A composite biocompatible material made of polyethyleneterephalate (Dacron) and polyetherurethane was fabricated as an aid to bone grafting for the reconstruction of large bony defects of the craniomaxillofacial regions. Bone graft material is placed within the confines of the Dacron-urethane implant and new bone forms to the shape imposed by the implant.

The principle application of this material has been for the reconstruction of defects of the neurocranium and of the mandible [1–5]. A number of other applications have been studied including reconstruction of long bone discontinuity defects [6], reconstruction of an infant's anterior chest wall [19], the prosthetic replacement of large defects of the cervical trachea [7] and as a potential material for a thrombo-resistant small diameter vascular prosthesis [8].

We have developed a biodegradable particulate composite bone cement consisting of a poly(propylene glycol-fumarate)-(methylmethacrylate) matrix mixed with calcium carbonate and tricalcium phosphate particulates. Previous ex-vivo studies suggest that this system provides sufficient strength for a number of potential clinical applications including structural reinforcement of osseous defects, supplementation of internal fixation of age-related fractures, and delivery of antibiotics to treat osteomyelitis. Ex-vivo degradation assays have also shown that the cement approximates physiologic conditions of bone remodeling as it degrades. In order to evaluate the in-vivo responses to this material, we implanted cement specimens subcutaneously in rats for up to 84 days. Compressive strength of the subcutaneous implants increased linearly through day 21 to 4.91 MPa, then decreased linearly by day 84 to less than 1 MPa. We conclude that this PPFMMA system is biocompatible and biodegradable, and has the potential for use as an orthopedic bone cement. Future studies will be directed toward characterizing the intraosseous histological response and at coordinating the rate of cement degradation with bony ingrowth.

Clinical situations that require techniques to fill defects of bone are common in the surgical care of Orthopaedic patients. The options currently available to the surgeon are autograft bone (bone from the same person), allograft bone (bone from a deceased donor), and bone cement. Each of these options has a mix of desirable and undesirable properties, and the choice of one of them necessarily involves some degree of compromise. We have been developing a novel, degradable, polymeric composite biomaterial to function as an alternative to the currently available options. The design goals for this biomaterial are that the material be sterilizable without loss of its mechanical and biological properties, available to the surgeon in the sterile operating field on short notice, moldable such that it can fill irregularly shaped defects, harden over a time span of ten to fifteen minutes, provide the reconstructed skeletal region with mechanical properties of the same order of magnitude as those of the bone it replaces, degrade over a period of weeks to months, be replaced by new bone, and maintain a specified minimum mechanical strength during the period of degradation and new bone growth. In this study we asked two questions. First, would the material maintain a minimum compressive strength greater than 5 Megapascals (MPa) and a minimum compressive modulus greater than 100 MPa over a twelve week period in a simulated body fluid environment? Second, would the material degrade in vivo in a rat proximal tibia model?

A process has been developed to manufacture biodegradable composite foams of poly(DL-lactic- co-glycolic acid) (PLGA) and hydroxyapatite short fibers for use in bone regeneration. The processing technique allows the manufacture of three-dimensional foam scaffolds and involves the formation of a composite material consisting of a porogen material (either gelatin microspheres or salt particles) and hydroxyapatite short fibers embedded in a PLGA matrix. After the porogen is leached out, an open-cell composite foam remains which has a pore size and morphology defined by the porogen. The foam porosity can be controlled by altering the volume fraction of porogen used to make the composite material. Foams made using NaCl particles as a porogen were manufactured with porosities as high as 0.84±0.01 (n=3). The short hydroxyapatite fibers served to reinforce the PLGA. The compressive yield strength of foams manufactured using gelatin microspheres as a porogen was found to increase with fiber content. Foams with compressive yield strengths up to 2.82±0.63 MPa (n=3) with porosities of 0.47±0.01 (n=3) were manufactured using 30% by weight hydroxyapatite fibers in the initial composite prior to leaching. These composite foams with improved mechanical properties may also be expected to have enhanced osteoconductivity and hence provide a novel material which may prove useful in the field of bone regeneration.

An artificial ligament anchor has been designed and tested in goats. The anchor may allow direct bone anchorage of artificial anterior cruciate ligaments.

Reduction of wear and wear debris is one of the most important areas of research presently in the field of orthopedic devices. It is speculated that wear debris is one of the contributing factors in the cascade of events that lead to osteolysis. In this regard it is very important to be able to evaluate in vitro the wear of UHMWPE produced by various manufacturing methods. Presently the three most common methods of wear testing are: pin-on-flat, pin-on-disk, and hip simulator.

Wear evaluation was performed on gamma irradiated UHMWPE that was manufactured by three different processes: extrusion, direct compression molding, and isostatic compression molding. The wear evaluation consisted of pin-on-flat and hip simulator testing.

omparison of the results from these two different types of tests show that the two tests would rank the wear resistance of the UHMWPE in the same order. However, there is a variation in the difference of the wear rates between the two tests. The pin-on-flat results show that the direct and isostatic compression molded material had approximately 50% less wear than the extruded material whereas the hip simulator results show that the isostatic compression molded material had 16% less wear than the extruded material. The difference in the results of these two tests are the effects of a combination of factors including the mechanical and material properties of the UHN4WPE, modes of wear that are active, the state of stress (constant vs. cyclic) in the specimens, third body contamination of the lubricant, bacterial degradation of the bovine serum lubricant, etc. Both tests are very important and necessary in the evaluation of wear of orthopedic materials.

Novel polymers with good mechanical properties are being developed as degradable matrices for bone growth and regeneration. The poly(anhydride-co-imides) were synthesized from trimellitylimidoglycine and 1,6-bis(p-carboxyphenoxy)hexane in molar compositions of 10:90, 30:70 and 50:50. These polymers have compressive strengths (23–57 MPa), which are similar to human cortical bone. 1 In vitro degradation was performed under acidic (pH 5), physiological (pH 7.4), and basic (pH 10) conditions. The degradation rate increased under basic conditions and by increasing the amount of trimellitylimidoglycine in the polymer backbone. Two erosion zones were observed in the polymers by microscopy. In vivo polymer degradation was evaluated by characterizing polymer discs implanted in subcutaneous tissue of rats over a 56 day time period. Copolymers with the highest ratio of trimellitylimidoglycine in the polymer backbone were completely degraded by 56 days, the other compositions remained in the tissue as solid pellets at this time. In vivo degradation was much slower than the corresponding in vitro degradation.

Numerous research groups currently are working to develop microcapsules, microspheres, and nanoparticles able to function as effective drug carriers. Much effort is focused on forming biodegradable particles from iactide-glycolide copolymers (PLGA)1−3. Although microparticles prepared from PLGA copolymers have had many successes, PLGA copolymers are not ideal drug carriers. Many other materials conceptually could be formed into suitable particulate drug carriers: synthetic polymers other than PLGA, natural polymers, chemical derivatives of natural polymers, selected inorganics, and nonpolymeric lipids. The purpose of this paper is not to discuss the advantages and limitations of each of these classes of carrier materials, but to contrast the features of PLGA copolymers with those of potentially competitive natural polymers. PLGA copolymers are used as the reference standard, because they are an approved family of biodegradable drug carrier polymers utilized by many research groups globally.

Coronary artery atherosclerosis is the leading cause of death in the United States. Restenosis following percutaneous transluminal balloon angioplasty (PTCA) remains the limiting factor in the use of this treatment for coronary artery disease. Restenosis occurs in 30% of patients within 6 months. The restenotic lesion is a fibroproliferative response with resulting smooth muscle cell migration, proliferation and extracellular matrix production. Despite a decade of research there is no effective strategy for preventing restenosis in man.

Cationic gelatin was evaluated as a non-viral vector for cell transfection. We hypothesized that cationic gelatin would be a nontoxic alternative to already existing viral and non-viral cationic vectors. Cationic gelatin was synthesized by modifying gelatin with hexanediamine. Complexation of cationic gelatin with psv-β-gal plasmid caused an electrophoretic mobility shift of the plasmid. Cationic gelatin/DNA complexes were optimized in terms of transfection efficiency in CHODUK XB1 and COS 7 cell lines. Maximal gene expression for both cell types occurred in serum free medium with chloroquine (100 μM) at cationic gelatin/DNA ratios of approximately 2 and 7. In comparison with DEAE dextran, polylysine and Lipofectamine, cationic gelatin was the most efficient in transfecting COS 7 cells, with up to 18% cells transfected. In a dye reduction cytotoxicity assay, cationic gelatin caused < 5% of cells to become nonviable at a concentration of 100 μg/ml, while the other transfection reagents tested at the same concentration caused 25–100% of cell death. These results suggest that cationic gelatin holds promise as an effective vehicle for gene delivery to mammalian cells.

The structural denaturation of polypeptides and other macromolecular pharmaceuticals upon surface adsorption from an aqueous environment is almost inevitable. Molecular denaturation, coupled with a net increase in entropy, accounts for the net negative ΔG and frequent irreversible nature of surface adsorption. The consequence of this interaction is that surface immobilized drugs lose their dynamic freedom and thus, all too often, their biological activity.

This phenomenon has complicated the development of drug delivery vehicles. In this communication, a drug delivery system based on a novel surface modification process to help reverse the constraining activity of surfaces is described. Beginning with preformed carbon ceramic nanoparticles and self-assembled calcium-phosphate dihydrate particles (colloidal precipitation) to which glassy carbohydrates are then allowed to adsorb as a nanometer thick surface coating, a molecular carrier is formed. The carbohydrate coating functions as a dehydroprotectant and stabilizes subsequently non-covalently bound immobilized members of biochemically reactive surface members such as pharmaceuticals.

Many of the physical properties of this enabling system have been characterized in vitro and in animal models. Antigen delivery, drug delivery, and enzyme stabilization experiments are described.

One of the challenges in the field of tissue engineering is the development of optimal materials for use as scaffolds to support cell growth and tissue development. For this purpose, we are developing synthetic, biodegradable polymers with functional sites that provide the opportunity to covalently attach biologically active molecules to the polymers, so they can predictably interact with cells in a favorable manner to enhance cell attachment and growth. The preparation of poly(L-lactic acid-co-aspartic acid) comb-like graft copolymers from poly(L-lactic acid-co-β-benzyl-L-aspartate), and the casting of polymer films by solvent evaporation were carried out.

We studied the feasibility of creating new tissue engineered tendons, using bovine tendon fibroblasts (tenocytes) attached to synthetic biodegradable polymer scaffolds in athymic mice. Calffore- and hind-limbs were obtained from a local slaughterhouse within 6 hours of sacrifice. Tenocytes were isolated from the calf tendons. Cells were seeded onto an array of fibers composed of polymer (PGA) configured either as a random mesh of fibers, or as an array of parallel fibers. Fifty cell-polymer constructs were implanted subcutaneously in athymic mice and harvested at 3, 6, 8, 10 and 12 weeks. Grossly, all excised specimens resembled the tendons from which the cells had been isolated. Histologic sections stained with hematoxylin and eosin (H&E) and Masson's trichrome showed cells arranged longitudinally within parallel collagen fibers in the periphery. Centrally, collagen fibers were more randomly arranged, although they seemed to attain a parallel arrangement of cells and fibers over time. By 10 weeks, specimens showed very similar histologic characteristics to normal tendon. Histologically, 12-week samples were virtually identical to normal tendon. When longitudinal polymer fibers seeded with cell had been implanted, the collagen fibers seen in the neo-tendons became organized at an earlier interval of time. Biomechanical tests demonstrated linear increase in tensile strength of the neo-tendons over time. Eight-week specimens showed 30% the tensile strength of normal tendon samples of similar size. By 12 weeks, tensile strength was already 57% that of normal bovine tendon.

The ability to create bone from periosteum and biodegradable polymer may have significant utility in reconstructive orthopedic and plastic surgery. Polyglycolic acid (PGA) serves as a biodegradable matrix which can be configured to a desirable shape and structure. This study was conducted to generate new bone tissue from periosteum and PGA polymer and to compare the tissue to the bone tissue generated from periosteal cells seeded onto PGA polymer. Bovine periosteum, harvested from fresh calf limbs, was placed either directly onto PGA polymer (1 cm2) or onto tissue culture dishes for periosteal cell isolation. In Medium 199 media with antibiotics and ascorbic acid, the periosteum/PGA construct was cultured for one week, then implanted into the dorsal subcutaneous space of nude mice. Periosteal cells, cultured from pieces of periosteum for two weeks, were isolated into cell suspension and seeded (˜l-3× 107 cells) onto PGA polymer (1 cm2); after one week in culture, the periosteal cell-seeded polymer was implanted into the subcutaneous space of athymic mice. Specimens, harvested at 4, 8, and 14 week intervals, were evaluated grossly and histologically. The periosteum/PGA constructs showed an organized cartilage matrix with early evidence of bone formation at 4 weeks, a mixture of bone and cartilage at 8 weeks, and a complete bone matrix at 14 weeks. Constructs created from periosteal cells seeded onto polymer showed presence of disorganized cartilage at 4 and 8 weeks, and a mixture of bone and cartilage at 14 weeks. Periosteum placed directly onto polymer will form an organized cartilage and bone matrix earlier than constructs formed from periosteal cell-seeded polymer. This data suggests that PGA is an effective scaffold for periosteal cell attachment and migration to produce bone which may offer new approaches to reconstructive surgery.

Biodegradable polymer scaffolds have been used to engineer new tissues or organs by culturing cells on them. The degradation, structure and properties of fibrous nonwoven poly(glycolic acid) (PGA) scaffolds (2 mm thick and 10 mm in diameter) were studied over 9 weeks in tissue culture medium at 37°C under mixing condition. After 3 days of in vitro culture, the mass of the scaffolds increased slightly (5.6%) due to hydration and/or adsorption, but it decreased thereafter. After 9 weeks, only 12.5% of the mass were retained. The melting point of the scaffolds decreased from 218.1°C to 186.0°C in the first 3 weeks, as measured with differential scanning calorimetry (DSC). No melting peak could be identified for later times (6 weeks and 9 weeks). The crystallinity of the scaffolds doubled over the first 11 days, but decreased thereafter. The glass transition temperature of the degrading scaffolds (36–39°C) was lower than that of the dry starting scaffolds (40°C) presumably due to the plasticizing effect of absorbed water and other low molecular weight molecules. The PGA scaffolds without cells lost their structural integrity and mechanical strength completely in 2 to 3 weeks. In contrast, the neocartilage constructs regenerated from the PGA scaffolds and bovine chondrocytes kept their structural integrity throughout the in vitro culture study. After 12 weeks of in vitro culture, the biomechanical properties of the neocartilage constructs reached the same orders of magnitude as those of normal bovine cartilage.

Engineering liver tissue using hepatocyte transplantation may provide a new approach for treating a variety of liver diseases. However, techniques to transplant hepatocytes and promote their survival must be developed. We have developed systems to transplant hepatocytes on highly porous (95%), biodegradable sponges, and to regulate the survival of cultured hepatocytes by releasing specific growth factors in the cellular environment. Sponges were fabricated from poly (L, lactic acid) (PLLA) and polyvinyl alcohol using a particulate leaching technique. Epidermal growth factor and insulin, critical factors for hepatocyte growth and survival in culture, were incorporated into microspheres fabricated from poly (lactic-co-glycolic acid) (PLGA) utilizing a double emulsion technique. The incorporated factors were released in a controlled manner over one month in vitro, and the released factors maintained their biological activity, as measured by their ability to promote hepatocyte growth and survival in culture. The growth factor-containing microspheres could be transplanted with hepatocytes using the porous sponges, and the localized, sustained release of these factors improved hepatocyte engraftment 2-fold. These studies suggest that hepatocyte containing tissues can be engineered using cell transplantation, and that regulating the microenvironment of transplanted cells can control their engraftment.

Poly(ß-hydroxybutyrate-co-13-hydroxyvalerate) have been recently proposed as degradable biomaterials for drug delivery systems, sutures, bone plates and short-term implants. Three P-B\HV (7, 14 & 22 % HV) films were analyzed for in vitro cytotoxicity and aqueous accelerated degradation, in vivo degradation and tissue reactions. The PHB/HV materials and extracts elicit few or mild toxic responses, do not lead in vivo to tissue necrosis or abscess formation, but provoke acute inflammatory reactions slightly decreasing with the time. The degradation of PHB/HV polymers present low rates in vitro as well as in vivo. The weight loss rate generally increases with the copolymer composition (HV content) and ranges from 0.15- 0.30 (in vitro) to 0.25 %/day (in vivo). Compositional and physico-chemical changes in PHB/HV materials were rapidly detected during the accelerated hydrolysis, but were much slower to appear in vivo. The structural and mechanical integrity of PHB/HV materials tend to disappear early in vitro as well as in vivo. After 90 wks in dorsal muscular tissues of adult sheep, there was no significant dissolution of the PHB/HV polymer, 50–60% of the initial weight still remaining. PHB/HV polymers are biodegradable materials, either by hydrolysis or implantation, but with extremely low dissolution or degradation rates.

Implantable polymeric drug-delivery devices have been constructed to deliver drugs at welldefined rates. Typically, these devices have been designed to deliver drugs at a constant rate, or in response to the concentration of a certain body metabolite. For some drugs, pulsatile delivery is sought. For example, under normal conditions, human growth hormone is released in the body in periodic bursts. Current treatments for HGH deficiency often fail because HGH is not administered following the endogenous pattern. Thus, pulsatile hormone-replacement therapy should be considered. Also, it may be useful to deliver in a periodic, pulsatile manner drugs that exhibit significant acute tolerance.

Currently, an oscillator is under development that is fueled by endogenous compounds and contains a variable-permeability membrane. The membrane's permeability to the substrate of an enzymatic reaction is assumed to be dependent on the concentration of the product of the reaction in a manner that displays product inhibition. Under certain conditions, this negative-feedback control can lead to oscillations in the membrane's permeability to substrate. If the membrane's permeability to a drug is simultaneously affected, then this will lead to oscillatory drug release.

We report encouraging initial studies. A simple theoretical model has been developed for the membrane oscillator, and results of simulations based on the model are discussed.

Diffusion-cell studies have been performed with a variable-permeability poly(N-isopropylacrylamide- co-methacrylic acid) hydrogel membrane. Using glucose as a probe solute, the results show that lowering the pH induces hydrogel volume collapse and cessation of glucose permeation across the membrane.

Langmuir-Blodgett (LB) films of the hemicyanine dyes 4-(4-dihexadecylaminostyryl)- N-methylpyridinium iodide and 4-(4-dioctylaminostyryl)-N-propylsulfonate pyridinium mixed with octadecanoic acid have been deposited onto H2O-swollen poly(2-vinylpyridine) (P2VP) as mass transport barriers. The transport properties of these structures have been studied both with and without the application of an electric field in the range 0 ≤ E ≤ 100 V/cm, by observing the rate of permeation of both anionic (fluorescein) and zwitterionic (rhodamine B) fluorophores. The apparent diffusion coefficient at E = 0 decreases exponentially with the number of monolayers through which the probe molecule must permeate, in agreement with a hole-mediated permeation model. Application of an external electric field is observed to control the rate and direction of the mass transport of the probe molecule across the barrier layer. The electric field effect is both spatially reversible, i.e. the probe can be transported in either direction across the barrier layer, and temporally reversible, i.e. the permeability cycles with the field between large values when the field is on and small values when it is not applied. The results are consistent with an interpretation in which electroporation is the dominant mechanism for transport in the field-on state.

Polysaccharides, including cellulosic derivatives such as hydroxypropylcellulose (HPC), are used extensively in the pharmaceutical industry due to their biocompatibility and self-organization properties. While drug delivery vehicles employing, for instance, aqueous polysaccharide gels are desirable, production of such gels can be hindered by tremendously high solution viscosity. In this work, we describe a novel means by which to reduce the viscosity and enhance the solubility of aqueous HPC. Here, the efficacy of several additives which promote HPC viscosity reduction through molecular salting-in is examined by dynamic rheology and light/electron microscopy.