Precision Extrusion Deposition Research Articles

Development and assessment of modified-honeycomb-structure scaffold for bone tissue engineering

Scaffolds for bone tissue engineering should have sufficient mechanical properties comparable with those of the surrounding native bone tissue. Therefore, it is necessary to improve the mechanical properties, especially compressive strength, of 3D scaffolds for bone tissue engineering applications. Various studies have focused on the variation or manipulation of structures or materials, for example, the Kagome-structure scaffold or polycaprolactone/hydroxyapatite composite scaffold. In this study, we propose a modified honeycomb structure for 3D bone-tissue-engineering scaffolds. This is a 3D honeycomb structure with pores at its walls to enhance the interconnectivity. The honeycomb structure is known to be the strongest structure with respect to its weight. Therefore, the honeycomb structure inspired us to apply it to bone-tissue-engineering scaffolds, and its 3D interconnectivity was enhanced by adding pores in its walls without a considerable decrease in its mechanical strength. By means of numerical analysis, the compressive stiffness of the modified-honeycomb-structure scaffold was investigated, and it was found that the effective compressive modulus of the modified-honeycomb-structure scaffold was significantly superior to those of Kagome-structure and grid-structure scaffolds having similar porosity of 50% and main pore size of 500 µm. Meanwhile, the Kagome-structure scaffold had the highest compressive modulus among the reported 3D interconnected scaffolds. Moreover, the modified-honeycomb-structure scaffolds were successfully fabricated with polycaprolactone (PCL) using a lab-made bio-printer with a precision extrusion deposition (PED) system employing a nozzle with a size of 50 µm, and a compressive test using a UTM was performed to prove the numerical result, in which the effective compressive modulus of the modified-honeycomb-structure scaffold was found to be superior to that of the Kagome-structure scaffold. Furthermore, we assessed cell proliferation, and the modified-honeycomb-structured scaffold was more favorable for cell proliferation than the Kagome-structure and grid-structure scaffolds. • Modified-honeycomb scaffold was proposed and successfully fabricated with PCL. • Compressive stiffness of proposed scaffold was evaluated numerically. • Compressive stiffness of proposed scaffold was validated experimentally. • Proposed scaffold has the highest compressive stiffness among the control groups. • Proposed scaffold promote in-vitro cell behavior similar to the control groups.

3D Printed Masks for Powders and Viruses Safety Protection Using Food Grade Polymers: Empirical Tests.

The production of 3D printed safety protection devices (SPD) requires particular attention to the material selection and to the evaluation of mechanical resistance, biological safety and surface roughness related to the accumulation of bacteria and viruses. We explored the possibility to adopt additive manufacturing technologies for the production of respirator masks, responding to the sudden demand of SPDs caused by the emergency scenario of the pandemic spread of SARS-COV-2. In this study, we developed different prototypes of masks, exclusively applying basic additive manufacturing technologies like fused deposition modeling (FDM) and droplet-based precision extrusion deposition (db-PED) to common food packaging materials. We analyzed the resulting mechanical characteristics, biological safety (cell adhesion and viability), surface roughness and resistance to dissolution, before and after the cleaning and disinfection phases. We showed that masks 3D printed with home-grade printing equipment have similar performances compared to the industrial-grade ones, and furthermore we obtained a perfect face fit by customizing their shape. Finally, we developed novel approaches to the additive manufacturing post-processing phases essential to assure human safety in the production of 3D printed custom medical devices.

Design of a novel procedure for the optimization of the mechanical performances of 3D printed scaffolds for bone tissue engineering combining CAD, Taguchi method and FEA

In order to increase manufacturing and experimental efficiency, a certain degree of control over design performances before realization phase is recommended. In this context, this paper presents an integrated procedure to design 3D scaffolds for bone tissue engineering. The procedure required a combination of Computer Aided Design (CAD), Finite Element Analysis (FEA), and Design methodologies Of Experiments (DOE), firstly to understand the influence of the design parameters, and then to control them.Based on inputs from the literature and limitations imposed by the chosen manufacturing process (Precision Extrusion Deposition), 36 scaffold architectures have been drawn. The porosity of each scaffold has been calculated with CAD. Thereafter, a generic scaffold material was considered and its variable parameters were combined with the geometrical ones according to the Taguchi method, i.e. a DOE method. The compressive response of those principal combinations was simulated by FEA, and the influence of each design parameter on the scaffold compressive behaviour was clarified. Finally, a regression model was obtained correlating the scaffold's mechanical performances to its geometrical and material parameters. This model has been applied to a novel composite material made of polycaprolactone and innovative bioactive glass. By setting specific porosity (50%) and stiffness (0.05 GPa) suitable for trabecular bone substitutes, the model selected 4 of the 36 initial scaffold architectures. Only these 4 more promising geometries will be realized and physically tested for advanced indications on compressive strength and biocompatibility.

Analysis of polycaprolactone scaffolds fabricated via precision extrusion deposition for control of craniofacial tissue mineralization.

Recurrence of cranial bone fusion following surgical resection in craniosynostosis patients commonly requires additional surgical procedures. Surgical implantation of engineered 3D scaffolds that control tissue mineralization could be utilized to diminish recurrence of fusion. This study investigated the ability of composite scaffolds to control tissue mineralization when cultured in vitro. Precision-engineered scaffolds with calvarial cells were cultured in vitro at the Department of Orthodontics and Pediatric Dentistry, University of Michigan. Polycaprolactone (PCL) scaffolds were fabricated using a novel precision extrusion deposition technique. Polyethylene glycol (PEG) hydrogel was coated onto select scaffolds to inhibit mineralization. MC3T3E1(C4) calvarial cells were cultured with scaffolds in media containing ascorbate and phosphate to promote osteoblast differentiation and mineralization. Scaffolds were assayed for osteoblast differentiation by alkaline phosphatase assay. Scaffolds were assayed for mineralization by nano-computed tomography (nano-CT) and by von Kossa staining of histologic sections. MC3T3E1(C4) cells differentiated into osteoblasts and formed mineral when cultured on uncoated PCL scaffolds. MC3T3E1(C4) cells were significantly diminished in their ability to differentiate into osteoblasts when cultured on hydrogel-coated scaffold. Results of this study indicate that this novel printing technology can be used to fabricate 3D scaffolds to promote and inhibit tissue mineralization in a region-specific manner. Future studies are needed to establish utility of such scaffolds in vivo.

Fabrication of Microfluidic Manifold by Precision Extrusion Deposition and Replica Molding for Cell-Laden Device

A PED (precision extrusion deposition)/replica molding process enables scaffold guided tissue engineering of a heterocellular microfluidic device. We investigate two types of cell-laden devices: the first with a 3D microfluidic manifold fully embedded in a PDMS (polydimethylsiloxane) substrate and the second a channel network on the surface of the PDMS substrate for cell printing directly into device channels. Fully embedded networks are leak-resistant with simplified construction methods. Channels exposed to the surface are used as mold to hold bioprinted cell-laden matrix for controlled cell placement throughout the network from inlet to outlet. The result is a 3D cell-laden microfluidic device with improved leak-resistance (up to 2.0 mL/min), pervasive diffusion and control of internal architecture.

Fabrication of three-dimensional scaffolds using precision extrusion deposition with an assisted cooling device

In the field of biofabrication, tissue engineering and regenerative medicine, there are many methodologies to fabricate a building block (scaffold) which is unique to the target tissue or organ that facilitates cell growth, attachment, proliferation and/or differentiation. Currently, there are many techniques that fabricate three-dimensional scaffolds; however, there are advantages, limitations and specific tissue focuses of each fabrication technique. The focus of this initiative is to utilize an existing technique and expand the library of biomaterials which can be utilized to fabricate three-dimensional scaffolds rather than focusing on a new fabrication technique. An expanded library of biomaterials will enable the precision extrusion deposition (PED) device to construct three-dimensional scaffolds with enhanced biological, chemical and mechanical cues that will benefit tissue generation. Computer-aided motion and extrusion drive the PED to precisely fabricate micro-scaled scaffolds with biologically inspired, porosity, interconnectivity and internal and external architectures. The high printing resolution, precision and controllability of the PED allow for closer mimicry of tissues and organs. The PED expands its library of biopolymers by introducing an assisting cooling (AC) device which increases the working extrusion temperature from 120 to 250 °C. This paper investigates the PED with the integrated AC's capabilities to fabricate three-dimensional scaffolds that support cell growth, attachment and proliferation. Studies carried out in this paper utilized a biopolymer whose melting point is established to be 200 °C. This polymer was selected to illustrate the newly developed device's ability to fabricate three-dimensional scaffolds from a new library of biopolymers. Three-dimensional scaffolds fabricated with the integrated AC device should illustrate structural integrity and ability to support cell attachment and proliferation.

Accelerated differentiation of osteoblast cells on polycaprolactone scaffolds driven by a combined effect of protein coating and plasma modification

A combined effect of protein coating and plasma modification on the quality of the osteoblast–scaffold interaction was investigated. Three-dimensional polycaprolactone (PCL) scaffolds were manufactured by the precision extrusion deposition (PED) system. The structural, physical, chemical and biological cues were introduced to the surface through providing 3D structure, coating with adhesive protein fibronectin and modifying the surface with oxygen-based plasma. The changes in the surface properties of PCL after those modifications were examined by contact angle goniometry, surface energy calculation, surface chemistry analysis (XPS) and surface topography measurements (AFM). The effects of modification techniques on osteoblast short-term and long-term functions were examined by cell adhesion, proliferation assays and differentiation markers, namely alkaline phosphatase activity (ALP) and osteocalcin secretion. The results suggested that the physical and chemical cues introduced by plasma modification might be sufficient for improved cell adhesion, but for accelerated osteoblast differentiation the synergetic effects of structural, physical, chemical and biological cues should be introduced to the PCL surface.

Fabrication and plasma treatment of 3D polycaprolactane tissue scaffolds for enhanced cellular function

This paper reports a solid free-form fabrication (SFF) technology-based precision extrusion deposition (PED) process to manufacture three-dimensional (3D) polycaprolactane (PCL) scaffolds and their surface treatment with a plasma source for enhanced osteoblast cell adhesion and proliferation. The PED process allows us to manufacture tissue engineering scaffolds based on designed geometry with complete interconnectivity and controllable porosity. The as-fabricated PCL scaffolds have a pattern with a 0/90° strut configuration of 300 µm pore size and 250 µm strut width. In order to improve cellular activity on 3D PCL scaffolds, they were surface-treated with an oxygen-based plasma source. The surface hydrophilicity and total surface energy of PCL was increased with plasma treatment. Comparisons of different plasma treatment times, including 30 seconds, and 1, 2, 3, 5 and 7 minutes, were performed to identify the plasma treatment duration suggesting higher cellular adhesion and proliferation. The maximum value of total surface energy and its components (polar and dispersive) was observed in 3-min treated PCL scaffolds. In addition, the positive effect of plasma treatment was observed in stregth of cell adhesion, which was increased 55% on 3-min plasma-treated scaffolds compared to untreated and other plasma treatment duriations. Cell culture study over a 7-day period also showed that the cell number on 3-min treated scaffolds is 3-fold the number of cells on untreated scaffolds.

Recent Progress on the Development of Porous Bioactive Calcium Phosphate for Biomedical Applications

Hydroxyapatite (HA) and tricalcium phosphate are two members of the calcium phosphate compounds which have been used clinically for many years. Their good biocompatibility is attributed by its similar chemical composition to that of bone material. Porous calcium phosphate ceramics have found enormous use in biomedical applications including bone tissue regeneration, cell proliferation, and drug delivery. In bone tissue engineering it has been applied as filling material for bone defects and augmentation, artificial bone graft material, and prosthesis revision surgery. Their high surface area leads to excellent osteoconductivity and resorbability providing fast bone ingrowth. Many efforts on the development of porous calcium phosphates can be observed from a considerable numbers of patents which have been filled recently on various methods for preparing porous calcium phosphate for applications of bone implant, chromatography and so on. Porous calcium phosphate can be produced by a variety of methods including conversion of natural bones, ceramic foaming technique, polymeric sponge method, gel casting of foams, solvent casting/ salt leaching method, selective laser sintering, precision extrusion deposition, starch consolidation, microwave processing, slip casting, and electrophoretic deposition technique. Some of these methods have been combined to fabricate porous calcium phosphate with improved properties. These combination methods have yielded some promising results. This paper discusses briefly the fundamental aspects of porous calcium phosphate for biomedical applications as well as the various techniques used to prepare porous calcium phosphate.

Fabrication of three-dimensional polycaprolactone/hydroxyapatite tissue scaffolds and osteoblast-scaffold interactions in vitro

Computer-aided tissue-engineering approach was used to develop a novel precision extrusion deposition (PED) process to directly fabricate Polycaprolactone (PCL) and composite PCL/hydroxyapatite (PCL–HA) tissue scaffolds. The process optimization was carried out to fabricate both PCL and PCL–HA (25% concentration by weight of HA) with a controlled pore size and internal pore structure of the 0°/90° pattern. Two groups of scaffolds having 60% and 70% porosity and with pore sizes of 450 and 750 μm, respectively, were evaluated for their morphology and compressive properties using scanning electron microscopy (SEM) and mechanical testing. Our results suggested that inclusion of HA significantly increased the compressive modulus from 59 to 84 MPa for 60% porous scaffolds and from 30 to 76 MPa for 70% porous scaffolds. In vitro cell-scaffolds interaction study was carried out using primary fetal bovine osteoblasts to assess the feasibility of scaffolds for bone tissue-engineering application. The cell proliferation and differentiation were calculated by Alamar Blue assay and by determining alkaline phosphatase activity. The osteoblasts were able to migrate and proliferate over the cultured time for both PCL as well as PCL–HA scaffolds. Our study demonstrated the viability of the PED process to the fabricate PCL and PCL–HA composite scaffolds having necessary mechanical property, structural integrity, controlled pore size and pore interconnectivity desired for bone tissue engineering.

3D microtomographic characterization of precision extruded poly-epsilon-caprolactone scaffolds.

One of the dominant approaches to tissue engineering is the seeding of biodegradable, biocompatible polymer scaffolds with progenitor cells prior to 3D culture or implantation. The microarchitecture of these scaffolds has direct effects upon the ability of cells to attach, migrate, and differentiate. Microtomographic (micro-CT) scanners enable high-speed 3D characterization of the salient features of these polymer scaffolds. A micro-CT scan followed by 3D reconstruction of serial image sections can determine porosity, pore size, pore interconnectivity, strut size, and overall 3D microarchitecture. In this study, four polymer samples with different microarchitectures were manufactured through precision extrusion deposition free-form fabrication and subsequently characterized through micro-CT analysis. A desktop micro-CT scanner was used to examine each sample at approximately 19.1-micron resolution. 2D analyses and 3D reconstructions of core regions of each sample were performed. These results illustrate that qualitative and quantitative analysis of polymer scaffolds is possible using micro-CT and 3D reconstruction techniques.