Karina Arcaute

Stereolithography of spatially controlled multi-material bioactive poly(ethylene glycol) scaffolds.

Challenges remain in tissue engineering to control the spatial, mechanical, temporal and biochemical architectures of scaffolds. Unique capabilities of stereolithography (SL) for fabricating multi-material spatially controlled bioactive scaffolds were explored in this work. To accomplish multi-material builds, a mini-vat setup was designed allowing for self-aligning X-Y registration during fabrication. The mini-vat setup allowed the part to be easily removed and rinsed, and different photocrosslinkable solutions to be easily removed and added to the vat. Two photocrosslinkable hydrogel biopolymers, poly(ethylene glycol) dimethacrylate (PEG-dma, MW 1000) and poly(ethylene glycol) diacrylate (PEG-da, MW 3400), were used as the primary scaffold materials. Multi-material scaffolds were fabricated by including controlled concentrations of fluorescently labeled dextran, fluorescently labeled bioactive PEG or bioactive PEG in different regions of the scaffold. The presence of the fluorescent component in specific regions of the scaffold was analyzed with fluorescent microscopy, while human dermal fibroblast cells were seeded on top of the fabricated scaffolds with selective bioactivity and phase contrast microscopy images were used to show specific localization of cells in the regions patterned with bioactive PEG. Multi-material spatial control was successfully demonstrated in features down to 500 microm. In addition, the equilibrium swelling behavior of the two biopolymers after SL fabrication was determined and used to design constructs with the specified dimensions at the swollen state. The use of multi-material SL and the relative ease of conjugating different bioactive ligands or growth factors to PEG allows for the fabrication of tailored three-dimensional constructs with specified spatially controlled bioactivity.

Fused deposition modeling of patient‐specific polymethylmethacrylate implants

Purpose – The purpose of this paper is to investigate the use of medical‐grade polymethylmethacrylate (PMMA) in fused deposition modeling (FDM) to fabricate porous customized freeform structures for several applications including craniofacial reconstruction and orthopaedic spacers. It also aims to examine the effects of different fabrication conditions on porosity and mechanical properties of PMMA samples.Design/methodology/approach – The building parameters and procedures to properly and consistently extrude PMMA filament in FDM for building 3D structures were determined. Two experiments were performed that examined the effects of different fabrication conditions, including tip wipe frequency, layer orientation, and air gap (AG) (or distance between filament edges) on the mechanical properties and porosity of the fabricated structures. The samples were characterized through optical micrographs, and measurements of weight and dimensions of the samples were used to calculate porosity. The yield strength, s...

Effects of environmental conditions, aging, and build orientations on the mechanical properties of ASTM type I specimens manufactured via stereolithography

Purpose – The purpose of this paper is to investigate the effects of aging, pre‐conditioning, and build orientation on the mechanical properties of test samples fabricated using stereolithography (SL) and a commercially available resin.Design/methodology/approach – American Society for Testing and Materials (ASTM) Standard D638 Type I specimens were manufactured in a Viper si2 SL system using WaterShed™ 11120 resin. The specimens were manufactured in two different build setups, designed to fit batches of 18 or 24 specimens with different build orientations. The specimens were randomly tested in tension, and a design of experiments (DOE) was used to determine the effect of aging (4, 30 or 120 days), pre‐conditioning (ambient, desiccant, or ASTM recommended conditioning), and build orientation (flat, on an edge, or vertical) on the ultimate tensile stress (UTS) and elastic modulus (E) of SL fabricated samples. Additionally, the fractured samples were imaged using scanning electron microscopy (SEM) to charac...

Practical Use of Hydrogels in Stereolithography for Tissue Engineering Applications

In recent years, additive manufacturing (AM) or rapid prototyping (RP) technologies, initially developed to create prototypes prior to production for the automotive, aerospace, and other industries, have found applications in tissue engineering (TE) and their use is growing rapidly. RP technologies are increasingly demonstrating the potential for fabricating biocompatible 3D structures with precise control of the micro- and macro-scale characteristics. Several comprehensive reviews on the use of RP technologies, also known as solid freeform fabrication, Additive Manufacturing, direct digital manufacturing, and other names, have been published recently [1–4].

Stereolithography of PEG hydrogel multi-lumen nerve regeneration conduits

Peripheral nerve regeneration conduits available today are single lumen conduits. Multi-lumen conduits offer advantages over currently available conduits in that multiple lumen better mimic the natural structure of the nerve, provide a greater surface area for neurite extension, and allow for more precisely located growth factors or support cells within the scaffold. This work describes and demonstrates the use of the stereolithography (SL) rapid prototyping technique for fabricating multi-lumen nerve guidance conduits (NGCs) out of photopolymerizable poly(ethylene glycol) (PEG). NGCs were fabricated from PEG-dimethacrylate (PEG-dma) molecular weight 1000 with 30% (w/v) aqueous solution and 0.5% (w/v) of the photoinitiator Irgacure 2959. The selection of the PEG-dma and photoinitiator concentration was based on previous work [13]. A 3D Systems 250/50 SL machine with a 250 μm laser beam diameter was used for the experiments in a slightly modified process where the NGCs were fabricated on a glass slide within a small flat-bottom cylindrical container placed on top of the SL machine’s original build platform. SL successfully manufactured three-dimensional, multi-layered and multi-material NGCs with varying overall NGC lengths and lumen sizes. Minimum lumen size, spacing, and geometric accuracy were constrained by the laser beam diameter and path, curing characteristics of the polymer solution, and UV transmission properties of the polymer solution and cured PEG-dma. Overall lengths of the NGCs were constrained by the ability of the conduit to self-support its own construction. Multiple material conduits were demonstrated by varying the build solution during the layering process. In summary, SL shows promise for fabrication of bioactive NGCs using PEG hydrogels, and the use of SL in this application offers the additional advantage of easily scaling up for mass production.Copyright

'Three-Dimensional PEG Hydrogel Construct Fabrication using Stereolithography,'

Layered manufacturing (LM) using stereolithography (SL) of aqueous polymer solutions was accomplished so three-dimensional (3D) tissue engineered scaffolds with complex distributions of bioactive agents could be produced. Successful LM with embedded channel architectures required investigation of hydrogel thickness or cure depth as a function of photoinitiator type and concentration, energy dosage, and polymer concentration in solution. Poly(ethylene glycol) dimethacrylate (PEG-dma) with an average molecular weight of 1000 in quantities of 20% and 30% (w/v) was prepared in distilled water. Different concentrations of two photoinitiators (PIs), Sarcure1121 (2-hydroxy-2-methyl-1-phenyl-1-propanone) and Irgacure 2959 (2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone), were used to vary gel thickness at select energy dosages by controlling the scan speed of the SL machines ultraviolet scanning system. Gel thickness was a strong function of PI type and concentration, energy dosage, and PEG-dma concentration, especially at the low PI concentrations required for implantation. The gel thickness curves were utilized to demonstrate LM for two construct geometries where different layer thicknesses were required to successfully fabricate the constructs. This work demonstrates the effective use of SL as a processing technique for complex 3D tissue scaffolds and addresses some practical considerations associated with the use of hydrogels in LM.

Patient-Specific Compliant Vessel Manufacturing Using Dip-Spin Coating of Rapid Prototyped Molds

A procedure for manufacturing cardiovascular system models using patient-specific data, rapid prototyping, and a multistep dip-spin coating process is presented here. Improvements to a previously developed process permitted the fabrication of flexible complex vascular replicas. The primary improvement included the development of a two-axis rotation mechanism that enabled a pseudorandom rotation of the coated mold in space, providing uniform coats. Other improvements included the use of a low viscosity (1500-2000 cP) silicone solution that allowed for complete coverage of the mold, and developing a procedure for fixing defects. The dip-spin coating procedure was shown to be effective for the manufacture of compliant cardiovascular membranes, such as an arterial bypass graft with an internal flow passage and an abdominal aorta with nonuniform radial geometry, tapered diameters, bifurcations, and small branches. Results from a design of experiments comparing two dipping setups demonstrated that horizontally dipping the model produced coatings with more uniform thicknesses along the length of the model when compared to vertical dipping. For a 250-mm-long model, the difference in thickness between the top and bottom of the membrane was 0.42 ±0.069 mm and 0.09 ±0.077 mm for vertical and horizontal dippings, respectively. Mold diameter also affected the thickness of the membrane, with membrane thickness increasing as mold diameter decreased. Thickness data comparing locations at approximately the same height of the mold but with different diameters showed thicknesses of 2.54±0.198 mm and 1.95±0.140 mm for 7.85 mm and 15.20 mm diameters, respectively. Moreover, the differences in thickness between these locations were 0.60 ±0.128 mm and 0.58 ±0.231 mm for vertical and horizontal dippings, respectively; thus, membrane thickness variations occurred with mold diameter irrespective of the dipping setup. Depending on the prescribed tolerance for membrane thickness, the vertical dipping setup may be recommended for use because (1) it was easier to use since only the mold was immersed in the coating solution and no special protection of the dipping mechanism was required and (2) it produced fewer defects in the coatings since the solution always dripped from downfacing surfaces of the mold. Using this dip-spin coating procedure, patient-specific cardiovascular membranes can be manufactured and used in the development of medical devices, research requiring accurate anatomical models, and education and training.

Single-Lumen and Multi-Lumen Poly(Ethylene Glycol) Nerve Conduits Fabricated by Stereolithography for Peripheral Nerve Regeneration In Vivo

BACKGROUND The use of nerve conduits to facilitate nerve regrowth after peripheral nerve injury is limited to defects less than 3 cm. The purpose of this study is to determine the capability of novel single and multi-lumen poly(ethylene glycol) (PEG) conduits manufactured by stereolithography to promote peripheral nerve regeneration. MATERIALS AND METHODS Eight Sprague Dawley rats with sharp transection injuries of the sciatic nerve were randomly assigned to receive single-lumen or multi-lumen PEG conduits to bridge a 10-mm gap. Sciatic nerve and conduit samples were harvested after 5 weeks, and axon number, myelin thickness, fiber diameter, and g-ratio were analyzed. The contralateral intact nerve was also harvested for comparison. RESULTS Partial nerve regeneration was observed in three out of four single-lumen conduits and one out of four multi-lumen conduits. Axon number in the single-lumen regenerated nerve approached that of the contralateral intact nerve at 4,492 ± 2,810.0 and 6,080 ± 627.9 fibers/mm(2), respectively. The percentage of small fibers was greater in the single-lumen conduit compared with the intact nerve, whereas myelin thickness and g-ratio were consistently greater in the autologous nerve. Axon regrowth through the multi-lumen conduits was severely limited. CONCLUSION Single-lumen stereolithography-manufactured PEG nerve conduits promote nerve regeneration, with regenerating axon numbers approaching that of normal nerve. Multi-lumen conduits demonstrated significantly less nerve regeneration, possibly due to physical properties of the conduit inhibiting growth. Further studies are necessary to compare the efficacy of the two conduits for functional recovery and to elucidate the reasons underlying their differences in nerve regeneration potential.