Three-Dimensional Printing and Cell Therapy for Wound Repair

Efficient fabrication of 3D bioprinted functional sensory neurons using an inducible Neurogenin-2 human pluripotent stem cell line

Three-dimensional (3D) tissue models have gained recognition for their improved ability to mimic the native cell microenvironment compared to traditional two-dimensional models. This progress has been driven by advances in tissue-engineering technologies such as 3D bioprinting, a promising method for fabricating biomimetic living tissues. While bioprinting has succeeded in generating various tissues to date, creating neural tissue models remains challenging. In this context, we present an accelerated approach to fabricate 3D sensory neuron (SN) structures using a transgenic human pluripotent stem cell (hPSC)-line that contains an inducible Neurogenin-2 (NGN2) expression cassette. The NGN2 hPSC line was first differentiated to neural crest cell (NCC) progenitors, then incorporated into a cytocompatible gelatin methacryloyl-based bioink for 3D bioprinting. Upregulated NGN2 expression in the bioprinted NCCs resulted in induced SN (iSN) populations that exhibited specific cell markers, with 3D analysis revealing widespread neurite outgrowth through the scaffold volume. Calcium imaging demonstrated functional activity of iSNs, including membrane excitability properties and voltage-gated sodium channel (NaV) activity. This efficient approach to generate 3D bioprinted iSN structures streamlines the development of neural tissue models, useful for the study of neurodevelopment and disease states and offering translational potential.

Three-dimensional printed exoskeletons and orthoses for the upper limb-A systematic review

This systematic review aims to assess and summarize the current landscape in exoskeletons and orthotic solutions developed for upper limb medical assistance, which are partly or fully produced using 3-dimensional printing technologies and contain at least the elbow or the shoulder joints. The initial search was conducted on Web of Science, PubMed, and IEEEXplore, resulting in 92 papers, which were reduced to 72 after removal of duplicates. From the application of the inclusion and exclusion criteria and selection questionnaire, 33 papers were included in the review, being divided according to the analyzed joints. The analysis of the selected papers allowed for the identification of different solutions that vary in terms of their target application, actuation type, 3-dimensional printing techniques, and material selection, among others. The results show that there has been far more research on the elbow joint than on the shoulder joint, which can be explained by the relative complexity of the latter. Moreover, the findings of this study also indicate that there is still a gap between the research conducted on these devices and their practical use in real-world conditions. Based on current trends, it is anticipated that the future of 3-dimensional printed exoskeletons will revolve around the use of flexible and high-performance materials, coupled with actuated devices. These advances have the potential to replace the conventional fabrication methods of exoskeletons with technologies based on additive manufacturing.

3D printing metal implants in orthopedic surgery: Methods, applications and future prospects

Background

Currently, metal implants are widely used in orthopedic surgeries, including fracture fixation, spinal fusion, joint replacement, and bone tumor defect repair. However, conventional implants are difficult to be customized according to the recipient's skeletal anatomy and defect characteristics, leading to difficulties in meeting the individual needs of patients. Additive manufacturing (AM) or three-dimensional (3D) printing technology, an advanced digital fabrication technique capable of producing components with complex and precise structures, offers opportunities for personalization.

Methods

We systematically reviewed the literature on 3D printing orthopedic metal implants over the past 10 years. Relevant animal, cellular, and clinical studies were searched in PubMed and Web of Science. In this paper, we introduce the 3D printing method and the characteristics of biometals and summarize the properties of 3D printing metal implants and their clinical applications in orthopedic surgery. On this basis, we discuss potential possibilities for further generalization and improvement.

Results

3D printing technology has facilitated the use of metal implants in different orthopedic procedures. By combining medical images from techniques such as CT and MRI, 3D printing technology allows the precise fabrication of complex metal implants based on the anatomy of the injured tissue. Such patient-specific implants not only reduce excessive mechanical strength and eliminate stress-shielding effects, but also improve biocompatibility and functionality, increase cell and nutrient permeability, and promote angiogenesis and bone growth. In addition, 3D printing technology has the advantages of low cost, fast manufacturing cycles, and high reproducibility, which can shorten patients' surgery and hospitalization time. Many clinical trials have been conducted using customized implants. However, the use of modeling software, the operation of printing equipment, the high demand for metal implant materials, and the lack of guidance from relevant laws and regulations have limited its further application.

Conclusions

There are advantages of 3D printing metal implants in orthopedic applications such as personalization, promotion of osseointegration, short production cycle, and high material utilization. With the continuous learning of modeling software by surgeons, the improvement of 3D printing technology, the development of metal materials that better meet clinical needs, and the improvement of laws and regulations, 3D printing metal implants can be applied to more orthopedic surgeries.

The translational potential of this paper

Precision, intelligence, and personalization are the future direction of orthopedics. It is reasonable to believe that 3D printing technology will be more deeply integrated with artificial intelligence, 4D printing, and big data to play a greater role in orthopedic metal implants and eventually become an important part of the digital economy. We aim to summarize the latest developments in 3D printing metal implants for engineers and surgeons to design implants that more closely mimic the morphology and function of native bone.

3D Printing as a Technological Strategy for the Personalized Treatment of Wound Healing

Wound healing is a dynamic process which involves stages of hemostasis, inflammation, proliferation and remodeling. Any error in this process results in abnormal wound healing, generating financial burdens for health systems and even affecting the physical and mental health of the patient. Traditional dressings do not meet the complexities of ideal treatment in all types of wounds. For this reason, in the last decades, different materials for drug delivery and for the treatment of wounds have been proposed reaching novel level of standards, such as 3D printing techniques. The use of natural or synthetic polymers, and the correct design of these printed products loaded with cells and/or combined with active compounds, can generate an effective system for the treatment of wounds, improving the healing process and generating customized dressings according to the patient needs. This manuscript provides a comprehensive review of different types of 3D printing techniques, as well as its use in wound healing and its different stages, including the advantages and limitations of additive manufacturing and future perspectives.

3D Printing Technologies in Personalized Medicine, Nanomedicines, and Biopharmaceuticals

3D printing technologies enable medicine customization adapted to patients' needs. There are several 3D printing techniques available, but majority of dosage forms and medical devices are printed using nozzle-based extrusion, laser-writing systems, and powder binder jetting. 3D printing has been demonstrated for a broad range of applications in development and targeting solid, semi-solid, and locally applied or implanted medicines. 3D-printed solid dosage forms allow the combination of one or more drugs within the same solid dosage form to improve patient compliance, facilitate deglutition, tailor the release profile, or fabricate new medicines for which no dosage form is available. Sustained-release 3D-printed implants, stents, and medical devices have been used mainly for joint replacement therapies, medical prostheses, and cardiovascular applications. Locally applied medicines, such as wound dressing, microneedles, and medicated contact lenses, have also been manufactured using 3D printing techniques. The challenge is to select the 3D printing technique most suitable for each application and the type of pharmaceutical ink that should be developed that possesses the required physicochemical and biological performance. The integration of biopharmaceuticals and nanotechnology-based drugs along with 3D printing ("nanoprinting") brings printed personalized nanomedicines within the most innovative perspectives for the coming years. Continuous manufacturing through the use of 3D-printed microfluidic chips facilitates their translation into clinical practice.

Autologous wound margin point columnar full‐thickness skin grafting combined with negative pressure wound therapy improves wound healing in refractory diabetic foot ulcers

Diabetic lower extremity ulcers (DLEUs) are a severe complication of diabetes mellitus (DM) and are difficult to heal. This study aimed to explore the efficacy of autologous point columnar full-thickness skin graft taken from the ulcer wound margin combined with negative pressure wound therapy (NPWT) in refractory DLEUs. This is a prospective cohort study. A total of 40 inpatients with refractory DLEUs were recruited in the Diabetes Foot Center of Guangxi Zhuang Autonomous Region People's Hospital from October 2019 to November 2021. According to the doctors' professional suggestions and the patients' personal wishes, these enrolled patients were divided into two groups based on different topical wound management: the graft group (n = 18) and the conventional wound therapeutic (CWT) group (n = 22). The efficacy evaluations included the time to complete re-epithelialization of the wound and healing speed within 14 days of graft treatment or after 14 days of graft treatment in the two groups. Before the treatment, the graft group had a significantly larger ulcer area than the CWT group [27.22 (15.28, 46.59) versus 10.92 (7.00, 24.93) cm² , P < .01]. However, the time to complete wound re-epithelialization in the graft group was shorter than in the CWT group [58.22 ± 30.60 versus 86.09 ± 49.54 d, P < .05]. Meanwhile, the healing speed in graft group was markedly faster than in CWT group, whether within 14 days [0.60 (0.40, 0.92) versus 0.16 (0.07, 0.34) cm² /d, P < .01] or after 14 days of graft treatment [0.57 (0.45, 0.91) versus 0.13 (0.08, 0.27) cm² /d, P < .01]. However, the total treatment cost in the graft group was lower than in the CWT group [419.59 ± 137.20 versus 663.97 ± 497.02 $, P < .05]. The novel treatment modality of autologous full-thickness skin graft taken from the ulcer wound margin combined with NPWT has hereby proposed for the first time, and is a safe, effective, and reliable method with a good performance-to-cost ratio to promote wound healing and shorten the healing time for DLEUs.

Development of bioactive catechol functionalized nanoparticles applicable for 3D bioprinting

Efficient wound treatments to target specific events in the healing process of chronic wounds constitute a significant aim in regenerative medicine. In this sense, nanomedicine can offer new opportunities to improve the effectiveness of existing wound therapies. The aim of this study was to develop catechol bearing polymeric nanoparticles (NPs) and to evaluate their potential in the field of wound healing. Thus, NPs wound healing promoting activities, potential for drug encapsulation and controlled release, and further incorporation in a hydrogel bioink formulation to fabricate cell-laden 3D scaffolds are studied. NPs with 2 and 29 M % catechol contents (named NP2 and NP29) were obtained by nanoprecipitation and presented hydrodynamic diameters of 100 and 75 nm respectively. These nanocarriers encapsulated the hydrophobic compound coumarin-6 with 70% encapsulation efficiency values. In cell culture studies, the NPs had a protective effect in RAW 264.7 macrophages against oxidative stress damage induced by radical oxygen species (ROS). They also presented a regulatory effect on the inflammatory response of stimulated macrophages and promoted upregulation of the vascular endothelial growth factor (VEGF) in fibroblasts and endothelial cells. In particular, NP29 were used in a hydrogel bioink formulation using carboxymethyl chitosan and hyaluronic acid as polymeric matrices. Using a reactive mixing bioprinting approach, NP-loaded hydrogel scaffolds with good structural integrity, shape fidelity and homogeneous NPs dispersion, were obtained. The in vitro catechol NPs release profile of the printed scaffolds revealed a sustained delivery. The bioprinted scaffolds supported viability and proliferation of encapsulated L929 fibroblasts over 14 days. We envision that the catechol functionalized NPs and resulting bioactive bioink presented in this work offer promising advantages for wound healing applications, as they: 1) support controlled release of bioactive catechol NPs to the wound site; 2) can incorporate additional therapeutic functions by co-encapsulating drugs; 3) can be printed into 3D scaffolds with tailored geometries based on patient requirements.

3D bioprinting: current status and trends—a guide to the literature and industrial practice

The multidisciplinary research field of bioprinting combines additive manufacturing, biology and material sciences to create bioconstructs with three-dimensional architectures mimicking natural living tissues. The high interest in the possibility of reproducing biological tissues and organs is further boosted by the ever-increasing need for personalized medicine, thus allowing bioprinting to establish itself in the field of biomedical research, and attracting extensive research efforts from companies, universities, and research institutes alike. In this context, this paper proposes a scientometric analysis and critical review of the current literature and the industrial landscape of bioprinting to provide a clear overview of its fast-changing and complex position. The scientific literature and patenting results for 2000–2020 are reviewed and critically analyzed by retrieving 9314 scientific papers and 309 international patents in order to draw a picture of the scientific and industrial landscape in terms of top research countries, institutions, journals, authors and topics, and identifying the technology hubs worldwide. This review paper thus offers a guide to researchers interested in this field or to those who simply want to understand the emerging trends in additive manufacturing and 3D bioprinting.

Graphic abstract

3D-Printed Products for Topical Skin Applications: From Personalized Dressings to Drug Delivery

3D printing has been widely used for the personalization of therapies and on-demand production of complex pharmaceutical forms. Recently, 3D printing has been explored as a tool for the development of topical dosage forms and wound dressings. Thus, this review aims to present advances related to the use of 3D printing for the development of pharmaceutical and biomedical products for topical skin applications, covering plain dressing and products for the delivery of active ingredients to the skin. Based on the data acquired, the important growth in the number of publications over the last years confirms its interest. The semisolid extrusion technique has been the most reported one, probably because it allows the use of a broad range of polymers, creating the most diverse therapeutic approaches. 3D printing has been an excellent field for customizing dressings, according to individual needs. Studies discussed here imply the use of metals, nanoparticles, drugs, natural compounds and proteins and peptides for the treatment of wound healing, acne, pain relief, and anti-wrinkle, among others. The confluence of 3D printing and topical applications has undeniable advantages, and we would like to encourage the research groups to explore this field to improve the patient's life quality, adherence and treatment efficacy.

Smart and Biomimetic 3D and 4D Printed Composite Hydrogels: Opportunities for Different Biomedical Applications

In recent years, smart/stimuli-responsive hydrogels have drawn tremendous attention for their varied applications, mainly in the biomedical field. These hydrogels are derived from different natural and synthetic polymers but are also composite with various organic and nano-organic fillers. The basic functions of smart hydrogels rely on their ability to change behavior; functions include mechanical, swelling, shaping, hydrophilicity, and bioactivity in response to external stimuli such as temperature, pH, magnetic field, electromagnetic radiation, and biological molecules. Depending on the final applications, smart hydrogels can be processed in different geometries and modalities to meet the complicated situations in biological media, namely, injectable hydrogels (following the sol-gel transition), colloidal nano and microgels, and three dimensional (3D) printed gel constructs. In recent decades smart hydrogels have opened a new horizon for scientists to fabricate biomimetic customized biomaterials for tissue engineering, cancer therapy, wound dressing, soft robotic actuators, and controlled release of bioactive substances/drugs. Remarkably, 4D bioprinting, a newly emerged technology/concept, aims to rationally design 3D patterned biological matrices from synthesized hydrogel-based inks with the ability to change structure under stimuli. This technology has enlarged the applicability of engineered smart hydrogels and hydrogel composites in biomedical fields. This paper aims to review stimuli-responsive hydrogels according to the kinds of external changes and t recent applications in biomedical and 4D bioprinting.

Therapeutic Efficacy of Artificial Skin Produced by 3D Bioprinting

The skin protects the body from external barriers. Certain limitations exist in the development of technologies to rapidly prepare skin substitutes that are therapeutically effective in surgeries involving extensive burns and skin transplantation. Herein, we fabricated a structure similar to the skin layer by using skin-derived decellularized extracellular matrix (dECM) with bioink, keratinocytes, and fibroblasts using 3D-printing technology. The therapeutic effects of the produced skin were analyzed using a chimney model that mimicked the human wound-healing process. The 3D-printed skin substitutes exhibited rapid re-epithelialization and superior tissue regeneration effects compared to the control group. These results are expected to aid the development of technologies that can provide customized skin-replacement tissues produced easily and quickly via 3D-printing technology to patients.

Development and Evaluation of a Human Skin Equivalent in a Semiautomatic Microfluidic Diffusion Chamber

There is an increasing demand for transdermal transport measurements to optimize topical drug formulations and to achieve proper penetration profile of cosmetic ingredients. Reflecting ethical concerns the use of both human and animal tissues is becoming more restricted. Therefore, the focus of dermal research is shifting towards in vitro assays. In the current proof-of-concept study a three-layer skin equivalent using human HaCaT keratinocytes, an electrospun polycaprolactone mesh and a collagen-I gel was compared to human excised skin samples. We measured the permeability of the samples for 2% caffeine cream using a miniaturized dynamic diffusion cell (“skin-on-a-chip” microfluidic device). Caffeine delivery exhibits similar transport kinetics through the artificial skin and the human tissue: after a rapid rise, a long-lasting high concentration steady state develops. This is markedly distinct from the kinetics measured when using cell-free constructs, where a shorter release was observable. These results imply that both the established skin equivalent and the microfluidic diffusion chamber can serve as a suitable base for further development of more complex tissue substitutes.

Recent Advances in 3D Printing for Parenteral Applications

3D printing has emerged as an advanced manufacturing technology in the field of pharmaceutical sciences. Despite much focus on enteral applications, there has been a lack of research focused on potential benefits of 3D printing for parenteral applications such as wound dressings, biomedical devices, and regenerative medicines. 3D printing technologies, including fused deposition modeling, vat polymerization, and powder bed printing, allow for rapid prototyping of personalized medications, capable of producing dosage forms with flexible dimensions based on patient anatomy as well as dosage form properties such as porosity. Considerations such as printing properties and material selection play a key role in determining overall printability of the constructs. These parameters also impact drug release kinetics, and mechanical properties of final printed constructs, which play a role in modulating immune response upon insertion in the body. Despite challenges in sterilization of printed constructs, additional post-printing processing procedures, and lack of regulatory guidance, 3D printing will continue to evolve to meet the needs of developing effective, personalized medicines for parenteral applications.

Recent Advances in the Design of Three-Dimensional and Bioprinted Scaffolds for Full-Thickness Wound Healing

Three-dimensional (3D) printed scaffolds have recently emerged as an innovative treatment option for patients with critical-sized skin wounds. Current approaches to managing life-threatening wounds include skin grafting and application of commercially sourced skin substitutes. However, these approaches are not without several challenges. Limited donor tissue and donor site morbidity remain a concern for tissue grafting, while engineered skin substitutes fail to fully recapitulate the complex native environment required for wound healing. The implementation of 3D printed dermal scaffolds offers a potential solution for these shortcomings. Spatial control over scaffold structure, the ability to incorporate multiple materials and bioactive ingredients, enables the creation of conditions specifically optimized for wound healing. Three-dimensional bioprinting, a subset of 3D printing, allows for the replacement of lost cell populations and secreted active compounds that contribute to tissue repair and recovery. The replacement of damaged and lost cells delivers beneficial effects directly, or synergistically, supporting injured tissue to recover its native state. Despite encouraging results, the promise of 3D printed scaffolds has yet to be realized. Further improvements to current material formulations and scaffold designs are required to achieve the goal of clinical adoption. Herein, we provide an overview of 3D printing techniques and discuss several strategies for healing of full-thickness wounds by using 3D printed acellular scaffolds or bioprinted cellular scaffolds, aimed at translating this technology to the clinical management of skin lesions. We identify the challenges associated with designing and optimizing printed tissue replacements, and discuss the future perspectives of this emerging option for managing patients who present with critical-sized life-threatening cutaneous wounds.

3D Propolis-Sodium Alginate Scaffolds: Influence on Structural Parameters, Release Mechanisms, Cell Cytotoxicity and Antibacterial Activity

In this study, the main aim was to fabricate propolis (Ps)-containing wound dressing patches using 3D printing technology. Different combinations and structures of propolis (Ps)-incorporated sodium alginate (SA) scaffolds were developed. The morphological studies showed that the porosity of developed scaffolds was optimized when 20% (v/v) of Ps was added to the solution. The pore sizes decreased by increasing Ps concentration up to a certain level due to its adhesive properties. The mechanical, swelling-degradation (weight loss) behaviors, and Ps release kinetics were highlighted for the scaffold stability. An antimicrobial assay was employed to test and screen antimicrobial behavior of Ps against Escherichia coli and Staphylococcus aureus strains. The results show that the Ps-added scaffolds have an excellent antibacterial activity because of Ps compounds. An in vitro cytotoxicity test was also applied on the scaffold by using the extract method on the human dermal fibroblasts (HFFF2) cell line. The 3D-printed SA–Ps scaffolds are very useful structures for wound dressing applications.

Application of 3D Bioprinting Technologies to the Management and Treatment of Diabetic Foot Ulcers

Diabetes mellitus (DM) is a chronic metabolic disease with increasing prevalence worldwide. Diabetic foot ulcers (DFUs) are a serious complication of DM. It is estimated that 15-25% of DM patients develop DFU at least once in their lifetime. The lack of effective wound dressings and targeted therapy for DFUs often results in prolonged hospitalization and amputations. As the incidence of DM is projected to rise, the demand for specialized DFU wound management will continue to increase. Hence, it is of great interest to improve and develop effective DFU-specific wound dressings and therapies. In the last decade, 3D bioprinting technology has made a great contribution to the healthcare sector, with the development of personalized prosthetics, implants, and bioengineered tissues. In this review, we discuss the challenges faced in DFU wound management and how 3D bioprinting technology can be applied to advance current treatment methods, such as biomanufacturing of composite 3D human skin substitutes for skin grafting and the development of DFU-appropriate wound dressings. Future co-development of 3D bioprinting technologies with novel treatment approaches to mitigate DFU-specific pathophysiological challenges will be key to limiting the healthcare burden associated with the increasing prevalence of DM.

Thread Size and Polymer Composition of 3D Printed and Electrospun Wound Dressings Affect Wound Healing Outcomes in an Excisional Wound Rat Model

Thread size and polymer composition are critical properties to consider for achieving a positive healing outcome with a wound dressing. Three-dimensional (3D) printed scaffolds and electrospun mats both offer distinct advantages as replaceable wound dressings. This research aims to determine if the thread size and polymer compositions of the scaffolds affect skin wound healing outcomes, an aspect that has not been adequately explored. Using a modular polymer platform, four polyester direct-write 3D printed scaffolds and electrospun mats were fabricated into wound dressings. The dressings were applied to splinted, full thickness skin wounds in an excisional wound rat model and evaluated against control wounds to which no dressing was applied. Wound closure rates and reduction of the wound bed width were not affected by the thread size or polymer composition. However, epidermal thickness was larger in wounds treated with electrospun dressings and was slightly affected by the polymer composition. Two of the four tested polymer compositions lead to delayed reorganization of granulation tissues. Moreover, enhanced angiogenesis was seen in wounds treated with 3D printed dressings compared to those treated with electrospun dressings. The results from this study can be used to inform the choice of dressing architecture and polymer compositions to achieve positive wound healing outcomes.

Lidocaine-Loaded Solid Lipid Microparticles (SLMPs) Produced from Gas-Saturated Solutions for Wound Applications

The delivery of bioactive agents using active wound dressings for the management of pain and infections offers improved performances in the treatment of wound complications. In this work, solid lipid microparticles (SLMPs) loaded with lidocaine hydrochloride (LID) were processed and the formulation was evaluated regarding its ability to deliver the drug at the wound site and through the skin barrier. The SLMPs of glyceryl monostearate (GMS) were prepared with different LID contents (0, 1, 2, 4, and 10 wt.%) using the solvent-free and one-step PGSS (Particles from Gas-Saturated Solutions) technique. PGSS exploits the use of supercritical CO2 (scCO2) as a plasticizer for lipids and as pressurizing agent for the atomization of particles. The SLMPs were characterized in terms of shape, size, and morphology (SEM), physicochemical properties (ATR-IR, XRD), and drug content and release behavior. An in vitro test for the evaluation of the influence of the wound environment on the LID release rate from SLMPs was studied using different bioengineered human skin substitutes obtained by 3D-bioprinting. Finally, the antimicrobial activity of the SLMPs was evaluated against three relevant bacteria in wound infections (Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa). SLMPs processed with 10 wt.% of LID showed a remarkable performance to provide effective doses for pain relief and preventive infection effects.

Recent Trends in Three-Dimensional Bioinks Based on Alginate for Biomedical Applications

Three-dimensional (3D) bioprinting is an appealing and revolutionary manufacturing approach for the accurate placement of biologics, such as living cells and extracellular matrix (ECM) components, in the form of a 3D hierarchical structure to fabricate synthetic multicellular tissues. Many synthetic and natural polymers are applied as cell printing bioinks. One of them, alginate (Alg), is an inexpensive biomaterial that is among the most examined hydrogel materials intended for vascular, cartilage, and bone tissue printing. It has also been studied pertaining to the liver, kidney, and skin, due to its excellent cell response and flexible gelation preparation through divalent ions including calcium. Nevertheless, Alg hydrogels possess certain negative aspects, including weak mechanical characteristics, poor printability, poor structural stability, and poor cell attachment, which may restrict its usage along with the 3D printing approach to prepare artificial tissue. In this review paper, we prepare the accessible materials to be able to encourage and boost new Alg-based bioink formulations with superior characteristics for upcoming purposes in drug delivery systems. Moreover, the major outcomes are discussed, and the outstanding concerns regarding this area and the scope for upcoming examination are outlined.

Laser-Induced Forward Transfer: A Method for Printing Functional Inks

Laser-induced forward transfer (LIFT) is a direct-writing technique based in the action of a laser to print a small fraction of material from a thin donor layer onto a receiving substrate. Solid donor films have been used since its origins, but the same principle of operation works for ink liquid films, too. LIFT is a nozzle-free printing technique that has almost no restrictions in the particle size and the viscosity of the ink to be printed. Thus, LIFT is a versatile technique capable for printing any functional material with which an ink can be formulated. Although its principle of operation is valid for solid and liquid layers, in this review we put the focus in the LIFT works performed with inks or liquid suspensions. The main elements of a LIFT experimental setup are described before explaining the mechanisms of ink ejection. Then, the printing outcomes are related with the ejection mechanisms and the parameters that control their characteristics. Finally, the main achievements of the technique for printing biomolecules, cells, and materials for printed electronic applications are presented.

[Current concepts and new developments of 3D printing in trauma surgery]

The use of 3D printing (synonyms "rapid prototyping" and "additive manufacturing") has played an increasing role in the industry for many years and finds more and more interest and application in musculoskeletal surgery, especially orthopedic trauma surgery.In this article the current literature is systematically reviewed, presented and evaluated in a condensed and comprehensive way according to anatomical (upper and lower extremities) and functional aspects. As many of the publications analyzed were feasibility studies, the degree of evidence is low and methodological weaknesses are obvious and numerous; however, this pioneering work is extremely stimulating and important for further development because the technical, medical and economic potential of this technology is huge and interesting for all those involved in the treatment of musculoskeletal problems.

Biofabrication of thick vascularized neo-pedicle flaps for reconstructive surgery

Wound chronicity due to intrinsic and extrinsic factors perturbs adequate lesion closure and reestablishment of the protective skin barrier. Immediate and proper care of chronic wounds is necessary for a swift recovery and a reduction of patient vulnerability to infection. Advanced therapies supplemented with standard wound care procedures have been clinically implemented to restore aberrant tissue; however, these treatments are ineffective if local vasculature is too compromised to support minimally-invasive strategies. Autologous "flaps", which are tissues equipped with their own hierarchical vascular supply, can be harvested from one region of the patient and transplanted to the wound where it is reperfused upon microsurgical anastomosis to appropriate recipient vessels. Despite the success of autologous flap transfer, these procedures are extremely invasive, incur obligatory donor-site morbidity, and require sufficient donor-tissue availability, microsurgical expertise, and specialized equipment. 3D-bioprinting modalities, such as extrusion-based bioprinting, can be used to address the clinical constraints of autologous flap transfer, primarily addressing donor-site morbidity and tissue availability. This advancement in regenerative medicine allows the biofabrication of heterogeneous tissue structures with high shape fidelity and spatial resolution to generate biomimetic constructs with the anatomically-precise geometries of native tissue to ensure tissue-specific function. Yet, meaningful progress toward this clinical application has been limited by the lack of vascularization required to meet the nutrient and oxygen demands of clinically relevant tissue volumes. Thus, various criteria for the fabrication of functional tissues with hierarchical, patent vasculature must be considered when implementing 3D-bioprinting technologies for deep, chronic wounds.

Quantitative ultrasound imaging of cell-laden hydrogels and printed constructs

In the present work we have revisited the application of quantitative ultrasound imaging (QUI) to cellular hydrogels, by using the reference phantom method (RPM) in combination with a local attenuation compensation algorithm. The investigated biological samples consisted of cell-laden collagen hydrogels with PC12 neural cells. These cell-laden hydrogels were used to calibrate the integrated backscattering coefficient (IBC) as a function of cell density, which was then used to generate parametric images of local cell density. The image resolution used for QUI and its impact on the relative IBC error was also investigated. Another important contribution of our work was the monitoring of PC12 cell proliferation. The cell number estimates obtained via the calibrated IBC compared well with data obtained using a conventional quantitative method, the MTS assay. Evaluation of spectral changes as a function of culture time also provided additional information on the cell cluster size, which was found to be in close agreement with that observed by microscopy. Last but not least, we also applied QUI on a 3D printed cellular construct in order to illustrate its capabilities for the evaluation of bioprinted structures. STATEMENT OF SIGNIFICANCE: While there is intensive research in the areas of polymer science, biology, and 3D bio-printing, there exists a gap in available characterisation tools for the non-destructive inspection of biological constructs in the three-dimensional domain, on the macroscopic scale, and with fast data acquisition times. Quantitative ultrasound imaging is a suitable characterization technique for providing essential information on the development of tissue engineered constructs. These results provide a detailed and comprehensive guide on the capabilities and limitations of the technique.

Sulfated polysaccharide-based scaffolds for orthopaedic tissue engineering

Given their native-like biological properties, high growth factor retention capacity and porous nature, sulfated-polysaccharide-based scaffolds hold great promise for a number of tissue engineering applications. Specifically, as they mimic important properties of tissues such as bone and cartilage they are ideal for orthopaedic tissue engineering. Their biomimicry properties encompass important cell-binding motifs, native-like mechanical properties, designated sites for bone mineralisation and strong growth factor binding and signaling capacity. Even so, scientists in the field have just recently begun to utilise them as building blocks for tissue engineering scaffolds. Most of these efforts have so far been directed towards in vitro studies, and for these reasons the clinical gap is still substantial. With this review paper, we have tried to highlight some of the important chemical, physical and biological features of sulfated-polysaccharides in relation to their chondrogenic and osteogenic inducing capacity. Additionally, their usage in various in vivo model systems is discussed. The clinical studies reviewed herein paint a promising picture heralding a brave new world for orthopaedic tissue engineering.

Development and use of biomaterials as wound healing therapies

There is a vast number of treatments on the market for the management of wounds and burns, representing a multi-billion dollar industry worldwide. These include conventional wound dressings, dressings that incorporate growth factors to stimulate and facilitate the wound healing process, and skin substitutes that incorporate patient-derived cells. This article will review the more established, and the recent advances in the use of biomaterials for wound healing therapies, and their future direction.

The inevitability of change

Change is an absolute so long as time does not stand still. We should expect it, embrace it, and try to predict its direction. Dermatology, as a specialty practice, has been changing rapidly over the past 30 years concurrent with the changes in medicine. What are these changes, how did they come about, and what may be the consequences? The goal of this review is to follow the march of time, as we move from one era to the other in step with what is happening in the world as a whole and the United States in particular. The growth of our specialty, Dermatology, is divided into 3 eras which are quite different in generational cultures. The first era spanning the 1980s and 1990s is dubbed as "old school." The second era begins with the new century, 2000 until today. This era will forever be remembered as the business era, the rise of elite cultures, and the losses and threats to academia. The third era begins now; it is that of technology which is fast progressing into the future. One can theoretically project what may occur during this technologic revolution and the directions in medicine as a whole. Dermatology can be at the forefront of this era or it could be lost as a whole if we do nothing to keep up. These eras are based on my personal experience as a dermatologist in a large academic institution in the United States and may not apply to other communities or societies elsewhere. The United States serves as a good example of a western technologically oriented society that is often emulated by others.

3D printing and its applications in orthopaedic trauma: A technological marvel

BACKGROUND

With rapid emergence of 3D printing technology, surgeons have recently started to apply this for nearly all areas of orthopaedic trauma surgery. Computed tomography or magnetic resonance images of trauma patients can be utilized for making graspable objects from 3D reconstructed images. Patient specific anatomical models can thereby be created. They enhance surgeon's knowledge of their patients' precise patho-anatomy, regarding both traumatized bones and soft tissue as well as normal areas, and therefore help in accurate preoperative planning. 3D printed patient specific instrumentation can help to achieve precise implant placement, and better surgical results. Most importantly, customized implants, casts, orthoses and prosthetics can be manufactured to match an individual's anatomy. Three dimensional (3D) printing, also called as 'additive manufacturing' and 'rapid prototyping' is considered as the "second industrial revolution", and this appears to be especially true for orthopaedic trauma surgery.

METHODS

A literature search was performed for extracting all papers related to 3D Printing applications in orthopaedics and allied sciences on the Pubmed, and SCOPUS; using suitable key terms and Boolean operators ("3D Printing" OR "3 dimensional printing" OR "3D printed" OR "additive manufacturing" OR "rapid prototyping") AND (''Orthopaedics" OR "Orthopaedics'') AND ("Trauma" OR "Injury")in June 2018. Search was also performed in Web of Science, Cochrane Central Register of Controlled Trials and Cochrane Database of Systematic Reviews. No limits were set on the time period or evidence level, as 3D printing in orthopaedics is relatively recent and mainly low level evidence is available. Titles and abstracts were screened and all duplicate and unrelated papers were excluded. Papers related to orthopaedic trauma were manually selected for this review.

RESULTS

The search on Pubmed retrieved 144 Papers and similar search on SCOPUS retrieved 94 papers. Additional searches did not reveal more relevant papers. After excluding duplicates and unrelated papers, and on screening of titles and abstracts, 59 papers were considered for review. Papers related to spine fractures only were not included, as they have been covered in another paper in this journal issue.

CONCLUSION

All over the world, orthopaedic Surgeon's and allied professionals and scientists are enthusiastically using 3D printing technology for designing patient specific models, instrumentation, implants, orthosis and prosthesis, besides 3D bioprinting of bone and cartilage scaffolding, and the same has been applied for nearly all areas of orthopaedic trauma surgery, from head to foot.