Extraluminal distraction enterogenesis using shape-memory polymer

Fabrication of Shape Memory Polymer Endovascular Thrombectomy Device for Treating Ischemic Stroke

Stroke is the second result for death and ischemic stroke constitutes most of all stroke cases. Ischemic stroke takes place when blood clot or embolus blocks cerebral vessel and interrupts blood flow, which often leads to brain damage, permanent disability, or death. There is a 4.5-h (golden hour) treatment window to restore blood flow prior to permanent neurological impairment results. Current stroke treatments consist mechanical system or thrombolytic drug therapy to disrupt or dissolve thrombus. Promising method for stroke treatment is mechanical retrieving of thrombi employing device deployed endovascularly. Advent of smart materials has led to research fabrication of several minimally invasive endovascular devices that take advantage of new materials capabilities. One of these capabilities is shape memory, is capability of material to store temporary form, then activate to primary shape as subjected to stimuli. Shape memory polymers (SMPs) are employed as good materials for thrombectomy device fabrication. Therefore, current review presents thrombectomy device development and fabrication with SMPs. Design, performance, limitations, and in vitro or in vivo clinical results of SMP-based thrombectomy devices are identified. Review also sheds light on SMP's future outlook and recommendations for thrombectomy device application, opening a new era for advanced materials in materials science.

Distraction Enterogenesis in Rats: A Novel Approach for the Treatment of Short Bowel Syndrome

BACKGROUND

Surgeons often encounter patients with intestinal failure due to inadequate intestinal length ("short bowel syndrome"/SBS). Treatment in these patients remains challenging and the process of physiologic adaptation may take years to complete, which frequently requires parenteral nutrition. We propose a proof-of-concept mechanical bowel elongation approach using a self-expanding prototype of an intestinal expansion sleeve (IES) for use in SBS to accelerate the adaptation process.

METHODS

IESs were deployed in the small intestines of Sprague Dawley rats. Mechanical characterization of these prototypes was performed. IES length-tension relationships and post-implant bowel expansion were measured ex vivo. Bowel histology before and after implantation was evaluated.

RESULTS

IES mechanical studies demonstrated decreasing expansive force with elongation. The deployment of IES devices produced an immediate 21 ± 8% increase in bowel length (p < 0.001, n = 11). Mechanical load testing data showed that the IESs expressed maximum expansive forces at 50% compression of the initial pre-contracted length. The small-intestine failure load in the rats was 1.88 ± 21 N. Intestinal histology post deployment of the IES showed significant expansive changes compared to unstretched bowel tissue.

CONCLUSIONS

IES devices were scalable to the rat intestinal model in our study. The failure load of the rat small intestine was many times higher than the force exerted by the contraction of the IES. Histology demonstrated preservation of intestinal structure with some mucosal erosion. Future in vivo rat studies on distraction enterogenesis with this IES should help to define this organogenesis phenomenon.

Current short bowel syndrome management: An era of improved outcomes and continued challenges

Prior to the late 1960s, pediatric short bowel syndrome was a frequently fatal disease. Currently, pediatric interdisciplinary bowel rehabilitation centers report very high survival rates. The mortality trends, up-to-date definitions, incidence, causes, and clinical manifestations of short bowel syndrome are reviewed. Emphasis is placed upon the nutritional, medical, and surgical advances that have contributed to the dramatic improvement in outcomes for pediatric short bowel syndrome patients. Recent findings and remaining challenges are highlighted.

Biomechanical Force Prediction for Lengthening of Small Intestine during Distraction Enterogenesis

Distraction enterogenesis has been extensively studied as a potential treatment for short bowel syndrome, which is the most common form of intestinal failure. Different strategies including parenteral nutrition and surgical lengthening to manage patients with short bowel syndrome are associated with high complication rates. More recently, self-expanding springs have been used to lengthen the small intestine using an intraluminal axial mechanical force, where this biomechanical force stimulates the growth and elongation of the small intestine. Differences in physical characteristics of patients with short bowel syndrome would require a different mechanical force—this is crucial in order to achieve an efficient and safe lengthening outcome. In this study, we aimed to predict the required mechanical force for each potential intestinal size. Based on our previous experimental observations and computational findings, we integrated our experimental measurements of patient biometrics along with mechanical characterization of the soft tissue into our numerical simulations to develop a series of computational models. These computational models can predict the required mechanical force for any potential patient where this can be advantageous in predicting an individual’s tissue response to spring-mediated distraction enterogenesis and can be used toward a safe delivery of the mechanical force.

Heating/Solvent Responsive Shape-Memory Polymers for Implant Biomedical Devices in Minimally Invasive Surgery: Current Status and Challenge

This review is about the fundamentals and practical issues in applying both heating and solvent responsive shape memory polymers (SMPs) for implant biomedical devices via minimally invasive surgery. After revealing the general requirements in the design of biomedical devices based on SMPs and the fundamentals for the shape-memory effect in SMPs, the underlying mechanisms, characterization methods, and several representative biomedical applications, including vascular stents, tissue scaffolds, occlusion devices, drug delivery systems, and the current R&D status of them, are discussed. The new opportunities arising from emerging technologies, such as 3D printing, and new materials, such as vitrimer, are also highlighted. Finally, the major challenge that limits the practical clinical applications of SMPs at present is addressed.

Optimization of In-Continuity Spring-Mediated Intestinal Lengthening

BACKGROUND

Spring-mediated intestinal lengthening has been studied in numerous animal models to effectively achieve up to a 3-fold increase in length. In this study we are interested in optimizing this method of spring lengthening.

METHODS

Juvenile mini-Yucatan pigs underwent laparotomy for spring implantation. Springs were secured by plicating the intestine around the springs. In one set of experiments, varying degrees of plication were compared to determine the necessary narrowing needed to confine the spring. In another set of experiments, dissolvable sutures were used for the plication to allow for spontaneous spring passage postoperatively. Intestinal segments were retrieved and evaluated for lengthening and histological changes.

RESULTS

Pigs tolerated their diet advancement to a regular diet postoperatively. 10% plication resulted in a 1.3-fold increase in length, while 50% plication resulted in a 2.7-fold increase in length (p<0.05). At two months postoperatively, the majority of springs had safely passed out of the intestine. All lengthened intestine showed significant growth histologically.

CONCLUSIONS

A 50% reduction in lumen diameter achieves optimal spring-mediated intestinal lengthening. Springs can safely pass out of the intestine, thus avoiding a second operation for spring removal. These results may be important in developing future therapies for short bowel syndrome.

LEVEL OF EVIDENCE

Level I experimental study.

Review of Polymeric Materials in 4D Printing Biomedical Applications

The purpose of 4D printing is to embed a product design into a deformable smart material using a traditional 3D printer. The 3D printed object can be assembled or transformed into intended designs by applying certain conditions or forms of stimulation such as temperature, pressure, humidity, pH, wind, or light. Simply put, 4D printing is a continuum of 3D printing technology that is now able to print objects which change over time. In previous studies, many smart materials were shown to have 4D printing characteristics. In this paper, we specifically review the current application, respective activation methods, characteristics, and future prospects of various polymeric materials in 4D printing, which are expected to contribute to the development of 4D printing polymeric materials and technology.

Restoring gut physiology in short bowel patients: from bench to clinical application of autologous intestinal reconstructive procedures

Introduction: Short bowel syndrome represents the leading etiology that causes intestinal failure both in children and adults. Total parenteral nutrition support has dramatically improved the prognosis for these patients but, if related irreversible complications occur, the alternative is represented by surgery and/or transplantation. Areas covered: Autologous gastrointestinal reconstructive procedures are a feasible, alternative approach with good long-term outcome data inexperienced surgical centers. Expert opinion: Ongoing innovative efforts have driven the surgical options for successful autologous reconstructive surgery: bowel elongation/tapering techniques (LILT, STEP, and the new SILT) together with the 'reversed bowel segment' procedure are now recognized procedures and all must be tailored to the individual patient needs to obtain the optimal result in terms of enteral autonomy. Background laboratory experimentation with new procedures e.g. options for bowel dilation techniques and distraction-induced enterogenesis, may provide additional management and treatment modalities.

Intestinal lengthening via multiple in-continuity springs

BACKGROUND

Short bowel syndrome is a debilitating condition with few effective treatments. Spring-mediated distraction enterogenesis can be used to lengthen intestine. The purpose of this study is to determine whether multiple springs in series can safely increase the total amount of lengthening.

METHODS

Juvenile mini-Yucatan pigs each received three nitinol springs placed within their jejunum. Plication was used to narrow the intestine around each spring to secure them. Compressed springs were used in the experimental group, while uncompressed springs were used in the control group. The intestine was examined 3 weeks later for lengthening and histologic changes.

RESULTS

All pigs tolerated diets postoperatively with continued weight gain, and no dilation or obstruction of the intestine was observed. Segments of intestine that contained compressed springs had a significant increase in length from 2.5 cm to 3.9 ± 0.2 cm per spring, compared to segments containing control springs that showed no change (p < 0.001).

CONCLUSIONS

Intestinal plication can be safely used to secure multiple springs in series to achieve intestinal lengthening without compromising intestinal function. Using several springs at once allows for a greater amount of total lengthening. This is a promising model that has potential in the treatment of short bowel syndrome.

Expanding intestinal segment using osmotic hydrogel: An in vivo study

Intestinal circumferential expansion is essential for bowel lengthening in patients with Short Bowel Syndrome. We hypothesized use of an endoluminal osmotic hydrogel expander (EOHE) as a novel approach for intestinal expansion. An EOHE was introduced into an isolated intestinal segment of New Zealand rabbits, with a similar segment created as a control. After 4weeks, the segments were retrieved for analysis. Weight, inflammatory markers and fluoroscopy data was recorded weekly. EOHE allowed successful expansion of intestinal segments from 4.68 ± 0.35 to 9.79 ± 0.35 cm (p = 0.01). Increase in intestinal length was 167.8 ± 35.21% in segments with EOHE vs. 23.03 ± 4.2% in the control group (p < 0.01). A significant intestinal dilatation (214.4 ± 1.58 vs. 34.59 ± 1.23%, p < 0.01) was demonstrated. Hematoxylin and eosin stain revealed conservation of intestinal architecture with muscle hypertrophy and flattening of the epithelium possibly due to compression. No reduction of rabbit weight, inflammatory markers or liver damage was described. EOHE appears to produce safe intestinal expansion, achieving increased length and dilatation suitable for lengthening procedure. This approach may allow development of similar techniques to expand bowel in short bowel patients. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1304-1309, 2019.

Double plication for spring-mediated in-continuity intestinal lengthening in a porcine model

BACKGROUND

Short bowel syndrome is a condition with substantial morbidity and mortality, yet definitive therapies are lacking. Distraction enterogenesis uses mechanical force to "grow" new intestine. In this study, we examined whether intestinal plication can be used to safely achieve spring-mediated intestinal lengthening in a functioning segment of jejunum in its native position.

METHODS

A total of 12 juvenile, miniature Yucatan pigs underwent laparotomy to place either compressed springs or expanded springs within a segment of jejunum (n = 6 per group). The springs were secured within the jejunum by performing intestinal plication to narrow the intestinal lumen around the spring. After 3 weeks, the jejunum was retrieved and examined for lengthening and for histologic changes.

RESULTS

There were no intraoperative or postoperative complications, and the pigs tolerated their diets and gained weight. Segments of jejunum containing expanded springs showed no significant change in length over the 3 weeks. In contrast, jejunum containing compressed springs showed nearly a 3-fold increase in length (P < .001). Histology of the retrieved jejunum showed a significant increase in thickness of the muscularis propria and in crypt depth relative to normal jejunum.

CONCLUSION

Intestinal plication is effective in securing endoluminal springs to lengthen the jejunum. This approach is a clinically relevant model because it allows for normal GI function and growth of animals during intestinal lengthening, which may be useful in lengthening intestine in patients with short bowel syndrome.

Double plication for spring-mediated intestinal lengthening of a defunctionalized Roux limb

BACKGROUND

Spring-mediated distraction enterogenesis has been shown to increase the length of an intestinal segment. The goal of this study is to use suture plication to confine a spring within an intestinal segment while maintaining luminal patency to the rest of the intestine.

METHODS

Juvenile mini-Yucatan pigs underwent placement of nitinol springs within a defunctionalized Roux limb of jejunum. A 20 French catheter was passed temporarily, and sutures were used to plicate the intestinal wall around the catheter at both ends of the encapsulated spring. Uncompressed springs placed in plicated segments and springs placed in nonplicated segments served as controls. The intestine was examined approximately 3 weeks after spring placement.

RESULTS

In the absence of plication, springs passed through the intestine within a week. Double plication allowed the spring to stay within the Roux limb for 3 weeks. Compared to uncompressed springs that showed no change in the length of plicated segments, compressed springs caused a significant 1.7-fold increase in the length of plicated segments.

CONCLUSIONS

Intestinal plication is an effective method to confine endoluminal springs. The confined springs could lengthen intestine that maintains luminal patency. This approach may be useful to lengthen intestine in patients with short bowel syndrome.

LEVEL OF EVIDENCE

Level I Experimental Study.

Three-dimensionally printed surface features to anchor endoluminal spring for distraction enterogenesis

Spring-mediated distraction enterogenesis has been studied as a novel treatment for short bowel syndrome (SBS). Previous approaches are limited by multiple surgeries to restore intestinal continuity. Purely endoluminal devices require a period of intestinal attachment for enterogenesis. The purpose of this study is to modify the device to prevent premature spring migration in a porcine model. Two models were created in juvenile mini-Yucatan pigs for the placement of three-dimensionally printed springs. (1) Two Roux-en-y jejunojenostomies with two Roux limbs were made. A spring with bidirectional hooked surface features was placed in one Roux limb and a spring with smooth surface was placed in the other Roux limb. (2) The in-continuity model had both hooked and smooth surface springs placed directly in intestinal continuity. Spring location was evaluated by weekly radiographs, and the intestine was retrieved after 2 to 4 weeks. Springs with smooth surfaces migrated between 1 to 3 weeks after placement in both porcine models. Springs with bidirectional hooked surface features were anchored to the intestine for up to 4 weeks without migration. Histologically, the jejunal architecture showed significantly increased crypt depth and muscularis thickness compared to normal jejunum. Bidirectional features printed on springs prevented the premature migration of endoluminal springs. These novel spring anchors allowed for their endoluminal placement without any sutures. This approach may lead to the endoscopic placement of the device for patients with SBS.

Mechanisms for intestinal regeneration

PURPOSE OF REVIEW

The purpose of this review is to briefly summarize the notable structures and pathways in intestinal epithelial growth before presenting the current main areas of active research in intestinal regeneration. As a rapidly advancing field, a number of breakthroughs have recently been made related to the culture of intestinal stem cells (ISCs) and to the engineering of intestinal tissue.

RECENT FINDINGS

ISCs can be derived from fibroblasts and can be cultured in hydrogels under xenogeneic-free conditions. Intestinal organoids can be cultured with neural crest cells to form small intestinal tissues with neuromuscular networks. Endoluminal devices can be placed inside the native intestine to exert mechanical force to induce novel tissue growth.

SUMMARY

A number of recent advances in the field of intestinal regeneration are encouraging and suggest that novel therapies for a wide range of intestinal disorders may be developed in the near future. There are still a number of obstacles before such stem cell therapies can be safely used in humans.

New insights and interventions for short bowel syndrome

PURPOSE OF REVIEW

This review summarizes recent innovations in the treatment of patients with short bowel syndrome.

RECENT FINDINGS

The use of surgical procedures, growth factor stimulation, and bioengineering approaches to increase absorptive surface area of the intestine is examined. While the morphology of the intestine is clearly altered by these interventions, it is less clear that the overall function of the intestine is improved.

SUMMARY

Continued innovations will likely bring about new therapeutic options for patients with short bowel syndrome. Careful evaluations of the impact of these interventions await controlled clinical trials.

Scalability of an endoluminal spring for distraction enterogenesis

INTRODUCTION

Techniques of distraction enterogenesis have been explored to provide increased intestinal length to treat short bowel syndrome (SBS). Self-expanding, polycaprolactone (PCL) springs have been shown to lengthen bowel in small animal models. Their feasibility in larger animal models is a critical step before clinical use.

METHODS

Juvenile mini-Yucatan pigs underwent jejunal isolation or blind ending Roux-en-y jejunojejunostomy with insertion of either a PCL spring or a sham PCL tube. Extrapolated from our spring characteristics in rodents, proportional increases in spring constant and size were made for porcine intestine.

RESULTS

Jejunal segments with 7mm springs with k between 9 and 15N/m demonstrated significantly increased lengthening in isolated segment and Roux-en-y models. Complications were noted in only two animals, both using high spring constant k>17N/m. Histologically, lengthened segments in the isolated and Roux models demonstrated significantly increased muscularis thickness and crypt depth. Restoration of lengthened, isolated segments back into continuity was technically feasible after 6weeks.

CONCLUSION

Self-expanding, endoluminal PCL springs, which exert up to 0.6N force, safely achieve significant intestinal lengthening in a translatable, large-animal model. These spring characteristics may provide a scalable model for the treatment of SBS in children.

Working group reports: evaluation of the evidence to support practice guidelines for nutritional care of preterm infants-the Pre-B Project

The "Evaluation of the Evidence to Support Practice Guidelines for the Nutritional Care of Preterm Infants: The Pre-B Project" is the first phase in a process to present the current state of knowledge and to support the development of evidence-informed guidance for the nutritional care of preterm and high-risk newborn infants. The future systematic reviews that will ultimately provide the underpinning for guideline development will be conducted by the Academy of Nutrition and Dietetics' Evidence Analysis Library (EAL). To accomplish the objectives of this first phase, the Pre-B Project organizers established 4 working groups (WGs) to address the following themes: 1) nutrient specifications for preterm infants, 2) clinical and practical issues in enteral feeding of preterm infants, 3) gastrointestinal and surgical issues, and 4) current standards of infant feeding. Each WG was asked to 1) develop a series of topics relevant to their respective themes, 2) identify questions for which there is sufficient evidence to support a systematic review process conducted by the EAL, and 3) develop a research agenda to address priority gaps in our understanding of the role of nutrition in health and development of preterm/neonatal intensive care unit infants. This article is a summary of the reports from the 4 Pre-B WGs.