Effect of rapidly resorbable calcium phosphates and a calcium phosphate bone cement on the expression of bone-related genes and proteinsin vitro

Osteogenic Effect of a Bioactive Calcium Alkali Phosphate Bone Substitute in Humans

(1) Background: The desire to avoid autograft harvesting in implant dentistry has prompted an ever-increasing quest for bioceramic bone substitutes, which stimulate osteogenesis while resorbing in a timely fashion. Consequently, a highly bioactive silicon containing calcium alkali orthophosphate (Si-CAP) material was created, which previously was shown to induce greater bone cell maturation and bone neo-formation than β-tricalcium phosphate (β-TCP) in vivo as well as in vitro. Our study tested the hypothesis that the enhanced effect on bone cell function in vitro and in sheep in vivo would lead to more copious bone neoformation in patients following sinus floor augmentation (SFA) employing Si-CAP when compared to β-TCP. (2) Methods: The effects of Si-CAP on osteogenesis and Si-CAP resorbability were evaluated in biopsies harvested from 38 patients six months after SFA in comparison to β-TCP employing undecalcified histology, histomorphometry, and immunohistochemical analysis of osteogenic marker expression. (3) Results: Si-CAP as well as β-TCP supported matrix mineralization and bone formation. Apically furthest away from the original bone tissue, Si-CAP induced significantly higher bone formation, bone-bonding (bone-bioceramic contact), and granule resorption than β-TCP. This was in conjunction with a higher expression of osteogenic markers. (4) Conclusions: Si-CAP induced higher and more advanced bone formation and resorbability than β-TCP, while β-TCP's remarkable osteoconductivity has been widely demonstrated. Hence, Si-CAP constitutes a well-suited bioactive graft choice for SFA in the clinical arena.

A tissue engineered 3D printed calcium alkali phosphate bioceramic bone graft enables vascularization and regeneration of critical-size discontinuity bony defects in vivo

Introduction: Recently, efforts towards the development of patient-specific 3D printed scaffolds for bone tissue engineering from bioactive ceramics have continuously intensified. For reconstruction of segmental defects after subtotal mandibulectomy a suitable tissue engineered bioceramic bone graft needs to be endowed with homogenously distributed osteoblasts in order to mimic the advantageous features of vascularized autologous fibula grafts, which represent the standard of care, contain osteogenic cells and are transplanted with the respective blood vessel. Consequently, inducing vascularization early on is pivotal for bone tissue engineering. The current study explored an advanced bone tissue engineering approach combining an advanced 3D printing technique for bioactive resorbable ceramic scaffolds with a perfusion cell culture technique for pre-colonization with mesenchymal stem cells, and with an intrinsic angiogenesis technique for regenerating critical size, segmental discontinuity defects in vivo applying a rat model. To this end, the effect of differing Si-CAOP (silica containing calcium alkali orthophosphate) scaffold microarchitecture arising from 3D powder bed printing (RP) or the Schwarzwalder Somers (SSM) replica fabrication technique on vascularization and bone regeneration was analyzed in vivo. In 80 rats 6-mm segmental discontinuity defects were created in the left femur. Methods: Embryonic mesenchymal stem cells were cultured on RP and SSM scaffolds for 7d under perfusion to create Si-CAOP grafts with terminally differentiated osteoblasts and mineralizing bone matrix. These scaffolds were implanted into the segmental defects in combination with an arteriovenous bundle (AVB). Native scaffolds without cells or AVB served as controls. After 3 and 6 months, femurs were processed for angio-µCT or hard tissue histology, histomorphometric and immunohistochemical analysis of angiogenic and osteogenic marker expression. Results: At 3 and 6 months, defects reconstructed with RP scaffolds, cells and AVB displayed a statistically significant higher bone area fraction, blood vessel volume%, blood vessel surface/volume, blood vessel thickness, density and linear density than defects treated with the other scaffold configurations. Discussion: Taken together, this study demonstrated that the AVB technique is well suited for inducing adequate vascularization of the tissue engineered scaffold graft in segmental defects after 3 and 6 months, and that our tissue engineering approach employing 3D powder bed printed scaffolds facilitated segmental defect repair.

Nurse's A-Phase-Silicocarnotite Ceramic-Bone Tissue Interaction in a Rabbit Tibia Defect Model

Calcium phosphate materials are widely used as bone substitutes due to their bioactive and biodegradable properties. Also, the presence of silicon in their composition seems to improve the bioactivity of the implant and promote bone tissue repair. The aim of this study was to develop a novel ceramic scaffold by partial solid-state sintering method with a composition lying in the field of the Nurse’s A-phase–silicocarnotite, in the tricalcium phosphate–dicalcium silicate (TCP–C₂S) binary system. Also, we evaluated its osteogenic and osteoconductive properties after being implanted into tibia defects in New Zealand rabbits. X-ray, microcomputer tomography, and histomorphometry studies demonstrated that this porous ceramic is highly biocompatible and it has excellent osteointegration. The material was being progressively reabsorbed throughout the study and there was no unspecified local or systemic inflammatory response observed. These results suggest that ceramic imitates the physicochemical characteristics of bone substitutes used in bone reconstruction.

Osteogenic Differentiation of Human Mesenchymal Stromal Cells on Surface-Modified Titanium Alloys for Orthopedic and Dental Implants

Purpose

Surface properties of titanium alloys, used for orthopedic and dental applications, are known to affect implant interactions with host tissues. Osteointegration, bone growth and remodeling in the area surrounding the implants can be implemented by specific biomimetic treatments; these allow the preparation of micro/nanostructured titanium surfaces with a thickened oxide layer, doped with calcium and phosphorus ions. We have challenged these experimental titanium alloys with primary human bone marrow stromal cells to compare the osteogenic differentiation outcomes of the cells once they are seeded onto the modified surfaces, thus simulating a prosthetic device-biological interface of clinical relevance.

Methods

A specific anodic spark discharge was the biomimetic treatment of choice, providing experimental titanium disks treated with different alkali etching approaches. The disks, checked by electron microscopy and spectroscopy, were subsequently used as substrates for the proliferation and osteogenic differentiation of human cells. Expression of markers of the osteogenic lineage was assessed by means of qualitative and quantitative PCR, by cytochemistry, immunohistochemistry Western blot and matrix metalloprotease activity analyses.

Results

Metal surfaces were initially less permissive for cell growth. Untreated control substrates were less efficient in sustaining mineralized matrix deposition upon osteogenic induction of the cells. Interestingly, bone sialo protein and matrix metalloprotease 2 levels were enhanced on experimental metals compared to control surfaces, particularly for titanium oxide coatings etched with KOH.

Discussion

As a whole, the KOH-modification of titanium surfaces seems to allow the best osteogenic differentiation of human mesenchymal stromal cells, representing a possible plus for future clinical prosthetic applications.

Effect of bone sialoprotein coated three-dimensional printed calcium phosphate scaffolds on primary human osteoblasts

The combination of the two techniques of rapid prototyping 3D-plotting and bioactive surface functionalization is presented, with emphasis on the in vitro effect of Bone Sialoprotein (BSP) on primary human osteoblasts (hOBs). Our primary objective was to demonstrate the BSP influence on the expression of distinctive osteoblast markers in hOBs. Secondary objectives included examinations of the scaffolds' surface and the stability of BSP-coating as well as investigations of cell viability and proliferation. 3D-plotted calcium phosphate cement (CPC) scaffolds were coated with BSP via physisorption. hOBs were seeded on the coated scaffolds, followed by cell viability measurements, gene expression analysis and visualization. Physisorption is an effective method for BSP-coating. Coating with higher BSP concentrations leads to enhanced BSP release. Two BSP concentrations (50 and 200 μg/mL) were examined in this study. The lower BSP concentration (50 µg/mL) decreased ALP and SPARC expression, whereas the higher BSP concentration (200 μg/mL) did not change gene marker expression. Enhanced cell viability was observed on BSP-coated scaffolds on day 3. hOBs developed a polygonal shape and connected in an intercellular network under BSP influence. Quantitative cell morphology analyses demonstrated for BSP-coated CPCs an enhanced cell area and reduced circularity. The strength of the above-mentioned effects of BSP-coated scaffolds in vivo is unknown, and future work is focusing on bone ingrowth and vascularization in vivo. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2565-2575, 2018.

Development of a synthetic tissue engineered three-dimensional printed bioceramic-based bone graft with homogenously distributed osteoblasts and mineralizing bone matrix in vitro

Over the last decade there have been increasing efforts to develop three-dimensional (3D) scaffolds for bone tissue engineering from bioactive ceramics with 3D printing emerging as a promising technology. The overall objective of the present study was to generate a tissue engineered synthetic bone graft with homogenously distributed osteoblasts and mineralizing bone matrix in vitro, thereby mimicking the advantageous properties of autogenous bone grafts and facilitating usage for reconstructing segmental discontinuity defects in vivo. To this end, 3D scaffolds were developed from a silica-containing calcium alkali orthophosphate, using, first, a replica technique - the Schwartzwalder-Somers method - and, second, 3D printing, (i.e. rapid prototyping). The mechanical and physical scaffold properties and their potential to facilitate homogenous colonization by osteogenic cells and extracellular bone matrix formation throughout the porous scaffold architecture were examined. Osteoblastic cells were dynamically cultured for 7 days on both scaffold types with two different concentrations of 1.5 and 3 × 10⁹ cells/l. The amount of cells and bone matrix formed and osteogenic marker expression were evaluated using hard tissue histology, immunohistochemical and histomorphometric analysis. 3D-printed scaffolds (RPS) exhibited more micropores, greater compressive strength and silica release. RPS seeded with 3 × 10⁹ cells/l displayed greatest cell and extracellular matrix formation, mineralization and osteocalcin expression. In conclusion, RPS displayed superior mechanical and biological properties and facilitated generating a tissue engineered synthetic bone graft in vitro, which mimics the advantageous properties of autogenous bone grafts, by containing homogenously distributed terminally differentiated osteoblasts and mineralizing bone matrix and therefore is suitable for subsequent in vivo implantation for regenerating segmental discontinuity bone defects. Copyright © 2016 John Wiley & Sons, Ltd.

Electrospun poly (3-hydroxybutyrate-co-3-hydroxyvalerate)/hydroxyapatite scaffold with unrestricted somatic stem cells for bone regeneration

The combination of scaffolds and cells can be useful in tissue reconstruction. In this study, nanofibrous poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/nanohydroxyapatite (nano-HAp) scaffolds, filled with unrestricted somatic stem cells (USSCs), were used for healing calvarial bone in rat model. The healing effects of these scaffolds, with and without stem cells, in bone regeneration were investigated by computed tomography (CT) analysis and pathology assays after 28 days of grafting. The results of CT analysis showed that bone regeneration on the scaffolds, and the amounts of regenerated new bone for polymer/nano-HAp scaffold with USSC, was significantly greater than the scaffold without cell and untreated control samples. Therefore, the combination of scaffold especially with USSC could be considered as a useful method for bone regeneration.

Bone reconstruction in rat calvarial defects by chitosan/hydroxyapatite nanoparticles scaffold loaded with unrestricted somatic stem cells

Calcium phosphates are one of the biomaterials that are used for bone regeneration. In this study, Hydroxyapatite (HAp) nanoparticles with chitosan gel filled with unrestricted somatic stem cells (USSCs) were used for healing calvarial bone in rat model. The healing effects of these injectable scaffolds with and without stem cells for bone regeneration were investigated by computed tomography (CT) analysis and pathology assays after 28 days of grafting. The results of CT analysis showing bone regeneration on the scaffolds, also the amounts of regenerated new bone for USSC scaffold was significantly greater than the scaffold without cell and untreated controls. Therefore, the combination of scaffold especially with USSC is considered as a useful method for bone regeneration.

Bone formation in calvarial defects by injectable nanoparticular scaffold loaded with stem cells

OBJECTIVE

Calcium phosphates are one of biomaterials that are used for bone regeneration. In this study, calcium phosphate nanoparticles such as hydroxyapatite (HA)/fluorapatite (FA),with chitosan gel filled with unrestricted somatic stem cells (USSCs) were used for healing calvarial bone in rat model.

METHODS

The healing effects of these injectable scaffolds, with and without stem cells, in bone regeneration were investigated by computed tomography (CT) analysis and pathology assays after 28 days of grafting.

RESULTS

The results of CT analysis showed that bone regeneration on the scaffolds, and the amounts of regenerated new bone for USSC scaffold were significantly greater than the scaffold without cell and untreated controls.

CONCLUSION

Therefore, the combination of scaffold especially with USSC could be considered as a useful method for bone regeneration.

Biodegradation process of α-tricalcium phosphate and α-tricalcium phosphate solid solution bioceramics in vivo: a comparative study

This article reports the structure and morphology of the in vivo interface between implants composed of either a tricalcium phosphate (αTCP) or αTCP doped with 3.0 wt% dicalcium silicate (αTCP(ss)) ceramic, and natural bone of rabbit tibias. Both interfaces developed a new bone layer in direct contact with the implants after 4 and 8 weeks of implantation. The specimens were examined using analytical scanning and transmission electron microscopy, up to the lattice plane resolution level. Degradation processes of the implants developed at the interfaces encouraged osseous tissue ingrowth into the periphery of the material, changing the microstructure of the implants. The ionic exchange initiated at the implant interface with the environment was essential in the integration process of the implant, through a dissolution–precipitation–transformation mechanism. The interfaces developed normal biological and chemical activities and remained reactive over the 8-week period. Organized collagen fibrils were found at the αTCP(ss)/bone interface after 4 weeks, whereas a collagen-free layer was present around the Si-free αTCP implants. These findings suggest that the incorporation of silicate ions into αTCP ceramic promotes processes of the bone remodeling at the bone/αTCP(ss) interface, hence the solubility rate of the aTCP(ss) material decreased.

Premixed injectable calcium phosphate cement with excellent suspension stability

Premixed injectable calcium phosphate cement (p-ICPC) pastes have advantages over aqueous injectable calcium phosphate cement (a-ICPC) because p-ICPC remain stable during storage and harden only after placement into the defect. This paper focused on the suspension stability of p-ICPC paste by using fumed silica as a stabilizing agent and propylene glycol (PEG) as a continuous phase. Multiple light scanning techniques were first applied to evaluate the suspension stability. The results indicated that fumed silica effectively enhanced the suspension stability of p-ICPC pastes. The stabilizing effect of fumed silica results from the network structure formed in PEG because of its thixotropy. The p-ICPC could be eventually hydrated to form hydroxyapatite under aqueous circumstances by the unique replacement between water and PEG. p-ICPC (1) not only possesses proper thixotropy and compressive strength but has good injectability as well. p-ICPC (1) was cytocompatible and had no adverse effect on the attachment and proliferation of MG-63 cells in vitro. These observations may have applicability to the development of other nonaqueous injectable biomaterials for non-immediate filling and long-term storage.

RANKL delivery from calcium phosphate containing PLGA microspheres

Ideally, bone substitute materials would undergo cell-mediated degradation during the remodeling process of the host bone tissue while being replaced by newly formed bone. In an attempt to exploit the capacity of Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL) to stimulate osteoclast-like cells formation, this study explored different loading methods for RANKL in injectable calcium phosphate cement (CPC) and the effect on release and biological activity. RANKL was loaded via the liquid phase of CPC by adsorption onto or incorporation into poly(lactic-co-glycolic acid) (PLGA) microspheres with two different morphologies (i.e., hollow and dense), which were subsequently embedded in CPC. As controls nonembedded PLGA-microspheres were used as well as plain CPC scaffolds with RANKL adsorbed onto the surface. RANKL release and activity were evaluated by Reverse Phase High-Performance Liquid Chromatography (RP-HPLC) and osteoclast-like cells formation in cell culture experiments. Results indicated that sustained release of active RANKL can be achieved upon RANKL adsorption to PLGA microspheres, whereas inactive RANKL was released from CPC-PLGA formulations with RANKL incorporated within the microspheres or within the liquid phase of the CPC. These results demonstrate that effective loading of RANKL in injectable CPC is only possible via adsorption to PLGA microspheres, which are subsequently embedded within the CPC-matrix.

Osteoinductivity of calcium phosphate mediated by connexin 43

Recent reports have alluded to the osteoinductive properties of calcium phosphate, yet the cellular processes behind this are not well understood. To gain insight into the molecular mechanisms of this phenomenon, we have conducted a series of in vitro and in vivo experiments using a scaffoldless three dimensional (3D) dental pulp cell (DPC) construct as a physiologically relevant model. We demonstrate that amorphous calcium phosphate (ACP) alters cellular functions and 3D spatial tissue differentiation patterns by increasing local calcium concentration, which modulates connexin 43 (Cx43)-mediated gap junctions. These observations indicate a chemical mechanism for osteoinductivity of calcium phosphates. These results provide new insights for possible roles of mineral phases in bone formation and remodeling. This study also emphasizes the strong effect of scaffold materials on cellular functions and is expected to advance the design of future tissue engineering materials.

Combining technologies to create bioactive hybrid scaffolds for bone tissue engineering

Combining technologies to engineer scaffolds that can offer physical and chemical cues to cells is an attractive approach in tissue engineering and regenerative medicine. In this study, we have fabricated polymer-ceramic hybrid scaffolds for bone regeneration by combining rapid prototyping (RP), electrospinning (ESP) and a biomimetic coating method in order to provide mechanical support and a physico-chemical environment mimicking both the organic and inorganic phases of bone extracellular matrix (ECM). Poly(ethylene oxide terephthalate)-poly(buthylene terephthalate) (PEOT/PBT) block copolymer was used to produce three dimensional scaffolds by combining 3D fiber (3DF) deposition, and ESP, and these constructs were then coated with a Ca-P layer in a simulated physiological solution. Scaffold morphology and composition were studied using scanning electron microscopy (SEM) coupled to energy dispersive X-ray analyzer (EDX) and Fourier Tranform Infrared Spectroscopy (FTIR). Bone marrow derived human mesenchymal stromal cells (hMSCs) were cultured on coated and uncoated 3DF and 3DF + ESP scaffolds for up to 21 d in basic and mineralization medium and cell attachment, proliferation, and expression of genes related to osteogenesis were assessed. Cells attached, proliferated and secreted ECM on all the scaffolds. There were no significant differences in metabolic activity among the different groups on days 7 and 21. Coated 3DF scaffolds showed a significantly higher DNA amount in basic medium at 21 d compared with the coated 3DF + ESP scaffolds, whereas in mineralization medium, the presence of coating in 3DF+ESP scaffolds led to a significant decrease in the amount of DNA. An effect of combining different scaffolding technologies and material types on expression of a number of osteogenic markers (cbfa1, BMP-2, OP, OC and ON) was observed, suggesting the potential use of this approach in bone tissue engineering.

Repair of rabbit femoral condyle bone defects with injectable nanohydroxyapatite/chitosan composites

Repair of massive bone loss remains a challenge to the orthopaedic surgeons. Autologous and allogenic bone grafts are choice for bone reconstructive surgery, but limited availability, risks of transmittable diseases and inconsistent clinical performances have prompted the development of tissue engineering. In the present work, the bone regeneration potential of nanohydroxyapatite/chitosan composite scaffolds were compared with pure chitosan scaffolds when implanted into segmental bone defects in rabbits. Critical size bone defects (6 mm diameter, 10 mm length) were created in the left femoral condyles of 43 adult New Zealand white rabbits. The femoral condyle bone defects were repaired by nanohydroxyapatite/chitosan compositions, pure chitosan or left empty separately. Defect-bridging was detected by plain radiograph and quantitative computer tomography at eight and 12 weeks after surgery. Tissue samples were collected for gross view and histological examination to determine the extent of new bone formation. Eight weeks after surgery, more irregular osteon formation was observed in the group treated with nanohydroxyapatite/chitosan composites compared with those treated with pure chitosan. 12 weeks after surgery, complete healing of the segmental bone defect was observed in the nanohydroxyapatite/chitosan-group, while the defect was still visible in the chitosan-group, although the depth of the defect had diminished. These observations suggest that the injectable nanohydroxyapatite/chitosan scaffolds are potential candidate materials for regeneration of bone loss.

Allograft bone matrix versus synthetic bone graft substitutes

Autologous bone is used very often in the treatment of fresh fractures, delayed unions and non-unions. Alternatives have included allografts and in recent years also demineralized bone matrix. The growing availability of good synthetic bone grafts and their advantages in safety and avoiding donor-site morbidity are the reasons that these products are being used more and more. There are on the market a wide variety of substitutes with different capabilities. Nevertheless autologous bone graft is still considered as the gold standard and will be discussed here in that context. Osteoconductive, osteogenic and osteoinductive products will also be classified and their advantages and disadvantages described.

Bioinorganics and biomaterials: bone repair

The field of bioinorganics is well established in the development of a variety of therapies. However, their application to bone regeneration, specifically by way of localized delivery from functional implants, is in its infancy and is the topic of this review. The toxicity of inorganics is species, dose and duration specific. Little is known about how inorganic ions are effective therapeutically since their use is often the result of serendipity, observations from nutritional deficiency or excess and genetic disorders. Many researchers point to early work demonstrating a role for their element of interest as a micronutrient critical to or able to alter bone growth, often during skeletal development, as a basis for localized delivery. While one can appreciate how a deficiency can cause disruption of healing, it is difficult to explain how a locally delivered excess in a preclinical model or patient, which is presumably of normal nutritional status, can evoke more bone or faster healing. The review illustrates that inorganics can positively affect bone healing but various factors make literature comparisons difficult. Bioinorganics have the potential to have just as big an impact on bone regeneration as recombinant proteins without some of the safety concerns and high costs.

Calcium phosphate combination biomaterials as human mesenchymal stem cell delivery vehicles for bone repair

A new class of biomimetic, bioresorbable apatitic calcium phosphate cement (CPC) was recently developed. The handling characteristics, and the ability to harden at body temperature in the presence of physiological saline, make this material an attractive clinical bone substitute and delivery vehicle for therapeutic agents in orthopedic applications. The major challenge with the material is formulating an injectable paste with options for cell delivery, in order to regenerate new bone faster and with high quality. In this study, three different additives and/or viscosity modifiers (carboxymethylcellulose, silk, and alginate) were incorporated into a CPC matrix. Injectability, cell viability, cell proliferation, surface morphology, and gene expression for osteogenesis of hMSCs were all evaluated. Injectable CPC-gel composites with cell protection were achieved. The CPC modified with alginate provided the best results based on cell proliferation, ALP and collagen production, and osteogenic transcript increases (for ALP, type I collagen, BSP, and OP). Furthermore, osteogenic analysis indicated lineage-specific differentiation of hMSCs into osteogenic outcomes. The results suggest that CPC mixed with alginate can be used as a cell delivery vehicle for bone regeneration.

Effect of bone graft substitute on marrow stromal cell proliferation and differentiation

Marrow stromal cells (MSCs) are ideally suited for tissue engineered bone grafts since they have the potential to regenerate bone, but may also maintain the homeostasis of the repaired tissue through their ability for self-renewal. An ideal bone graft substitute should support MSC self-renewal as well as differentiation to ensure complete bone defect regeneration and maintenance. The purpose of this investigation was to determine the effect of different substrate materials on MSC expansion and differentiation. Calcium polyphosphate (CPP), bone and hydroxyapatite/tricalcium phosphate (HA/TCP) were seeded with rat MSCs and maintained in culture conditions that promote cell expansion. At 0, 3, 7, 14, and 21 days cell numbers were determined by measuring their metabolic activity using a MTT assay and the frequency of cycling cells by 24 hr BrdU incorporation. Osteogenic, chondrogenic, and adipogenic marker expression in these cultures was measured by qRT-PCR. An initial drop in cell numbers was observed on all substrates. CPP and bone, but not HA/TCP supported an increase in proliferating cells at day 14 and 21. In addition, no upregulation of mature bone markers was observed in cells cultured on CPP and bone, which suggests that these substrates support the expansion of undifferentiated MSCs. In contrast, cell numbers on HA/TCP decreased with time and only rare BrdU positive cells were observed. This decrease in proliferation correlated with the down regulation of osteogenic progenitor markers and the substantial increase in mature osteocyte markers, indicating that HA/TCP favors MSC differentiation and maturation along the osteogenic lineage.

N-acetyl cysteine improves affinity of beta-tricalcium phosphate granules for cultured osteoblast-like cells

Enhancement of bone substitute's biocompatibility may accelerate healing of surrounding bone. Although widely used as a biodegradable alloplastic bone substitute for alveolar bone augmentation, the osteocompatibility of beta-tricalcium phosphate (β-TCP) remains to be proven. The adverse cellular response to biomaterials is associated with oxidative stress. We hypothesized that commercially available β-TCP granules for clinical use, caused oxidative stress and was not optimal in osteocompatibility and that application of antioxidant amino acid derivative N-acetyl cysteine (NAC) would improve osteoblastic responses to the material. Only 20% of rat calvarial osteoblasts cultured on β-TCP granules remained viable at 24 h after seeding as opposed to 90% on polystyrene. Cell death on β-TCP granules was characterized by necrosis. However, the percentage of viable osteoblasts cultured on β-TCP granules showed a 100% increase with pre-treatment with NAC. NAC restored suppressed alkaline phosphatase activity on β-TCP granules at day 5. Intracellular ROS level on β-TCP granules was 16-fold greater than that on polystyrene, but decreased by half with pre-treatment with NAC. Cell death and intracellular ROS elevation were also induced in polystyrene culture under β-TCP granules even when the osteoblasts were not in direct contact with the β-TCP granules. NAC, however, prevented induction of cell death and elevation of intracellular ROS under β-TCP granules. These results indicate that commercially available β-TCP granules negatively affect cultured osteoblastic viability and function via oxidative stress and that NAC improves these negative responses to the material. This implies enhanced bone regeneration around biodegradable calcium phosphate-based bone substitute by NAC.

Relationships between degradability of silk scaffolds and osteogenesis

Bone repairs represent a major focus in orthopedic medicine with biomaterials as a critical aspect of the regenerative process. However, only a limited set of biomaterials are utilized today and few studies relate biomaterial scaffold design to degradation rate and new bone formation. Matching biomaterial remodeling rate towards new bone formation is important in terms of the overall rate and quality of bone regeneration outcomes. We report on the osteogenesis and metabolism of human bone marrow derived mesenchymal stem cells (hMSCs) in 3D silk scaffolds. The scaffolds were prepared with two different degradation rates in order to study relationships between matrix degradation, cell metabolism and bone tissue formation in vitro. SEM, histology, chemical assays, real-time PCR and metabolic analyses were assessed to investigate these relationships. More extensively mineralized ECM formed in the scaffolds designed to degrade more rapidly, based on SEM, von Kossa and type I collagen staining and calcium content. Measures of osteogenic ECM were significantly higher in the more rapidly degrading scaffolds than in the more slowly degrading scaffolds over 56 days of study in vitro. Metabolic analysis, including glucose and lactate levels, confirmed the degradation rate differences with the two types of scaffolds, with the more rapidly degrading scaffolds supporting higher levels of glucose consumption and lactate synthesis by the hMSCs upon osteogenesis, in comparison to the more slowly degrading scaffolds. The results demonstrate that scaffold degradation rates directly impact the metabolism of hMSCs, and in turn the rate of osteogenesis. An understanding of the interplay between cellular metabolism and scaffold degradability should aid in the more rational design of scaffolds for bone regeneration needs both in vitro and in vivo.

Influence of different modifications of a calcium phosphate bone cement on adhesion, proliferation, and osteogenic differentiation of human bone marrow stromal cells

Collagen and noncollagenous proteins of the extracellular bone matrix are able to stimulate bone cell activities and bone healing. The modification of calcium phosphate bone cements used as temporary bone replacement materials with these proteins seems to be a promising approach to accelerate new bone formation. In this study, we investigated adhesion, proliferation, and osteogenic differentiation of human bone marrow stromal cells (hBMSC) on Biocement D/collagen composites which have been modified with osteocalcin and O-phospho-L-serine. Modification with osteocalcin was carried out by its addition to the cement precursor before setting as well as by functionalization of the cement samples after setting and sterilization. hBMSC were cultured on these samples for 28 days with and without osteogenic supplements. We found a positive impact especially of the phosphoserine-modifications but also of both osteocalcin-modifications on differentiation of hBMSC indicated by higher expression of the osteoblastic markers matrix metalloproteinase-13 and bone sialo protein II. For hBMSC cultured on phosphoserine-containing composites, an increased proliferation has been observed. However, in case of the osteocalcin-modified samples, only osteocalcin adsorbed after setting and sterilization of the cement samples was able to promote initial adhesion and proliferation of hBMSC. The addition of osteocalcin before setting results in a finer microstructure but the biological activity of osteocalcin might be impaired due to the sterilization process. Thus, our data indicate that the initial adhesion and proliferation of hBMSC is enhanced rather by the biological activity of osteocalcin than by the finer microstructure.

Effect of functional end groups of silane self-assembled monolayer surfaces on apatite formation, fibronectin adsorption and osteoblast cell function

Bioactive glass (BG) can directly bond to living bone without fibrous tissue encapsulation. Key mechanistic steps of BG's activity are attributed to calcium phosphate formation, surface hydroxylation and fibronectin (FN) adsorption. In the present study, self-assembled monolayers (SAMs) of alkanesilanes with different surface chemistry (OH, NH(2) and COOH) were used as a model system to mimic BG's surface activity. Calcium phosphate (Ca-P) was formed on SAMs by immersion in a solution that simulates the electrolyte content of physiological fluids. FN adsorption kinetics and monolayer coverage was determined on SAMs with or without Ca-P coating. The surface roughness was also examined on these substrates before and after FN adsorption. The effects of FN-adsorbed, Ca-P-coated SAMs on the function of MC3T3-E1 were evaluated by cell growth, expression of alkaline phosphatase activity and actin cytoskeleton formation. We demonstrate that, although the FN monolayer coverage and the root mean square (rms) roughness are similar on --OH and --COOH terminated SAMs with or without Ca-P coating, higher levels of ALP activity, more actin cytoskeleton formation and more cell growth are obtained on --OH- and --COOH-terminated SAMs with Ca-P coating. In addition, although the FN monolayer coverage is higher on Ca-P-coated --NH(2)-terminated SAMs and SiO(x) surfaces, higher levels of ALP activity and more cell growth are obtained on Ca-P-coated --OH- and --COOH-terminated SAMs. Thus, with the same Ca-P coatings, different surface functional groups have different effects on the function of osteoblastic cells. These findings represent new insights into the mechanism of bioactivity of BG and thereby may lead to designing superior constructs for bone grafting.

In vitro surface reaction layer formation and dissolution of calcium phosphate cement-bioactive glass composites

Composites of hydrated calcium phosphate cement (CPC) and bioactive glass (BG) containing Si were immersed in vitro to study the effect of chemical composition on surface reaction layer formation and dissolution/precipitation behavior. The solutions used were 0.05 M tris hydroxymethyl aminomethane/HCl (tris buffer), tris buffer supplemented with plasma electrolyte (TE) with pH 7.4 at 37 degrees C, and this solution complemented with 10% newborn bovine serum (TES). The post-immersion solutions were analyzed for changes in Ca, PO(4) and Si concentrations. The reacted surfaces were analyzed using Fourier transform infrared (FTIR), and scanning electron microscopy with energy dispersive x-ray analysis. The sample weight variations after immersion were also determined. The results showed that the composition of the bioactive composite CPCs greatly affected their behavior in solution and the formation of apatite bioactive surface reaction layers. After immersion in the TE solution, Ca ions were taken up by all samples during the entire immersion duration. Initially, the P ion concentration increased sharply, and then decreased. This reaction pattern reveals the formation of an amorphous calcium phosphate layer on the surface of these composite CPCs. FTIR revealed that the layer was, in fact, poorly crystallized Ca-deficient carbonate apatite. The thickness of the layer was 12-14 microm and it was composed of rod-like apatite with directional arrangement. For immersion in the TES solution, the Ca and Si ion concentrations showed a similar behavior to that in TE, but the release rate of Si ions was higher. FTIR revealed that after TES immersion, not only did the typical, poorly crystallized, Ca-deficient carbonated apatite form, as it did in TE, but also the serum proteins co-adsorbed on the surface and thereby affected the surface reaction layer formation. A thinner apatite layer was formed and was composed of a micro-porous layer comprising rounded particles in a glue-like matrix. The addition of BG to the CPCs to create composite CPCs obviously is at the basis of this altered behavior of the cements. All data combined are useful for the design and optimization of degradable implant materials for use in bone tissue repair and regeneration procedures.

In vitro investigation of orthopedic titanium-coated and brushite-coated surfaces using human osteoblasts in the presence of gentamycin

Anti-infective coatings have been developed to protect the surfaces of cementless implants from bacterial colonization that is known to be a prerequisite for device-related infection. The aim of this study is to investigate the effect of brushite-coated arthroplasty surfaces on human osteoblasts and to evaluate the impact of concomitant exposure to gentamycin. We cultured human osteoblasts (hFOB 1.19) on brushite-coated and uncoated titanium alloy in the presence of gentamycin and analyzed cell function and vitality. Our results show that brushite-coated titanium alloy surfaces supported the function of osteoblasts and the expression of extracellular matrix even in the presence of highly dosed gentamycin. Brushite-coated titanium alloy surfaces supported osteogenic function, indicating that this coating could enhance implant osteointegration in vivo. Concomitant exposure to gentamycin slightly decreased osteoblastic activity in vitro, suggesting that there might also be negative effects in vivo. However, in vivo studies are necessary to validate these in vitro findings.

Effect of rapidly resorbable bone substitute materials on the temporal expression of the osteoblastic phenotype in vitro

Ideally, bioactive ceramics for use in alveolar ridge augmentation should possess the ability to activate bone formation and, thus, cause the differentiation of osteoprogenitor cells into osteoblasts at their surfaces. Therefore, in order to evaluate the osteogenic potential of novel bone substitute materials, it is important to examine their effect on osteoblastic differentiation. This study examines the effect of rapidly resorbable calcium-alkali-orthophosphates on osteoblastic phenotype expression and compares this behavior to that of beta-tricalcium phosphate (TCP) and bioactive glass 45S5. Test materials were three materials (denominated GB14, GB9, GB9/25) with a crystalline phase Ca(2)KNa(PO(4))(2) and with a small amorphous portion containing either magnesium potassium phosphate (GB14) or silica phosphate (GB9 and GB9/25, which also contains Ca(2)P(2)O(7)); and a material with a novel crystalline phase Ca(10)[K/Na](PO(4))(7) (material denominated 352i). SaOS-2 human bone cells were grown on the substrata for 3, 7, 14, and 21 days, counted, and probed for an array of osteogenic markers. GB9 had the greatest stimulatory effect on osteoblastic proliferation and differentiation, suggesting that this material possesses the highest potency to enhance osteogenesis. GB14 and 352i supported osteoblast differentiation to the same or a higher degree than TCP, whereas, similar to bioactive glass 45S5, GB9/25 displayed a greater stimulatory effect on osteoblastic phenotype expression, indicating that GB9/25 is also an excellent material for promoting osteogenesis.

Effect of beta-tricalcium phosphate particles with varying porosity on osteogenesis after sinus floor augmentation in humans

This study examines the effect of two beta-tricalcium phosphate (TCP) particulate bone grafting materials with varying porosity on bone formation and on osteogenic marker expression 6 months after sinus floor augmentation. Unilateral sinus grafting was performed in 20 patients using a combination (4:1 ratio) of beta-TCP particles with 35% porosity (TCP-C) or 65% porosity (TCP-CM) and autogenous bone chips. At implant placement cylindrical biopsies were sampled and processed for immunohistochemical analysis of resin embedded sections. Sections were stained for collagen type I (Col I), alkaline phosphatase (ALP), osteocalcin (OC) and bone sialoprotein (BSP). Furthermore, the area fraction of newly formed bone as well as the particle area fraction were determined histomorphometrically first, apically close to the Schneiderian membrane and second, in the center of the cylindrical biopsies. In the TCP-CM patient group a larger amount of bone formation and particle degradation was observed in the apical area and thus at the largest distance from the crestal bone compared to the TCP-C group. Good bone bonding behaviour was observed with both materials. This was accompanied by expression of ALP, Col I, BSP and OC in the newly formed bone and osteogenic mesenchym in contact with the degrading particles. Both TCP materials supported bone formation in the augmented sinus floor. Six months after implantation of both types of beta-TCP particles, bone formation and matrix mineralization was still actively progressing in the tissue surrounding the particles. Consequently, a greater porosity appears to be advantageous for enhancing bone formation and particle degradation.

Calcium phosphate bone cements, functionalized with VEGF: release kinetics and biological activity

Calcium phosphate bone cements are of great interest for bone replacement since the nanocrystalline structure allows their remodelling into native bone tissue. A strategy to accelerate vascularization of the implant region is the functionalization with vascular endothelial growth factor (VEGF), which is known to mediate angiogenesis in vivo. In this study, the release of recombinant human VEGF (rhVEGF(165)) following physical adsorption to Biocement D (BioD) and several modifications were investigated. Our data demonstrate a high VEGF binding capacity of BioD and a sustained release with a moderate initial burst. A proliferation assay using endothelial cells revealed maintenance of biological activity of VEGF after release from BioD. Release behavior of BioD was not improved by modification with mineralized collagen type I, as well as with a combination of mineralized collagen with O-phospho-L-serine and sodium citrate, respectively. In contrast, a positive impact of these modifications on the activity of released VEGF was observed; in case of the phosphoserine- and sodium citrate-modified cements, the biological efficacy of released VEGF was even higher than that of nonreleased control VEGF. We conclude that the bone implant material BioD and, especially, the phosphoserine modification may support activation of angiogenesis by delivery of VEGF in a local and sustained manner.

Growth of human osteoblast-like cells on beta-tricalciumphosphate (TCP) membranes with different structures

Bioresorb, a bioactive, bioresorbable bone replacement material, consisting of pure beta-tricalciumphos phate (TCP) ceramic, was evaluated in cell culture with human osteoblast-like cells. The aim of our study was to investigate the influence of TCP on the growth behavior of human osteoblast-like cells. Different granule sizes and plate sizes were used in this study: Granule sizes 500-1000 microm, 1000-2000 microm and 2000-5000 microm; plate sizes 1.7 mm, 2.0 mm and 2.2 mm. Under scanning electron microscopic (SEM) observations the cell colonization on the surface of the biomaterial and the tissue compatibility were studied. Thin sections were used to study the growth of human osteoblast-like cells inside the biomaterial. It could be clearly shown that all investigated biomaterials are tissue compatible and that the size and structure (granule or plate) of the biomaterial effects the colonization rate. Bioresorb plates enhance the colonization comparable to granule. The results obtained by SEM and thin sections were confirmed immunhistochemically by the nonradioactive assay EZ4U - EASY FOR YOU.In conclusion, all investigated sizes and structures of Bioresorb are tissue compatible but the cell growth is much better on plates than on granule small in size. The results suggest that the plates may be favourable useful as scaffold for regrowth of bone.

The Cytocompatibility and Early Osteogenic Characteristics of an Injectable Calcium Phosphate Cement

In this study, the cytocompatibility and early osteogenic characteristics of rat bone marrow cells (RBMCs) on injectable calcium phosphate (CaP) cement (Calcibon) were investigated. In addition to unmodified CaP cement discs, 2 other treatments were given to the discs: preincubation in MilliQ and sintering at different temperatures. After primary culture, RBMCs were dropwise seeded on the discs and cultured for 12 days. The samples were evaluated in terms of cell viability, morphology (live and dead assays and scanning electron microscopy (SEM)), cell proliferation (deoxyribonucleic acid (DNA) analyses), early cell differentiation (alkaline phosphatase (ALP) activity), and physicochemical analyses (x-ray diffraction (XRD)). The live and dead, DNA, and SEM results showed that Calcibon discs without any additional treatment were not supporting osteoblast-like cells in vitro. There were fewer cells, and cell layers were detached from the disc surface. Therefore, different preincubation periods and sintering temperatures were evaluated to improve the cytocompatibility of the CaP cement. Preincubating discs in MilliQ for periods of 1, 4, 8, and 12 weeks resulted in the hydrolysis of alpha-tri calcium phosphate (TCP) into an apatite-like structure with some beta-TCP, as shown with XRD, but the material was not cytocompatible. Sintering the discs between 800 degrees C and 1100 degrees C resulted in conversion of alpha-TCP to beta-TCP with some hydroxyapatite and an increase in crystallinity. Eventually, the discs sintered at 1100 degrees C achieved better cell attachment, more-abundant cell proliferation, and earlier differentiation than other sintered (600 degrees C, 800 degrees C, and 1000 degrees C), preincubated, and unmodified specimens. On basis of our results, we conclude that in vivo results with CaP-based cements do not guarantee in vitro applicability. Furthermore, unmodified Calcibon is not cytocompatible in vitro, although preincubation of the material results in a more-favorable cell response, sintering of the material at 1100 degrees C results in the best osteogenic properties. In contrast to in vivo studies, the Calcibon CaP cement is not suitable as a scaffold for cell-based tissue-engineering strategies.

A method for immunohistochemical detection of osteogenic markers in undecalcified bone sections

To evaluate the osteogenic potential of novel implant materials, it is important to examine their effect on osteoblastic differentiation. Characterizing the tissue response at the bone-biomaterial interface in vivo at a molecular level would contribute significantly to enhancing our understanding of tissue integration of endosseous implant materials. We describe here a new technique that overcomes difficulties commonly associated with performing immunohistochemistry on undecalcified sawed sections of bone. Sheep mandible specimens were fixed in an ethanol based fixative to maintain adequate antigenicity of the tissue. As a result, it was possible to omit antigen retrieval at high temperature for recovery of antigenicity, and detachment of sections from the slides was avoided. Following dehydration and infiltration, the specimens were embedded in a resin composed of polymethylmethacrylate and polybutylmethacrylate. Polymerization was achieved by adding benzoylperoxide and N,N-dimethyl-toluidine. This resin was selected because it maintained the antigenicity of the tissue, provided adequate properties for cutting 50 microm thick sections, and it facilitated deacrylizing the sawed sections. Acid-resistant acrylic slides were glued to the blocks using an epoxy resin based two-component adhesive to avoid detachment of the slides during the deacrylation procedure. Samples were stained for alkaline phosphatase, type I collagen, osteonectin, osteopontin, osteocalcin and bone sialoprotein. The EnVision + trade mark dextran polymer conjugate two-step visualization system was applied for immunohistochemical detection of these bone matrix proteins. This procedure yielded positive staining for the osteogenic markers in cells and matrix components. The protocol described here facilitates the use of immunohistochemistry on resin embedded sawed sections of bone and provides a convenient and reliable method that can be used routinely for immunohistochemical analysis of hard tissue specimens containing implant materials.

Biodegradation process of alpha-TCP particles and new bone formation in a rabbit cranial defect model

The purpose of the present study was to observe the biodegradation process of pure alpha-tricalcium phosphate (alpha-TCP) particles and to determine the efficacy of alpha-TCP as a space maintainer in a bone defect. We used 14 rabbits and prepared two cranial bone defects in each rabbit. One defect was left empty as a control, whereas the other was filled with alpha-TCP particles about 300 mum in diameter. Animals were sacrificed at 1 week, 4 weeks, and 8 weeks. The cranial bone was then embedded either in paraffin wax for the preparation of decalcified specimens, or in polyester resin for the preparation of nondecalcified specimens. All specimens were evaluated histologically and histomorphometrically. As a consequence of the degradation of alpha-TCP, a "reticulate structure" appeared in the particles at 1 week and new bone was observed in this structure at 8 weeks. The amount of new bone between the control and experimental groups was not significantly different at any of the time points. However, in the experimental group, new bone at the surface of alpha-TCP was evident even in the center of the defect whereas fibrous connective tissue was dominant in the control group. These results indicate that alpha-TCP is a degradable osteoconductive material that is able to act as a space maintainer for bone regeneration when applied to a bone defect. While there was no significant difference in total bone formation between the experimental and negative control groups, the space-maintaining and osteoconductive properties of the particles may result in more complete bone formation in longer-term studies.

Rheological properties of concentrated aqueous injectable calcium phosphate cement slurry

In this paper, the steady and dynamic rheological properties of concentrated aqueous injectable calcium phosphate cement (CPC) slurry were investigated. The results indicate that the concentrated aqueous injectable CPC showed both plastic and thixotropic behavior. As the setting process progressed, the yield stress of CPC slurry was raised, the area of the thixotropic hysteresis loop was enlarged, indicating that the strength of the net structure of the slurry had increased. The results of dynamic rheological behavior indicate that the slurry presented the structure similar to viscoelastic body and the property of shear thinning at the beginning. During the setting process, the slurry was transformed from a flocculent structure to a net structure, and the strength increased. Different factors had diverse effects on the rheological properties of the CPC slurry in the setting process, a reflection of the flowing properties (or injection), and the microstructure development of this concentrated suspension. Raising the powder-to-liquid ratio decreased the distance among the particles, increased the initial strength, and shortened the setting time. In addition, raising the temperature improved the initial strength, increased the order of reaction, and shortened the setting time, which was favorable to the setting process. The particle size of the raw material had much to do with the strength of original structure and setting time. The storage module G' of CPC slurry during the setting process followed the rule of power law function G'=A exp(Bt), which could be applied to forecast the setting time, and the calculated results thereafter are in agreement with the experimental data.

Does seeding density affectin vitro mineral nodules formation in novel composite scaffolds?

This study investigated the human alveolar osteoblasts (AOs) proliferation and extracellular matrix formation at seeding density of 0.05, 0.1, 0.2, 0.4, and 0.8 million (M) per 3x4x4 mm3 on medical grade polycaprolactone-tricalcium phosphate (mPCL-TCP) scaffolds designed for bone regeneration. Over 80-90% of the initial seeded cells were retained in the scaffolds after 24 h. AOs bridged over pores at density of 0.2M/scaffold and below, but formed cell balls at density of 0.4M/scaffold and above. At seeding density of 0.2M and below, cell proliferation increased with time having DNA content peaked to 1600 ng/scaffold at day 21 and 28, respectively, whereas at 0.4 and 0.8M, the corresponding DNA content decreased to 1600 ng in 28 days. At day 7, higher alkaline phosphatase (ALP) activity and higher osteocalcin (OCN) secretion were detected at 0.2M/scaffold and below. After 28 days, multilayered cell-sheet formation and collagen fibers were observed at all densities. ALP and OCN in matrix and mineral nodules were found mainly at the border of AOs-scaffold construct. These findings demonstrated that the density of 0.2M and below per 3 x 4 x 4 mm(3) scaffold resulted in better cell proliferation and extracellular matrix synthesis, potentially resulting in better mineralized tissue formation.

Characterization of Osteogenically Induced Adipose Tissue-Derived Precursor Cells in 2-Dimensional and 3-Dimensional Environments

Earlier reports on a putative precursor cell population in adipose tissue showed differentiation along several mesodermal lineages, leading some to think that adipose tissue can be a source of cells applicable in regenerative medicine. However, characterizations of these adipose-derived precursor cells (ADPC) in the 3-dimensional (3-D) environment, especially within the area of bone-specific composite scaffolds, have been lacking. In this study, ADPC plated on culture flasks or seeded on medical grade polycaprolactone-tricalcium phosphate scaffolds (mPCL-CaP) were able to differentiate along the osteogenic lineages in both 2-D and 3-D environments as assessed with immunohistochemistry of osteo-related proteins, reverse transcriptase-polymerase chain reactions and alkaline phosphatase assay. The mPCL-CaP scaffolds provided adipose-derived cells (ADC) with a suitable environment as determined by DNA and metabolic assays, light, confocal and scanning electron microscopy. Flow cytometry revealed ADC to be CD29+, CD44+, CD73+, CD90+ and CD14-, CD31-, CD34-, CD45-, CD71-, and therefore showed the absence of hematopoietic stem cells but possibly the presence of pericytes and mescenchymal stem cells with osteogenic potential. The results of this study demonstrated the potential of using ADPC in combination with mPCL-CaP scaffolds for bone regenerative medicine.

Effect of Collagen-I Modified Composites on Proliferation and Differentiation of Human Alveolar Osteoblasts

Collagen modification of scaffolds has been reported to promote matrix mineralization as an effective way to increase osseointegration of implants. The aim of this study was to investigate in vitro proliferation and differentiation of human alveolar osteoblasts (AOs) on medical-grade polycaprolactone–tricalcium phosphate (mPCL-TCP 80:20) scaffolds after collagen modification (mPCL-TCP-c) for 28 days. Collagen modification significantly increased the scaffold’s protein adsorption ability, and improved the initial seeding efficiency and cell attachment at day 1, compared with non-collagen-modified scaffolds. However, the total DNA content of both groups reached similar levels with no significant difference at 28 days’ culture. AOs were observed to spread along the collagen fibres and form extensive collagenous fibres with mineral nodules embedded, while multilayered cell sheets were formed in mPCL-TCP scaffolds. During culture, alkaline phosphatase (ALP) activity increased three- to five-fold in both groups, and collagen modification did not significantly affect either the metabolic rate or ALP activity kinetics of AOs. During osteogenic differentiation, similar gene expression of collagen type-I, osterix, osteopontin, and osteocalcin were detected in both groups. The mPCL-TCP group showed better organized mineralized tissue, but the mPCL-TCP-c showed more scattered and unorganized tissue. These results indicate that collagen modification improved the scaffold’s protein adsorption ability and encouraged initial cell attachment and distribution, but promoted fibrous-like tissue formation rather than mineralized tissue.

Premixed rapid-setting calcium phosphate composites for bone repair

Although calcium phosphate cement (CPC) is promising for bone repair, its clinical use requires on site powder-liquid mixing. To shorten surgical time and improve graft properties, it is desirable to develop premixed CPC in which the paste remains stable during storage and hardens only after placement into the defect. The objective of this study was to develop premixed CPC with rapid setting when immersed in a physiological solution. Premixed CPCs were formulated using the following approach: Premixed CPC = CPC powder + nonaqueous liquid + gelling agent + hardening accelerator. Three premixed CPCs were developed: CPC-monocalcium phosphate monohydrate (MCPM), CPC-chitosan, and CPC-tartaric. Setting time for these new premixed CPCs ranged from 5.3 to 7.9 min, significantly faster than 61.7 min for a premixed control CPC reported previously (p < 0.05). SEM revealed the formation of nano-sized needle-like hydroxyapatite crystals after 1 d immersion and crystal growth after 7 d. Diametral tensile strength for premixed CPCs at 7 d ranged from 2.8 to 6.4 MPa, comparable to reported strengths for cancellous bone and sintered porous hydroxyapatite implants. Osteoblast cells attained a normal polygonal morphology on CPC-MCPM and CPC-chitosan with cytoplasmic extensions adhering to the nano-hydroxyapatite crystals. In summary, fast-setting premixed CPCs were developed to avoid the powder-liquid mixing in surgery. The pastes hardened rapidly once immersed in physiological solution and formed hydroxyapatite. The cements had strengths matching those of cancellous bone and sintered porous hydroxyapatite and non-cytotoxicity similar to conventional non-premixed CPC.

Study on the self-setting property and thein vitro bioactivity of ?-Ca2SiO4

This study sought to investigate the physical and chemical properties of beta-dicalcium silicate (beta-Ca(2)SiO(4)) in order to evaluate its use as an injectable bioactive cement filler. Workable beta-Ca(2)SiO(4) pastes with a liquid-to-powder (L/P) ratio of 1.0-1.2 could be injected for 10-30 min (nozzle diameter 2.0 mm) and enabled initial setting times of 60-180 min. The setting process yielded cellular structures with compressive strengths of 4.8-28.8 MPa after 2-28 days. The paste was soaked in simulated body fluid (SBF), and the results demonstrated that it exhibited a moderate degradation and could induce carbonated hydroxyapatite formation. The ionic products of the paste dissolution enhanced a proliferative response of fibroblasts compared with the cells cultured alone, and this cement could also support adhesion and spreading of the mesenchymal stem cells. Finally, with the use of gentamicin as a model drug, it was found that a high dose of drug release from the paste was maintained for 14 days, and there was a sustained release over 4 weeks. This combination of properties indicates that the novel beta-Ca(2)SiO(4) cement might be suitable for potential applications in the biomedical field, preferentially as materials for bone/dental repair and controlled drug-delivery systems.