The correlation between rheological properties and extrusion-based printability in bioink artifact quantification

Biocompatible composite hydrogel with on-demand swelling-shrinking properties for 4D bioprinting

Hydrogels with tunable swelling and shrinking properties are of great interest in biomedical applications, particularly in wound healing, tissue regeneration, and drug delivery. Traditional hydrogels often fail to achieve high swelling without mechanical failure. In contrast, high-swelling hydrogels can absorb large amounts of liquid, expanding their volume by 10-1000 times, due to low crosslink density and the presence of hydrophilic groups. Additionally, some high-swelling hydrogels can also shrink in response to external stimuli, making them promising candidates for applications like on-demand drug delivery and biosensing. An emerging application of high-swelling hydrogels is four-dimensional (4D) printing, where controlled swelling induces structural transformations in a 3D printed construct. However, current hydrogel systems show limited swelling capacity, restricting their ability to undergo significant shape changes. To address these limitations, we developed a high-swelling composite hydrogel, termed SwellMA, by combining gelatin methacryloyl (GelMA) and sodium polyacrylate (SPA). SwellMA exhibits a swelling capacity over 500% of its original area and can increase its original water weight by 100-fold, outperforming existing materials in 4D bioprinting. Furthermore, SwellMA constructs can cyclically swell and shrink on-demand upon changing the ionic strength of the aqueous solution. Additionally, SwellMA demonstrates superior cytocompatibility and cell culture properties than SPA, along with enhanced 3D printing fidelity. These findings demonstrate SwellMA's potential for advanced 4D printing and a broad range of biomedical applications requiring precise and dynamic control over hydrogel swelling and shrinking.

Advancements in GelMA/ceramic composites for dental applications: integration with portable 4D bioprinting technologies

Recent advancements in biofabrication have positioned gelatin methacrylate (GelMA)/ceramic composites combined with portable 4D bioprinting as a groundbreaking approach for next-generation dental therapies. GelMA hydrogels, functionalized with ceramic nanoparticles such as hydroxyapatite, zirconia, and bioactive glass, exhibit superior mechanical properties, enhanced bioactivity, and improved osseointegration capabilities compared to conventional hydrogels. These composites uniquely combine GelMA's favorable biological properties (including cell-adhesive RGD motifs and tunable photocrosslinking) with the structural stability and bioactivity of ceramic fillers. When integrated with portable bioprinters, these materials enable precise, chairside fabrication of dynamic, patient-specific constructs capable of adapting to the oral environment's complex biomechanical demands. This review systematically examines the material science behind GelMA/ceramic composites, focusing on how ceramic incorporation enhances printability, mechanical strength, and biological performance; the design and operation of portable bioprinters for dental applications; and their combined potential in addressing clinical challenges such as periodontal tissue regeneration, dentin-pulp complex repair, and customized implant fabrication. We highlight recent breakthroughs, including stimuli-responsive scaffolds for guided tissue regeneration and in situ bioprinting techniques for pulp revascularization. The discussion extends to current limitations in material-bioprinter compatibility, sterilization challenges, and regulatory pathways while outlining future directions toward clinical translation.

Three-step crosslinking dependent self-bending transformation of a nano-spherical mineralized collagen laden 4D printed sodium alginate scaffold for bone regeneration

Although 3D printed scaffolds are widely used in irregularly shaped bone defects, additional steps often need to be introduced when fabricating structures with curvature. In contrast, 4D printing has a unique advantage in the fabrication of scaffolding with a curved structure. Bone defects such as skull is generally curved, so a self-bending scaffold would be more appropriate for the cranial defect site. This paper presents a novel self-bending SAGMA hydrogel was loaded with nano-spherical mineralized collagen, then fabricated by a 4D printing method, which achieves adjustable self-bending through three-step crosslinking. When subjected to UV light irradiation, variations in gradient of photo-crosslinking are induced within the scaffold. This gradient of photo-crosslinking serves as the foundation for the scaffold's self-bending. The scaffold exhibited self-bending after crosslinking with calcium ions and chitosan, respectively, with curvature ranging from 0.05 mm-1 to 0.446 mm-1. In vivo experiments demonstrated the efficacy of the scaffold in enhancing the repair of cranial bone defects and promoting new bone formation in rats, as evidenced by microcomputed tomography and histochemical analysis. Therefore, this self-bending scaffold provides a potentially effective method for the clinical treatment of skull defects with curvature.

Predicting rheological properties of HAMA/GelMA hybrid hydrogels via machine learning

- Rheological properties are pivotal in determining the printability of biomaterials, directly impacting the success of 3D bioprinted constructs. Understanding the intricate relationship between biomaterial formulations, rheological behavior and printability can facilitate the advancement and rapid development of biomaterials. Herein, we critically measured the rheological properties of hyaluronic acid methacrylate (HAMA)/gelatin methacrylate (GelMA) hybrid hydrogels with varied formulations and generated a dataset to train a machine learning (ML) model. By utilizing four well-known algorithms, we developed the ML model for the viscosity and shear stress of HAMA/GelMA hydrogel mixtures. To improve model interpretability, we further created a multilayer perceptron framed model, known as HydroThermoMLP, by incorporating the Redlich-Kister polynomial as the thermodynamic representation of viscosity of mixtures. To accomplish the MLP learning on limited data, the shared loss function was formulated on the basis of the R-K presentation to guide the joint training process. The established HydroThermoMLP model, while maintaining the same accuracy as Random Forest, produces outputs that adhere to thermodynamic constraints and instill confidence in generalization applications with a simple algorithm informed by the R-K polynomial. It presents a robust predictive ML tool to forecast the viscosity of hybrid hydrogels and direct the design of biomaterials while appropriately abiding by thermodynamic constraints as essential guidelines.

3-Dimensional printing and bioprinting in neurological sciences: applications in surgery, imaging, tissue engineering, and pharmacology and therapeutics

The rapid evolution of three-dimensional printing (3DP) has significantly impacted the medical field. In neurology for instance, 3DP has been pivotal in personalized surgical planning and education. Additionally, it has facilitated the creation of implants, microfluidic devices, and optogenetic probes, offering substantial implications for medical and research applications. Additionally, 3D printed nasal casts are showing great promise for targeted brain drug delivery. 3DP has also aided in creating 3D "phantoms" aligning with advancements in neuroimaging, and in the design of intricate objects for investigating the neurobiology of sensory perception. Furthermore, the emergence of 3D bioprinting (3DBP), a fusion of 3D printing and cell biology, has created new avenues in neural tissue engineering. Effective and ethical creation of tissue-like biomimetic constructs has enabled mechanistic, regenerative, and therapeutic evaluations. While individual reviews have explored the applications of 3DP or 3DBP, a comprehensive review encompassing the success stories across multiple facets of both technologies in neurosurgery, neuroimaging, and neuro-regeneration has been lacking. This review aims to consolidate recent achievements of both 3DP and 3DBP across various neurological science domains to encourage interdisciplinary research among neurologists, neurobiologists, and engineers, in order to promote further exploration of 3DP and 3DBP methodologies to novel areas of neurological science research and practice.

3D printed extended-release hydrochlorothiazide tablets

In this study 3D printed tablets (printlets) with extended release of hydrochlorothiazide (HHT) as model active ingredient were designed and developed. Four formulations, F0.1SSE, F1SSE, F0.1DLP and F1DLP, have been manufactured and characterized, using non-typical semi-solid extrusion (SSE) with UV light solidification and digital light processing (DLP) techniques. Obtained rheological studies pointed out to F1SSE and F1DLP as more suitable for SSE and DLP printing, respectively. Photopolymerization process between photopolymer (PEGDA) and photoinitiator (DPPO; 0.1% and 1%) was investigated using FTIR, with PCA modeling utilized to analyze spectral variations over time and estimate crosslinking kinetics. SSE printlets averaged ∼6.5 mm in diameter, ∼3 mm in height and ∼110 mg in mass, while DLP printlets averaged ∼8.5 mm in diameter, ∼2.5 mm in height, with masses of ∼170 mg (F0.1DLP) and ∼220 mg (F1DLP). All four formulations complied to the requirements of European pharmacopeia for uniformity of dosage units of single dose preparations. In vitro release studies indicated extended-release profiles in both 0.1M Hydrochloric acid (HCl) and phosphate buffer pH 6.8 for SSE and DLP printlets. The release kinetics of HHT from the printlets were modeled to fit First order, Higuchi, Korsmeyer-Peppas and Hixson-Crowell equations and the most probable ones were determined based on the R2 values and Akaike information criterion. FTIR and Raman spectroscopic analyses of printlets confirmed the presence of characteristic peaks from both, HHT and excipients, as well as modifications in bonds due to the photopolymeric reaction.

Study on Printability Evaluation of Alginate/Silk Fibroin/Collagen Double-Cross-Linked Inks and the Properties of 3D Printed Constructs

In recent years, biological 3D printing has garnered increasing attention for tissue and organ repair. The challenge with 3D-printing inks is to combine mechanical properties as well as biocompatibility. Proteins serve as vital structural components in living systems, and utilizing protein-based inks can ensure that the materials maintain the necessary biological activity. In this study, we incorporated two natural biomaterials, silk fibroin (SF) and collagen (COL), into a low-concentration sodium alginate (SA) solution to create novel composite inks. SF and COL were modified with glycidyl methacrylate (GMA) to impart photo-cross-linking properties. The UV light test and 1H NMR results demonstrated successful curing of silk fibroin (SF) and collagen (COL) after modification and grafting. Subsequently, the printability of modified silk fibroin (RSFMA)/SA with varying concentration gradients was assessed using a set of three consecutive printing models, and the material's properties were tested. The research results prove that the addition of RSFMA and ColMA enhances the printability of low-concentration SA solutions, with the Pr values increasing from 0.85 ± 0.02 to 0.90 ± 0.03 and 0.92 ± 0.02, respectively, and the mechanical strength increasing from 0.19 ± 0.01 to 0.28 ± 0.01 and 0.38 ± 0.01 MPa; cytocompatibility has also been improved. Furthermore, rheological tests indicated that all of the inks exhibited shear thinning properties. CCK-8 experiments demonstrated that the addition of ColMA increased the cytocompatibility of the ink system. Overall, the utilization of SF and COL-modified SA materials as inks represents a promising advancement in 3D-printed ink technology.

Evaluation of the printability of agar and hydroxypropyl methylcellulose gels as gummy formulations: Insights from rheological properties

The trial-and-error method currently used to create formulations with excellent printability demands considerable time and resources, primarily due to the increasing number of variables involved. Rheology serves as a relatively rapid and highly beneficial method for assessing materials and evaluating their effectiveness as 3D constructs. However, the data obtained can be overwhelming, especially for users lacking experience in this field. This study examined the rheological properties of formulations of agar, hydroxypropyl methylcellulose, and the model drug caffeine, alongside exploring their printability as gummy formulations. The gels' rheological properties were characterized using oscillatory and rotational experiments. The correlation between these gels' rheological properties and their printability was established, and three clusters were formed based on the rheological properties and printability of the samples using principal component analysis. Furthermore, the printability was predicted using the sample's rheological property that correlated most with printability, the phase angle δ, and the regression models resulted in an accuracy of over 80%. Although these relationships merit confirmation in later studies, this study suggests a quantitative definition of the relationship between printability and one rheological property and can be used for the development of formulations destined for extrusion 3D printing.