In vitro degradation of novel bioactive polycaprolactone—20% tricalcium phosphate composite scaffolds for bone engineering

Biocomposites and hybrid biomaterials based on calcium orthophosphates

The state-of-the-art of biocomposites and hybrid biomaterials based on calcium orthophosphates that are suitable for biomedical applications is presented in this review. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through successful combinations of the desired properties of matrix materials with those of fillers (in such systems, calcium orthophosphates might play either role), innovative bone graft biomaterials can be designed. Various types of biocomposites and hybrid biomaterials based on calcium orthophosphates, either those already in use or being investigated for biomedical applications, are extensively discussed. Many different formulations, in terms of the material constituents, fabrication technologies, structural and bioactive properties as well as both in vitro and in vivo characteristics, have already been proposed. Among the others, the nanostructurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using biocomposites and hybrid biomaterials based on calcium orthophosphates in the selected applications are highlighted. As the way from the laboratory to the hospital is a long one, and the prospective biomedical candidates have to meet many different necessities, this review also examines the critical issues and scientific challenges that require further research and development.

Bioactive composites for bone tissue engineering

One of the major challenges for bone tissue engineering is the production of a suitable scaffold material. In this review the currently available composite material options are considered and the methods of production and assessing the scaffolds are also discussed. The production routes range from the use of porogens to produce the porosity through to controlled deposition methods. The testing regimes include mechanical testing of the produced materials through to in vivo testing of the scaffolds. While the ideal scaffold material has not yet been produced, progress is being made.

Biological and mechanical properties of novel composites based on supramolecular polycaprolactone and functionalized hydroxyapatite

Supramolecular polymers based on quadruple hydrogen-bonding ureido-pyrimidinone (UPy) moieties hold promise as dynamic/stimuli-responsive materials in applications such as tissue engineering. Here, a new class of materials is introduced: supramolecular polymer composites. We show that despite the highly ordered structure and tacticity-dependent nature of hydrogen-bonded supramolecular polymers, the bioactivity of these polymers can be tuned through composite preparation with bioceramics. These novel supramolecular composites combine the superior processability of supramolecular polymers with the excellent bioactivity and mechanical characteristics of bioceramics. In particular, the bioactive composites prepared from supramolecular polycaprolactone and UPy-grafted hydroxyapatite (HApUPy) are described that can be easily formed into microporous biomaterials. The compression moduli increased about 40 and 90% upon composite preparation with HAp and HApUPy, respectively, as an indication to improved mechanical properties. These new materials show excellent potential as microporous composite scaffolds for the adhesion and proliferation of rat mesenchymal stem cells (rMSCs) as a first step toward bone regeneration studies; rMSCs proliferate about 2 and 2.7 times faster on the conventional composite with HAp and the supramolecular composite with (HApUPy) than on the neat PCL1250(UPy)(2).

Preparation and mechanical property of poly(ε-caprolactone)-matrix composites containing nano-apatite fillers modified by silane coupling agents

This study aims to improve the tensile strength and elastic modulus of nano-apatite/poly(ε-caprolactone) composites by silane-modification of the nano-apatite fillers. Three silane coupling agents were used to modify the surfaces of nano-apatite particles and composites of silanized apatite and PCL were prepared by a technique incorporating solvent dispersion, melting-blend and hot-pressing. The results showed that the silane coupling agents successfully modified the surfaces of nano-apatite fillers, and the crystallization temperatures of the silanized apatite/PCL composites were the higher than that of the non-silanized control material, although the melting temperature of the composites remained almost unaffected by silanization. The ultimate tensile strength and elastic modulus of the silanized composites reached 22.60 MPa and 1.76 GPa, as a result of the improved interfacial bonding and uniform dispersion of nano-apatite fillers. This study shows that the processing technique and silanization of nano-apatite particles can effectively improve the tensile strength and elastic modulus of nano-apatite/PCL composites.

In vitro and in vivo evaluation of the effects of demineralized bone matrix or calcium sulfate addition to polycaprolactone-bioglass composites

The objective of this study was to improve the efficacy of polycaprolactone/bioglass (PCL/BG) bone substitute using demineralized bone matrix (DBM) or calcium sulfate (CS) as a third component. Composite discs involving either DBM or CS were prepared by compression moulding. Bioactivity of discs was evaluated by energy dispersive X-ray spectroscopy (ESCA) and scanning electron microscopy (SEM) following simulated body fluid incubation. The closest Calcium/Phosphate ratio to that of hydroxyl carbonate apatite crystals was observed for PCL/ BG/DBM group (1.53) after 15 day incubation. Addition of fillers increased microhardness and compressive modulus of discs. However, after 4 and 6-week PBS incubations, PCL/BG/DBM discs showed significant decrease in modulus (from 266.23 to 54.04 and 33.45 MPa, respectively) in parallel with its highest water uptakes (36.3 and 34.7%). Discs preserved their integrity with only considerable weight loss (7.5-14.5%) in PCL/BG/DBM group. In vitro cytotoxicity tests showed that all discs were biocompatible.

Preparation and characterization of hydroxyapatite/polycaprolactone-chitosan composites

Hydroxyapatite (HA)/polycaprolactone (PCL)-chitosan (CS) composites were prepared by melt-blending. For the composites, the amount of HA was varied from 0% to 30% by weight. The morphology, structure and component of the composites were evaluated using environmental scanning electron microscope, X-ray diffraction and Fourier transform infrared spectroscope. The tensile properties were evaluated by tensile test. The bioactivity and degradation property were investigated after immersing in simulated body fluid (SBF) and physiological saline, respectively. The results show that the addition of HA to PCL-CS matrix tends to suppress the crystallization of PCL but improves the hydrophilicity. Adding HA to the composites decreases the tensile strength and elongation at break but increases the tensile modulus. After immersing in SBF for 14 days, the surface of HA/PCL-CS composites are covered by a coating of carbonated hydroxyapatite with low crystallinity, indicating the excellent bioactivity of the composites. Soaking in the physiological saline for 28 days, the molecular weight of PCL decreases while the mass loss of the composites and pH of physiological saline increase to 5.86% and 9.54, respectively, implying a good degradation property of the composites.

In Vitro Cytotoxicity of Bacterial Cellulose Scaffolds Used for Tissue-engineered Bone

The in vitro degradation and cytotoxicity of bacterial cellulose (BC) and its degradation products were studied for potential applications in bone tissue engineering. Emission scanning electron microscope was used to observe the morphology of original materials and their degradation products. The degradation was evaluated by measuring the concentration of reducing sugar by using ultraviolet spectrophotometer. Bone forming osteoblast (OB) cells and infinite culture cell line L929 fibroblasts were used to measure the cytotoxicity of materials using the MTT assay. Both types of cells proliferated normally with the BC and its degradation products with a cytotoxicity graded of 0–1. Nevertheless, the bone-forming target OB cells were more susceptible to cytotoxicity than the infinite culture fibroblast cells L929 fibroblasts. The results indicate that the BC is not very cytotoxic and that tissue functional cells are more suitable for evaluating the cytotoxicity of biomedical materials.

Customizing the degradation and load-bearing profile of 3D polycaprolactone-tricalcium phosphate scaffolds under enzymatic and hydrolytic conditions

The degradation of polycaprolactone-20% tricalcium phosphate (PCL-TCP) scaffolds was customized for dentoalveolar augmentation applications, where 5-6 months period is optimal. The scaffolds were treated with either 3M sodium hydroxide (NaOH) or 0.1% lipase solution for a total of 108 h. A greater degree of degradation and reduction in the physical properties of the scaffolds was observed in the lipase treated when compared with NaOH-treated scaffolds. After 108 h, increases in weight loss and average porosity of the scaffolds in the lipase-treated group measured 90.6% and 22.9%, respectively, when compared with 52.8% and 11.8% in the NaOH-treated group. The mechanical testing results revealed a similar trend, with a complete loss of compressive strength and modulus measured as early as 60 h in the lipase-treated group. The honeycomblike architecture was well preserved throughout the experiment only for the NaOH-treated scaffolds in addition to a favorable surface roughness ideal for bone-regeneration applications. In conclusion, pretreatment with NaOH demonstrates a simple approach for tailoring the physical properties and degradation rate of PCL-TCP scaffolds for the potential use as biomaterials targeted for dentoalveolar bone-regeneration procedures.

The synergic effect of polylactide fiber and calcium phosphate particle reinforcement in poly epsilon-caprolactone-based composite scaffolds

In this work, three-dimensional porous composite scaffolds, based on poly(epsilon-caprolactone) (PCL), were fabricated through the combination of a filament winding technique and a phase inversion/salt leaching process. Sodium chloride crystals were used as the porogen agent, and poly(lactic acid) (PLA) fibers and calcium phosphates as reinforcement. The aim of the current work is to assess the effective synergistic role of bioactive particles (i.e. alpha-tricalcium phosphates (alpha-TCP)) and PLA fibers on the morphology and mechanical response of the final scaffold. Morphological investigations performed on fiber-reinforced composite scaffolds with different PCL/alpha-TCP volume ratios (0%, 13%, 20% and 26%) show a high porosity degree (ca. 80%), pore interconnection and a homogeneous distribution of pores within the scaffold. More specifically, a bimodal pore size distribution was observed. This comprised microporosity (pores with radii ranging from 0.1 to 10 microm, which were strictly related to solvent extraction) and macroporosity (pores with radii from 10 to 300 microm, which were ascribable to the leaching of porogen elements). Static compressive tests showed that the effect of alpha-TCP on the mechanical response was to increase the elastic modulus up to a maximum value of 2.21+/-0.24 MPa, depending on the concentration of alpha-TCP added. This effect may be explained through the interaction of calcium-deficient hydroxyapatite crystals, formed as a consequence of a hydrolysis reaction of alpha-TCP, and the fiber-reinforced polymer matrix. The correct balance between chemical composition and spatial organization of reinforcement systems allows the attainment of an ideal compromise between mechanical response and bioactive potential, facilitating the development of composite scaffolds for bone tissue engineering applications.

Fabrication of biphasic calcium phosphates/polycaprolactone composites by melt infiltration process

Synthesis and characterization of material properties of biphasic calcium phosphates (BCP)/polycaprolactone (PCL) composites, which were obtained by melt infiltration of PCL using porous BCP bodies, were investigated. Using 70 vol.% of poly methyl methacrylate (PMMA) powder as a pore-forming agent, porous BCP bodies were obtained by pressure less sintering depending on the temperature. The porous bodies obtained showed interconnected, spherical pores about 200 microm in diameter. Densification of the pore frame improved and grain growth increased remarkably as the sintering temperature increased. Molten PCL was infiltrated into porous BCP bodies to obtain the BCP/PCL composites. The material properties such as the relative density, hardness, bending strength, and elastic modulus of BCP/PCL composite, which was sintered at 1200 degrees C, were 95.7%, 11.2 Hv, 31.6 MPa and 10.2 GPa, respectively.

The degradation profile of novel, bioresorbable PCL-TCP scaffolds: an in vitro and in vivo study

Degradation studies of scaffolds are important in bone tissue engineering. Previously, novel poly(epsilon-caprolactone)-20% tricalcium phosphate (PCL-TCP) based scaffolds were developed and proven useful for bone regeneration. In this study in vitro degradation analyses were carried out with the PCL-TCP scaffolds immersed in standard culture medium for 24 weeks. In vivo degradation was performed with the scaffolds implanted in the abdomen of rats for the same period of time. Results demonstrated greater degradation of PCL-TCP scaffolds in vivo than in vitro. At 24 weeks, the increase of average porosity of the scaffolds in vivo was 29.2% compared to 2.65% in vitro. Gel permeation chromatography (GPC) analysis revealed a decrease of 29% and 20% respectively in the Mn and Mw values after 24 weeks in vitro. However, a significant decrease in Mn and Mw values (79.6% and 88.7% respectively) were recorded in vivo. The mechanical properties however, were relatively similar and closely match those of cancellous bone even at 24 weeks. The results showed that the scaffold can be used for dentoalveolar reconstruction and PCL-TCP scaffolds have shown to possess the potential to degrade within the desired time period of 5-6 months and favorable mechanical properties.