Biomedical subjects

D J Mooney

Publications and source records attributed to D J Mooney.

At least 37 records · Page 2Linked to original sources

PubMed2001

Promoting angiogenesis in engineered tissues.

There is a tremendous need for organs and tissues to replace those lost due to diseases or trauma. In theory, transplanting cells on biomaterial matrices can create functional tissue. A critical question, however, is how to supply cells embedded within large cell-polymer constructs with sufficient oxygen and nutrients to sustain their survival and proliferation, and allow for the integration of the developing tissue with the surrounding tissue. A rapid and high level of vascularization of transplanted polymer-cell matrices is essential in tissue engineering approaches to meet these challenges. This review summarizes the current approaches and materials under development in our laboratory to promote angiogenesis in engineered tissues.

Alginates↗

PubMed2001

Polymeric delivery of proteins and plasmid DNA for tissue engineering and gene therapy.

In vivo gene expression can be altered by locally delivered DNA and proteins. The ability to deliver bioactive macromolecules, such as proteins and plasmid DNA, over controllable time frames represents a challenging engineering problem. Considerable success has been achieved with polymeric delivery systems that provide the capability to change cell function either acutely or chronically. This review focuses on controlled delivery of proteins and plasmid DNA from polymers and on the effects of controlled delivery on gene expression, and introduces some cell biological and biochemical parameters to be considered when delivering macromolecules to change cell behavior.

Animals↗

PubMed2000

Comparative study of seeding methods for three-dimensional polymeric scaffolds.

Development of tissue-engineered devices may be enhanced by combining cells with porous absorbable polymeric scaffolds before implantation. The cells are seeded throughout the scaffolds and allowed to proliferate in vitro for a predetermined amount of time. The distribution of cells throughout the porous material is one critical component determining success or failure of the tissue-engineered device. This can influence both the successful integration of the device with the host tissue as well as the development of a vascularized network throughout the entire scaffold volume. This research sought to compare different seeding and proliferation methods to select an ideal method for a polyglycolide/aortic endothelial cell system. Two seeding environments, static and dynamic, and three proliferation environments, static, dynamic, and bioreactor, were analyzed, for a total of six possible methods. The six seeding and proliferation combinations were analyzed following a 1-week total culture time. It was determined that for this specific system, dynamic seeding followed by a dynamic proliferation phase is the least promising method and dynamic seeding followed by a bioreactor proliferation phase is the most promising.

Animals↗

PubMed2000

Bioabsorbable polymer scaffolds for tissue engineering capable of sustained growth factor delivery.

Engineering new tissues utilizing cell transplantation on biodegradable polymer matrices is an attractive approach to treat patients suffering from the loss or dysfunction of a number of tissues and organs. The matrices must maintain structural integrity during the process of tissue formation, and promote the vascularization of the developing tissue. A number of molecules (angiogenic factors) have been identified that promote the formation of new vascular beds from endothelial cells present within tissues, and the localized, controlled delivery of these factors from a matrix may allow an enhanced vascularization of engineered tissues. We have developed a gas foaming polymer processing approach that allows the fabrication of three-dimensional porous matrices from bioabsorbable materials (e.g., copolymers of lactide and glycolide [PLG]) without the use of organic solvents or high temperatures. The effects of several processing parameters (e.g., gas type, polymer composition and molecular weight) on the process were studied. Several gases (CO(2), N(2), He) were utilized in the fabrication process, but only CO(2) resulted in the formation of highly porous, structurally intact matrices. Crystalline polymers (polylactide and polyglycolide) did not form porous matrices, while amorphous copolymers (50:50, 75:25, and 85:15 ratio of lactide:glycolide) foamed to yield matrices with porosity up to 95%. The mechanical properties of matrices were also regulated by the choice of PLG composition and molecular weight. Angiogenic factors (e.g., vascular endothelial growth factor) were subsequently incorporated into matrices during the fabrication process, and released in a controlled manner. Importantly, the released growth factor retains over 90% of its bioactivity. In summary, a promising system for the incorporation and delivery of angiogenic factors from three-dimensional, biodegradable polymer matrices has been developed, and the fabrication process allows incorporation under mild conditions.

Absorption↗

PubMed2000

Use of internal bioabsorbable PLGA "finger-type" stents in a rabbit tracheal reconstruction model.

OBJECTIVES: To design and develop a biodegradable tracheal stent that can be used internally to stabilize and support surgically reconstructed airways. DESIGN: In vitro mechanical and degradative properties of 80:20 poly(D,L-lactide-co-glycolide) (PLGA) "finger-like" stents were determined. The stents were then tested in vivo in rabbits that underwent anterior patch tracheoplasties with fascia lata grafts. Comparisons were made between a control group and an internal stent group for stridor development, overall group mortality, reconstructed airway lumen size, and histological findings. SUBJECTS: Twenty-five New Zealand white rabbits. RESULTS: The average dry modulus for the internal stents was 6800 kPa. All of the internal stents cracked by 4 weeks in buffer solution. Significant mass loss was not noted in vitro until after 5 weeks in buffer solution. By 14 weeks, the stents were nearly 100% degraded. The attrition rate for the control group was 23% compared with 17% for the experimental group. The stridor rate for the control group was also higher at 38% compared with 17% for the stented group. The stented rabbits had a significantly smaller average stenosis (23%) across the entire reconstruction site than the control group (34%) (P<.05). CONCLUSION: Biodegradable PLGA stents degrade in a predictable fashion and have a statistically significant effect in augmenting anterior patch tracheoplasties with fascia lata grafts in rabbits.

Animals↗

PubMed2000

Growth of continuous bonelike mineral within porous poly(lactide-co-glycolide) scaffolds in vitro.

Strategies to engineer bone have focused on the use of natural or synthetic degradable materials as scaffolds for cell transplantation or as substrates to guide bone regeneration. The basic requirements of the scaffold material are biocompatibility, degradability, mechanical integrity, and osteoconductivity. A major design problem is satisfying each of these requirements with a single scaffold material. This study addresses this problem by describing an approach to combine the biocompatibility and degradability of a polymer scaffold with the osteoconductivity and mechanical reinforcement of a bonelike mineral film. We report the nucleation and growth of a continuous carbonated apatite mineral on the interior pore surfaces of a porous, degradable polymer scaffold via a one step, room temperature incubation process. A 3-dimensional, porous scaffold of the copolymer 85:15 poly(lactide-co-glycolide) was fabricated by a solvent casting, particulate leaching process. Fourier transform IR spectroscopy and scanning electron microscopy (SEM) analysis after different incubation times in a simulated body fluid (SBF) demonstrate the growth of a continuous bonelike apatite layer within the pores of the polymer scaffold. Quantification of phosphate on the scaffold displays the growth and development of the mineral film over time with an incorporation of 0.43 mg of phosphate (equivalent to 0.76 mg of hydroxyapatite) per scaffold after 14 days in SBF. The compressive moduli of polymer scaffolds increased fivefold with formation of a mineral film after a 16-day incubation time as compared to control scaffolds. In summary, this biomimetic treatment provides a simple, one step, room temperature method for surface functionalization and subsequent mineral nucleation and growth on biodegradable polymer scaffolds for tissue engineering.

Analysis of Variance↗

PubMed2000

Sustained and controlled release of daunomycin from cross-linked poly(aldehyde guluronate) hydrogels.

We have incorporated daunomycin, an antineoplastic agent, into a biodegradable hydrogel through a labile covalent bond. In brief, sodium alginate was chemically broken down to low molecular weight and followed by oxidation to prepare poly(aldehyde guluronate). Adipic dihydrazide was used to incorporate the drug into the polymer backbone and cross-link the polymer to form hydrogels. Daunomycin can be released from the hydrogel after the hydrolysis of the covalent linkage between the drug and the polymer. A wide range of release profiles of daunomycin (e.g., from 2 days to 6 weeks) has been achieved using these materials, and the biological activity of the released daunomycin was maintained.

Aldehydes↗

PubMed2000

Porous carriers for biomedical applications based on alginate hydrogels.

Macroporous scaffolds are typically utilized in tissue engineering applications to allow for the migration of cells throughout the scaffold and integration of the engineered tissue with the surrounding host tissue. A method to form macroporous beads with an interconnected pore structure from alginate has been developed by incorporating gas pockets within alginate beads, stabilizing the gas bubbles with surfactants, and subsequently removing the gas. Macroporous scaffolds could be formed from alginate with different average molecular weights (5-200 kDa) and various surfactants. The gross morphology, amount of interconnected pores, and total void volume was investigated both qualitatively and quantitatively. Importantly, macroporous alginate beads supported cell invasion in vitro and in vivo.

Alginates↗

PubMed2000

Smooth muscle cell adhesion to tissue engineering scaffolds.

Synthetic polyesters of lactic and glycolic acid, and the extracellular matrix molecule collagen are among the most widely-utilized scaffolding materials in tissue engineering. However, the mechanism of cell adhesion to these tissue engineering scaffolds has not been extensively studied. In this paper, the mechanism of adhesion of smooth muscle cells to these materials was investigated. Vitronectin was found to be the predominant matrix protein adsorbed from serum-containing medium onto polyglycolic acid, poly(lactic co-glycolic) acid, and collagen two-dimensional films and three-dimensional scaffolds. Fibronectin adsorbed to both materials as well, although to a much lower density. Smooth muscle cell adhesion was mediated through specific integrin receptors interacting with these adsorbed proteins, as evidenced by both immunostaining and blocking studies. The receptors involved in adhesion included the alpha(v)beta5 to vitronectin, the alpha5beta1 to fibronectin and the alpha2beta1 to collagen I. Identification of the specific receptors used to adhere to these polymers clarifies why smooth muscle tissue development differs on these scaffolds, and may allow one to design tissue formation by controlling the surface chemistry of tissue engineering scaffolds.

Adsorption↗

PubMed2000

Sustained release of vascular endothelial growth factor from mineralized poly(lactide-co-glycolide) scaffolds for tissue engineering.

Strategies to engineer bone tissue have focused on either: (1) the use of scaffolds for osteogenic cell transplantation or as conductive substrates for guided bone regeneration; or (2) release of inductive bioactive factors from these scaffold materials. This study describes an approach to add an inductive component to an osteoconductive scaffold for bone tissue engineering. We report the release of bioactive vascular endothelial growth factor (VEGF) from a mineralized, porous, degradable polymer scaffold. Three dimensional, porous scaffolds of the copolymer 85 : 15 poly(lactide-co-glycolide) were fabricated by including the growth factor into a gas foaming/particulate leaching process. The scaffold was then mineralized via incubation in a simulated body fluid. Growth of a bone-like mineral film on the inner pore surfaces of the porous scaffold is confirmed by mass increase measurements and quantification of phosphate content within scaffolds. Release of 125I-labeled VEGF was tracked over a 15 day period to determine release kinetics from the mineralized scaffolds. Sustained release from the mineralized scaffolds was achieved, and growth of the mineral film had only a minor effect on the release kinetics from the scaffolds. The VEGF released from the mineralized and non-mineralized scaffolds was over 70% active for up to 12 days following mineralization treatment, and the growth of mineral had little effect on total scaffold porosity.

Biocompatible Materials↗

PubMed2000

Survival and function of rat hepatocytes cocultured with nonparenchymal cells or sinusoidal endothelial cells on biodegradable polymers under flow conditions.

BACKGROUND/PURPOSE: The authors have investigated hepatocyte transplantation using biodegradable polymer scaffolds as a possible treatment of end-stage liver disease. The purpose of this study was to investigate the survival rate and function of hepatocytes alone or cocultured with other cell types on 3-dimensional biodegradable polymers for 7 days under continuous flow conditions in vitro. METHODS: Hepatocytes (group 1, n = 8), hepatocytes with nonparenchymal cells (group 2, n = 7), or hepatocytes with sinusoidal endothelial cells (group 3, n = 6) were isolated from Lewis rats and seeded onto the polymer scaffolds. The polymer devices subsequently were placed under continuous flow conditions for 7 days. Albumin production from the constructs was measured each day, and urea nitrogen synthesis was examined on day 7. The devices also were examined by histology at day 7. RESULTS: Histology results showed the presence of numerous viable hepatocytes on polymer devices, with no differences in hepatocyte viability between the 3 groups. Albumin secretion in the culture medium gradually decreased by day 7. There also were no significant differences in albumin production or urea nitrogen synthesis between the 3 groups at day 7. CONCLUSIONS: Hepatocytes could survive on the 3-dimensional polymer scaffolds under flow conditions for 7 days, and albumin secretion and urea synthesis of hepatocytes were seen at day 7. Nonparenchymal cells and sinusoidal endothelial cells had no measurable effect on hepatocyte function in our continuous flow culture system.

Animals↗

PubMed2000

Dynamic seeding and in vitro culture of hepatocytes in a flow perfusion system.

Our laboratory has investigated hepatocyte transplantation using biodegradable polymer matrices as an alternative treatment to end-stage liver disease. One of the major limitations has been the insufficient survival of an adequate mass of transplanted cells. This study investigates a novel method of dynamic seeding and culture of hepatocytes in a flow perfusion system. In experiment I, hepatocytes were flow-seeded onto PGA scaffolds and cultured in a flow perfusion system for 24 h. Overall metabolic activity and distribution of cells were assessed by their ability to reduce MTT. DNA quantification was used to determine the number of cells attached. Culture medium was analyzed for albumin content. In Experiment II, hepatocyte/polymer constructs were cultured in a perfusion system for 2 and 7 days. The constructs were examined by SEM and histology. Culture medium was analyzed for albumin. In experiment I, an average of 4.4 X 10(6) cells attached to the scaffolds by DNA quantification. Cells maintained a high metabolic activity and secreted albumin at a rate of 13 pg/cell/day. In experiment II, SEM demonstrated successful attachment of hepatocytes on the scaffolds after 2 and 7 days. Cells appeared healthy on histology and maintained a high rate of albumin secretion through day 7. Hepatocytes can be dynamically seeded onto biodegradable polymers and survive with a high rate of albumin synthesis in the flow perfusion culture system.

Albumins↗

PubMed2000

Combining chondrocytes and smooth muscle cells to engineer hybrid soft tissue constructs.

Engineering new tissues using cell transplantation may provide a valuable tool for reconstructive surgery applications. Chondrocyte transplantation in particular has been successfully used to engineer new tissue masses due to the low metabolic requirements of these cells. However, the engineered cartilaginous tissue is too rigid for many soft tissue applications. We propose that hybrid tissue engineered from chondrocytes and smooth muscle cells could reflect mechanical properties intermediate between these two cell types. In this study, rat aortic smooth muscle cells and pig auricular chondrocytes were co-cultured on polyglycolic acid fiber-based matrices to address this hypothesis. Mixed cell suspensions were seeded by agitating the polymer matrices and a cell suspension with an orbital shaker. After seeding, cell-polymer constructs were cultured in stirred bioreactors for 8 weeks. The cell density and extracellular matrix (collagen, elastin, and glycosaminoglycan) content of the engineered tissues were determined biochemically. After 8 weeks in culture, the hybrid tissue had a high cell density (5.8 x 108 cells/cm(3)), and elastin (519 microg/g wet tissue sample), collagen (272 microg/g wet tissue sample), and glycosaminoglycan (GAG; 10 microg/g wet tissue sample) content. Mechanical testing indicated the compressive modulus of the hybrid tissues after 8 weeks to be 40.8 +/- 4.1 kPa and the equilibrium compressive modulus to be 8.4 +/- 0.8 kPa. Thus, these hybrid tissues exhibited intermediate stiffness; they were less stiff than native cartilage but stiffer than native smooth muscle tissue. This tissue engineering approach may be useful to engineer tissues for a variety of reconstructive surgery applications.

Animals↗

PubMed2000

The growth and morphological behavior of salivary epithelial cells on matrix protein-coated biodegradable substrata.

The purpose of this study was to examine the growth and morphology of a salivary epithelial cell line (HSG) in vitro on several biodegradable substrata as an important step toward developing an artificial salivary gland. The substrates examined were poly-L-lactic acid (PLLA), polyglycolic acid (PGA), and two co-polymers, 85% and 50% PLGA, respectively. The substrates were formed into 20- to 25-mm disks, and the cells were seeded directly onto the polymers or onto polymers coated with specific extracellular matrix proteins. The two copolymer substrates became friable over time in aqueous media and proved not useful for these experiments. The purified matrix proteins examined included fibronectin (FN), laminin (LN), collagen I, collagen IV, and gelatin. In the absence of preadsorbed proteins, HSG cells did not attach to the polymer disks. The cells, in general, behaved similarly on both PLLA and PGA, although optimal results were obtained consistently in PLLA. On FN-coated PLLA disks, HSG cells were able to form a uniform monolayer, which was dependent on time and FN concentration. Coating of disks with LN, collagen I, and gelatin also promoted monolayer growth. This study defines the conditions necessary for establishing a monolayer organization of salivary epithelial cells with rapid proliferation on a biodegradable substrate useful for tissue engineering.

Artificial Organs↗

PubMed2000

Engineered bone development from a pre-osteoblast cell line on three-dimensional scaffolds.

Bone regeneration is based on the hypothesis that healthy progenitor cells, either recruited or delivered to an injured site, can ultimately regenerate lost or damaged tissue. Three-dimensional porous polymer scaffolds may enhance bone regeneration by creating and maintaining a space that facilitates progenitor cell migration, proliferation, and differentiation. As an initial step to test this possibility, osteogenic cells were cultured on scaffolds fabricated from biodegradable polymers, and bone development on these scaffolds was evaluated. Porous polymer scaffolds were fabricated from biodegradable polymers of lactide and glycolide. MC3T3-E1 cells were statically seeded onto the polymer scaffolds and cultured in vitro in the presence of ascorbic acid and beta-glycerol phosphate. The cells proliferated during the first 4 weeks in culture and formed a space-filling tissue. Collagen messenger RNA levels remained high in these cells throughout the time in culture, which is consistent with an observed increase in collagen deposition on the polymer scaffold. Mineralization of the deposited collagen was initially observed at 4 weeks and subsequently increased. The onset of mineralization corresponded to increased mRNA levels for two osteoblast-specific genes: osteocalcin and bone sialoprotein. Culture of cell/polymer constructs for 12 weeks led to formation of a three-dimensional tissue with architecture similar to that of native bone. These studies demonstrate that osteoblasts within a three-dimensional engineered tissue follow the classic differentiation pathway described for two-dimensional culture. Polymer scaffolds such as these may ultimately be used clinically to enhance bone regeneration by delivering or recruiting progenitor cells to the wound site.

3T3 Cells↗

PubMed2000

Biodegradable external tracheal stents and their use in a rabbit tracheal reconstruction model.

OBJECTIVES/HYPOTHESIS: To design and develop an external biodegradable tracheal stent for use in airway reconstructive surgery. STUDY DESIGN: Experimental model. METHODS: Biodegradable external tracheal stents were fabricated from polyglycolic acid and poly(D,L-lactide-co-glycolide) (85:15). In vitro studies were performed to analyze the mechanical properties and degradative characteristics of these stents. Then the stents were tested in vivo in an anterior tracheal reconstruction model in New Zealand white rabbits. RESULTS: The average dry modulus for the external stents was 1,800 kilopascal (kPa). All of the external stents cracked by 4 weeks in buffer solution. Significant mass loss was not appreciated until after 10 weeks in solution, but by 20 weeks the stents were nearly 100% degraded. In the in vivo portion of the study, the attrition rate for the control group was 23.1% versus 50% for the external stent group. The stridor rate was approximately 38% for both groups Of the rabbits that survived the entire 3 months of the study, the stented group, when measured by a balloon catheter method, had more patent airways than the control group, with an average stenosis of 27.8% versus 47.2%, respectively (P < .05). However, more accurate postmortem cast measurements of the internal airways did not confirm this. CONCLUSIONS: The external biodegradable tracheal stent employed in this study degraded in a predictable fashion and may provide a new method to augment surgical reconstruction of the anterior tracheal wall.

Absorbable Implants↗

PubMed2000

Scaffolds for engineering smooth muscle under cyclic mechanical strain conditions.

Cyclic mechanical strain has been demonstrated to enhance the development and function of engineered smooth muscle (SM) tissues, but appropriate scaffolds for engineering tissues under conditions of cyclic strain are currently lacking. These scaffolds must display elastic behavior, and be capable of inducing an appropriate smooth muscle cell (SMC) phenotype in response to mechanical signals. In this study, we have characterized several scaffold types commonly utilized in tissue engineering applications in order to select scaffolds that exhibit elastic properties under appropriate cyclic strain conditions. The ability of the scaffolds to promote an appropriate SMC phenotype in engineered SM tissues under cyclic strain conditions was subsequently analyzed. Poly(L-lactic acid)-bonded polyglycolide fiber-based scaffolds and type I collagen sponges exhibited partially elastic mechanical properties under cyclic strain conditions, although the synthetic polymer scaffolds demonstrated significant permanent deformation after extended times of cyclic strain application. SM tissues engineered with type I collagen sponges subjected to cyclic strain were found to contain more elastin than control tissues, and the SMCs in these tissues exhibited a contractile phenotype. In contrast, SMCs in control tissues exhibited a structure more consistent with the nondifferentiated, synthetic phenotype. These studies indicate the appropriate choice of a scaffold for engineering tissues in a mechanically dynamic environment is dependent on the time frame of the mechanical stimulation, and elastic scaffolds allow for mechanically directed control of cell phenotype in engineered tissues.

Animals↗

PubMed2000

The impact of tissue engineering on dentistry.

BACKGROUND: Tissue engineering is a novel and highly exciting field of research that aims to repair damaged tissues as well as create replacement (bioartificial) organs. OVERVIEW: The authors provide a general review of the principles underlying key tissue engineering strategies, as well as the typical components used. Several examples of preclinical and clinical progress are presented. These include passive approaches, such as dental implants, and inductive approaches that activate cells with specific molecular signals. PRACTICE IMPLICATIONS: Tissue engineering will have a considerable effect on dental practice during the next 25 years. The greatest effects will likely be related to the repair and replacement of mineralized tissues, the promotion of oral wound healing and the use of gene transfer adjunctively.

Animals↗