Hydrophobicity as a design criterion for polymer scaffolds in bone tissue engineering

Porous polymeric scaffolds play a key role in most tissue-engineering strategies. A series of non-degrading porous scaffolds was prepared, based on bulk-copolymerisation of 1-vinyl-2-pyrrolidinone (NVP) and n-butyl methacrylate (BMA), followed by a particulate-leaching step to generate porosity. Biocompatibility of these scaffolds was evaluated in vitro and in vivo. Furthermore, the scaffold materials were studied using the so-called demineralised bone matrix (DBM) as an evaluation system in vivo. The DBM, which is essentially a part of a rat femoral bone after processing with mineral acid, provides a suitable environment for ectopic bone formation, provided that the cavity of the DBM is filled with bone marrow prior to subcutaneous implantation in the thoracic region of rats. Various scaffold materials, differing with respect to composition and, hence, hydrophilicity, were introduced into the centre of DBMs. The ends were closed with rat bone marrow, and ectopic bone formation was monitored after 4, 6, and 8 weeks, both through X-ray microradiography and histology. The 50:50 scaffold particles were found to readily accommodate formation of bone tissue within their pores, whereas this was much less the case for the more hydrophilic 70:30 counterpart scaffolds. New healthy bone tissue was encountered inside the pores of the 50:50 scaffold material, not only at the periphery of the constructs but also in the center. Active osteoblast cells were found at the bone-biomaterial interfaces. These data indicate that the hydrophobicity of the biomaterial is, most likely, an important design criterion for polymeric scaffolds which should promote the healing of bone defects. Furthermore, it is argued that stable, non-degrading porous biomaterials, like those used in this study, provide an important tool to expand our comprehension of the role of biomaterials in scaffold-based tissue engineering approaches.     

Bioreactor system using noninvasive imaging and mechanical stretch for biomaterial screening

Screening of biomaterial and tissue systems in vitro, for guidance of performance in vivo, remains a major requirement in the field of tissue engineering. It is critical to understand how culture stimulation affects both tissue construct maturation and function, with the goal of eliminating resource-intensive trial-and-error screening and better matching specifications for various in vivo needs. In this article a multifunctional and robust bioreactor design that addresses this need is presented. The design enables a range of mechanical inputs, durations, and frequencies to be applied in coordination with noninvasive optical assessments. A variety of biomaterial systems, including micro- and nano-fiber and porous sponge biomaterials, as well as cell-laden tissue engineering constructs were used in validation studies to demonstrate the versatility and utility of this new bioreactor design. The silk-based biomaterials highlighted in these studies offered several unique optical signatures for use in label-free nondestructive imaging that allowed for sequential profiling. Both short- and long-term culture studies were conducted to evaluate several practical scenarios of usage: on a short-term basis, the authors demonstrate that construct cellularity can be monitored by usage of nonpermanent dyes; on a more long-term basis, the authors show that cell ingrowth can be monitored by green-fluorescent protein (GFP)-labeling, and construct integrity probed with concurrent load/displacement data. The ability to nondestructively track cells, biomaterials, and new matrix formation without harvesting designated samples at each time point will lead to less resource-intensive studies and should enhance our understanding and the discovery of biomaterial designs related to functional tissue engineering.     

In vivo magnetic resonance imaging and relaxometry study of a porous hydrogel implanted in the trapezius muscle of rabbits

In vivo magnetic resonance imaging (MRI) and relaxometry were performed to assess noninvasively the tissue reaction and the biological integration of hydrogels made of poly[N-(2-hydroxypropyl) methacrylamide] (PHPMA) after implantation in the trapezius muscle of rabbits. The benefits of incorporating RGD peptide sequences in the polymer backbone were also investigated. The histological status of each implant was probed by the trend of their transversal relaxation times, T(2), while their biocompatibility was evaluated by analyzing the host tissue response through the evolution of the relaxation times of the adjacent muscle tissue. MR results showed the good acceptability of both hydrogels by the host tissue. The transversal relaxation curves of each implant exhibited two distinct phases as a function of implantation time: (1) a monoexponential phase, dominated by the influx of fluids inside the implants; and (2) a biexponential phase related to the infiltration of cells and the granulation tissue formation within the porous structure of each polymer. These MR findings were correlated with the results of conventional histological analyses. The present study demonstrates the effectiveness of MR methods in noninvasively monitoring the biocompatibility and histological status of implanted porous biomaterials.     

A new approach to the rationale discovery of polymeric biomaterials

This paper attempts to illustrate both the need for new approaches to biomaterials discovery as well as the significant promise inherent in the use of combinatorial and computational design strategies. The key observation of this Leading Opinion Paper is that the biomaterials community has been slow to embrace advanced biomaterials discovery tools such as combinatorial methods, high-throughput experimentation, and computational modeling in spite of the significant promise shown by these discovery tools in materials science, medicinal chemistry and the pharmaceutical industry. It seems that the complexity of living cells and their interactions with biomaterials has been a conceptual as well as a practical barrier to the use of advanced discovery tools in biomaterials science. However, with the continued increase in computer power, the goal of predicting the biological response of cells in contact with biomaterials surfaces is within reach. Once combinatorial synthesis, high-throughput experimentation, and computational modeling are integrated into the biomaterials discovery process, a significant acceleration is possible in the pace of development of improved medical implants, tissue regeneration scaffolds, and gene/drug delivery systems.     

Angiogenesis with biomaterial-based drug- and cell-delivery systems

Angiogenesis, the formation of new blood vessels from existing ones, is an important event in several biological processes, including wound healing. It plays a key role in determining the final functionality and integration of any implanted medical device. In addition, angiogenesis is a required event for organ development and has been accepted as a rate-limiting step in engineering tissue replacements. Besides these regenerative processes, uncontrolled angiogenesis is also involved in a number of pathologies, including tumor growth and metastases. Like angiogenesis, biomaterials also play a role in wound healing after medical device implantation and in tissue engineering. Interactions between the device biomaterials and host tissue will factor into the final device integration. Additionally, tissue-engineering strategies utilize biomaterials to a great extent because the paradigm of tissue engineering involves the use of cells, growth factors and scaffolding matrices in order to regenerate or replace tissue. Since almost all tissues are three-dimensional, the biomaterial scaffold plays an integral role in the paradigm. This review will emphasize the influence of biomaterials on angiogenesis as it applies to medical device implantation, tissue engineering and therapies for pathological angiogenesis.     

Angiogenesis with biomaterial-based drug- and cell-delivery systems

Angiogenesis, the formation of new blood vessels from existing ones, is an important event in several biological processes, including wound healing. It plays a key role in determining the final functionality and integration of any implanted medical device. In addition, angiogenesis is a required event for organ development and has been accepted as a rate-limiting step in engineering tissue replacements. Besides these regenerative processes, uncontrolled angiogenesis is also involved in a number of pathologies, including tumor growth and metastases. Like angiogenesis, biomaterials also play a role in wound healing after medical device implantation and in tissue engineering. Interactions between the device biomaterials and host tissue will factor into the final device integration. Additionally, tissue-engineering strategies utilize biomaterials to a great extent because the paradigm of tissue engineering involves the use of cells, growth factors and scaffolding matrices in order to regenerate or replace tissue. Since almost all tissues are three-dimensional, the biomaterial scaffold plays an integral role in the paradigm. This review will emphasize the influence of biomaterials on angiogenesis as it applies to medical device implantation, tissue engineering and therapies for pathological angiogenesis.     

Controlled release of dexamethasone from peptide nanofiber gels to modulate inflammatory response

New biomaterials that have the ability to locally suppress an immune response could have broad therapeutic use in the treatment of diseases characterized by acute or chronic inflammation or as a strategy to facilitate improved efficacy in cell or tissue transplantation. We report here on the preparation of a modular peptide amphiphile (PA) capable of releasing an anti-inflammatory drug, dexamethasone (Dex), by conjugation via a labile hydrazone linkage. This molecule self-assembled in water into long supramolecular nanofibers when mixed with a similar PA lacking the drug conjugate, and the addition of calcium salt to screen electrostatic repulsion between nanofibers promoted gel formation. These nanofiber gels demonstrated sustained release of soluble Dex for over one month in physiologic media. The Dex released from these gels maintained its anti-inflammatory activity when evaluated in?vitro using a human inflammatory reporter cell line and furthermore preserved cardiomyocyte viability upon induced oxidative stress. The ability of this gel to mitigate the inflammatory response in cell transplantation strategies was evaluated using cell-surrogate polystyrene microparticles suspended in the nanofiber gel that were then subcutaneously injected into mice. Live animal luminescence imaging using the chemiluminescent reporter molecule luminol showed a significant reduction in inflammation at the site where particles were injected with Dex-PA compared to the site of injection for particles within a control PA in the same animal. Histological evidence suggested a marked reduction in the number of infiltrating inflammatory cells when particles were delivered within Dex-PA nanofiber gels, and very little inflammation was observed at either 3 days or 21 days post-implantation. The use of Dex-PA could facilitate localized anti-inflammatory activity as a component of biomaterials designed for various applications in regenerative medicine and could specifically be a useful module for PA-based therapies. More broadly, these studies define a versatile strategy for facile synthesis of self-assembling peptide-based materials with the ability to control drug release.     

Reduction of abdominal adhesions using composite collagen-GAG implants for ventral hernia repair

Structural biomaterials can restore abdominal wall integrity but may cause adhesions to the underlying viscera. Collagen-glycosaminoglycan (CG) matrices induce the formation of connective tissue and may reduce adhesion formation to permanent biomaterials such as polypropylene (PP) mesh. Composite implants were created by interposing PP mesh within a porous CG matrix created composite implants. The implants were cross-linked with glutaraldehyde one group (CG-G/PP) or left untreated (CG-nG/PP) and compared to PP mesh. At 4 weeks, the abdominal wall was assessed for the degree of adhesions. The composite implants developed a nascent connective tissue-like structure that reduced adhesions to the bowel. The thickest connective tissue developed in the CG-G/PP group (0.7 +/- 0.1 mm) and thinnest in the PP mesh (0.05 +/- 0.01 mm). The surface area covered with adhesions was greatest in the PP group (72 +/- 17%) compared with the CG-G/PP group (28 +/- 15%) or the CG-nG/PP group (21 +/- 8%). Bowel preferentially adhered to the PP mesh, whereas omentum had some adherence to all constructs. Integrating a biodegradable extracellular matrix analog with a permanent structural biomaterial reduced adhesions in this animal model. Alterations in cross-linking of the CG matrix altered the biological response. This technology may be useful in reconstructive surgery by reducing adhesion formation, while maintaining the strength of permanent structural biomaterials.     

In vivo fluorescence imaging of apoptosis during foreign body response

Quantification of apoptotic tissues during inflammatory processes induced by biomaterials is challenging in?vivo. Here we present a non-invasive method using a fluorescence imaging system which facilitates intermittent snap shots of the current state of local apoptotic tissue. For this purpose, apoptotic cells around two different subcutaneously implanted materials (titanium discs and copper-coated titanium discs) in hairless but immunocompetent mice were quantified after 4, 8 and 23 days of implantation. For validation, the results of fluorescence signals were compared to the histology of the inflammatory tissue using apoptotic-specific TUNEL-, macrophage-specific F4/80-, neutrophile-specific NIMP-R14- and chloroacetate esterase-staining. We could demonstrate that the fluorescence signals were well suited to quantify the extent of apoptosis in?vivo and this is a good indication for the biocompatibility of biomaterials. This study shows that non-invasive monitoring of tissue processes following the implantation of biomaterials is possible in?vivo and may help to reduce the number of animals in studies addressing biocompatibility.     

Non-invasive characterization of structure and morphology of silk fibroin biomaterials using non-linear microscopy

Designing biomaterial scaffolds remains a major challenge in tissue engineering. Key to this challenge is improved understanding of the relationships between the scaffold properties and its degradation kinetics, as well as the cell interactions and the promotion of new matrix deposition. Here we present the use of non-linear spectroscopic imaging as a non-invasive method to characterize not only morphological, but also structural aspects of silkworm silk fibroin-based biomaterials, relying entirely on endogenous optical contrast. We demonstrate that two photon excited fluorescence and second harmonic generation are sensitive to the hydration, overall beta sheet content and molecular orientation of the sample. Thus, the functional content and high resolution afforded by these non-invasive approaches offer promise for identifying important connections between biomaterial design and functional engineered tissue development. The strategies described also have broader implications for understanding and tracking the remodeling of degradable biomaterials under dynamic conditions both in vitro and in vivo.     

Development of a biological scaffold engineered using the extracellular matrix secreted by skeletal muscle cells

The performance of implantable biomaterials derived from decellularized tissue, including encouraging results with skeletal muscle, suggests that the extracellular matrix (ECM) derived from native tissue has promising regenerative potential. Yet, the supply of biomaterials derived from donated tissue will always be limited, which is why the in-vitro fabrication of ECM biomaterials that mimic the properties of tissue is an attractive alternative. Towards this end, our group has utilized a novel method to collect the ECM that skeletal muscle myoblasts secrete and form it into implantable scaffolds. The cell derived ECM contained several matrix constituents, including collagen and fibronectin that were also identified within skeletal muscle samples. The ECM was organized into a porous network that could be formed with the elongated and aligned architecture observed within muscle samples. The ECM material supported the attachment and in-vitro proliferation of cells, suggesting effectiveness for cell transplantation, and was well tolerated by the host when examined in-vivo. The results suggest that the ECM collection approach can be used to produce biomaterials with compositions and structures that are similar to muscle samples, and while the physical properties may not yet match muscle values, the in-vitro and in-vivo results indicate it may be a suitable first generation alternative to tissue derived biomaterials.     

A collagen-glycosaminoglycan co-culture model for heart valve tissue engineering applications

In order to develop efficient design strategies for a tissue-engineered heart valve, in vivo and in vitro models of valvular structure and cellular function require extensive characterisation. Collagen and glycosaminoglycans (GAGs) provide unique functional characteristics to the heart valve structure. In the current study, type I collagen-GAG hydrogels were investigated as biomaterials for the creation of mitral valve tissue. Porcine mitral valve interstitial cells (VICs) and endothelial cells (VECs) were isolated and co-cultured for 4 weeks in hydrogel constructs composed of type I collagen. The metabolic activity and tissue organisation of mitral valve tissue constructs was evaluated in the presence and absence of chondroitin sulphate (CS) GAG, and comparisons were made with normal mitral valve tissue. Both collagen and collagen-CS mitral valve constructs contracted to form tissue-like structures in vitro. Biochemical assay demonstrated that over 75% of CS was retained within collagen-CS constructs. Morphological examination demonstrated enhanced VEC surface coverage in collagen-CS constructs compared to collagen constructs. Ultrastructural analysis revealed basement membrane synthesis and cell junction formation by construct VECs, with an increased matrix porosity observed in collagen-CS constructs. Immunohistochemical analyses demonstrated enhanced extracellular matrix production in collagen-CS constructs, including expression of elastin and laminin by VICs. Both native valve and collagen-CS construct VECs also expressed the vasoactive molecule, eNOS, which was absent from collagen construct VECs. The present study demonstrates that collagen gels can be used as matrices for the in vitro synthesis of tissue structures resembling mitral valve tissue. Addition of CS resulting in a more porous model was shown to positively influence the bioactivity of seeded valve cells and tissue remodelling. Collagen-GAG matrices may hold promise for a potential use in heart valve tissue engineering and improved understanding of heart valve biology.     

Analysis of 3D bone ingrowth into polymer scaffolds via micro-computed tomography imaging

This paper illustrates the utility of micro-computed tomography (micro-CT) to study the process of tissue engineered bone growth. A micro-CT facility for imaging and visualising biomaterials in three dimensions (3D) is described. The facility is capable of acquiring 3D images made up of 2000(3) voxels on specimens up to 60mm in extent with resolutions down to 2 microm. This allows the 3D structure of tissue engineered materials to be imaged across three orders of magnitude of detail. The capabilities of micro-CT are demonstrated by imaging the Haversian network within human femoral cortical bone (distal diaphysis) and bone ingrowth into a porous scaffold at varying resolutions. Phase identification combined with 3D visualisation enables one to observe the complex topology of the canalicular system of the cortical bone. Imaging of the tissue engineered bone at a scale of 1cm and resolutions of 10 microm allows visualisation of the complex ingrowth of bone into the polymer scaffold. Further imaging at 2 microm resolution allows observation of bone ultra-structure. These observations illustrate the benefits of tomography over traditional techniques for the characterisation of bone morphology and interconnectivity and performs a complimentary role to current histomorphometric techniques.     

Impact of sterilization on the porous design and cell behavior in collagen sponges prepared for tissue engineering

This study investigates the impact of different sterilization processes on structural integrity and stability of collagen sponges designed for tissue engineering. Collagen sponges with uniform pore size (20 microm) were sterilized either with ethylene oxide (EO) or gamma irradiation (2.5 Mrad). Gamma-sterilized sponges showed a dramatic decrease of resistance against enzyme degradation and severe shrinkage after cell seeding. Collapsed porosity inhibited fibroblasts and barred completely the human umbilical vein endothelial cell ingrowth into the sponges. On the contrary, the porous structure and stability of EO-sterilized sponges remained almost unaltered. Fibroblasts and endothelial cells exhibited favorable proliferation and migration within sponges with normal morphology. Tubular formation by seeded endothelial cells occurred early in the first week. Therefore, we emphasize that the impact of sterilization of biomaterials is substantial and any new procedure has to be evaluated by correlating the impact of the procedure on the porous structure with cell proliferation behavior.     

Geometry of Artificial ECM: Sizes of Pores Controlling Phenotype Expression in BMP-Induced Osteogenesis and Chondrogenesis

This study aims to elucidate the feasible geometry of the scaffolds in bone and periodontal tissue engineering. Several biomaterials with different geometries are compared in terms of their patterns of ectopic BMP-induced chondrogenesis and osteogenesis. The materials include a honeycomb-shaped hydroxyapatite (HCHAP) with different tunnel sizes, a laser-perforated collagen membrane (LPM), and CPSA bioglass fibers. Implanted pellets were removed at 1-4 weeks and analyzed for bone and cartilage formation histologically and biochemically. Porous particles of hydroxyapatite (PPHAP), porous blocks of hydroxyapatite (PBHAP), and LPM did not induce detectable cartilage formation. In straight tunnel structures with various diameters in honeycomb-shaped hydroxyapatite (HCHAP), tunnels with smaller diameters (approximately 0.1 mm) induced cartilage followed by bone formation, while one with a larger diameter (0.35 mm) directly induced bone formation within the tunnels. It is concluded that the "vasculature-inducing geometry" of the carrier as an ECM is crucially important for osteogenesis.     

Geometry of artificial ECM: sizes of pores controlling phenotype expression in BMP-induced osteogenesis and chondrogenesis

This study aims to elucidate the feasible geometry of the scaffolds in bone and periodontal tissue engineering. Several biomaterials with different geometries are compared in terms of their patterns of ectopic BMP-induced chondrogenesis and osteogenesis. The materials include a honeycomb-shaped hydroxyapatite (HCHAP) with different tunnel sizes, a laser-perforated collagen membrane (LPM), and CPSA bioglass fibers. Implanted pellets were removed at 1-4 weeks and analyzed for bone and cartilage formation histologically and biochemically. Porous particles of hydroxyapatite (PPHAP), porous blocks of hydroxyapatite (PBHAP), and LPM did not induce detectable cartilage formation. In straight tunnel structures with various diameters in honeycomb-shaped hydroxyapatite (HCHAP), tunnels with smaller diameters (approximately 0.1 mm) induced cartilage followed by bone formation, while one with a larger diameter (0.35 mm) directly induced bone formation within the tunnels. It is concluded that the "vasculature-inducing geometry" of the carrier as an ECM is crucially important for osteogenesis.     

Biomaterials based strategies for skeletal muscle tissue engineering: Existing technologies and future trends

Skeletal muscles have a robust capacity to regenerate, but under compromised conditions, such as severe trauma, the loss of muscle functionality is inevitable. Research carried out in the field of skeletal muscle tissue engineering has elucidated multiple intrinsic mechanisms of skeletal muscle repair, and has thus sought to identify various types of cells and bioactive factors which play an important role during regeneration. In order to maximize the potential therapeutic effects of cells and growth factors, several biomaterial based strategies have been developed and successfully implemented in animal muscle injury models. A suitable biomaterial can be utilized as a template to guide tissue reorganization, as a matrix that provides optimum micro-environmental conditions to cells, as a delivery vehicle to carry bioactive factors which can be released in a controlled manner, and as local niches to orchestrate in situ tissue regeneration. A myriad of biomaterials, varying in geometrical structure, physical form, chemical properties, and biofunctionality have been investigated for skeletal muscle tissue engineering applications. In the current review, we present a detailed summary of studies where the use of biomaterials favorably influenced muscle repair. Biomaterials in the form of porous three-dimensional scaffolds, hydrogels, fibrous meshes, and patterned substrates with defined topographies, have each displayed unique benefits, and are discussed herein. Additionally, several biomaterial based approaches aimed specifically at stimulating vascularization, innervation, and inducing contractility in regenerating muscle tissues are also discussed. Finally, we outline promising future trends in the field of muscle regeneration involving a deeper understanding of the endogenous healing cascades and utilization of this knowledge for the development of multifunctional, hybrid, biomaterials which support and enable muscle regeneration under compromised conditions.     

Pathogenesis of catheter-related infections: lessons for new designs

In the last decade, two main strategies have been employed in the prevention of catheter-related infections: the creation of anti-adhesive biomaterials using physicochemical methods, and the incorporation of antimicrobial or antiseptic agents into current polymer biomaterials. There has been limited success with the first approach. Intravascular catheters and cuffs with an antimicrobial coating have been developed in recent years. Nevertheless, preventive strategies should avoid the use of therapeutic antibiotics. Exposure to antimicrobial agents could favor the development of resistance or the expression of genes responsible for biofilm formation. The use of these catheters should be restricted to situations where the rate of infection is high despite adherence to other strategies that do not incorporate antimicrobial agents. Better knowledge of the pathogenesis of catheter-related infections will facilitate the design of new devices that avoid the use of antimicrobial agents and decrease the risk of associated bloodstream infections. This could include the use of 'biospecific polymers' coated with anti-adhesive molecules or the use of agents which might block the expression of genes controlling biofilm formation for the most prevalent pathogens.     

Effect of the pore structure of bioactive glass balls on biocompatibility in vitro and in vivo

We prepared porous bioactive glass (BG) balls with various pore architectures using a modified version of a polymer templating technique which is generally used for the synthesis of mesoporous BG. Sol-gel derived porous BG is an excellent candidate as a graft material for bone tissue regeneration due to its good bone forming bioactivity and biodegradability. The biodegradability is largely related to the pore architecture and affects its biocompatibility. The pore architecture of the BG balls was controllable by changing the reaction time in chloroform. The relationship between the pore architecture of the BG balls and biocompatibility were studied using MC3T3-E1 pre-osteoblast cells in vitro and the rabbit calvarial model in vivo 8 weeks after implantation. The mesoporous BG balls (BG0) and porous BG beads with a hierarchical pore structure on the nano- to microscale (BG0.5 and BG2) showed a good cell proliferation response and differentiation behavior in vitro and in vivo without serious toxicity. These hierarchically porous structures also enhanced osteoconductivity. However, the existence of too many microscale pores in the BG balls (BG24) led to their rapid biodegradation and, consequently, to serious negative effects in vitro and in vivo. The pore architecture of the BG balls greatly influenced their biocompatibility, as well as bone formation, and should be carefully controlled when designing new materials for use in bioapplications. The porous BG balls with hierarchical pores on the nano- to microscale exhibit favorable biocompatibility in vitro and promise excellent potential applications in the field of biomaterials, such as tissue regeneration and drug storage.     

Assessment of tissue ingrowth rates in polyurethane scaffolds for tissue engineering

The continuous development of new biomaterials for tissue engineering and the enhancement of tissue ingrowth into existing scaffolds, using growth factors, create the necessity for developing adequate tools to assess tissue ingrowth rates into porous biomaterials. Current histomorphometric techniques evaluating rates of tissue ingrowth tend either to measure the overall tissue content in an entire sample or to depend on the user to indicate a front of tissue ingrowth. Neither method is particularly suitable for the assessment of tissue ingrowth rates, as these methods either lack the sensitivity required or are problematic when there is a tissue ingrowth gradient rather than an obvious tissue ingrowth front. This study describes a histomorphometric method that requires little observer input, is sensitive, and renders detailed information for the assessment of tissue ingrowth rates into porous biomaterials. This is achieved by examining a number of computer-defined concentric zones, which are based on the distance of a pixel from the scaffold edge. Each zone is automatically analyzed for tissue content, eliminating the need for user definition of a tissue ingrowth front and thus reducing errors and observer dependence. Tissue ingrowth rates in two biodegradable polyurethane scaffolds (Estane and polycaprolactone-polyurethane [PCLPU]) specifically designed for tissue engineering of the knee meniscus were assessed. Samples were subcutaneously implanted in rats with follow-up until 6 months. Especially at the earlier follow-up points, PCLPU scaffolds showed significantly higher tissue ingrowth rates than Estane scaffolds, making the PCLPU scaffold a promising candidate for further studies investigating meniscus tissue engineering.