Numerical Analysis for Non-Uniformity of Balloon-Expandable Stent Deployment Driven by Dogboning and Foreshortening

PURPOSE

Stenting is the most common intervention for arteriosclerosis treatment; however, the success of the treatment depends on the incidence of in-stent restenosis (ISR). Stent deployment characteristics are major influencers of ISR and can be measured in terms of dogboning, asymmetry, and foreshortening. This study aimed to analyse the implications of balloon and stent-catheter assembly parameters on the stent deployment characteristics.

METHODS

Experimental approach to analyse the impact of the balloon and stent-catheter assembly parameters on stent deployment characteristics is a time-consuming and complex task, whereas numerical methods prove to be quick, efficient, and reliable. In this study, eleven finite element models were employed to analyse non-uniform balloon stent expansion pattern, comprised of variation in, stent axial position on balloon, balloon length, balloon folding pattern, and balloon wall thickness.

RESULTS

Obtained results suggest that the axially noncentral position of the stent on balloon and variable balloon thickness lead to non-uniform stent deployment pattern. Also, it was proved that variation in balloon length and balloon folding pattern influence deployment process.

CONCLUSION

Improved positional accuracies, uniform balloon wall thickness, and selection of the appropriate length of a balloon for selected stent configuration will help to minimize dogboning, asymmetry, and foreshortening during non-uniform stent expansion, thereby reducing the risk of restenosis. The stated numerical approach will be helpful to optimize stent catheter assembly parameters thus minimizing in-vitro tests and product development time.

Bioadhesives for musculoskeletal tissue regeneration

Natural or synthetic materials designed to adhere to biological components, bioadhesives, have received significant attention in clinics and surgeries. As a result, there are several commercially available, FDA-approved bioadhesives used for skin wound closure, hemostasis, and sealing tissue gaps or cracks in soft tissues. Recently, the application of bioadhesives has been expanded to various areas including musculoskeletal tissue engineering and regenerative medicine. The instant establishment of a strong adhesion force on tissue surfaces has shown potential to augment repair of connective tissues. Bioadhesives have also been applied to secure tissue grafts to host bodies and to fill or seal gaps in musculoskeletal tissues caused by injuries or degenerative diseases. In addition, the injectability equipped with the instant adhesion formation may provide the great potential of bioadhesives as vehicles for localized delivery of cells, growth factors, and small molecules to facilitate tissue healing and regeneration. This review covers recent research progress in bioadhesives as focused on their applications in musculoskeletal tissue repair and regeneration. We also discuss the advantages and outstanding challenges of bioadhesives, as well as the future perspective toward regeneration of connective tissues with high mechanical demand.

Infiltration and In-Tissue Polymerization of Photocross-Linked Hydrogel for Effective Fixation of Implants into Cartilage-An In Vitro Study

Effective and biocompatible fixation of implants into cartilage defects has yet to be successfully achieved. [Poly-d,l-lactic acid/polyethyleneglycol/poly-d,l-lactic acid] (PDLLA-PEG) is a chondrosupportive scaffold that is photocross-linked using the visible-light photoinitiator lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP). Interestingly, LAP and its monomer DLLA-EG are able to infiltrate the cartilage and form hydrogels upon the detection of light. After the infiltration of LAP and DLLA-EG into the implant and host cartilage, an interconnected and continuous hydrogel structure is formed which fixes the implant within the host cartilage. A mechanical test shows that the infiltrated group displays a significantly higher push-out force than the group that has not been infiltrated (the traditional fibrin fixation group). Surprisingly, the in-cartilage hydrogel also reduces the release of sulfated glycosaminoglycan from cartilage explants. However, infiltration does not affect the cell viability or the expression of cartilage marker genes. This new strategy thus represents a biocompatible and efficient method to fix implants into host tissues.

Applications of Computer Modeling and Simulation in Cartilage Tissue Engineering

BACKGROUND

Advances in cartilage tissue engineering have demonstrated noteworthy potential for developing cartilage for implantation onto sites impacted by joint degeneration and injury. To supplement resource-intensive in vivo and in vitro studies required for cartilage tissue engineering, computational models and simulations can assist in enhancing experimental design.

METHODS

Research articles pertinent to cartilage tissue engineering and computer modeling were identified, reviewed, and summarized. Various applications of computer modeling for cartilage tissue engineering are highlighted, limitations of in silico modeling are addressed, and suggestions for future work are enumerated.

RESULTS

Computational modeling can help better characterize shear stresses generated by bioreactor fluid flow, refine scaffold geometry, customize the mechanical properties of engineered cartilage tissue, and model rates of cell growth and dynamics. Thus, results from in silico studies can help resourcefully enhance in vitro and in vivo studies; however, the limitations of these studies, such as the underlying assumptions and simplifications applied in each model, should always be addressed and justified where applicable. In silico models should also seek validation and verification when possible.

CONCLUSION

Future studies may adopt similar approaches to supplement in vitro trials and further investigate effects of mechanical stimulation on chondrocyte and stem cell dynamics. Additionally, as precision medicine, machine learning, and powerful open-source software become more popular and accessible, applications of multi-scale and multiphysics computational models in cartilage tissue engineering are expected to increase.

Effect of interface mechanical discontinuities on scaffold-cartilage integration

A consistent lack of lateral integration between scaffolds and adjacent articular cartilage has been exhibited in vitro and in vivo. Given the mismatch in mechanical properties between scaffolds and articular cartilage, the mechanical discontinuity that occurs at the interface has been implicated as a key factor, but remains inadequately studied. Our objective was to investigate how the mechanical environment within a mechanically loaded scaffold-cartilage construct might affect integration. We hypothesized that the magnitude of the mechanical discontinuity at the scaffold-cartilage interface would be related to decreased integration. To test this hypothesis, chondrocyte seeded scaffolds were embedded into cartilage explants, pre-cultured for 14 days, and then mechanically loaded for 28 days at either 1N or 6N of applied load. Constructs were kept either peripherally confined or unconfined throughout the duration of the experiment. Stress, strain, fluid flow, and relative displacements at the cartilage-scaffold interface and within the scaffold were quantified using biphasic, inhomogeneous finite element models (bFEMs). The bFEMs indicated compressive and shear stress discontinuities occurred at the scaffold-cartilage interface for the confined and unconfined groups. The mechanical strength of the scaffold-cartilage interface and scaffold GAG content were higher in the radially confined 1N loaded groups. Multivariate regression analyses identified the strength of the interface prior to the commencement of loading and fluid flow within the scaffold as the main factors associated with scaffold-cartilage integration. Our study suggests a minimum level of scaffold-cartilage integration is needed prior to the commencement of loading, although the exact threshold has yet to be identified. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Implant strategy affects scaffold stability and integrity in cartilage treatment

PURPOSE

To identify the most appropriate implantation strategy for a novel chondral scaffold in a model simulating the early post-operative phase, in order to optimize the implant procedure and reduce the risk of early failure.

METHODS

Eight human cadaveric limbs were strapped to a continuous passive motion device and exposed to extension-flexion cycles (0°-90°). Chondral lesions (1.8 cm diameter) were prepared on condyles, patella and trochlea for the implant of a bi-layer collagen-hydroxyapatite scaffold. The first set-up compared four fixation techniques: press-fit (PF) vs. fibrin glue (FG) vs. pins vs. sutures; the second compared circular and square implants; the third investigated stability in a weight-bearing simulation. The scaffolds were evaluated using semi-quantitative Drobnic and modified Bekkers scores.

RESULTS

FG presented higher total Drobnic and Bekkers scores compared to PF (both p = 0.002), pins (p = 0.013 and 0.001) and sutures (p = 0.001 and < 0.0005). Pins offered better total Drobnic and Bekkers scores than PF in the anterior femoral condyles (p = 0.007 and 0.065), similar to FG. The comparison of round and square implants applied by FG showed worst results for square lesions (Drobnic score p = 0.049, Bekkers score p = 0.037). Finally, load caused worst overall results (Drobnic p = 0.018).

CONCLUSIONS

FG improves the fixation of this collagen-HA scaffold regardless of lesion location, improving implant stability while preserving its integrity. Pins represent a suitable option only for lesions of the anterior condyles. Square scaffolds present weak corners, therefore, round implants should be preferred. Finally, partial weight-bearing simulation significantly affected the scaffold. These findings may be useful to improve surgical technique and post-operative management of patients, to optimize the outcome of chondral scaffold implantation.

Arthroscopic airbrush assisted cell implantation for cartilage repair in the knee: a controlled laboratory and human cadaveric study

OBJECTIVE

The objective of this study was to investigate the feasibility of arthroscopic airbrush assisted cartilage repair.

METHODS

An airbrush device (Baxter) was used to spray both human expanded osteoarthritic chondrocytes and choncrocytes with their pericellular matrix (chondrons) at 1 × 10(6) cells/ml fibrin glue (Tissucol, Baxter) in vitro. Depth-dependent cell viability was assessed for both methods with confocal microscopy. Constructs were cultured for 21 days to assess matrix production. A controlled human cadaveric study (n = 8) was performed to test the feasibility of the procedure in which defects were filled with either arthroscopic airbrushing or needle extrusion. All knees were subjected to 60 min of continuous passive motion and scored on outline attachment and defect filling.

RESULTS

Spraying both chondrocytes and chondrons in fibrin glue resulted in a homogenous cell distribution throughout the scaffold. No difference in viability or matrix production between application methods was found nor between chondrons and chondrocytes. The cadaveric study revealed that airbrushing was highly feasible, and that defect filling through needle extrusion was more difficult to perform based on fibrin glue adhesion and gravity-induced seepage. Defect outline and coverage scores were consistently higher for extrusion, albeit not statistically significant.

CONCLUSION

Both chondrons and chondrocytes can be evenly distributed in a sprayed fibrin glue scaffold without affecting viability while supporting matrix production. The airbrush technology is feasible, easier to perform than needle extrusion and allows for reproducible arthroscopic filling of cartilage defects.

Fibrin glue improves osteochondral scaffold fixation: study on the human cadaveric knee exposed to continuous passive motion

OBJECTIVE

To evaluate stability and integrity of bi-layer and three-layer collagen-hydroxyapatite (C-HA) osteochondral scaffolds in a human cadaveric knee exposed to continuous passive motion (CPM) with and without loading and the role of added fibrin glue to improve the press-fit fixation of C-HA scaffolds.

DESIGN

Osteochondral lesions (2.0 × 1.5 cm) were chiseled out on both condyles and trochlea in eight human cadaveric knees. A total of 24 bi-layer (5 mm, four in each condyle) or three-layer C-HA scaffolds (8 mm, eight in the trochlea, four in each condyle) were first press-fit implanted and underwent testing with CPM, 90 cycles, 0°-90°. The second set of 24 scaffolds was implanted in cleaned lesions with the addition of fibrin glue. Two knees with fibrin glue fixation were additionally exposed to 15 kg loading, with 30 cycles of CPM, 0°-30°. Then, the knees were reopened and the scaffolds were evaluated using semi-quantitative Drobnic and modified Bekkers scores.

RESULTS

All but two scaffolds remained in the lesions site throughout CPM. Two implants failed: both were bi-layer osteochondral scaffolds, press-fit implanted at the lateral femoral condyle (LFC). A statistically significant difference was obtained between press-fit and fibrin glue implants with both Drobnic (2.9 ± 0.7 vs 4.3 ± 0.1, P < 0.0005) and Bekkers (3.3 ± 1.0 vs 5.0 ± 0.1, P < 0.0005) scores. Additional knee loading did not affect fibrin glue scaffold fixation or integrity.

CONCLUSION

This cadaveric study showed fibrin glue notably improved bi-layer or three-layer C-HA scaffold press-fit fixation regardless of lesion location. It is therefore recommended that fibrin glue be used during surgery to improve early post-operative C-HA scaffold stability and integrity.

Fibrin Sealant: The Only Approved Hemostat, Sealant, and Adhesive-a Laboratory and Clinical Perspective

Background. Fibrin sealant became the first modern era material approved as a hemostat in the United States in 1998. It is the only agent presently approved as a hemostat, sealant, and adhesive by the Food and Drug Administration (FDA). The product is now supplied as patches in addition to the original liquid formulations. Both laboratory and clinical uses of fibrin sealant continue to grow. The new literature on this material also continues to proliferate rapidly (approximately 200 papers/year). Methods. An overview of current fibrin sealant products and their approved uses and a comprehensive PubMed based review of the recent literature (February 2012, through March 2013) on the laboratory and clinical use of fibrin sealant are provided. Product information is organized into sections based on a classification system for commercially available materials. Publications are presented in sections based on both laboratory research and clinical topics are listed in order of decreasing frequency. Results. Fibrin sealant remains useful hemostat, sealant, and adhesive. New formulations and applications continue to be developed. Conclusions. This agent remains clinically important with the recent introduction of new commercially available products. Fibrin sealant has multiple new uses that should result in further improvements in patient care.