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Critical-sized bone defects (CSBD) represent a significant clinical challenge, stimulating researchers to seek new methods for successful bone reconstruction. The aim of this systematic review is to assess whether bone marrow stem cells (BMSCs) combined with tissue-engineered scaffolds have demonstrated improved bone regeneration in the treatment of CSBD in large preclinical animal models. A search of electronic databases (PubMed, Embase, Web of Science, and Cochrane Library) focused on in vivo large animal studies identified ten articles according to the following inclusion criteria: 1. in vivo large animal models with segmental bone defects; 2. treatment with tissue-engineered scaffolds combined with BMSCs; 3. the presence of a control group; 4. a minimum of a histological analysis outcome. ARRIVE guidelines were used for quality assessment and SYRCLE's risk of bias tool was used to define internal validity. The results demonstrated that tissue-engineered scaffolds, either from autografts or allografts, when combined with BMSCs provide improved bone mineralization and bone formation, including a critical role in the remodeling phase of bone healing. BMSCs-seeded scaffolds showed improved biomechanical properties and microarchitecture properties of the regenerated bone when compared to untreated and scaffold-alone groups. This review highlights the efficacy of tissue engineering strategies for the repair of extensive bone defects in pre-clinical large-animal models. In particular, the use of mesenchymal stem cells, combined with bio-scaffolds seems to be a successful method in comparison to cell-free scaffolds.

Vascularized composite allografts (VCAs) can restore fully functional anatomic units in patients with limb amputations or severe facial tissue loss. However, acute rejection of the skin is frequently observed and underscores the importance of developing tolerance induction protocols. In this study, we have characterized the skin immune system in VCAs. We demonstrate infiltration of recipient leukocytes, regardless of rejection status, and in tolerant mixed hematopoietic chimeras, the co‐existence of these cells with donor leukocytes in the absence of rejection. Here we characterize the dermal T cell and epidermal Langerhans cell components of the skin immune system in our porcine model of VCA tolerance, and the kinetics of cutaneous chimerism in both of these populations in VCAs transplanted to tolerant and nontolerant recipients, as well as in host skin. Furthermore, in biopsies from the first patient to receive a hand transplant in our program, we demonstrate the presence of recipient T cells in the skin of the transplanted limb in the absence of clinical or histological evidence of rejection. The authors show that recipient leukocytes infiltrate the skin of vascularized composite allografts and, in tolerant large animal recipients and in an immunosuppressed hand recipient, coexist with donor leukocytes without evidence of rejection.

Chondrocyte deformation influences disease progression and tissue regeneration in load-bearing joints. In this work, we found that viscoelasticity of dynamic covalent crosslinks temporally modulates the biophysical transmission of physiologically relevant compressive strains to encapsulated chondrocytes. Chondrocytes in viscoelastic alky-hydrazone hydrogels demonstrated (91.4 ± 4.5%) recovery of native rounded morphologies during mechanical deformation, whereas primarily elastic benzyl-hydrazone hydrogels significantly limited morphological recovery (21.2 ± 1.4%).

Full-thickness skin loss is a challenging problem due to limited reconstructive options, demanding 75 million surgical procedures annually in the United States. Autologous skin grafting is the gold standard treatment, but results in donor-site morbidity and poor aesthetics. Numerous skin substitutes are available on the market to date, however, none truly functions as full-thickness skin due to lack of a vascular network. The creation of an autologous full-thickness skin analogue with a vascular pedicle would result in a paradigm shift in the management of wounds and in reconstruction of full-thickness skin defects. To create a clinically relevant foundation, we generated an acellular skin flap scaffold (SFS) with a perfusable vascular pedicle of clinically relevant size by perfusion decellularization of porcine fasciocutaneous flaps. We then analyzed the yielded SFS for mechanical properties, biocompatibility, and regenerative potential in vitroand in vivo. Furthermore, we assessed the immunological response using an in vivomodel. Finally, we recellularized the vascular compartment of an SFS and reconnected it to a recipient's blood supply to test for perfusability. Perfusion decellularization removed all cellular components with preservation of native extracellular matrix composition and architecture. Biaxial testing revealed preserved mechanical properties. Immunologic response and biocompatibility assessed via implantation and compared with native xenogenic skin and commercially available dermal substitutes revealed rapid neovascularization and complete tissue integration. Composition of infiltrating immune cells showed no evidence of allorejection and resembled the inflammatory phase of wound healing. Implantation into full-thickness skin defects demonstrated good tissue integration and skin regeneration without cicatrization. We have developed a protocol for the generation of an SFS of clinically relevant size, containing a vascular pedicle, which can be utilized for perfusion decellularization and, ultimately, anastomosis to the recipient vascular system after precellularization. The observed favorable immunological response and good tissue integration indicate the substantial regenerative potential of this platform.

Most of the present knowledge on submarine landslides relies upon back-analysis of post-failure deposits identified using geophysical techniques. In this paper, the runout of slides on rigid bases is explored using the material point method (MPM) with focus on the geotechnical aspects of the morphologies. In MPM, the sliding material and bases are discretised into a number of Lagrangian particles, and a background Eulerian mesh is employed to update the state of the particles. The morphologies of the slide can be reproduced by tracking the Lagrangian particles in the dynamic processes. A real case history of a submarine slide is back-analyzed with the MPM and also a depth-averaged method. Runout of the slides from steep slopes to moderate bases are reproduced. Then different combinations of soil and basal parameters are assumed to trigger runout mechanisms of elongation, block sliding and spreading. The runout distances predicted by the MPM match well with those from large deformation finite element analysis for the elongation and block sliding patterns. Horst and grabens are shaped in a spreading pattern. However, the current MPM simulations for materials with high sensitivities are relatively mesh sensitive.

Most of the present knowledge on submarine landslides relies upon back-analysis of post-failure deposits identified using geophysical techniques. In this paper, the runout of slides on rigid bases is explored using the material point method (MPM) with focus on the geotechnical aspects of the morphologies. In MPM, the sliding material and bases are discretised into a number of Lagrangian particles, and a background Eulerian mesh is employed to update the state of the particles. The morphologies of the slide can be reproduced by tracking the Lagrangian particles in the dynamic processes. A real case history of a submarine slide is back-analyzed with the MPM and also a depth-averaged method. Runout of the slides from steep slopes to moderate bases are reproduced. Then different combinations of soil and basal parameters are assumed to trigger runout mechanisms of elongation, block sliding and spreading. The runout distances predicted by the MPM match well with those from large deformation finite element analysis for the elongation and block sliding patterns. Horst and grabens are shaped in a spreading pattern. However, the current MPM simulations for materials with high sensitivities are relatively mesh sensitive.

•Identification of human bone marrow mesenchymal cells with osteopontin (SPP1) overexpression in patients with MDS.•SPP1 expression in comparable mesenchymal stromal cell populations plays protective roles in disease progression in an MDS mouse model.

Porcine allogeneic skin constructs of keratinocytes and fibroblasts without APCs are rejected similarly to normal allogeneic skin. Donors develop anti-MHC I alloantibodies but not anti-MHC II ones. Accelerated rejection to second grafts from MHC-incompatible and compatible donors suggests immunization against minor histocompatibility antigens. Supplemental digital content is available in the text.

Injuries to the articular cartilage surface are challenging to repair because cartilage possesses a limited capacity for self-repair. The outcomes of current clinical procedures aimed to address these injuries are inconsistent and unsatisfactory. We have developed a novel method for generating hyaline articular cartilage to improve the outcome of joint surface repair. A suspension of 107swine chondrocytes was cultured under reciprocating motion for 14 days. The resulting dynamic self-regenerating cartilage (dSRC) was placed in a cartilage ring and capped with fibrin and collagen gel. A control group consisted of chondrocytes encapsulated in fibrin gel. Constructs were implanted subcutaneously in nude mice and harvested after 6 weeks. Gross, histological, immunohistochemical, biochemical, and biomechanical analyses were performed. In swine patellar groove, dSRC was implanted into osteochondral defects capped with collagen gel and compared to defects filled with osteochondral plugs, collagen gel, or left empty after 6 weeks. In mice, the fibrin- and collagen-capped dSRC constructs showed enhanced contiguous cartilage matrix formation over the control of cells encapsulated in fibrin gel. Biochemically, the fibrin and collagen gel dSRC groups were statistically improved in glycosaminoglycan and hydroxyproline content compared to the control. There was no statistical difference in the biomechanical data between the dSRC groups and the control. The swine model also showed contiguous cartilage matrix in the dSRC group but not in the collagen gel and empty defects. These data demonstrate the survivability and successful matrix formation of dSRC under the mechanical forces experienced by normal hyaline cartilage in the knee joint. The results from this study demonstrate that dSRC capped with hydrogels successfully engineers contiguous articular cartilage matrix in both nonload-bearing and load-bearing environments.

Advancement of engineered ear in clinical practice is limited by several challenges. The complex, largely unsupported, three-dimensional auricular neocartilage structure is difficult to maintain. Neocartilage formation is challenging in an immunocompetent host due to active inflammatory and immunological responses. The large number of autologous chondrogenic cells required for engineering an adult human-sized ear presents an additional challenge because primary chondrocytes rapidly dedifferentiate during in vitroculture. The objective of this study was to engineer a stable, human ear-shaped cartilage in an immunocompetent animal model using expanded chondrocytes. The impact of basic fibroblast growth factor (bFGF) supplementation on achieving clinically relevant expansion of primary sheep chondrocytes by in vitroculture was determined. Chondrocytes expanded in standard medium were either combined with cryopreserved, primary passage 0 chondrocytes at the time of scaffold seeding or used alone as control. Disk and human ear-shaped scaffolds were made from porous collagen; ear scaffolds had an embedded, supporting titanium wire framework. Autologous chondrocyte-seeded scaffolds were implanted subcutaneously in sheep after 2 weeks of in vitroincubation. The quality of the resulting neocartilage and its stability and retention of the original ear size and shape were evaluated at 6, 12, and 20 weeks postimplantation. Neocartilage produced from chondrocytes that were expanded in the presence of bFGF was superior, and its quality improved with increased implantation time. In addition to characteristic morphological cartilage features, its glycosaminoglycan content was high and marked elastin fiber formation was present. The overall shape of engineered ears was preserved at 20 weeks postimplantation, and the dimensional changes did not exceed 10%. The wire frame within the engineered ear was able to withstand mechanical forces during wound healing and neocartilage maturation and prevented shrinkage and distortion. This is the first demonstration of a stable, ear-shaped elastic cartilage engineered from auricular chondrocytes that underwent clinical-scale expansion in an immunocompetent animal over an extended period of time.

Articular cartilage remains a significant clinical challenge to repair because of its limited self-healing capacity. Interest has grown in the delivery of autologous chondrocytes to cartilage defects, and combining cell-based therapies with scaffolds that capture aspects of native tissue and allow cell-mediated remodeling could improve outcomes. Currently, scaffold-based therapies with encapsulated chondrocytes permit matrix production; however, resorption of the scaffold often does not match the rate of matrix production by chondrocytes, which can limit functional tissue regeneration. Here, we designed a hybrid biosynthetic system consisting of poly(ethylene glycol) (PEG) endcapped with thiols and crosslinked by norbornene-functionalized gelatin via a thiol-ene photopolymerization. The protein crosslinker was selected to facilitate chondrocyte-mediated scaffold remodeling and matrix deposition. Gelatin was functionalized with norbornene to varying degrees (∼4–17 norbornenes/gelatin), and the shear modulus of the resulting hydrogels was characterized (<0.1–0.5 kPa). Degradation of the crosslinked PEG-gelatin hydrogels by chondrocyte-secreted enzymes was confirmed by gel permeation chromatography. Finally, chondrocytes encapsulated in these biosynthetic scaffolds showed significantly increased glycosaminoglycan deposition over just 14 days of culture, while maintaining high levels of viability and producing a distributed matrix. These results indicate the potential of a hybrid PEG-gelatin hydrogel to permit chondrocyte-mediated remodeling and promote articular cartilage matrix production. Tunable scaffolds that can easily permit chondrocyte-mediated remodeling may be useful in designing treatment options for cartilage tissue engineering applications. Articular cartilage remains a significant clinical challenge to repair because of its limited self-healing capacity. In this manuscript, a biosynthetic scaffold crosslinked by both gelatin and poly(ethylene glycol) (PEG) was developed to encapsulate primary cartilage cells, also known as chondrocytes. This hybrid scaffold facilitated cartilage-specific extracellular matrix (ECM) molecule deposition by permitting cell-mediated, localized degradation of the construct so that encapsulated chondrocytes had pericellular space to generate tissue. Furthermore, the data show that the mechanical properties of this gel can be easily modified and this system can be formed in situ at a defect site via a photopolymerizable reaction. The results of this manuscript indicate the potential of this novel system in designing treatment options for cartilage tissue regeneration applications.

Madariaga et al report that donor-matched myocutaneous vascularized composite allografts are rejected when transplanted into miniature swine stably tolerant to fully mismatched heart and/or kidney grafts following a 12-day treatment with cyclosporine, demonstrating tissue-specific tolerance requirements.

Background: Despite encouraging outcomes in vascularized composite allograft (VCA) transplantation, the risks of chronic immunosuppression limit widespread applicability. It has been suggested that infusion of donor bone marrow along with the VCA may reduce the level of immunosuppression required to prevent clinical VCA rejection. However, no clear evidence has yet been presented to confirm the role of donor bone marrow in the prevention of rejection. In this study we investigated the immunologic effects of concurrent bone marrow transplantation in a large animal VCA model. Methods: MGH miniature swine (n=4) received a non-myeloablative conditioning regimen consisting of low-dose total body irradiation, T-cell depletion, a short course of Cyclosporine A, with or without varying doses of donor bone marrow cells in combination with a complete MHC-mismatched VCA. Animals were monitored daily for signs of rejection or graft versus host disease. Chimerism levels were assessed using flow cytometry and in vitroassays were performed to assess for donor-specific responses. Results: Transient chimerism was prolonged with increased bone marrow cell doses and total body irradiation. While animals that received BMC infusions did not have significantly prolonged VCA acceptance following cessation of immunosuppression compared to animals that received conditioning without BMCs, they demonstrated better early clinical outcomes and demonstrated donor-specific unresponsiveness during the presence of detectable chimerism. Conclusions: Detectable mixed chimerism following bone marrow transplantation and VCA mitigates donor-specific responses and acute rejection episodes, but does not appear to be sufficient for tolerance induction.

Objective Our goal was to engineer cartilage in vivousing auricular chondrocytes that underwent clinically relevant expansion and using methodologies that could be easily translated into health care practice.Design Sheep and human chondrocytes were isolated from auricular cartilage biopsies and expanded in vitro. To reverse dedifferentiation, expanded cells were either mixed with cryopreserved P0 chondrocytes at the time of seeding onto porous collagen scaffolds or proliferated with basic fibroblast growth factor (bFGF). After 2-week in vitroincubation, seeded scaffolds were implanted subcutaneously in nude mice for 6 weeks. The neocartilage quality was evaluated histologically; DNA and glycosaminoglycans were quantified. Cell proliferation rates and collagen gene expression profiles were assessed.Results Clinically sufficient over 500-fold chondrocyte expansion was achieved at passage 3 (P3); cell dedifferentiation was confirmed by the simultaneous COL1A1/3A1 gene upregulation and COL2A1 downregulation. The chondrogenic phenotype of sheep but not human P3 cells was rescued by addition of cryopreserved P0 chondrocytes. With bFGF supplementation, chondrocytes achieved clinically sufficient expansion at P2; COL2A1 expression was not rescued but COL1A1/3A1genes were downregulated. Although bFGF failed to rescue COL2A1 expression during chondrocyte expansion in vitro, elastic neocartilage with obvious collagen II expression was observed on porous collagen scaffolds after implantation in mice for 6 weeks.Conclusions Both animal and human auricular chondrocytes expanded with low-concentration bFGF supplementation formed high-quality elastic neocartilage on porous collagen scaffolds in vivo.

Centrifugation is a popular processing method, with an unclear mechanism of action. Hypotheses include fat concentration, reduced inflammatory response by removal of blood, and concentration of adipose-derived stem cells. The authors performed multiple experiments to determine the role of centrifugation and compared it with a different processing method (meshgauze technique).

A brief outline is given of the basis of analysis used in two computer programs, PIGLET and DEFPIG, for analysis of pile group response. A comparison of the capabilities of each program is presented and then a parametric study is made of a sixpile group to illustrate the similarities and differences between the two programs. Two series of field tests on groups of piles are then analysed by DEFPIG and PIGLET, and it is shown that the predictions from each are consistent and in generally good agreement with the field data. The comparisons suggest that each program may be used with confidence for practical problems, particularly in conjunction with single pile load test data.

In most soil types, it is generally assumed that the shaft capacity of a pile is identical under both tensile and compressive loading. However, there is widespread experimental evidence that in sand the shaft capacity is significantly lower for tensile loading, or uplift, than for compressive loading. This paper describes the results of a parametric study that was conducted to explore the theoretical basis for such differences. It is shown that the primary cause of lower tensile capacity is due to a Poisson's ratio effect, and that the ratio of tensile to compressive shaft capacity may be expressed as a function of the relative compressibility of the pile and the slenderness ratio. Design recommendations are proposed, and corroborated with results from highquality field tests.

Capsular contracture is the most common complication following the insertion of breast implants. Within a decade, half of patients will develop capsular contracture, leading to significant morbidity and need for reoperation. There is no preventative treatment available and the recurrence rate remains high. Photochemical tissue passivation is a novel tissue-stabilization technique that results in collagen cross-linking. It can rapidly link collagen fibers in situ, preserving normal tissue architecture. By using this therapy to passivate the collagenous tissues of the implant pocket, the authors hope to prevent the development of pathogenic collagen bundles and subsequent capsule contracture.

Tissue-engineered cartilage has historically been an attractive alternative treatment option for auricular reconstruction. However, the ability to reliably generate autologous auricular neocartilage in an immunocompetent preclinical model should first be established. The objectives of this study were to demonstrate engineered autologous auricular cartilage in the immunologically aggressive subcutaneous environment of an immunocompetent animal model, and to determine the impact of in vitroculture duration of chondrocyte-seeded constructs on the quality of neocartilage maturation in vivo. Auricular cartilage was harvested from eight adult sheep; chondrocytes were isolated, expanded in vitro, and seeded onto fibrous collagen scaffolds. Constructs were cultured in vitrofor 2, 6, and 12 weeks, and then implanted autologously in sheep and in control nude mice for 6 and 12 weeks. Explanted tissue was stained with hematoxylin and eosin, safranin O, toluidine blue, collagen type II, and elastin. DNA and glycosaminoglycans (GAGs) were quantified. The quality of cartilage engineered in sheep decreased with prolonged in vitroculture time. Superior cartilage formation was demonstrated after 2 weeks of in vitroculture; the neocartilage quality improved with increased implantation time. In nude mice, neocartilage resembled native sheep auricular cartilage regardless of the in vitroculture length, with the exception of elastin expression. The DNA quantification was similar in all engineered and native cartilage (p>0.1). All cartilage engineered in sheep had significantly less GAG than native cartilage (p<0.02); significantly more GAG was observed with increased implantation time (p<0.02). In mice, the GAG content was similar to that of native cartilage and became significantly higher with increased in vitroor in vivodurations (p<0.02). Autologous auricular cartilage was successfully engineered in the subcutaneous environment of an ovine model using expanded chondrocytes seeded on a fibrous collagen scaffold after a 2-week in vitroculture period.

We have previously reported that Massachusetts General Hospital miniature swine, which had accepted class I–mismatched kidneys long-term after 12 days of high-dose cyclosporine A, uniformly accepted donor-major histocompatibility complex (MHC)–matched kidneys without immunosuppression but rejected donor MHC-matched split-thickness skin grafts by day 25, without changes in renal graft function or antidonor in vitro responses. We have now tested whether this “split tolerance” would also be observed for the primarily vascularized skin of vascularized composite allografts (VCAs).

Fat grafting has become routine in plastic surgery because of low donor-site morbidity, a low complication rate, and fast recovery time. The optimal technique, however, has yet to be defined. Two critical variables are pressure and shear, both defined as force divided by area. In this study, the authors examined the effect of pressure and shear on human fat grafts in a nude mouse model.

The most commonly performed skin rejuvenation procedure, laser resurfacing, is associated with adverse events and significant expense. The authors have developed a novel device that uses micro-coring needles to remove tissue in a fractional pattern and avoid the side effects of laser therapy. The authors compare the efficacy of these needles to standard needles in a pig model.

Numerous studies on engineering cartilage utilizing chondrocytes from juvenile animal sources have been reported. However, there are many unknown aspects of engineering cartilage using human chondrocytes—especially from middle-aged or elderly adults—which are critical for clinical application of tissue engineering in the field of orthopedic surgery. The primary aim of this study was to engineer neocartilage tissue from 50–60-year-old human chondrocytes in comparison to engineered cartilage made from juvenile swine chondrocytes (JSCs). Articular chondrocytes from middle-aged, nonarthritic humans and juvenile swine were isolated and placed in culture for expansion. The chondrocytes (passage 1) were mixed in fibrin gel at 40–60×106cells/mL until polymerization. Cells/nodule constructs and devitalized cartilage–cells/hydrogel–devitalized cartilage constructs (three-layered model) were implanted into subcutaneous pockets of nude mice for 12, 18, and 24 weeks. The specimens were evaluated histologically, biochemically, and biomechanically. This allowed for direct comparison of the cartilage engineered from human versus swine cells. Histological analysis demonstrated that samples engineered utilizing chondrocytes from middle-aged adults accumulated basophilic, sulfated glycosaminoglycans (sGAG), and abundant type II collagen around the cells in a manner similar to that seen in samples engineered using JSCs at all time points. Biochemical analysis revealed that samples made with human cells had about 40%–60% of the amount hydroxyproline of native human cartilage, a trend parallel to that observed in the specimens made with swine chondrocytes. The amount of sGAG in the human chondrocyte specimens was about one-and-a-half times the amount in native human cartilage, whereas the amount in the samples made with swine chondrocytes was always less than native cartilage. The biomechanical analysis revealed that the stiffness and tensile of samples made with human cells were in a pattern similar to that seen with swine chondrocytes. This study demonstrates that chondrogenesis using articular chondrocytes from middle-aged adults can be achieved in a predictable and reliable manner similar to that shown in studies using cells from juvenile animals and can form the basis of engineering cartilage with degradable scaffolds in this patient population.

The reconstruction, repair, and regeneration of the external auricular framework continue to be one of the greatest challenges in the field of tissue engineering. To replace like with like, we should emulate the native structure and composition of auricular cartilage by combining a suitable chondrogenic cell source with an appropriate scaffold under optimal in vitroand in vivoconditions. Due to the fact that a suitable and reliable substitute for auricular cartilage has yet to be engineered, hand-carved autologous costal cartilage grafts and ear-shaped porous polyethylene implants are the current treatment modalities for auricular reconstruction. However, over the last decade, significant advances have been made in the field of regenerative medicine and tissue engineering. A variety of scaffolds and innovative approaches have been investigated as alternatives to using autologous carved costal cartilage or porous polyethylene implants. A review of recent developments and the current state of the art and science is presented, focusing on scaffolds, cell sources, seeding densities, and mechanical characteristics of tissue-engineered auricular cartilage.

Fat grafting bench research is difficult because many traditional endpoints cannot be used reliably with adipocytes. Manual cell counting with trypan blue is a common method of measuring cell viability. There are, however, multiple known limitations, including human error, inability to analyze cell size, overestimation of adipocyte viability, and labor intensity. In this study, the authors demonstrate the effectiveness of an improved method of accurate adipocyte analysis using an automated cell counter.

Autologous fat grafting is currently undergoing a renaissance. However, fat grafts are limited by unpredictable survival. Poloxamers can act as tissue surfactants. These nonionic surfactants have been shown to stabilize the membranes of damaged cells and to protect against injury and apoptosis in numerous models. This study was designed to investigate the ability of poloxamers to protect harvested adipocytes and to increase fat graft survival.

Engineered cartilage composed of a patient's own cells can become a feasible option for auricular reconstruction. However, distortion and shrinkage of ear-shaped constructs during scaffold degradation and neocartilage maturation in vivohave hindered the field. Scaffolds made of synthetic polymers often generate degradation products that cause an inflammatory reaction and negatively affect neocartilage formation in vivo. Porous collagen, a natural material, is a promising candidate; however, it cannot withstand the contractile forces exerted by skin and surrounding tissue during normal wound healing. We hypothesised that a permanent support in the form of a coiled wire embedded into a porous collagen scaffold will maintain the construct's size and ear-specific shape. Half-sized human adult ear-shaped fibrous collagen scaffolds with and without embedded coiled titanium wire were seeded with sheep auricular chondrocytes, cultured in vitrofor up to 2 weeks, and implanted subcutaneously on the backs of nude mice. After 6 weeks, the dimensional changes in all implants with wire support were minimal (2.0% in length and 4.1% in width), whereas significant reduction in size occurred in the constructs without embedded wire (14.4% in length and 16.5% in width). No gross distortion occurred over the in vivostudy period. There were no adverse effects on neocartilage formation from the embedded wire. Histologically, mature neocartilage extracellular matrix was observed throughout all implants. The amount of DNA, glycosaminoglycan, and hydroxyproline in the engineered cartilage were similar to that of native sheep ear cartilage. The embedded wire support was essential for avoiding shrinkage of the ear-shaped porous collagen constructs.

The objective of this study was to fabricate hydrogel matrix-engineered biosynthetic cartilage using a porous poly(vinyl alcohol) hydrogel (PVA-H) and articular chondrocytes. Chondrocytes were suspended in fibrin gel (FG) or saline carriers and injected into porous PVA-H discs and three-layered constructs (PVA-H between devitalized cartilage). After implantation in nude mice, PVA discs were explanted at 6 weeks and subjected to creep testing for a 20 h period. The three-layered constructs were explanted at 12 weeks and subjected to tensile testing to determine the strength of the interface between the engineered hydrogel and devitalized cartilage. Histological analysis revealed PVA-H porous channels occupied by chondrocytes. Extracellular matrix was identified by Safranin-O and toluidine blue stains. Immunohistochemical analysis revealed a positive stain for COL II and scant staining for COL I. Creep and relaxation response of PVA-FG-chondrocyte constructs was similar to that of native cartilage. The presence of cells and FG significantly enhanced the integration strength of layered constructs (p< 0.05). These results demonstrate that porous PVA-H in combination with FG and chondrocytes provides a favorable microenvironment for tissue engineering of articular cartilage, creating a biosynthetic construct that can adhere to native devitalized articular cartilage utilizing hydrogel matrix-engineered technology.

In this study we investigated the histological, biochemical, and integrative features of the neocartilage using swine auricular chondrocytes photoencapsulated into two poly(ethylene glycol) dimethacrylate (PEGDM) copolymer hydrogels of a different degradation profile: degradable (PEG-4,5LA-DM) and nondegradable (PEGDM) macromers in molar ratios of 60:40 and 70:30. Integration of the engineered tissue with existing native cartilage was examined using an articular cartilaginous ring model. Experimental group samples (total n= 96) were implanted subcutaneously into nude mice and harvested at 6, 12, and 18 weeks. Nonimplanted constructs (total n= 16) were used as controls for quantification of DNA, glycosaminoglycan, and hydroxyproline. Histologically, neocartilage resembled both the cellular population and composition of the extracellular matrix of the native swine auricular cartilage. DNA content demonstrated that the photoencapsulated chondrocytes were capable of survival and proliferation over time. Both glycosaminoglycan and hydroxyproline contents appeared higher in the neotissue, which was supported by less degradable PEGDM hydrogel. Integration of neocartilage with surrounding native cartilage improved with time, resulting in the development of tight integration interface. PEGDM copolymer hydrogels can support in vivochondrogenesis by photoencapsulating auricular chondrocytes.