Bone graft substitutes

In Vivo Analysis of Porous Bioactive Silicon Carbide Scaffold for Craniofacial Bone Augmentation

BACKGROUND

Bone augmentation is a vital area of research because of its high clinical demand and the reported complications associated with the available biomaterials. Purpose: The study assess the role of decellurized skeletal muscle (DSM) when combined with synthesized porous bioactive silicon carbide (SiC) ceramic and evaluated its ability to augment bone calvaria in a rat model.

MATERIAL AND METHODS

Eighteen rats were divided into 2 groups; group 1 (n=9), SiC discs (10 × 0.2 mm) pre-treated with 20% NaOH were placed as an onlay grafts on calvarial bone. Meanwhile, in group 2 (n=9), SiC discs pre-treated with 20% NaOH (10 × 0.2 mm) were covered with DSM. After 12 weeks, the grafted tissues were harvested and examined using cone-beam computed tomography, mechanical testing, and histologic analysis.

RESULTS

Cone-beam computed tomography for group 2 showed more radio-opacity for the remnant of SiC compared with native bone. The surface area and volume of radio-opacity were 2.48 mm2 ± 1.6 and 14.9 ± 7.8 mm3, respectively. The estimated quantitative average surface area of the radio-opacity for group 1 and volume were 2.55 mm2 ± (Sd=3.7) and 11.25 ± (Sd=8.9), respectively. Mechanically, comparable values of the flexural strength and statistically significant higher modulus of elasticity of calvaria in group 1 compared with group 2 and control (P<0.001). Histologically, group 2 region of woven bone was seen close to the lamellar bone (native bone), and there was immature bone present near the implanted SiC.

CONCLUSION

The tested construct made of SiC/DSM has potential to osteointegrate into native bone, making it a suitable material for bone augmentation.

An injectable porous bioactive magnesium phosphate bone-cement foamed with calcium carbonate and citric acid for periodontal bone regeneration

Magnesium phosphate cement (MPC) has been evaluated as a novel bone substitute owing to its favorable biocompatibility, plasticity, and osteogenic potential. However, the low porosity of MPC prevents growth factors and osteoblasts from fully growing into the material, thereby limiting its clinical use. In this study, different concentrations (0-5%) of calcium carbonate and citric acid (CA) were used as foaming agents to prepare porous MPC. The MPC containing 3% CaCO₃/CA exhibited the best physicochemical properties, including greater porosity, improved injectability, extended setting time, and decreased hydration temperature. The proliferation and adhesion of cells on 3%CaCO₃/CA-MPC were higher than those on MPC alone. To explore its osteogenesis in vivo, 3% CaCO₃/CA-MPC and Bio-Oss® bone powder were implanted into periodontal bone defects in rats for 4 weeks and 12 weeks, respectively. Micro-CT and histological analysis demonstrated the improved bone regeneration of 3%CaCO₃/CA-MPC compared to the blank group (P < 0.05); it had slightly lower bone regeneration than the Bio-Oss® group but no statistical difference. The results indicated that porous MPC foamed with calcium carbonate and CA improved its physicochemical properties and enhanced its biocompatibility, making it a promising material for bone regeneration.

Scaffolds and coatings for bone regeneration

Bone tissue has an astonishing self-healing capacity yet only for non-critical size defects (<6 mm) and clinical intervention is needed for critical-size defects and beyond that along with non-union bone fractures and bone defects larger than critical size represent a major healthcare problem. Autografts are, still, being used as preferred to treat large bone defects. Mostly, due to the presence of living differentiated and progenitor cells, its osteogenic, osteoinductive and osteoconductive properties that allow osteogenesis, vascularization, and provide structural support. Bone tissue engineering strategies have been proposed to overcome the limited supply of grafts. Complete and successful bone regeneration can be influenced by several factors namely: the age of the patient, health, gender and is expected that the ideal scaffold for bone regeneration combines factors such as bioactivity and osteoinductivity. The commercially available products have as their main function the replacement of bone. Moreover, scaffolds still present limitations including poor osteointegration and limited vascularization. The introduction of pores in scaffolds are being used to promote the osteointegration as it allows cell and vessel infiltration. Moreover, combinations with growth factors or coatings have been explored as they can improve the osteoconductive and osteoinductive properties of the scaffold. This review focuses on the bone defects treatments and on the research of scaffolds for bone regeneration. Moreover, it summarizes the latest progress in the development of coatings used in bone tissue engineering. Despite the interesting advances which include the development of hybrid scaffolds, there are still important challenges that need to be addressed in order to fasten translation of scaffolds into the clinical scenario. Finally, we must reflect on the main challenges for bone tissue regeneration. There is a need to achieve a proper mechanical properties to bear the load of movements; have a scaffolds with a structure that fit the bone anatomy.

Nanomedicine: is it lost in translation?

By the end of 2017 more than 200,000 scientific research articles had been published about nanomedicine. Out of this vast number only a few of the reported nanoconstructs reached clinical trials for various applications, including the diagnosis and treatment of several cancers, and the treatment of infections and other non-cancerous diseases. 30 years after the pioneering work in this field of research, the low product yield at the end of research pipeline leads to a question that is asked by many: 'had nanomedicine been lost in translation?' In this review, we will discuss the landscape of nanomedicine regarding cancer treatment and miscellaneous applications as well as some obstacles toward full utilization of this powerful therapeutic tool and suggest a few solutions to improve the current translational value of nanomedicine research.

Cell Colonization Ability of a Commercialized Large Porous Alveolar Scaffold

The use of filling biomaterials or tissue-engineered large bone implant-coupling biocompatible materials and human bone marrow mesenchymal stromal cells seems to be a promising approach to treat critical-sized bone defects. However, the cellular seeding onto and into large porous scaffolds still remains challenging since this process highly depends on the porous microstructure. Indeed, the cells may mainly colonize the periphery of the scaffold, leaving its volume almost free of cells. In this study, we carry out an in vitro study to analyze the ability of a commercialized scaffold to be in vivo colonized by cells. We investigate the influence of various physical parameters on the seeding efficiency of a perfusion seeding protocol using large manufactured bone substitutes. The present study shows that the velocity of the perfusion fluid and the initial cell density seem to impact the seeding results and to have a negative effect on the cellular viability, whereas the duration of the fluid perfusion and the nature of the flow (steady versus pulsed) did not show any influence on either the fraction of seeded cells or the cellular viability rate. However, the cellular repartition after seeding remains highly heterogeneous.

Simple and economic elaboration of high purity CaCO3 particles for bone graft applications using a spray pyrolysis technique

CaCO₃ particles obtained using spray pyrolysis possess all the requirements to constitute promising multi-purpose materials for bone graft applications.

Composite ECM-alginate microfibers produced by microfluidics as scaffolds with biomineralization potential

A novel approach to produce artificial bone composites (microfibers) with distinctive features mimicking natural tissue was investigated. Currently proposed inorganic materials (e.g. apatite matrixes) lack self-assembly and thereby limit interactions between cells and the material. The present work investigates the feasibility of creating "bio-inspired materials" specifically designed to overcome certain limitations inherent to current biomaterials. We examined the dimensions, morphology, and constitutive features of a composite hydrogel which combined an alginate based microfiber with a gelatin solution or a particulate form of urinary bladder matrix (UBM). The effectiveness of the composite microfibers to induce and modulate osteoblastic differentiation in three-dimensional (3D) scaffolds without altering the viability and morphological characteristics of the cells was investigated. The present study describes a novel alginate microfiber production method with the use of microfluidics. The microfluidic procedure allowed for precise tuning of microfibers which resulted in enhanced viability and function of embedded cells.

A mild one-pot process for synthesising hydroxyapatite/biomolecule bone scaffolds for sustained and controlled antibiotic release

The release of active molecules or the control of nosocomial infections for improved osteoinduction is ideally addressed by a bone substitute material. For this purpose, the feasibility of a mild one-pot process is probed for incorporating directly active proteins and antibiotics in a hydroxyapatite (HAp) based scaffold. The effect of two serum model proteins, bovine serum albumin (BSA) and fibrinogen (FIB), on the microstructure, on selected mechanical properties as well as on degradation behaviour and on protein release are investigated. By protein incorporation, the porosity can be adjusted between 54 and 70% especially due to the foaming ability of BSA. The addition of 5 wt% FIB doubles the biaxial flexural strength up to 6 MPa in comparison to samples without proteins (3 MPa). Protein release experiments show that a rapid release takes place within the first days (between around 3% for FIB and 38% for BSA). As a possible application for osteomyelitis treatment, vancomycin and gentamicin were subsequently added instead of proteins to study their release behaviour and their antibacterial activity, respectively. A controlled antibiotic release was observed for a period of 18 d. By varying the protein type, mixture and quantity, the mechanical strength porosity as well as the protein release and calcium solubility can be controlled. Our studies underpin the suitability of this mild one-pot process as a promising simple-to-use platform for controlled local drug release and bone treatment.

Osteoblastic differentiation under controlled bioactive ion release by silica and titania doped sodium-free calcium phosphate-based glass

Sodium-free phosphate-based glasses (PGs) doped with both SiO2 and TiO2 (50P2O5-40CaO-xSiO2-(10-x)TiO2, where x=10, 7, 5, 3, and 0mol%) were developed and characterised for controlled ion release applications in bone tissue engineering. Substituting SiO2 with TiO2 directly increased PG density and glass transition temperature, indicating a cross-linking effect of Ti on the glass network which was reflected by significantly reduced degradation rates in an aqueous environment. X-ray diffraction confirmed the presence of Ti(P2O7) in crystallised TiO2-containing PGs, and nuclear magnetic resonance showed an increase in Q(1) phosphate species with increasing TiO2 content. Substitution of SiO2 with TiO2 also reduced hydrophilicity and surface energy. In biological assays, MC3T3-E1 pre-osteoblasts effectively adhered to the surface of PG discs and the incorporation of TiO2, and hence higher stability of the PG network, significantly increased cell viability and metabolic activity indicating the biocompatibility of the PGs. Addition of SiO2 increased ionic release from the PG, which stimulated alkaline phosphatase (ALP) activity in MC3T3-E1 cells upon ion exposure. The incorporation of 3mol% TiO2 was required to stabilise the PG network against unfavourable rapid degradation in aqueous environments. However, ALP activity was greatest in PGs doped with 5-7mol% SiO2 due to up-regulation of ionic concentrations. Thus, the properties of PGs can be readily controlled by modifying the extent of Si and Ti doping in order to optimise ion release and osteoblastic differentiation for bone tissue engineering applications.

β-TCP-polylactide composite scaffolds with high strength and enhanced permeability prepared by a modified salt leaching method

A modified particulate leaching method for fabrication of strong calcium phosphate-polymer composite scaffolds with improved pore interconnectivity is reported. The scaffolds were produced by mixing precompacted composite granules (β-TCP with 40vol% PLA) of different size and density with salt particles followed by high pressure consolidation (at room temperature or 120°C) and porogen dissolution. The scaffolds' compressive strength and Darcy's permeability were found to be inversely related and to be strongly dependent on the processing parameters. The use of precompacted granules instead of the loose β-TCP-PLA powder allowed us to increase permeability by three orders of magnitude while maintaining load bearing characteristics. Scaffolds with 50% porosity prepared from large (300-420μm) composite granules of β-TCP-40vol% PLA and salt porogen particles of comparable size exhibited the best combination of compressive strength (4-6MPa) and permeability (1.3-1.6×10(-10)m(2)) falling within the range of trabecular bone.

Osteogenic effect of low-temperature-heated porcine bone particles in a rat calvarial defect model

The current study was designed to investigate the chemical and physical properties of porcine-derived xenografts of different crystallinity (low and high) and to evaluate their osteogenic potential. Porcine femur bone underwent a heat treatment process at 400°C (P400) and 1200°C (P1200) and was then milled into particles of 1 mm or less. In X-ray diffraction, P400 exhibited a low crystallinity compared with that of P1200, as indicated by the relatively wide diffraction peaks. Brunauer-Emmett-Teller analysis revealed that P400 also had a wider surface area than P1200. In micro-CT scan analysis of specimens in a rat calvarial defect model, bone mineral density of the P400 group was significantly higher than that of the P1200 group (p < 0.01). New bone formation was also remarkably higher at 8 weeks in the P400 group, which showed more new osteocytes in the lacuna compared with the P1200 group. In this study, low crystalline bone particles were obtained at low processing temperature (at temperature of 400°C) and achieved superior new bone formation compared with the high crystalline bone particles created at a higher process temperature (1200°C). It can be concluded that lower process temperature bone particles might provide a more effective graft material for enhancing bone formation. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 102A: 3609-3617, 2014.

In Situ Tooth Replica Custom Implant: A 3-Dimensional Finite Element Stress and Strain Analysis

This study is a phase of a biomechanical study, a part of a research program concerned with the new concept of in situ tooth replication. The purpose of the study was to evaluate tooth replica under each of two possible circumstances: (1) attachment via periodontal ligament and (2) osseointegration. Replicas were made of Cortoss, a bioactive glass, bone substitute. Three-dimensional finite element analysis was used to assess the stresses and strains resulting from each of 2 types of loads: off-vertical pressure and vertical point force acting on natural mandibular second premolar and corresponding replicas. Natural tooth tolerated 19 MPa pressure or 85 N vertical force, periodontally attached replica tolerated 15 MPa pressure or 80 N force, and osseointegrated replica tolerated 23 MPa pressure or 217 N force.

Bioactive glass incorporation in calcium phosphate cement-based injectable bone substitute for improved in vitro biocompatibility and in vivo bone regeneration

In this work, we fabricated injectable bone substitutes modified with the addition of bioactive glass powders synthesized via ultrasonic energy-assisted hydrothermal method to the calcium phosphate-based bone cement to improve its biocompatibility. The injectable bone substitutes was initially composed of a powder component (tetracalcium phosphate, dicalcium phosphate dihydrate and calcium sulfate dehydrate) and a liquid component (citric acid, chitosan and hydroxyl-propyl-methyl-cellulose) upon which various concentrations of bioactive glass were added: 0%, 10%, 20% and 30%. Setting time and compressive strength of the injectable bone substitutes were evaluated and observed to improve with the increase of bioactive glass content. Surface morphologies were observed via scanning electron microscope before and after submersion of the samples to simulated body fluid and increase in apatite formation was detected using x-ray diffraction machine. In vitro biocompatibility of the injectable bone substitutes was observed to improve with the addition of bioactive glass as the proliferation/adhesion behavior of cells on the material increased. Human gene markers were successfully expressed using real time-polymerase chain reaction and the samples were found to promote cell viability and be more biocompatible as the concentration of bioactive glass increases. In vivo biocompatibility of the samples containing 0% and 30% bioactive glass were evaluated using Micro-CT and histological staining after 3 months of implantation in male rabbits’ femurs. No inflammatory reaction was observed and significant bone formation was promoted by the addition of bioactive glass to the injectable bone substitute system.

Mimicking the morphology of long bone

The aim of this work was to mimic the stratified structure of the median region of long bones. Starting from this desideratum, more COLL/HA composite materials with different morphology were synthesized and characterized, each of these materials mimicking one layer of long bone (endo- and periosteum, compact and cancellous bony tissue). Stratified bone grafts were obtained by assembling these layers; the obtained grafts were similar to the median region of long bones. Even though, natural bones have a more complex microstructure, this is a pioneering work since for the first time a stratified COLL/HA composite material similar to bone was produced.

Desenvolvimento e caracterização de membranas rígidas, osteocondutoras e reabsorvíveis de polihidroxibutirato e hidroxiapatita para regeneração periodontal

A regeneração tecidual guiada (RTG) utiliza membranas para favorecer a regeneração dos tecidos periodontais danificados pela doença periodontal. As membranas usadas ainda apresentam limitações, principalmente quanto à capacidade de manter o espaço do defeito. Dois biomateriais de origem brasileira, a hidroxiapatita (HAP) e o polihidroxibutirato (PHB), foram utilizados para fabricar membranas rígidas para RTG, contendo 25, 35 ou 50% de HAP em matriz de PHB pelo método de moldagem por injeção. As membranas apresentaram alta cristalinidade, sendo que, inicialmente, a topografia de superfície era pouco complexa em que os grânulos de HAP não estavam expostos. As membranas foram desgastadas com broca odontológica, de modo similar à cirurgia para sua implantação in vivo. Este procedimento resultou na exposição dos grânulos de HAP numa superfície com poros e estruturas lineares de dimensões que variaram de 3,55 µm ± 1,14 a 75,98 µm ± 30,76, portanto, característica microtopográfica. Observou-se, ainda, que a HAP é responsável por conferir uma topografia de superfície mais complexa às membranas. Portanto, espera-se que membranas com as características de rigidez e superfície microtopográfica possam proporcionar estabilidade ao defeito periodontal e permitir migração celular mais intensa, assim favorecendo a regeneração periodontal.

An evaluation of the processing conditions, structure, and properties (biaxial flexural strength and antibacterial efficacy) of sintered strontium–zinc–silicate glass ceramics

The use of artificial bone grafts has increased in order to satisfy a growing demand for bone replacement materials. Initial mechanical stability of synthetic bone grafts is very advantageous for certain clinical applications. Coupled with the advantage of mechanical strength, a material with inherent antibacterial properties would be very beneficial. A series of strontium-doped zinc silicate (Ca–Sr–Na–Zn–Si) glass ceramics have been characterized in terms of their crystalline structure, biaxial flexural strength and antibacterial efficacy based on the identification of optimum sintering conditions. All three glass ceramics, namely, BT110, BT111, and BT112 were found to be fully crystalline, with BT111 and BT112 comprising of biocompatible crystalline phases. The biaxial flexural strengths of the three glass ceramics ranged from 70 to 149 MPa and were shown to be superior to those of clinically established ceramics in dry conditions and following incubation in simulated physiological conditions. The bacteriostatic effect for each glass ceramic was also established, where BT112 showed an inhibitory effect against three of the most common bacteria found at implantation sites, namely, Enterococcus faecalis, methicillin-resistant Staphylococcus aureus (MRSA), and Pseudomonas aeruginosa. The results of the evaluation suggest that the materials studied offer advantages over current clinical materials and indicate the potential suitability of the glass ceramics as therapeutic bone grafts.

Fabrication and characterization of hierarchically organized nanoparticle-reinforced nanofibrous composite scaffolds

Two different techniques were used to fabricate nanoparticle-reinforced nanofibrous scaffolds with different organizations of the minerals. First, a three-dimensional (3D) cylindrical nanofibrous scaffold made of poly-L-lactide and poly(L-lactide)/collagen (1:1) was fabricated using a modified electrospinning method. An alternating dipping method and a flow version of it were used to mineralize the 3D scaffolds. Flow mineralization was found to significantly improve the distribution of the mineral nanoparticles throughout the 3D nanofibrous scaffold, while mineral nanoparticles were found only on the periphery of the static mineralized scaffold. As a result of the mineral nanoparticle distribution, the compressive strength and modulus of the flow mineralized scaffold was found to be significantly greater than that of the static mineralized scaffold, despite having a lower mineral content. Energy-dispersive X-ray analysis and X-ray diffraction studies suggest that the mineral was composed of heterogeneous phases of calcium phosphates. This study demonstrates the importance of hierarchical and deliberate organization of the nanocomponents to optimize the mechanical properties, as is often found in nature.

In Situ Tooth Replica Custom Implant: Rationale, Material, and Technique

This study introduced a new concept of an in situ, custom-made, tooth replica dental implant. It was obtained by injecting a self-set, nonresorbable polymer type bone graft substitute into the tooth socket after extraction. Based on its cited properties, new composite bone cement Cortoss was suggested. The properties were reviewed and evaluated. The technique of application was described with a simulation model presented that appeared simple. Apparently, immediate duplication of tooth anatomy was achieved; thus, the concept might have the potentials of spontaneous adaptation and stabilization, preservation of alveolar bone, increasing implant-bone surface area, better load distribution, and bone stimulation. Modifications were also described to manage cases of resorbed alveolar bone as well as long-standing extracted teeth. Investigations were still required to assess the performance of the material and if modifications would be needed.

Chitosan-poly(lactide-co-glycolide) microsphere-based scaffolds for bone tissue engineering: in vitro degradation and in vivo bone regeneration studies

Natural polymer chitosan and synthetic polymer poly(lactide-co-glycolide) (PLAGA) have been investigated for a variety of tissue engineering applications. We have previously reported the fabrication and in vitro evaluation of a novel chitosan/PLAGA sintered microsphere scaffold for load-bearing bone tissue engineering applications. In this study, the in vitro degradation characteristics of the chitosan/PLAGA scaffold and the in vivo bone formation capacity of the chitosan/PLAGA-based scaffolds in a rabbit ulnar critical-sized-defect model were investigated. The chitosan/PLAGA scaffold showed slower degradation than the PLAGA scaffold in vitro. Although chitosan/PLAGA scaffold showed a gradual decrease in compressive properties during the 12-week degradation period, the compressive strength and compressive modulus remained in the range of human trabecular bone. Chitosan/PLAGA-based scaffolds were able to guide bone formation in a rabbit ulnar critical-sized-defect model. Microcomputed tomography analysis demonstrated that successful bridging of the critical-sized defect on the sides both adjacent to and away from the radius occurred using chitosan/PLAGA-based scaffolds. Immobilization of heparin and recombinant human bone morphogenetic protein-2 on the chitosan/PLAGA scaffold surface promoted early bone formation as evidenced by complete bridging of the defect along the radius and significantly enhanced mechanical properties when compared to the chitosan/PLAGA scaffold. Furthermore, histological analysis suggested that chitosan/PLAGA-based scaffolds supported normal bone formation via intramembranous formation.

Biological therapy of bone defects: the immunology of bone allo-transplantation

IMPORTANCE OF THE FIELD

Bone is one of the most transplanted tissues worldwide. Autograft is the ideal bone graft but is not widely used because of donor site morbidity and restricted availability. Allograft is easily accessible but can transmit infections and elicit an immune response.

AREAS COVERED IN THIS REVIEW

This review identifies all in vitro and in vivo evidence of immune responses following bone transplantation and highlights methods of improving host tolerance to bone allotransplantation.

WHAT THE READER WILL GAIN

In humans, the presence of anti-HLA specific antibodies against freeze-dried and fresh-frozen bone allografts has been demonstrated. Fresh-frozen bone allograft can still generate immune reactions whilst freeze-dried bone allografts present with less immunogenicity but have less structural integrity. This immune response can have an adverse effect on the graft's incorporation and increase the incidence of rejection. Decreasing the immune reaction against the allograft by lowering the immunogenic load of the graft or lowering the host immune response, would result in improved bone incorporation.

TAKE HOME MESSAGE

It is essential that the complex biological processes related to bone immunogenicity are understood, since this may allow the development of safer and more successful ways of controlling the outcome of bone allografting.

Preliminary investigation of novel bone graft substitutes based on strontium-calcium-zinc-silicate glasses

Bone graft procedures typically require surgeons to harvest bone from a second site on a given patient (Autograft) before repairing a bone defect. However, this results in increased surgical time, excessive blood loss and a significant increase in pain. In this context a synthetic bone graft with excellent histocompatibility, built in antibacterial efficacy and the ability to regenerate healthy tissue in place of diseased tissue would be a significant step forward relative to current state of the art philosophies. We developed a range of calcium-strontium-zinc-silicate glass based bone grafts and characterised their structure and physical properties, then evaluated their in vitro cytotoxicity and in vivo biocompatibility using standardised models from the literature. A graft (designated BT109) of composition 0.28SrO/0.32ZnO/0.40 SiO(2) (mol fraction) was the best performing formulation in vitro shown to induce extremely mild cytopathic effects (cell viability up to 95%) in comparison with the commercially available bone graft Novabone (cell viability of up to 72%). Supplementary to this, the grafts were examined using the standard rat femur healing model on healthy Wister rats. All grafts were shown to be equally well tolerated in bone tissue and new bone was seen in close apposition to implanted particles with no evidence of an inflammatory response within bone. Complimentary to this BT109 was implanted into the femurs of ovariectomized rats to monitor the response of osteoporotic tissue to the bone grafts. The results from this experiment indicate that the novel grafts perform equally well in osteoporotic tissue as in healthy tissue, which is encouraging given that bone response to implants is usually diminished in ovariectomized rats. In conclusion these materials exhibit significant potential as synthetic bone grafts to warrant further investigation and optimisation.

Comparison of in vitro and in vivo Bioactivity of SrO—CaO—ZnO—SiO2 Glass Grafts

A range of calcium—strontium—zinc—silicate glass grafts are developed. Following characterization, their ability to form an apatite layer in simulated body fluid (SBF) is evaluated. Concurrently, their in vivo biocompatibility is determined. These glasses are incapable of forming an apatite layer in SBF. However, in vivo, each glass is well tolerated with new bone formation apparent in close apposition to implanted particles and no evidence of an inflammatory response. Such results are contrary to much of the literature and indicate that forecasting a materials ability to bond to bone based on SBF experiments may provide a false negative result.

Effect of increasing titanium dioxide content on bulk and surface properties of phosphate-based glasses

There is an ingoing need for more effective and less costly bone substitute materials. In a previous study, addition of titanium dioxide (TiO2) up to 5 mol.% was shown to be effective in controlling glass degradation, and this was reflected in enhanced gene expression and bone-forming capacity of phosphate-based glasses. In the current study, incorporation of the maximum possible amount of TiO2 has been attempted in order to further improve the biological response of these glasses. This report describes the physical, surface properties and short-term response of an osteoblast cell line (MG63) on phosphate glasses doped with the maximum possible TiO2 content. The results showed that a maximum of 15 mol.% TiO2 can be incorporated into the ternary formulations while maintaining their amorphous nature; such incorporation was associated with a significant increase in density and glass transition temperature. On crystallization, X-ray diffraction analysis showed the presence of TiP2O7 and NaCa(PO3)3 as the main phases for all TiO2-containing glasses, while beta-(CaP2O6) was only detected for 10 and 15 mol.% TiO2 glasses. The degradation rate, however, was significantly reduced by an order of magnitude with incorporation of 10 and 15 mol.% TiO2, and this was reflected in the released ions. This change in the bulk properties, produced with TiO2 incorporation, was also associated with a significant change in the hydrophilicity and surface reactivity of these glasses. Even though the addition of TiO2 reduced the hydrophilicity and the surface free energy of these glasses compared to TiO2 free composition, TiO2-containing glasses still have a significantly reactive surface layer compared to Thermanox. Generally glasses with 5-15 mol.% TiO2 supported MG63 cell growth and maintained high cell viability for up to 7 days culture, which is comparable to Thermanox. Based on the results obtained from this study, TiO2-containing phosphate glasses are promising substrates for bone tissue engineering applications.

Effect of surface modification of polymer beads on the mechanical properties of acrylic bone cement

The effect of surface modification of polymer filler on the static mechanical properties of acrylic bone cement was studied. The surface of polymer beads was modified with carboxylic and amino groups by photochemical reaction with azide compounds. Monomer modifiers (maleic anhydride, methacrylic acid and p-aminostyrene) are attached to the functionalized surface of polymer beads. Functional allyl groups, which are capable of the graft polymerisation reaction, are attached to the surface via photochemical reaction with N-(2-nitro-4-azidophenyl)-N-(-propen) amine. This approach to bone cement provides the additional covalent bonds between the polymer beads and the inter-bead matrix. The static mechanical properties of bone cements containing modified polymer beads were investigated and compared with the static mechanical properties of unmodified cements. The absolute values of compressive strength for the modified and unmodified cements were found to be similar. An increase in flexural strength for the modified cements (dry and after water storage) was observed. The structure of the surface functional groups affects the methyl methacrylate grafting resulting in a higher value of flexural strength for the maleic anhydride- and p-aminostyrene-modified cements. The scanning electron microscopy examination of the fracture surface of the cement samples showed an improvement of the adhesion between the beads and the matrix after modification.

Development of a new calcium sulphate-based composite using alginate and chemically modified chitosan for bone regeneration

In this work we developed a novel calcium sulphate-based composite in which the hemihydrate calcium sulphate (CHS) can be encapsulated in a polymeric biodegradable and biocompatible matrix, in order to retain the structural integrity and decrease the bioresorption rate in bone regeneration applications. Two polymers were employed to realize this system: chitosan (Ch) and sodium alginate (Alg), both already widely used in biotechnological and biomedical applications. Chitosan was modified in order to obtain a water soluble polymer, the N-succinylchitosan (sCh). The reaction was performed with succinic anhydride in presence of pyridine and confirmed by FT-IR and NMR analyses. Finely ground Alg and sCh powders were mixed in different compositions with CHS and by adding water to the powder mixture it was obtained a mouldable paste that sets in few hours. Thermogravimetric analyses coupled with solvent extraction performed on the composite proved the alginate crosslinking in the presence of CHS. Mechanical studies carried out on composites of different compositions demonstrated that the blend of the two polymeric components causes a substantial synergistic reinforcement of composites. The presence of carboxylic groups on sCh chain in addition to those of alginate could enhance the chelating power of polysaccharide mixture. The results obtained with morphological analyses (SEM) further confirmed the hypotesis of the synergistic effect between alginate and N-succinylchitosan in presence of calcium sulphate. In vitro cytotoxicity tests proved that the developed system was not cytotoxic.

A Novel Injectable Poly(ɛ-caprolactone)/Calcium Sulfate System for Bone Regeneration: Synthesis and Characterization

A novel poly(epsilon-caprolactone)/calcium sulfate system was prepared and characterized in order to enhance calcium sulfate (gypsum) performance as bone graft substitute overcoming its brittleness and fast resorption rate. A poly(epsilon-caprolactone) (PCL) photo-crosslinkable derivative (PCLf) was synthesized by reaction of a low molecular weight PCL diol with methacryloyl chloride and confirmed by FT-IR and 1H NMR analyses. An injectable and easy mouldable mixture of PCLf and calcium sulfate hemi-hydrate (PCLf/CHS) was obtained. Thermal analyses and solvent extraction proved the occurrence of PCLf photo-crosslinking, even in the presence of CHS, in a time suitable for clinical applications. Swelling studies demonstrated that the encapsulation of the inorganic filler increases network hydrophilicity making it more permeable to water. Scanning electron microscopy, performed on crosslinked PCLf/CHS and on the same material after incubation in a PBS solution, showed the feasibility to obtain, in situ, gypsum entrapped into a degradable polymeric network. In vitro cytotoxicity tests, performed according to ISO 10993-5, proved that the developed system was not cytotoxic supporting its potential use in tissue engineering as a new, injectable, photocurable bone graft material. SEM micrograph of calcium sulfate di-hydrate (gypsum) entrapped in the PCL network.

Biological Behaviour of Bonelike® Graft Implanted in the Tibia of Humans

This paper reports the ability of Bonelike® to regenerate bone defected areas when implanted in the tibia of 3 patients (average age of 59 years) during a high tibial osteotomy (HTO) to treat medial compartment osteoarthritis of the knee. Bonelike® is a synthetic bone graft designed to mimic the inorganic composition of bone using a patent process that consists of liquid sintering hydroxyapatite in the presence of CaO-P2O5 based glass. The preliminary clinical evaluation performed showed that an intimate contact between new formed bone and Bonelike® was established (67±10 %), with no fibrous interface. Therefore, Bonelike® is a single-handedly viable osteoconductive synthetic grafting material as it has been demonstrated from the profiles of radiological, histological and scanning electron microscopy analyses for the six months implantation period.