Engineering cartilage growth and development

Novel nano-rough polymers for cartilage tissue engineering

This study presents an innovative method for creating a highly porous surface with nanoscale roughness on biologically relevant polymers, specifically polyurethane (PU) and polycaprolactone (PCL). Nanoembossed polyurethane (NPU) and nanoembossed polycaprolactone (NPCL) were produced by the casting of PU and PCL over a plasma-deposited, spiky nanofeatured crystalline titanium (Ti) surface. The variables used in the process of making the spiky Ti surface can be altered to change the physical properties of the spiky particles, and thus, the cast polymer substrate surface can be altered. The spiky Ti surface is reusable to produce additional nanopolymer castings. In this study, control plain PU and PCL polymers were produced by casting the polymers over a plain Ti surface (without spikes). All polymer surface morphologies were characterized using both scanning electron microscopy and atomic force microscopy, and their surface energies were measured using liquid contact angle measurements. The results revealed that both NPU and NPCL possessed a higher degree of nanometer surface roughness and higher surface energy compared with their respective unaltered polymers. Further, an in vitro study was carried out to determine chondrocyte (cartilage-producing cells) functions on NPU and NPCL compared with on control plain polymers. Results of this study provided evidence of increased chondrocyte numbers on NPU and NPCL compared with their respective plain polymers after periods of up to 7 days. Moreover, the results provide evidence of greater intracellular protein production and collagen secretion by chondrocytes cultured on NPU and NPCL compared with control plain polymers. In summary, the present in vitro results of increased chondrocyte functions on NPU and NPCL suggest these materials may be suitable for numerous polymer-based cartilage tissue-engineering applications and, thus, deserve further investigation.

Repair of calvarial defects in rabbits with platelet-rich plasma as the scaffold for carrying bone marrow stromal cells

OBJECTIVE

Platelet-rich plasma (PRP) is becoming a new application in tissue engineering and a developing area for clinicians and researchers because it is a natural source of growth factors, many of which can accelerate and promote bone regeneration. However, few studies have reported the potentiality of using PRP as a scaffold in bone tissue engineering. The present study investigated the feasibility of using PRP as a scaffold to carry bone marrow stromal cells (BMSCs) to repair calvarial defects in a rabbit model.

STUDY DESIGN

The primary cultured BMSCs were divided into 2 groups. One group was induced with dexamethasone and the other was not induced. Full-thickness bone defects of 5-mm diameter (4 defects per calvarium) were created on the calvaria of 10 New Zealand white rabbits. PRP or whole blood was used, respectively to incorporate the induced or uninduced BMSCs. Then, the composites were activated and applied to repair the defects. The samples were harvested 8 weeks later and bone regeneration was assessed grossly and analyzed by radiographic or histologic examination.

RESULTS

Eight weeks after the implantation of the materials, substantial bone regeneration was observed at the calvarial defect restored with PRP incorporating the induced BMSCs. Less new bone formation was observed at the defect implanted with PRP incorporating the uninduced BMSCs. In contrast, no bone regeneration was detected at the defects implanted with the whole blood incorporating BMSCs, whether the BMSCs were induced or not.

CONCLUSIONS

PRP can be used as a scaffold to carry in vitro expanded BMSCs to repair a rabbit's calvarial defect, but its inductive ability to BMSCs was limited.

Cartilage regeneration with highly-elastic three-dimensional scaffolds prepared from biodegradable poly(L-lactide-co-epsilon-caprolactone)

Compressive mechanical stimuli are crucial in regenerating cartilage with tissue engineering, which creates a need for scaffolds that can maintain their mechanical integrity while delivering mechanical signals to adherent cells during strain applications. With these goals in mind, the aim of this study was to develop a mechano-active scaffold that facilitated effective cartilaginous tissue formation under dynamic physiological environments. Using a gel-pressing method, we fabricated a biodegradable and highly-elastic scaffold from poly(L-lactide-co-epsilon-caprolactone) (PLCL; 5:5), with 85% porosity and a 300-500-microm pore size, and we compared it to control scaffolds made of rigid polylactide (PLA) or poly(lactide-co-glycolide) (PLGA). After tensile mechanical tests and recovery tests confirmed the elasticity of the PLCL scaffolds, we seeded them with rabbit chondrocytes, cultured them in vitro, and subcutaneously implanted them into nude mice for up to eight weeks. The PLCL scaffolds possessed a completely rubber-like elasticity, were easily twisted and bent, and exhibited an almost complete (over 97%) recovery from applied strain (up to 500%); the control PLA scaffolds showed little recovery. In vitro and in vivo accumulations of extracellular matrix on the cell-PLCL constructs demonstrated that they could not only sustain but also significantly enhance chondrogenic differentiation. Moreover, the mechanical stimulation of the dynamic in vivo environment promoted deposition of the chondral extracellular matrix onto the PLCL. In contrast, on the PLA scaffolds, most of the chondrocytes had de-differentiated and formed fibrous tissues. In a rabbit defect model, the groups treated with PLCL scaffolds exhibited significantly enhanced cartilage regeneration compared to groups harboring an empty control or PLGA scaffolds. These results indicated that the mechano-active PLCL scaffolds effectively delivered mechanical signals associated with biological environments to adherent chondrocytes, suggesting that these elastic PLCL scaffolds could successfully be used for cartilage regeneration.

Principles of cartilage tissue engineering in TMJ reconstruction

Diseases and defects of the temporomandibular joint (TMJ), compromising the cartilaginous layer of the condyle, impose a significant treatment challenge. Different regeneration approaches, especially surgical interventions at the TMJ's cartilage surface, are established treatment methods in maxillofacial surgery but fail to induce a regeneration ad integrum. Cartilage tissue engineering, in contrast, is a newly introduced treatment option in cartilage reconstruction strategies aimed to heal cartilaginous defects. Because cartilage has a limited capacity for intrinsic repair, and even minor lesions or injuries may lead to progressive damage, biological oriented approaches have gained special interest in cartilage therapy. Cell based cartilage regeneration is suggested to improve cartilage repair or reconstruction therapies. Autologous cell implantation, for example, is the first step as a clinically used cell based regeneration option. More advanced or complex therapeutical options (extracorporeal cartilage engineering, genetic engineering, both under evaluation in pre-clinical investigations) have not reached the level of clinical trials but may be approached in the near future. In order to understand cartilage tissue engineering as a new treatment option, an overview of the biological, engineering, and clinical challenges as well as the inherent constraints of the different treatment modalities are given in this paper.

Autologous Injectable Tissue-Engineered Cartilage by Using Platelet-Rich Plasma: Experimental Study in a Rabbit Model

PURPOSE

Platelet-rich plasma (PRP) has been widely applied to promote tissue healing and used as a novel injectable scaffold in bone tissue engineering. However, there is no report about its feasibility to support chondrogenesis. This study aimed to investigate the feasibility of a PRP carrier to deliver chondrocytes and regenerate cartilage tissues in a rabbit model via injection.

MATERIALS AND METHODS

Eight New Zealand rabbits were divided into a chondrocytes/PRP group (n = 4) and a PRP-alone group (n = 4). Chondrocytes harvested from the auricular root of New Zealand rabbits were cultured and harvested. The chondrocytes were then mixed with PRP solution to generate chondrocytes/PRP composites with final cellular density of 5.0 x 10(7)/mL. Bovine thrombin was used as a cross-linking agent to gel chondrocytes/PRP composites, then, the composites were injected subcutaneously into the dorsal tissue of cell donor animals. As controls, PRP alone was injected into another 4 rabbits. At the second month after injection, rabbits were prepared for magnetic resonance imaging. The samples were then harvested for macroscopical examination, histological analysis, and glycosaminoglycan quantification.

RESULTS

Two months after injection, the hard knobbles were easily palpated under the dorsal skin of the animals in the chondrocytes/PRP group, and magnetic resonance images showed the presence of cartilage-like tissues. In histological analysis, formation of new cartilage was observed in the chondrocytes/PRP composites. Safranin-O staining and Masson's trichrome staining showed proteoglycan and collagen were produced in matrices. In contrast, no tissue formed in the PRP-alone group.

CONCLUSIONS

This study suggests the feasibility of using PRP as injectable scaffold seeded with chondrocytes to regenerate cartilage and showed the potential of using this method for the reconstruction of cartilage defects.

Autologous Fat Transfer for Facial Recontouring: Is There Science behind the Art?

BACKGROUND

Clinical use of autologous fat grafts for facial soft-tissue augmentation has grown in popularity in the plastic surgery community, despite a perceived drawback of unpredictable results.

METHODS

The authors' review of the literature and their current techniques of autologous fat transfer focused on (1) the donor site, (2) aspiration methods, (3) local anesthesia, (4) centrifugation and washing, (5) exposure to cold and air, (6) addition of growth factors, (7) reinjection methods, and (8) longevity of fat grafts.

RESULTS

Clinical experience and basic science data showed a slight preference for the following: harvesting abdominal fat with "nontraumatic," blunt cannula technique, preparation by means of centrifugation without washing or addition of growth factors, and immediate injection of small amounts of fat by means of multiple passes. Quantitative evidence of clinical fat survivability and predictability of volume restoration does not exist, yet reports of patient satisfaction with this procedure do. Clinicians report the need for revisionary procedures to optimize results.

CONCLUSIONS

Although there is an increased trend in replacement of soft-tissue volume with autologous fat transfer, the literature fails to provide definitive evidence of fat survival. A large-scale clinical assessment using three-dimensional volumetric imaging would provide useful outcome data.

Compressive biomechanical properties of human nasal septal cartilage

BACKGROUND

Nasal septal cartilage is frequently used in nasal reconstruction and is a common source of chondrocytes for cartilage tissue engineering. The biomechanical properties of septal cartilage have yet to be fully defined and this limits the ability to compare it to the various alternative tissue-implant materials or tissue-engineered neocartilage. Given the unique structure and orientation of the septum within the nose, we sought to investigate anisotropic behaviors of septal cartilage in compression and correlate this to the concentration of glycosaminoglycans (GAG) and collagen within the cartilage.

METHODS

Human nasal septal cartilage specimens were tested in confined compression, with each sample analyzed in a medial orientation and also either a vertical or caudal-cephalic orientation, with the order of tests randomized. The equilibrium confined compression (aggregate) modulus, HAO, and the permeability, kp, at different offset compression levels were obtained for each compression test. After testing, the cartilage samples were solubilized, and the concentrations of GAG and collagen were obtained.

RESULTS

Forty-nine compression tests (24 medial, 12 vertical, 13 caudal-cephalic) were run on cartilage specimens obtained from 21 patients. There was a significant effect of orientation on compression modulus, HAO, with the vertical (0.7 +/- 0.12 MPa) and caudal-cephalic (0.66 +/- 0.01 MPa) orientations being significantly stiffer (p = 0.05) than the medial orientation (0.44 +/- 0.04 MPa). There was a trend of an orientation effect on kp at 15% offset compression (p = 0.12) and a borderline significant effect of orientation on kp at 30% offset compression (p = 0.05), demonstrating the M orientation to be more permeable than both the vertical and caudal-cephalic orientations. Both univariate and multivariate analysis did not demonstrate a significant effect of order of compression, age, gender, thickness, dry/wet weight, GAG, or collagen on either HAO, or kp values (p > 0.05).

CONCLUSION

This study provides new information on the compressive properties of septal cartilage along different axes of compression. The results demonstrate that human septal cartilage is anisotropic; the compressive stiffness is higher in the vertical and caudal-cephalic orientations than in the medial orientation. Additionally, the medial orientation tends to have the greatest permeability. The data obtained in this study provide a reference to which various craniofacial reconstruction materials and tissue-engineered neocartilage can be compared.

Transplanted tissue-engineered cartilage

OBJECTIVE

To evaluate the feasibility of transplanting sculpted autogenous tissue-engineered cartilage (TEC) with the hope that it will retain precise 3-dimensional morphologic features after transplantation. Transplanted TEC is described in terms of the gross morphologic and histologic characteristics in contrast to pretransplanted TEC.

METHODS

Synthetic scaffolds of a polyglycolic acid and poly-l-lactic acid polymer, coated with chondrocytes derived from rabbit auricular cartilage in concentrations ranging from 2.7 x 10(6)/mL to 6 x 10(7)/mL, were incubated in vivo on the dorsum of a rabbit for 8 weeks and then retrieved. The resultant TEC specimens were then sculpted into defined shapes and transplanted into a different location in the same rabbit, where they were allowed to incubate for another 8 weeks. The specimens were then retrieved and compared with the TEC before transplantation according to size, weight, and histomorphometric analysis.

RESULTS

Thirteen chondrocyte-laden templates were successfully engineered to develop TEC. In each case, they were sculpted and transplanted to a different site in the same rabbit. Eight weeks after transplantation, all sculpted TEC specimens lost their original 3-dimensional morphologic features and experienced a significant decrease in mass. Histologically, the staining intensity of both hemotoxylin-eosin and safranin O was dramatically reduced following transplantation. In addition, there was a reduction in chondrocyte viability. Two consistent histologic findings were a foreign-body reaction to the synthetic polymer and ongoing cellular activity directed toward the formation of bone.

CONCLUSIONS

Transplanting autogenous TEC does not allow the preservation of precise morphologic features that are needed for clinical implantation. The osteogenic progression and foreign-body reaction must also be controlled.

Cell-based therapies and tissue engineering

Tissue engineering is a rapidly evolving discipline that may some-day afford surgeons a limitless supply of autologous tissue for transplantation or allow in situ tissue regeneration. A number of biologic, engineering, and clinical challenges continue to face tissue engineers and surgeons alike. One important example is the choice of an appropriate cell scaffold that promotes growth and is eventually resorbed by the body. Although the application of bioengineered tissue is specific to the anatomic areas of interest,continued advances bring tissue engineering closer to reality in all areas of otolaryngology.