The advancements in the field of additive manufacturing have led to the significant developments in the field of biomedical sciences. This combinational progression has led to implementation of 3D printed biological components, such as cartilage, bone parts, skin layers, and other implants. Moreover, the inception of this technology in tissue engineering through integration of living cells for specific functions is another achievement bringing about a revolution in biomedical sciences. This research article aims at providing an in-depth review of the development in the additive manufacturing technologies that have been utilized for bioprinting of various tissue types, including dermal layers, bone implants, cardio-vascular parts, etc. The authors will also discuss the challenges and limitations in the technology considering the biocompatibility, mechanical properties, and incorporation of functional materials to make these artificially 3D printed components mimic properties to human biology.
Ti6Al4V alloy of titanium is a significant biomaterial due to its biocompatible nature, but it lacks required bioactivity to make it mimic properties to a human bone. Thus, hydroxyl-apatite (HAp), an inorganic compound found in human bones, is generally coated onto Ti6Al4V substrates to improve their bio-characteristics. But, HAp itself lacks certain bio-functionalities, such as allowing tissue bone regeneration and poor binding to the Ti6Al4V substrate, which results in osteoporosis and reduced bioactivity of the bio-implant, respectively. The proposed way out for this is the further doping of HAp with Strontium (Sr) for enabling tissue bone regeneration as well as addition of Polydopamine (PDA) for improved adhesion of HAp-based coatings with the substrate. Moreover, PDA results in increased drug delivery area and thus can be used as a material for enhancing resistance to bacterial growth. The present study demonstrates an experimental work on deposition of HAp, HAp with PDA and HAp with PDA and Sr coatings deposited onto Ti6Al4V alloy by means of biomimetic coating technique. Initially the pure HAp coatings were deposited using 10 SBF (simulated body fluid) solution and optimized in terms of time duration for desired coating uniformity. Then, for the optimized coating duration, the PDA pretreated Ti6Al4V substrates were coated, utilizing HAp, and Sr (at two different compositions) combinations were deposited through modified 10 SBF solutions. The characterization involving microstructural analysis and phase detection was performed for all these coatings using Scanned Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD) of the coated substrates and adhesion strength was calculated using a standard pull out adhesion test ISO 13779–4. The study showed an effective and comparatively cheap method of depositing organic coatings using biomimetic technique to obtain improved bio-functionalities in metallic implants at low temperatures.
The current investigation aims to develop hydroxyapatite-based biofunctional composite coatings on polydopamine-treated porous 3D-printed Ti6Al4V alloy implant specimens for orthopedic uses. The porous 3D-printed implants based on Ashby Gibson’s mathematical model for cellular materials are fabricated at a 65% level of porosity, so as to attain the mechanical strength of human bones. Further, the addition of strontium and silver in hydroxyapatite for improved biocompatibility of the 3D-printed implant to enhance its biofunctionality and its validation is performed. The resulting coated substrates are subjected to a series of morphological, elemental, phase, mechanical, and biological tests. When subjected to the uniaxial compression, the values for modulus of elasticity and yield strength of 3D-printed substrates are compared to the targeted value of elastic modulus and yield strength for the human bones (10–30 GPa and 148–240 MPa, respectively). The effect of polydopamine-treated 3D-printed Ti6Al4V substrates on the coating compositions of calcium and phosphorus has been compared to the untreated samples. The coating thickness and adhesion strength have been calculated and compared for different coating groups. All the samples, except untreated pure hydroxyapatite samples, displayed antimicrobial activity for both the gram-positive and gram-negative bacteria in the zone inhibition test. Hence, the current experiment provides a novel option to fabricate porous Ti6Al4V scaffolds, with a low-temperature surface coating to attain improved biofunctionality for orthopedic applications.
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