Methacrylated Silk Fibroin Additive Manufacturing of Shape Memory Constructs with Possible Application in Bone Regeneration

: Methacrylated silk (Sil-MA) is a chemically modified silk fibroin specifically designed to be crosslinkable under UV light, which makes this material applicable in additive manufacturing techniques and allows the prototyping and development of patient-specific 2D or 3D constructs. In this study, we produced a thin grid structure based on crosslinked Sil-MA that can be withdrawn and ejected and that can recover its shape after rehydration. A complete chemical and physical characterization of Sil-MA was first conducted. Additionally, we tested Sil-MA biocompatibility according to the International Standard Organization protocols (ISO 10993) ensuring the possibility of using it in future trials. Sil-MA was also tested to verify its ability to support osteogenesis. Overall, Sil-MA was shown to be biocompatible and osteoconductive. Finally, two different additive manufacturing technologies, a Digital Light Processing (DLP) UV projector and a pneumatic extrusion technique, were used to develop a Sil-MA grid construct. A proof-of-concept of its shape-memory property was provided. Together, our data support the hypothesis that Sil-MA grid constructs can be injectable and applicable in bone regeneration applications

Molecularly Imprinted Silk Fibroin Nanoparticles

Nanosized biomimetics prepared by the strategy of molecular imprinting, that is, the stamping of recognition sites by means of a template-assisted synthesis, are demonstrating potential as plastic antibodies in medicine, proving effective for cell imaging and targeted therapies. Most molecularly imprinted nanoparticles (MIP-NPs) are currently made of soft matter, such as polyacrylamide and derivatives. Yet, MIP-NPs biocompatibility is crucial for their effective translation into clinical uses. Here, we propose the original idea to synthesize fully biocompatible molecularly imprinted nanoparticles starting from the natural polymer silk fibroin (MIP SF-NPs), which is nontoxic and highly biocompatible. The conditions to produce MIP SF-NPs of different sizes (dmean ∼ 50 nm; dmean ∼ 100 nm) were set using the response surface method. The stamping of a single, high affinity (KD = 57 × 10-9 M), and selective recognition site per silk fibroin nanoparticle was demonstrated, together with the confirmation of nontoxicity. Additionally, MIP SF-NPs were used to decorate silk microfibers and silk nanofibers, providing a general means to add entailed biofunctionalities to materials

Imaging the Morphological Structure of Silk Fibroin Constructs through Fluorescence Energy Transfer and Confocal Microscopy

Silk fibroin is a well-known biopolymer that is used in several applications in which interactions with biological tissue are required. Fibroin is extremely versatile and can be shaped to form several constructs that are useful in tissue engineering applications. Confocal imaging is usually performed to test cell behavior on a construct, and, in this context, the fibroin intrinsic fluorescence is regarded as a problem. In addition, the intrinsic fluorescence is not intense enough to provide useful morphological images. In fact, to study the construct’s morphology, other techniques are used (i.e., SEM and Micro-CT). In this work, we propose a method based on fluorescence energy transfer (FRET) to suppress the fibroin intrinsic fluorescence and move it to a higher wavelength that is accessible to confocal microscopy for direct imaging. This was done by creating two FRET couples by dispersing two fluorophores (2,5-diphenyloxazole (PPO) and Lumogen F Violet 570 (LV)) into the fibroin matrix and optimizing their percentages to suppress the fibroin intrinsic fluorescence. With the optimized composition, we produced an electrospun mat, and the dimensions of the fibers were accurately determined by confocal microscopy

Design of experiment rational optimization of an inkjet deposition of silver on Kapton

In this work we presented a statistical method to optimize the production of conductive layers by inkjet printing. This statistical method, namely Design of Experiment (DOE), was applied to the deposition of silver nanoparticle ink on Kapton. The process optimization was conducted by a double step. In the first phase, we optimized the getting waveform assigned to the piezoelectric head to form the ink drop in order to have the drop with the smaller diameter and standard deviation. In the second step, we optimized the area covered by the deposition of a specific pattern. The deposition strategy was then optimized to best reproduce the theoretical pattern. The entire process was conducted by analyzing the images acquired with a high-resolution camera and successively using DOE to fit the data and determine empirical models linking the process parameters to the measured outcome. These models allowed us to optimize the process by solving a system of equations giving a quantification on the printing quality

A thermal-mechanical investigation for the optimization of silicon microheaters for gas sensing applications

Nowadays, the development of silicon microheaters as substrates for chemoresistive gas sensors are becoming crucial for the development of devices that meet market requirements. Indeed, the adoption of silicon microfabrication process allows for large scale production of cheap, small and low power microheaters. However, there is still a lack of in-depth investigation for the optimization of the microheater design, aiming at identifying the best trade-off in between low power consumption and mechanical stability of the device. In this work, a predictive thermal-mechanical model is proposed, based on heat transfer simulation, mechanical failure analysis and thermal characterization

Porous Thermoplastic Molded Regenerated Silk Crosslinked by the Addition of Citric Acid

Thermoplastic molded regenerated silk fibroin was proposed as a structural material in tissue engineering applications, mainly for application in bone. The protocol allows us to obtain a compact non-porous material with a compression modulus in the order of a Giga Pascal in dry conditions (and in the order of tens of MPa in wet conditions). This material is produced by compressing a lyophilized silk fibroin powder or sponge into a mold temperature higher than the glass transition temperature. The main purpose of the produced resin was the osteofixation and other structural applications in which the lack of porosity was not an issue. In this work, we introduced the use of citric acid in the thermoplastic molding protocol of silk fibroin to obtain porosity inside the structural material. The citric acid powder during the compression acted as a template for the pore formation. The mean pore diameter achieved by the addition of the higher amount of citric acid was around 5 μm. In addition, citric acid could effectively crosslink the silk fibroin chain, improving its mechanical strength. This effect was proved both by evaluating the compression modulus (the highest value recorded was 77 MPa in wet conditions) and by studying the spectra obtained by Fourier transform infrared spectroscopy. This protocol may be applied in the near future to the production of structural bone scaffolds

Dataset of the Optimization of a Low Power Chemoresistive Gas Sensor: Predictive Thermal Modelling and Mechanical Failure Analysis

open6Over the last few years, employment of the standard silicon microfabrication techniques for the gas sensor technology has allowed for the development of ever-small, low-cost, and low-power consumption devices. Specifically, the development of silicon microheaters (MHs) has become well established to produce MOS gas sensors. Therefore, the development of predictive models that help to define a priori the optimal design and layout of the device have become crucial, in order to achieve both low power consumption and high mechanical stability. In this research dataset, we present the experimental data collected to develop a specific and useful predictive thermal-mechanical model for high performing silicon MHs. To this aim, three MH layouts over three different membrane sizes were developed by using the standard silicon microfabrication process. Thermal and mechanical performances of the produced devices were experimentally evaluated, by using probe stations and mechanical failure analysis, respectively. The measured thermal curves were used to develop the predictive thermal model towards low power consumption. Moreover, a statistical analysis was finally introduced to cross-correlate the mechanical failure results and the thermal predictive model, aiming at MH design optimization for gas sensing applications. All the data collected in this investigation are shown.openGaiardo, Andrea; Novel, David; Scattolo, Elia; Bucciarelli, Alessio; Bellutti, Pierluigi; Pepponi, GiancarloGaiardo, Andrea; Novel, David; Scattolo, Elia; Bucciarelli, Alessio; Bellutti, Pierluigi; Pepponi, Giancarl

A Thermal‐Reflow‐Based Low‐Temperature, High‐Pressure Sintering of Lyophilized Silk Fibroin for the Fast Fabrication of Biosubstrates

Solid fibroin is a bulk nonporous material that can be prepared with two methods: a liquid–gel–solid transition from a fibroin solution or a sintering procedure starting from silk powder. Both methods have their own disadvantages: the first requires several weeks and the process is size dependent; the second requires high temperatures. To overcome these limitations, a low‐temperature sintering procedure based on a thermal‐reflow is proposed in this work to produce in fast‐fashion monoliths of solid fibroin. Thermal‐reflow is a well‐known mechanism that takes place when the glass transition temperature of the material is lower than the temperature used to process it. Water plays an important role decreasing the glass transition temperature down to 40 °C. For the first time, a thermal reflow is conducted on lyophilized silk fibroin at 40 °C, associating to the water addition a high‐pressure compression. To optimize the process, a full factorial design of experiment is used. The material is then studied in the crucial phases by digital scanning calorimetry, Fourier‐transform infrared spectroscopy, and scanning electron microscopy. Finally, a mechanical characterization and a preliminary in vitro test are conducted

A Thermal‐Reflow‐Based Low‐Temperature, High‐Pressure Sintering of Lyophilized Silk Fibroin for the Fast Fabrication of Biosubstrates

Solid fibroin is a bulk nonporous material that can be prepared with two methods: a liquid–gel–solid transition from a fibroin solution or a sintering procedure starting from silk powder. Both methods have their own disadvantages: the first requires several weeks and the process is size dependent; the second requires high temperatures. To overcome these limitations, a low‐temperature sintering procedure based on a thermal‐reflow is proposed in this work to produce in fast‐fashion monoliths of solid fibroin. Thermal‐reflow is a well‐known mechanism that takes place when the glass transition temperature of the material is lower than the temperature used to process it. Water plays an important role decreasing the glass transition temperature down to 40 °C. For the first time, a thermal reflow is conducted on lyophilized silk fibroin at 40 °C, associating to the water addition a high‐pressure compression. To optimize the process, a full factorial design of experiment is used. The material is then studied in the crucial phases by digital scanning calorimetry, Fourier‐transform infrared spectroscopy, and scanning electron microscopy. Finally, a mechanical characterization and a preliminary in vitro test are conducted