Bioresorbable airway splint created with a three-dimensional printer

Tissue engineering

Ultimately much work remains to be done in the companion fields of biomaterials and stem cells. Nonetheless, the monumental progress in TE that has been reported in the studies summarized here demonstrates that regenerative approaches to problems in general surgery need to be explored in more depth. Furthermore, the surgical disciplines of reconstruction and transplantation need to recognize their research counterparts in TE, given its potential to actualize freedom from immunosuppression, one of the most elusive goals in modern surgery. The engineering and proliferation of autologous cells, tissues, and organs ex vivo before surgical operation can significantly reduce the obstacles current practitioners are intimately familiar with: donor site morbidity and immunologic rejection. Therefore, in addition to the truly exciting research and development prospects and implications for the commercial sector, patients with end-stage diseases and debilitating injury stand to gain the most from clinically adapted TE therapies.

Tissue engineering and regenerative medicine: a year in review

It is an exciting time to be involved in tissue engineering and regenerative medicine (TERM) research. Despite its relative youth, the field is expanding fast and breaking new ground in both the laboratory and clinically. In this "Year in Review," we highlight some of the high-impact advances in the field. Building upon last year's article, we have identified the recent "hot topics" and the key publications pertaining to these themes as well as ideas that have high potential to direct the field. Based on a modified methodology grounded on last year's approach, we have identified and summarized some of the most impactful publications in five main themes: (1) pluripotent stem cells: efforts and hurdles to translation, (2) tissue engineering: complex scaffolds and advanced materials, (3) directing the cell phenotype: growth factor and biomolecule presentation, (4) characterization: imaging and beyond, and (5) translation: preclinical to clinical. We have complemented our review of the research directions highlighted within these trend-setting studies with a discussion of additional articles along the same themes that have recently been published and have yet to surface in citation analyses. We conclude with a discussion of some really interesting studies that provide a glimpse of the high potential for innovation of TERM research.

Tracheomalacia is associated with lower FEV1 and Pseudomonas acquisition in children with CF

BACKGROUND

Tracheomalacia (TM) occurs in approximately 1 in 2,100 children. Because the trachea develops abnormally in animal models of cystic fibrosis (CF), we hypothesized this may also occur in children with CF, increasing their risk of TM.

PURPOSE

To examine the prevalence and clinical consequences of TM in children with CF.

METHODS

We studied children with CF born between 1995 and 2012. TM was defined as dynamic collapse of the trachea, and the severity was recorded as described in the chart. The effect of TM on patient outcomes, including FEV1 , CT changes, and acquisition of CF pathogens, was assessed using a longitudinal patient dataset.

RESULTS

Eighty-nine percent of children with CF had at least one bronchoscopy (n = 97/109). Fifteen percent of these children had TM described in any bronchoscopy report (n = 15/97). Of the patients with TM, eight had meconium ileus (P = 0.003) and all were pancreatic insufficient. Pseudomonas aeruginosa infection occurred 1.3 years earlier among children with TM (P = 0.01). Starting FEV1 values by age 8 were diminished by over 18% of predicted for patients with TM. Life-threatening episodes of airway obstruction occurred in 3 of 15 patients with CF and TM, including one leading to death. Gender, prematurity, and hepatic disease were not associated with TM. No difference was observed in the frequency of bronchiectasis.

CONCLUSIONS

TM is significantly more common in infants and children with CF than in the general population and is associated with airway obstruction and earlier Pseudomonas acquisition.

Airway tissue engineering: an update

INTRODUCTION

Prosthetic materials, autologous tissues, cryopreserved homografts and allogeneic tissues have thus far proven unsuccessful in providing long-term functional solutions to extensive upper airway disease and damage. Research is therefore focusing on the rapidly expanding fields of regenerative medicine and tissue engineering in order to provide stem cell-based constructs for airway reconstruction, substitution and/or regeneration.

AREAS COVERED

Advances in stem cell technology, biomaterials and growth factor interactions have been instrumental in guiding optimization of tissue-engineered airways, leading to several first-in-man studies investigating stem cell-based tissue-engineered tracheal transplants in patients. Here, we summarize current progress, outstanding research questions, as well as future directions within the field.

EXPERT OPINION

The complex immune interaction between the transplant and host in vivo is only beginning to be untangled. Recent progress in our understanding of stem cell biology, decellularization techniques, biomaterials and transplantation immunobiology offers the prospect of transplanting airways without the need for lifelong immunosuppression. In addition, progress in airway revascularization, reinnervation and ever-increasingly sophisticated bioreactor design is opening up new avenues for the construction of a tissue-engineered larynx. Finally, 3D printing is a novel technique with the potential to render microscopic control over how cells are incorporated and grown onto the tissue-engineered airway.

Utilizing Three-Dimensional Printing Technology to Assess the Feasibility of High-Fidelity Synthetic Ventricular Septal Defect Models for Simulation in Medical Education

Background:

The current educational approach for teaching congenital heart disease (CHD) anatomy to students involves instructional tools and techniques that have significant limitations. This study sought to assess the feasibility of utilizing present-day three-dimensional (3D) printing technology to create high-fidelity synthetic heart models with ventricular septal defect (VSD) lesions and applying these models to a novel, simulation-based educational curriculum for premedical and medical students.

Methods:

Archived, de-identified magnetic resonance images of five common VSD subtypes were obtained. These cardiac images were then segmented and built into 3D computer-aided design models using Mimics Innovation Suite software. An Objet500 Connex 3D printer was subsequently utilized to print a high-fidelity heart model for each VSD subtype. Next, a simulation-based educational curriculum using these heart models was developed and implemented in the instruction of 29 premedical and medical students. Assessment of this curriculum was undertaken with Likert-type questionnaires.

Results:

High-fidelity VSD models were successfully created utilizing magnetic resonance imaging data and 3D printing. Following instruction with these high-fidelity models, all students reported significant improvement in knowledge acquisition ( P < .0001), knowledge reporting ( P < .0001), and structural conceptualization ( P < .0001) of VSDs.

Conclusions:

It is feasible to use present-day 3D printing technology to create high-fidelity heart models with complex intracardiac defects. Furthermore, this tool forms the foundation for an innovative, simulation-based educational approach to teach students about CHD and creates a novel opportunity to stimulate their interest in this field.

The billion cell construct: will three-dimensional printing get us there?

Effective utilization of three-dimensional printing for tissue and organ engineering remains nontrivial. Here, Jordan Miller identifies key challenges and discusses conceptual targets on the horizon.

How structure relates to function—across spatial scales, from the single molecule to the whole organism—is a central theme in biology. Bioengineers, however, wrestle with the converse question: will function follow form? That is, we struggle to approximate the architecture of living tissues experimentally, hoping that the structure we create will lead to the function we desire. A new means to explore the relationship between form and function in living tissue has arrived with three-dimensional printing, but the technology is not without limitations.

Experimental validation of 3D printed patient-specific implants using digital image correlation and finite element analysis

With the dawn of 3D printing technology, patient-specific implant designs are set to have a paradigm shift. A topology optimization method in designing patient-specific craniofacial implants has been developed to ensure adequate load transfer mechanism and restore the form and function of the mid-face. Patient-specific finite element models are used to design these implants and to validate whether they are viable for physiological loading such as mastication. Validation of these topology optimized finite element models using mechanical testing is a critical step. Instead of inserting the implants into a cadaver or patient, we embed the implants into the computer-aided skull model of a patient and, fuse them together to 3D print the complete skull model with the implant. Masticatory forces are applied in the molar region to simulate chewing and measure the stress-strain trajectory. Until recently, strain gages have been used to measure strains for validation. Digital Image Correlation (DIC) method is a relatively new technique for full-field strain measurement which provides a continuous deformation field data. The main objective of this study is to validate the finite element model of patient-specific craniofacial implants against the strain data from the DIC obtained during the mastication simulation and show that the optimized shapes provide adequate load-transfer mechanism. Patient-specific models are obtained from CT scans. The principal maximum and minimum strains are compared. The computational and experimental approach to designing patient-specific implants proved to be a viable technique for mid-face craniofacial reconstruction.

Three-dimensional printing of tissue phantoms for biophotonic imaging

We have investigated the potential of tissue phantoms fabricated with thermosoftening- and photopolymerization-based three-dimensional (3D) printers for use in evaluation of biophotonic imaging systems. The optical properties of printed polymer samples were measured and compared to biological tissues. Phantoms with subsurface channels as small as 0.2 mm in diameter were fabricated and imaged with microscopy, x-ray microtomography, and optical coherence tomography to characterize morphology. These phantoms were then implemented to evaluate the penetration depth of a hyperspectral reflectance imaging system used in conjunction with a near-infrared contrast agent. Results indicated that 3D printing may provide a suitable platform for performance testing in biophotonics, although subsurface imaging is critical to mitigate printer-to-printer variability in matrix homogeneity and feature microstructure.

Evolving marine biomimetics for regenerative dentistry

New products that help make human tissue and organ regeneration more effective are in high demand and include materials, structures and substrates that drive cell-to-tissue transformations, orchestrate anatomical assembly and tissue integration with biology. Marine organisms are exemplary bioresources that have extensive possibilities in supporting and facilitating development of human tissue substitutes. Such organisms represent a deep and diverse reserve of materials, substrates and structures that can facilitate tissue reconstruction within lab-based cultures. The reason is that they possess sophisticated structures, architectures and biomaterial designs that are still difficult to replicate using synthetic processes, so far. These products offer tantalizing pre-made options that are versatile, adaptable and have many functions for current tissue engineers seeking fresh solutions to the deficiencies in existing dental biomaterials, which lack the intrinsic elements of biofunctioning, structural and mechanical design to regenerate anatomically correct dental tissues both in the culture dish and in vivo.

Tissue-engineered tracheal reconstruction using three-dimensionally printed artificial tracheal graft: preliminary report

Three-dimensional printing has come into the spotlight in the realm of tissue engineering. We intended to evaluate the plausibility of 3D-printed (3DP) scaffold coated with mesenchymal stem cells (MSCs) seeded in fibrin for the repair of partial tracheal defects. MSCs from rabbit bone marrow were expanded and cultured. A half-pipe-shaped 3DP polycaprolactone scaffold was coated with the MSCs seeded in fibrin. The half-pipe tracheal graft was implanted on a 10 × 10-mm artificial tracheal defect in four rabbits. Four and eight weeks after the operation, the reconstructed sites were evaluated bronchoscopically, radiologically, histologically, and functionally. None of the four rabbits showed any sign of respiratory distress. Endoscopic examination and computed tomography showed successful reconstruction of trachea without any collapse or blockage. The replaced tracheas were completely covered with regenerated respiratory mucosa. Histologic analysis showed that the implanted 3DP tracheal grafts were successfully integrated with the adjacent trachea without disruption or granulation tissue formation. Neo-cartilage formation inside the implanted graft was sufficient to maintain the patency of the reconstructed trachea. Scanning electron microscope examination confirmed the regeneration of the cilia, and beating frequency of regenerated cilia was not different from those of the normal adjacent mucosa. The shape and function of reconstructed trachea using 3DP scaffold coated with MSCs seeded in fibrin were restored successfully without any graft rejection.

Treatment of severe porcine tracheomalacia with a 3-dimensionally printed, bioresorbable, external airway splint

IMPORTANCE

The study demonstrates use of a novel intervention for severe tracheobronchomalacia (TBM).

OBJECTIVE

To test a novel, 3-dimensionally (3D) printed, bioresorbable airway splint for efficacy in extending survival in a porcine model of severe, life-threatening TBM.

DESIGN AND PARTICIPANTS

A randomized, prospective animal trial was used to evaluate an external airway splint as treatment of severe, life-threatening TBM in a multi-institutional, multidisciplinary collaboration between a biomedical engineering department and an academic animal surgery center. Six 2-month-old Yorkshire pigs underwent tracheal cartilage division and inner tracheal lumen dissociation and were randomly assigned to splint treatment (n = 3) or control groups (n = 3). Two additional pigs had the splint placed over their normal trachea.

INTERVENTIONS

A 3D-printed, bioresorbable airway splint was assessed in a porcine animal model of life-threatening TBM. The open-cylindrical, bellow-shaped, porous polycaprolactone splint was placed externally and designed to suspend the underlying collapsed airway. Two additional animals were splinted without model creation.

MAIN OUTCOMES AND MEASURES

The observer-based Westley Clinical Croup Scale was used to assess the clinical condition of animals postoperatively. Animal survival time was noted.

RESULTS

Complete or nearly complete tracheal lumen collapse was observed in each animal, with resolution of symptoms in all of the experimental animals after splint placement. Using our severe TBM animal model, survival was significantly longer in the experimental group receiving the airway splint after model creation than in the control group (P = .0495).

CONCLUSIONS AND RELEVANCE

A multidisciplinary effort producing a computer-aided designed, computer-aided manufactured bioresorbable tracheobronchial splint was tested in a porcine model of severe TBM and was found to extend survival time. Mortality in the splinted group was ascribed to the TBM model based on the lack of respiratory distress in splinted pigs, long-term survival in animals implanted with the splint without TBM, and necropsy findings.

Endoscopic treatment of tracheal stenosis

For all cases of tracheal obstructions surgery should be considered first. Interventional endoscopic procedures can provide immediate relief. Intraluminally growing tumors can be resected with laser, argon-plasma coagulation, an electrosurgical knife or cryo-probe. Photodynamic therapy of smaller tracheal tumors can be curative. Narrowing from intramural tumor growth or wall destruction requires internal splinting with an airway stent. Scar strictures can be dilated with balloons but the biotrauma may stimulate new scarring. In benign strictures and malacias, tracheal stents should only be placed if all other methods are exhausted. Complications including stent migration, mucostasis, halitosis and granulation tissue development must be considered. Most important for a good outcome is a multidisciplinary approach.

Soft tissue engineering in craniomaxillofacial surgery

Craniofacial soft tissue reconstruction may be required following trauma, tumor resection, and to repair congenital deformities. Recent advances in the field of tissue engineering have significantly widened the reconstructive armamentarium of the surgeon. The successful identification and combination of tissue engineering, scaffold, progenitor cells, and physiologic signaling molecules has enabled the surgeon to design, recreate the missing tissue in its near natural form. This has resolved the issues like graft rejection, wound dehiscence, or poor vascularity. Successfully reconstructed tissue through soft tissue engineering protocols would help surgeon to restore the form and function of the lost tissue in its originality. This manuscript intends to provide a glimpse of the basic principle of tissue engineering, contemporary, and future direction of this field as applied to craniofacial surgery.

The chemistry of cyborgs--interfacing technical devices with organisms

The term "cyborg" refers to a cybernetic organism, which characterizes the chimera of a living organism and a machine. Owing to the widespread application of intracorporeal medical devices, cyborgs are no longer exclusively a subject of science fiction novels, but technically they already exist in our society. In this review, we briefly summarize the development of modern prosthetics and the evolution of brain-machine interfaces, and discuss the latest technical developments of implantable devices, in particular, biocompatible integrated electronics and microfluidics used for communication and control of living organisms. Recent examples of animal cyborgs and their relevance to fundamental and applied biomedical research and bioethics in this novel and exciting field at the crossroads of chemistry, biomedicine, and the engineering sciences are presented.