3D Printing of Strontium Silicate Microcylinder-Containing Multicellular Biomaterial Inks for Vascularized Skin Regeneration

VEGF-delivering PEG hydrogels promote vascularization in the porcine subcutaneous space

For cell therapies, the subcutaneous space is an attractive transplant site due to its large surface area and accessibility for implantation, monitoring, biopsy, and retrieval. However, its poor vascularization has catalyzed research to induce blood vessel formation within the site to enhance cell revascularization and survival. Most studies focus on the subcutaneous space of rodents, which does not recapitulate important anatomical features and vascularization responses of humans. Herein, we evaluate biomaterial-driven vascularization in the porcine subcutaneous space. Additionally, we report the first use of cost-effective fluorescent microspheres to quantify perfusion in the porcine subcutaneous space. We investigate the vascularization-inducing efficacy of vascular endothelial growth factor (VEGF)-delivering synthetic hydrogels based on 4-arm poly(ethylene) glycol macromers with terminal maleimides (PEG-4MAL). We compare three groups: a non-degradable hydrogel with a VEGF-releasing PEG-4MAL gel coating (Core+VEGF gel); an uncoated, non-degradable hydrogel (Core-only); and naïve tissue. After 2 weeks, Core+VEGF gel has significantly higher tissue perfusion, blood vessel area, blood vessel density, and number of vessels compared to both Core-only and naïve tissue. Furthermore, healthy vital signs during surgery and post-procedure metrics demonstrate the safety of hydrogel delivery. We demonstrate that VEGF-delivering synthetic hydrogels induce robust vascularization and perfusion in the porcine subcutaneous space.

Three-dimensional bioprinting of tissue-engineered skin: Biomaterials, fabrication techniques, challenging difficulties, and future directions: A review

As an emerging new manufacturing technology, Three-dimensional (3D) bioprinting provides the potential for the biomimetic construction of multifaceted and intricate architectures of functional integument, particularly functional biomimetic dermal structures inclusive of cutaneous appendages. Although the tissue-engineered skin with complete biological activity and physiological functions is still cannot be manufactured, it is believed that with the advances in matrix materials, molding process, and biotechnology, a new generation of physiologically active skin will be born in the future. In pursuit of furnishing readers and researchers involved in relevant research to have a systematic and comprehensive understanding of 3D printed tissue-engineered skin, this paper furnishes an exegesis on the prevailing research landscape, formidable obstacles, and forthcoming trajectories within the sphere of tissue-engineered skin, including: (1) the prevalent biomaterials (collagen, chitosan, agarose, alginate, etc.) routinely employed in tissue-engineered skin, and a discerning analysis and comparison of their respective merits, demerits, and inherent characteristics; (2) the underlying principles and distinguishing attributes of various current printing methodologies utilized in tissue-engineered skin fabrication; (3) the present research status and progression in the realm of tissue-engineered biomimetic skin; (4) meticulous scrutiny and summation of the extant research underpinning tissue-engineered skin inform the identification of prevailing challenges and issues.

Reactive Oxygen Species Scavenging Injectable Hydrogel Potentiates the Therapeutic Potential of Mesenchymal Stem Cells in Skin Flap Regeneration

Cell-based therapies offer tremendous potential for skin flap regeneration. However, the hostile microenvironment of the injured tissue adversely affects the longevity and paracrine effects of the implanted cells, severely reducing their therapeutic effectiveness. Here, an injectable hydrogel (nGk) with reactive oxygen species (ROS) scavenging capability, which can amplify the cell viability and functions of encapsulated mesenchymal stem cells (MSCs), is employed to promote skin flap repair. nGk is formulated by dispersing manganese dioxide nanoparticles (MnO2 NPs) in a gelatin/κ-carrageenan hydrogel, which exhibits satisfactory injectable properties and undergoes a sol-gel phase transition at around 40 °C, leading to the formation of a solid gel at physiological temperature. MnO2 NPs enhance the mechanical properties of the hydrogel and give it the ability to scavenge ROS, thus providing a cell-protective system for MSCs. Cell culture studies show that nGk can mitigate the oxidative stress, improve cell viability, and boost stem cell paracrine function to promote angiogenesis. Furthermore, MSC-loaded nGk (nGk@MSCs) can improve the survival of skin flaps by promoting angiogenesis, reducing inflammatory reactions, and attenuating necrosis, providing an effective approach for tissue regeneration. Collectively, injectable nGk has substantial potential to enhance the therapeutic benefits of MSCs, making it a valuable delivery system for cell-based therapies.

Biofabrication Strategies for Oral Soft Tissue Regeneration

Gingival recession, a prevalent condition affecting the gum tissues, is characterized by the exposure of tooth root surfaces due to the displacement of the gingival margin. This review explores conventional treatments, highlighting their limitations and the quest for innovative alternatives. Importantly, it emphasizes the critical considerations in gingival tissue engineering leveraging on cells, biomaterials, and signaling factors. Successful tissue-engineered gingival constructs hinge on strategic choices such as cell sources, scaffold design, mechanical properties, and growth factor delivery. Unveiling advancements in recent biofabrication technologies like 3D bioprinting, electrospinning, and microfluidic organ-on-chip systems, this review elucidates their precise control over cell arrangement, biomaterials, and signaling cues. These technologies empower the recapitulation of microphysiological features, enabling the development of gingival constructs that closely emulate the anatomical, physiological, and functional characteristics of native gingival tissues. The review explores diverse engineering strategies aiming at the biofabrication of realistic tissue-engineered gingival grafts. Further, the parallels between the skin and gingival tissues are highlighted, exploring the potential transfer of biofabrication approaches from skin tissue regeneration to gingival tissue engineering. To conclude, the exploration of innovative biofabrication technologies for gingival tissues and inspiration drawn from skin tissue engineering look forward to a transformative era in regenerative dentistry with improved clinical outcomes.

Immunomodulatory multicellular scaffolds for tendon-to-bone regeneration

Limited motor activity due to the loss of natural structure impedes recovery in patients suffering from tendon-to-bone injury. Conventional biomaterials focus on strengthening the regenerative ability of tendons/bones to restore natural structure. However, owing to ignoring the immune environment and lack of multi-tissue regenerative function, satisfactory outcomes remain elusive. Here, combined manganese silicate (MS) nanoparticles with tendon/bone-related cells, the immunomodulatory multicellular scaffolds were fabricated for integrated regeneration of tendon-to-bone. Notably, by integrating biomimetic cellular distribution and MS nanoparticles, the multicellular scaffolds exhibited diverse bioactivities. Moreover, MS nanoparticles enhanced the specific differentiation of multicellular scaffolds via regulating macrophages, which was mainly attributed to the secretion of PGE2 in macrophages induced by Mn ions. Furthermore, three animal results indicated that the scaffolds achieved immunomodulation, integrated regeneration, and function recovery at tendon-to-bone interfaces. Thus, the multicellular scaffolds based on inorganic biomaterials offer an innovative concept for immunomodulation and integrated regeneration of soft/hard tissue interfaces.

A heparin-functionalized bioink with sustained delivery of vascular endothelial growth factor for 3D bioprinting of prevascularized dermal constructs

Skin tissue engineering faces challenges due to the absence of vascular architecture, impeding the development of permanent skin replacements. To address this, a heparin-functionalized 3D-printed bioink (GH/HepMA) was formulated to enable sustained delivery of vascular endothelial growth factor (VEGF), comprising 0.3 % (w/v) hyaluronic acid (HA), 10 % (w/v) gelatin methacrylate (GelMA), and 0.5 % (w/v) heparin methacrylate (HepMA). The bioink was then used to print dermal constructs with angiogenic functions, including fibroblast networks and human umbilical vein endothelial cell (HUVEC) networks. GH/HepMA, with its covalently cross-linked structure, exhibits enhanced mechanical properties and heparin stability, allowing for a 21-day sustained delivery of VEGF. Cytocompatibility experiments showed that the GH/HepMA bioink supported fibroblast proliferation and promoted collagen I production. With VEGF present, the GH/HepMA bioink promoted HUVEC proliferation, migration, as well as the formation of a richer capillary-like network. Furthermore, HA within the GH/HepMA bioink enhanced rheological properties and printability. Additionally, 3D-bioprinted dermal constructs showed significant deposition of collagen I and III and mature stable capillary-like structures along the axial direction. In summary, this study offers a promising approach for constructing biomimetic multicellular skin substitutes with angiogenesis-induced functions.

Analysis of bioprinting strategies for skin diseases and injuries through structural and temporal dynamics: historical perspectives, research hotspots, and emerging trends

This study endeavors to investigate the progression, research focal points, and budding trends in the realm of skin bioprinting over the past decade from a structural and temporal dynamics standpoint. Scholarly articles on skin bioprinting were obtained from WoSCC. A series of bibliometric tools comprising R software, CiteSpace, HistCite, and an alluvial generator were employed to discern historical characteristics, evolution of active topics, and upcoming tendencies in the area of skin bioprinting. Over the past decade, there has been a consistent rise in research interest in skin bioprinting, accompanied by an extensive array of meaningful scientific collaborations. Concurrently, diverse dynamic topics have emerged during various periods, as substantiated by an aggregate of 22 disciplines, 74 keywords, and 187 references demonstrating citation bursts. Four burgeoning research subfields were discerned through keyword clustering-namely, #3 'in situbioprinting', #6 'vascular', #7 'xanthan gum', and #8 'collagen hydrogels'. The keyword alluvial map reveals that Module 1, including 'transplantation' etc, has primarily dominated the research module over the previous decade, maintaining enduring relevance despite annual shifts in keyword focus. Additionally, we mapped out the top six key modules from 2023 being 'silk fibroin nanofiber', 'system', 'ionic liquid', 'mechanism', and 'foot ulcer'. Three recent research subdivisions were identified via timeline visualization of references, particularly Clusters #0 'wound healing', #4 'situ mineralization', and #5 '3D bioprinter'. Insights derived from bibliometric analyses illustrate present conditions and trends in skin bioprinting research, potentially aiding researchers in pinpointing central themes and pioneering novel investigative approaches in this field.

Silicon-containing nanomedicine and biomaterials: materials chemistry, multi-dimensional design, and biomedical application

The invention of silica-based bioactive glass in the late 1960s has sparked significant interest in exploring a wide range of silicon-containing biomaterials from the macroscale to the nanoscale. Over the past few decades, these biomaterials have been extensively explored for their potential in diverse biomedical applications, considering their remarkable bioactivity, excellent biocompatibility, facile surface functionalization, controllable synthesis, etc. However, to expedite the clinical translation and the unexpected utilization of silicon-composed nanomedicine and biomaterials, it is highly desirable to achieve a thorough comprehension of their characteristics and biological effects from an overall perspective. In this review, we provide a comprehensive discussion on the state-of-the-art progress of silicon-composed biomaterials, including their classification, characteristics, fabrication methods, and versatile biomedical applications. Additionally, we highlight the multi-dimensional design of both pure and hybrid silicon-composed nanomedicine and biomaterials and their intrinsic biological effects and interactions with biological systems. Their extensive biomedical applications span from drug delivery and bioimaging to therapeutic interventions and regenerative medicine, showcasing the significance of their rational design and fabrication to meet specific requirements and optimize their theranostic performance. Additionally, we offer insights into the future prospects and potential challenges regarding silicon-composed nanomedicine and biomaterials. By shedding light on these exciting research advances, we aspire to foster further progress in the biomedical field and drive the development of innovative silicon-composed nanomedicine and biomaterials with transformative applications in biomedicine.

3D bioprinting bioglass to construct vascularized full-thickness skin substitutes for wound healing

Constructing three-dimensional (3D) bioprinted skin tissues that accurately replicate the mechanical properties of native skin and provide adequate oxygen and nutrient support remains a formidable challenge. In this study, we incorporated phosphosilicate calcium bioglasses (PSCs), a type of bioactive glass (BG), into the bioinks used for 3D bioprinting. The resulting bioink exhibited mechanical properties and biocompatibility that closely resembled those of natural skin. Utilizing 3D bioprinting technology, we successfully fabricated full-thickness skin substitutes, which underwent comprehensive evaluation to assess their regenerative potential in treating full-thickness skin injuries in rats. Remarkably, the skin substitutes loaded with PSCs exhibited exceptional angiogenic activity, as evidenced by the upregulation of angiogenesis-related genes in vitro and the observation of enhanced vascularization in wound tissue sections in vivo. These findings conclusively demonstrated the outstanding efficacy of PSCs in promoting angiogenesis and facilitating the repair of full-thickness skin wounds. The insights garnered from this study provide a valuable reference strategy for the development of skin tissue grafts with potent angiogenesis-inducing capabilities.

Engineered dermis loaded with confining forces promotes full-thickness wound healing by enhancing vascularisation and epithelialisation

Tissue-engineered skin is ideal for clinical wound repair. Restoration of skin tissue defects using tissue-engineered skin remains a challenge owing to insufficient vascularisation. In our previous study, we developed a 3D bioprinted model with confined force loading and demonstrated that the confined force can affect vascular branching, which is regulated by the YAP signalling pathway. The mechanical properties of the model must be optimised to suture the wound edges. In this study, we explored the ability of a GelMA-HAMA-fibrin scaffold to support the confined forces created by 3D bioprinting and promote vascularisation and wound healing. The shape of the GelMA-HAMA-fibrin scaffold containing 3% GelMA was affected by the confined forces produced by the embedded cells. The GelMA-HAMA-fibrin scaffold was easy to print, had optimal mechanical properties, and was biocompatible. The constructs were successfully sutured together after 14 d of culture. Scaffolds seeded with cells were transplanted into skin tissue defects in nude mice, demonstrating that the cell-seeded GelMA-HAMA-fibrin scaffold, under confined force loading, promoted neovascularisation and wound restoration by enhancing blood vessel connections, creating a patterned surface, growth factors, and collagen deposition. These results provide further insights into the production of hydrogel composite materials as tissue-engineered scaffolds under an internal mechanical load that can enhance vascularisation and offer new treatment methods for wound healing. STATEMENT OF SIGNIFICANCE: Tissue-engineered skin is ideal for use in clinical wound repair. However, treatment of tissue defects using synthetic scaffolds remains challenging, mainly due to slow and insufficient vascularization. Our previous study developed a 3D bioprinted model with confined force loading, and demonstrated that confined force can affect vascular branching regulated by the YAP signal pathway. The mechanical properties of the construct need to be optimized for suturing to the edges of wounds. Here, we investigated the ability of a GelMA-HAMA-fibrin scaffold to support the confined forces created by 3D bioprinting and promote vascularization in vitro and wound healing in vivo. Our findings provide new insight into the development of degradable macroporous composite materials with mechanical stimulation as tissue-engineered scaffolds with enhanced vascularization, and also provide new treatment options for wound healing.

3D multicellular micropatterning biomaterials for hair regeneration and vascularization

Hair loss caused by the abnormal functions of hair follicles in skin can seriously impact the quality of an individual's life. The development of sophisticated skin tissue-engineered constructs is required to enable the function recovery of hair follicles. However, effective hair regrowth in skin substitutes still remains a great challenge. In this study, a 3D multicellular micropattern was successfully fabricated by arranging the hair follicle-related cells orderly distributed in the interval of vascular-cell networks via bioprinting technology. By combining the stable biomimetic micropattern structure and the bio-inducing substrate incorporated with magnesium silicate (MS) nanomaterials, the 3D multicellular micropattern possessed significant follicular potential and angiogenic capacity in vitro. Furthermore, the 3D multicellular micropattern with MS incorporation contributed to efficient hair regrowth during skin tissue regeneration in both immunodeficient mice and androgenetic alopecia (AGA) mice models. Thus, this study proposes a novel 3D micropatterned multicellular system assembling a biomimetic micro-structure and modulating the cell-cell interaction for hair regeneration during skin reconstruction.

Strontium-doped mesoporous bioglass nanoparticles for enhanced wound healing with rapid vascularization

Tissue engineered skin and its substitutes have a promising future in wound healing. However, enabling fast formation of blood vessels during the wound healing process is still a huge challenge to the currently available wound substitutes. In this work, active mesoporous bioglass nanoparticles with a high specific surface area and doped with strontium (Sr) were fabricated for rapid microvascularization and wound healing. The as-prepared bioglass nanoparticles with Sr ions significantly promoted the proliferation of fibroblasts and microvascularization of human umbilical vein endothelial cells in vitro. Silk fibroin sponges encapsulating the nanoparticles accelerated wound healing by promoting the formation of blood vessels and epithelium in vivo. This work provides a strategy for the design and development of active biomaterials for enhancing wound healing by rapid vascularization and epithelial reconstruction.

Xonotlite Nanowire-Containing Bioactive Scaffolds for the Therapy of Defective Adipose Tissue in Breast Cancer

Considering the challenge in the treatment of severe breast tumor patients, xonotlite nanowire-containing bioactive scaffolds (Fe3O4-CS-GelMA) were fabricated by the 3D-printing technique for the therapy of injured adipose tissue after surgery. Importantly, benefiting from the excellent magnetothermal performance of Fe3O4 microspheres, Fe3O4-CS-GelMA scaffolds could effectively kill tumor cells in vitro and suppress breast cancer in vivo under an alternating magnetic field, and the tumor did not recur in 2 weeks. In addition, attributed to the released bioactive inorganic ions, Fe3O4-CS-GelMA composite scaffolds could effectively promote the expression of adipogenesis-related genes and proteins of adipose-derived stem cells (ADSCs) via the PI3K-AKT signaling pathway in vitro. Furthermore, Fe3O4-CS-GelMA scaffolds with ADSCs could obviously stimulate the formation of adipose in vivo, compared with that of pure GelMA without inorganic components. Therefore, this study offers a promising strategy for the therapy of breast tumors after the surgical excision of breast carcinoma.

Biomimetic Liquid Crystal-Modified Mesoporous Silica-Based Composite Hydrogel for Soft Tissue Repair

The reconstruction of blood vessels plays a critical role in the tissue regeneration process. However, existing wound dressings in tissue engineering face challenges due to inadequate revascularization induction and a lack of vascular structure. In this study, we report the modification of mesoporous silica nanospheres (MSNs) with liquid crystal (LC) to enhance bioactivity and biocompatibility in vitro. This LC modification facilitated crucial cellular processes such as the proliferation, migration, spreading, and expression of angiogenesis-related genes and proteins in human umbilical vein endothelial cells (HUVECs). Furthermore, we incorporated LC-modified MSN within a hydrogel matrix to create a multifunctional dressing that combines the biological benefits of LC-MSN with the mechanical advantages of a hydrogel. Upon application to full-thickness wounds, these composite hydrogels exhibited accelerated healing, evidenced by enhanced granulation tissue formation, increased collagen deposition, and improved vascular development. Our findings suggest that the LC-MSN hydrogel formulation holds significant promise for the repair and regeneration of soft tissues.

3D-printed GelMA/CaSiO3 composite hydrogel scaffold for vascularized adipose tissue restoration

The increased number of mastectomies, combined with rising patient expectations for cosmetic and psychosocial outcomes, has necessitated the use of adipose tissue restoration techniques. However, the therapeutic effect of current clinical strategies is not satisfying due to the high demand of personalized customization and the timely vascularization in the process of adipose regeneration. Here, a composite hydrogel scaffold was prepared by three-dimensional (3D) printing technology, applying gelatin methacrylate anhydride (GelMA) as printing ink and calcium silicate (CS) bioceramic as an active ingredient for breast adipose tissue regeneration. The in vitro experiments showed that the composite hydrogel scaffolds could not only be customized with controllable architectures, but also significantly stimulated both 3T3-L1 preadipocytes and human umbilical vein endothelial cells in multiple cell behaviors, including cell adhesion, proliferation, migration and differentiation. Moreover, the composite scaffold promoted vascularized adipose tissue restoration under the skin of nude mice in vivo. These findings suggest that 3D-printed GelMA/CS composite scaffolds might be a good candidate for adipose tissue engineering.

Multicellular Bioprinting of Biomimetic Inks for Tendon-to-Bone Regeneration

Tendon-to-bone interface has a hierarchical structure and gradient component that are conducive to distributing the stresses to achieve movement. Conventional biomaterials lack the capacity to induce synchronous repair of multiple tissues, resulting in the failure of the interface repair. Biomimetic strategies have attracted enormous attention in the field of complex structure regeneration because they can meet the different physiological requirements of multiple tissues. Herein, a biomimetic ink mimicking tendon/bone tissues is developed by combining tendon/bone-related cells and Mo-containing silicate (MS) bioceramics. Subsequently, biomimetic multicellular scaffolds are fabricated to achieve the simulation of the hierarchical structure and cellular composition of tendon-to-bone interfaces by the spatial distribution of the biomimetic inks via 3D bioprinting, which is of great significance for inducing the regeneration of complex structures in the interface region. In addition, attributed to the desirable ionic microenvironment created by MS bioceramics, the biomimetic scaffolds possess the dual function of inducing tendon/bone-related cells tenogenic and osteogenic differentiation in vitro, and promote the integrated regeneration of tendon-to-bone interfaces in vivo. The study offers a feasible strategy to construct biomimetic multicellular scaffolds with bifunction for inducing multi-lineage tissue regeneration, especially for regenerating soft-to-hard tissue interfaces.

3D-Printed Functional Hydrogel by DNA-Induced Biomineralization for Accelerated Diabetic Wound Healing

Chronic wounds in diabetic patients are challenging because their prolonged inflammation makes healing difficult, thus burdening patients, society, and health care systems. Customized dressing materials are needed to effectively treat such wounds that vary in shape and depth. The continuous development of 3D-printing technology along with artificial intelligence has increased the precision, versatility, and compatibility of various materials, thus providing the considerable potential to meet the abovementioned needs. Herein, functional 3D-printing inks comprising DNA from salmon sperm and DNA-induced biosilica inspired by marine sponges, are developed for the machine learning-based 3D-printing of wound dressings. The DNA and biomineralized silica are incorporated into hydrogel inks in a fast, facile manner. The 3D-printed wound dressing thus generates provided appropriate porosity, characterized by effective exudate and blood absorption at wound sites, and mechanical tunability indicated by good shape fidelity and printability during optimized 3D printing. Moreover, the DNA and biomineralized silica act as nanotherapeutics, enhancing the biological activity of the dressings in terms of reactive oxygen species scavenging, angiogenesis, and anti-inflammation activity, thereby accelerating acute and diabetic wound healing. These bioinspired 3D-printed hydrogels produce using a DNA-induced biomineralization strategy are an excellent functional platform for clinical applications in acute and chronic wound repair.

The applications of 3D printing in wound healing: the external delivery of stem cells and antibiosis

As the global number of chronic wound patients rises, the financial burden and social pressure on patients increase daily. Stem cells have emerged as promising tissue engineering seed cells due to their enriched sources, multidirectional differentiation ability, and high proliferation rate. However, delivering them in vitro for the treatment of skin injury is still challenging. In addition, bacteria from the wound site and the environment can significantly impact wound healing. In the last decade, 3D bioprinting has dramatically enriched cell delivery systems. The produced scaffolds by this technique can be precisely localized within cells and perform antibacterial actions. In this review, we summarized the 3D bioprinting-based external delivery of stem cells and their antibiosis to improve wound healing.

Recent Advances in Decellularized Matrix-Derived Materials for Bioink and 3D Bioprinting

As an emerging 3D printing technology, 3D bioprinting has shown great potential in tissue engineering and regenerative medicine. Decellularized extracellular matrices (dECM) have recently made significant research strides and have been used to create unique tissue-specific bioink that can mimic biomimetic microenvironments. Combining dECMs with 3D bioprinting may provide a new strategy to prepare biomimetic hydrogels for bioinks and hold the potential to construct tissue analogs in vitro, similar to native tissues. Currently, the dECM has been proven to be one of the fastest growing bioactive printing materials and plays an essential role in cell-based 3D bioprinting. This review introduces the methods of preparing and identifying dECMs and the characteristic requirements of bioink for use in 3D bioprinting. The most recent advances in dECM-derived bioactive printing materials are then thoroughly reviewed by examining their application in the bioprinting of different tissues, such as bone, cartilage, muscle, the heart, the nervous system, and other tissues. Finally, the potential of bioactive printing materials generated from dECM is discussed.

3D printed wound constructs for skin tissue engineering: A systematic review in experimental animal models

Wound dressings are one of the most used treatments for chronic wounds. Moreover, 3D printing has been emerging as a promising strategy for printing 3D printed wound constructs, being able of manufacturing multi layers, with a solid 3D structure. Although all these promising effects of 3D printed wound constructs, there is still few studies and limited understanding of the interaction of these dressings with skin tissue and their effect on the process of skin wound healing. In this context, the aim of this work was to perform a systematic review of the literature to examine the effects of 3D printed wound constructs on the process of skin wound healing in animal models. The articles were selected from three databases following Medical Subject Headings (MeSH) descriptors "3D printing," "skin," "wound," and "in vivo." After the selection, exclusion and inclusion criteria, nine articles were analyzed. This review confirms the significant benefits of using 3D printed wound constructs for skin repair and regeneration. All the used inks demonstrated the ability of mimicking the structure of skin tissue and promoting cell adhesion, proliferation, migration, and mobility. Furthermore, in vivo findings showed full wound closure in most of the studies, with well-organized dermal and epidermal layers.

Emerging 3D bioprinting applications in plastic surgery

Plastic surgery is a discipline that uses surgical methods or tissue transplantation to repair, reconstruct and beautify the defects and deformities of human tissues and organs. Three-dimensional (3D) bioprinting has gained widespread attention because it enables fine customization of the implants in the patient's surgical area preoperatively while avoiding some of the adverse reactions and complications of traditional surgical approaches. In this paper, we review the recent research advances in the application of 3D bioprinting in plastic surgery. We first introduce the printing process and basic principles of 3D bioprinting technology, revealing the advantages and disadvantages of different bioprinting technologies. Then, we describe the currently available bioprinting materials, and dissect the rationale for special dynamic 3D bioprinting (4D bioprinting) that is achieved by varying the combination strategy of bioprinting materials. Later, we focus on the viable clinical applications and effects of 3D bioprinting in plastic surgery. Finally, we summarize and discuss the challenges and prospects for the application of 3D bioprinting in plastic surgery. We believe that this review can contribute to further development of 3D bioprinting in plastic surgery and provide lessons for related research.

3D printing of cell-delivery scaffolds for tissue regeneration

Tissue engineering strategy that combine biomaterials with living cells has shown special advantages in tissue regeneration and promoted the development of regenerative medicine. In particular, the rising of 3D printing technology further enriched the structural design and composition of tissue engineering scaffolds, which also provided convenience for cell loading and cell delivery of living cells. In this review, two types of cell-delivery scaffolds for tissue regeneration, including 3D printed scaffolds with subsequent cell-seeding and 3D cells bioprinted scaffolds, are mainly reviewed. We devote a major part to present and discuss the recent advances of two 3D printed cell-delivery scaffolds in regeneration of various tissues, involving bone, cartilage, skin tissues etc. Although two types of 3D printed cell-delivery scaffolds have some shortcomings, they do have generally facilitated the exploration of tissue engineering scaffolds in multiple tissue regeneration. It is expected that 3D printed cell-delivery scaffolds will be further explored in function mechanism of seeding cells in vivo, precise mimicking of complex tissues and even organ reconstruction under the cooperation of multiple fields in future.

Inorganic-based biomaterials for rapid hemostasis and wound healing

The challenge for the treatment of severe traumas poses an urgent clinical need for the development of biomaterials to achieve rapid hemostasis and wound healing. In the past few decades, active inorganic components and their derived composites have become potential clinical products owing to their excellent performances in the process of hemorrhage control and tissue repair. In this review, we provide a current overview of the development of inorganic-based biomaterials used for hemostasis and wound healing. We highlight the methods and strategies for the design of inorganic-based biomaterials, including 3D printing, freeze-drying, electrospinning and vacuum filtration. Importantly, inorganic-based biomaterials for rapid hemostasis and wound healing are presented, and we divide them into several categories according to different chemistry and forms and further discuss their properties, therapeutic mechanisms and applications. Finally, the conclusions and future prospects are suggested for the development of novel inorganic-based biomaterials in the field of rapid hemostasis and wound healing.

Recent Advances in Functional Wound Dressings

Significance: Nowadays, the wound dressing is no longer limited to its primary wound protection ability. Hydrogel, sponge-like material, three dimensional-printed mesh, and nanofiber-based dressings with incorporation of functional components, such as nanomaterials, growth factors, enzymes, antimicrobial agents, and electronics, are able to not only prevent/treat infection but also accelerate the wound healing and monitor the wound-healing status. Recent Advances: The advances in nanotechnologies and materials science have paved the way to incorporate various functional components into the dressings, which can facilitate wound healing and monitor different biological parameters in the wound area. In this review, we mainly focus on the discussion of recently developed functional wound dressings. Critical Issues: Understanding the structure and composition of wound dressings is important to correlate their functions with the outcome of wound management. Future Directions: "All-in-one" dressings that integrate multiple functions (e.g., monitoring, antimicrobial, pain relief, immune modulation, and regeneration) could be effective for wound repair and regeneration.

Synergistic Effect of Static Magnetic Fields and 3D-Printed Iron-Oxide-Nanoparticle-Containing Calcium Silicate/Poly-ε-Caprolactone Scaffolds for Bone Tissue Engineering

In scaffold-regulated bone regeneration, most three-dimensional (3D)-printed scaffolds do not provide physical stimulation to stem cells. In this study, a magnetic scaffold was fabricated using fused deposition modeling with calcium silicate (CS), iron oxide nanoparticles (Fe₃O₄), and poly-ε-caprolactone (PCL) as the matrix for internal magnetic sources. A static magnetic field was used as an external magnetic source. It was observed that 5% Fe₃O₄ provided a favorable combination of compressive strength (9.6 ± 0.9 MPa) and degradation rate (21.6 ± 1.9% for four weeks). Furthermore, the Fe₃O₄-containing scaffold increased in vitro bioactivity and Wharton's jelly mesenchymal stem cells' (WJMSCs) adhesion. Moreover, it was shown that the Fe₃O₄-containing scaffold enhanced WJMSCs' proliferation, alkaline phosphatase activity, and the osteogenic-related proteins of the scaffold. Under the synergistic effect of the static magnetic field, the CS scaffold containing Fe₃O₄ can not only enhance cell activity but also stimulate the simultaneous secretion of collagen I and osteocalcin. Overall, our results demonstrated that Fe₃O₄-containing CS/PCL scaffolds could be fabricated three dimensionally and combined with a static magnetic field to affect cell behaviors, potentially increasing the likelihood of clinical applications for bone tissue engineering.

Functionalizing multi-component bioink with platelet-rich plasma for customized in-situ bilayer bioprinting for wound healing

In-situ three-dimensional (3D) bioprinting has been emerging as a promising technology designed to rapidly seal cutaneous defects according to their contour. Improvements in the formulations of multi-component bioink are needed to support cytocompatible encapsulation and biological functions. Platelet-rich plasma (PRP), as a source of patient-specific autologous growth factors, exhibits capabilities in tissue repair and rejuvenation. This study aimed to prepare PRP-integrated alginate-gelatin (AG) composite hydrogel bioinks and evaluate the biological effects in vitro and in vivo. 3D bioprinted constructs embedded with dermal fibroblasts and epidermal stem cells were fabricated using extrusion strategy. The integration of PRP not only improved the cellular behavior of seeded cells, but regulate the tube formation of vascular endothelial cells and macrophage polarization in a paracrine manner, which obtained an optimal effect at an incorporation concentration of 5%. For in-situ bioprinting, PRP integration accelerated the high-quality wound closure, modulated the inflammation and initiated the angiogenesis compared with the AG bioink. In conclusion, we revealed the regenerative potential of PRP, readily available at the bedside, as an initial signaling provider in multi-component bioink development. Combined with in-situ printing technology, it is expected to accelerate the clinical translation of rapid individualized wound repair.

3D printing of pharmaceuticals: approach from bench scale to commercial development

Background

The three-dimensional (3D) printing is paradigm shift in the healthcare sector. 3D printing is platform technologies in which complex products are developed with less number of additives. The easy development process gives edge over the conventional methods. Every individual needs specific dose treatment. ‘One size fits all’ is the current traditional approach that can shift to more individual specific in 3D printing. The present review aims to cover different perspectives regarding selection of drug, polymer and technological aspects for 3D printing. With respect to clinical practice, regulatory issue and industrial potential are also discussed in this paper.

Main body

The individualization of medicines with patient centric dosage form will become reality in upcoming future. It provides individual’s need of dose by considering genetic profile, physiology and diseased condition. The tailormade dosages with unique drug loading and release profile of different geometrical shapes and sizes can easily deliver therapeutic dose. The technology can fulfill growing demand of efficiency in the dose accuracy for the patient oriented sectors like pediatric, geriatric and also easy to comply with cGMP requirements of regulated market. The clinical practice can focus on prescribing each individual’s necessity of dose.

Conclusion

In the year 2015, FDA approved first 3D printed drug product, which is initiator in the new phase of manufacturing of pharmaceuticals. The tailormade formulations can be made in future for personalized medications. Regulatory approval from agencies can bring the 3DP product into the market. In the future, formulators can bring different sector-specific products for personalized need through 3DP pharmaceutical product.

Graphical Abstract

Bioactive inorganic particles-based biomaterials for skin tissue engineering

The challenge for treatment of severe cutaneous wound poses an urgent clinical need for the development of biomaterials to promote skin regeneration. In the past few decades, introduction of inorganic components into material system has become a promising strategy for improving performances of biomaterials in the process of tissue repair. In this review, we provide a current overview of the development of bioactive inorganic particles-based biomaterials used for skin tissue engineering. We highlight the three stages in the evolution of the bioactive inorganic biomaterials applied to wound management, including single inorganic materials, inorganic/organic composite materials, and inorganic particles-based cell-encapsulated living systems. At every stage, the primary types of bioactive inorganic biomaterials are described, followed by citation of the related representative studies completed in recent years. Then we offer a brief exposition of typical approaches to construct the composite material systems with incorporation of inorganic components for wound healing. Finally, the conclusions and future directions are suggested for the development of novel bioactive inorganic particles-based biomaterials in the field of skin regeneration.

Innovative Treatment Strategies to Accelerate Wound Healing: Trajectory and Recent Advancements

Wound healing is highly specialized dynamic multiple phase process for the repair of damaged/injured tissues through an intricate mechanism. Any failure in the normal wound healing process results in abnormal scar formation, and chronic state which is more susceptible to infections. Chronic wounds affect patients’ quality of life along with increased morbidity and mortality and are huge financial burden to healthcare systems worldwide, and thus requires specialized biomedical intensive treatment for its management. The clinical assessment and management of chronic wounds remains challenging despite the development of various therapeutic regimens owing to its painstakingly long-term treatment requirement and complex wound healing mechanism. Various conventional approaches such as cell therapy, gene therapy, growth factor delivery, wound dressings, and skin grafts etc., are being utilized for promoting wound healing in different types of wounds. However, all these abovementioned therapies are not satisfactory for all wound types, therefore, there is an urgent demand for the development of competitive therapies. Therefore, there is a pertinent requirement to develop newer and innovative treatment modalities for multipart therapeutic regimens for chronic wounds. Recent developments in advanced wound care technology includes nanotherapeutics, stem cells therapy, bioengineered skin grafts, and 3D bioprinting-based strategies for improving therapeutic outcomes with a focus on skin regeneration with minimal side effects. The main objective of this review is to provide an updated overview of progress in therapeutic options in chronic wounds healing and management over the years using next generation innovative approaches. Herein, we have discussed the skin function and anatomy, wounds and wound healing processes, followed by conventional treatment modalities for wound healing and skin regeneration. Furthermore, various emerging and innovative strategies for promoting quality wound healing such as nanotherapeutics, stem cells therapy, 3D bioprinted skin, extracellular matrix-based approaches, platelet-rich plasma-based approaches, and cold plasma treatment therapy have been discussed with their benefits and shortcomings. Finally, challenges of these innovative strategies are reviewed with a note on future prospects.

Spindle-Like Zinc Silicate Nanoparticles Accelerating Innervated and Vascularized Skin Burn Wound Healing

The treatment of severe burn injuries is a crucial challenge in skin tissue engineering. Severe burns are always accompanied with large-area neurovascular networks damage, leading to the lack of excitation functions and difficulty in self-healing. Therefore, it is of great importance to develop biomaterials which can not only promote wound healing but also simultaneously reconstruct cutaneous neurovascular networks. In this study, Zn₂ SiO₄ (ZS) nanoparticles-incorporated bioactive nanofibrous scaffolds are designed for innervated and vascularized skin burn wound healing. ZS nanoparticles with spindle-like morphology are synthesized via a facile hydrothermal method. The incorporation of ZS nanoparticles endows the scaffolds with excellent angiogenic and neurogenic activities in vitro. Additionally, in vivo results show that the ZS nanoparticles-incorporated scaffolds have favorable re-epithelialization, innervation, and vascularization abilities through local release of bioactive Zn and Si ions from ZS nanoparticles, leading to rapid wound healing featuring with newly formed blood vessels and nerve fibers. Taken together, this study suggests that the spindle-like ZS nanoparticles are useful bioactive agents for stimulating vascularization and innervation of functional skin repair. The bioactive inorganic nanoparticles may be used for multifunctional tissue regeneration.

Functionalized gelatin/strontium hydrogel bearing endothelial progenitor cells for accelerating angiogenesis in wound tissue regeneration

While polymer hydrogels are frequently utilized as wound dressings, they lack the sufficient bioactivity necessary to promote re-epithelialization and angiogenesis. In this work, a therapeutic angiogenesis complex is developed using a mixture of dopamine-modified polyhedral oligomeric silsesquioxane (Dopa-POSS), strontium ions (Sr²⁺ ions) photocrosslinked gelatin methacryloyl (GelMA) hydrogel and endothelial progenitor cells (EPCs) for full-thickness burn wound healing. Dopa-POSS is used to reinforce the hydrogel, and Sr²⁺ ions stabilizer is densely incorporated inside the network of GelMA hydrogels by ultraviolet cross-linking, thus effectively enhancing the hydrogel mechanical strength. The multifunctional GelMA hydrogels comprised gelatin's arginine-glycine-aspartate (RGD) patterns and active Sr²⁺ ions that promote EPC biological activity and proliferation. Notably, the Sr²⁺ ions in the functional hydrogels substantially enhanced EPC proliferation in a three-dimensional environment, migration, and angiogenesis-related protein expression. After 14 days, the Gel/Sr²⁺@POSS/EPCs composite hydrogel substantially accelerates and enhances the new blood vessel development process, collagen deposition, and re-epithelialization with the almost closed wounds and newly created tissue. Thus, UV-crosslinked Gel/Sr²⁺@POSS hydrogels functionalized with EPCs can be a potentially beneficial therapeutic system for full-thickness burn wound healing.

3D Printing: Applications in Tissue Engineering, Medical Devices, and Drug Delivery

The gemstone of 3-dimensional (3D) printing shines up from the pyramid of additive manufacturing. Three-dimensional bioprinting technology has been predicted to be a game-changing breakthrough in the pharmaceutical industry since the last decade. It is fast evolving and finds its seats in a variety of domains, including aviation, defense, automobiles, replacement components, architecture, movies, musical instruments, forensic, dentistry, audiology, prosthetics, surgery, food, and fashion industry. In recent years, this miraculous manufacturing technology has become increasingly relevant for pharmaceutical purposes. Computer-aided drug (CAD) model will be developed by computer software and fed into bioprinters. Based on material inputs, the printers will recognize and produce the model scaffold. Techniques including stereolithography, selective laser sintering, selective laser melting, material extrusion, material jetting, inkjet-based, fused deposition modelling, binder deposition, and bioprinting expedite the printing process. Distinct advantages are rapid prototyping, flexible design, print on demand, light and strong parts, fast and cost-effective, and environment friendly. The present review gives a brief description of the conceptional 3-dimensional printing, followed by various techniques involved. A short note was explained about the fabricating materials in the pharmaceutical sector. The beam of light is thrown on the various applications in the pharma and medical arena.

The 3D Bioprinted Scaffolds for Wound Healing

Skin tissue engineering and regeneration aim at repairing defective skin injuries and progress in wound healing. Until now, even though several developments are made in this field, it is still challenging to face the complexity of the tissue with current methods of fabrication. In this review, short, state-of-the-art on developments made in skin tissue engineering using 3D bioprinting as a new tool are described. The current bioprinting methods and a summary of bioink formulations, parameters, and properties are discussed. Finally, a representative number of examples and advances made in the field together with limitations and future needs are provided.