Search

Collagen is the most abundant component of mammalian extracellular matrices. As such, the development of materials that mimic the biological and mechanical properties of collagenous tissues is an enduring goal of the biomaterials community. Despite the development of molded and 3D printed collagen hydrogel platforms, their use as biomaterials and tissue engineering scaffolds is hindered by either low stiffness and toughness or processing complexity. Here, we demonstrate the development of stiff and tough biohybrid composites by combining collagen with a zwitterionic hydrogel through simple mixing. This combination led to the self-assembly of a nanostructured fibrillar network of collagen that was ionically linked to the surrounding zwitterionic hydrogel matrix, leading to a composite microstructure reminiscent of soft biological tissues. The addition of 5-15 mg mL -1 collagen and the formation of nanostructured fibrils increased the elastic modulus of the composite system by 40% compared to the base zwitterionic matrix. Most notably, the addition of collagen increased the fracture energy nearly 11-fold ([Formula: see text] 180 J m -2 ) and clearly delayed crack initiation and propagation. These composites exhibit elastic modulus ([Formula: see text] 0.180 MJ) and toughness ([Formula: see text]0.617 MJ m -3 ) approaching that of biological tissues such as articular cartilage. Maintenance of the fibrillar structure of collagen also greatly enhanced cytocompatibility, improving cell adhesion more than 100-fold with >90% cell viability.

This article describes the compositional, mechanical, and structural differences between collagen gels fabricated from different sources and processing methods. Despite extensive use of collagen in the manufacturing of biomaterials and implants, there is little information as to the variation in properties based on collagen source or processing methods. As such, differences in purity and composition may affect gel structure and mechanical performance. Using mass spectrometry, we assessed protein composition of collagen from seven different sources. The mechanics and gelation kinetics of each gel were assessed through oscillatory shear rheology. Scanning electron microscopy enabled visualization of distinct differences in fiber morphology. Mechanics and gelation kinetics differed with source and processing method and were found to correlate with differences in composition. Gels fabricated from telopeptide-containing collagens had higher storage modulus (144 vs. 54 Pa) and faster gelation (251 vs. 734 s) compared to atelocollagens, despite having lower purity (93.4 vs. 99.8%). For telopeptide-containing collagens, as collagen purity increased, storage modulus increased and fiber diameter decreased. As α1/α2 chain ratio increased, fiber diameter increased and gelation slowed. As such, this study provides an examination of the effects of collagen processing on key quality attributes for use of collagen gels in biomedical contexts., (© 2021 Wiley Periodicals LLC.)

Intervertebral disc (IVD) herniations are currently treated with interventions that leave the IVD with persistent lesions prone to further herniations. Annulus fibrosus (AF) repair has become of interest as a method to seal defects in the IVD and prevent reherniation, but this requires strong adhesion of the implanted biomaterial to the native AF tissue. Our group has previously developed a high-density collagen (HDC) gel for AF repair and tested its efficacy in vivo, but its adhesion to the AF could be improved. Increased cell adhesion to cartilage has previously been reported through chondroitinase ABC (ChABC) digestion, which removes proteoglycans and increases access to cell binding motifs. Such approaches could also increase biomaterial adhesion to tissue, but the effects of ChABC digestion on AF have yet to be investigated. In this study, ovine AF tissue was digested with either 10 U/mL ChABC or saline for up to 10 min and the effect of this treatment on collagen adhesion between AF tissue samples was investigated by histology and mechanical testing in a lap-shear configuration. ChABC digestion removed proteoglycans within the AF in a time-dependent fashion and enhanced adhesion of the HDC gel to the AF. ChABC digestion increased the elastic toughness and total shear energy of the HDC gel-AF interface by 88% and 46% respectively. ChABC treatment enhanced the adhesion of the HDC gel to the AF without significantly decreasing native AF cell viability. Thus, ChABC digestion is a viable method to improve adhesion of biomaterials for AF repair. STATEMENT OF SIGNIFICANCE: Intervertebral disc herniations are currently treated with interventions that leave persistent lesions in the annulus fibrosus that are prone to further herniations. Annular repair is a promising method to seal lesions and prevent reherniation, but requires strong adhesion of the implanted biomaterial to native annulus fibrosus. Since large proteoglycans like aggrecan occupy regions of the extracellular matrix between collagen fibers in the annulus fibrosus, we hypothesized that removing proteoglycans via chondroitinase digestion would increase the adhesion of annular repair hydrogels. This investigation demonstrated that chondroitinase removed proteoglycans within annulus fibrosus tissue, enhanced the interaction of an injected collagen gel with the native tissue, and mechanically improved adhesion between the collagen gel and annulus fibrosus. This is the first study of its kind to evaluate the biochemical and mechanical effects of short-term chondroitinase digestion on annulus fibrosus tissue., (Copyright © 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

An advantage of bioprinting is the ability to incorporate cells into the hydrogel bioink allowing for precise control over cell placement within a construct. Previous work found that the printability of collagen bioinks is highly dependent on their rheological properties. The effect of cell density on collagen rheological properties and, therefore, printability has not been assessed. Therefore, the objective of this study was to determine the effects of incorporating cells on the rheology and printability of collagen bioinks. Primary chondrocytes, at densities relevant to cartilage tissue engineering (up to 100 × 10 6 cells ml -1 ), were incorporated into 8 mg ml -1 collagen bioinks. Bioink rheological properties before, during, and after gelation as well as printability were assessed. Cell-laden printed constructs were also cultured for up to 14 d to assess longer-term cell behavior. The addition of cells resulted in an increase in the storage modulus and viscosity of the collagen before gelation. However, the storage modulus after gelation and the rate of gelation decreased with increasing cell density. Theoretical models were compared to the rheological data to suggest frameworks that could be used to predict the rheological properties of cell-laden bioinks. Printability testing showed that improved printability could be achieved with higher cell densities. Fourteen-day culture studies showed that the printing process had no adverse effects on the viability or function of printed cells. Overall, this study shows that collagen bioinks are conducive to bioprinting with a wide range of cell densities while maintaining high printability and chondrocyte viability and function.

Background: Our group has previously demonstrated in vivo annulus fibrosus repair in animal models using an acellular, riboflavin crosslinked, high-density collagen (HDC) gel., Objective: To assess if seeding allogenic mesenchymal stem cells (MSCs) into this gel yields improved histological and radiographic benefits in an in vivo sheep model of annular injury., Methods: Fifteen lumbar intervertebral discs (IVDs) were randomized into 4 groups: intact, injury only, injury + acellular gel treatment, or injury + MSC-seeded gel treatment. Sheep were sacrificed at 6 wk. Disc height index (DHI), Pfirrmann grade, nucleus pulposus area, and T2 relaxation time (T2-RT) were calculated for each IVD and standardized to healthy controls from the same sheep. Quantitative histological assessment was also performed using the Han scoring system., Results: All treated IVDs retained gel plugs on gross assessment and there were no adverse perioperative complications. The MSC-seeded gel treatment group demonstrated statistically significant improvement over other experimental groups in DHI (P = .002), Pfirrmann grade (P < .001), and T2-RT (P = .015). There was a trend for greater Han scores in the MSC-seeded gel-treated discs compared with injury only and acellular gel-treated IVDs (P = .246)., Conclusion: MSC-seeded HDC gel can be delivered into injured IVDs and maintained safely in live sheep to 6 wk. Compared with no treatment and acellular HDC gel, our data show that MSC-seeded HDC gel improves outcomes in DHI, Pfirrmann grade, and T2-RT. Histological analysis shows improved annulus fibrosus and nucleus pulposus reconstitution and organization over other experimental groups as well., (Copyright © 2018 by the Congress of Neurological Surgeons.)

Study Design: Ovine in vivo study., Objective: To perform lateral approach lumbar surgery in an ovine model to administer an injectable riboflavin cross-linked high-density collagen (HDC) gel and to assess its ability to mitigate intervertebral disc (IVD) degeneration after induced annulus fibrosus (AF) injury., Summary of Background Data: Biological-based injectable gels have shown efficacy in restoring biomechanical, radiographic, and histological parameters in IVD-injured animal models. Riboflavin cross-linked HDC gel has previously demonstrated retention of nucleus pulposus (NP) tissue, reduced loss of disc height, and prevention of terminal cellular degenerative changes in rat-tail spines. However, this biological therapy has never been tested in large animal models., Methods: Forty lumbar IVDs were accessed from eight sheep via lateral approach surgery. IVDs were randomly assigned to healthy control, injury and HDC treatment, or negative control with injury and no treatment. IVD injury was carried out using a drill-bit through the AF followed by needle puncture of the NP. Sheep were followed for 16 weeks and underwent qualitative/quantitative magnetic resonance imaging, x-ray, and histological analyses of collagen and proteoglycan content., Results: The lateral approach to the ovine lumbar spine to deliver HDC gel proved to be safe and reproducible. IVDs treated with the HDC gel revealed less degenerative changes at the microscopic level based on AF and NP histology. However, mean Pfirrmann grade, T2 relaxation time, NP voxel size, and disc height index were not significantly different between the two injury groups., Conclusion: Injectable HDC gel can be administered safely via lateral approach surgery in an ovine AF injury model. IVDs treated with HDC gel demonstrated less degeneration at the microscopic level though radiographic changes were slight when comparing treated to untreated IVDs. Future studies will need to elucidate the role of injury technique and time frame for follow-up in correlating histological and radiographical outcomes., Level of Evidence: N /A.

Novel tissue engineered and biomaterial approaches to treat intervertebral disc (IVD) degeneration focus on single aspects of the progressive disease and hence are insufficient repair strategies. In this study, annulus fibrosus (AF) and nucleus pulposus (NP) biomaterial repair strategies were used individually and combined to treat IVD degeneration modeled in ex vivo rat-tail motion segments by annulotomy and nucleotomy. An injectable riboflavin cross-linked high-density collagen gel patched defects in the AF, while NP repair consisted of injections of a modified hyaluronic acid (HA) hydrogel. Qualitative imaging showed the annulotomy and nucleotomy successfully herniated NP material, while the HA NP injections restored intact NP morphology and the collagen AF patches sealed AF defects. Assessed by quantitative T2 magnetic resonance imaging, combined repair treatments yielded disc hydration not significantly different than intact hydration, while AF and NP repairs alone only restored ∼1/3 of intact hydration. Mechanical testing showed NP injections alone recovered on average ∼35% and ∼40% of the effective instantaneous and equilibrium moduli. The combined treatment comprising biomaterial AF and NP repair was effective at increasing NP hydration from NP repair alone, however HA injections alone are sufficient to improve mechanical properties., Statement of Significance: Intervertebral disc degeneration affects an estimated 90% of individuals throughout their life, and is a candidate pathology for tissue engineered repair. The current standard of clinical care reduces spinal articulation and leads to further degeneration along the spine, hence great interest in a regenerative medicine therapy. Literature studies focused on biomaterial repair strategies for treating degenerated discs have partially restored native disc function, however no studies have reported the use of combined therapies to address multiple aspects of disc degeneration. This initial investigation screened injectable biomaterial repair strategies ex vivo, and through complementary outcome measures showed a combined therapy restores disc function better than individual approaches. This study is the first of its kind to address multiple aspects of disc degeneration, using clinically-oriented biomaterials in a well-established animal model., (Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Collagen has shown promise as a bioink for extrusion-based bioprinting, but further development of new collagen bioink formulations is necessary to improve their printability. Screening these formulations by measuring print accuracy is a costly and time consuming process. We hypothesized that rheological properties of the bioink before, during, and/or after gelation can be used to predict printability. In this study, we investigated the effects of riboflavin photocrosslinking and pH on type I collagen bioink rheology before, during, and after gelation and directly correlated these findings to the printability of each bioink formulation. From the riboflavin crosslinking study, results showed that riboflavin crosslinking increased the storage moduli of collagen bioinks, but the degree of improvement was less pronounced at higher collagen concentrations. Dots printed with collagen bioinks with riboflavin crosslinking exhibited smaller dot footprint areas than those printed with collagen bioinks without riboflavin crosslinking. From the pH study, results showed that gelation kinetics and final gel moduli were highly pH dependent and both exhibited maxima around pH 8. The shape fidelity of printed lines was highest at pH 8-9.5. The effect of riboflavin crosslinking and pH on cell viability was assessed using bovine chondrocytes. Cell viability in collagen gels was found to decrease after blue light activated riboflavin crosslinking but was not affected by pH. Correlations between rheological parameters and printability showed that the modulus associated with the bioink immediately after extrusion and before deposition was the best predictor of bioink printability. These findings will allow for the more rapid screening of collagen bioink formulations.

The meniscus acts as a stabilizer, lubricator, and load distributer in the knee joint. The mechanical stability of the meniscus depends on its connection to the underlying bone by a fibrocartilage to bone transition zone called the meniscal enthesis. Tissue engineered menisci hold great promise as a treatment alternative however lack a means of integrated fixation to the underlying bone needed in order for a tissue engineered meniscal replacement to be successful. Tissue engineering the meniscal enthesis is a difficult task given the complex gradients of cell type, mineral, and extracellular matrix molecules. Therefore, there is a need for a simplified and high throughput enthesis model to test experimental parameters. The goal of this study was to develop a simplified enthesis model to test collagen integration with decellularized bone. We found that injection molding collagen into tubing loaded with decellularized bone plugs resulted in a scaffold with three regions: bone, bone-collagen, and collagen. Furthermore, collagen formation was directed in the axial direction by using mechanical fixation at the bony ends. The results of this study showed that this technique can be used to mimic the native enthesis morphology and serves as ideal test platform to generate a model tissue engineered enthesis., Statement of Significance: The meniscal enthesis is a complex structure that is essential to mechanical stability of the meniscus and the knee joint. Several studies document the development of anatomically shaped tissue engineered meniscus constructs, but none have focused on how to integrate such tissues with underlying bone. This study establishes a simplified construct to model the meniscal enthesis composed of a collagen gel seeded with meniscal fibrochondrocytes integrated with decellularized cancellous bone. Mechanical fixation at the bony ends induced tissue integration of fibers into the bony tissue, which is critical for mechanical performance and has yet to be shown in enthesis literature. Our test platform is amenable to targeted experiments investigating mineralization gradients, collagen fiber alignment, cell population phenotype, and media conditioning with experimental impact on enthesis studies for meniscus, tendon, and ligament., (Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Mesenchymal stem cells (MSCs) have been investigated with promising results for meniscus healing and tissue engineering. While MSCs are known to contribute to extracellular matrix (ECM) production, less is known about how MSCs produce and align large organized fibers for application to tissue engineering the meniscus. The goal of this study was to investigate the capability of MSCs to produce and organize ECM molecules compared to meniscal fibrochondrocytes (FCCs). Bovine FCCs and MSCs were encapsulated in an anatomically accurate collagen meniscus using monoculture and co-culture of each cell type. Each meniscus was mechanically anchored at the horns to mimic the physiological fixation by the meniscal entheses. Mechanical fixation generates a static mechanical boundary condition previously shown to induce formation of oriented fiber by FCCs. Samples were cultured for 4 weeks and then evaluated for biochemical composition and fiber development. MSCs increased the glycosaminoglycan (GAG) and collagen production in both co-culture and monoculture groups compared to FCC monoculture. Collagen organization was greatest in the FCC monoculture group. While MSCs had increased matrix production, they lacked the fiber organization capabilities of FCCs. This study suggests that GAG production and fiber formation are linked. Co-culture can be used as a means of balancing the synthetic properties of MSCs and the matrix remodeling capabilities of FCCs for tissue engineering applications.

The meniscus is a dense fibrocartilage tissue that withstands the complex loads of the knee via a unique organization of collagen fibers. Attempts to condition engineered menisci with compression or tensile loading alone have failed to reproduce complex structure on the microscale or anatomic scale. Here we show that axial loading of anatomically shaped tissue-engineered meniscus constructs produced spatial distributions of local strain similar to those seen in the meniscus when the knee is loaded at full extension. Such loading drove formation of tissue with large organized collagen fibers, levels of mechanical anisotropy, and compressive moduli that match native tissue. Loading accelerated the development of native-sized and aligned circumferential and radial collagen fibers. These loading patterns contained both tensile and compressive components that enhanced the major biochemical and functional properties of the meniscus, with loading significantly improved glycosaminoglycan (GAG) accumulation 200-250%, collagen accumulation 40-55%, equilibrium modulus 1000-1800%, and tensile moduli 500-1200% (radial and circumferential). Furthermore, this study demonstrates local changes in mechanical environment drive heterogeneous tissue development and organization within individual constructs, highlighting the importance of recapitulating native loading environments. Loaded menisci developed cartilage-like tissue with rounded cells, a dense collagen matrix, and increased GAG accumulation in the more compressively loaded horns, and fibrous collagen-rich tissue in the more tensile loaded outer 2/3, similar to native menisci. Loaded constructs reached a level of organization not seen in any previous engineered menisci and demonstrate great promise as meniscal replacements.

Open annular defects compromise the ability of the annulus fibrosus to contain nuclear tissue in the disc space, and therefore lead to disc herniation with subsequent degenerative changes to the entire intervertebral disc. This study reports the use of riboflavin crosslinked high-density collagen gel for the repair of annular defects in a needle-punctured rat-tail model. High-density collagen has increased stiffness and greater hydraulic permeability than conventional low-density gels; riboflavin crosslinking further increases these properties. This study found that treating annular defects with crosslinked high-density collagen inhibited the progression of disc degeneration over 18 weeks compared to untreated control discs. Histological sections of FITC-labeled collagen gel revealed an early tight attachment to host annular tissue. The gel was subsequently infiltrated by host fibroblasts which remodeled it into a fibrous cap that bridged the outer disrupted annular fibers and partially repaired the defect. This repair tissue enhanced retention of nucleus pulposus tissue, maintained physiological disc hydration, and preserved hydraulic permeability, according to MRI, histological, and mechanical assessments. Degenerative changes were partially reversed in treated discs, as indicated by an increase in nucleus pulposus size and hydration between weeks 5 and 18. The collagen gel appeared to work as an instant sealant and by enhancing the intrinsic healing capabilities of the host tissue., (Copyright © 2015. Published by Elsevier Ltd.)

A herniated intervertebral disc often causes back pain when disc tissue is displaced through a damaged annulus fibrosus. Currently, the only methods available for annulus fibrosus repair involve mechanical closure of defect, which does little to address biological healing in the damaged tissue. Collagen hydrogels are injectable and have been used to repair annulus defects in vivo. In this study, high-density collagen hydrogels at 5, 10, and 15 mg/mL were used to repair defects made to intact rat caudal intervertebral discs in vitro. A group of gels at 15 mg/mL were also cross-linked with riboflavin at 0.03 mM, 0.07 mM, or 0.10 mM. These cross-linked, high-density collagen gels maintained their presence in the defect under loading and contributed positively to the mechanical response of damaged discs. Discs exhibited increases to 95% of undamaged effective equilibrium and instantaneous moduli as well as up to fourfold decreases in effective hydraulic permeability from the damaged discs. These data suggest that high-density collagen gels may be effective at restoring mechanical function of injured discs as well as potential vehicles for the delivery of biological agents such as cells or growth factors that may aid in the repair of the annulus fibrosus., (© 2014 Wiley Periodicals, Inc.)

This study investigated the effect of mechanical anchoring on the development of fiber organization and anisotropy in anatomically shaped tissue engineered menisci. Bovine meniscal fibrochondrocytes were mixed with collagen and injected into molds designed to produce meniscus implants with 12 mm extensions at each horn. After a day of static culture, 10 and 20mg/ml collagen menisci were either clamped or unclamped and cultured for up to 8 weeks. Clamped menisci were anchored in culture trays throughout culture to mimic the native meniscus horn attachment sites, restrict contraction circumferentially, and encourage circumferential alignment. Clamped menisci retained their size and shape, and by 8 weeks developed circumferential and radial fiber organization that resembled native meniscus. Clamping also increased collagen accumulation and improved mechanical properties compared to unclamped menisci. Enhanced organization in clamped menisci was further reflected in the development of anisotropic tensile properties, with 2-3 fold higher circumferential moduli compared to radial moduli, a similar ratio to native meniscus. Ten and 20mg/ml clamped menisci had similar levels of organization, with 20mg/ml menisci producing larger diameter fibers and significantly better mechanical properties. Collectively, these data demonstrate the benefit of using bio-inspired mechanical boundary conditions to drive the formation of a highly organized collagen fiber network., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Study Design: Animal in vivo study., Objective: To test the capability of high-density collagen gel to repair annular defects., Summary of Background Data: Annular defects are associated with spontaneous disc herniations and disc degeneration, which can lead to significant morbidity. Persistent annular defects after surgical discectomies can increase reherniation rates. Several synthetic and biological materials have been developed for annular repair. This is the first study to test an injectable biomaterial in vivo., Methods: We punctured caudal intervertebral discs in 42 athymic rats, using an 18-gauge needle to create an annular defect. High-density collagen (HDC), either alone or cross-linked with riboflavin (RF), was injected into the defect. There were 4 separate study groups: HDC, HDC cross-linked with either 0.25 mM RF or 0.50 mM RF, and a negative control that was punctured and not treated. The animals were followed for 5 weeks; radiographs were used to assess disc heights and magnetic resonance images were used to evaluate degenerative changes. We developed an algorithm on the basis of T2-relaxation time measurements to assess the size of the nucleus pulposus. Tails were collected for histological analysis to evaluate disc degeneration and measure the cross-sectional area of the nucleus pulposus., Results: After 5 weeks, the control and the uncross-linked HDC groups both showed signs of progressive degenerative changes with minimal or no residual nucleus pulposus tissue in the disc space. Cross-linking significantly improved the ability of HDC gels to repair annular defects. The 0.50 mM RF cross-linked group showed only a slight decrease in nuclear tissue when compared with healthy discs, with no signs of intervertebral disc (IVD) degeneration. The annulus fibrosus was partially repaired by a fibrous cap that bridged the defect. Host fibroblasts infiltrated and remodeled the injected collagen., Conclusion: HDC is capable of repairing annular defects induced by needle puncture. The stiffness of HDC can be modified by riboflavin cross-linking and seems to positively affect the repair mechanism. These results need to be replicated in a larger animal model., Level of Evidence: N/A.

Numerous studies have described the effects of matrix stiffening on cell behavior using two-dimensional synthetic surfaces; however, less is known about the effects of matrix stiffening on cells embedded in three-dimensional in vivo-like matrices. A primary limitation in investigating the effects of matrix stiffness in three dimensions is the lack of materials that can be tuned to control stiffness independently of matrix density. Here, we use collagen-based scaffolds where the mechanical properties are tuned using non-enzymatic glycation of the collagen in solution, prior to polymerization. Collagen solutions glycated prior to polymerization result in collagen gels with a threefold increase in compressive modulus without significant changes to the collagen architecture. Using these scaffolds, we show that endothelial cell spreading increases with matrix stiffness, as does the number and length of angiogenic sprouts and the overall spheroid outgrowth. Differences in sprout length are maintained even when the receptor for advanced glycation end products is inhibited. Our results demonstrate the ability to de-couple matrix stiffness from matrix density and structure in collagen gels, and that increased matrix stiffness results in increased sprouting and outgrowth., (Copyright © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Background: Rapid, effective host cell invasion and vascularization is essential for durable incorporation of avascular tissue-replacement scaffolds. In this study, the authors sought to qualitatively and quantitatively determine which of two commercially available products (i.e., Strattice and Integra) facilitates more rapid cellular and vascular invasion in a murine model of graft incorporation., Methods: Integra and Strattice were implanted subcutaneously into the dorsa of C57BL/6 mice; harvested after 3, 7, or 14 days; and stained with hematoxylin and eosin, 4',6-diamidino-2-phenylindole, and immunohistochemical stains for CD31 and α-smooth muscle actin. Exponential decay equations describing cellular invasion through each layer were fit to each material/time point. Mean cell density and cell frequency maps were created denoting extent of invasion by location within the scaffold., Results: Qualitative analysis demonstrated extensive cellular infiltration into Integra by 3 days and increasing over the remaining 14 days. Invasion of Strattice was sparse, even after 14 days. α-Smooth muscle actin immunohistochemistry revealed blood vessel formation within Integra by 14 days but no analogous neovascularization in Strattice. Mean decay equations for Integra and Strattice were y = 76.3(0.59) and y = 75.5(0.33), respectively. Both cell density measurements and frequency mapping demonstrated that, at all time points, Integra manifested a greater density/depth of cellular invasion when compared with Strattice., Conclusions: These data confirm empiric clinical observations that Integra is more rapidly invaded than Strattice when placed in a suitable host bed. A remnant microvasculature template is not sufficient for effective cellular ingrowth into an artificial tissue construct. These findings provide insight into means for improving future dermal replacement products.

Cell-matrix interactions transmit a wealth of information about the extracellular environment. In return, a variety of responses from the cell are initiated by changes in the matrix. One such response involves the positive regulation of matrix metalloproteinases (MMPs) by alpha2beta1 integrin attaching to a specific extracellular matrix component, collagen. This study explores the relationship between mechanical and biochemical functions of alpha2beta1 integrins as it pertains to regulating matrix remodeling. To understand this relationship, the individual influences of MMP activity and alpha2beta1 integrin function on collagen gel contraction were studied. We have observed little evidence of mutual participation in matrix remodeling by the alpha2beta1 integrin and MMP activity in cell models where alpha2 is minimally expressed. In cells expressing high levels of alpha2, we see an increase in gel contraction that is enhanced by MMP activity. Measuring tension as it builds within the gel reveals that alpha2beta1 integrin presence correlates with force output but is insensitive to MMP activity. These data strongly suggest that alpha2beta1 regulates collagen gel remodeling through multiple simultaneous mechanisms including force generation and modulation of MMP activity.