Development and characterization of solvent-based 3D printed polylactic acid/45S5 bioactive glass composites for soft and hard tissue engineering.

With the benefit of offering hydrolysis breakdown and bio-resorption of its products, polylactic acid (PLA) is among the most frequently utilized polymers for many biomedical applications. Composites made of polylactic acid (PLA) and bioactive substances such as bioactive glass (BG) are developing as novel biomaterials because they comprise the mechanical properties and bioactivity of bioactive glass (BG) with the conformability and bio absorption of PLA. In this work, composites of PLA/BG were produced by employing the solvent-based three-dimensional printing process. To accomplish this, 0-2 wt% of BG particles (size ≤ 2 µm) were added to PLA. The resulting composite mix was then fed into a solvent-based 3D printer for the layer-by-layer construction of composites. According to the SEM/EDX investigation, BG particles were evenly dispersed throughout the polymer matrix which resulted in the interfacial bonding between them. FTIR and XRD analysis showed that PLA and BG did not interact chemically. All the composites were evaluated for cytocompatibility by in vitro cellular tests, which also proved their suitability as a substrate for NIH 3T3 cell adherence and growth. The composites were also found to be good in terms of hemocompatibility and platelet adhesion. In conclusion, additional studies on these materials were encouraged by the successful outcomes, which suggested that 3D-printed composite scaffolds consisting of PLA and BG particles might be useful in soft and hard tissue engineering.

A facile 3D bio-fabrication of customized tubular scaffolds using solvent-based extrusion printing for tissue-engineered tracheal grafts.

Tracheal implantation remains a major therapeutic challenge due to the unavailability of donors and the lack of biomimetic tubular grafts. Fabrication of biomimetic tracheal scaffolds of suitable materials with matched rigidity, enhanced flexibility and biocompatibility has been a major challenge in the field of tracheal reconstruction. In this study, customized tubular grafts made up of FDA-approved polycaprolactone ( PCL ) and polyurethane ( PU ) were fabricated using a novel solvent-based extrusion 3D printing. The printed scaffolds were investigated by various physical, thermal, and mechanical characterizations such as contact angle measurement, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), radial compression, longitudinal compression, and cyclic radial compression. In this study, the native goat trachea was used as a reference for the fabrication of different types of scaffolds (cylindrical, bellow-shaped, and spiral-shaped). The mechanical properties of the goat trachea were also compared to find suitable formulations of PCL / PU . Spiral-shaped scaffolds were found to be an ideal shape based on longitudinal compression and torsion load maintaining clear patency. To check the long-term implantation, in vitro degradation test was performed for all the 3D printed scaffolds and it was found that blending of PU with PCL reduced the degradation behavior. The printed scaffolds were further evaluated for biocompatibility assay, live/dead assay, and cell adhesion assay using bone marrow-derived human mesenchymal stem cells (hMSCs). From biomechanical and biological assessments, PCL 70 / PU 30 of spiral-shaped scaffolds could be a suitable candidate for the development of tracheal regenerative applications.

Corrosion behavior and degradation mechanism of micro-extruded 3D printed ordered pore topological Fe scaffolds.

The fabrication of ordered pore topological structures (OPTS) with an improved biodegradation profile offers unique attributes required for bone reconstruction. These attributes consisted of fully interconnected porous structure, bone-mimicking mechanical properties, and the possibility of fully regenerating bony defects. Most of the biomaterials based on magnesium were associated with the problem of too fast degradation rate. Here, the present aim was based on the fabrication of ordered pore topological Fe structures (OPTFS) using micro-extrusion-based 3D printing followed by pressureless microwave sintering. Two different kinds of pore features namely randomly distributed interconnected micropores and designed interconnected macropores were investigated. Static in vitro degradation results inferred that the H-2 mm pore size of hexagonal based ordered pore topological Fe structures (H-OPTFS) exhibited the highest degradation rate of 6.45 mg cm-2  day-1 on the 28th day. Electrochemical results revealed that the corrosion current density of the T-1 Fe sample with 44% porosity increased nearly by a multiple of three times as compared to dense Fe (from 16.79 to 44.63  µAcm-2). Similarly, these results showed more significance in H-2 mm pores size (with highest 66% porosity) of H-OPTFS as compared to H-1.75 mm and H-1.5 mm pore size of H-OPTFS (≈2 times higher degradation rate than H-1.5 mm pore size). Moreover, the MG63 osteoblast cell line was adhered to and proliferated significantly throughout the surface and illustrated more than 80% cell viability of the prepared porous Fe scaffold. The analyzed results have shown the potential of fabricated OPTFS could be considered for biomedical applications.

Thermal changes during drilling in human femur by rotary ultrasonic bone drilling machine: A histologic and ultrastructural study.

Undue heat production in surgical bone drilling leads to osteonecrosis and can be an important cause of failure of osteosynthesis, impaired healing, and loosening of implants following orthopedic surgery. The present work aims to minimize heat production below the critical temperature for thermal osteonecrosis (i.e., 47°C) and obviate thermal bone damage due to drilling. A total of 20 samples from the shaft of the human femur were obtained at autopsies and drilling was performed at room temperature by an operation theater (OT) compatible rotary ultrasonic bone drilling (RUBD) machine. K-type thermocouples were used to measure the temperature rise during drilling and the physical changes of the bone samples were observed by infrared gama camera. Light microscopic and transmission electron microscopic studies were performed to evaluate the bone cell damage. The maximum temperature recorded in RUBD (40.6 ± 1.3°C) was much below the critical temperature for thermal osteonecrosis (p < .05) at the rotational speed of 2000 rpm. Light microscopic and ultrastructural studies also revealed that there was no appreciable damage to the bone cells. Conventional bone drilling (CD) on the other hand recorded much higher temperature (66.6 ± 3.2°C), tissue burn and bone cell necrosis. Hence, RUBD machine has a potentiality for its use in orthopedic surgery and may provide better results.

Statistical modelling and optimization of print quality and mechanical properties of customized tubular scaffolds fabricated using solvent-based extrusion 3D printing process.

Tissue-engineered tubular scaffolds offer huge potential to heal or replace the diseased organ parts like blood vessels, trachea, oesophagus and ureter. However, manufacturing these scaffolds in various scales and shapes is always challenging and requires progressive technology. Developing a flexible and accurate manufacturing method is a major developmental direction in the field of tubular scaffold fabrication. In this context, the present work presents a novel solvent-based extrusion 3D printing which allows extruding over a rotating mandrel to fabricate tubular scaffolds of polycaprolactone (PCL) and polyurethane (PU). Experimental runs were planned as per the central composite design (CCD) to evaluate the effects of input parameters like infill density, layer thickness, print speed and percentage of PU on the output responses like printing quality and mechanical characteristics. The printing quality was quantified by measuring average surface roughness of the printed scaffolds and mechanical properties were evaluated by measuring radial compressive load, and percentage of elongation. The experimental investigations revealed that printing quality was improved at higher infill densities and was deteriorated at higher print speeds and layer thicknesses. Similarly, the radial compressive load was improved with the increase in infill density and was decreased with an increase in layer thickness, print speed and percentage of PU. The percentage of elongation was found to improve at higher infill densities and percentages of PU and was reduced with an increase in layer thickness and print speed. Additionally, a multi-objective optimization using Genetic Algorithm was used to evaluate the optimum conditions to minimize surface roughness and maximizing radial compression load and percentage of elongation. Finally, a case study was performed by comparing the mechanical properties of tubular organs and scaffolds from the existing reports and results of the present work.

Evaluation of in vitro corrosion behavior of zinc-hydroxyapatite and zinc-hydroxyapatite-iron as biodegradable composites.

Zinc (Zn) based biomaterials have been emerged as one of the capable biodegradable materials for biomedical applications because of the ideal degradation properties. In the present work, corrosion kinetics of Zn-hydroxyapatite (HA), and Zn-HA-iron (Fe) materials developed using microwave sintering process were investigated. The effect of the inclusion of HA and Fe in Zn on corrosion properties have been evaluated in the simulated body fluid solution. Further, the wettability test of the developed composites was performed to confirm the hydrophilic nature of the surface of all samples. Zn-3HA was found to have better hydrophilicity as compared to other samples. Increased corrosion rate and pH of Zn-5HA-2Fe samples were attributed to the addition of HA and Fe in the Zn matrix. The corrosion rate and weight loss rate from electrochemical and immersion testing of all samples were found in the order from highest to lowest: Zn-5HA-2Fe > Zn-3HA > Zn-3HA-2Fe > Zn. The highest cell viability nearly 100% was obtained for Zn-3HA samples, whereas other samples also showed sufficient biocompatibility to be utilized for biomedical applications.

A comparative analysis of solvent cast 3D printed carbonyl iron powder reinforced polycaprolactone polymeric stents for intravascular applications.

In the present research, the effectiveness of developed methodology based on solvent cast 3D printing technique was investigated by printing the different geometries of the stents. The carbonyl iron powder (CIP) reinforced polycaprolactone (CIPC) was used to print three pre-existing stent designs such as ABBOTT BVS1.1, PALMAZ-SCHATZ, and ART18Z. The physicochemical behavior was analyzed by X-ray diffraction and scanning electron microscopy. The radial compression test, three-point bending test and stent deployment test were carried out to analyze the mechanical behavior. The degradation behavior of the stents was investigated in static as well as dynamic environment. To investigate the hemocompatible and cytocompatible behaviors of the stents, platelet adhesion test, hemolysis test, protein adsorption, in vitro cell viability test, and live/dead cell viability assay were performed. The results revealed that stents had the adequate mechanical properties to perform the necessary functions in the human coronary. The degradation studies showed slower degradation rate in the dynamic environment in comparison to static environment. in vitro biological analysis indicated that the stents represented excellent resistance to thrombosis, hemocompatible functions as well as cytocompatible nature. The results concluded that PALMAZ-SCHATZ stent represented better mechanical properties, cell viability, blood compatibility, and degradation behavior.

Effect of Drilling Techniques on Microcracks and Pull-Out Strength of Cortical Screw Fixed in Human Tibia: An In-Vitro Study.

The strength between the cortical screw and bone following an orthopaedic implant surgery is an important determinant for the success of osteosynthesis. An excessive axial cutting force during drilling produces microcracks in the bone surface, resulting in reduced strength between the screw and bone, resulting in loosening of implant. The present work, investigates the influence of drilling parameters on microcracks generated in the drilled surface and pull-out strength of screw fixed in cortical bone of human tibia. The holes were drilled by two different techniques: conventional surgical bone drilling (CSBD) and rotary ultrasonic bone drilling (RUBD), by a recently developed operation theatre (OT) compatible machine. Cutting force generated in drilling of human tibia using RUBD was 30-40% lesser than that of CSBD. Scanning electron microscopy (SEM) also revealed that RUBD produced significantly lesser and thinner microcracks than that of CSBD in human bones. Biomechanical pull-out test results showed that, the pull-out strength of screws inserted into drilled holes by RUBD was much higher (100-150%) than that of CSBD. A significant difference in pull-out strength (p < 0.05) between RUBD and CSBD was revealed by statistical analysis at 95% confidence interval.

An in-vitro study of temperature rise during rotary ultrasonic bone drilling of human bone.

Temperature rise in surgical bone drilling is an important factor that leads to death of the bone cells, known as Osteonecrosis, and results into poor osteosynthesis i.e. implant failure. The present work aims to study the temperature rise during bone drilling by a recently developed operation theatre (OT) compatible machine. The temperature during the drilling process was recorded from K-type thermocouple devices, which were embedded in the human tibial bone at four different positions (at 0.5 mm, 1.0 mm, 1.5 mm, and 2.0 mm) from the drilling site. Comparative study revealed that rotary ultrasonic bone drilling (RUBD) technique produced lesser temperature (40 - 50%) than conventional drilling on human tibia. Statistical model was developed to predict the temperature rise in RUBD process using response surface methodology (RSM), and the optimum parameters were determined using Genetic Algorithm. Analysis of variance (ANOVA) was carried out at a confidence interval of 95 percent (α = 0.05) to determine the influence of various drilling parameters such as rotational speed, feed rate, drill diameter and abrasive particle size on temperature rise. It was observed that the rotational speed was responsible for the maximum temperature rise (51.8%) followed by drill diameter (18.8%), and abrasive particle size (14.3%); whereas, the feed rate contributed minimal (4%) temperature rise.

Biological and mechanical characterization of biodegradable carbonyl iron powder/polycaprolactone composite material fabricated using three-dimensional printing for cardiovascular stent application.

Biological and mechanical properties of biodegradable polymeric composite materials are strongly influenced by the choice of appropriate reinforcement in the polymer matrix. Non-compatibility of material in the vascular system could obstruct the way of the biological fluids. The concept of development of polymeric composite material for vascular implants is to provide enough support to the vessel and to restore the vessel in the natural state after degradation. In this research, the polycaprolactone composite materials (carbonyl iron powder/polycaprolactone) were developed by reinforcement of the 0%-2% of carbonyl iron powder using the solvent cast three-dimensional printing technique. The physicochemical properties of developed composites were characterized in conjunction with mechanical and biological properties. The mechanical characterizations were assessed by uniaxial tensile testing as well as flexibility testing. The results of mechanical testing assured that carbonyl iron powder/polycaprolactone composites have shown desirable properties for vascular implants. Besides the mechanical characterization, in vitro biological investigations of carbonyl iron powder/polycaprolactone were done for analyzing blood compatibility and cytocompatibility. The results revealed that the materials developed were biocompatible, less hemolytic, and having non-thrombogenic properties indicating the promising applications in the field of cardiovascular applications.

Effects of rotary ultrasonic bone drilling on cutting force and temperature in the human bones.

Efficacy and outcomes of osteosynthesis depend on various factors including types of injury and repair, host factors, characteristics of implant materials and type of implantation. One of the most important host factors appears to be the extent of bone damage due to the mechanical force and thermal injury which are produced at cutting site during bone drilling. The temperature above the critical temperature (47 °C) produces thermal osteonecrosis in the bones. In the present work, experimental investigations were performed to determine the effect of drilling parameters (rotational speed, feed rate and drill diameter) and techniques (conventional surgical bone drilling and rotary ultrasonic bone drilling) on cutting force and temperature generated during bone drilling. The drilling experiments were performed by a newly developed bone drilling machine on different types of human bones (femur, tibia and fibula) having different biological structure and mechanical behaviour. The bone samples were procured from male cadavers with the age of second to fourth decades. The results revealed that there was a significant difference (p < 0.05) in cutting force and temperature rise for rotary ultrasonic bone drilling and conventional surgical bone drilling. The cutting force obtained in rotary ultrasonic bone drilling was 30%-40%, whereas temperature generated was 50%-55% lesser than conventional surgical bone drilling process for drilling in all types of bones. It was also found that the cutting force increased with increasing feed rate, drill diameter and decrease in rotational speed, whereas increasing rotational speed, drill diameter and feed rate resulted in higher heat generation during bone drilling. Both the techniques revealed that the axial cutting force and the temperature rise were significantly higher in femur and tibia compared with the fibula for all combinations of process parameters.

Experimental investigations and statistical modeling of cutting force and torque in rotary ultrasonic bone drilling of human cadaver bone.

Cutting force and torque are important factors in the success of the bone drilling process. In the recent past, many attempts have been made to reduce the cutting force and torque in the bone drilling process. In this work, drilling on human cadaver bones has been performed using rotary ultrasonic bone drilling process to investigate the effect of drilling parameters on cutting force and torque. The experimental work was carried on a recently developed rotary ultrasonic bone drilling machine for surgical operations. The experimental work was performed in two phases. The first phase includes a comparative study between rotary ultrasonic bone drilling and conventional surgical bone drilling, to study the influence of various drilling parameters (rotational speed, drill diameter, and drilling tool feed rate) on the cutting force and torque. The results revealed that the cutting force and torque produced during drilling operations in rotary ultrasonic bone drilling were lesser (30%-40%) than conventional surgical bone drilling. In the second phase, response surface methodology was used to perform the statistical modeling of cutting force and torque in rotary ultrasonic bone drilling process. Analysis of variance was performed at a confidence interval of 95% to analyze the significant contribution (p < 0.05) of process parameters (drilling speed, feed rate, drill diameter, and abrasive particle size) on the responses (cutting force and torque). The confirmatory experiments were performed to validate the developed statistical models. It was found that both cutting force and torque decrease with increase in drilling speed and increases with the increasing drill diameter, feed rate, and abrasive particle size.

Machining forces in ultrasonic-vibration assisted end milling.

Ultrasonic assisted milling (UAM) is one of the advancements in the area of conventional milling process. Literature suggests that superpositioning of ultrasonic vibration with milling process improves its efficacy by reducing forces and improving surface finish. In the present study experimental investigations were carried out to evaluate the effect of process parameters (power of ultrasonic vibration (UP), rotational speed, axial depth of cut (DOC) and feed rate) on the cutting responses (average cutting force and the standard deviation in cutting forces). An experimental setup was designed and developed to perform UAM process with axial vibrations. The end mill used in this setup was designed by performing harmonic analysis on ANSYS workbench. UAM experiments based on central composite design (CCD) technique were performed on Al6063 aluminum alloy. Analysis of variance (ANOVA) was performed and regression equations were obtained. Further, the obtained results were analyzed to study the effect of machining parameters on the responses. The developed models were then validated by performing experiments on random and optimized set of process parameters. The ANOVA results suggested that the most effective parameter for cutting forces was feed rate, however its standard deviation was affected by rotational speed. Also the assistance of axial vibration reduced the average cutting force and increased its standard deviation. In order to evaluate the effect of axial ultrasonic vibrations, simulations were performed to study the cutting kinematics in UAM process. The simulations showed that the presence of torsional vibration at the cutting tip, caused intermittent cutting during UAM.

Experimental assessment of biomechanical properties in human male elbow bone subjected to bending and compression loads.

This work discusses the biomechanical testing of 3 elbow bones, namely the humerus, ulna, and radius. There is a need to identify the mechanical properties of the bones at the organ level. The following tests were performed: 3-point bending, fracture toughness, and axial compression. Six sets of whole-bone samples of human male cadaveric humerus, ulna, and radius (age of donor: 35 to 56 years) were tested. The results were analyzed for statistical significance by 2-stage, repeated-measure analysis of variance (ANOVA). The difference between the bending strength of the humerus, ulna, and radius was statistically significant ( P = .001) when compared to one another. However, the fracture toughness and compressive strength were observed to be similar for the 3 bones. The knowledge of mechanical properties of elbow bones can aid in the design of elbow implants and upper limb protection systems, and also allow us to identify criteria for injury. Further, knowledge of the mechanical properties of the elbow bones can aid in calibrating simulations through finite elements analysis.