Lay-down Pattern Research Articles

Enhanced Bone Healing in Critical-Sized Rabbit Femoral Defects: Impact of Helical and Alternate Scaffold Architectures.

This study investigates the effect of scaffold architecture on bone regeneration, focusing on 3D-printed polylactic acid-bioceramic calcium phosphate (PLA-bioCaP) composite scaffolds in rabbit femoral condyle critical defects. We explored two distinct scaffold designs to assess their influence on bone healing and scaffold performance. Structures with alternate (0°/90°) and helical (0°/45°/90°/135°/180°) laydown patterns were manufactured with a 3D printer using a fused deposition modeling technique. The scaffolds were meticulously characterized for pore size, strut thickness, porosity, pore accessibility, and mechanical properties. The in vivo efficacy of these scaffolds was evaluated using a femoral condyle critical defect model in eight skeletally mature New Zealand White rabbits. Then, the results were analyzed micro-tomographically, histologically, and histomorphometrically. Our findings indicate that both scaffold architectures are biocompatible and support bone formation. The helical scaffolds, characterized by larger pore sizes and higher porosity, demonstrated significantly greater bone regeneration than the alternate structures. However, their lower mechanical strength presented limitations for use in load-bearing sites.

An explainable machine learning-based probabilistic framework for the design of scaffolds in bone tissue engineering.

Recently, 3D-printed biodegradable scaffolds have shown great potential for bone repair in critical-size fractures. The differentiation of the cells on a scaffold is impacted among other factors by the surface deformation of the scaffold due to mechanical loading and the wall shear stresses imposed by the interstitial fluid flow. These factors are in turn significantly affected by the material properties, the geometry of the scaffold, as well as the loading and flow conditions. In this work, a numerical framework is proposed to study the influence of these factors on the expected osteochondral cell differentiation. The considered scaffold is rectangular with a 0/90 lay-down pattern and a four-layered strut made of polylactic acid with a 5% steel particle content. The distribution of the different types of cells on the scaffold surface is estimated through a scalar stimulus, calculated by using a mechanobioregulatory model. To reduce the simulation time for the computation of the stimulus, a probabilistic machine learning (ML)-based reduced-order model (ROM) is proposed. Then, a sensitivity analysis is performed using the Shapley additive explanations to examine the contribution of the various parameters to the framework stimulus predictions. In a final step, a multiobjective optimization procedure is implemented using genetic algorithms and the ROM, aiming to identify the material parameters and loading conditions that maximize the percentage of surface area populated by bone cells while minimizing the area corresponding to the other types of cells and the resorption condition. The results of the performed analysis highlight the potential of using ROMs for the scaffold design, by dramatically reducing the simulation time while enabling the efficient implementation of sensitivity analysis and optimization procedures.

3D Printed Piezoelectric BaTiO3/Polyhydroxybutyrate Nanocomposite Scaffolds for Bone Tissue Engineering.

Bone defects are a significant health problem worldwide. Novel treatment approaches in the tissue engineering field rely on the use of biomaterial scaffolds to stimulate and guide the regeneration of damaged tissue that cannot repair or regrow spontaneously. This work aimed at developing and characterizing new piezoelectric scaffolds to provide electric bio-signals naturally present in bone and vascular tissues. Mixing and extrusion were used to obtain nanocomposites made of polyhydroxybutyrate (PHB) as a matrix and barium titanate (BaTiO3) nanoparticles as a filler, at BaTiO3/PHB compositions of 5/95, 10/90, 15/85 and 20/80 (w/w%). The morphological, thermal, mechanical and piezoelectric properties of the nanocomposites were studied. Scanning electron microscopy analysis showed good nanoparticle dispersion within the polymer matrix. Considerable increases in the Young's modulus, compressive strength and the piezoelectric coefficient d31 were observed with increasing BaTiO3 content, with d31 = 37 pm/V in 20/80 (w/w%) BaTiO3/PHB. 3D printing was used to produce porous cubic-shaped scaffolds using a 90° lay-down pattern, with pore size ranging in 0.60-0.77 mm and good mechanical stability. Biodegradation tests conducted for 8 weeks in saline solution at 37 °C showed low mass loss (∼4%) for 3D printed scaffolds. The results obtained in terms of piezoelectric, mechanical and chemical properties of the nanocomposite provide a new promising strategy for vascularized bone tissue engineering.

Design, fabrication, and characterization of 3D-printed ABS and PLA scaffolds potentially for tissue engineering

Additive manufacturing technologies are getting attention as a prospective substitute for conventional medical implant production methods owing to their unique manufacturing properties. In addition, biomaterials are required for bone repair and tissue engineering (BTE) techniques to provide scaffolds with the necessary biological and structural properties and improved performance. In this study, widely available biocompatible materials acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) are utilized for the design, fabrication, simulation, and mechanical characterization of 3D-printed scaffolds with two lay-down patterns potentially for bone tissue engineering. Mechanical properties of the 3D-printed scaffolds are determined by compression test and finite element analysis (FEA). Moreover, scanning electron microscope (SEM) images are also analyzed to determine the printing accuracy of the scaffolds. The porosity of the scaffolds is estimated both theoretically and through the liquid displacement method. Finally, the comparative analysis between PLA and ABS scaffolds indicates that the PLA scaffold has a higher potential for bone tissue regeneration. This study provides a notable engineering contribution by using a cost-efficient and easily available biomaterial as an alternative to bone tissue.

Highly compliant biomimetic scaffolds for small diameter tissue-engineered vascular grafts (TEVGs) produced via melt electrowriting (MEW)

Biofabrication approaches toward the development of tissue-engineered vascular grafts (TEVGs) have been widely investigated. However, successful translation has been limited to large diameter applications, with small diameter grafts frequently failing due to poor mechanical performance, in particular mismatched radial compliance. Herein, melt electrowriting (MEW) of poly(ϵ-caprolactone) has enabled the manufacture of highly porous, biocompatible microfibre scaffolds with physiological anisotropic mechanical properties, as substrates for the biofabrication of small diameter TEVGs. Highly reproducible scaffolds with internal diameter of 4.0 mm were designed with 500 and 250 µm pore sizes, demonstrating minimal deviation of less than 4% from the intended architecture, with consistent fibre diameter of 15 ± 2 µm across groups. Scaffolds were designed with straight or sinusoidal circumferential microfibre architecture respectively, to investigate the influence of biomimetic fibre straightening on radial compliance. The results demonstrate that scaffolds with wave-like circumferential microfibre laydown patterns mimicking the architectural arrangement of collagen fibres in arteries, exhibit physiological compliance (12.9 ± 0.6% per 100 mmHg), while equivalent control geometries with straight fibres exhibit significantly reduced compliance (5.5 ± 0.1% per 100 mmHg). Further mechanical characterisation revealed the sinusoidal scaffolds designed with 250 µm pores exhibited physiologically relevant burst pressures of 1078 ± 236 mmHg, compared to 631 ± 105 mmHg for corresponding 500 µm controls. Similar trends were observed for strength and failure, indicating enhanced mechanical performance of scaffolds with reduced pore spacing. Preliminary in vitro culture of human mesenchymal stem cells validated the MEW scaffolds as suitable substrates for cellular growth and proliferation, with high cell viability (>90%) and coverage (>85%), with subsequent seeding of vascular endothelial cells indicating successful attachment and preliminary endothelialisation of tissue-cultured constructs. These findings support further investigation into long-term tissue culture methodologies for enhanced production of vascular extracellular matrix components, toward the development of the next generation of small diameter TEVGs.

3D printed scaffold design for bone defects with improved mechanical and biological properties

Bone defect treatment is still a challenge in clinics, and synthetic bone scaffolds with adequate mechanical and biological properties are highly needed. Adequate waste and nutrient exchange of the implanted scaffold with the surrounded tissue is a major concern. Moreover, the risk of mechanical instability in the defect area during regular activity increases as the defect size increases. Thus, scaffolds with better mass transportation and mechanical properties are desired.This study introduces 3D printed polymeric scaffolds with a continuous pattern, ZigZag-Spiral pattern, for bone defects treatments. This pattern has a uniform distribution of pore size, which leads to uniform distribution of wall shear stress which is crucial for uniform differentiation of cells attached to the scaffolds. The mechanical, mass transportation, and biological properties of the 3D printed scaffolds are evaluated. The results show that the presented scaffolds have permeability similar to natural bone and, with the same porosity level, have higher mechanical properties than scaffolds with conventional lay-down patterns 0–90° and 0–45°.Finally, human mesenchymal stem cells are seeded on the scaffolds to determine the effects of geometrical microstructure on cell attachment and morphology. The results show that cells in scaffold with ZigZag-Spiral pattern infilled pores gradually, while the other patterns need more time to fill the pores. Considering mechanical, transportation, and biological properties of the considered patterns, scaffolds with ZigZag-Spiral patterns can mimic the properties of cancellous bones and be a better choice for treatments of bone defects.

Additive manufacturing and technical strategies for improving outcomes in breast reconstructive surgery

It has been widely reported that breast reconstruction improves the quality of life of women who undergo mastectomy for breast cancer. <br />This approach provides many psychological advantages. Today, different techniques are available for the breast oncoplastic surgeon <br />that involve the use of breast implants and autologous tissues, also offering interesting results in terms of aesthetic and patient-reported <br />outcomes. On the other hand, advanced technologies and design strategies (i.e. design for additive manufacturing, reverse engineering) <br />may allow the development of customised porous structures with tailored morphological, mechanical, biological, and mass transport <br />properties. For this reason, the current study deals with the challenges, principles, and methods of developing 3D additive manufactured <br />structures in breast reconstructive surgery. Specifically, the aim was to design 3D additive manufactured poly(ε-caprolactone) scaffolds <br />with different architectures (i.e. lay-down patterns). Preliminary mechanical and biological analyses have shown the effect of the lay-<br />down pattern on the performances of the manufactured structures.

Accurate Prediction of Melt Electrowritten Laydown Patterns from Simple Geometrical Considerations

AbstractMelt electrowriting (MEW), an electrohydrodynamic additive manufacturing technology, can produce polymer structures with micrometer resolution. Unlike conventional direct writing of fluids, the laydown pattern often deviates from the programmed one, due to a lag in the electrified jet. MEW of increasingly complex patterns currently entails a cumbersome trial‐and‐error procedure of adjusting printing parameters to ensure good accuracy. This issue is addressed with a geometrical model that predicts the expected printed fiber path, based on the coded trajectory, critical translation speed, and the collector speed. The influence of the process parameters on the jet lag is investigated and a general equation for the lag computation is implemented into the model. The presented model can evaluate the printing result up to ten times more accurate than the designed collector movement path and thus assist in identifying printing defects and adjustment of the printing G‐code in advance.

3D printed Sr-containing composite scaffolds: Effect of structural design and material formulation towards new strategies for bone tissue engineering

The use of composite materials, processed as 3D tissue-like scaffolds, has been widely investigated as a promising strategy for bone tissue engineering applications. Also, additive manufacturing technologies such as fused deposition modelling (FDM) have greatly contributed to the manufacture of patient-specific scaffolds with predefined pore structures and intricate geometries. However, conventional FDM techniques require the use of materials exclusively in the form of filaments, which in order to produce composite scaffolds lead to additional costs for the fabrication of precursor filaments as well as multi-step production methods. In this study, we propose the use of an advantageous extrusion-based printing technology, which provides the opportunity to easily co-print biomaterials, starting from their raw forms, and by using a single-step manufacturing and solvent-free process. Poly(e-caprolactone) (PCL), an FDA approved biodegradable material, was used as polymeric matrix while hydroxyapatite (HA) and strontium substituted HA (SrHA), at various contents were introduced as a bioactive reinforcing phase capable of mimicking the mineral phase of natural bone. Three different architectures for each material formulation were designed, and subsequently the effect of composition variations and structural designs was analysed in terms of physico-chemical, mechanical and biological performance. A correlation between architecture and compressive modulus, regardless the formulation tested, was observed demonstrating how the laydown pattern influences the resulting 3D printed scaffolds’ stiffness. Furthermore, in vitro cell culture by using TERT Human Mesenchymal Stromal Cells (hTERT-MSCs) revealed that Sr-containing composite scaffolds showed greater levels of mineralisation and osteogenic potential in comparison to bare PCL and pure HA.

3D printed PCL scaffold reinforced with continuous biodegradable fiber yarn: A study on mechanical and cell viability properties

In this study, poly (ε‐caprolactone) (PCL) scaffolds were printed and reinforced, simultaneously, with biodegradable poly glycolic acid (PGA) suture yarn, as a continuous reinforcing fiber, in the Fused Deposition Modeling (FDM) 3D printing process. Albeit PCL is a suitable material for biomedical applications, its low mechanical properties, and low degradation rate have limited its usage. A biocompatible suture yarn was used as the reinforcing material to enhance the mechanical properties and biodegradation characteristics, via an innovative method of continuous fiber embedding in the FDM process. The reinforced PCL samples were 3D printed with the setting porosity value of 60% and 0°/60°/120° lay-down pattern. The mechanical and biological properties of the scaffolds were tested to prove the effectiveness of the produced scaffolds for bone substitute purposes. Mechanical properties assessments showed that with a 22 vol.% suture yarn content in the 3D printed PCL scaffolds, the tensile strength, and elastic modulus remarkably increased up to 374% and 775%, respectively. The degradation of the reinforced PCL was 20 times higher than that of the non-reinforced PCL samples, after ten weeks, dominated by the fiber degradation phenomenon. After three days of cell culture, the proliferation assay of the built scaffovd the non-toxicity of the reinforced PCL.

The effect of introduction of filament shift on degradation behaviour of PLGA- and PLCL-based scaffolds fabricated via additive manufacturing

The degradation rate of polyester scaffolds has been emphasised as one of the main areas of concern in bone tissue engineering. In ideal conditions, the degradation of polymeric constructs should match regeneration of the injured tissue. Thus, there is an imperative need to strictly define and understand determinants influencing the degradation rate of scaffolds. In this study, we focused on the effect of filament shift introduction on degradation behaviour of the polymeric-based scaffolds. The poly(l-lactide-co-glycolide) (PLGA), poly(l-lactide-co-ε-caprolactone) (PLCL) and their tricalcium-phosphate-loaded (TCP) composites containing 20 and 40 wt% of filler, were utilized to fabricate constructs using modified fused deposition modeling (FDM). The scaffolds were designed with filament lay-down pattern of 0°/90° and with or without the modifications of filament distance in n+2 layer, shifted and non-shifted constructs were obtained, respectively. To investigate the degradation profile, the change of mass, pH, water absorption and initial molecular weight (Mw0) loss was observed during the degradation study in phosphate buffered saline (PBS) at 37 °C for up to 48 weeks. The scaffold morphology was evaluated utilizing scanning electron microscopy (SEM) and the visualization of the topography was performed utilizing atomic force microscopy (AFM). Surface area to volume ratio (SVR) and porosity were determined using micro-computed tomography (μCT). The fluid flow simulations were used to define the permeability of two investigated groups of scaffolds. The results of this study clearly demonstrate the accelerating effect of filament shift introduction on degradation behaviour in the scaffolds with similar porosity and SVR. The decrease of Mw0 was significantly higher in case of all shifted samples. We assume that faster degradation of shifted constructs may be attributed to their tortuosity, making them less permeable and prone to the degradation, as the result of the accumulation of acidic products in the tortuous architecture of the samples. Thus, the effect of introduction of filament shift into scaffold architecture comprise an attractive approach to influence the degradation rate in case of bone regeneration with the use of polyesters scaffolds.

Integrating finite element modelling and 3D printing to engineer biomimetic polymeric scaffolds for tissue engineering

ABSTRACTThe suitability of a scaffold for tissue engineering is determined by a number of interrelated factors. The biomaterial should be biocompatible and cell instructive, with a porosity and pore interconnectivity that facilitates cellular migration and the transport of nutrients and waste products into and out of the scaffolds. For the engineering of load bearing tissues, the scaffold may also be required to possess specific mechanical properties and/or ensure the transfer of mechanical stimuli to cells to direct their differentiation. Achieving these design goals is challenging, but could potentially be realised by integrating computational tools such as finite element (FE) modelling with three-dimensional (3D) printing techniques to assess how scaffold architecture and material properties influence the performance of the implant. In this study we first use Fused Deposition Modelling (FDM) to modulate the architecture of polycaprolactone (PCL) scaffolds, exploring the influence of varying fibre diameter, spacing and laydown pattern on the structural and mechanical properties of such scaffolds. We next demonstrate that a simple FE modelling strategy, which captures key aspects of the printed scaffold’s actual geometry and material behaviour, can be used to accurately model the mechanical characteristics of such scaffolds. We then show the utility of this strategy by using FE modelling to help design 3D printed scaffolds with mechanical properties mimicking that of articular cartilage. In conclusion, this study demonstrates that a relatively simple FE modelling approach can be used to inform the design of 3D printed scaffolds to ensure their bulk mechanical properties mimic specific target tissues.

The Impact of Melt Electrowritten Scaffold Design on Porosity Determined by X-Ray Microtomography.

Melt electrowriting (MEW) is an additive manufacturing (AM) technique using thermoplastic polymers to produce microscale structures, including scaffolds for tissue engineering. MEW scaffolds have, in general, high porosities and can be designed with different fiber diameters, spacings, and laydown patterns. The need for a reliable method for scaffold characterization is essential for quality assurance and research purposes. In this study, we describe the use of submicrometer X-ray tomography for the generation of local thickness maps of volume porosity of 16 different scaffold groups, comprising 2 diameter groups, 2 fiber spacing groups, and 4 different laydown patters (0/90°, 0/60/120°, 0/45/90/135°, and 0/30/60/90/120/150°), all made using a custom-built MEW printer with medical-grade poly(ɛ-caprolactone). The results showed a porosity range between 77.7% and 90.7% for all the scaffolds. Moreover, the influence of the scaffold regularity and flatness in the more regular pore shapes (0/90°, 0/60/120°) lead to the shift of the local thickness graph to one side, and thus the prevalence of one pore size. This nondestructive method for MEW scaffold characterization overcomes the limitations of microscopic methods of pore shape and size estimation.Impact StatementMelt electrowriting is an AM technology that bridges the gap between solution electrospinning and melt microextrusion technologies. It can be applied to biomaterials and tissue engineering by making a spectrum of scaffolds with various laydown patterns at dimensions not previously studied. Using submicrometer X-ray tomography, a “fingerprint” of porosity for such scaffolds can be obtained and used as an important measure for quality control, to ensure that the scaffold fabricated is the one designed and allows the selection of specific scaffolds based on desired porosities.

Quasi-static and dynamic in vitro mechanical response of 3D printed scaffolds with tailored pore size and architectures

Scaffold-based Tissue Engineering represents the most promising approach for the regeneration of load bearing skeletal tissues, in particular bone and cartilage. Scaffolds play major role in this process by providing a physical template for cells to adhere and proliferate whilst ensuring an adequate biomechanical support at the defect site. Whereas the quasi static mechanical properties of porous polymeric scaffolds are well documented, the response of these constructs under high strain compressive rates remain poorly understood. Therefore, this study investigates, for the first time, the influence of pore size and geometry on the mechanical behaviour of Polycaprolactone (PCL) scaffolds under quasi static and dynamic conditions. 3D printed scaffolds with varied pore sizes and geometries were obtained using different filament distances (FD) and lay-down patterns, respectively. In particular, by fixing the lay-down pattern at 0/90° and varying the FD between 480 and 980 μm it was possible to generate scaffolds with square pores with dimensions in the range of 150–650 μm and porosities of 59–79%. On the other hand, quadrangular, hexagonal, triangular and complex pore geometries with constant porosity (approx. 70%) were obtained at a fixed FD of 680 μm and imposing four different lay-down patterns of 0/90, 0/60/120, 0/45/90/135 and 0/30/60/90/120/150°, respectively. The mechanical response of printed scaffolds was assessed under two different compression loading regimes spanning five distinct strain rates, from 10−2 to 2000 s−1, using two different apparatus: a conventional screw-driven testing machine (Instron 4483) and a Split Hopkinson pressure bar (SHPB) equipped with a set of A201 Flexi-force™ (FF) force sensors and a pulse shaper. Our results show that the mechanical properties of PCL scaffolds are not strain rate sensitive between 1300 and 2000 s−1 and these strongly depend on the pore size (porosity) rather than pore geometry. Those findings are extremely relevant for the engineering of bone tissue scaffolds with enhanced mechanical stability by providing new data describing the mechanical response of these constructs at high strain rates as well as the at the transition between quasi static and dynamic regimes.

Enhanced osteogenic activity by MC3T3-E1 pre-osteoblasts on chemically surface-modified poly(ε-caprolactone) 3D-printed scaffolds compared to RGD immobilized scaffolds

In bone tissue engineering, the intrinsic hydrophobicity and surface smoothness of three-dimensional (3D)-printed poly(ε-caprolactone) scaffolds hamper cell attachment, proliferation and differentiation. This intrinsic hydrophobicity of poly(ε-caprolactone) can be overcome by surface modifications, such as surface chemical modification or immobilization of biologically active molecules on the surface. Moreover, surface chemical modification may alter surface smoothness. Whether surface chemical modification or immobilization of a biologically active molecule on the surface is more effective to enhance pre-osteoblast proliferation and differentiation is currently unknown. Therefore, we aimed to investigate the osteogenic response of MC3T3-E1 pre-osteoblasts to chemically surface-modified and RGD-immobilized 3D-printed poly(ε-caprolactone) scaffolds. Poly(ε-caprolactone) scaffolds were 3D-printed consisting of strands deposited layer by layer with alternating 0°/90° lay-down pattern. 3D-printed poly(ε-caprolactone) scaffolds were surface-modified by either chemical modification using 3 M sodium hydroxide (NaOH) for 24 or 72 h, or by RGD-immobilization. Strands were visualized by scanning electron microscopy. MC3T3-E1 pre-osteoblasts were seeded onto the scaffolds and cultured up to 14 d. The strands of the unmodified poly(ε-caprolactone) scaffold had a smooth surface. NaOH treatment changed the scaffold surface topography from smooth to a honeycomb-like surface pattern, while RGD immobilization did not alter the surface topography. MC3T3-E1 pre-osteoblast seeding efficiency was similar (44%–54%) on all scaffolds after 12 h. Cell proliferation increased from day 1 to day 14 in unmodified controls (1.9-fold), 24 h NaOH-treated scaffolds (3-fold), 72 h NaOH-treated scaffolds (2.2-fold), and RGD-immobilized scaffolds (4.5-fold). At day 14, increased collagenous matrix deposition was achieved only on 24 h NaOH-treated (1.8-fold) and RGD-immobilized (2.2-fold) scaffolds compared to unmodified controls. Moreover, 24 h, but not 72 h, NaOH-treated scaffolds, increased alkaline phosphatase activity by 5-fold, while the increase by RGD immobilization was only 2.5-fold. Only 24 h NaOH-treated scaffolds enhanced mineralization (2.0-fold) compared to unmodified controls. In conclusion, RGD immobilization (0.011 μg mg−1 scaffold) on the surface and 24 h NaOH treatment of the surface of 3D-printed PCL scaffold both enhance pre-osteoblast proliferation and matrix deposition while only 24 h NaOH treatment results in increased osteogenic activity, making it the treatment of choice to promote bone formation by osteogenic cells.

User interface tool for a novel plasma-assisted bio-additive extrusion system

PurposeThis paper aims to describe the control software of a novel manufacturing system called plasma-assisted bio-extrusion system (PABS), designed to produce complex multi-material and functionally graded scaffolds for tissue engineering applications. This fabrication system combines multiple pressure-assisted and screw-assisted printing heads and plasma jets. Control software allows the users to create single or multi-material constructs with uniform pore size or pore size gradients by changing the operation parameters, such as geometric parameters, lay-down pattern, filament distance, feed rate and layer thickness, and to produce functional graded scaffolds with different layer-by-layer coating/surface modification strategies by using the plasma modification system.Design/methodology/approachMATLAB GUI is used to develop the software, including the design of the user interface and the implementation of all mathematical programing for both multi-extrusion and plasma modification systems.FindingsBased on the user definition, G programing codes are generated, enabling full integration and synchronization with the hardware of PABS. Single, multi-material and functionally graded scaffolds can be obtained by manipulating different materials, scaffold designs and processing parameters. The software is easy to use, allowing the efficient control of the PABS even for the fabrication of complex scaffolds.Originality/valueThis paper introduces a novel additive manufacturing system for tissue engineering applications describing in detail the software developed to control the system. This new fabrication system represents a step forward regarding the current state-of-the-art technology in the field of biomanufacturing, enabling the design and fabrication of more effective scaffolds matching the mechanical and surface characteristics of the surrounding tissue and enabling the incorporation of high number of cells uniformly distributed and the introduction of multiple cell types with positional specificity.

Feasibility of Polycaprolactone Scaffolds Fabricated by Three-Dimensional Printing for Tissue Engineering of Tunica Albuginea.

PurposeTo investigate the feasibility of a polycaprolactone (PCL) scaffold fabricated by three-dimensional (3D) printing for tissue engineering applications for tunica albuginea.Materials and MethodsPCL scaffolds were fabricated by use of a 3D printing system. Two scaffolds were fabricated that differed in the architecture of the lay-down pattern: a 90°PCL scaffold and a 45°PCL scaffold. Mechanical properties were measured to compare tensile strength between the two scaffold types. The scaffolds were characterized by scanning electron microscope (SEM) images. The scaffolds were seeded with fibroblast cells, and the ability of these scaffolds to support the cells was evaluated by immunofluorescence staining.ResultsThe PCL scaffolds had well-structured shapes, regular arrays, and good interconnection in SEM images. The horizontal and vertical Young's modulus coefficients were 13 and 12 MPa for the 90°PCL scaffold and 19 and 21 MPa for the 45°PCL scaffold, respectively. Microscopy images revealed that human fibroblast cells covered the entire scaffold surface. Immunofluorescence staining of ER-TR7 confirmed that the fibroblast cells remained viable and proliferated throughout the time course of the culture.ConclusionsThis preliminary study provides experimental evidence for the feasibility of 3D printing of PCL scaffolds for tissue engineering applications of tunica albuginea.

Poly-l-lactic acid: Pellets to fiber to fused filament fabricated scaffolds, and scaffold weight loss study

Poly-l-lactic acid (PLLA) is a bioresorbable polymer used in a variety of biomedical applications. Many 3D printers employ the fused filament fabrication (FFF) approach with the ubiquitous low-cost poly-lactic acid (PLA) fiber. However, use of the FFF approach to fabricate scaffolds with medical grade PLLA polymer remains largely unexplored. In this study, high molecular weight PL-32 pellets were extruded into ∼1.7mm diameter PLLA fiber. Melt rheometric data of the PLLA polymer was analyzed and demonstrated pseudo-plastic behavior with a flow index of n=0.465 (<1). Differential scanning calorimetry (DSC) was conducted using samples from the extruded fiber to obtain thermal properties. DSC of the 3D printed struts was also analyzed to assess changes in thermal properties due to FFF. The DSC and rheometric analysis results were subsequently used to define appropriate FFF process parameters. Constant porosity scaffolds were FFF 3D printed with 4 distinct laydown patterns; 0/90° rectilinear (control), 45/135° rectilinear, Archimedean chords, and honeycomb using the in-house developed custom multi-modality 3D bioprinter (CMMB). The effect of laydown pattern on scaffold bulk erosion (weight loss) was studied by immersion in phosphate-buffered saline (PBS) over a 6-month period and measured monthly. A repeated measures analysis of variance (ANOVA) was performed to identify statistically significant differences between mean percent weight loss of the four laydown patterns at each time point (1–6 months). The resulting data follows distinct temporal trends, but no statistically significant differences between means at individual time points were found. Cross-sectional scanning electron microscope (SEM) images of the 6-month degraded scaffolds showed noticeable structural deterioration. The study demonstrates successful processing of PLLA fiber from PL-32 pellets and FFF-based 3D printing of bioresorbable scaffolds with pre-defined laydown patterns using medical grade PLLA polymer which could prove beneficial in biomedical applications.

Effects of 3D-bioplotted polycaprolactone scaffold geometry on human adipose-derived stem cell viability and proliferation

PurposeThis study aims to investigate the effect of three-dimensional (3D)- bioplotted polycaprolactone (PCL) scaffold geometry on the biological and mechanical characteristics of human adipose-derived stem cell (hASC) seeded constructs.Design/methodology/approachFour 3D-bioplotted scaffold disc designs (Ø14.5 × 2 mm) with two levels of strand–pore feature sizes and two strand laydown patterns (0°/90° or 0°/120°/240°) were evaluated for hASC viability, proliferation and construct compressive stiffness after 14 days of in vitro cell culture.FindingsScaffolds with the highest porosity (smaller strand–pore size in 0°/120°/240°) yielded the highest hASC proliferation and viability. Further testing of this design in a 6-mm thick configuration showed that cells were able to penetrate and proliferate throughout the scaffold thickness. The design with the lowest porosity (larger strand–pore size in 0°/90°) had the highest compression modulus after 14 days of culture, but resulted in the lowest hASC viability. The strand laydown pattern by itself did not influence the compression modulus of scaffolds. The 14-day cell culture also did not cause significant changes in compressive properties in any of the four designs.Originality/valuehASC hold great potential for musculoskeletal tissue engineering applications because of their relative ease of harvest, abundance and differentiation abilities. This study reports on the effects of 3D-bioplotted scaffold geometry on mechanical and biological characteristics of hASC-seeded PCL constructs. The results provide the basis for future studies which will use this optimal scaffold design to develop constructs for hASC-based osteochondral tissue engineering applications.

Robust formulation for the design of tissue engineering scaffolds: A comprehensive study on structural anisotropy, viscoelasticity and degradation of 3D scaffolds fabricated with customized desktop robot based rapid prototyping (DRBRP) system

This study investigates the scaffolds' structural anisotropy (i.e. the effect of loading direction), viscoelasticity (i.e. the effect of cross head speed or strain rate), and the influence of simulated physiological environment (PBS solution at 37°C) on the mechanical properties. Besides, the in vitro degradation study has also been performed that evaluates the effect of variation in material and lay-down pattern on the scaffolds' degradation kinetics in terms of mass loss, and change in morphological and mechanical properties. Porous three dimensional (3D) scaffolds of polycarprolactone (PCL) and polycarprolactone-polyethylene glycol (PCL-PEG) were developed by laying down the microfilaments directionally layer-by-layer using an in-house built computer-controlled extrusion and deposition process, called desktop robot based rapid prototyping (DRBRP) system. The loading direction, strain rate and physiological environment directly influenced the mechanical properties of the scaffolds. In vitro degradation study demonstrated that both PCL and PCL-PEG scaffolds realized homogeneous hydrolytic degradation via surface erosion resulting in a consistent and predictable mass loss. The linear mass loss caused uniform and linear increase in porosity that accordingly led to the decrease in mechanical properties. The synthetic polymer had the potential to modulate hydrophilicity and/or degradability and consequently, the biomechanical properties of the scaffolds by varying the polymer constituents.