4D Printing of Shape Memory Vascular Stent Based on βCD-g-Polycaprolactone

Advances in 4D Bioprinting: The Next Frontier in Regenerative Medicine and Tissue Engineering Applications

4D bioprinting is a critical advancement in tissue engineering and regenerative medicine (TERM), enabling the creation of structures that dynamically respond to environmental stimuli over time. This review investigates various fabrication techniques and responsive materials that are central to these fields. It underscores the integration of multi‐material and biocomposite approaches in 4D bioprinting, which is crucial for fabricating complex and functional constructs with heterogeneous properties. Using 4D bioprinting techniques enhances the mimicry of natural tissue characteristics, offering tailored responses and improved integration with biological systems. Furthermore, this study highlights the synergy between 4D bioprinting and tissue engineering and demonstrates the technology's potential for developing tissues and organs. In regenerative medicine, 4D bioprinting's applications extend to creating smart implants and advanced drug delivery systems that adapt to the body's changes, promoting healing and tissue regeneration. Finally, the challenges and future directions of 4D bioprinting are also explored and emphasize its transformative impact on biomedical engineering and the future of healthcare.

Integrative Modeling and Experimental Insights into 3D and 4D Printing Technologies

This review focuses on advancements in polymer science as it relates to three-dimensional (3D) and four-dimensional (4D) printing technologies, with a specific emphasis on applications in the biomedical field. While acknowledging the breadth of 3D and 4D printing applications, this paper concentrates on the use of polymers in creating biomedical devices and the challenges associated with their implementation. It explores integrative modeling and experimental insights driving innovations in these fields, focusing on sustainable manufacturing with biodegradable polymers, a comparative analysis of 3D and 4D printing techniques, and applications in biomedical devices. Additionally, the review examines the materials used in both 3D and 4D printing, offering a detailed comparison of their properties and applications. By highlighting the transformative potential of these technologies in various industrial and medical applications, the paper underscores the importance of continued research and development. The scope of this review also includes an overview of future research directions to address current challenges, enhance material capabilities, and explore practical applications.

Multimaterial 3D and 4D Bioprinting of Heterogenous Constructs for Tissue Engineering

Additive manufacturing (AM), which is based on the principle of layer-by-layer shaping and stacking of discrete materials, has shown significant benefits in the fabrication of complicated implants for tissue engineering (TE). However, many native tissues exhibit anisotropic heterogenous constructs with diverse components and functions. Consequently, the replication of complicated biomimetic constructs using conventional AM processes based on a single material is challenging. Multimaterial 3D and 4D bioprinting (with time as the fourth dimension) has emerged as a promising solution for constructing multifunctional implants with heterogenous constructs that can mimic the host microenvironment better than single-material alternatives. Notably, 4D-printed multimaterial implants with biomimetic heterogenous architectures can provide a time-dependent programmable dynamic microenvironment that can promote cell activity and tissue regeneration in response to external stimuli. This paper first presents the typical design strategies of biomimetic heterogenous constructs in TE applications. Subsequently, the latest processes in the multimaterial 3D and 4D bioprinting of heterogenous tissue constructs are discussed, along with their advantages and challenges. In particular, the potential of multimaterial 4D bioprinting of smart multifunctional tissue constructs is highlighted. Furthermore, this review provides insights into how multimaterial 3D and 4D bioprinting can facilitate the realization of next-generation TE applications.

4D Printing for Biomedical Applications

4D (bio-)printing endows 3D printed (bio-)materials with multiple functionalities and dynamic properties. 4D printed materials have been recently used in biomedical engineering for the design and fabrication of biomedical devices, such as stents, occluders, microneedles, smart 3D-cell engineered microenvironments, drug delivery systems, wound closures, and implantable medical devices. However, the success of 4D printing relies on the rational design of 4D printed objects, the selection of smart materials, and the availability of appropriate types of external (multi-)stimuli. Here, this work first highlights the different types of smart materials, external stimuli, and design strategies used in 4D (bio-)printing. Then, it presents a critical review of the biomedical applications of 4D printing and discusses the future directions of biomedical research in this exciting area, including in vivo tissue regeneration studies, the implementation of multiple materials with reversible shape memory behaviors, the creation of fast shape-transformation responses, the ability to operate at the microscale, untethered activation and control, and the application of (machine learning-based) modeling approaches to predict the structure-property and design-shape transformation relationships of 4D (bio)printed constructs.

Water-Induced Expanded Bilayer Vascular Graft with Good Hemocompatibility and Biocompatibility

Shape memory polymer (SMP) vascular grafts are promising interventional vascular grafts for cardiovascular disease (CAD) treatment; However, hemocompatibility and biocompatibility, which are the critical issues for the SMP vascular grafts, are not systematically concerned. Furthermore, the water-induced SMP grafts are more convenient and safer than the thermally induced ones in case of the bioapplication. Herein, in this work, the new water-induced expanded bilayer vascular graft with the inner layer of crosslinked poly(ε-caprolactone) (cPCL) and the outer layer of water-induced SMP of regenerated chitosan/polyvinyl alcohol (RCS/PVA) are prepared by hot pressing and programming approaches. The results show that the inner and outer layer surfaces of the prepared grafts are smooth, and they exhibit good interfacial interaction properties. The bilayer grafts show good mechanical properties and can be expanded in water with a diameter expansion of ≈30%. When compared with commercial expanded polytetrafluoroethylene (ePTFE), the bilayer graft shows better hemocompatibility (platelet adhesion, hemolysis rate, various clotting times, and plasma recalcification time (PRT)) and in vitro and in vivo biocompatibility, which thus is a promising material for the vascular graft.

Clinical situations for which 3D Printing is considered an appropriate representation or extension of data contained in a medical imaging examination: vascular conditions

BACKGROUND

Medical three-dimensional (3D) printing has demonstrated utility and value in anatomic models for vascular conditions. A writing group composed of the Radiological Society of North America (RSNA) Special Interest Group on 3D Printing (3DPSIG) provides appropriateness recommendations for vascular 3D printing indications.

METHODS

A structured literature search was conducted to identify all relevant articles using 3D printing technology associated with vascular indications. Each study was vetted by the authors and strength of evidence was assessed according to published appropriateness ratings.

RESULTS

Evidence-based recommendations for when 3D printing is appropriate are provided for the following areas: aneurysm, dissection, extremity vascular disease, other arterial diseases, acute venous thromboembolic disease, venous disorders, lymphedema, congenital vascular malformations, vascular trauma, vascular tumors, visceral vasculature for surgical planning, dialysis access, vascular research/development and modeling, and other vasculopathy. Recommendations are provided in accordance with strength of evidence of publications corresponding to each vascular condition combined with expert opinion from members of the 3DPSIG.

CONCLUSION

This consensus appropriateness ratings document, created by the members of the 3DPSIG, provides an updated reference for clinical standards of 3D printing for the care of patients with vascular conditions.

Three/Four-Dimensional Printed PLA Nano/Microstructures: Crystallization Principles and Practical Applications

Compared to traditional methods, three/four-dimensional (3D/4D) printing technologies allow rapid prototyping and mass customization, which are ideal for preparing nano/microstructures of soft polymer materials. Poly (lactic acid) (PLA) is a biopolymer material widely used in additive manufacturing (AM) because of its biocompatibility and biodegradability. Unfortunately, owing to its intrinsically poor nucleation ability, a PLA product is usually in an amorphous state after industrial processing, leading to some undesirable properties such as a barrier property and low thermal resistance. Crystallization mediation offers a most practical way to improve the properties of PLA products. Herein, we summarize and discuss 3D/4D printing technologies in the processing of PLA nano/microstructures, focusing on crystallization principles and practical applications including bio-inspired structures, flexible electronics and biomedical engineering mainly reported in the last five years. Moreover, the challenges and prospects of 3D/4D printing technologies in the fabrication of high-performance PLA materials nano/microstructures will also be discussed.

4D Printing in Biomedical Engineering: Advancements, Challenges, and Future Directions

4D printing has emerged as a transformative technology in the field of biomedical engineering, offering the potential for dynamic, stimuli-responsive structures with applications in tissue engineering, drug delivery, medical devices, and diagnostics. This review paper provides a comprehensive analysis of the advancements, challenges, and future directions of 4D printing in biomedical engineering. We discuss the development of smart materials, including stimuli-responsive polymers, shape-memory materials, and bio-inks, as well as the various fabrication techniques employed, such as direct-write assembly, stereolithography, and multi-material jetting. Despite the promising advances, several challenges persist, including material limitations related to biocompatibility, mechanical properties, and degradation rates; fabrication complexities arising from the integration of multiple materials, resolution and accuracy, and scalability; and regulatory and ethical considerations surrounding safety and efficacy. As we explore the future directions for 4D printing, we emphasise the need for material innovations, fabrication advancements, and emerging applications such as personalised medicine, nanomedicine, and bioelectronic devices. Interdisciplinary research and collaboration between material science, biology, engineering, regulatory agencies, and industry are essential for overcoming challenges and realising the full potential of 4D printing in the biomedical engineering landscape.

Additive manufacturing of vascular stents

With the advancement of additive manufacturing (AM), customized vascular stents can now be fabricated to fit the curvatures and sizes of a narrowed or blocked blood vessel, thereby reducing the possibility of thrombosis and restenosis. More importantly, AM enables the design and fabrication of complex and functional stent unit cells that would otherwise be impossible to realize with conventional manufacturing techniques. Additionally, AM makes fast design iterations possible while also shortening the development time of vascular stents. This has led to the emergence of a new treatment paradigm in which custom and on-demand-fabricated stents will be used for just-in-time treatments. This review is focused on the recent advances in AM vascular stents aimed at meeting the mechanical and biological requirements. First, the biomaterials suitable for AM vascular stents are listed and briefly described. Second, we review the AM technologies that have been so far used to fabricate vascular stents as well as the performances they have achieved. Subsequently, the design criteria for the clinical application of AM vascular stents are discussed considering the currently encountered limitations in materials and AM techniques. Finally, the remaining challenges are highlighted and some future research directions are proposed to realize clinically-viable AM vascular stents. STATEMENT OF SIGNIFICANCE: Vascular stents have been widely used for the treatment of vascular disease. The recent progress in additive manufacturing (AM) has provided unprecedented opportunities for revolutionizing traditional vascular stents. In this manuscript, we review the applications of AM to the design and fabrication of vascular stents. This is an interdisciplinary subject area that has not been previously covered in the published review articles. Our objective is to not only present the state-of-the-art of AM biomaterials and technologies but to also critically assess the limitations and challenges that need to be overcome to speed up the clinical adoption of AM vascular stents with both anatomical superiority and mechanical and biological functionalities that exceed those of the currently available mass-produced devices.

Fused Deposition Modeling and Characterization of Heat Shape Memory Poly(lactic) Acid-Based Porous Vascular Scaffold

Shape memory polymers have received widespread attention from researchers because of their low density, shape variety, responsiveness to the environment, and transparency. This study deals with heat-shape memory polymers (SMPs) based on polylactic acid (PLA) for designing and fabricating a novel porous vascular scaffold to treat vascular restenosis. The solid isotropic material penalization method (SIMP) was applied to optimize the vascular scaffolds. Based on the torsional torque loading of Hyperworks Optistruct and the boundary conditions, the topological optimization model of a vascular scaffold unit was established. Forward and reverse hybrid modeling technology was applied to complete the final stent structure's assembly. The glass transition temperature for the present SMPs is 42.15 °C. With the increase in temperature, the ultimate tensile strength of the SMPs is reduced from 29.5 MPa to 11.6 MPa. The maximum modulus at room temperature was around 34 MPa. Stress relaxation curves show that the material classification is a "thermoset" polymer. The superb mechanical properties, the transition temperature of the SMPs, and the recovery ratio made it a feasible candidate for a vascular scaffold. A circular tube based on the shape memory polymers was presented as an example for analyzing the recovery ratio in an unfolding state. A higher recovery ratio was obtained at a temperature of 65 °C with a tube thickness of 2 mm. Finally, the proposed porous vascular scaffold was successfully fabricated, assessed, and compared with the original and previously developed vascular scaffolds. The proposed scaffold structure regains its initial shape with a recovery ratio of 98% (recovery temperature of 47 °C) in 16 s. The tensile strength, Young's modulus, and bending strength of the proposed scaffold were 29.5 MPa, 695.4 MPa, and 6.02 MPa, respectively. The results showed that the proposed scaffold could be regarded as a potential candidate for a vascular implantation.

A Biocompatible 4D Printing Shape Memory Polymer as Emerging Strategy for Fabrication of Deployable Medical Devices

The rapid development of 4D printing provides a potential strategy for the fabrication of deployable medical devices (DMD). The minimally invasive surgery to implant the DMD into the body is critical, 4D printing DMD allows the well-defined device to be implanted with a high-compacted shape and transformed into their designed shape to meet the requirement. Herein, a 4D printing tissue engineering material is developed with excellent biocompatibility and shape memory effect based on the photocrosslinked polycaprolactone (PCL). The fast thiol-acrylate click reaction is applied for photocrosslinking of the acrylates capped star polymer (s-PCL-MA) with poly-thiols, that enable the 3D printing for the DMD fabrication. The cell viability, erythrocyte hemolysis, and platelet adhesion results indicate the excellent biocompatibility of the 4D printing polymer, especially the biological subcutaneous implantation results confirm the promote tissue growth and good histocompatibility. A 4D printing stent with deformable shape and recovery at a temperature close to human body temperature demonstrated the potential application as DMD. In addition, the everolimus is loaded to the polymer (ps1-PCL) through host-guest coordination with β-cyclodextrin as the core of the star polymer, which shows sustained drug release and improved body's inflammatory response.

Research Progress of Shape Memory Polymer and 4D Printing in Biomedical Application

As a kind of smart material, shape memory polymer (SMP) shows great application potential in the biomedical field. Compared with traditional metal-based medical devices, SMP-based devices have the following characteristics: 1) The adaptive ability allows the biomedical device to better match the surrounding tissue after being implanted into the body by minimally invasive implantation; 2) it has better biocompatibility and adjustable biodegradability; 3) mechanical properties can be regulated in a large range to better match with the surrounding tissue. 4D printing technology is a comprehensive technology based on smart materials and 3D printing, which has great application value in the biomedical field. 4D printing technology breaks through the technical bottleneck of personalized customization and provides a new opportunity for the further development of the biomedical field. This paper summarizes the application of SMP and 4D printing technology in the field of bone tissue scaffolds, tracheal scaffolds, and drug release, etc. Moreover, this paper analyzes the existing problems and prospects, hoping to provide a preliminary discussion and useful reference for the application of SMP in biomedical engineering.

3D printing technique applied in vaginoplasty: A case report

Background

We present the first case report of the treatment of congenital vaginal atresia by 3D-printed patient-specific vaginal scaffold from China.

Case presentation

A 17-year-old female patient was referred to our department for treatment of congenital vaginal atresia and complications arising from previous failed operations. Pelvic examination was conducted to understand the morphological characteristics and severity of stenosis, and based on which we designed our prototypes of vaginal scaffold using software UG NX10.0. We finally obtained our patient-specific mold, which was 50 mm in length, 28 mm in diameter, 2 mm of thickness with a whole weight of 7.6 g, and it was made of polycaprolactone. After removing scar tissues caused by vaginal stenosis, an 8 cm long artificial tunnel was created, and then the polycaprolactone (PCL) vaginal mold was placed and sutured. The patient had no discomfort after surgery and was discharged 3 days after the surgery. Follow-up for 1 year after surgery, through hysteroscopy and colposcopy, it was found that the cervix was smooth, the vaginal wall was covered with stratified squamous epithelium, and the vaginal wall was soft and lubricated, which was close to a normal vagina. The incompletely absorbed mold was taken out one year after the operation. Hysteroscopy and colposcopy were performed one year and two years after the mold was taken out. The vagina was unobstructed and the length was about 12 cm. The appearance of the vaginal wrinkles was normal. The patient's quality of sexual life was good.

Conclusion

Our team tried to treat congenital vaginal atresia by 3D-printed patient-specific vaginal scaffold, which can effectively reduce patient complications and reduce patient pain. Through long-term follow-up, we found that this technique has achieved favorable results and improved the patient's quality of sexual life.

4D Printing Applications in the Development of Smart Cardiovascular Implants

Smart materials are able to react to different stimuli and adapt their shape to the environment. Although the development of 3D printing technology increased the reproducibility and accuracy of scaffold fabrication, 3D printed scaffolds can still be further improved to resemble the native anatomy. 4D printing is an innovative fabrication approach combining 3D printing and smart materials, also known as stimuli-responsive materials. Especially for cardiovascular implants, 4D printing can promisingly create programmable, adaptable prostheses, which facilitates implantation and/or create the topology of the target tissue post implantation. In this review, the principles of 4D printing with a focus on the applied stimuli are explained and the underlying 3D printing technologies are presented. Then, according to the type of stimulus, recent applications of 4D printing in constructing smart cardiovascular implants and future perspectives are discussed.

Enhanced Shape Memory Metal-Coordinated Poly(aryl ether ketone)s with Tunable Gradient-Deformation Behaviors as well as Self-Healing and Reprocessing Abilities

Reversible dynamic bonds are able to crack and recombine upon external stimuli, which endow polymers with exceptional self-healing, reprocessing, and reversible deformation ability. In this paper, we integrated the metal coordination bonds into shape memory poly(aryl ether ketone) (PAEK) to fabricate smart materials with multifunctionalities. Through tuning the metal ion content and species, the enhancement of shape memory behaviors was achieved, including the high recovery ratio (over 98%) and fixity ratio (over 98%), which was closely related to the synergic effect of the intrinsic motion ability of PAEK matrix and the cracking-recombination of coordination bonds. Besides, through the combination of the components with different Cu²⁺ contents, in addition to the components with Fe²⁺ coordination bonds, we fabricated the gradient shape memory structures with controllable shape memory and recovery behaviors. The manipulation of gradient coordination bonds resulted in different shape recovery speeds and directions. Furthermore, due to the dynamic cracking-recombination of coordination bonds, the metal-coordinated PAEK material exhibited the great self-healing and reprocessing performances, which were significant for largely extending its application range.

Exploiting the fundamentals of biological organization for the advancement of biofabrication

The field of biofabrication continues to progress, offering higher levels of spatial control, reproducibility, and functionality. However, we remain far from recapitulating what nature has achieved. Biological systems such as tissues and organs are assembled from the bottom-up through coordinated supramolecular and cellular processes that result in their remarkable structures and functionalities. In this perspective, we propose that incorporating such biological assembling mechanisms within fabrication techniques, offers an opportunity to push the boundaries of biofabrication. We dissect these mechanisms into distinct biological organization principles (BOPs) including self-assembly, compartmentalization, diffusion-reaction, disorder-to-order transitions, and out-of-equilibrium processes. We highlight recent work demonstrating the viability and potential of these approaches to enhance scalability, reproducibility, vascularization, and biomimicry; as well as current challenges to overcome.