Differentiation of Equine Mesenchymal Stem Cells into Cells of Osteochondral Lineage: Potential for Osteochondral Tissue Engineering

Damage to the hyaline cartilage of the joint surface and osteochondral fractures are key factors leading to the development of osteoarthritis in racehorses, representing a significant cause of racehorse retirement. To tissue-engineer an osteochondral unit that is suitable for joint repair, incorporation of a zone of calcified cartilage should be considered so as to mimic its in vivo counterpart. To date, equine mesenchymal stem cells (eMSCs) have been reported to have multilineage differentiation potential. Yet the generation of a zone of calcified cartilage using eMSCs has not been reported. This work is an initial attempt to generate a zone of calcified cartilage using eMSCs as the single source of cells and collagen as the scaffolding material. Main advantages of using eMSCs over equine deep zone chondrocytes for the generation of a zone of calcified cartilage include no donor site morbidity and their ease of expansion in culture. Initially, we fabricated cartilage-like tissues and bone-like tissues in vitro by differentiating eMSCs towards chondrogenic and osteogenic lineages for 21 days, respectively. We then aggregated the cartilage-like and bone-like tissues together with a layer of undifferentiated eMSCs-collagen gel in between to generate a 3-layer osteochondral unit. A zone of calcified cartilage was found between the cartilage-like and bone-like layers after a 14-day culture in chondrogenic differentiation medium. These results provide a solution towards tissue engineering of equine osteochondral units with interfacial zone without using chondrocytes harvested from the deep zone of healthy articular cartilage, and contribute to the future development of osteochondral tissue engineering strategies for human cartilage injuries in the long run.

Multiphoton microfabrication and micropatterning (MMM) - An all-in-one platform for engineering biomimetic soluble cell niches

Engineered biomimetic cell niches represent a valuable in vitro tool for investigating physiological and pathological cellular activities, while developing an all-in-one technology to engineer cell niches, particularly soluble cell niche factors, with retained bioactivities, remains challenging. Here, we report a mask-free, non-contact and biocompatible multiphoton microfabrication and micropatterning (MMM) technology in engineering a spatially and quantitatively controllable bone morphogenetic protein-2 (BMP-2) soluble niche, by immobilizing optimally biotinylated BMP-2 (bBMP-2) on micro-printed neutravidin (NA) micropatterns. Notably, the micropatterned NA bound-bBMP-2 niche elicited a more sustained and a higher level of the downstream Smad signaling than that by free BMP-2, in C2C12 cells, suggesting the advantages of immobilizing soluble niche factors on engineered micropatterns or scaffold materials. This work reports a universal all-in-one cell niche engineering platform and contributes to reconstituting heterogeneous native soluble cell niches for signal transduction modeling and drug screening studies.

Cell-derived matrices (CDM)-Methods, challenges and applications

Extracellular matrix (ECM) provides both physical support and bioactive signals such as growth factors and cytokines to cells at their microenvironment or niche. Engineering the matrix niche becomes an important approach to study or manipulate cellular fate. This work presents an overview on the reconstitution of the ECM niche through a wide range of approaches ranging from coating culture dish with ECM molecules to decellularization of native tissues. In particular, we focused on reconstituting the complex ECM niche through cell-derived matrix (CDM) by reviewing the methodological approaches used in our group to derive ECM from mature cells such as chondrocytes and nucleus pulposus cells (NPCs), undifferentiated stem cells such as mesenchymal stem cells (MSCs), as well as MSCs undergoing chondrogenic and osteogenic differentiation, in 2D or 3D models. Specific attention has also been given to key factors that should be considered in various applications and challenges in relation to the CDM. Last but not the least, a few future perspectives and their significance have been proposed.

Multiphoton Fabrication of Fibronectin-Functionalized Protein Micropatterns: Stiffness-Induced Maturation of Cell-Matrix Adhesions in Human Mesenchymal Stem Cells

Cell-matrix adhesions are important structures governing the interactions between cells and their microenvironment at the cell-matrix interface. The focal complex (FC) and focal adhesion (FA) have been substantially investigated in conventional planar culture systems using fibroblasts as an in vitro model. However, the formation of more mature types of cell-matrix adhesion in human mesenchymal stem cells (hMSCs), including fibrillar adhesion (FBA) and 3D matrix adhesion (3DMA), have not been fully elucidated. Here we investigate the niche factor(s) that influence(s) the maturation of FBA and 3DMA by using multiphoton fabrication-based micropatterning. First, the bovine serum albumin (BSA)-made protein micropatterns were functionalized by incorporating various concentrations of fibronectin (FN) in fabrication solution. The amount of cross-linked FN is positively correlated with the initial concentration of FN in the reaction liquid, as verified by immunofluorescence staining. On the other hand, the anisotropic FN-functionalized micropatterns were fabricated by varying the length (i.e., in-plane stiffness) and height (i.e., bending stiffness) of micropatterns, respectively. Finally, hMSCs were cultured on these micropatterns for 2 h and 1 day to determine the formation of FBA and 3DMA, respectively, using immunofluorescence staining. Results demonstrated that FN-functionalized micropatterns with high anisotropy in x-y dimension benefit FBA maturation. Furthermore, niche factors such as higher bending and in-plane stiffness and the presence of abundant fibronectin have a positive effect on the maturation of FN-based cell-matrix adhesion. These findings could provide some new perspectives on designing platforms for further cell niche study and rationalizing scaffold design for tissue engineering.

Tick bite and Lyme disease-related emergency department encounters in New Hampshire, 2010-2014

Lyme disease (LD) is a common tick-borne disease in New Hampshire (NH). While LD is a reportable condition and cases are counted for public health surveillance, many more people receive care for tick bites or diagnoses of LD than are reflected in surveillance data. NH's emergency department (ED) data system was queried for tick bite and LD-related encounters. Chief complaint text was queried for words related to LD or tick bites. International Classification of Diseases 9th Revision (ICD-9) codes were queried for the LD diagnosis code (088.81). Emergency department patient data were matched to reportable disease data to determine the proportion of ED patients reported to the health department as a suspected LD case. Data were analysed to calculate frequencies for key demographic and reporting characteristics. From 2010 to 2014, 13,615 tick bite or LD-related ED encounters were identified in NH, with most due to tick bites (76%). Of 3,256 patients with a LD-related ED encounter, 738 (23%) were reported to the health department as a suspected LD case. The geographic distribution of ED patients was similar to reported LD cases; however, the regions of the state that experienced higher rates of ED encounters were different than the regions that observed higher rates of reported LD cases. Seasonal distribution of ED encounters peaked earlier than reported LD cases with a second peak in the fall. While age and sex distribution was similar among ED patients and reported LD cases, the rates for children 5 years and younger and adults 65 years and older were greater for ED encounters. Patients frequently visit the ED to seek care for tick bites and suspected LD. Results of ED data analyses can be used to target education, in particular for ED providers and the public through timely distribution of evidence-based educational materials and training programmes.

Time-stretch microscopy on a DVD for high-throughput imaging cell-based assay

Cell-based assay based on time-stretch imaging is recognized to be well-suited for high-throughput phenotypic screening. However, this ultrafast imaging technique has primarily been limited to suspension-cell assay, leaving a wide range of solid-substrate assay formats uncharted. Moreover, time-stretch imaging is generally restricted to intrinsic biophysical phenotyping, but lacks the biomolecular signatures of the cells. To address these challenges, we develop a spinning time-stretch imaging assay platform based on the functionalized digital versatile disc (DVD). We demonstrate that adherent cell culture and biochemically-specific cell-capture can now be assayed with time-stretch microscopy, thanks to the high-speed DVD spinning motion that naturally enables on-the-fly cellular imaging at an ultrafast line-scan rate of >10MHz. As scanning the whole DVD at such a high speed enables ultra-large field-of-view imaging, it could be favorable for scaling both the assay throughput and content as demanded in many applications, e.g. drug discovery, and rare cancer cell screening.

Sustained Delivery of Bioactive GDNF from Collagen and Alginate-Based Cell-Encapsulating Gel Promoted Photoreceptor Survival in an Inherited Retinal Degeneration Model

Encapsulated-cell therapy (ECT) is an attractive approach for continuously delivering freshly synthesized therapeutics to treat sight-threatening posterior eye diseases, circumventing repeated invasive intravitreal injections and improving local drug availability clinically. Composite collagen-alginate (CAC) scaffold contains an interpenetrating network that integrates the physical and biological merits of its constituents, including biocompatibility, mild gelling properties and availability. However, CAC ECT properties and performance in the eye are not well-understood. Previously, we reported a cultured 3D CAC system that supported the growth of GDNF-secreting HEK293 cells with sustainable GDNF delivery. Here, the system was further developed into an intravitreally injectable gel with 1x10⁴ or 2x10⁵ cells encapsulated in 2mg/ml type I collagen and 1% alginate. Gels with lower alginate concentration yielded higher initial cell viability but faster spheroid formation while increasing initial cell density encouraged cell growth. Continuous GDNF delivery was detected in culture and in healthy rat eyes for at least 14 days. The gels were well-tolerated with no host tissue attachment and contained living cell colonies. Most importantly, gel-implanted in dystrophic Royal College of Surgeons rat eyes for 28 days retained photoreceptors while those containing higher initial cell number yielded better photoreceptor survival. CAC ECT gels offers flexible system design and is a potential treatment option for posterior eye diseases.

Injectable microcryogels reinforced alginate encapsulation of mesenchymal stromal cells for leak-proof delivery and alleviation of canine disc degeneration

In situ crosslinked thermo-responsive hydrogel applied for minimally invasive treatment of intervertebral disc degeneration (IVDD) may not prevent extrusion of cell suspension from injection site due to high internal pressure of intervertebral disc (IVD), causing treatment failure or osteophyte formation. In this study, mesenchymal stromal cells (MSCs) were encapsulated in alginate precursor and loaded into previously developed macroporous PGEDA-derived microcryogels (PMs) to form three-dimensional (3D) microscale cellular niches, enabling non-thermo-responsive alginate hydrogel to be injectable. The PMs reinforced alginate hydrogel showed superior elasticity compared to alginate hydrogel alone and could well protect encapsulated cells through injection. Chondrogenic committed MSCs in the injectable microniches expressed higher level of nucleus pulposus (NP) cell markers compared to 2D cultured cells. In an ex vivo organ culture model, injection of MSCs-laden PMs into NP tissue prevented cell leakage, improved cell retention and survival compared to free cell injection. In canine IVDD models, alleviated degeneration was observed in MSCs-laden PMs treated group after six months which was superior to other treated groups. Our results provide in-depth demonstration of injectable alginate hydrogel reinforced by PMs as a leak-proof cell delivery system for augmented regenerative therapy of IVDD in canine models.

Assessment of intracranial collaterals on CT angiography in anterior circulation acute ischemic stroke

BACKGROUND AND PURPOSE

Intracranial collaterals influence the prognosis of patients treated with intravenous tissue plasminogen activator in acute anterior circulation ischemic stroke. We compared the methods of scoring collaterals on pre-tPA brain CT angiography for predicting functional outcomes in acute anterior circulation ischemic stroke.

MATERIALS AND METHODS

Two hundred consecutive patients with acute anterior circulation ischemic stroke treated with IV-tPA during 2010-2012 were included. Two independent neuroradiologists evaluated intracranial collaterals by using the Miteff system, Maas system, the modified Tan scale, and the Alberta Stroke Program Early CT Score 20-point methodology. Good and extremely poor outcomes at 3 months were defined by modified Rankin Scale scores of 0-1 and 5-6 points, respectively.

RESULTS

Factors associated with good outcome on univariable analysis were younger age, female sex, hypertension, diabetes mellitus, atrial fibrillation, small infarct core (ASPECTS ≥8), vessel recanalization, lower pre-tPA NIHSS scores, and good collaterals according to Tan methodology, ASPECTS methodology, and Miteff methodology. On multivariable logistic regression, only lower NIHSS scores (OR, 1.186 per point; 95% CI, 1.079-1.302; P = .001), recanalization (OR, 5.599; 95% CI, 1.560-20.010; P = .008), and good collaterals by the Miteff method (OR, 3.341; 95% CI, 1.203-5.099; P = .014) were independent predictors of good outcome. Poor collaterals by the Miteff system (OR, 2.592; 95% CI, 1.113-6.038; P = .027), Maas system (OR, 2.580; 95% CI, 1.075-6.187; P = .034), and ASPECTS method ≤5 points (OR, 2.685; 95% CI, 1.156-6.237; P = .022) were independent predictors of extremely poor outcomes.

CONCLUSIONS

Only the Miteff scoring system for intracranial collaterals is reliable for predicting favorable outcome in thrombolyzed acute anterior circulation ischemic stroke. However, poor outcomes can be predicted by most of the existing methods of scoring intracranial collaterals.

Photochemically crosslinked collagen annulus plug: a potential solution solving the leakage problem of cell-based therapies for disc degeneration

Intra-disc injection of mesenchymal stem cells (MSCs) to treat disc degeneration may lead to unfavorable complications, particularly osteophyte formation. Development of an effective method to block the injection portal, prevent the leakage of injected cells and materials and, hence, prevent osteophyte formation is of the utmost importance before MSC-based therapies can be applied in a clinical setting. Here we seek to alleviate the cell leakage problem and the associated complication osteophyte formation by developing an injectable annulus plug to block the injection portal during intra-disc delivery. Specifically, we fabricated a needle-shaped collagen plug by photochemical crosslinking and successfully delivered it intra-discally, in association with MSCs in collagen microsphere carriers, using a custom-made delivery device. The mechanical performance of the plug and its effectiveness in reducing cell leakage were evaluated ex vivo under compression and in torsion push-out tests. The results demonstrate that the plug survived physiologically relevant loadings and significantly reduced leakage and enhanced retention of the injected materials. Finally, a pilot in vivo study in rabbits was conducted to evaluate the performance of the plug. Microcomputed tomography imaging and histology revealed that the plug significantly reduced osteophyte formation. This work suggests the potential of the annulus plug as an adjunct or annulus closure device for intra-disc delivery of cells and materials.

Bidirectional and mutually beneficial interactions between human mesenchymal stem cells and osteoarthritic chondrocytes in micromass co-cultures

Aim: Mesenchymal stem cell (MSC)-based therapy presents a promising approach for treating osteoarthritis (OA). However, the molecular interactions between MSCs and OA chondrocytes (OACs) are not known. This study aims to investigate the bidirectional interactions between human MSCs (hMSCs) and human OACs (hOACs) in a 3D co-culture system. Materials & methods: hMSC–collagen microspheres were cultured in hOAC-conditioned medium or co-cultured with hOAC–collagen microspheres. Growth characteristics, glycosaminoglycan (GAG) production, gene expression of major OA-associated chondrogenic markers, including SOX9, COL2A1, ACAN and MMP13, were investigated in both cell types. Results: Both the conditioned medium and the co-culture induced MSC chondrogenesis with enhanced GAG production, SOX9 gene and protein expression, and gene expression of ACAN and COL2A1. Meanwhile, the co-culture also induced hOACs to partially resume the lost chondrogenic phenotype as shown by reduced proliferation, enhanced GAG production when hMSCs were chondrogenically predifferentiated, and reduced MMP13 gene expression. Conclusion: This work suggests that 3D co-culture of hMSCs and hOACs is mutually beneficial to each other, suggesting the potential therapeutic effect of delivering hMSC in scaffolds directly to OA defects.

Chemical modification of collagen improves glycosaminoglycan retention of their co-precipitates

Being prevalent extracellular matrix components, collagen and glycosaminoglycan (GAG) are co-precipitated as scaffolds for tissue regeneration. However, the amount of GAG incorporated and its long-term retention present a persistent problem. In this study, chemical modifications, namely deamination, methylation and amination, were used to alter the net charge of collagen prior to fabrication of collagen-GAG co-precipitate. While most GAGs were lost in the untreated group and the deaminated group within 1 day, methylation and amination of collagen retained over 20% and 40% GAG after 6 days, respectively. Moreover, over 60% of GAG retention was achieved in the aminated group after cell seeding for 8 days. Furthermore, amination of collagen increased the GAG/hydroxyproline ratio in the co-precipitate to >4.5, approaching that of native nucleus pulposus. Ultrastructural analysis showed that the aminated group contains abundant granular substances resembling the extracellular matrix of native nucleus pulposus. Despite lower initial cell adhesion than untreated, all modified scaffolds promoted proliferation of human mesenchymal stem cells (hMSCs) and showed >95% cell viability at all time points. Cell morphology was distinct among the different groups, being round in the untreated control and methylated groups but elongated in deaminated and aminated groups. hMSCs adhered to scaffolds via collagen receptor integrin α2β1 in all groups, while all but the aminated group showed extensive expression of the general matrix receptor integrin αv. This work reports an effective method, namely amination of collagen, to improve GAG incorporation and retention in collagen-GAG co-precipitates, facilitating the fabrication of GAG-rich collagenous scaffold for intervertebral disc tissue engineering.

Changing trends in rectal cancer surgery in Ontario: 2002-2009

AIM

The safety and efficacy of laparoscopic surgery for colon cancer have been demonstrated in large, multicentre clinical trials. The study aimed to determine the use of laparoscopic surgery for rectal cancer in Ontario over a 7-year period.

METHOD

We conducted a retrospective study examining rates of elective rectal cancer surgery among 10.5 million adults in Ontario, Canada, from 1 April 2002 to 31 March 2009. We linked the Canadian Institute for Health Information Discharge Abstract Database, the Registered Persons Database and the database of the Ontario Cancer Registry to assess procedures used over the period. Data on demographics were collected. Trends were assessed using time series analysis.

RESULTS

Over the 7-year period, 8189 open and 1079 laparoscopic elective operations for rectal cancer were identified. The annual rate of laparoscopic rectal cancer procedures increased from 0.60 per 100,000 population in 2003 to 2.24 per 100,000 population in 2008 (P < 0.01). Laparoscopic patients were similar to open with respect to age (66.5 ± 11.8 vs 66.2 ± 12.1 years; standardized difference 0.02), gender (63.2%vs 59.4%; standardized difference 0.08), Charlson Comorbidity Index score (standardized difference < 0.1) and socioeconomic status (standardized difference < 0.1).

CONCLUSION

Laparoscopic rectal cancer surgery rates are increasing in Ontario. Ongoing research regarding the long-term safety and effectiveness of the laparoscopic approach for rectal cancer surgeries may lead to greater increases in its utilization.

Compression-induced alignment and elongation of human mesenchymal stem cell (hMSC) in 3D collagen constructs is collagen concentration dependent

Controlling cell organization is important in tissue engineering. Guidance by aligned features on scaffolds or stimulation by physical signals can be used to induce cell alignment. We have previously demonstrated a preferred alignment of human MSCs (hMSCs) along the compression loading axis in 3D collagen construct. In this study, we aim to investigate the collagen concentration dependence of the compression-induced hMSC organization. Results demonstrated that the compression-induced alignment and elongation of hMSCs exhibited a biphasic dose-dependent relationship with collagen concentration, and associated well with both collagen ligand density and elastic modulus of the constructs. Moreover, collagen concentration and compression loading significantly affected the expression level of integrin beta 1 and antibody neutralization against this molecule aborted the compression-induced alignment and elongation responses.

Trends in colon cancer surgery in Ontario: 2002-2009

AIM

The safety and efficacy of laparoscopic surgery for colon cancer is well established but its uptake in the province has not been previously explored. We report an investigation of the trends of open and laparoscopic surgery for colon cancer in Ontario, Canada.

METHOD

A retrospective cross-sectional time-series analysis examining population-based rates of elective surgery for colon cancer among 10.5 million adults in Ontario was conducted from 1 April 2002 to 31 March 2009. Databases were linked to assess quarterly elective procedure rates over time.

RESULTS

During the study period, 3950 laparoscopic and 13 048 open elective colon cancer operations were performed in Ontario. The overall quarterly rate of colon cancer surgery remained stable at an average of 5.8 per 100000 population (P=0.10). From the first and last quarter, the rate of laparoscopic operations increased nearly threefold from 0.8 to 2.2 per 100000 population with a notable increase after 2005 (P<0.01). In contrast, open surgery decreased by more than 30% from 5.3 to 3.5 per 100 000 population (P<0.01). If current trends continue, the projected proportion of laparoscopic colon operations is estimated to reach 41% by 2015. Patients receiving open surgery had a significantly higher preoperative comorbidity (Charlson comorbidity score≥3) than those having laparoscopy (47.8%vs 39.1%, standardized difference 0.26).

CONCLUSION

Trends in Ontario of laparoscopic colon cancer surgery show an increase between 2002 and 2009, but the incidence remains lower than for open surgery.

Nanofibrous collagen nerve conduits for spinal cord repair

Nerve regeneration in an injured spinal cord is often restricted, contributing to the devastating outcome of neurologic impairment below the site of injury. Although implantation of tissue-engineered scaffolds has evolved as a potential treatment method, the outcomes remain sub-optimal. One possible reason may be the lack of topographical signals from these constructs to provide contact guidance to invading cells or regrowing axons. Nanofibers mimic the natural extracellular matrix architecturally and may therefore promote physiologically relevant cellular phenotypes. In this study, the potential application of electrospun collagen nanofibers (diameter=208.2±90.4 nm) for spinal cord injury (SCI) treatment was evaluated in vitro and in vivo. Primary rat astrocytes and dorsal root ganglias (DRGs) were seeded on collagen-coated glass cover slips (two-dimensional [2D] substrate controls), and randomly oriented or aligned collagen fibers to evaluate scaffold topographical effects on astrocyte behavior and neurite outgrowth, respectively. When cultured on collagen nanofibers, astrocyte proliferation and expression of glial fibrillary acidic protein (GFAP) were suppressed as compared to cells on 2D controls at days 3 (p<0.05) and 7 (p<0.01). Aligned fibers resulted in elongated astrocytes (elongation factor >4, p<0.01) and directed the orientation of neurite outgrowth from DRGs along fiber axes. In the contrast, neurites emanated radially on randomly oriented collagen fibers. By forming collagen scaffolds into spiral tubular structures, we demonstrated the feasibility of using electrospun nanofibers for the treatment of acute SCI using a rat hemi-section model. At days 10 and 30 postimplantation, extensive cellular penetration into the constructs was observed regardless of fiber orientation. However, scaffolds with aligned fibers appeared more structurally intact at day 30. ED1 immunofluorescent staining revealed macrophage invasion by day 10, which decreased significantly by day 30. Neural fiber sprouting as evaluated by neurofilament staining was observed as early as day 10. In addition, GFAP immunostained astrocytes were found only at the boundary of the lesion site, and no astrocyte accumulation was observed in the implantation area at any time point. These findings indicate the feasibility of fabricating 3D spiral constructs using electrospun collagen fibers and demonstrated the potential of these scaffolds for SCI repair.

Tissue engineering for intervertebral disk degeneration

Many challenges confront intervertebral disk engineering owing to complexity and the presence of extraordinary stresses. Rebuilding a disk of native function could be useful for removal of the symptoms and correction of altered spine kinematics. Improvement in understanding of disk properties and techniques for disk engineering brings promise to the fabrication of a functional motion segment for the treatment of disk degeneration. Increasing sophistication of techniques available in biomedical sciences will bring its application into clinics. This review provides an account of current progress and challenges of intervertebral disk bioengineering and discusses means to move forward and toward bedside translation.

Three-dimensional culture of rabbit nucleus pulposus cells in collagen microspheres

BACKGROUND

Degenerative disc disease poses an increasing threat to our quality of life as we age. Existing treatments have limitations. New treatment modalities focusing on biologic rather than surgical approach would be appealing.

PURPOSE

Culturing intervertebral disc cells in a three-dimensional (3D) model that can retain cellular characteristics and phenotype is a critical step toward understanding how the disc cells respond to and interact with extrinsic signals before better therapeutics can be derived.

STUDY DESIGN

In this work, we studied the culture of rabbit nucleus pulposus (NP) cells in a collagen microsphere system and compared their cell morphology and expression of a few potential phenotypic markers with that in monolayer culture.

METHODS

Specifically, rabbit NP cells isolated from both young and old animals were encapsulated and cultured in collagen microspheres with different monomeric concentrations and with different cell encapsulation density for different period of time. Evaluation on the growth kinetics, the viability, the cell morphology, the expression of Types I and II collagen, glycosaminoglycans (GAGs), and Keratin 19, and the ultrastructure of the fiber meshwork were conducted to compare the microsphere 3D culture system and the traditional monolayer cultures.

RESULTS

Nucleus pulposus cells in two-dimensional culture lost the phenotypic expression of Type II collagen and keratin 19 and expressed Type I collagen. In contrast, the 3D collagen microsphere culture system consistently outperformed the traditional monolayer culture in maintaining a round morphology and preserving the phenotypes of NP cells with persistent expression of Type II collagen and Keratin 19. These cells also remodeled the template collagen matrix in the microspheres by depositing new matrices, including collagen Type II and GAGs in a cell seeding density and collagen concentration dependent manner.

CONCLUSIONS

This study demonstrates the appeal of the 3D collagen microsphere system for NP cell culture over traditional monolayer culture because it preserves the phenotypic characteristics of NP cells. This system also enables the NP cells to remodel the template collagen matrix by depositing new matrices, suggesting an innovative way to reconstitute cell-specific and native tissue-like environment in vitro for future studies on stem cell matrix niche and interactions of NP cell with extrinsic factors.

Photochemical crosslinked electrospun collagen nanofibers: synthesis, characterization and neural stem cell interactions

Currently available crosslinking methods for electrospun collagen nanofibers do not preserve the fibrous architecture over prolonged periods of time. In addition, electrospinning of collagen often involves solvents that lead to extensive protein denaturation. In this study, we demonstrate the advantage of acetic acid over 1,1,1,3,3,3 hexafluoroisopropanol (HFP) in preventing collagen denaturation. A novel photochemical crosslinking method using rose bengal as the photoinitiator is also introduced. Using circular dichorism analyses, we demonstrate the fraction of collagen helical structure to be significantly greater in acetic acid-spun fibers than HFP-spun fibers (28.9 +/- 5.9% vs. 12.5 +/- 2.0%, p < 0.05). By introducing 0.1% (w/v) rose bengal into collagen fibers and subjecting these scaffolds to laser irradiation at a wavelength of 514 nm for 100 sec, biodegradable crosslinked scaffolds were obtained. Scaffold degradation as evaluated by soaking crosslinked collagen scaffolds in PBS at 37 degrees C, indicated a mass loss of 47.7 +/- 7.4% and 68.9 +/- 24.7% at day 7 and day 15, respectively. However, these scaffolds retained fibrous architecture for at least 21 days under physiological conditions. Neural stem cell line, C17.2, cultured on crosslinked collagen scaffolds proliferated after 7 days by forming a confluent layer of cells with extensive cellular projections that were indicative of neurite outgrowth. Taken together, these findings support the potential of acetic acid-electrospun photochemical crosslinked collagen nanofibers for neural tissue engineering.

Correlation between compositional and mechanical properties of human mesenchymal stem cell-collagen microspheres during chondrogenic differentiation

Mesenchymal stem cell (MSC)-based engineering is promising for cartilage repair. However, the compositional mechanical relationship of the engineered structures has not been extensively studied, given the importance of such relationship in native cartilage tissues. In this study, a novel human MSC-collagen microsphere system was used to study the compositional mechanical relationship during in vitro chondrogenic differentiation using histological and biochemical methods and a microplate compression assay. The mechanical property was found positively correlating with newly deposited cartilage-relevant matrices, glycosaminoglycan, and type II collagen, and with the collagen crosslinker density, in agreement with the presence of thick collagen bundles upon structural characterization. On the other hand, the mechanical property negatively correlates with type I collagen and total collagen, suggesting that the initial collagen matrix scaffold of the microsphere system was being remodeled by the differentiating human MSCs. This study also demonstrated the application of a simple, sensitive, and nondestructive tool for monitoring the progression of chondrogenic differentiation of MSCs in tissue-engineered constructs and therefore contributes to future development of novel cartilage repair strategies.

In vitro generation of an osteochondral interface from mesenchymal stem cell-collagen microspheres

Creating biological interfaces between mechanically dissimilar tissues is a key challenge in complex tissue engineering. An osteochondral interface is essential in preventing mechanical failure and maintaining normal function of cartilage. Despite tremendous efforts in developing osteochondral plugs, formation of the osteochondral interface with proper zonal organization has not yet been reported. Here, we present a mesenchymal stem cell-collagen microsphere-based approach for complex tissue engineering and demonstrate in vitro formation of a stem cell-derived osteochondral interface with calcified cartilage interface separating a non-calcified cartilage layer and an underlying bone layer. Cells at the interface region are hypertrophic chondrocytes while the extracellular matrix in this region contains collagen type II and X, calcium deposits and vertically running fibers. The simultaneous presence of appropriate medium and configuration during co-culture is necessary for the interface formation.

Decellularization of chondrocyte-encapsulated collagen microspheres: a three-dimensional model to study the effects of acellular matrix on stem cell fate

Extracellular matrix (ECM) partially constitutes the stem cell niche. Reconstituting the ECM niche in a three-dimensional (3D) configuration will significantly enhance our understanding of how stem cells interact with and respond to the ECM niche. In this study, we aimed to reconstitute a glycosaminoglycan (GAG)-rich ECM using a microencapsulation technology, produce acellular matrix using a decellularization technique, and investigate the effect of acellular matrix on stem cell fate by repopulating the matrix with human mesenchymal stem cells (hMSCs). We demonstrated that porcine chondrocytes were able to deposit a GAG-rich ECM within the 3D collagen microsphere. All decellularization treatment groups resulted in significant removal of chondrocyte nuclei, but acellular matrix was only achieved using 2% sodium deoxycholate. Nevertheless, decellularization resulted in significant loss in GAG content in almost all treatment groups, and the 2% sodium deoxycholate group was able to preserve about 40% of the GAGs compared with the control group. We further demonstrated that hMSCs seeded onto the decellularized microspheres were able to survive and penetrate into the centre, while hMSCs seeded in the acellular matrix showed positive immunostaining against sox9, indicating that they may be differentiating toward the chondrogenic lineage without the need to supplement the chondrogenic differentiation medium.

Scaffolding in tissue engineering: general approaches and tissue-specific considerations

Scaffolds represent important components for tissue engineering. However, researchers often encounter an enormous variety of choices when selecting scaffolds for tissue engineering. This paper aims to review the functions of scaffolds and the major scaffolding approaches as important guidelines for selecting scaffolds and discuss the tissue-specific considerations for scaffolding, using intervertebral disc as an example.

In vitro chondrogenic differentiation of human mesenchymal stem cells in collagen microspheres: influence of cell seeding density and collagen concentration

Given the inadequacies of existing repair strategies for cartilage injuries, tissue engineering approach using biomaterials and stem cells offers new hope for better treatments. Recently, we have fabricated injectable collagen-human mesenchymal stem cell (hMSC) microspheres using microencapsulation. Apart from providing a protective matrix for cell delivery, the collagen microspheres may also act as a bio-mimetic matrix facilitating the functional remodeling of hMSCs. In this study, whether the encapsulated hMSCs can be pre-differentiated into chondrogenic phenotype prior to implantation has been investigated. The effects of cell seeding density and collagen concentration on the chondrogenic differentiation potential of hMSCs have been studied. An in vivo implantation study has also been conducted. Fabrication of cartilage-like tissue micro-masses was demonstrated by positive immunohistochemical staining for cartilage-specific extracellular matrix components including type II collagen and aggrecan. The meshwork of collagen fibers was remodeled into a highly ordered microstructure, characterized by thick and parallel bundles, upon differentiation. Higher cell seeding density and higher collagen concentration favored the chondrogenic differentiation of hMSCs, yielding increased matrix production and mechanical strength of the micro-masses. These micro-masses were also demonstrated to integrate well with the host tissue in NOD/SCID mice.

Fabrication of nano-fibrous collagen microspheres for protein delivery and effects of photochemical crosslinking on release kinetics

Protein compatibility is important for protein drug delivery using microsphere-based devices. Collagen has excellent protein compatibility but has poor mechanical stability for microsphere fabrication and open meshwork for controlled release. In this study, a protein-compatible fabrication method for injectable collagen microspheres has been developed. The surface morphology, interior microstructure and protein release characteristics of collagen microspheres were investigated. Moreover, effects of photochemical crosslinking on these characteristics were also studied. Finally, the mechanisms governing the protein release and the retention of protein bioactivity were studied. Stable and injectable collagen microspheres consisting of nano-fibrous meshwork were successfully fabricated under ambient conditions in an organic solvent and crosslinking reagent-free manner. These microspheres have open meshwork and showed large initial burst and rapid release of proteins. Photochemical crosslinking significantly reduced the initial burst effect and controlled the protein release in a photosensitizer dose-dependent manner without significantly altering the mesh size. We further demonstrated that there was significantly higher protein retention within the photochemically crosslinked collagen microspheres as compared with the uncrosslinked, suggesting a secondary retention mechanism. Lastly, both surfactant treatment and photochemical crosslinking did not compromise the bioactivity of the encapsulated proteins. In summary, this study reports a novel collagen microsphere-based protein delivery system and demonstrates the possibility to use photochemical crosslinking as the secondary retention mechanism for proteins.

Self-assembled collagen–human mesenchymal stem cell microspheres for regenerative medicine

Mesenchymal stem cells (MSCs)-based therapy is a promising approach in regenerative medicine and tissue engineering. However, the outcomes of existing treatments have not been satisfactory owing to suboptimal localization to implantation site, poor viability, low engraftment efficacy and lack of functional remodeling of the delivered cells. Therefore, adopting an effective cell delivery modality is among the biggest technological challenges for successful clinical applications of MSC-based therapy. We developed a novel microencapsulation technique producing self-assembled collagen-MSC microspheres and demonstrated that these microspheres could serve as excellent cell delivery devices as they were stable, injectable and able to provide a protective, growth- and migration-supporting matrix to MSCs. We also showed that MSCs could preserve their stem cell nature upon microencapsulation and easily be localized with retained viability upon in vivo implantation. These microspheres present novel cell delivery devices with optimal biological and functional profile that may facilitate clinical applications of MSC-based therapy.

Photochemical cross-linking for collagen-based scaffolds: a study on optical properties, mechanical properties, stability, and hematocompatibility

Collagen presents an attractive biomaterial for tissue engineering because of its excellent biocompatibility and negligible immunogenicity. However, some intrinsic features related to the mechanical stability and thrombogenicity limit its applications in orthopedic and vascular tissue engineering. Photochemical cross-linking is an emerging technique able to stabilize tissue grafts and improve the physicochemical properties of collagen-based structures. However, other important properties of collagen-based structures and the effect of processing parameters on these properties have not been explored. In this study, we aim to investigate the dose dependence of tensile and swelling properties on two parameters, namely, laser energy fluence and rose Bengal photosensitizer concentration. We also study the compression properties using cyclic compression test, long-term stability using subcutaneous implantation, and hematocompatibility using platelets adhesion test, of cross-linked collagen structures. Moreover, because limited optical penetration in turbid media is the major obstacle for light-based techniques, we also characterize the optical properties, which partially determine the effective optical penetration depth in collagen gel samples, during photochemical cross-linking. Laser energy fluence and rose Bengal concentration are important parameters affecting the cross-linking efficiency, which was characterized as the mechanical and the swelling properties, in a dose-dependent manner. Under the experimental conditions in this study, the peak fluence was 12.5 J/cm2 and the minimal rose Bengal concentration for effective cross-linking was >0.00008% (0.786 micromol). Photochemical cross-linking also enhanced the compression strength and long-term stability of collagen structures without compromising the tissue compatibility. Furthermore, photochemical cross-linking reduced platelet adhesion and abolished fibrin mesh formation, thereby improving the hematocompatibility of collagen structures. These results suggest the feasibility of using the photochemically cross-linked collagen structures for orthopedic and vascular tissue engineering. Finally, the effective optical penetration depth in collagen gel samples is wavelength and rose Bengal concentration dependent, and was approximately 12 mm at 514 nm at 0.001% (9.825 micromol), the rose Bengal concentration mostly used in this study.

Mathematical modeling of guided neurite extension in an engineered conduit with multiple concentration gradients of nerve growth factor (NGF)

Neurotrophic factors such as nerve growth factor (NGF) provide essential cues to navigate growing axon toward their targets. Concentration and concentration gradient of NGF are key parameters affecting the growth rate and direction of neurites and axons. However, the maximum distance for guided nerve growth under stimulation of a single concentration gradient is limited and is thus unfavorable in nerve regeneration. Since the sensitivity of PC12 cells to NGF signals is restorable even after brief removal of the factors, exposure to multiple concentration gradients of the factor can achieve longer distances and greater rates of guided growth. In this study, a mathematical model simulating nerve growth in a virtually constructed nerve conduit incorporating multiple NGF concentration gradients is established. Using a genetic algorithm, optimized initial profiles of NGF able to achieve 4.5 cm of guided growth with a significantly improved growth rate has been obtained. The model also predicts an inverse relationship between the diffusion coefficient of the factor and the neurite growth rate. This model provides a useful tool for evaluating various conduit designs before fabrication and evaluation.

Supplementation-time dependence of growth factors in promoting tendon healing

Growth factors potentially promote tendon healing. Understanding the right time to administer growth factors and the dosage of growth factors are prerequisites for designing effective cytokine therapy. We investigated the supplementation-time dependence of the effects of platelet-derived growth factor isoform B at various dosages on tendon healing, and the temporal responsiveness of healing tendon toward platelet-derived growth factor. Platelet-derived growth factor isoform B at various dosages (0, 10, 100, or 1000 ng) was delivered into the gap wound of rat patellar tendons via microsyringe injection on Day 3 or Day 7 after injury. Tendon specimens were harvested on Day 14 for measurement of cell proliferation, pyridinoline content, and mechanical properties. We found increased proliferative response only when the growth factor was supplemented on Day 3 after injury, whereas supplementation on Day 7 resulted in greater peak load, cross-sectional area, and pyridinoline content. The ultimate stress did not change. Our findings suggest supplementation of platelet-derived growth factor isoform B at Day 7 benefits the mechanical properties and maturation of healing tendons. We also found platelet-derived growth factor receptor beta expressing cells at the remodeling site as much as 6 months after injury, suggesting healing tendon also may be responsive to long-term delivery of platelet-derived growth factor.

Photochemical crosslinking improves the physicochemical properties of collagen scaffolds

Collagen is a natural biomaterial with excellent biocompatibility. However, unprocessed collagen has low stability and weak mechanical strength, which limits its application in tissue engineering. The current study aimed to improve the physicochemical properties of collagen scaffolds by using photochemical crosslinking. Collagen gel was reconstituted and photochemically crosslinked by using laser irradiation in the presence of a photosensitizer. Scanning electron microscope was used to characterize the surface and cross-sectional morphology. Stress-strain relationship and other mechanical properties were determined by uniaxial tensile tests. Thermostability and water-binding capacities also were analyzed by using differential scanning calorimetry and swelling ratio measurements, respectively. Photochemically crosslinked porous structures showed fine microstructure with interconnected micron-sized pores, whereas uncrosslinked controls only showed macrosheet-like structures. The stabilizing effect of photochemical crosslinking also was revealed by retaining the three-dimensional lamellae-like structures after thermal analysis in crosslinked membranes but not in the controls. Photochemical crosslinking also significantly reduced the swelling ratio, improved the stress-strain relationship, peak load, ultimate stress, rupture strain, and tangent modulus of collagen membranes. The current study showed that an innovative photochemical crosslinking process was able to produce collagen scaffolds with fine microstructures; to strengthen, stiffen, and stabilize collagen membranes; and to modify their swelling ratio. This may broaden the use of collagen-based scaffolds in tissue engineering, particularly for weight-bearing tissues.

Four-dimensional imaging and quantification of gene expression in early developing zebrafish (Danio rerio) embryos

Four-dimensional (4D) imaging is a powerful tool for studying three-dimensional (3D) changes in an organism through time. Different imaging systems for obtaining 3D data from in vivo specimens have been developed but usually involved large and expensive machines. We successfully used a simple inverted compound microscope and a commercially available program to study and quantify in vivo changes in sonic hedgehog (shh) expression during early development in a green fluorescence protein (GFP) transgenic zebrafish (Danio rerio) line. We applied the 4D system to study the effect of 100 microM cadmium exposure on shh expression. In control zebrafish embryos, shh:GFP expression was detected at about 9 h post-fertilization (hpf) and increased steadily in the next 7 h, peaking at about 17 hpf and decreasing in the following 4 h. In the same time period, different shh expression volumes were observed in cadmium-treated and control embryos. Embryos affected by cadmium-exposure demonstrated a down-regulation in shh expression. The number of GFP-expressing cells measured by flow cytometry decreased, and expression of neurogenin-1, a downstream target of the shh signaling pathway, was down-regulated, providing additional supporting data on the effects of cadmium on shh. In summary, we demonstrated the setup of a 4D imaging system and its application to the quantification of gene expression.

Photochemical repair of Achilles tendon rupture in a rat model1

BACKGROUND

Photochemical tissue bonding (PTB) is an emerging technique for bonding or sealing tissue surfaces that requires light and a photoactive dye for its effect. The potential of PTB for tendon repair was assessed in a rat model.

MATERIALS AND METHODS

The optical properties of bovine tendon were determined ex vivo to gauge the depth of light penetration as a function of wavelength and dosimetry parameters were established for PTB repair of ruptured tendon. PTB was then tested in vivo to repair transected tendons in Sprague-Dawley rats. Repair strengths were measured using a strain gauge up to 14 days post treatment.

RESULTS

The effective penetration depth in tendon was estimated to be 0.68 mm at 514 nm. Following PTB treatment of mechanically ruptured tendon, significant bonding was dependent on the presence of both light and dye and attained a plateau strength at a fluence of 125 J/cm2. In a subsequent in vivo study to investigate PTB for repair of transected rat Achilles tendon, the ultimate stress required to break the repaired tendon was measured immediately after irradiation and at 7 and 14 days post-repair. Results showed that the difference in the ultimate stress between control and PTB treatment groups was statistically significant immediately after treatment and at 7 days (p = 0.04) but not 14 days (p = 0.75) post-repair.

CONCLUSIONS

PTB provides a benefit to tendon repair at early stages in repair and is worthy of further investigation as a potential surgical adjunct for tendon repair in orthopedic surgeries.

Immunomodulating Effects of CKBM on the Cytokine Production in Peripheral Blood Mononuclear Cells (PBMCs) from Healthy Volunteers

The current study investigated the immunomodulating effect of CKBM on cytokine induction in peripheral blood mononuclear cells (PBMCs) isolated from 20 healthy volunteers. Cytometric Bead Analysis (CBA) was used to study IL-2, IL-4, IL-6, IL-10, TNF-alpha and IFN-gamma. TNF-alpha and IL-6 were significantly increased in a CKBM dose- and time-dependent manner. Flow cytometry analysis showed an increased intracellular staining of IL-6 but not of TNF-alpha in CKBM treated PBMCs. In addition, MTT cell cytotoxicity assay showed that CKBM concentrations below 5% did not significantly affect the metabolic activities of PBMCs. The current study indicated that CKBM may modulate the immune response by inducing the secretions of TNF-alpha and IL-6, which are cytokine mediators of innate immunity and inflammation preparing or "priming" the body to combat diseases.

Increased expression of matrix metalloproteinase 1 (MMP1) in 11 patients with patellar tendinosis

We studied the expression of procollagen type I, matrix metalloproteinase 1 (MMP1) and tissue inhibitor of metalloproteinase 1 (TIMP-1) by immunohistochemistry in human patellar tendinosis tissues and healthy patellar tendons. In situ gelatin zymography was used to detect collagenolytic activities. The productions of MMP1, TIMP1 and gelatinolytic activities were compared in cell cultures from tendinosis samples and controls. Tendinosis tissues and cultures showed an increase in the expression level of MMP1 and a decrease in that of TIMP1, a condition favoring collagen degradation. Gelatinolytic activities in tendinosis tissues and cultures were elevated. Collagenolysis is a striking feature in patellar tendinosis.

Enhancement of porcine skin graft adherence using a light-activated process

BACKGROUND

Skin grafts are widely used in plastic surgery, and burn and ulcer wound management. Rapid and sustained adherence, the ability to resist shear stress, and a void-free surface-to-surface contact are critical to the success of graft survival. Mechanical and adhesive fixation aids are currently used to achieve graft adherence and they are not free of problems. Photochemical tissue bonding (PTB) is an emerging laser technique with numerous applications in surgical specialties. In the current study, PTB was investigated as a means to bond and enhance the adherence of skin grafts.

METHODS

In this study, ex vivo porcine skin grafts treated with a photosensitizing dye, rose bengal (RB), were approximated dermis-to-dermis and irradiated with visible light from an argon laser at 514 nm. The adherence of the skin grafts was measured immediately after irradiation. Dose-response relationships between the light and the dye with adherence of the grafts were established. The surface temperature of the skin under irradiation was monitored and the viability of the skin cells in the grafts was also measured.

RESULTS

Results showed that the skin graft adherence was RB dose-dependent in a statistically significant manner with the concentration of RB reaching a plateau value of 0.1% (w/v) of RB. Graft adhesion also increased with laser fluence up to 504 J/cm(2) in the presence of 0.1% RB. No fluence dependence was observed in the absence of RB. Thermogram results showed that the maximal surface temperature during irradiation was less than 40 degrees C. Histological investigation and trypan blue exclusion assays demonstrated that skin grafts retained cell viability and collagen organization after PTB.

CONCLUSIONS

This ex vivo study demonstrates that PTB using argon laser irradiation and RB enhances skin graft adherence by forming dermal-dermal bonding. The increase in adherence is a function of the concentration of RB and the laser fluence. The results also suggest that the PTB is a potentially safe procedure because it is nonthermal in nature and does not significantly affect the skin cell viability.

Variance analysis applied to a stroke pathway: how this can improve efficiency of healthcare delivery

INTRODUCTION

Stroke is a complicated disease that requires a multidisciplinary approach for its management. We postulated that variance analysis applied to a stroke pathway, by identifying major problem areas and encouraging timely corrective actions, would lead to more efficient healthcare delivery to hospitalised stroke patients.

MATERIALS AND METHODS

Prospectively collected variance data from consecutive stroke patients discharged from a tertiary hospital in Singapore during a 3-month period in 2000 were used to identify the major variances causing increased length of stay. These were compared and contrasted to variance data collected during the same 3-month period in the subsequent year (2001), after the implementation of stroke pathway and the availability of monthly variance analysis reports. Patient characteristics and outcome measures were also compared between the two study periods.

RESULTS

The four major variances that accounted for increased length of stay were, in descending order of the number of patients affected, awaiting bed availability in step-down facilities, delay in head computed tomographic scan performance, awaiting family's decision on discharge plan and incomplete application submitted to step-down facilities. After implementation of the stroke pathway with ongoing variance analysis, all four variances showed different extent of improvements. There were no significant differences in patient characteristics between the two study periods, whereas the average length of stay significantly diminished in the late study period with a trend for decreased in-hospital mortality, compared to the early study period.

CONCLUSION

Variance analysis applied in the context of a stroke pathway was effective in identifying major variances causing increased length of stay. This allowed targeted intervention to improve efficiency of healthcare delivery to stroke patients.

Effects of basic fibroblast growth factor (bFGF) on early stages of tendon healing: a rat patellar tendon model

We studied the effects of basic fibroblast growth factor (bFGF) on cell proliferation, type III collagen expression, ultimate stress and the pyridinoline content in the early stages of healing in rat patellar tendon. 96 male Sprague Dawley rats were injected with increasing doses of basic fibroblast growth factor (bFGF) at 3 days after a "window defect" was induced in the mid-part of the patellar tendon. They were killed at 7 and 14 days after the injury. A dose-dependent increase in the number of proliferating cells and the level of expression of type III collagen was demonstrated at only 7 days post-injury. On the other hand, we found no effects of bFGF on ultimate stress and the pyridinoline content of healing tendons. Only time significantly affected both strength-associated parameters. We showed that in vivo supplementation with bFGF affected the initial events of healing such as cell proliferation and type III collagen expression.

An equilibrium model of endothelial cell adhesion via integrin-dependent and integrin-independent ligands

Endothelial cell adhesion can be enhanced by supplementing integrin-mediated adhesion via fibronectin with the high-affinity avidin-biotin system in which biotin is covalently linked to membrane proteins and avidin binds to biotinylated surfaces (Bhat et al. J Biomed Mater Res 1998;41:377-85). An equilibrium model was extended to explain detachment of spreading cells following exposure to flow for this two ligand system. The two different receptor-ligand systems were treated as springs in parallel in which the equilibrium dissociation constant was a function of the separation distance of the cell from the surface. Flow experiments were performed to measure the endothelial cell adhesion strength as a function of the extent of biotinylation of the endothelium. Surfaces contained adsorbed fibronectin, avidin or both ligands. The contact area between the cell membrane and substrate was measured using total internal reflection fluorescence microscopy. Estimates of the unstressed dissociation constant for fibronectin and avidin were determined from data for adhesion strength and contact area of each ligand separately. Using these unstressed equilibrium constants, the model predicted, with reasonable accuracy, the strength of endothelial cell adhesion to surfaces containing fibronectin and avidin. The results indicate that as the extent of biotinylation increases, the avidin-biotin system contributes a larger fraction of the total adhesion strength but the maximum contribution of the avidin-biotin system is less than 50%. The magnitude of the affinity constant and force per bond for the avidin-biotin system are consistent with detachment by extraction of receptors from the cell. The resulting increase in the adhesion strength on surfaces with both avidin-biotin and fibronectin is due to the increase in contact area and the larger number of bonds formed.

Pyridinoline in relation to ultimate stress of the patellar tendon during healing: an animal study

The ultimate stress of the central one-third of the patellar tendon was studied in a gap wound-healing model in the rat. The specimens were also analyzed for collagen and nonreducible crosslinks, as measured by hydroxyproline and pyridinoline content, respectively. Thirty days after injury, the ultimate stress of the healing patellar tendon was restored to an average of 71% of the control value and remained constant over time. The pyridinoline content of the healing tendon was twice the control value by 30 days after injury and reached a plateau; however, the hydroxyproline content did not change significantly over time. Stepwise regression analysis demonstrated that pyridinoline was a better biochemical marker for ultimate stress than was hydroxyproline. The current study provides insights into the functional behaviour of the healing patellar tendon by establishing the relationship between the two biochemical components and the ultimate stress of the healing patellar tendon. This study also suggests the possibility of using pyridinoline content as an indirect marker of the ultimate stress because in vivo assessment is impossible.

Effect of basic fibroblast growth factor. An in vitro study of tendon healing

The effect of basic fibroblast growth factor on the proliferative and chemotactic response of cultured rat patellar tendon fibroblasts was studied in an in vitro wound closure model. In quiescent confluent fibroblast culture, a uniform cell free zone, or wound, was generated mechanically as an in vitro wound. The width of the cell free zone was measured at 0, 6, 12, and 24 hours after the injury, in the presence of 0, 2, 10, or 50 mg/mL of basic fibroblast growth factor. Basic fibroblast growth factor, at a concentration of 10 ng/mL, significantly accelerated wound closure, resulting in almost complete closure by 24 hours after the injury. Basic fibroblast growth factor, at a concentration of 2 ng/mL, significantly enhanced cell proliferation as estimated by 5-Bromo-2'-deoxyuridine incorporation, but increasing the concentration of the growth factor to 50 ng/mL did not show additional improvement. Thus, the enhancement of wound closure by basic fibroblast growth factor may be caused by the cell proliferative response, rather than by chemotaxis.