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Journal ArticleDOI

A novel strategy to enhance interfacial adhesion in fiber-reinforced calcium phosphate cement

TL;DR: The aim of the present work was to improve the interfacial adhesion between fibers and matrix to obtain tougher biocompatible fiber-reinforced calcium phosphate cements (FRCPCs), which resulted in an increase of the work of fracture (several hundred-fold increase), while the elastic modulus and bending strength were maintained similar to the materials without additives.
Abstract: Calcium phosphate cements (CPCs) are extensively used as synthetic bone grafts, but their poor toughness limits their use to non-load-bearing applications. Reinforcement through introduction of fibers and yarns has been evaluated in various studies but always resulted in a decrease in elastic modulus or bending strength when compared to the CPC matrix. The aim of the present work was to improve the interfacial adhesion between fibers and matrix to obtain tougher biocompatible fiber-reinforced calcium phosphate cements (FRCPCs). This was done by adding a polymer solution to the matrix, with chemical affinity to the reinforcing chitosan fibers, namely trimethyl chitosan (TMC). The improved wettability and chemical affinity of the chitosan fibers with the TMC in the liquid phase led to an enhancement of the interfacial adhesion. This resulted in an increase of the work of fracture (several hundred-fold increase), while the elastic modulus and bending strength were maintained similar to the materials without additives. Additionally the TMC-modified CPCs showed suitable biocompatibility with an osteoblastic cell line.

Summary (2 min read)

Introduction

  • Synthetic bone grafts, but their poor toughness limits their use to nonload-bearing applications.
  • Reinforcement through introduction of fibers and yarns has been evaluated in various studies but always resulted in a decrease in elastic modulus or bending strength when compared to the CPC matrix.
  • The aim of the present work was to improve the interfacial adhesion between fibers and matrix to obtain tougher biocompatible fiberreinforced calcium phosphate cements .
  • This was done by adding a polymer solution to the matrix, with chemical affinity to the reinforcing chitosan fibers, namely trimethyl chitosan (TMC).
  • Additionally the TMC-modified CPCs showed suitable biocompatibility with an osteoblastic cell line.

A novel strategy to enhance interfacial adhesion in fiber-reinforced calcium phosphate

  • An improvement of the mechanical performance of these materials, and particularly a mitigation of their brittle behavior, would significantly extend the applicability of CPCs.
  • For the last 15 years, several strategies have been evaluated to reinforce CPCs with fibers (Canal & Ginebra 2011; Krüger & Groll 2012).
  • The excellent adhesion between the PMMA particles and the PMMA matrix is due to the chemical affinity between the liquid and the solid phase.
  • Thus, the aim of this work was to develop a biocompatible fiber-reinforced CPC with improved mechanical properties using chitosan as common polymer in the matrix and in the fibers, with the hypothesis that having an additive of similar nature would increase the chemical interactions between matrix and fibers, which would in turn result in a higher toughness.

2.1 Fiber reinforced calcium phosphate cements

  • Fiber-reinforced calcium phosphate cements were prepared by mixing a solid phase containing α-tricalcium phosphate (α-TCP) and chitosan fibers with a liquid phase.
  • The solid phase consisted of in-house made α-TCP obtained by solid-state reaction of a 2:1 molar mixture of calcium hydrogen phosphate (CaHPO4, Sigma–Aldrich C7263) and calcium carbonate (CaCO3, Sigma–Aldrich C4830) at 1400 °C for 15 h followed by quenching in air.
  • Detailed powder characteristics are described elsewhere (Espanol et al. 2009).
  • To prepare FRCPCs, chitosan fibers were mixed with the CPCs powder.
  • In all cases the specimens were set in Ringer’s solution (0.15 M sodium chloride solution) for 7 days at 37ºC.

2.2 Physico-chemical characterization

  • The static contact angle of chitosan films with water or 1 w/v % TMC solution as wetting liquids was evaluated.
  • It was not possible to measure the contact angle on CPCs –and their composites with chitosan fibers– due to their inherent microporosity and hydrophilicity.
  • The assay consists in determining the time needed for the Gillmore needle to fail to make a perceptible circular indentation on the cement surface, counting as time zero the start of mixing.
  • The cement’s phase composition was calculated with a semi-quantitative analysis (Chung 1974), which consisted in integrating the area of the three peaks with highest intensity and taking into account the reference intensity constant of their corresponding components.
  • The specimens were tested in wet conditions, right after extraction from the setting liquid (ASTM 2008).

2.3 Biological characterization

  • Pre-osteoblastic MG-63 cells (purchased from ATCC) were used to evaluate the effect of trimethyl chitosan modification of the cement matrix on the proliferation of the cells in direct contact with the materials.
  • Afterwards the samples were rinsed in sterile PBS and pre-incubated for 1 h with supplemented media at 37°C.
  • The absorbance values were transformed to cell number by using a standard curve.
  • The number of viable cells was visualized after 1, 3 and 7 days using live/dead staining kit (Life Technologies, USA).
  • The morphology of the MG-63 cells cultured on the cement specimens as well as the cement microstructures were visualized by Field Emission Scanning Electron Microscopy (FE-SEM, device: FIB Zeiss Neon40).

3. Results

  • The crystalline phases of the end-products of the cementitious reaction were analyzed after 7 days (Fig. 2, Table 3).
  • The addition of TMC in the liquid phase did not modify the toughness (measured as WOF) of the samples without fibers (C ≈ TMC).
  • Interestingly, the elastic modulus (Fig. 3b) of the cement containing both chitosan matrix and 8 wt% chitosan fibers (TMC-8f) was similar to that of a cement containing only TMC solution in the matrix, which highlights the relevance of adding TMC in the matrix to increase the fiber-matrix adhesion.
  • The pH of the media in contact with TMC samples was hardly modified, especially after 2 days and on, being between 7 and 7.4 for all the samples (Fig. 5b), so this is not expected to influence cell adhesion or proliferation.
  • The FRCPCs had a significantly improved toughness (measured as work of fracture) and at the same time the elastic modulus and bending strength were maintained in comparison to samples containing chitosan only as fibers or only as additive.

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TL;DR: In vitro bone filling composite materials that release ciprofloxacin to kill any remaining bacteria and contain bioceramic to help the bone to heal showed great potential to be developed into bone filler materials for the treatment of osteomyelitis or other bone related infections.
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TL;DR: In this paper, the potential of plasma surface modification of polylactide (PLA) fibers for reinforcement of calcium phosphate cements (CPCs) was evaluated for non-stress bearing applications.
Abstract: Calcium phosphate cements (CPCs) are extensively used as synthetic bone grafts, but their poor mechanical properties limit their applicability to non-stress-bearing applications. The aim of the present work is to evaluate the potential of plasma surface modification of polylactide (PLA) fibers for reinforcement of CPCs. Oxygen low-pressure plasma was employed at different treatment times and the surface properties of the untreated and plasma-treated PLA were evaluated. Plasma treatment on the PLA fibers reduced the setting times of the PLA–CPC composites and improved their flexural properties.

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  • ...The first study was based on plasma activation of poly-L-lactic acid fibers to obtain new polar functional groups on the fiber surface, with the aim of improving their wettability and consequently obtain enhanced adhesion of the fibers to the apatitic cement (Canal et al. 2014)....

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  • ...the adhesion at the interface fibers-matrix employing O2 plasma were able to achieve around 60% improvement in WOF (Canal et al. 2014), while our current approach reaches a 300% improvement...

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  • ...These studies were based on the activation of the fiber surface by low temperature plasma treatments (Canal et al. 2014; Maenz et al. 2014)....

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  • ...Previous strategies to improve the adhesion at the interface fibers-matrix employing O2 plasma were able to achieve around 60% improvement in WOF (Canal et al. 2014), while our current approach reaches a 300% improvement in WOF....

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TL;DR: In this article, the effects of fiber volume fraction on mechanical properties and macroporosity, and the biocompatibility of a calcium phosphate cement (CPC)-fiber composite were investigated.
Abstract: Calcium phosphate cement (CPC) sets in situ to form solid hydroxyapatite, can conform to complex cavity shapes without machining, has excellent osteoinductivity, and is able to be resorbed and replaced by new bone. Therefore, CPC is promising for craniofacial and orthopaedic repairs. However, its low strength and lack of macroporosity limit its use. This study investigated CPC reinforcement with absorbable fibers, the effects of fiber volume fraction on mechanical properties and macroporosity, and the biocompatibility of CPC-fiber composite. The liquid phase of CPC in this study was the weak acidic solution of chitosan. Chitosan has favourable biocompatibility, which has high viscosity in solution. The incorporation of chitosan could improve the handling properties of CPC. The liquid phase contained citric acid could strongly improve the hydration rate of CPC, which shortened the setting time and increased the compressive strength of CPC. In addition, the weak acidic environment around the biomaterials could accelerate the degradation of CPC, which was important to bone tissue engineering. The rationale was that large-diameter absorbable fibers would initially strengthen the CPC graft, then dissolve to form long cylindrical macropores for colonization by osteoblasts. Compressive strength was measured vs. fiber volume fraction from 0% (CPC Control without fibers) to 70%. Animal experiment showed that the material had osteoinductivity and biodegradability when the material was implanted into the muscle pouches in the thigh of rabbits. Compressive strength (mean ± SD; n=3) of CPC with 70% fibers was 0.8± 0.1 MPa. Long cylindrical macropores 100~300 μm in diameter were created in CPC after fiber dissolution, and the CPC-fiber scaffold reached a total porosity of 75.1±1.2% with 70% fibers. The new CPC-fiber formulation had good potentiality of ectopic bone induction. The method of using large-diameter absorbable fibers in bone graft for mechanical properties and formation of long cylindrical macropores for bone ingrowth may be applicable to other tissue engineering materials.

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  • ...This correlates well with other works (Xu et al. 2000; Xu & Quinn 2002; Xu 2004; Xu & Simon Jr. 2004; Gorst et al. 2006), where the addition of fibers or meshes caused a decrease in the elastic modulus with respect to the unreinforced sample....

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  • ...Regarding the biological characterization of these materials, a previous study by Wu et al. (Wu et al. 2013) evaluated the effect of the addition of chitosan fibers in a CPC on osteoblast-like cells....

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Journal ArticleDOI
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Abstract: Premixed calcium phosphate cements can reduce handling complications that are associated with the mixing of cements in the operating room. However, to extend the clinical indication of ceramic cements their mechanical properties need to be further improved. The incorporation of a polymeric material with intrinsically high tensile properties could possibly assist in increasing the mechanical properties of calcium phosphate cement. In this study polymer microparticles made from poly(lactid-co-glycolide) plasticised with poly(ethylene glycol) 400 (PLGA/PEG microparticles) were added in amounts of up to 5 wt% to a premixed acidic calcium phosphate cement. The PLGA/PEG microparticles added undergo a shape transformation at 37 °C, which could give a better integration between polymer microparticles and ceramic cement compared with polymer microparticles lacking this property. The results showed that the incorporation of 1.25 wt% PLGA/PEG microparticles increased the compressive strength by approximately 20% up ...

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  • ...Polymeric additives have earlier been used in CPCs with the purpose of improving their mechanical properties, injectability, resorption rate and biocompatibility (Dorozhkin 2009; Neumann & Epple 2006; Low et al. 2010; Perez et al. 2012; Engstrand et al. 2013)....

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