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Journal ArticleDOI

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

01 Nov 2017-Journal of The Mechanical Behavior of Biomedical Materials (Elsevier)-Vol. 75, pp 495-503

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.

AbstractCalcium 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.

Topics: Fiber (53%), Elastic modulus (51%)

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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Elsevier Editorial System(tm) for Journal of
the Mechanical Behavior of Biomedical Materials
Manuscript Draft
Manuscript Number: JMBBM-D-17-00539R1
Title: A novel strategy to enhance interfacial adhesion in fiber-
reinforced calcium phosphate cement
Article Type: Research Paper
Corresponding Author: Professor Maria-Pau Ginebra,
Corresponding Author's Institution: Technical University of Catalonia
First Author: Sara Gallinetti
Order of Authors: Sara Gallinetti; Gemma Mestres; Cristina Canal;
Cecilia Persson; Maria-Pau Ginebra
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.

Graphical Abstract (for review)

Highlights
HIGHLIGHTS
Calcium phosphate cements were reinforced with chitosan fibers and soluble chitosan
The chemical affinity of fibers and matrix improved interfacial adhesion
Mechanical reinforcement was achieved thanks to a good fiber-matrix adhesion
Fiber-reinforced cements were significantly tougher than non-reinforced analogues
The modified cement matrix supported osteoblast proliferation
Highlights (for review)

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- 1 -
A novel strategy to enhance interfacial adhesion in fiber-reinforced calcium phosphate
cement
Sara Gallinetti
1,2,3§
, Gemma Mestres
, Cristina Canal
1, 2
, Cecilia Persson
3
, Maria-Pau Ginebra
1,2
*
–––––––––
1
Biomaterials, Biomechanics and Tissue Engineering Group, Dpt. Materials Science and
Metallurgy, Universitat Politècnica de Catalunya (UPC), Eduard Maristany 10-14,
08019 Barcelona, Spain
Barcelona Research Center in Multiscale Science and Engineering, UPC, Barcelona, Spain
3
Materials in Medicine Group, Division of Applied Materials Science, Department of Engineering
Sciences, Uppsala University, Box 534, 751 21 Uppsala, Sweden.
4
Division of Microsystems and Technology, Uppsala University, Department of Engineering
Sciences, Uppsala University, Box 534, 751 21 Uppsala, Sweden.
*e-mail: maria.pau.ginebra@upc.edu
§
Both authors contributed equally
–––––––––
*Manuscript
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- 2 -
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.
Keywords: calcium phosphate cement, chitosan, fiber reinforced, interfacial adhesion, toughness,
work of fracture.

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References
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Abstract: All the information relating to the quantitative composition of a mixture is coded and stored in its X-ray diffraction pattern. It has been the goal of X-ray diffraction analysts since the discovery of X-rays to retrieve and decode this information directly from the X-ray diffraction pattern rather than resort to calibration curves or internal standards. This goal appears to be attained by the application of the `matrix-flushing theory' and the now-proposed `adiabatic principle' in applied X-ray diffraction analysis. The matrix-flushing theory offers a simple intensity-concentration equation free from matrix effects which degenerates to `auto-flushing' for binary systems. The adiabatic principle establishes that the intensity–concentration relationship between each and every pair of components in a multi component system is not perturbed by the presence or absence of other components. A key equation is derived which conducts the decoding process. Both the matrix-flushing theory and the adiabatic principle are experimentally verified.

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  • ...The cement’s phase composition was calculated with a semi-quantitative analysis (Chung 1974),...

    [...]

  • ...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....

    [...]


Journal ArticleDOI
TL;DR: Compared with the bone of adults, that of children had a lower modulus of elasticity, a lower bending strength, and a lower ash content, but the children's bone deflected more and absorbed more energy before breaking.
Abstract: Specimens of femoral cortical bone from eighteen subjects between two and forty-eight years old were loaded in bending. Compared with the bone of adults, that of children had a lower modulus of elasticity, a lower bending strength, and a lower ash content. However, the children's bone deflected more and absorbed more energy before breaking. It also tended to absorb more energy after fracture had started. The typical greenstick fracture surface of many specimens of children's bone requires more energy for its production than the relatively smooth surface of adult specimens.

408 citations


"A novel strategy to enhance interfa..." refers background in this paper

  • ...The toughness of CPCs ranges from 0.010-0.050 kJ/m 2 in their work of fracture (WOF) (Canal & Ginebra 2011), which is far below the work of fracture of bone, reported to be between 1.5 and 15 kJ/m 2 (Currey & Butler 1975)....

    [...]

  • ...Notwithstanding, the value obtained for TMC-8f (0.4 kJ/m 2 ) is still lower than the WOF described for cortical bone, which has been reported to range between 1.5 and 15 kJ/m 2 (Currey & Butler 1975)....

    [...]


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Abstract: Recently, much attention has been paid to chitosan as a potential polysaccharide resource. Although several efforts have been reported to prepare functional derivatives of chitosan by chemical modifications, few attained their antimicrobial activity against plant pathogens. The present paper aims to present an overview of the antimicrobial effects, mechanisms, and applications of a biopolymer chitosan and its derivatives in crop protection. In addition, this paper takes a closer look at the physiochemical properties and chemical modifications of chitosan molecule. The recent growth in this field and the latest research papers published will be introduced and discussed.

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  • ...Among the different polymers, chitosan is of interest mainly because it is biodegradable, biocompatible, and it can be processed into several products including flakes, fine powders, beads, membranes, fibers, and gels (Badawy & Rabea 2011)....

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Abstract: Trimethyl chitosan ammonium iodide was obtained by reaction of a low acetyl content chitosan with methyl iodide and sodium hydroxide under controlled conditions. The role of sodium iodide as an electrostatic charges screening salt is discussed. The reaction was performed in several steps to obtain derivatives of chitosan at various degrees of quaternization with a limit value near 64%. For a degree of quaternization greater than 25%, these polymers are soluble in water, whatever the pH.

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"A novel strategy to enhance interfa..." refers background in this paper

  • ...derivative (Domard et al. 1986), was added to the cement liquid phase, and chitosan fibers were...

    [...]

  • ...As chitosan is poorly soluble in water, trimethyl chitosan (TMC), which is a more soluble chitosan derivative (Domard et al. 1986), was added to the cement liquid phase, and chitosan fibers were used as reinforcing agents....

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TL;DR: The injectability of a ceramic scaffold, a macroporous CPC, was studies for the first time and may be useful in surgical sites that are not freely accessible by open surgery or when using minimally invasive techniques.
Abstract: Calcium phosphate cement (CPC) can be molded and self-hardens in vivo to form resorbable hydroxyapatite with excellent osteoconductivity. The objective of this study was to develop an injectable, macroporous and strong CPC, and to investigate the effects of porogen and absorbable fibers. Water-soluble mannitol was used as porogen and mixed with CPC at mass fractions from 0% to 50%. CPC with 0-40% mannitol was fully extruded under a syringe force of 10 N. The paste with 50% mannitol required a 100-N force which extruded only 66% of the paste. At fiber volume fraction of 0-5%, the paste was completely extruded. However, at 6% and 7.5% fibers, some fibers were left in the syringe after the paste was extruded. The injectable CPC scaffold had a flexural strength (mean+/-sd; n=5) of (3.2+/-1.0) MPa, which approached the reported strengths for sintered porous hydroxyapatite implants and cancellous bone. In summary, the injectability of a ceramic scaffold, a macroporous CPC, was studies for the first time. Processing parameters were tailored to achieve high injectability, macroporosity, and strength. The injectable and strong CPC scaffold may be useful in surgical sites that are not freely accessible by open surgery or when using minimally invasive techniques.

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  • ...These approaches have allowed either an increase of the mechanical properties (Zhang & Xu 2005) or to couple good mechanical properties and macroporosity, increasing the degradation rate and allowing cell infiltration in the material (Xu et al. 2006; Xu et al. 2007)....

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