Moncy V. Jose

Aligned PLGA/HA nanofibrous nanocomposite scaffolds for bone tissue engineering.

Aligned nanofibrous scaffolds based on poly(d,l-lactide-co-glycolide) (PLGA) and nano-hydroxyapatite (nano-HA) were synthesized by electrospinning for bone tissue engineering. Morphological characterization using scanning electron microscopy showed that the addition of different amounts of nano-HA (1, 5, 10 and 20wt.%) increased the average fiber diameter from 300nm (neat PLGA) to 700nm (20% nano-HA). At higher concentrations (>or=10%), agglomeration of HA was observed and this had a marked effect at 20% concentration whereby the presence of nano-HA resulted in fiber breaking. Thermal characterization showed that the fast processing of electrospinning locked in the amorphous character of PLGA; this resulted in a decrease in the glass transition temperature of the scaffolds. Furthermore, an increase in the glass transition temperature was observed with increasing nano-HA concentration. The dynamic mechanical behavior of the scaffolds reflected the morphological observation, whereby nano-HA acted as reinforcements at lower concentrations (1% and 5%) but acted as defects at higher concentrations (10% and 20%). The storage modulus value of the scaffolds increased from 441MPa for neat PLGA to 724MPa for 5% nano-HA; however, further increasing the concentration leads to a decrease in storage modulus, to 371MPa for 20% nano-HA. Degradation characteristics showed that hydrophilic nano-HA influenced phosphate-buffered saline uptake and mass loss. The mechanical behavior showed a sinusoidal trend with a slight decrease in modulus by week 1 due to the plasticizing effect of the medium followed by an increase due to shrinkage, and a subsequent drop by week 6 due to degradation.

Mechano-morphological studies of aligned nanofibrous scaffolds of polycaprolactone fabricated by electrospinning

Mechanical and morphological studies of aligned nanofibrous meshes of poly(ε-caprolactone) (PCL) fabricated by electrospinning at different collector rotation speeds (0, 3000 and 6000 rpm) for application as bone tissue scaffolds are reported. SEM, XRD and DSC analyses were used for the morphological characterization of the nanofibers. Scaffolds have a nanofibrous morphology with fibers (majority) having a diameter in the range of 550–350 nm (depending on fiber uptake rates) and an interconnected pore structure. With the increase of collector rotation speed, the nanofibers become more aligned and oriented perpendicular to the axis of rotation. Deposition of fibers at higher fiber collection speeds has a profound effect on the morphology and mechanical properties of individual fibers and also the bulk fibrous meshes. Nanoindentation was used for the measurement of nanoscopic mechanical properties of individual fibers of the scaffolds. The hardness and Youngs modulus of aligned fibers measured by nanoindentation decreased with collector rotation speeds. This reveals the difference in the local microscopic structure of the fibers deposited at higher speeds. The sequence of nanoscopic mechanical properties (hardness and modulus) of three fibers is PCL at 0 rpm > PCL at 3000 rpm > PCL at 6000 rpm. This may be explained due to the decrease in crystallinity of fibers at higher uptake rates. However, uni-axial tensile properties of (bulk) scaffolds (tensile strength and modulus) increased with increasing collector rotation speed. The average ultimate tensile strength of scaffolds (along the fiber alignment) increased from 2.21 ± 0.23 MPa for PCL at uptake rate of zero rpm, to a value of 4.21 ± 0.35 MPa for PCL at uptake rate of 3000 rpm and finally to 9.58 ± 0.71 MPa for PCL at 6000 rpm. Similarly, the tensile modulus increased gradually from 6.12 ± 0.8 MPa for PCL at uptake rate of zero rpm, to 11.93 ± 1.22 MPa for PCL at uptake rate of 3000 rpm and to 33.20 ± 1.98 MPa for PCL at 6000 rpm. The sequence of macroscopic mechanical properties (tensile strength and modulus) of three fibers, from highest to lowest, is PCL at 0 rpm < PCL at 3000 rpm < PCL at 6000 rpm. This is attributed to the increased fiber alignment and packing and decrease in inter-fiber pore size at higher uptake rates.

Aligned bioactive multi-component nanofibrous nanocomposite scaffolds for bone tissue engineering.

The ability to mimic the chemical, physical and mechanical properties of the natural extra-cellular matrix is a key requirement for tissue engineering scaffolds to be successful. In this study, we successfully fabricated aligned nanofibrous multi-component scaffolds for bone tissue engineering using electrospinning. The chemical features were mimicked by using the natural components of bone: collagen and nano-hydroxyapatite along with poly[(D,L-lactide)-co-glycolide] as the major component. Anisotropic features were mimicked by aligning the nanofibers using a rotating mandrel collector. We evaluated the effect of incorporation of nano-HA particles to the system. The morphology and mechanical properties revealed that,at low concentrations, nano-HA acted as a reinforcement. However, at higher nano-HA loadings, it was difficult to disrupt aggregations and, hence, a detrimental effect was observed on the overall scaffold properties. Thermal analysis showed that there were slight interactions between the individual components even though the polymers existed as a two-phase system. Preliminary in vitro cell-culture studies revealed that the scaffold supported cell adhesion and spreading. The cells assumed a highly aligned morphology along the direction of fiber orientation. Protein adsorption experiments revealed that the synergistic effect of increased surface area and the presence of nano-HA in the polymer matrix enhanced total protein adsorption. Crosslinking with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride resulted in improved mechanical properties of the scaffolds and improved degradation stability, under physiological conditions.

Freeze-dried acellular dermal matrix graft: effects of rehydration on physical, chemical, and mechanical properties.

OBJECTIVES To test the effect of rehydration time over the range prescribed in the manufacturers protocol on (1) the biomechanical properties and on (2) the recovery and stabilization of the collagenous matrix of AlloDerm. METHODS A sterile dish containing warm saline solution was prepared, and samples rehydrated for 5 min. Subsequently, three other dishes with the solution were prepared and samples assigned into three groups according to the total rehydration time: 10 min (G1), 20 min (G2), and 40 min (G3). Uni-axial tensile testing was used to assess the biomechanical properties of the different groups and the control (dry condition). Physico-chemical properties were examined by Fourier transform infrared spectroscopy (FT-IR), and differential scanning calorimetry (DSC) as a function of rehydration time. RESULTS ANOVA revealed a significant change in tensile strength (p=0.0269) and in elastic modulus (p=0.0306) for AlloDerm following different rehydration times. The lowest tensile strength was in the dry condition, whereas the highest was achieved after a 40 min rehydration. The shortest rehydration periods did not result in a statistically significant (p>0.05) change in elastic modulus. However, after 40 min the elastic modulus increased significantly when compared to the shortest periods. FT-IR confirmed the protein backbone recovery of the graft matrix after rehydration. DSC scans of rehydrated samples showed visible shifts in the denaturation temperature to higher values compared to as-received sample (dry) suggesting stronger polymer-water bridge formation, supporting the increase in the biomechanical properties. SIGNIFICANCE The current study suggests that there are major changes on the biomechanical properties of the collagenous graft as rehydration time increases, which were also structurally confirmed by the physico-chemical analyses. Clinicians must be aware that the rehydration times of the manufacturers protocol result in a significant range in mechanical and physico-chemical properties. Therefore, a rehydration time of at least 20 min guarantees not only better handling and mechanical properties but, most importantly, supplies a material that closely resembles the natural tissue.

Acellular dermal matrix graft: Synergistic effect of rehydration and natural crosslinking on mechanical properties

This investigation studied how the incorporation of a natural crosslinking agent, genipin (Gp), into the AlloDerm® (AD) rehydration protocol affects the biomechanical properties and the stability of the collagenous matrix. AD is a minimally processed, noncrosslinked, freeze-dried collagen-based graft. Samples were immersed in a saline solution for 5 min and then randomly assigned for further rehydration (30 min) into three groups, according to the crosslinking agent: G1-control (saline), G2-1 wt % genipin, and G3-1 wt % glutaraldehyde. Gp crosslinking for a prolonged time of 6 h (G4) was also investigated. After washing (5 min), samples were mechanically tested wet in tension. G2 demonstrated a significantly higher ultimate tensile strength (UTS) and E relative to G1. However, G3 did not show a noteworthy increase in these properties. A significant enhancement in UTS was found when Gp exposure time was increased from 30 min to 6 h. FT-IR revealed a protein backbone with no significant peak shifting for all samples due to crosslinking. However, a considerable decrease in -NH(2) peak intensity occurred due to crosslinking reactions. Additionally, DSC analyses indicated an important shift in the denaturation temperature for crosslinked samples. SEM micrographs revealed no alterations in the native fibrous morphology after crosslinking. Simultaneous genipin incorporation during the rehydration protocol of AlloDerm significantly enhances its biomechanical properties.