Page 80 - IJB-2-2

Structural, mechanical and in vitro studies on pulsed laser deposition of hydroxyapatite on additive manufactured polyamide substrate

[4]
fixation devices . The success of implantation is re- CAD data [18,19] .
liant on the chosen biomaterial, design, mechanical The surface of the implant is the first part which
properties and chosen method of fabrication. Conven- interacts with the host tissue, hence surface modifica-
tional processes suffer from the following drawbacks: tions are very essential to enhance the biocompatibil-
higher relative cost, inability to produce complex de- ity [20] . Various techniques have been developed to en-
signs, poor customisation, immune rejection and dif- hance the compatibility of implants with the bone,
[5]
ficulties in shaping bone grafts for bone defects . such as grit blasting and acid etching of implant sur-
Current biomaterial research has focused on develop- face [21,22] and coating with bioactive materials [23−25]
ing implants that are both customised and surface en- which is a more popular technique. Hydroxyapatite
gineered to improve bone healing [6,7] . An ideal implant (HA) is a commonly used bioactive material to pro-
necessitates customisation because it can mimic the mote the compatibility of implants since it has proven
original anatomy as closely as possible and increases that the material will provide good biocompatibility
osseointegration [8,9] . The above said requirements of and good osseointegration. Coating with HA can be
implants can be obtained by (i) direct designing of done by many techniques with desired features like
implants with data procured from CT/MRI scan, which surface chemistry, energy, roughness, morphology and
provides a realistic designing of the implants and spa- crystallinity [26−28] , which influences the cellular re-
tially correct images for preoperative diagnosis and sponse to biomaterials. Techniques like plasma spray-
surgical planning; (ii) fabricating such custom-design ing [29] , flame spraying [30] , ion-beam process [31] , elec-
model with many computer assisted manufacturing trophoretic deposition [32] , radio frequency sputtering [33] ,
technology without any tooling or process planning. biomimetic coating [34] and a combination of these tech-
Additive manufacturing (AM) is becoming an in- niques are commonly used. However, these techniques
creasingly preferred technique in the field of medicine are unable to fulfil the necessary features for enhanced
due to certain unique merits such as absence of physi- cell growth [35] , but pulsed laser deposition (PLD) yi-
cal tooling or process planning [10] . The materials used elds almost high quality HA coating with uniform and
for fabrication of bioproducts can be classified as dense layer and high adhesion to the substrate [36,37] .
biometals, bioceramics, biopolymers and biocomposi- The cell has a capacity to sense features like surface
ties. Among these, biopolymers are most intensively chemistry [38] , size [39] , elasticity [40] , and topography [41]
investigated particularly for extracellular matrix tissue of the implant surface and shows a change in prolif-
engineering, prosthetic devices and drug delivery ap- eration and cellular differentiation. Cell behaviour can
plications. Polyethylene (PE), polyurethane (PU), pol- be enhanced by generating 3D surface features in the
yamide (PA), polytetrafluoroethylene (PTFE), poly- form of micro/nano grooves, pits, pin holes and ran-
methyl methacrylate (PMMA), etc., are in biopoly- dom surface roughness which could stimulate cell
mers, since they have a wide range of mechanical, attachment. The presence of functional groups like
synthesising technique, degradable property and ver- carboxylic acid (-COOH), amine (-NH 2), hydroxyl
satility. They are rapidly replacing other groups of bio- (-OH), carbonate (-CO 3), phosphate (-PO 3), etc. at the
materials such as metals and ceramics [11] . Among var- surface favours the adsorption of the protein [42] . In
ious polymeric materials, polyamide is an inert biocom- addition to other surface properties, mechanical prop-
patible polymer [12] which is generally used to make erties of the thin film also play a significant role in
3D scaffolds [13,14] , sutures and wound dressings [15] . Al- vivo as most implant materials are found to fail due to
though this material contains the same amide linkage cracking and decohesion leading to detachment. Such
found in polypeptides, their rate of biodegradation is interaction between the implant and the surrounding
so low that it is often reported as non-biodegrada- environment occurring at the interface is investigated
ble [16,17] . To improve the bioactivity of polyamide, via the in vitro test. Cell line studies [43] are commonly
bioceramic materials can be physically blended with accepted for such investigations. Primary culture of
polyamide or coated over the surface of the scaffold or cells on the surface is able to multiply or expand in
implant made with polyamide. Selective Laser Sinter- vitro and can also be differentiated to synthesise an
ing (SLS) of AM technique has an advantage of bui- extracellular matrix which substantiates the biological
lding implants from a variety of biomaterials espe- investigation.
cially biopolymers, as the process uses lasers that sin- In this study, HA was successfully deposited on AM
ters selectively thin layers of powder according to the polyamide substrate using pulsed Nd:YAG laser in

86 International Journal of Bioprinting (2016)–Volume 2, Issue 2