Effects of synergistic reinforcement and absorbable fiber strength on hydroxyapatite bone cement

Human Umbilical Cord Mesenchymal Stem Cells: Current Literature and Role in Periodontal Regeneration

Periodontal disease can cause irreversible damage to tooth-supporting tissues such as the root cementum, periodontal ligament, and alveolar bone, eventually leading to tooth loss. While standard periodontal treatments are usually helpful in reducing disease progression, they cannot repair or replace lost periodontal tissue. Periodontal regeneration has been demonstrated to be beneficial in treating intraosseous and furcation defects to varied degrees. Cell-based treatment for periodontal regeneration will become more efficient and predictable as tissue engineering and progenitor cell biology advance, surpassing the limitations of present therapeutic techniques. Stem cells are undifferentiated cells with the ability to self-renew and differentiate into several cell types when stimulated. Mesenchymal stem cells (MSCs) have been tested for periodontal regeneration in vitro and in humans, with promising results. Human umbilical cord mesenchymal stem cells (UC-MSCs) possess a great regenerative and therapeutic potential. Their added benefits comprise ease of collection, endless source of stem cells, less immunorejection, and affordability. Further, their collection does not include the concerns associated with human embryonic stem cells. The purpose of this review is to address the most recent findings about periodontal regenerative mechanisms, different stem cells accessible for periodontal regeneration, and UC-MSCs and their involvement in periodontal regeneration.

Periodontal Bone-Ligament-Cementum Regeneration via Scaffolds and Stem Cells

Periodontitis is a prevalent infectious disease worldwide, causing the damage of periodontal support tissues, which can eventually lead to tooth loss. The goal of periodontal treatment is to control the infections and reconstruct the structure and function of periodontal tissues including cementum, periodontal ligament (PDL) fibers, and bone. The regeneration of these three types of tissues, including the re-formation of the oriented PDL fibers to be attached firmly to the new cementum and alveolar bone, remains a major challenge. This article represents the first systematic review on the cutting-edge researches on the regeneration of all three types of periodontal tissues and the simultaneous regeneration of the entire bone-PDL-cementum complex, via stem cells, bio-printing, gene therapy, and layered bio-mimetic technologies. This article primarily includes bone regeneration; PDL regeneration; cementum regeneration; endogenous cell-homing and host-mobilized stem cells; 3D bio-printing and generation of the oriented PDL fibers; gene therapy-based approaches for periodontal regeneration; regenerating the bone-PDL-cementum complex via layered materials and cells. These novel developments in stem cell technology and bioactive and bio-mimetic scaffolds are highly promising to substantially enhance the periodontal regeneration including both hard and soft tissues, with applicability to other therapies in the oral and maxillofacial region.

Fabrication of alginate modified brushite cement impregnated with antibiotic: Mechanical, thermal, and biological characterizations

Treatment of postsurgical infections, associated with orthopedic surgeries, has been a major concern for orthopedics. Several strategies including systematic and local administration of antibiotics have been proposed to this regard. The present work focused on fabricating alginate (Alg) modified brushite (Bru) cements, which could address osteogeneration and local antibiotic demands. To find the proper method of drug incorporation, Gentamicin sulfate (Gen) was loaded into the samples in the form of solution or powder. Several characterization tests including compression test, morphology, cytotoxicity, and cell adhesion assays were carried out to determine the proper concentration of Alg as a modifier of the Bru cement. The results indicated that addition of 1 wt% Alg led to superior mechanical and biological properties of the cement. Moreover, Alg addition changed the morphology of the cement from plate and needle-like structures to petal-like structure. Fourier transform infrared spectroscopy results confirmed the successful loading of Gen on the cements, specifically when Gen solution was used, and X-Ray Diffractometer result indicated that Gen caused a decrease in crystalline size. Furthermore, thermal analysis revealed that Gen-loaded sample had more stable structure as the transformation temperature slightly shifted to a higher one. The stability study confirmed the chemical stability and adequate mechanical performance of the cements within 1 month of soaking time. Finally, the addition of Alg has a positive impact on the release behavior at low concentration of Gen solution so that 20% decrease within 2 weeks of release experiment was remarkably detected.

The Addition of Poly(Vinyl Alcohol) Fibers to Apatitic Calcium Phosphate Cement Can Improve Its Toughness

Calcium phosphate cements, and in particular hydroxyapatite cements, have been widely investigated for use as bone void fillers due to their chemical similarity to bone and related osteoconductivity. However, they are brittle, which limits their use to non-load-bearing applications. The aim of the current study was to improve the toughness of hydroxyapatite cements through fiber reinforcement. The effect of the addition of hydrophilic, poly(vinyl-alcohol) (PVA) fibers to hydroxyapatite cement was evaluated in terms of mechanical properties, including compressive strength, diametral tensile strength and toughness (work of fracture), as well as setting time, phase composition and cement morphology. The fiber reinforcement enhanced the fracture resistance of the hydroxyapatite cement, but also simultaneously reduced the compressive strength and setting time of the cements. However, cement with 5 wt % of fibers (of the powder component) could be considered a good compromise, with a compressive strength of 46.5 ± 4.6 MPa (compared to 62.3 ± 12.8 MPa of that without fibers), i.e., still much greater than that of human trabecular bone (0.1–14 MPa). A significantly higher diametral tensile strength (9.2 ± 0.4 MPa) was found for this cement compared to that without fibers (7.4 ± 1.5 MPa). The work of fracture increased four times to 9.1 ± 1.5 kJ/m² in comparison to the pristine apatite. In summary, the hydroxyapatite cements could be reinforced by suitable amounts of PVA fibers, which resulted in enhancing the material’s structural integrity and ductility, and increased the material’s resistance to cracking.

Highly flexible and degradable dual setting systems based on PEG-hydrogels and brushite cement

With respect to the composition of natural bone, we established a degradable dual setting system of different poly(ethylene glycol) (PEG)-based hydrogels combined with a brushite cement. The idea was to reinforce the inorganic calcium phosphate mineral phase with an organic, polymeric phase to alter the cement's properties towards ductility and elasticity. Extremely flexible samples were produced via this dual setting approach with a fully reversible elasticity of the samples containing high molecular weight PEG-based hydrogel precursors. Using the decalcifying agent EDTA, the whole inorganic phase was dissolved due to Ca²⁺-complexation and dimensionally stable hydrogels were obtained, indicating a homogenous polymeric phase within the composites. This was also confirmed by SEM-analysis, where no discontinuities or agglomerations of the phase were observed. Additional XRD-measurements proved a significant influence of the coherent polymeric matrix on the conversion from β-TCP/MCPA to brushite with a decrease in signal intensity. The results confirmed a parallelly running process of setting reaction and gelation without an inhibition of the conversion to brushite and the formation of interpenetrating networks of hydrogel and cement. The strengths of this newly developed dual setting system are based on the material degradability as well as flexibility, which can be a promising tool for bone regeneration applications in non-load bearing craniomaxillofacial defects.

STATEMENT OF SIGNIFICANCE

Brushite based calcium phosphate cements (CPCs) are known as bone replacement materials, which degrade in vivo and are replaced by native bone. However, the pure inorganic material shows a brittle fracture behavior. Here, the addition of a polymeric phase can influence the mechanical properties to create more ductile and flexible materials. This polymeric phase should ideally form during cement setting by a polymerization reaction to achieve high polymer loads without altering cement viscosity and it should be degradable in vivo similar to the cement itself. Therefore, we developed a dual setting system based on simultaneous cement setting of brushite and lactide modified poly(ethylene glycol) dimethacrylate (PEG-PLLA-DMA)-based hydrogel. It was evident that the gels form a continuous phase within the cement after radical polymerization with a strong reduction of cement brittleness.

Combined delivery of bone morphogenetic protein-2 and insulin-like growth factor-1 from nano-poly (γ-glutamic acid)/β-tricalcium phosphate-based calcium phosphate cement and its effect on bone regeneration in vitro

In this study, nano-doped calcium phosphate cement delivery systems (poly (γ-glutamic acid)/β-tricalcium phosphate/calcium phosphate ceramics and nano (γ-glutamic acid)/β-tricalcium phosphate/calcium phosphate ceramic) were fabricated, and low doses (10 µg/g) of two growth factors, insulin-like growth factor-1 and bone morphogenetic protein-2, were encapsulated then sequentially released. We characterized the delivery systems using Fourier transform infrared spectroscopy and X-ray diffraction and measured washout resistance and compressive strength, and thus optimized the most appropriate proportioning of delivery systems for the two growth factors. One of the growth factors was absorbed by the nano-poly (γ-glutamic acid)/β-tricalcium phosphate, which was then mixed into the calcium phosphate ceramic solid phase to create a new solid phase calcium phosphate ceramic. Nano-poly (γ-glutamic acid)/β-tricalcium phosphate/calcium phosphate ceramic carriers were then prepared by blending the new calcium phosphate ceramic solid phase powder with a solution of the remaining growth factor. The effects of different release patterns (studying sequential behavior) of insulin-like growth factor-1 and bone morphogenetic protein-2 on osteogenic proliferation and differentiation of the MC3t3-E1 mouse osteoblast cell were investigated. This combinational delivery system provided a controlled release of the two growth factors, in which nano-doping significantly affected their release kinetics. The incorporation of dual growth factors could potentially stimulate bone healing and promoting bone ingrowth processes at a low dose.

Enhanced bone formation in sheep vertebral bodies after minimally invasive treatment with a novel, PLGA fiber-reinforced brushite cement

BACKGROUND CONTEXT

Injectable, brushite-forming calcium phosphate cements (CPC) show potential for bone replacement, but they exhibit low mechanical strength. This study tested a CPC reinforced with poly(l-lactide-co-glycolide) acid (PLGA) fibers in a minimally invasive, sheep lumbar vertebroplasty model.

PURPOSE

The study aimed to test the in vivo biocompatibility and osteogenic potential of a PLGA fiber-reinforced, brushite-forming CPC in a sheep large animal model.

STUDY DESIGN/SETTING

This is a prospective experimental animal study.

METHODS

Bone defects (diameter: 5 mm) were placed in aged, osteopenic female sheep, and left empty (L2) or injected with pure CPC (L3) or PLGA fiber-reinforced CPC (L4; fiber diameter: 25 µm; length: 1 mm; 10% [wt/wt]). Three and 9 months postoperation (n=20 each), the structural and functional CPC effects on bone regeneration were documented ex vivo by osteodensitometry, histomorphometry, micro-computed tomography (micro-CT), and biomechanical testing.

RESULTS

Addition of PLGA fibers enhanced CPC osteoconductivity and augmented bone formation. This was demonstrated by (1) significantly enhanced structural (bone volume/total volume, shown by micro-CT and histomorphometry; 3 or 9 months) and bone formation parameters (osteoid volume and osteoid surface; 9 months); (2) numerically enhanced bone mineral density (3 and 9 months) and biomechanical compression strength (9 months); and (3) numerically decreased bone erosion (eroded surface; 3 and 9 months).

CONCLUSIONS

The PLGA fiber-reinforced CPC is highly biocompatible and its PLGA fiber component enhanced bone formation. Also, PLGA fibers improve the mechanical properties of brittle CPC, with potential applicability in load-bearing areas.

Silica Coating of Nonsilicate Nanoparticles for Resin-Based Composite Materials

This study was designed to develop and characterize a silica-coating method for crystalline nonsilicate ceramic nanoparticles (Al₂O₃, TiO₂, and ZrO₂). The hypothesis was that the coated nonsilicate nanoparticles would stably reinforce a polymeric matrix due to effective silanation. Silica coating was applied via a sol-gel method, with tetraethyl orthosilicate as a silica precursor, followed by heat treatment. The chemical and microstructural characteristics of the nanopowders were evaluated before and after silica coating through x-ray diffraction, BET (Brunauer-Emmett-Teller), energy-dispersive x-ray spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy analyses. Coated and noncoated nanoparticles were silanated before preparation of hybrid composites, which contained glass microparticles in addition to the nanoparticles. The composites were mechanically tested in 4-point bending mode after aging (10,000 thermal cycles). Results of all chemical and microstructural analyses confirmed the successful obtaining of silica-coated nanoparticles. Two distinct aspects were observed depending on the type of nanoparticle tested: 1) formation of a silica shell on the surface of the particles and 2) nanoparticle clusters embedded into a silica matrix. The aged hybrid composites formulated with the coated nanoparticles showed improved flexural strength (10% to 30% higher) and work of fracture (35% to 40% higher) as compared with composites formulated with noncoated nanoparticles. The tested hypothesis was confirmed: silanated silica-coated nonsilicate nanoparticles yielded stable reinforcement of dimethacrylate polymeric matrix due to effective silanation. The silica-coating method presented here is a versatile and promising novel strategy for the use of crystalline nonsilicate ceramics as a reinforcing phase of polymeric composite biomaterials.

N-carboxyethyl chitosan fibers prepared as potential use in tissue engineering

To improve the hydrophilicity of chitosan fiber, N-carboxyethyl chitosan fiber was prepared through Michael addition between chitosan fiber with acrylic acid. The structure was studied by (1)H NMR. The degree of N-substitution, measured via (1)H NMR, was easily varied from 0.10 to 0.51 by varying the molar ratio of acrylic acid to chitosan. Series of properties of N-carboxyethyl chitosan fiber including mechanical property, crystallinity, thermal property and in vitro degradation were investigated by Instron machine, X-ray diffraction and differential scanning calorimetry and thermogravimetric analysis, respectively. The results showed that, introducing the carboxyethyl group into the backbone chain of chitosan fiber destroyed the intra/intermolecular hydrogen bonding, leading to loss of the intra/intermolecular hydrogen bonding and improvement of hydrophilicity. Indirect cytotoxicity assessment of carboxyethyl chitosan fibers was investigated using a L929 cell line. And the obtained results clearly suggested that N-carboxyethyl chitosan fiber was nontoxic to L929 cells. The N-carboxyethyl chitosan fibers are potential as tissue engineering scaffolds.

Reinforcement Strategies for Load-Bearing Calcium Phosphate Biocements

Calcium phosphate biocements based on calcium phosphate chemistry are well-established biomaterials for the repair of non-load bearing bone defects due to the brittle nature and low flexural strength of such cements. This article features reinforcement strategies of biocements based on various intrinsic or extrinsic material modifications to improve their strength and toughness. Altering particle size distribution in conjunction with using liquefiers reduces the amount of cement liquid necessary for cement paste preparation. This in turn decreases cement porosity and increases the mechanical performance, but does not change the brittle nature of the cements. The use of fibers may lead to a reinforcement of the matrix with a toughness increase of up to two orders of magnitude, but restricts at the same time cement injection for minimal invasive application techniques. A novel promising approach is the concept of dual-setting cements, in which a second hydrogel phase is simultaneously formed during setting, leading to more ductile cement–hydrogel composites with largely unaffected application properties.

Mechanical properties of α-tricalcium phosphate-based bone cements incorporating regenerative biomaterials for filling bone defects exposed to low mechanical loads

Calcium phosphate-based cements with enhanced regenerative potential are promising biomaterials for the healing of bone defects in procedures such as percutaneous vertebroplasty. With a view to the use of such cements for low load bearing applications such as sinus augmentation or filling extraction sites. However, the inclusion of certain species into bone cement formulations has the potential to diminish the mechanical properties of the formulations and thereby reduce their prospects for clinical translation. Consequently, we have prepared α-tricalcium phosphate (α-TCP)-based bone cements including materials that we would expect to improve their regenerative potential, and describe the mechanical properties of the resulting formulations herein. Formulations incorporated α-TCP, hydroxyapatite, biopolymer-thickened wetting agents, sutures, and platelet poor plasma. The mechanical properties of the composites were composition dependent, and optimized formulations had clinically relevant mechanical properties. Such calcium phosphate-based cements have potential as replacements for cements such as those based on polymethylmethacrylate.

Effects of adding resorbable phosphate glass fibres and PLA to calcium phosphate bone cements

BACKGROUND

Calcium phosphate cements (CPCs), due to their biocompatibility and degradation properties, are being widely investigated as a replacement to more commonly used polymethylmethacrylate (PMMA) for vertebroplasty. CPCs have shown the potential to be replaced by host bone tissue during the healing/remodelling process. However, brittleness and comparatively low strength restrict the use of CPC in load-bearing applications. Although porous CPC can integrate with bone over time, slow degradation profiles and poor interconnectivity between pores restricts osseointegration to the top layer of CPC only.

METHODS

Polylactic acid (PLA) and phosphate glass fibres (PGFs) were incorporated in a CPC matrix to overcome the problem of inherent brittleness and limited osseointegration.

RESULTS

Incorporation of PLA and PGFs within CPC was successful in achieving a much less brittle CPC matrix without affecting the mechanical properties of CPC. The area under the stress-strain curve showed that the total energy to failure of the CPC hybrid was significantly greater than that of the CPC control.

CONCLUSIONS

The methodology adopted here to add PLA within the CPC matrix may also allow for incorporation of PLA cross-linked biochemicals. Micrographic studies revealed that it was possible to confer control over pore size, shape and interconnectivity without negatively affecting the mechanical properties of the cement. This tailorable porosity could potentially lead to better osseointegration within CPC.

Current progress in bioactive ceramic scaffolds for bone repair and regeneration

Bioactive ceramics have received great attention in the past decades owing to their success in stimulating cell proliferation, differentiation and bone tissue regeneration. They can react and form chemical bonds with cells and tissues in human body. This paper provides a comprehensive review of the application of bioactive ceramics for bone repair and regeneration. The review systematically summarizes the types and characters of bioactive ceramics, the fabrication methods for nanostructure and hierarchically porous structure, typical toughness methods for ceramic scaffold and corresponding mechanisms such as fiber toughness, whisker toughness and particle toughness. Moreover, greater insights into the mechanisms of interaction between ceramics and cells are provided, as well as the development of ceramic-based composite materials. The development and challenges of bioactive ceramics are also discussed from the perspective of bone repair and regeneration.

Calcium phosphate cements for bone substitution: chemistry, handling and mechanical properties

Since their initial formulation in the 1980s, calcium phosphate cements (CPCs) have been increasingly used as bone substitutes. This article provides an overview on the chemistry, kinetics of setting and handling properties (setting time, cohesion and injectability) of CPCs for bone substitution, with a focus on their mechanical properties. Many processing parameters, such as particle size, composition of cement reactants and additives, can be adjusted to control the setting process of CPCs, concomitantly influencing their handling and mechanical performance. Moreover, this review shows that, although the mechanical strength of CPCs is generally low, it is not a critical issue for their application for bone repair--an observation not often realized by researchers and clinicians. CPCs with compressive strengths comparable to those of cortical bones can be produced through densification and/or homogenization of the cement matrix. The real limitation for CPCs appears to be their low fracture toughness and poor mechanical reliability (Weibull modulus), which have so far been only rarely studied.

Self-setting calcium orthophosphate formulations

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are bioactive and biodegradable grafting bioceramics in the form of a powder and a liquid. After mixing, both phases form pastes, which set and harden forming either a non-stoichiometric calcium deficient hydroxyapatite or brushite. Since both of them are remarkably biocompartible, bioresorbable and osteoconductive, self-setting calcium orthophosphate formulations appear to be promising bioceramics for bone grafting. Furthermore, such formulations possess excellent molding capabilities, easy manipulation and nearly perfect adaptation to the complex shapes of bone defects, followed by gradual bioresorption and new bone formation. In addition, reinforced formulations have been introduced, which might be described as calcium orthophosphate concretes. The discovery of self-setting properties opened up a new era in the medical application of calcium orthophosphates and many commercial trademarks have been introduced as a result. Currently such formulations are widely used as synthetic bone grafts, with several advantages, such as pourability and injectability. Moreover, their low-temperature setting reactions and intrinsic porosity allow loading by drugs, biomolecules and even cells for tissue engineering purposes. In this review, an insight into the self-setting calcium orthophosphate formulations, as excellent bioceramics suitable for both dental and bone grafting applications, has been provided.

Poly(propylene fumarate) reinforced dicalcium phosphate dihydrate cement composites for bone tissue engineering

Calcium phosphate cements have many desirable properties for bone tissue engineering, including osteoconductivity, resorbability, and amenability to rapid prototyping-based methods for scaffold fabrication. In this study, we show that dicalcium phosphate dihydrate (DCPD) cements, which are highly resorbable but also inherently weak and brittle, can be reinforced with poly(propylene fumarate) (PPF) to produce strong composites with mechanical properties suitable for bone tissue engineering. Characterization of DCPD-PPF composites revealed significant improvements in mechanical properties for cements with a 1.0 powder to liquid ratio. Compared with nonreinforced controls, flexural strength improved from 1.80 ± 0.19 MPa to 16.14 ± 1.70 MPa, flexural modulus increased from 1073.01 ± 158.40 MPa to 1303.91 ± 110.41 MPa, maximum displacement during testing increased from 0.11 ± 0.04 mm to 0.51 ± 0.09 mm, and work of fracture improved from 2.74 ± 0.78 J/m(2) to 249.21 ± 81.64 J/m(2) . To demonstrate the utility of our approach for scaffold fabrication, 3D macroporous scaffolds were prepared with rapid prototyping technology. Compressive testing revealed that PPF reinforcement increased scaffold strength from 0.31 ± 0.06 MPa to 7.48 ± 0.77 MPa. Finally, 3D PPF-DCPD scaffolds were implanted into calvarial defects in rabbits for 6 weeks. Although the addition of mesenchymal stem cells to the scaffolds did not significantly improve the extent of regeneration, numerous bone nodules with active osteoblasts were observed within the scaffold pores, especially in the peripheral regions. Overall, the results of this study suggest that PPF-DCPD composites may be promising scaffold materials for bone tissue engineering.

Calcium phosphate ceramic systems in growth factor and drug delivery for bone tissue engineering: a review

Calcium phosphates (CaPs) are the most widely used bone substitutes in bone tissue engineering due to their compositional similarities to bone mineral and excellent biocompatibility. In recent years, CaPs, especially hydroxyapatite and tricalcium phosphate, have attracted significant interest in simultaneous use as bone substitute and drug delivery vehicle, adding a new dimension to their application. CaPs are more biocompatible than many other ceramic and inorganic nanoparticles. Their biocompatibility and variable stoichiometry, thus surface charge density, functionality, and dissolution properties, make them suitable for both drug and growth factor delivery. CaP matrices and scaffolds have been reported to act as delivery vehicles for growth factors and drugs in bone tissue engineering. Local drug delivery in musculoskeletal disorder treatments can address some of the critical issues more effectively and efficiently than the systemic delivery. CaPs are used as coatings on metallic implants, CaP cements, and custom designed scaffolds to treat musculoskeletal disorders. This review highlights some of the current drug and growth factor delivery approaches and critical issues using CaP particles, coatings, cements, and scaffolds towards orthopedic and dental applications.

Polymeric additives to enhance the functional properties of calcium phosphate cements

The vast majority of materials used in bone tissue engineering and regenerative medicine are based on calcium phosphates due to their similarity with the mineral phase of natural bone. Among them, calcium phosphate cements, which are composed of a powder and a liquid that are mixed to obtain a moldable paste, are widely used. These calcium phosphate cement pastes can be injected using minimally invasive surgery and adapt to the shape of the defect, resulting in an entangled network of calcium phosphate crystals. Adding an organic phase to the calcium phosphate cement formulation is a very powerful strategy to enhance some of the properties of these materials. Adding some water-soluble biocompatible polymers in the calcium phosphate cement liquid or powder phase improves physicochemical and mechanical properties, such as injectability, cohesion, and toughness. Moreover, adding specific polymers can enhance the biological response and the resorption rate of the material. The goal of this study is to overview the most relevant advances in this field, focusing on the different types of polymers that have been used to enhance specific calcium phosphate cement properties.

Effect of cell seeding density on proliferation and osteodifferentiation of umbilical cord stem cells on calcium phosphate cement-fiber scaffold

Calcium phosphate cement (CPC) can fill complex-shaped bone defects and set in situ to form a scaffold with intimate adaptation to neighboring bone. The objectives of this study were to determine (1) the effects of fiber length and alginate microbead volume fraction on CPC mechanical properties, and (2) the effect of cell seeding density of human umbilical cord mesenchymal stem cells (hUCMSCs) on their proliferation and osteodifferentiation on CPC. Adding microbeads to CPC degraded the strength. However, increasing the fiber length improved the mechanical properties. Strength and elastic modulus of CPC-microbead-fiber scaffold matched those reported for cancellous bone. When the cell seeding density was increased from 50k to 300k, the cell viability, osteodifferentiation, and bone mineral synthesis also increased. When the seeding density was further increased to 500k, the osteodifferentiation and mineralization decreased. Hence, the 300k seeding density was optimal for CPC-microbead-fiber under the specified conditions. At day 8, alkaline phosphatase (ALP) gene expression of hUCMSCs with seeding density of 300k was threefold the ALP at 150k, and 200-fold the ALP at 50k. At day 14, osteocalcin and runt-related transcription factor 2 with cell seeding density of 300k was fourfold those at 50k. At day 14, mineralization by hUCMSCs at seeding density of 300k was 5-fold the mineralization at 150k, and 25-fold that at 50k. In conclusion, the effect of stem cell seeding density on CPC was determined for the first time. At low cell densities, cell viability and mineralization increased with seeding density. However, a higher seeding density was not necessarily better, and an optimal seeding density on CPC resulted in the best osteodifferentiation and mineralization. The stem cell-seeded CPC-fiber scaffold with excellent osteodifferentiation and mineralization is promising for orthopedic and craniofacial applications.

Osteogenic media and rhBMP-2-induced differentiation of umbilical cord mesenchymal stem cells encapsulated in alginate microbeads and integrated in an injectable calcium phosphate-chitosan fibrous scaffold

The need for bone tissue engineering has increased as the world population ages. The objectives of this study were to (1) develop a novel human umbilical cord mesenchymal stem cell (hUCMSC)-encapsulating, fiber-reinforced injectable calcium phosphate cement (CPCF) scaffold, and (2) investigate the effects of osteogenic media delivery, preosteodifferentiation, and bone morphogenetic protein-2 (BMP-2) delivery on hUCMSC osteodifferentiation inside CPCF for the first time. CPCF was developed using calcium phosphate powders, chitosan, and absorbable fibers. Four types of hUCMSC-encapsulating constructs were fabricated: control media in alginate hydrogel microbeads in CPCF; osteogenic media in microbeads; preosteodifferentiation; and recombinant human BMP-2 (rhBMP-2) in microbeads. The hUCMSCs inside CPCF maintained good viability, successfully differentiated into the osteogenic lineage, and synthesized bone minerals. The preosteodifferentiation method yielded high gene expressions of alkaline phosphatase, osteocalcin, collagen, and osterix, as well as alkaline phosphatase protein synthesis. The mineralization for the preosteodifferentiation constructs exceeded those of the rhBMP-2 group at 1-7 days, and was slightly lower than the rhBMP-2 group at 21 days. Mineralization of the rhBMP-2 group was 12-fold that of the control constructs at 21 days. In conclusion, although the BMP-2 delivery promoted osteodifferentiation, the preosteodifferentiation method and the ostegenic media method with hUCMSCs in CPCF were also promising for bone regeneration. hUCMSCs may be an effective alternative to the gold-standard bone marrow MSCs, which require an invasive procedure to harvest. The novel injectable stem cell-CPCF construct may be useful in minimally invasive and other orthopedic surgeries.

Deriving fast setting properties of tetracalcium phosphate/dicalcium phosphate anhydrous bone cement with nanocrystallites on the reactant surfaces

OBJECTIVE

This study attempts to reveal how nanocrystallites on the ceramic surfaces of non-dispersive calcium phosphate cement (nd-CPC) participate in setting processes as compared with conventional CPC (c-CPC).

METHODS

The compositions and morphologies of CPC during the early setting reactions were studied with X-ray diffraction and a scanning transmission electron microscope equipped with an energy dispersive spectroscopy system. The pH values and dispersive properties of CPC during the early setting reactions were investigated as well as the compressive strength of nd-CPC after 24h of immersion with varying liquid to powder ratios.

RESULTS

The mechanical strength of nd-CPC was approximately 60MPa after a 24h immersion in simulate body solution with a P/L ratio between 3.3 and 4.2g/mL. The nanocrystallites on the particle surfaces of nd-CPC were shown to grow rapidly and provided interlocking sites that allowed rapid development of the apatite phase in the cement, and were also shown to be non-dispersive in solution as determined by an injection test of c-CPC.

CONCLUSIONS

The interlocking particles produced by whisker growth on the ceramic particles or new crystallites formed between the ceramic particles caused the cement to be non-dispersive in solution. The particles of reactants with nanocrystallites on surfaces also gave this cement the ability to be shaped easily as a paste during an operation or to be injected into a cavity.

Calcium Orthophosphate Cements and Concretes

In early 1980s, researchers discovered self-setting calcium orthophosphate cements, which are a bioactive and biodegradable grafting material in the form of a powder and a liquid. Both phases form after mixing a viscous paste that after being implanted, sets and hardens within the body as either a non-stoichiometric calcium deficient hydroxyapatite (CDHA) or brushite, sometimes blended with unreacted particles and other phases. As both CDHA and brushite are remarkably biocompartible and bioresorbable (therefore, in vivo they can be replaced with newly forming bone), calcium orthophosphate cements represent a good correction technique for non-weight-bearing bone fractures or defects and appear to be very promising materials for bone grafting applications. Besides, these cements possess an excellent osteoconductivity, molding capabilities and easy manipulation. Furthermore, reinforced cement formulations are available, which in a certain sense might be described as calcium orthophosphate concretes. The concepts established by calcium orthophosphate cement pioneers in the early 1980s were used as a platform to initiate a new generation of bone substitute materials for commercialization. Since then, advances have been made in the composition, performance and manufacturing; several beneficial formulations have already been introduced as a result. Many other compositions are in experimental stages. In this review, an insight into calcium orthophosphate cements and concretes, as excellent biomaterials suitable for both dental and bone grafting application, has been provided.

Mesenchymal stem cell proliferation and differentiation on an injectable calcium phosphate-chitosan composite scaffold

Calcium phosphate cement (CPC) can be molded or injected to form a scaffold in situ, has excellent osteoconductivity, and can be resorbed and replaced by new bone. However, its low strength limits CPC to non-stress-bearing repairs. Chitosan could be used to reinforce CPC, but mesenchymal stem cell (MSC) interactions with CPC-chitosan scaffold have not been examined. The objective of this study was to investigate MSC proliferation and osteogenic differentiation on high-strength CPC-chitosan scaffold. MSCs were harvested from rat bone marrow. At CPC powder/liquid (P/L) mass ratio of 2, flexural strength (mean+/-sd; n=5) was (10.0+/-1.1) MPa for CPC-chitosan, higher than (3.7+/-0.6) MPa for CPC (p<0.05). At P/L of 3, strength was (15.7+/-1.7)MPa for CPC-chitosan, higher than (10.2+/-1.8)MPa for CPC (p<0.05). Percentage of live MSCs attaching to scaffolds increased from 85% at 1 day to 99% at 14 days. There were (180+/-37) cells/mm(2) on scaffold at 1 day; cells proliferated to (1808+/-317) cells/mm(2) at 14 days. SEM showed MSCs with healthy spreading and anchored on nano-apatite crystals via cytoplasmic processes. Alkaline phosphatase activity (ALP) was (557+/-171) (pNPP mM/min)/(microg DNA) for MSCs on CPC-chitosan, higher than (159+/-47) on CPC (p<0.05). Both were higher than (35+/-32) of baseline ALP for undifferentiated MSCs on tissue-culture plastic (p<0.05). In summary, CPC-chitosan scaffold had higher strength than CPC. MSC proliferation on CPC-chitosan matched that of the FDA-approved CPC control. MSCs on the scaffolds differentiated down the osteogenic lineage and expressed high levels of bone marker ALP. Hence, the stronger CPC-chitosan scaffold may be useful for stem cell-based bone regeneration in moderate load-bearing maxillofacial and orthopedic applications.

Next generation calcium phosphate-based biomaterials

It has been close to a century since calcium phosphate materials were first used as bone graft substitutes. Numerous studies conducted in the last two decades have produced a wealth of information on the chemistry, in vitro properties, and biological characteristics of granular calcium phosphates and calcium phosphate cement biomaterials. An in depth analysis of several key areas of calcium phosphate cement properties is presented with the aim of developing strategies that could lead to break-through improvements in the functional efficacies of these materials.

Immersion behavior of gelatin-containing calcium phosphate cement

Calcium phosphate cements (CPCs) have many favorable properties that support their clinical use as bone defect repair. However, it is difficult to deliver to the required site and hard to compact adequately due to inherently low ductility of ceramics. The aim of this study focused on the effect of the gelatin content on properties of CPCs. The diametral tensile strength, morphology, and weight loss of gelatin cements were evaluated after immersion in physiological solution, in addition to setting time. The results indicated that the setting time significantly increased with increasing gelatin amount. The 2 wt.% gelatin could make CPCs attain the maximum strength value of 2.1 MPa at 15-day immersion, while 1.6 MPa for the cement without gelatin. It is concluded that the presence of gelatin improved mechanical properties of CPCs; in particular, 2 wt.% gelatin. CPCs containing 2 wt.% gelatin hardened in an acceptable time recommended for clinical applications.

Injectable and strong nano-apatite scaffolds for cell/growth factor delivery and bone regeneration

OBJECTIVES

Seven million people suffer bone fractures each year in the U.S., and musculoskeletal conditions cost $215 billion/year. The objectives of this study were to develop moldable/injectable, mechanically strong and in situ-hardening calcium phosphate cement (CPC) composite scaffolds for bone regeneration and delivery of osteogenic cells and growth factors.

METHODS

Tetracalcium phosphate [TTCP: Ca(4)(PO(4))(2)O] and dicalcium phosphate (DCPA: CaHPO(4)) were used to fabricate self-setting calcium phosphate cement. Strong and macroporous scaffolds were developed via absorbable fibers, biopolymer chitosan, and mannitol porogen. Following established protocols, MC3T3-E1 osteoblast-like cells (Riken, Hirosaka, Japan) were cultured on the specimens and inside the CPC composite paste carrier.

RESULTS

The scaffold strength was more than doubled via reinforcement (p<0.05). Relationships and predictive models were established between matrix properties, fibers, porosity, and overall composite properties. The cement injectability was increased from about 60% to nearly 100%. Cell attachment and proliferation on the new composite matched those of biocompatible controls. Cells were able to infiltrate into the macropores and anchor to the bone mineral-like nano-apatite crystals. For cell delivery, alginate hydrogel beads protected cells during cement mixing and setting, yielding cell viability measured via the Wst-1 assay that matched the control without CPC (p>0.1). For growth factor delivery, CPC powder:liquid ratio and chitosan content provided the means to tailor the rate of protein release from CPC carrier.

SIGNIFICANCE

New CPC scaffolds were developed that were strong, tough, macroporous and osteoconductive. They showed promise for injection in minimally invasive surgeries, and in delivering osteogenic cells and osteoinductive growth factors to promote bone regeneration. Potential applications include various dental, craniofacial, and orthopedic reconstructions.

Porous bioceramics reinforced by coating gelatin

Porous bioceramics with high porosity for bone tissue engineering were fabricated by the foam impregnation technique, but their mechanical strength was poor, only a mean compressive strength of 1.04+/-0.15 MPa and an mean elastic modulus of 0.1 GPa. In order to reinforce porous ceramics, the ceramic samples were immersed in 5% gelatin solution and gelatin coatings were formed on the inter-surface of their pores. It was found that the mean compressive strength value and the mean elastic modulus value of porous samples coated with gelatin were improved to 5.17+/-0.17 MPa and 0.3 GPa respectively without sacrificing their porosity greatly. Moreover composite samples were not as fragile as sintered ceramics. The results indicated that the gelatin coatings on the inter-surface of pores reinforced porous bioceramics effectively.

Self-setting properties of a β-dicalcium silicate reinforced calcium phosphate cement

Beta-dicalcium silicate was used to reinforce the injectable calcium phosphate cement (iCPC) for the first time in this study. The influence of the content of beta-dicalcium silicate on the mechanical properties, setting time, rheological properties, injectability, phase evolution, microstructure, and biodegradability of iCPC was systematically investigated. The results demonstrated that the addition of 8 wt % beta-dicalcium silicate obviously enhanced the compressive strength of the CPC from 26.5 to 47.5 MPa, and did not significantly influence the biodegradability, setting time, injectability, phase evolution, and microstructure of the CPC. The beta-dicalcium silicate-reinforced iCPC with relatively high mechanical property should have potential prospects for the wider applications in surgery such as orthopedics, oral, and maxillofacial surgery.

Strong, macroporous, and in situ-setting calcium phosphate cement-layered structures

Calcium phosphate cement (CPC) is highly promising for clinical uses due to its in situ-setting ability, excellent osteoconductivity and bone-replacement capability. However, the low strength limits its use to non-load-bearing applications. The objectives of this study were to develop a layered CPC structure by combining a macroporous CPC layer with a strong CPC layer, and to investigate the effects of porosity and layer thickness ratios. The rationale was for the macroporous layer to accept tissue ingrowth, while the fiber-reinforced strong layer would provide the needed early-strength. A biopolymer chitosan was incorporated to strengthen both layers. Flexural strength, S (mean+/-sd; n=6) of CPC-scaffold decreased from (9.7+/-1.2) to (1.8+/-0.3) MPa (p<0.05), when the porosity increased from 44.6% to 66.2%. However, with a strong-layer reinforcement, S increased to (25.2+/-6.7) and (10.0+/-1.4) MPa, respectively, at these two porosities. These strengths matched/exceeded the reported strengths of sintered porous hydroxyapatite implants and cancellous bone. Relationships were established between S and the ratio of strong layer thickness/specimen thickness, a/h:S=(17.6 a/h+3.2) MPa. The scaffold contained macropores with a macropore length (mean+/-sd; n=147) of (183+/-73) microm, suitable for cell infiltration and tissue ingrowth. Nano-sized hydroxyapatite crystals were observed to form the scaffold matrix of CPC with chitosan. In summary, a layered CPC implant, combining a macroporous CPC with a strong CPC, was developed. Mechanical strength and macroporosity are conflicting requirements. However, the novel functionally graded CPC enabled a relatively high strength and macroporosity to be simultaneously achieved. Such an in situ-hardening nano-apatite may be useful in moderate stress-bearing applications, with macroporosity to enhance tissue ingrowth and implant resorption.

Control of crystallinity of hydrated products in a calcium phosphate bone cement

In this study, a calcium phosphate cement (CPC), consisting of partially crystallized calcium phosphate (PCCP), was synthesized. X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR) and scanning electronic microscope (SEM) were used to characterize the cement. The results showed that by changing the ratio of amorphous calcium phosphate (ACP) to PCCP in the cement, hydrated products of controllable crystallinity were obtained. With increase in the relative amount of PCCP, the hydrated products changed gradually from very poor crystallinity with little needle-like hydroxyapatite (Hap) crystallites to relatively high crystallinity with more needle-like Hap crystallites; the compressive strength of the cement increased, and the degradation of the cement decreased. The cement was implanted into the tibia tubercle of healthy mature Zelanian white rabbits and the histological specimens were obtained after 4 and 16 weeks of implantation. The result revealed that this bone cement was biocompatible and showed very early osteoconductive properties. Thus, the CPC has potential for use in orthopedic surgery for filling non- load-bearing bone defects.