Printability and Critical Insight into Polymer Properties during Direct-Extrusion Based 3D Printing of Medical Grade Polylactide and Copolyesters

Toward high-resolution 3D-printing of pharmaceutical implants - A holistic analysis of relevant material properties and process parameters

In this work, filament-based 3D-printing, the most widely used sub-category of material extrusion additive manufacturing (MEAM), is presented as a promising manufacturing platform for the production of subcutaneous implants. Print nozzle diameters as small as 100 µm were utilized demonstrating MEAM of advanced porous internal structures at the given cylindrical implant geometry of 2 mm × 40 mm. The bottlenecks related to high-resolution MEAM of subcutaneous implants are systematically analyzed and the print process is optimized accordingly. Custom synthesized biodegradable phase-separated poly(ether ester) multiblock copolymers exhibiting appropriate melt viscosity at comparatively low printing temperatures of 135 °C and 165 °C were utilized as 3D-printing feedstock. The print process was optimized to minimize thermomechanical polymer degradation by employing print speeds of 30 mm∙s-1 in combination with a nozzle diameter of 150 µm at layer heights of 110 µm. These results portray the basis for further development of subcutaneous implantable drug delivery systems where drug release profiles can be tailored through the adaption of the internal implant structure, which cannot be achieved using existing manufacturing techniques.

Biodegradable and 3D printable lysine functionalized polycaprolactone scaffolds for tissue engineering applications

Tissue engineering (TE) has sparked interest in creating scaffolds with customizable properties and functional bioactive sites. However, due to limitations in medical practices and manufacturing technologies, it is challenging to replicate complex porous frameworks with appropriate architectures and bioactivity in vitro. To address these challenges, herein, we present a green approach that involves the amino acid (l-lysine) initiated polymerization of ɛ-caprolactone (CL) to produce modified polycaprolactone (PCL) with favorable active sites for TE applications. Further, to better understand the effect of morphology and porosity on cell attachment and proliferation, scaffolds of different geometries with uniform and interconnected pores are designed and fabricated, and their properties are evaluated in comparison with commercial PCL. The scaffold morphology and complex internal micro-architecture are imaged by micro-computed tomography (micro-CT), revealing pore size in the range of ~300-900 μm and porosity ranging from 30 to 70 %, while based on the geometry of scaffolds the compressive strength varied from 143 ± 19 to 214 ± 10 MPa. Additionally, the degradation profiles of fabricated scaffolds are found to be influenced by both the chemical nature and product design, where Lys-PCL-based scaffolds with better porosity and lower crystallinity degraded faster than commercial PCL scaffolds. According to in vitro studies, Lys-PCL scaffolds have produced an environment that is better for cell adhesion and proliferation. Moreover, the scaffold design affects the way cells interact; Lys-PCL with zigzag geometry has demonstrated superior in vitro vitality (>90 %) and proliferation in comparison to other designs. This study emphasizes the importance of enhancing bioactivity while meeting morphology and porosity requirements in the design of scaffolds for tissue engineering applications.

Influence of Polymeric Microparticle Size and Loading Concentration on 3D Printing Accuracy and Degradation Behavior of Composite Scaffolds

Successful employment of 3D printing for delivery of therapeutic biomolecules requires protection of their bioactivity on exposure to potentially inactivating conditions. Although intermediary encapsulation of the biomolecules in polymeric particulate delivery vehicles is a promising strategy for this objective, the inclusion of such particles in 3D printing formulations may critically impact the accuracy or precision of 3D printed scaffolds relative to their intended designed architectures, as well as the degradation behavior of both the scaffolds and the included particles. The present work aimed to elucidate the effect of poly(d,l-lactic-co-glycolic acid) particle size and loading concentration on material accuracy, machine precision, and degradation of 3D printed poly(ɛ-caprolactone)-based scaffolds. Using a main effects analysis, the sizes and loading concentrations of particle delivery vehicles investigated were found to have neither a beneficial nor disadvantageous influence on the metrics of printing quality such as material accuracy and machine precision. Meanwhile, particle loading concentration was determined to influence degradation rate, whereas printing temperature affected the trends in composite weight-average molecular weight. Neither of the two particle-related parameters (concentration nor diameter) was found to exhibit a significant effect on intra-fiber nor inter-fiber porosity. These findings evidence the capacity for controlled loading of particulate delivery vehicles in 3D printed scaffolds while preserving construct accuracy and precision, and with predictable dictation of composite degradation behavior for potential controlled release of encapsulated biomolecules.

Application of starch-rich mango by-product as filler for the development of an additive manufacturing filament compound

The surge in global polymeric waste underscores the imperative for biodegradable materials to substitute traditional polymers. Crucially, advancements are needed for emerging technologies like Materials Extrusion (ME) in additive manufacturing, where current biodegradable materials exhibit limitations. This work was based on the development of a biodegradable composite filament. The inner of the mango seed (kernel) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were used as raw materials. The properties of PHBV and mango by-product mixture were first evaluated by direct-extrusion printing. Then, the feasibility of manufacturing the filaments was studied. Initially, the kernel seed mango was characterized thermally, chemically, and morphologically by DSC, FTIR, and SEM, respectively. It was observed that the addition of mango by-product contributed to the decrease of PHBV crystallinity, resulting in the reduction of printed parts retraction and increases the Tg, as shown by the DMA. The structure of the native starch was preserved due to non-gelatinization, even after processing steps, as indicated by thermal, chemical, and morphological analyses. Finally, PHBV filaments containing mango by-products were fabricated, and prototypes were manufactured by ME to demonstrate the potential for market acceptance and commercialization of the studied filament.

Role of Rheology in Morphology Development and Advanced Processing of Thermoplastic Polymer Materials: A Review

This review presents fundamental knowledge and recent advances pertaining to research on the role of rheology in polymer processing, highlights the knowledge gap between the function of rheology in various processing operations and the importance of rheology in the development, characterization, and assessment of the morphologies of polymeric materials, and offers ideas for enhancing the processabilities of polymeric materials in advanced processing operations. Rheology plays a crucial role in the morphological evolution of polymer blends and composites, influencing the type of morphology in the case of blends and the quality of dispersion in the cases of both blends and composites. The rheological characteristics of multiphase polymeric materials provide valuable information on the morphologies of these materials, thereby rendering rheology an important tool for morphological assessment. Although rheology extensively affects the processabilities of polymeric materials in all processing operations, this review focuses on the roles of rheology in film blowing, electrospinning, centrifugal jet spinning, and the three-dimensional printing of polymeric materials, which are advanced processing operations that have gained significant research interest. This review offers a comprehensive overview of the fundamentals of morphology development and the aforementioned processing techniques; moreover, it covers all vital aspects related to the tailoring of the rheological characteristics of polymeric materials for achieving superior morphologies and high processabilities of these materials in advanced processing operations. Thus, this article provides a direction for future advancements in polymer processing. Furthermore, the superiority of elongational flow over shear flow in enhancing the quality of dispersion in multiphase polymeric materials and the role of extensional rheology in the advanced processing operations of these materials, which have rarely been discussed in previous reviews, have been critically analyzed in this review. In summary, this article offers new insights into the use of rheology in material and product development during advanced polymer-processing operations.

Review on the Degradation of Poly(lactic acid) during Melt Processing

This review paper presents an overview of the state of the art on process-induced degradation of poly(lactic acid) (PLA) and the relative importance of different processing variables. The sensitivity of PLA to degradation, especially during melt processing, is considered a significant challenge as it may result in deterioration of its properties. The focus of this review is on degradation during melt processing techniques such as injection molding and extrusion, and therefore it does not deal with biodegradation. Firstly, the general processing and fundamental variables that determine the degradation are discussed. Secondly, the material properties (for example rheological, thermal, and mechanical) are presented that can be used to monitor and quantify the degradation. Thirdly, the effects of different processing variables on the extent of degradation are reviewed. Fourthly, additives are discussed for melt stabilization of PLA. Although current literature reports the degradation reactions and clearly indicates the effect of degradation on PLA's properties, there are still knowledge gaps in how to select and predict the processing conditions that minimize process-induced degradation to save raw materials and time during production.

Block Copolymers in 3D/4D Printing: Advances and Applications as Biomaterials

3D printing is a manufacturing technique in constant evolution. Day by day, new materials and methods are discovered, making 3D printing continually develop. 3D printers are also evolving, giving us objects with better resolution, faster, and in mass production. One of the areas in 3D printing that has excellent potential is 4D printing. It is a technique involving materials that can react to an environmental stimulus (pH, heat, magnetism, humidity, electricity, and light), causing an alteration in their physical or chemical state and performing another function. Lately, 3D/4D printing has been increasingly used for fabricating materials aiming at drug delivery, scaffolds, bioinks, tissue engineering (soft and hard), synthetic organs, and even printed cells. The majority of the materials used in 3D printing are polymeric. These materials can be of natural origin or synthetic ones of different architectures and combinations. The use of block copolymers can combine the exemplary properties of both blocks to have better mechanics, processability, biocompatibility, and possible stimulus behavior via tunable structures. This review has gathered fundamental aspects of 3D/4D printing for biomaterials, and it shows the advances and applications of block copolymers in the field of biomaterials over the last years.

The Use of Graphene and Its Derivatives for the Development of Polymer Matrix Composites by Stereolithographic 3D Printing

Significant advances in graphene-based materials have facilitated the development of various composites structures in a diverse range of industry sectors. At present, the preparation of graphene-added materials is mainly developed through traditional methods. However, in recent years, additive manufacturing emerged as a promising approach that enables the printing of complex objects in a layer-by-layer fashion, without the need for moulds or machining equipment. This paper reviews the most recent reports on graphene-based photopolymerizable resins developed for stereolithography (SLA), with particular consideration for medical applications. The characteristics of the SLA technology, the most suitable raw materials and formulations and the properties of final 3D products are described. Throughout, a specific focus is placed on the mechanical properties and biocompatibility of the final 3D-printed object. Finally, remaining challenges and future directions are also discussed.

3D Printing of Polymeric Bioresorbable Stents: A Strategy to Improve Both Cellular Compatibility and Mechanical Properties

One of the leading causes of death is cardiovascular disease, and the most common cardiovascular disease is coronary artery disease. Percutaneous coronary intervention and vascular stents have emerged as a solution to treat coronary artery disease. Nowadays, several types of vascular stents share the same purpose: to reduce the percentage of restenosis, thrombosis, and neointimal hyperplasia and supply mechanical support to the blood vessels. Despite the numerous efforts to create an ideal stent, there is no coronary stent that simultaneously presents the appropriate cellular compatibility and mechanical properties to avoid stent collapse and failure. One of the emerging approaches to solve these problems is improving the mechanical performance of polymeric bioresorbable stents produced through additive manufacturing. Although there have been numerous studies in this field, normalized control parameters for 3D-printed polymeric vascular stents fabrication are absent. The present paper aims to present an overview of the current types of stents and the main polymeric materials used to fabricate the bioresorbable vascular stents. Furthermore, a detailed description of the printing parameters' influence on the mechanical performance and degradation profile of polymeric bioresorbable stents is presented.

Efficacy of treating segmental bone defects through endochondral ossification: 3D printed designs and bone metabolic activities

Three-dimensional printing (3D printing) is a promising technique for producing scaffolds for bone tissue engineering applications. Porous scaffolds can be printed directly, and the design, shape and porosity can be controlled. 3D synthetic biodegradable polymeric scaffolds intended for in situ bone regeneration must meet stringent criteria, primarily appropriate mechanical properties, good 3D design, adequate biocompatibility and the ability to enhance bone formation. In this study, healing of critical-sized (5 ​mm) femur defects of rats was enhanced by implanting two different designs of 3D printed poly(l-lactide-co-ε-caprolactone) (poly(LA-co-CL)) scaffolds seeded with rat bone marrow mesenchymal stem cells (rBMSC), which had been pre-differentiated in vitro into cartilage-forming chondrocytes. Depending on the design, the scaffolds had an interconnected porous structure of 300-500 ​μm and porosity of 50-65%. According to a computational simulation, the internal force distribution was consistent with scaffold designs and comparable between the two designs. Moreover, the defects treated with 3D-printed scaffolds seeded with chondrocyte-like cells exhibited significantly increased bone formation up to 15 weeks compared with empty defects. In all experimental animals, bone metabolic activity was monitored by positron emission tomography 1, 3, 5, 7, 11 and 14 weeks after surgery. This demonstrated a time-dependent relationship between scaffold design and metabolic activity. This confirmed that successful regeneration was highly reproducible. The in vitro and in vivo data indicated that the experimental setups had promising outcomes and could facilitate new bone formation through endochondral ossification.

Polymer-Based Constructs for Flexor Tendon Repair: A Review

A flexor tendon injury is acquired fast and is common for athletes, construction workers, and military personnel among others, treated in the emergency department. However, the healing of injured flexor tendons is stretched over a long period of up to 12 weeks, therefore, remaining a significant clinical problem. Postoperative complications, arising after traditional tendon repair strategies, include adhesion and tendon scar tissue formation, insufficient mechanical strength for early active mobilization, and infections. Various researchers have tried to develop innovative strategies for developing a polymer-based construct that minimalizes these postoperative complications, yet none are routinely used in clinical practice. Understanding the role such constructs play in tendon repair should enable a more targeted approach. This review mainly describes the polymer-based constructs that show promising results in solving these complications, in the hope that one day these will be used as a routine practice in flexor tendon repair, increasing the well-being of the patients. In addition, the review also focuses on the incorporation of active compounds in these constructs, to provide an enhanced healing environment for the flexor tendon.

Exosomes from 3T3-J2 promote expansion of tracheal basal cells to facilitate rapid epithelization of 3D-printed double-layer tissue engineered trachea

Functional epithelization plays a pivotal role in maintaining long-term lumen patency of tissue-engineered trachea (TET). Due to the slow migration of autologous epithelium, spontaneous epithelization process of transplanted TET is always tardive. Seeding tracheal basal cells (TBCs) on TET before transplantation might be favorable for accelerating epithelization, but rapid expansion of TBCs in vitro is still relatively intractable. In this study, we proposed a promising expansion strategy which enables the TBCs to proliferate rapidly in vitro. TBCs were isolated from the autologous tracheal mucosae of rabbit, and co-cultured with exosomes derived from 3T3-J2 cells. After co-culture with exosomal component, TBCs could vigorously proliferate in vitro and retained their multi-potency. It was in stark contrast to that the single-cultured TBCs could only be expand to passage 2 in about 30 days, moreover, the most majority of single-cultured cells entered late apoptotic stage. On the other hand, a bionic tubular double-layer scaffold with good mechanical property and bio-compatibility was designed and fabricated by 3D printing technology. Then TET with bi-lineage cell-type was constructed in vitro by implanting autologous chondrocytes on the outer-layer of scaffold, and TBCs on the inner-layer, respectively. And then TET was pre-vascularized in vivo, and pedicled transplanted to restore long-segmental defect in recipient rabbits. It was found that the chondrocytes and TBCs seeded on double-layer scaffolds developed well as expected. And almost complete coverage with ciliated epitheliums was observed on the lumen surface of TET 2-week after operation, in comparison with that the epithelization of TET without pre-seeding of TBCs accomplished nearly 2-month after operation. In conclusion, the promising expansion strategy of TBCs together with 3D-printed double-layer scaffolds facilitate the rapid epithelization process of transplanted TET, which might be of vital significance for clinical and translational medicine.

Understanding of how the properties of medical grade lactide based copolymer scaffolds influence adipose tissue regeneration: Sterilization and a systematic in vitro assessment

Aliphatic polyesters are the synthetic polymers most commonly used in the development of resorbable medical implants/devices. Various three-dimensional (3D) scaffolds have been fabricated from these polymers and used in adipose tissue engineering. However, their systematic evaluation altogether lacks, which makes it difficult to select a suitable degradable polymer to design 3D resorbable implants and/or devices able to effectively mimic the properties of adipose tissue. Additionally, the impact of sterilization methods on the medical devices, if any, must be taken into account. We evaluate and compare five different medical-grade resorbable polyesters with l-lactide content ranging from 50 to 100 mol% and exhibiting different physiochemical properties depending on the comonomer (d-lactide, ε-caprolactone, glycolide, and trimethylene carbonate). The salt-leaching technique was used to prepare 3D microporous scaffolds. A comprehensive assessment of physical, chemical, and mechanical properties of the scaffolds was carried out in PBS at 37 °C. The cell-material interactions and the ability of the scaffolds to promote adipogenesis of human adipose tissue-derived stem cells were assessed in vitro. The diverse physical and mechanical properties of the scaffolds, due to the different composition of the copolymers, influenced human adipose tissue-derived stem cells proliferation and differentiation. Scaffolds made from polymers which were above their glass transition temperature and with low degree of crystallinity showed better proliferation and adipogenic differentiation of stem cells. The effect of sterilization techniques (electron beam and ethylene oxide) on the polymer properties was also evaluated. Results showed that scaffolds sterilized with the ethylene oxide method better retained their physical and chemical properties. Overall, the presented research provides (i) a detailed understanding to select a degradable polymer that has relevant properties to augment adipose tissue regeneration and can be further used to fabricate medical devices/implants; (ii) directions to prefer a sterilization method that does not change polymer properties.

Effects of Two Melt Extrusion Based Additive Manufacturing Technologies and Common Sterilization Methods on the Properties of a Medical Grade PLGA Copolymer

Although bioabsorbable polymers have garnered increasing attention because of their potential in tissue engineering applications, to our knowledge there are only a few bioabsorbable 3D printed medical devices on the market thus far. In this study, we assessed the processability of medical grade Poly(lactic-co-glycolic) Acid (PLGA)85:15 via two additive manufacturing technologies: Fused Filament Fabrication (FFF) and Direct Pellet Printing (DPP) to highlight the least destructive technology towards PLGA. To quantify PLGA degradation, its molecular weight (gel permeation chromatography (GPC)) as well as its thermal properties (differential scanning calorimetry (DSC)) were evaluated at each processing step, including sterilization with conventional methods (ethylene oxide, gamma, and beta irradiation). Results show that 3D printing of PLGA on a DPP printer significantly decreased the number-average molecular weight (Mn) to the greatest extent (26% Mn loss, p < 0.0001) as it applies a longer residence time and higher shear stress compared to classic FFF (19% Mn loss, p < 0.0001). Among all sterilization methods tested, ethylene oxide seems to be the most appropriate, as it leads to no significant changes in PLGA properties. After sterilization, all samples were considered to be non-toxic, as cell viability was above 70% compared to the control, indicating that this manufacturing route could be used for the development of bioabsorbable medical devices. Based on our observations, we recommend using FFF printing and ethylene oxide sterilization to produce PLGA medical devices.

Effect of 3D Printing Temperature on Bioactivity of Bone Morphogenetic Protein-2 Released from Polymeric Constructs

Growth factors such as bone morphogenetic protein-2 (BMP-2) are potent tools for tissue engineering. Three-dimensional (3D) printing offers a potential strategy for delivery of BMP-2 from polymeric constructs; however, these biomolecules are sensitive to inactivation by the elevated temperatures commonly employed during extrusion-based 3D printing. Therefore, we aimed to correlate printing temperature to the bioactivity of BMP-2 released from 3D printed constructs composed of a model polymer, poly(propylene fumarate). Following encapsulation of BMP-2 in poly(DL-lactic-co-glycolic acid) particles, growth factor-loaded fibers were fabricated at three different printing temperatures. Resulting constructs underwent 28 days of aqueous degradation for collection of released BMP-2. Supernatants were then assayed for the presence of bioactive BMP-2 using a cellular assay for alkaline phosphatase activity. Cumulative release profiles indicated that BMP-2 released from constructs that were 3D printed at physiologic and intermediate temperatures exhibited comparable total amounts of bioactive BMP-2 release as those encapsulated in non-printed particulate delivery vehicles. Meanwhile, the elevated printing temperature of 90 °C resulted in a decreased amount of total bioactive BMP-2 release from the fibers. These findings elucidate the effects of elevated printing temperatures on BMP-2 bioactivity during extrusion-based 3D printing, and enlighten polymeric material selection for 3D printing with growth factors.

Recent Advances in 3D Printing of Polyhydroxyalkanoates: A Review

In the 21st century, additive manufacturing technologies have gained in popularity mainly due to benefits such as rapid prototyping, faster small production runs, flexibility and space for innovations, non-complexity of the process and broad affordability. In order to meet diverse requirements that 3D models have to meet, it is necessary to develop new 3D printing technologies as well as processed materials. This review is focused on 3D printing technologies applicable for polyhydroxyalkanoates (PHAs). PHAs are thermoplastics regarded as a green alternative to petrochemical polymers. The 3D printing technologies presented as available for PHAs are selective laser sintering and fused deposition modeling. Stereolithography can also be applied provided that the molecular weight and functional end groups of the PHA are adjusted for photopolymerization. The chemical and physical properties primarily influence the processing of PHAs by 3D printing technologies. The intensive research for the fabrication of 3D objects based on PHA has been applied to fulfil criteria of rapid and customized prototyping mainly in the medical area.

Filament extrusion of bioresorbable PDLGA for additive manufacturing utilising diatom biosilica to inhibit process-induced thermal degradation

Bone scaffolds are often fabricated by initially producing custom-made filaments by twin-screw extruder and subsequently fabricating into 3D scaffolds using fused deposition modelling. This study aims to directly compare the effect of two alternative silica-rich filler materials on the thermo-mechanical properties of such scaffolds after extrusion and printing. Poly (DL-lactide-co-glycolide) (PDLGA) was blended with either 45S5 Bioglass (5 wt %) or Biosilica (1 and 5 wt%) isolated from Cyclotella meneghiniana a freshwater diatom were tested. Diatom-PDLGA was found to have similar mechanical strength and ductility to pure-PDLGA, whereas Bioglass-PDLGA was found induce a more brittle behaviour. Bioglass-PDLGA was also found to have the lowest toughness in terms of energy absorption to failure. The TGA results suggested that significant thermal degradation in both the Bioglass filaments and scaffolds had occurred as a result of processing. However, diatom biosilica was found to inhibit thermal degradation of the PDLGA. Furthermore, evidence suggested the agglomeration of Bioglass particles occurred during processing the Bioglass-PDLGA filaments. Overall, diatom biosilica was found to be a promising candidate as a bone filler additive in 3D printed PDLGA scaffolds, whereas Bioglass caused some potentially detrimental effects on performance.

Chemokine SDF1 Mediated Bone Regeneration Using Biodegradable Poly(D,L-lactide-co-glycolide) 3D Scaffolds and Bone Marrow-Derived Mesenchymal Stem Cells: Implication for the Development of an "Off-the-Shelf" Pharmacologically Active Construct

There is an increasing need for bone substitutes for reconstructive orthopedic surgery following removal of bone tumors. Despite the advances in bone regeneration, the use of autologous mesenchymal stem cells (MSC) presents a significant challenge, particularly for the treatment of large bone defects in cancer patients. This study aims at developing new chemokine-based technology to generate biodegradable scaffolds that bind pharmacologically active proteins for regeneration/repair of target injured tissues in patients. Primary MSC were cultured from the uninvolved bone marrow (BM) of cancer patients and further characterized for "stemness". Their ability to differentiate into an osteogenic lineage was studied in 2D cultures as well as on 3D macroporous PLGA scaffolds incorporated with biomacromolecules bFGF and homing factor chemokine stromal-cell derived factor-1 (SDF1). MSC from the uninvolved BM of cancer patients exhibited properties similar to that reported for MSC from BM of healthy individuals. Macroporous PLGA discs were prepared and characterized for pore size, architecture, functional groups, thermostability, and cytocompatibility by ESEM, FTIR, DSC, and CCK-8 dye proliferation assay, respectively. It was observed that the MSC+PLGA+bFGF+SDF1 construct cultured for 14 days supported significant cell growth, osteo-lineage differentiation with increased osteocalcin expression, alkaline phosphatase secretion, calcium mineralization, bone volume, and soluble IL6 compared to unseeded PLGA and PLGA+MSC, as analyzed by confocal microscopy, biochemistry, ESEM, microCT imaging, flow cytometry, and EDS. Thus, chemotactic biomacromolecule SDF1-guided tissue repair/regeneration ability of MSC from cancer patients opens up the avenues for development of "off-the-shelf" pharmacologically active construct for optimal repair of the target injured tissue in postsurgery cancer patients, bone defects, damaged bladder tissue, and radiation-induced skin/mucosal lesions.

Extrusion 3D Printing of Polymeric Materials with Advanced Properties

3D printing is a rapidly growing technology that has an enormous potential to impact a wide range of industries such as engineering, art, education, medicine, and aerospace. The flexibility in design provided by this technique offers many opportunities for manufacturing sophisticated 3D devices. The most widely utilized method is an extrusion-based solid-freeform fabrication approach, which is an extremely attractive additive manufacturing technology in both academic and industrial research communities. This method is versatile, with the ability to print a range of dimensions, multimaterial, and multifunctional 3D structures. It is also a very affordable technique in prototyping. However, the lack of variety in printable polymers with advanced material properties becomes the main bottleneck in further development of this technology. Herein, a comprehensive review is provided, focusing on material design strategies to achieve or enhance the 3D printability of a range of polymers including thermoplastics, thermosets, hydrogels, and other polymers by extrusion techniques. Moreover, diverse advanced properties exhibited by such printed polymers, such as mechanical strength, conductance, self-healing, as well as other integrated properties are highlighted. Lastly, the stimuli responsiveness of the 3D printed polymeric materials including shape morphing, degradability, and color changing is also discussed.

Influence of Controlled Cooling on Crystallinity of Poly (L-Lactic Acid) Scaffolds after Hydrolytic Degradation

The use of hybrid manufacturing to produce bimodal scaffolds has represented a great advancement in tissue engineering. These scaffolds provide a favorable environment in which cells can adhere and produce new tissue. However, there are several areas of opportunity to manufacture structures that provide enough strength and rigidity, while also improving chemical integrity. As an advancement in the manufacturing process of scaffolds, a cooling system was introduced in a fused deposition modeling (FDM) machine to vary the temperature on the printing bed. Two groups of polylactic acid (PLA) scaffolds were then printed at two different bed temperatures. The rate of degradation was evaluated during eight weeks in Hank's Balanced Salt Solution (HBSS) in a controlled environment (37 °C-120 rpm) to assess crystallinity. Results showed the influence of the cooling system on the degradation rate of printed scaffolds after the immersion period. This phenomenon was attributable to the mechanism associated with alkaline hydrolysis, where a higher degree of crystallinity obtained in one group induced greater rates of mass loss. The overall crystallinity was observed, through differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), and Fourier transformed infrared spectroscopy (FTIR) analysis, to increase with time because of the erosion of some amorphous parts after immersion.

Engineering 3D degradable, pliable scaffolds toward adipose tissue regeneration; optimized printability, simulations and surface modification

We present a solution to regenerate adipose tissue using degradable, soft, pliable 3D-printed scaffolds made of a medical-grade copolymer coated with polydopamine. The problem today is that while printing, the medical grade copolyesters degrade and the scaffolds become very stiff and brittle, being not optimal for adipose tissue defects. Herein, we have used high molar mass poly(L-lactide-co-trimethylene carbonate) (PLATMC) to engineer scaffolds using a direct extrusion-based 3D printer, the 3D Bioplotter®. Our approach was first focused on how the printing influences the polymer and scaffold's mechanical properties, then on exploring different printing designs and, in the end, on assessing surface functionalization. Finite element analysis revealed that scaffold's mechanical properties vary according to the gradual degradation of the polymer as a consequence of the molar mass decrease during printing. Considering this, we defined optimal printing parameters to minimize material's degradation and printed scaffolds with different designs. We subsequently functionalized one scaffold design with polydopamine coating and conducted in vitro cell studies. Results showed that polydopamine augmented stem cell proliferation and adipogenic differentiation owing to increased surface hydrophilicity. Thus, the present research show that the medical grade PLATMC based scaffolds are a potential candidate towards the development of implantable, resorbable, medical devices for adipose tissue regeneration.