α-Tricalcium phosphate cement reinforced with silk fibroin: A high strength biomimetic bone cement with chloride-substituted hydroxyapatite.

In the past decades, bone defects have become an increasing factor in the development of disability in patients, impacting their quality of life. Large bone defects have minor chances to self-repair, requiring surgical intervention. Therefore, α-TCP-based cements are rigorously studied for the development of bone filling and replacement applications due to the possibility of application in minimally invasive procedures. However, α-TCP-based cements do not present adequate mechanical properties for most orthopedic applications. The aim of this study is to develop a biomimetic α-TCP cement reinforced with 0.250-1.000 wt% of silk fibroin using non-dialyzed SF solutions. Samples with SF additions higher than 0.250 wt% presented complete transformation of the α-TCP to a biphasic CDHA/HAp-Cl material, which could enhance the osteoconductivity of the material. Samples reinforced with concentrations of 0.500 wt% SF showed an increase of 450% of the fracture toughness and 182% of the compressive strength of the control sample, even with 31.09% porosity, which demonstrates good coupling between the SF and the CPs. All samples reinforced with SF showed a microstructure with smaller needle-like crystals when compared to the control sample, which possibly contributed to the material's reinforcement. Moreover, the composition of reinforced samples did not affect the cytotoxicity of the CPCs and enhanced the cell viability presented by the CPC without SF addition. Hence, biomimetic CPCs with mechanical reinforcement through the addition of SF were successfully obtained through the developed methodology, with the potential to be further evaluated as a suitable material for bone regeneration.

α-TCP-based calcium phosphate cements: A critical review.

Calcium phosphates are promising materials for applications in bone repair and substitution, particularly for their bioactivity and ability to form self-setting cements. Among them, α-tricalcium phosphate (α-TCP) stands out due to its high solubility, its hydration reaction and bioresorbability. The synthesis of α-TCP is particularly complex and the interactions between some of the synthesis parameters are still not completely understood. The variety of methods available to synthesize α-TCP has provided a substantial variance in the properties of α-TCP-based cements and the decision about which method, parameters and starting reagents will be used for the powder's synthesis is determinant of the properties of the resulting material. Therefore, this review paper focuses on α-TCP's synthesis and properties, presenting the synthesis methods currently in use as well as a discussion of how the synthesis parameters and the cement preparation affect the reactivity and mechanical properties of the material, providing a guide for the selection of the most suitable process for each α-TCP application. STATEMENT OF SIGNIFICANCE: α-TCP is a calcium phosphate and it is currently one of the most investigated bioceramics for applications that explore its bioresorbability and the hydration reaction of α-TCP-based cements. Despite the increasing number of publications on the topic, there are still aspects not well understood. This review article aims at contributing to this fascinating subject by offering an update on the state of the art of α-TCP's synthesis methods, while also addressing topics that are not often discussed about this material, such as the preparation of α-TCP-based cements and how its parameters affect the properties of the resulting cements.

Histological and structural evaluation of growth hormone and PLGA incorporation in macroporous scaffold of α-tricalcium phosphate cement.

An in vivo study was conducted to evaluate the effects of the incorporation of fibers of poly(lactic acid-co-glycolic acid, PLGA) and poly(isoprene) blend and recombinant human growth hormone (rhGH) in a macroporous scaffold of α-tricalcium phosphate cement (α-TCP) samples inserted into calvarial defects (8 mm in diameter) of 48 Wistar rats. The samples of α-TCP + PLGA/poly(isoprene) blend fibers were also submitted to a mechanical test of flexural strength. The animals of the different experimental groups [1] α-TCP (n = 6); [2] α-TCP + PLGA/poly(isoprene) blend fibers (n = 6); [3] α-TCP + rhGH, (n = 6) and [4] α-TCP + PLGA/poly(isoprene) blend fibers + rhGH, (n = 6) (the numbers within square brackets identify the experimental groups), after two weeks (subdivision "a") and four weeks (subdivision "b"), were euthanized and the implants removed for histological analysis. There was no statistical difference (p > 0.05) between the samples with and without fibers in the mechanical test. Light microscopy revealed good integration of the material in the host tissue, represented by tissue penetration into the macropores and adequate angiogenesis. In the two-week period, the groups [3a] and [4a] were significantly superior (p < 0.05) to the other groups with regard to angiogenesis and bone neoformation. In the four-week period, the group [3b] was significantly superior (p < 0.05) to the other groups with regard to bone neoformation. We conclude that the macroporous α-TCP scaffold used in this study has low mechanical resistance, is biocompatible and has significantly improved the osteoconductive capacity when rhGH is incorporated into its structure.

In vitro evaluation of poly (lactic-co-glycolic acid)/polyisoprene fibers for soft tissue engineering.

The polymeric blend of poly (lactic-co-glycolic acid) (PLGA) and polyisoprene (PI) has recently been explored for application as stents for tracheal stenosis and spring for the treatment of craniosynostosis. From the positive results presented in other biomedical applications comes the possibility of investigating the application of this material as scaffold for tissue engineering (TE), acquiring a deeper knowledge about the polymeric blend by exploring a new processing technique while attending to the most fundamental demands of TE scaffolds. PLGA/PI was processed into randomly oriented microfibers through the dripping technique and submitted to physical-chemical and in vitro characterization. The production process of fibers did not show an effect over the polymer's chemical composition, despite the fact that PLGA and PI were observed to be immiscible. Mechanical assays reinforce the suitability of these scaffolds for soft tissue applications. Skeletal muscle cells demonstrated increases in metabolic activity and proliferation to the same levels of the control group. Human dermal fibroblasts didn't show the same behaviour, but presented cell growth with the same development profile as presented in the control group. It is plausible to believe that PLGA/PI fibrous three-dimensional scaffolds are suitable for applications in soft tissue engineering. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2581-2591, 2017.

Glycerol salicylate-based containing α-tricalcium phosphate as a bioactive root canal sealer.

The use of bioactive materials instead of inert materials to fill the root canal space could be an effective approach to achieve a hermetic seal and stimulate the healing of periapical tissues. The purpose of this study was to develop and characterize an endodontic sealer based on a glycerol salicylate resin and α-tricalcium phosphate (αTCP) at physical and chemical properties. Different sealers were formulated using 70% of a glycerol salicylate resin and 30% of a mixture of calcium hydroxide and αTCP (0, 5, 10, or 15%, in weight). Sealers formulated were characterized based on setting time, in vitro degradation over time, pH, cytotoxicity, and mineral deposition. Sealers presented setting time ranging from 240 to 405 min, and basic pH over 8.21 after 28 days. Higher αTCP concentration leads to sealers with low solubility. Cell viability after 48 h in direct contact with sealers was similar to a commercial sealer used as reference. The 10% and 15% αTCP sealers exhibited a calcium-phosphate layer on the surface after immersion in water and SBF for 7 days. Glycerol salicylate sealers with 10% and 15% α-tricalcium phosphate showed reliable physical-chemical properties and apatite-forming ability.

Evaluation of scaffolds based on α-tricalcium phosphate cements for tissue engineering applications.

Growth of cells in 3-D porous scaffolds has gained importance in the field of tissue engineering. The scaffolds guide cellular growth, synthesize extracellular matrix and other biological molecules, and make the formation of tissues and functional organs easier. The aim of this study is to use α-tricalcium phosphate cement in order to obtain new types of scaffolds with the aid of paraffin spheres as pore generators. The porosity of the scaffolds produced with paraffin spheres was analyzed and compared to the literature, and the study of scaffold permeability using the Forchheimer equation allowed the analysis of pore interconnectivity. In vitro tests showed the behavior of scaffolds in solutions of simulated body fluid, and viability and cell proliferation were also evaluated. The results show the potential use of the materials developed for scaffolds for use in tissue engineering applications.

Injectability evaluation of tricalcium phosphate bone cement.

Calcium phosphate cements are biomaterials made from a mixture of calcium phosphate powder in aqueous solutions that forms a paste that reacts at the body temperature and hardens as a result of precipitation reactions. These cements are commonly used in dentistry and orthopedic bone filling surgeries, which require extremely invasive procedures. The challenge consists in formulating an injectable paste by additives incorporation. In this work, three different additives (carboxymethylcellulose, agar polymer and sodium alginate) were incorporated to tricalcium phosphate, in concentrations of 0.4, 0.8, 1.6, 3.2 and 6.4 wt.%. Injectability was evaluated through a new method developed for this purpose. Results showed that it was possible to obtain injectable compositions of alpha-tricalcium phosphate cement. It was verified that the injectability depends on the rheological behavior of the pastes and injection time. In this study, pastes with viscosity suitable for good homogenization and injection were obtained.

Evaluation of a double-setting alpha-tricalcium phosphate cement in eviscerated rabbit eyes.

PURPOSE: To evaluate the macroscopy, microstructure, and tissue reaction of a double-setting alpha-tricalcium phosphate bone cement used as an intraocular implant in rabbits. METHODS: The internal and external surface of the double-setting alpha-tricalcium phosphate implant was analyzed macroscopically and by scanning electron microscopy. Twelve New Zealand rabbits received 12-mm implants made of double-setting alpha-tricalcium phosphate cement after unilateral evisceration. Clinical evaluation was performed daily for the first 15 days after surgery and at 15-day intervals until the end of the study period. For histopathologic analysis, 3 animals per experimental period were submitted to enucleation at 15, 45, 90, and 180 days. RESULTS: On gross inspection, the external surface of the implant was solid, smooth, and compact. The microarchitecture was characterized by the formation of columns of hexagonal crystals with interconnecting channels forming micropores. No wound dehiscence, signs of infection, or implant extrusion were observed in any animal throughout the study period. Histologic examination revealed the formation of fibrovascular tissue surrounding the implants, and there were signs of minimal integration of the surface limiting the fibrocellular cap with the space previously occupied by the implant. CONCLUSIONS: The double-setting alpha-tricalcium phosphate implant behaved as an inert and non-integratable material. The lack of incorporation of this material by fibrovascular tissue is related to its characteristics of compactness and high resistance.