Karen J. L. Burg

Biomaterial developments for bone tissue engineering.

The development of bone tissue engineering is directly related to changes in materials technology. While the inclusion of materials requirements is standard in the design process of engineered bone substitutes, it is also critical to incorporate clinical requirements in order to engineer a clinically relevant device. This review presents the clinical need for bone tissue-engineered alternatives to the present materials used in bone grafting techniques, a status report on clinically available bone tissue-engineering devices, and recent advances in biomaterials research. The discussion of ongoing research includes the current state of osseoactive factors and the delivery of these factors using bioceramics and absorbable biopolymers. Suggestions are also presented as to the desirable design features that would make an engineered device clinically effective.

A Hydrogel Material for Plastic and Reconstructive Applications Injected into the Subcutaneous Space of a Sheep

Soft tissue reconstruction using tissue-engineered constructs requires the development of materials that are biocompatible and support cell adhesion and growth. The objective of this study was to evaluate the use of macroporous hydrogel fragments that were formed using either unmodified alginate or alginate covalently linked with the fibronectin cell adhesion peptide RGD (alginate-RGD). These materials were injected into the subcutaneous space of adult, domesticated female sheep and harvested for histological comparisons at 1 and 3 months. In addition, the alginate-RGD porous fragments were seeded with autologous sheep preadipocytes isolated from the omentum, and these cell-based constructs were also implanted. The results from this study indicate that both the alginate and alginate-RGD subcutaneous implants supported tissue and vascular ingrowth. Furthermore, at all time points of the experiment, a minimal inflammatory response and capsule formation surrounding the implant were observed. The implanted materials also maintained their sizes over the 3-month study period. In addition, the alginate-RGD fragments supported the adhesion and proliferation of sheep preadipocytes, and adipose tissue was present within the transplant site of these cellular constructs, which was not present within the biomaterial control sites.

Comparative study of seeding methods for three‐dimensional polymeric scaffolds

Development of tissue-engineered devices may be enhanced by combining cells with porous absorbable polymeric scaffolds before implantation. The cells are seeded throughout the scaffolds and allowed to proliferate in vitro for a predetermined amount of time. The distribution of cells throughout the porous material is one critical component determining success or failure of the tissue-engineered device. This can influence both the successful integration of the device with the host tissue as well as the development of a vascularized network throughout the entire scaffold volume. This research sought to compare different seeding and proliferation methods to select an ideal method for a polyglycolide/aortic endothelial cell system. Two seeding environments, static and dynamic, and three proliferation environments, static, dynamic, and bioreactor, were analyzed, for a total of six possible methods. The six seeding and proliferation combinations were analyzed following a 1-week total culture time. It was determined that for this specific system, dynamic seeding followed by a dynamic proliferation phase is the least promising method and dynamic seeding followed by a bioreactor proliferation phase is the most promising.

In vivo characterization of a porous hydrogel material for use as a tissue bulking agent

Tissue engineered biomaterial constructs are needed for plastic and reconstructive applications. To successfully form a space-filling tissue, the construct should induce a minimal inflammatory response, create minimal or no fibrotic capsule, and establish a vascular bed within the first few days after implantation to ensure survival of the implanted cells. In addition, the biomaterial should support cellular adhesion and induce tissue ingrowth. A macroporous hydrogel bead using sodium alginate covalently coupled with an arginine, glycine, and aspartic acid-containing peptide was created. A 6-month subcutaneous rat model study was performed to determine if the implanted material induced tissue ingrowth throughout the implantation area and maintained a three-dimensional vascular bed. The implanted materials produced a vascular bed, minimal inflammation and capsule formation, and good tissue ingrowth throughout the experiment. The material retained its bulking capacity by demonstration of no significant change of the cross-sectional area as measured from the center of the implants after the 2-week time point. In addition, the granulation tissue formed around the implant was loosely organized, and the surrounding tissue had integrated well with the implant. These results indicate that this material has the desired properties for the development of soft-tissue-engineering constructs.

Minimally invasive tissue engineering composites and cell printing

Injectable composites combined with tissue-printing technology for improved bioengineered devices. The invisible engineering problem, the one often ignored, is the design of a readily implantable, precisely assembled cellular construct. Previous studies have consistently shown that composite tissue-engineered devises are readily implanted via minimally invasive means and, in the systems tested, produce minimal inflammation and fibrous encapsulation. Gels of optimal viscosity are able to maintain separation between the cellular scaffold and allow tissue growth. Studies with the cell/substrate printing system have shown that it is possible to define, in a controlled manner, spatial arrangement of cells within a gel substrate.

Absorbable and Biodegradable Polymers

Absorbable and biodegradable polymers , Absorbable and biodegradable polymers , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Evaluation of smooth muscle cell response using two types of porous polylactide scaffolds with differing pore topography.

The goal of tissue engineering is to create bioartificial tissues for the replacement of failed or nonfunctional tissue. Porous tissue-engineered scaffolds may be created through a solvent-casting/porogen-leaching technique. Almost exclusively, sodium chloride (NaCl) is the porogen of choice. Previous studies have demonstrated the importance of porosity and pore size in cell adhesion and tissue development, yet the impact of porogen morphology and the chemical effect of porogen residual has not been fully explored. Poly-L-lactide (PLLA) scaffolds were manufactured by a solvent-casting, particulate-leaching method with either glucose or NaCl porogen in an effort to vary pore characteristics and, subsequently, cell adhesion and tissue development. Porogen influence on scaffold morphology and topography was compared via histological techniques and qualitative surface characteristics. Using an in vitro model, scaffolds were seeded with rat aortic smooth muscle cells (SMCs) and evaluated over a 28-day period. Cell attachment and proliferation were subsequently evaluated. Results indicate that initial SMC attachment is higher for scaffolds manufactured with NaCl rather than glucose. The proliferation of SMCs was higher for scaffolds manufactured with glucose and, by day 28, scaffolds manufactured with glucose supported a higher cell population than those processed using NaCl porogen.

Building off-the-shelf tissue-engineered composites

Rapid advances in technology have created the realistic possibility of personalized medicine. In 2000, Time magazine listed tissue engineering as one of the ‘hottest 10 career choices’. However, in the past decade, only a handful of tissue-engineered products were translated to the clinical market and none were financially viable. The reality of complex business planning and the high-investment, high-technology environment was not apparent, and the promise of tissue engineering was overstated. In the meantime, biologists were steadily applying three-dimensional benchtop tissue-culture systems for cellular research, but the systems were gelatinous and thus limited in their ability to facilitate the development of complex tissues. Now, the bioengineering literature has seen an emergence of literature describing biofabrication of tissues and organs. However, if one looks closely, again, the viable products appear distant. ‘Rapid’ prototyping to reproduce the intricate patterns of whole organs using large volumes of cellular components faces daunting challenges. Homogenous forms are being labelled ‘tissues’, but, in fact, do not represent the heterogeneous structure of the native biological system. In 2003, we disclosed the concept of combining rapid prototyping techniques with tissue engineering technologies to facilitate precision development of heterogeneous complex tissue-test systems, i.e. systems to be used for drug discovery and the study of cellular behaviour, biomedical devices and progression of disease. The focus of this paper is on the challenges we have faced since that time, moving this concept towards reality, using the case of breast tissue as an example.

EDTA enhances high-throughput two-dimensional bioprinting by inhibiting salt scaling and cell aggregation at the nozzle surface

Tissue‐engineering strategies may be employed in the development of in vitro breast tissue models for use in testing regimens of drug therapies and vaccines. The physical and chemical interactions that occur among cells and extracellular matrix components can also be elucidated with these models to gain an understanding of the progression of transformed epithelial cells into tumours and the ultimate metastases of tumour cells. The modified inkjet printer may be a useful tool for creating three‐dimensional (3D) in vitro models, because it offers an inexpensive and high‐throughput solution to microfabrication, and because the printer can be easily manipulated to produce varying tissue attributes. We hypothesized, however, that when ink is replaced with a biologically based fluid (i.e. a ‘bio‐ink’), specifically a serum‐free cell culture medium, printer nozzle failure can result from salt scale build‐up as fluid evaporates on the printhead surface. In this study, ethylene diamine tetra‐acetic acid (EDTA) was used as a culture medium additive to prevent salt scaling and cell aggregation during the bioprinting process. The results showed that EDTA, at a concentration typically found in commercially available trypsin solutions (0.53 mM), prevented nozzle failure when a serum‐free culture medium was printed from a nozzle at 1000 drops/s. Furthermore, increasing concentrations of EDTA appeared to mildly decrease aggregation of 4T07 cells. Cell viability studies were performed to demonstrate that addition of EDTA did not result in significant cell death. In conclusion, it is recommended that EDTA be incorporated into bio‐ink solutions containing salts that could lead to nozzle failure. Copyright

Salient haptic skills trainer: initial validation of a novel simulator for training force-based laparoscopic surgical skills.

BackgroundThere is an increasing need for efficient training simulators to teach advanced laparoscopic skills beyond those imparted by a box trainer. In particular, force-based or haptic skills must be addressed in simulators, especially because a large percentage of surgical errors are caused by the over-application of force. In this work, the efficacy of a novel, salient haptic skills simulator is tested as a training tool for force-based laparoscopic skills.MethodsThirty novices with no previous laparoscopic experience trained on the simulator using a pre-test–feedback–post-test experiment model. Ten participants were randomly assigned to each of the three salient haptic skills—grasping, probing, and sweeping—on the simulator. Performance was assessed by comparing force performance metrics before and after training on the simulator.ResultsData analysis indicated that absolute error decreased significantly for all three salient skills after training. Participants also generally decreased applied forces after training, especially at lower force levels. Overall, standard deviations also decreased after training, suggesting that participants improved their variability of applied forces.ConclusionsThe novel, salient haptic skills simulator improved the precision and accuracy of participants when applying forces with the simulator. These results suggest that the simulator may be a viable tool for laparoscopic force skill training. However, further work must be undertaken to establish full validity. Nevertheless, this work presents important results toward addressing simulator-based force-skills training specifically and surgical skills training in general.