In vivo degradation characteristics of bioabsorbable cross-pins in anterior cruciate ligament reconstruction

BackgroundWe evaluated degradation of bioabsorbable femoral cross-pins following anterior cruciate ligament (ACL) reconstruction.MethodsFour patients underwent ACL reconstruction using hamstring autograft with femoral fixation provided by a polylactic acid/polyglycolic acid copolymer (LactoSorb L15) cross-pin. Serial computed tomography (CT) scans were performed of the reconstructed knees at approximately 6 weeks, 4 months, 1 year and 2 years, postoperatively. A radiologist evaluated the scans for density of pins and surrounding bone and pin morphology.ResultsThe cross-pins demonstrated a relative reduction in density of 7.7%, 49.1%, and 75.0% at 4 months, 1 year and 2 years, respectively. Bone density values adjacent to the pin decreased by an mean of 8.6% between 6 weeks and 4 months. At one year an additional 14.2% reduction in bone density was seen but at 2 years the relative reduction in bone density had decreased to 7.4%. Evaluation of pin morphology revealed that minimal change had occurred after 6 weeks. At 4 months all of the pins were showing some morphologic changes on the surface, but none had fractured. After 1 year, two of the pins had fractured. By 2 years all of the pins had fractured. None of the pins had completely reabsorbed at 2 years postoperatively.ConclusionsLactoSorb L15 cross-pins for femoral fixation in ACL reconstruction remain largely unchanged 4 months postoperatively, suggesting that this device maintains the necessary structural integrity to allow early integration of soft tissue grafts within bone tunnels.Level of evidenceIV, case series.     

In vitro and in vivo behavior of self-reinforced bioabsorbable polymer and self-reinforced bioabsorbable polymer/bioactive glass composites

The aim of this study was to investigate the in vitro and in vivo properties and degradation of (1) self-reinforced (SR) lactide copolymer, P(L/DL)LA 70:30, and (2) SR composites of the same polylactide and bioactive glass 13-93. The following three polymer and polymer-bioactive glass samples were studied: SR-PLA70, SR-PLA70 + BaG15s, and SR-PLA70 + BaG20c. In vitro behavior was studied in a phosphate-buffered saline for 87 weeks at 37 degrees +/- 1 degrees C and a pH of 7.4 +/- 0.2. In vivo behavior was studied by implanting the rods in the dorsal subcutaneous tissue of rats (SR-PLA70 + BaG20c) or rabbits (SR-PLA70 and SR-PLA70 + BaG15s) for 48 weeks. The degradation of the specimens was evaluated by measuring the changes in mechanical properties, crystallinity and molecular weight of polymer, water absorption, weight loss, and structural changes. Results showed that the addition of bioactive glass filler modified the degradation kinetics and material morphology.     

可降解金属Mg-Nd-Zn-Zr镁合金的降解行为

背景：添加合金元素是改变镁合金微观结构和控制镁合金降解行为的有效方法。 目的：探讨Mg-Nd-Zn-Zr镁合金体内外的降解行为。 方法：①体外静态浸泡实验：在(37.0±0.5) ℃条件下,将Mg-Nd-Zn-Zr镁合金和纯镁各6个样品分别浸入 250 mL模拟体液中,浸泡过程中不搅拌振荡。静态浸泡第3,7,30天后从模拟体液中取出试样,扫描电镜及能谱分析分析Mg-Nd-Zn-Zr镁合金在模拟体液中的降解行为。②体内植入实验：在成年新西兰兔左侧股骨钻孔,实验组植入Mg-Nd-Zn-Zr镁合金,对照组植入钛合金,空白对照组不植入任何内植物。植入后1,2,4,8周,通过X射线观察内植物的位置及降解行为;植入后4,8周,通过扫描电镜观察Mg-Nd-Zn-Zr镁合金表面腐蚀产物,通过元素能谱分析腐蚀产物的成分,并计算材料降解速率。 结果与结论：①Mg-Nd-Zn-Zr镁合金浸泡于模拟体液中不同时间点的降解速率均低于纯镁组;浸泡30 d后,沉积于Mg-Nd-Zn-Zr镁合金表面的腐蚀产物主要是氧、碳、钠、镁、钙、磷和氯,去除腐蚀产物后Mg-Nd-Zn-Zr镁合金和纯镁表面均有腐蚀坑,但Mg-Nd-Zn-Zr镁合金表面腐蚀坑体积更小,分布更均匀,表明Mg-Nd-Zn-Zr镁合金和纯镁存在不同的腐蚀形式。②Mg-Nd-Zn-Zr镁合金植入动物体内后随时间延长逐渐降解,材料表面腐蚀产物及成分类似于体外浸泡实验。     

In vitro and in vivo testing of bioabsorbable antibiotic containing bone filler for osteomyelitis treatment

The use of local antibiotics from a biodegradable implant is appealing concept for treatment of chronic osteomyelitis. Our aim was to develop a new drug delivery system based on controlled ciprofloxacin release from poly(D/L-lactide). Cylindrical composite pellets (1.0 x 0.9 mm) were manufactured from bioabsorbable poly(D/L-lactide) matrix and ciprofloxacin (7.4 wt %). In vitro studies were carried out to delineate the release profile of the antibiotic and to verify its antimicrobial activity by means of MIC testing. A long-term study in rabbits was performed to validate the release of ciprofloxacin from the composite in vivo. Therapeutic level of ciprofloxacin (>2 microg/mL) was maintained between 60 and 300 days and the concentration remained below the potentially detrimental level of 20 microg/mL in vitro. The released ciprofloxacin had retained its antimicrobial properties against common pathogens. In an exploratory long-term in vivo study with three rabbits, ciprofloxacin could not be detected from the serum after moderate filling (160 mg) of the tibia (follow-up 168 days), whereas after high dosing (a total dose of 1,000 mg in both tibias) ciprofloxacin was found temporarily at low serum concentrations (14-34 ng/mL) during the follow-up of 300 days. The bone concentrations of ciprofloxacin could be measured in all samples at 168 and 300 days. The tested copolylactide matrix seems to be a promising option in selection of resorbable carriers for sustained release of antibiotics, but the composite needs modifications to promote ciprofloxacin release during the first 60 days of implantation.     

In vitro and in vivo studies on bioabsorbable ultra-high-strength poly(L-lactide) rods.

Ultra-high-strength poly(L-lactide) (PLLA) rods were fabricated using a drawing technique. Rods with a diameter of 3.2 mm and a draw ratio of 2.5:1 showed initial bending strength and modulus values of 240 MPa and 13 GPa, respectively. The purpose of this study was to investigate the in vitro and in vivo degradation of PLLA rods with a draw ratio of 2.5:1. The greater the rod diameter, the longer the bending strength was maintained in phosphate buffered saline at 37 degrees C. The bending strength retention of rods (diam. 3.2 mm) implanted in the subcutis of rabbits was almost equal to that of rods in the in vitro study, while those rods implanted in the medullary cavity of rabbit femora showed a slightly lower bending strength retention. Molecular weight was reduced to the greatest extent in the medullary cavity, followed by in the subcutis and in vitro. The weight of PLLA rods in the medullary cavity was reduced by 22% at 52 weeks and by 70% at 78 weeks after implantation. Histologically, no inflammatory or foreign body reaction was observed in the medullary cavity for 52 weeks. The drawn PLLA rods maintained a bending strength exceeding that of human cortical bone in the medullary canal for a period of 8 weeks, suggesting that the drawn PLLA rods may be useful in the repair of fractured human bones.     

Long-term in vivo degradation of poly-L-lactide (PLLA) in bone

The use of absorbable orthopedic implants has increased substantially during the last decade. Currently, most of them are fabricated from poly-L-lactide (PLLA), its co-polymers, or mixtures with other constituents. In vivo, PLLA persists for years after its surgical role has ended, which is confirmed by a long-term histological study of PLLA implanted in sheep either as functional interference screws or nonfunctional rods. The first tissue reaction is the sequestration of the implant within new bone during the initial 3 months. After a nonreactive period, a second tissue reaction is associated with the early signs of structural disintegration of the PLLA at 1 year. Subsequently, as the polymer mass reduces, it is replaced by a relatively avascular fibrous tissue containing macrophages and having an occasional multinucleated giant cell on the implant surface. After 3 years much of the polymer is still present, although as isolated fragments. The tissue reactions can be explained in terms of the physical chemistry of PLLA degradation. Though biocompatible, the excessive longevity of PLLA and the absence of its replacement by bone, indicates that despite being satisfactory clinically, it is not an ideal implant material, and that improved absorbable materials need to be developed.     

Mechanical properties and in vitro degradation of bioabsorbable self-expanding braided stents

The aim of this study was to characterize the mechanical and self-expansion properties of braided bioabsorbable stents. In total four different stents were manufactured from PLLA fibres using a braiding technique. The changes in radial pressure stiffness and diameter recovery of the stents were determined initially, and after insertion and release from a delivery device. The braided stents were compared to three commercially available metallic braided stents. The changes in physical and mechanical properties of the PLLA fibres and stents during in vitro degradation were investigated. After release from the delivery device, the PLLA stents did not fully recover to their original diameter. The radial pressure stiffness of the bioabsorbable stents was similar to that of the metallic stents. The in vitro degradation study showed that the stents would keep at least half of their initial radial pressure stiffness for more than 22 weeks.     

Mechanical properties and in vitro degradation of bioabsorbable self-expanding braided stents

The aim of this study was to characterize the mechanical and self-expansion properties of braided bioabsorbable stents. In total four different stents were manufactured from PLLA fibres using a braiding technique. The changes in radial pressure stiffness and diameter recovery of the stents were determined initially, and after insertion and release from a delivery device. The braided stents were compared to three commercially available metallic braided stents. The changes in physical and mechanical properties of the PLLA fibres and stents during in vitro degradation were investigated. After release from the delivery device, the PLLA stents did not fully recover to their original diameter. The radial pressure stiffness of the bioabsorbable stents was similar to that of the metallic stents. The in vitro degradation study showed that the stents would keep at least half of their initial radial pressure stiffness for more than 22 weeks.     

In vitro and in vivo degradation of oxidized acetyl- and ethyl-cellulose sponges

The objective of this study was to assess the in vitro and in vivo degradation properties of macroporous sponges composed of oxidized acetyl-cellulose (AC; 45.000 Mw) and ethyl-cellulose (EC; 50.000 Mw). The sponges were constructed by solvent-casting and particulate-leaching technique using a polymer concentration of 2.5 and 5.0% (w:v), and periodate oxidation. The resulting sponges were: AC2.5, AC5.0, EC2.5 and EC5.0. While AC sponges exhibited a gradual degradation overtime, EC sponges had a very slow in vitro mass loss. In general, sponges made up of 2.5% (w:v) polymer content degraded faster than the ones with 5.0% (w:v). The sponges degraded faster at pH 5.0, compared to pH 6.0 and 7.4 conditions. About 60%, 44% and 31% of dry mass loss was determined for AC2.5 sponges after 60 weeks at pH 5.0, pH 6.0 and pH 7.4 conditions, respectively; thus, ca. 21%, 13% and 12% of dry mass loss from EC2.5 sponges was observed at the same pH conditions, in the same order. The in vivo degradation studies were performed on Wistar rats (n = 24) for a duration of 60 weeks. In general, all sponge implants were well-tolerated by the subjects. While granulation tissue or fibrotic capsule was not formed around the sponges, neovascularization was observed. AC and EC sponges demonstrated an in vivo degradation behavior quite similar to that observed for the in vitro study conducted at pH 5.0 conditions. Histomorphometric analysis revealed that the in vivo degradation of AC2.5 and EC2.5 after 60 weeks was about 47% and 18%, respectively. The results indicate that oxidized acetyl cellulose may be considered as a partially degradable scaffold material for tissue engineering applications.     

In vivo and in vitro degradation of glycine/DL-lactic acid copolymers

A series of copolymers of glycine and DL-lactic acid with various compositions was synthesized and their in vivo and in vitro degradation behavior was studied. For the in vivo examination, discs of the copolymer films were subcutaneously implanted in rats. The in vitro studies were carried out in phosphate buffer at pH = 7.4 and 37 degrees C. The decrease in molecular weight, the loss of weight, and the tissue reactions of the different copolymers were determined after 2, 5, and 10 weeks. Poly(DL-lactic acid) was used as reference material. The in vivo and in vitro degradation behavior of the polymers was comparable. The decrease of molecular weight of the copolymers and poly(DL-lactic acid) in time was similar. The weight loss for copolymers with a higher mole fraction of glycine units started earlier. The copolymer with the highest content of glycine units disappeared completely within 10 weeks both in vivo and in vitro. The poly(DL-lactic acid) implant lost only 25% weight over the same period. Tissue reactions against all materials started with an acute inflammatory reaction caused by the trauma of implantation, followed by wound-healing processes, ending in a very mild foreign body reaction for the poly(DL-lactic acid) and a more excessive macrophage mediated foreign body reaction for the glycine/DL-lactic acid copolymers. The tissue reaction was more severe for polymers having a higher rate of degradation.     

In vitro and in vivo degradation behavior of acetylated chitosan porous beads

Chitosans with different degree of acetylation (DA, 10-50%) were synthesized by the acetylation reaction of deacetylated chitosan and acetic anhydride with different ratios. The porous beads (approx. 500 mum) fabricated from the acetylated chitosans were used to investigate the degradation behaviors of chitosans with different DA in vitro and in vivo. The in vitro degradation behavior of the acetylated chitosan beads was investigated in solutions of lysozyme and/or N-acetyl-beta-D-glucosaminidase (NAGase), which are enzymes for chitosan present in the human body. It was observed that the degradation rate of acetylated chitosans can be controlled by adjusting the DA value: the degradation increased with increasing DA value of the acetylated chitosans. It seemed that NAGase plays an important role for the full degradation of chitosans in the body, even though NAGase itself can not initiate the degradation of chitosans. The in vitro degradation behavior of the chitosans in the mixture solution of lysozyme and NAGase was more similar to the in vivo degradation behavior than in the single lysozyme or NAGase solution. It may be owing to the sequential degradation reaction of chitosans in the mixture solution of lysozyme and NAGase (initial degradation by lysozyme to low-molecular-weight species or oligomers and the following degradation by NAGase to monomer forms). The in vivo degradation rate of acetylated chitosan beads was faster than the in vitro degradation rate. The acetylated chitosan porous beads with different DA value (and thus different degradation time) can be widely applicable as cell carriers for tissue-engineering applications.     

In vivo biofunctionality comparison of different topographic PLLA scaffolds

In this work, the in vivo biodegradation of, biocompatibility of, and host response to various topographic scaffolds were investigated. Randomly oriented fibrous poly(L-lactide) (PLLA) nanofibers were fabricated using the electrospinning technique. A PLLA scaffold was obtained by salt leaching. Both the electrospun PLLA nanofibers and the salt-leaching PLLA scaffolds formed three-dimensional pore structures. Cytotoxicity studies, in which rat muscle-derived stem cells (rMDSCs) were grown on electrospun PLLA nanofibers or the salt-leaching PLLA scaffolds, revealed that the rMDSCs cell count on the PLLA nanofibers was slightly higher than that on the salt-leaching PLLA scaffolds. An in vivo study was carried out by implanting the scaffolds subcutaneously into rats to test the biodegradation, biocompatibility, and host response at regular intervals over 0-4 weeks. The degradation of the PLLA nanofibers 1, 2, and 4 weeks after initial implantation was more extensive than that observed for the salt-leaching PLLA scaffolds. PLLA nanofibers seeded the growth of larger fibrous tissue masses due to in vivo cellular infiltration into the randomly oriented fibrillar structures of the PLLA nanofibers. In addition, the inflammatory cell accumulation in PLLA nanofibers was lower than that in the salt-leaching PLLA scaffolds. These results indicate that the electrospun PLLA nanofibers may serve as a good scaffold to elicit fibrous cellular infiltration, to minimize host response, and to enhance tissue-scaffold integration.     

In vivo and in vitro degradation of poly(3-hydroxybutyrate) in rat

The inflammatory activity and biodegradation of poly(3-hydroxybutyrate) were examined. Poly(3-hydroxybutyrate) sheet did not cause any inflammation in the chorioallantoic membrane of the developing egg. The i.v. injection of 14C-labelled poly(3-hydroxybutyrate) granules showed that 86, 2.5 and 2.4% of the total radioactivity administered were distributed in the liver, spleen and lung, respectively, and the radioactivity decreased slowly but steadily in most tissues examined during 2 month. Crude extracts of rat tissues showed that the activity degraded the poly(3-hydroxybutyrate) granules in vitro.     

In vivo and in vitro degradation of monofilament absorbable sutures, PDS and Maxon

Two new absorbable monofilament suture materials polydioxanone and Maxon are being employed increasingly in abdominal surgery because of increased strength retention and decreased tissue reactivity compared with previously available materials. As part of our investigation of the behaviour of suture materials, 3-0 sutures of polydioxanone and Maxon were enclosed in nylon pouches, a technique developed for in vivo experiments to prevent cellular interaction with implanted devices. The pouched sutures were gas sterilized, then implanted in either the extrafascial space or peritoneal cavity for periods of 1-5 wk. Sterilized sutures were also incubated in Ringer's lactate at 37 degrees C. Tensile strength of the exposed sutures was measured. For a given suture material and duration of incubation, there was no significant difference in tensile strength degradation among the three test environments. Although the strength of unexposed Maxon is greater than that of polydioxanone, the residual strength of Maxon decreases more rapidly in use, so that, after 2 wk, the strength of polydioxanone is greater. Scanning electron microscope examination of the suture surfaces reveals that polydioxanone develops surface crazing with time, whereas the surface morphology of Maxon remains relatively unaltered.     

In vitro and in vivo degradation of porous poly(DL-lactic-co-glycolic acid) foams

This study investigated the in vitro degradation of porous poly(DL-lactic-co-glycolic acid) (PLGA) foams during a 20-week period in pH 7.4 phosphate-buffered saline (PBS) at 37 degrees C and their in vivo degradation following implantation in rat mesentery for up to 8 weeks. Three types of PLGA 85 : 15 and three types of 50 : 50 foams were fabricated using a solvent-casting, particulate-leaching technique. The two types had initial salt weight fraction of 80 and 90%, and a salt particle size of 106-150 microm, while the third type had 90% initial weight fraction of salt in the size range 0-53 microm. The porosities of the resulting foams were 0.82, 0.89, and 0.85 for PLGA 85 : 15, and 0.73, 0.87, and 0.84 for PLGA 50 : 50 foams, respectively. The corresponding median pore diameters were 30, 50, and 17 microm for PLGA 85: 15, and 19, 17, and 17 microm for PLGA 50 : 50. The in vitro and in vivo degradation kinetics of PLGA 85: 15 foams were independent of pore morphology with insignificant variation in foam weight, thickness, pore distribution, compressive creep behavior, and morphology during degradation. The in vitro foam half-lives based on the weight average molecular weight were 11.1 +/- 1.8 (80%, 106-150 microm), 12.0 +/- 2.0 (90%, 106-150 microm), and 11.6 +/- 1.3 (90%, 0-53 microm) weeks, similar to the corresponding values of 9.4 +/- 2.2, 14.3 +/- 1.5, and 13.7 +/- 3.3 weeks for in vivo degradation. In contrast, all PLGA 50 : 50 foams exhibited significant change in foam weight, water absorption, and pore distribution after 6-8 weeks of incubation with PBS. The in vitro foam half-lives were 3.3 +/- 0.3 (80%, 106-150 microm), 3.0 +/- 0.3 (90%, 106-150 microm), and 3.2 +/- 0.1 (90%, 0-53 microm) weeks, and the corresponding in vivo half-lives were 1.9 micro 0.1, 2.2 +/- 0.2, and 2.4 +/- 0.2 weeks. The significantly shorter half-lives of PLGA 50: 50 compared to 85: 15 foams indicated their faster degradation both in vitro and in vivo. In addition, PLGA 50: 50 foams exhibited significantly faster degradation in vivo as compared to in vitro conditions due to an autocatalytic effect of the accumulated acidic degradation products in the medium surrounding the implants. These results suggest that the polymer composition and environmental conditions have significant effects on the degradation rate of porous PLGA foams.     

Self-reinforced composites of bioabsorbable polymer and bioactive glass with different bioactive glass contents. Part II: In vitro degradation

The in vitro degradation behavior of self-reinforced bioactive glass-containing composites was investigated comparatively with plain self-reinforced matrix polymer. The materials used were spherical bioactive glass 13-93 particles, with a particle size distribution of 50-125 microm, as a filler material and bioabsorbable poly-L,DL-lactide 70/30 as a matrix material. The composites containing 0, 20, 30, 40 and 50 wt.% of bioactive glass were manufactured using twin-screw extruder followed by self-reinforcing. The samples studied were characterized determining the changes in mechanical properties, thermal properties, molecular weight, mass loss and water absorption in phosphate-buffered saline at 37 degrees C for up to 104 weeks. The results showed that the bioactive glass addition modified the degradation kinetics and material morphology of the matrix material. It was concluded that the optimal bioactive glass content depends on the applications of the composites. The results of this study could be used as a guideline when estimating the best filler content of other self-reinforced osteoconductive filler containing composites which are manufactured in a similar way.     

In vitro and in vivo degradation profile of aliphatic polyesters subjected to electron beam sterilization

Degradation characteristics in response to electron beam sterilization of designed and biodegradable aliphatic polyester scaffolds are relevant for clinically successful synthetic graft tissue regeneration. Scaffold degradation in vitro and in vivo were documented and correlated to the macroscopic structure and chemical design of the original polymer. The materials tested were of inherently diverse hydrophobicity and crystallinity: poly(L-lactide) (poly(LLA)) and random copolymers from L-lactide and ε-caprolactone or 1,5-dioxepan-2-one, fabricated into porous and non-porous scaffolds. After sterilization, the samples underwent hydrolysis in vitro for up to a year. In vivo, scaffolds were surgically implanted into rat calvarial defects and retrieved for analysis after 28 and 91days. In vitro, poly(L-lactide-co-1,5-dioxepan-2-one) (poly(LLA-co-DXO)) samples degraded most rapidly during hydrolysis, due to the pronounced chain-shortening reaction caused by the sterilization. This was indicated by the rapid decrease in both mass and molecular weight of poly(LLA-co-DXO). Poly(L-lactide-co-ε-caprolactone) (poly(LLA-co-CL)) samples were also strongly affected by sterilization, but mass loss was more gradual; molecular weight decreased rapidly during hydrolysis. Least affected by sterilization were the poly(LLA) samples, which subsequently showed low mass loss rate and molecular weight decrease during hydrolysis. Mechanical stability varied greatly: poly(LLA-co-CL) withstood mechanical testing for up to 182 days, while poly(LLA) and poly(LLA-co-DXO) samples quickly became too brittle. Poly(LLA-co-DXO) samples unexpectedly degraded more rapidly in vitro than in vivo. After sterilization by electron beam irradiation, the three biodegradable polymers present widely diverse degradation profiles, both in vitro and in vivo. Each exhibits the potential to be tailored to meet diverse clinical tissue engineering requirements.     

Resorbable materials of poly(L-lactide). VII. In vivo and in vitro degradation

In vivo and in vitro degradation of high molecular weight poly(L-lactide) used for internal bone fixation has been investigated. Within 3 months as-polymerized, microporous PLLA (Mv = 6.8-9.5 X 10(5] exhibited a massive strength-loss (sigma b = 68-75 MPa to sigma b = 4 MPa) and decrease of Mv (90-95%). At week 39, the first signs of resorption were evident (mass-loss 5 wt%). Except for dynamically loaded bone plates no differences between in vivo and in vitro degradation of PLLA were observed. The increase of crystallinity of PLLA upon degradation (up to 83%) is likely to be attributed to recrystallization of tie-chain segments. A more ductile PLLA exhibiting a lower rate of degradation was prepared by extraction of low molecular weight compounds with ethyl acetate.     

In vitro and in vivo degradation studies of a novel linear copolymer of lactide and ethylphosphate

Poly(lactide-co-ethylphosphate)s, a new class of linear phosphorus-containing copolymers made by chain-extending low-molecular-weight polylactide prepolymers with ethyl dichlorophosphate, were investigated for their in vitro and in vivo degradation mechanism and kinetics. Microspheres made from poly(lactide-co-ethylphosphate) were studied under both accelerated and normal in vitro degradation conditions. Gel permeation chromatography (GPC), 1H- and 31P-NMR, weight loss measurements, and differential scanning calorimetry (DSC) techniques were used to characterize the change of molecular weight (M(w)), chemical composition, and glass transition temperature (T(g)) of the degrading polymers. The results indicated that the copolymers degraded in a two-stage fashion, with cleavage of the phosphate-lactide linkages contributing mostly to the initial more rapid degradation phase and cleavage of the lactide-lactide bonds being responsible for the slower latter stage degradation. The decrease in the copolymer M(w) was accompanied by a continuous mass loss. Results from the accelerated degradation studies confirmed that the copolymers degraded into various monomers of the copolymers, which were non-toxic and biocompatible. A two-stage hydrolysis pathway was thus proposed to explain the degradation behavior of the copolymers. In vivo degradation studies performed in mice demonstrated a good in vitro and in vivo correlation for the degradation rates. In vivo clearance of the polymer was faster and without any lag phase. These copolymers are potentially advantageous for drug delivery and other biomedical applications where rapid clearance of the polymer carrier and repeated dosing capability are essential to the success of the treatment.     

In vitro biodegradability and mechanical properties of bioabsorbable bacterial cellulose incorporating cellulases

Bacterially produced cellulose is being actively studied as a novel scaffold material for wound care and tissue engineering applications. Bioabsorbability of the scaffold material is desired to enable improved restoration of targeted tissue. Recently, a bioabsorbable bacterial cellulose (BBC) incorporating cellulase enzymes has been demonstrated. It was revealed that some cellulases may lose up to 90% of their activity if present in a suboptimal pH environment. Therefore, a key challenge in the practical implementation of this approach rests in compensating for the variation in the wound or tissue pH, which may significantly reduce the activity of some enzymes. In this work, buffer ingredients were incorporated into the bacterial cellulose in order to create a more optimal pH microenvironment for the preferred acid cellulases, which are significantly less active at the biological pH 7.4. The results demonstrated that incorporation of buffer ingredients helped to retain the activity of the cellulases. The glucose released from degraded materials was also increased from 30% without incorporation of buffer ingredients to 97% in the presence of incorporated buffer ingredients at the suboptimal pH environment of 7.4. The use of simulated body fluid and simulated tissue padding, both mimicking the real wound environment, also demonstrated some improvements in terms of material degradation. Measurements of mechanical properties of materials revealed that BBC materials have tensile strength and extensibility similar to human skin, especially when hydrated with saline water prior to use.