapatite Microsphere Hybrid Scaffolds for Simultaneous Bone Regeneration and Load-Bearing

It is desirable to combine load-bearing and bone regeneration capabilities in a single bone tissue engineering scaffold. For this purpose, we developed a high strength hybrid scaffold using a sintered poly(lactic-co-glycolic acid) (PLGA)/nanohydroxyapatite (nHAP) microsphere cavity fitted with gelatin/nHAP cryogel disks in the center. Osteo-conductive/osteo-inductive nHAP was incorporated in 250⁻500 μm PLGA microspheres at 40% (w/w) as the base matrix for the high strength cavity-shaped microsphere scaffold, while 20% (w/w) nHAP was incorporated into gelatin cryogels as an embedded core for bone regeneration purposes. The physico-chemical properties of the microsphere, cryogel, and hybrid scaffolds were characterized in detail. The ultimate stress and Young's modulus of the hybrid scaffold showed 25- and 21-fold increases from the cryogel scaffold. In vitro studies using rabbit bone marrow-derived stem cells (rBMSCs) in cryogel and hybrid scaffolds through DNA content, alkaline phosphatase activity, and mineral deposition by SEM/EDS, showed the prominence of both scaffolds in cell proliferation and osteogenic differentiation of rBMSCs in a normal medium. Calcium contents analysis, immunofluorescent staining of collagen I (COL I), and osteocalcin (OCN) and relative mRNA expression of COL I, OCN and osteopontin (OPN) confirmed in vitro differentiation of rBMSCs in the hybrid scaffold toward the bone lineage. From compression testing, the cell/hybrid scaffold construct showed a 1.93 times increase of Young's modulus from day 14 to day 28, due to mineral deposition. The relative mRNA expression of osteogenic marker genes COL I, OCN, and OPN showed 5.5, 18.7, and 7.2 folds increase from day 14 to day 28, respectively, confirming bone regeneration. From animal studies, the rBMSCs-seeded hybrid constructs could repair mid-diaphyseal tibia defects in rabbits, as evaluated by micro-computed tomography (μ-CT) and histological analyses. The hybrid scaffold will be useful for bone regeneration in load-bearing areas.

Electrospun Silk Fibroin Nanofibrous Scaffolds with Two-Stage Hydroxyapatite Functionalization for Enhancing the Osteogenic Differentiation of Human Adipose-Derived Mesenchymal Stem Cells

The development of functional scaffolds with improved osteogenic potential is important for successful bone formation and mineralization in bone tissue engineering. In this study, we developed a functional electrospun silk fibroin (SF) nanofibrous scaffold functionalized with two-stage hydroxyapatite (HAp) particles, using mussel adhesive-inspired polydopamine (PDA) chemistry. HAp particles were first incorporated into SF scaffolds during the electrospinning process, and then immobilized onto the electrospun SF nanofibrous scaffolds containing HAp via PDA-mediated adhesive chemistry. We obtained two-stage HAp-functionalized SF nanofibrous scaffolds with improved mechanical properties and capable of providing a bone-specific physiological microenvironment. The developed scaffolds were tested for their ability to enhance the osteogenic differentiation of human adipose-derived mesenchymal stem cells (hADMSCs) in vitro and repair bone defect in vivo. To boost their ability for bone repair, we genetically modified hADMSCs with the transcriptional coactivator with PDZ-binding motif (TAZ) via polymer nanoparticle-mediated gene delivery. TAZ is a well-known transcriptional modulator that activates the osteogenic differentiation of mesenchymal stem cells (MSCs). Two-stage HAp-functionalized SF scaffolds significantly promoted the osteogenic differentiation of TAZ-transfected hADMSCs in vitro and enhanced mineralized bone formation in a critical-sized calvarial bone defect model. Our study shows the potential utility of SF scaffolds with nanofibrous structures and enriched inorganic components in bone tissue engineering.

Recombinant human BMP-7 grafted poly(lactide-co-glycolide)/hydroxyapatite scaffolds via polydopamine for enhanced calvarial repair

Polydopamine-assisted rhBMP-7 immobilization on PLGA/hydroxyapatite scaffold via phase inversion for enhanced calvarial repair in vivo.

Innovative biodegradable poly(L-lactide)/collagen/hydroxyapatite composite fibrous scaffolds promote osteoblastic proliferation and differentiation

The development of an artificial bone graft which can promote the regeneration of fractures or diseased bones is currently the most challenging aspect in bone tissue engineering. To achieve the purpose of promoting bone proliferation and differentiation, the artificial graft needs have a similar structure and composition of extracellular matrix. One-step electrospinning method of biocomposite nanofibers containing hydroxyapatite (HA) nanoparticles and collagen (Coll) were developed for potential application in bone tissue engineering. Nanocomposite scaffolds of poly(L-lactide) (PLLA), PLLA/HA, PLLA/Coll, and PLLA/Coll/HA were fabricated by electrospinning. The morphology, diameter, elements, hydrophilicity, and biodegradability of the composite scaffolds have been investigated. The biocompatibility of different nanocomposite scaffolds was assessed using mouse osteoblasts MC3T3-E1 in vitro, and the proliferation, differentiation, and mineralization of cells on different nanofibrous scaffolds were investigated. The results showed that PLLA/Coll/HA nanofiber scaffolds enhanced cell adhesion, spreading, proliferation, differentiation, mineralization, and gene expression of osteogenic markers compared to other scaffolds. In addition, the nanofibrous scaffolds maintained a stable composition at the beginning of the degradation period and morphology wastage and weight loss were observed when incubated for up to 80 days in physiological simulated conditions. The PLLA/Coll/HA composite nanofibrous scaffolds could be a potential material for guided bone regeneration.

Collagen and Hydroxyapatite Scaffolds Activate Distinct Osteogenesis Signaling Pathways in Adult Adipose-Derived Multipotent Stromal Cells

Osteogenic cell signaling pathway disruption varies among bone diseases. This investigation was designed to identify adipose-derived multipotent stromal cell (ASC) and bone graft scaffold combinations for local, targeted restoration of gene expression and extracellular matrix (ECM) deposition. Human ASC osteogenesis on bone graft materials was quantified following culture in stromal (S), osteogenic (O), or osteogenic for 48 h followed by stromal medium (OS) to test the two-part hypothesis: (1) identical ASC isolates on distinct bone graft scaffolds demonstrate unique viability, differentiation, ECM production, and gene expression in the same culture conditions; (2) identical ASC-bone graft scaffold combinations have different cell viability, differentiation, ECM production, and gene expression when cultured in S, O, or OS medium. Three commercially available bone graft scaffold materials, type I bovine collagen (C), hydroxyapatite + β-tricalcium phosphate + type I bovine collagen (HT), and β-tricalcium phosphate + type I bovine collagen (CT) were evaluated. Passage 3 ASCs were loaded onto scaffold blocks with a spinner flask bioreactor, and constructs were cultured up to 28 days. Cell viability, gene expression (alkaline phosphatase [ALPL], osteoprotegerin [TNFRSF11B], osteocalcin [BGLAP], cannabinoid receptors type I [CNR1] and II [CNR2], receptor activator of nuclear factor kappa β ligand [TNFSF11]), as well as ECM DNA, collagen, sulfated glycosaminoglycan, and protein content were quantified. Matrix organization was evaluated with scanning electron microscopy. Effects of scaffold, medium, or culture duration on cell viability were minimal. Significantly higher initial ALPL expression decreased with time, while BGLAP expression increased in HT constructs in O medium, and the constructs had the most abundant ECM components and ultrastructural organization. There was a similar, although delayed, pattern of gene expression and greater ECM collagen with less organization in C constructs in O medium. Higher CNR1 expression in C versus higher TNFRSF11B/TNFSF11 expression in HT constructs throughout the study support stimulation of unique osteogenic signaling pathways by identical cell isolates. These results suggest that bone scaffold composition may be used to selectively target specific osteogenic cell signaling pathways in ASC constructs to stimulate ECM deposition based on therapeutic needs.

In Situ Bone Tissue Engineering With an Endogenous Stem Cell Mobilizer and Osteoinductive Nanofibrous Polymeric Scaffolds

Classical bone tissue engineering involves the use of culture-expanded cells and scaffolds to produce tissue constructs for transplantation. Despite promising results, clinical adoption of these constructs has been limited due to various drawbacks, including extensive cell expansion steps, low cell survival rate upon transplantation, and the possibility of immuno-rejection. To bypass the ex vivo cell culture and transplantation process, the regenerative capacity of the host is exploited by mobilizing endogenous stem cells to the site of injury. Systemic injection of substance P (SP) induce mobilization of CD29⁺ CD105⁺ CD45^- cells from bone marrow and enhance bone tissue regeneration in a critical-sized calvarial bone defect model. To provide an appropriate environment for endogenous stem cells to survive and differentiate into osteogenic lineage cells, electrospun nanofibrous polycaprolactone (PCL) scaffolds are functionalized with hydroxyapatite (HA) particles via a polydopamine (PDA) coating to create highly osteoinductive PCL-PDA-HA scaffolds that are implanted in defects. The combination of the PCL-PDA-HA scaffold and SP treatment enhance in situ bone tissue formation in defects. Thus, this in situ bone regeneration strategy, which combines recruitment of endogenous stem cells from the bone marrow to defective sites and implantation of a highly biocompatible and osteoinductive cell-free scaffold system, has potential as an effective therapeutic in regenerative medicine.

In Vitro and in Vivo Study of Poly(Lactic⁻co⁻Glycolic) (PLGA) Membranes Treated with Oxygen Plasma and Coated with Nanostructured Hydroxyapatite Ultrathin Films for Guided Bone Regeneration Processes

The novelty of this study is the addition of an ultrathin layer of nanostructured hydroxyapatite (HA) on oxygen plasma modified poly(lactic–co–glycolic) (PLGA) membranes (PO₂) in order to evaluate the efficiency of this novel material in bone regeneration. Methods: Two groups of regenerative membranes were prepared: PLGA (control) and PLGA/PO₂/HA (experimental). These membranes were subjected to cell cultures and then used to cover bone defects prepared on the skulls of eight experimental rabbits. Results: Cell morphology and adhesion of the osteoblasts to the membranes showed that the osteoblasts bound to PLGA were smaller and with a lower number of adhered cells than the osteoblasts bound to the PLGA/PO₂/HA membrane (p < 0.05). The PLGA/PO₂/HA membrane had a higher percentage of viable cells bound than the control membrane (p < 0.05). Both micro-CT and histological evaluation confirmed that PLGA/PO₂/HA membranes enhance bone regeneration. A statistically significant difference in the percentage of osteoid area in relation to the total area between both groups was found. Conclusions: The incorporation of nanometric layers of nanostructured HA into PLGA membranes modified with PO₂ might be considered for the regeneration of bone defects. PLGA/PO₂/HA membranes promote higher osteosynthetic activity, new bone formation, and mineralisation than the PLGA control group.

In Vitro Bioactivity of One- and Two-Dimensional Nanoparticle-Incorporated Bone Tissue Engineering Scaffolds

This study investigates the effect of incorporation of one- or two-dimensional nanoparticles with distinct composition and morphology on the bioactivity of biodegradable, biocompatible polymer matrices. 0.2 wt% multiwalled carbon nanotubes, multiwalled graphene nanoribbons, graphene oxide nanoplatelets (GONPs), molybdenum disulfide nanoplatelets (MSNPs), or tungsten disulfide nanotubes (WSNTs) were uniformly dispersed in poly(lactic-co-glycolic acid) (PLGA) polymer. PLGA or nanoparticle-incorporated PLGA were then incubated with simulated body fluid (SBF) under physiological conditions for 1, 3, 7, or 14 days. Apatite collection on control and incorporated scaffolds was assessed. All groups showed apatite precipitate on the surface after 1 day of SBF incubation. After 14 days of SBF incubation, scaffolds incorporated with GONPs, MSNPs, or WSNTs showed significantly higher phosphate accumulation compared to PLGA scaffolds. Scaffolds incorporated with GONPs, MSNPs, or WSNTs should be studied in vivo to further investigate potential bioactivity, leading to enhanced integration and tissue repair at the bone-implant interface.

Resorbable Nanocomposites with Bone-Like Strength and Enhanced Cellular Activity

Bone cements for treatment of fractures at weight-bearing sites are subjected to dynamic physiological loading from daily activities. An ideal bone cement rapidly sets after injection, exhibits bone-like strength, stimulates osteogenic differentiation of endogenous cells, and resorbs at a rate aligned with patient biology. However, currently available materials fall short of these targeted properties. Nanocrystalline hydroxyapatite (nHA) enhances osteogenic differentiation, new bone formation, and osteoclast differentiation activity compared to amorphous or micron-scale crystalline hydroxyapatite. However, the brittle mechanical properties of nHA precludes its use in treatment of weight-bearing bone defects. In this study, we report settable nHA-poly(ester urethane) (PEUR) nanocomposites synthesized from nHA, lysine triisocyanate (LTI), and poly(caprolactone) triol via a solvent-free process. The nanocomposites are easily mixed and injected using a double-barrel syringe, exhibit mechanical properties exceeding those of conventional bone cements, enhance mineralization of osteoprogenitor cells in vitro, and undergo osteoclast-mediated degradation in vitro. This combination of properties cannot be achieved using other technologies, which underscores the potential of nHA-PEUR nanocomposites as a new approach for promoting bone healing at weight-bearing sites.

Macroporous Calcium Phosphate/Chitosan Composites Prepared via Unidirectional Ice Segregation and Subsequent Freeze-Drying

Calcium phosphate chitosan-based composites have gained much interest in recent years for biomedical purposes. In this paper, three-dimensional calcium phosphate chitosan-based composites with different mineral contents were produced using a green method called ice segregation induced self-assembly (ISISA). In this methodology, ice crystals were used as a template to produce porous structures from an aqueous solution of chitosan (CS) and hydroxyapatite (Hap) also containing acetic acid (pH = 4.5). For better characterization of the nature of the inorganic matter entrapped within the resulting composite, we performed either oxygen plasma or calcination processes to remove the organic matter. The nature of the phosphate salts was studied by XRD and NMR studies. Amorphous calcium phosphate (ACP) was identified as the mineral phase in the composites submitted to oxygen plasma, whereas crystalline Hap was obtained after calcination. SEM microscopy revealed the formation of porous structures (porosity around 80–85%) in the original composites, as well as in the inorganic matrices obtained after calcination, with porous channels of up to 50 µm in diameter in the former case and of up to 20 µm in the latter. The biocompatibility of the composites was assessed using two different cell lines: C2C12GFP premyoblastic cells and MC3T3 preosteoblastic cells.

Manufacturing and Characterization of Novel Electrospun Composite Comprising Polyurethane and Mustard Oil Scaffold with Enhanced Blood Compatibility

The objective of this work is to characterize and investigate the blood compatibility of polyurethane (PU)/mustard oil composites fabricated using electrospinning technique. The fabricated scaffold was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), thermogravimetric analysis (TGA) and contact angle measurements. The activated partial thromboplastin time (APPT), prothrombin time (PT) and the hemolytic assay were done to investigate the blood compatibility of the developed composites. The SEM results revealed that the fiber diameter of the composites (761 ± 123 nm) was reduced compared to pristine PU control. The interaction between PU and mustard oil was confirmed by FTIR as evident through the shifting of peaks. The fabricated composites depicted hydrophobic behavior as insinuated by the increase in contact angle measurements. PU/mustard composites displayed improved crystallinity as confirmed by TGA. Atomic force micrographs suggested that developed PU/mustard oil composites showed an increase in the surface roughness (Ra) compared to pure PU. The Ra of pure PU was observed to be 723 nm but for the fabricated PU/mustard oil composite the Ra was found to be 1298 nm (Ra). The hemolytic index value for pure PU and fabricated composites was observed to be 2.73% and 1.15% indicating that developed composites showed a non-hemolytic behavior signifying the safety of the composites with red blood cells. Hence the newly developed composites with improved physicochemical and blood compatibility properties may be considered as a potential candidate for fabricating cardiac patches and grafts.

Reliability of new poly (lactic-co-glycolic acid) membranes treated with oxygen plasma plus silicon dioxide layers for pre-prosthetic guided bone regeneration processes

BACKGROUND

The use of cold plasmas may improve the surface roughness of poly(lactic-co-glycolic) acid (PLGA) membranes, which may stimulate the adhesion of osteogenic mediators and cells, thus accelerating the biodegradation of the barriers. Moreover, the incorporation of metallic-oxide particles to the surface of these membranes may enhance their osteoinductive capacity. Therefore, the aim of this paper was to evaluate the reliability of a new PLGA membrane after being treated with oxygen plasma (PO2) plus silicon dioxide (SiO2) layers for guided bone regeneration (GBR) processes.

MATERIAL AND METHODS

Circumferential bone defects (diameter: 11 mm; depth: 3 mm) were created on the top of eight experimentation rabbits' skulls and were randomly covered with: (1) PLGA membranes (control), or (2) PLGA/PO2/SiO2 barriers. The animals were euthanized two months afterwards. A micromorphologic study was then performed using ROI (region of interest) colour analysis. Percentage of new bone formation, length of mineralised bone, concentration of osteoclasts, and intensity of ostheosynthetic activity were assessed and compared with those of the original bone tissue. The Kruskal-Wallis test was applied for between-group com Asignificance level of a=0.05 was considered.

RESULTS

The PLGA/PO2/SiO2 membranes achieved the significantly highest new bone formation, length of mineralised bone, concentration of osteoclasts, and ostheosynthetic activity. The percentage of regenerated bone supplied by the new membranes was similar to that of the original bone tissue. Unlike what happened in the control group, PLGA/PO2/SiO2 membranes predominantly showed bone layers in advanced stages of formation.

CONCLUSIONS

The addition of SiO2 layers to PLGA membranes pre-treated with PO2 improves their bone-regeneration potential. Although further research is necessary to corroborate these conclusions in humans, this could be a promising strategy to rebuild the bone architecture prior to rehabilitate edentulous areas.

Effects of HAp and TCP in constructing tissue engineering scaffolds for bone repair

TCP possesses superior long-term effects in structuring tissue engineering scaffold for bone repair compared to HAp, though TCP lags behind HAp in the early repair period.

Enhanced proliferation and osteogenic differentiation of MC3T3-E1 pre-osteoblasts on graphene oxide-impregnated PLGA–gelatin nanocomposite fibrous membranes

Currently, combining biodegradable polymeric scaffolds with living cells for bone repair has received significant attention.

A Review of Injectable Polymeric Hydrogel Systems for Application in Bone Tissue Engineering

Biodegradable, stimuli-responsive polymers are essential platforms in the field of drug delivery and injectable biomaterials for application of bone tissue engineering. Various thermo-responsive hydrogels display water-based homogenous properties to encapsulate, manipulate and transfer its contents to the surrounding tissue, in the least invasive manner. The success of bioengineered injectable tissue modified delivery systems depends significantly on their chemical, physical and biological properties. Irrespective of shape and defect geometry, injectable therapy has an unparalleled advantage in which intricate therapy sites can be effortlessly targeted with minimally invasive procedures. Using material testing, it was found that properties of stimuli-responsive hydrogel systems enhance cellular responses and cell distribution at any site prior to the transitional phase leading to gelation. The substantially hydrated nature allows significant simulation of the extracellular matrix (ECM), due to its similar structural properties. Significant current research strategies have been identified and reported to date by various institutions, with particular attention to thermo-responsive hydrogel delivery systems, and their pertinent focus for bone tissue engineering. Research on future perspective studies which have been proposed for evaluation, have also been reported in this review, directing considerable attention to the modification of delivering natural and synthetic polymers, to improve their biocompatibility and mechanical properties.

Characterization and Bioactivity Evaluation of (Polyetheretherketone/Polyglycolicacid)-Hydroyapatite Scaffolds for Tissue Regeneration

Bioactivity and biocompatibility are crucial for tissue engineering scaffolds. In this study, hydroxyapatite (HAP) was incorporated into polyetheretherketone/polyglycolicacid (PEEK/PGA) hybrid to improve its biological properties, and the composite scaffolds were developed via selective laser sintering (SLS). The effects of HAP on physical and chemical properties of the composite scaffolds were investigated. The results demonstrated that HAP particles were distributed evenly in PEEK/PGA matrix when its content was no more than 10 wt %. Furthermore, the apatite-forming ability became better with increasing HAP content after immersing in simulated body fluid (SBF). Meanwhile, the composite scaffolds presented a greater degree of cell attachment and proliferation than PEEK/PGA scaffolds. These results highlighted the potential of (PEEK/PGA)-HAP scaffolds for tissue regeneration.

In vivo comparative model of oxygen plasma and nanocomposite particles on PLGA membranes for guided bone regeneration processes to be applied in pre-prosthetic surgery: a pilot study

OBJECTIVES

To evaluate the bone regeneration potential of a new membrane fabricated with polyglycolide acid (PLGA) after being treated with oxygen plasma (PO2), and/or being functionalized with silicon dioxide (SiO2) or titanium dioxide (TiO2) nanoparticles.

METHODS

Bone defects (5 mm 3 mm) were produced on the top of 3 experimentation rabbits’ skulls and were covered with variously modified PLGA scaffolds. After the animals were sacrificed, neoformed bone (%), mineralized bone (mm), bone resorption (%), osteoclasts/mm2, and intensity of osteosynthetic activity, were assessed under microscope.

RESULTS

The following groups were formed depending on the type of membrane: PLGA (control); PLGA/PO2; PLGA/SiO2; PLGA/TiO2; PLGA/PO2/SiO2; and PLGA/PO2/TiO2. The histological sections showed bone layers in advanced stages of formation. The highest percentages of neoformed bone corresponded to PLGA/PO2/SiO2 membranes (59.07%; p = 0.31) followed by PLGA/PO2 barriers (50.27%). The controls showed the lowest mineralization (13.89 mm; p = 0.24). PLGA/TiO2 scaffolds exhibited the least bone resorption (4.45%; p = 0.77) and osteoclasts/ mm2 (1.58; p = 0.86). PLGA/SiO2 and PLGA/TiO2 membranes stimulated the maximum osteosynthetic activity.

CONCLUSIONS

The treatment of PLGA barriers with PO2 increased bone regeneration in rabbits. When comparing the effect of PO2/SiO2 and PO2/TiO2, higher percentages of neoformed bone were encountered after silicon-dioxide coating.

CLINICAL SIGNIFICANCE

The incorporation of SiO2 nanoparticles onto PO2-treated PLGA membranes was the most promising technique out of those investigated to promote bone formation in rabbits. The addition of SiO2 or TiO2 layers to PLGA substrates may stimulate the osteosynthetic activity, which might be useful to restore bone dimensions in preparation for naturally appearing dental prostheses.

The effects of lactate and acid on articular chondrocytes function: Implications for polymeric cartilage scaffold design

Poly (lactic-co-glycolic acid) (PLGA) and poly-l-lactate acid (PLLA) are biodegradable polymers widely utilized as scaffold materials for cartilage tissue engineering. Their acid degradation products have been widely recognized as being detrimental to cell function. However, the biological effects of lactate, rather than lactic acid, on chondrocytes have never been investigated. This is the major focus of this study. The amounts of lactate and the pH value (acid) of the PLGA and PLLA degradation medium were measured. The effects of PLGA and PLLA degradation medium, as well as different lactate concentrations and timing of exposure on chondrocytes proliferation and cartilage-specific matrix synthesis were investigated by various techniques including global gene expression profiling and gene knockdown experiments. It was shown that PLGA and PLLA degradation medium differentially regulated chondrocyte proliferation and matrix synthesis. Acidic pH caused by lactate inhibited chondrocyte proliferation and matrix synthesis. The effect of lactate on chondrocyte matrix synthesis was both time and dose dependent. A lactate concentration of 100mM and exposure duration of 8h significantly enhanced matrix synthesis. Lactate could also inhibit expression of cartilage matrix degradation genes in osteoarthritic chondrocytes, such as the major aggrecanase ADAMTS5, whilst promoting matrix synthesis simultaneously. Pulsed addition of lactate was shown to be more efficient in promoting COL2A1 expression. Global gene expression data and gene knock down experiments demonstrated that lactate promote matrix synthesis through up-regulation of HIF1A. These observed differential biological effects of lactate on chondrocytes would have implications for the future design of polymeric cartilage scaffolds.

STATEMENT OF SIGNIFICANCE

Lactic acid is a widely used substrate for polymers synthesis, PLGA and PLLA in particular. Although physical and biological modifications have been made on these polymers to make them be better cartilage scaffolds, little concern has been given on the biological effect of lactic acid, the main degradation product of these polymers, on chondrocytes. Our finding illustrates the differential biological function of lactate and acid on chondrocytes matrix synthesis. These results can facilitate future design of lactate polymers-based cartilage scaffolds.

In vitro investigation of nanohydroxyapatite/poly(L-lactic acid) spindle composites used for bone tissue engineering

Calcium phosphate ceramics such as synthetic hydroxyapatite and tricalcium phosphate are widely used in the clinic, but they stimulate less bone regeneration. In this paper, nano-hydroxyapatite/poly(L-lactic acid) (nano-HA/PLLA) spindle composites with good mechanical performance were fabricated by a modified in situ precipitation method. The HA part of composite, distributing homogenously in PLLA matrix, is spindle shape with size of 10-30 nm in diameter and 60-100 nm in length. The molar ratio of Ca/P in the synthesized nano-HA spindles was deduced as 1.52 from the EDS spectra, which is close to the stoichiometric composition of HA (Ca/P & 1.67). The compress strength is up to 150 MPa when the HA content increase to 20 %. The in vitro tests indicate that HA/PLLA bio-composites have good biodegradability and bioactivity when immersed in simulated body fluid solutions. All the results suggested that HA/PLLA nano-biocomposites are appropriate to be applied as bone substitute in bone tissue engineering.

HAp incorporated ultrafine polymeric fibers with shape memory effect for potential use in bone screw hole healing

In the clinical setting of bone fracture healing, hardware removal often causes localized microtrauma and residual screw holes may act as stress risers to place the patient at a risk of refracture. To address this noted issue, this study proposed to develop a biologically mimicking and mechanically self-actuated nanofibrous screw-like scaffold/implant for potential in situ bone regeneration. By incorporating nano-hydroxyapatite (HAp) into a shape memory copolymer poly(d,l-lactide-co-trimethylene carbonate) (PLMC) via co-electrospinning, composite nanofibers of HAp/PLMC with various HAp proportions (1, 2 and 3 wt%) were successfully generated. Morphological, thermal and mechanical properties as well as the shape memory effect of the resultant HAp/PLMC nanofibers were characterized using a variety of techniques. Thereafter, osteoblasts isolated from rat calvarial were cultured on the fibrous HAp/PLMC scaffold to assess its suitability for bone regeneration in vitro. We found that agglomerates gradually appeared on the fiber surface with increasing HAp loading fraction. The switching temperature for actuating shape recovery T_s (i.e., glass transition temperature T_g) of the fibrous HAp/PLMC was readily modulated to fall between 43.5 and 51.3 °C by varying the HAp loadings. Excellent shape memory properties were achieved for the HAp/PLMC composite nanofibers with a shape recovery ratio of R_r > 99% and shape fixity ratio of R_f > 99%, and the shape recovery force of the HAp/PLMC nanofibers was also strengthened compared to that of the HAp-free PLMC nanofibers. Moreover, we demonstrated that the engineered screw-like HAp/PLMC scaffold/implant (ϕ = 5 mm) was able to return from a slender bar to its original stumpy shape in a time frame of merely 8 s at 48 °C. Biological assay results corroborated that the incorporation of HAp to PLMC nanofibers significantly enhanced the alkaline phosphatase secretion as well as mineral deposition in bone formation. These attractive results warrant further investigation in vivo on the feasibility of applying the biomimicking nanofibrous HAp/PLMC scaffold with shape memory effect for bone screw hole healing.

Osteogenic Differentiation and Mineralization on Compact Multilayer nHA-PCL Electrospun Scaffolds in a Perfusion Bioreactor

BACKGROUND

Monolayer electrospun scaffolds have already been used in bone tissue engineering due to their high surface-tovolume ratio, interconnectivity, similarity to natural bone extracellular matrix (ECM), and simple production.

OBJECTIVES

The aim of this study was to evaluate the dynamic culture effect on osteogenic differentiation and mineralizationi into a compact cellular multilayer nHA-PCL electrospun construct. The dynamic culture was compared with static culture.

MATERIALS AND METHODS

The calcium content, alkaline phosphatase (ALP) activity and cell viability were investigated on days 3 and 7.

RESULTS

When the dynamic culture compared to static culture, the mineralization and ALP activity were increased in dynamic culture. After 7 days, calcium contents were 41.24 and 20.44 μg.(cm³)^-1, and also normalized ALP activity were 0.32 and 0.19 U.mg^-1 in dynamic and static culture, respectively. Despite decreasing the cell viability until day 7, the scanning electron microscopy (SEM) results showed that, due to higher mineralization, a larger area of the construct was covered with calcium deposition in dynamic culture.

CONCLUSIONS

The dynamic flow could improve ALP activity and mineralization into the compact cellular multilayer construct cultured in the perfusion bioreactor after 7 days. Fluid flow of media helped to facilitate the nutrients transportation into the construct and created uniform cellular construct with high mineralization. This construct can be applied for bone tissue engineering.

The influence of anisotropic nano- to micro-topography on in vitro and in vivo osteogenesis

AIM

Topographically modified substrates are increasingly used in tissue engineering to enhance biomimicry. The overarching hypothesis is that topographical cues will control cellular response at the cell-substrate interface.

MATERIALS & METHODS

The influence of anisotropically ordered poly(lactic-co-glycolic acid) substrates (constant groove width of ~1860 nm; constant line width of ~2220 nm; variable groove depth of ~35, 306 and 2046 nm) on in vitro and in vivo osteogenesis were assessed.

RESULTS & DISCUSSION

We demonstrate that substrates with groove depths of approximately 306 and 2046 nm promote osteoblast alignment parallel to underlined topography in vitro. However, none of the topographies assessed promoted directional osteogenesis in vivo.

CONCLUSION

2D imprinting technologies are useful tools for in vitro cell phenotype maintenance.