Biocompatibility study of as-polymerized poly(L-lactide) in rats using a cage implant system

Inflammation and dysfunction in human aortic endothelial cells associated with poly-l-lactic acid degradation in vitro are alleviated by curcumin

Poly-l-lactic acid (PLLA) is widely used in clinic, for example, as biodegradable coronary artery stents. However, inflammatory responses in endothelial cells associated with PLLA degradation are relatively undefined. We previously reported inflammation in human aortic endothelial cells (HAEC) in vitro and in vivo. Here, we further assessed inflammatory injury, including cell migration, cell function, and inflammatory cytokines expressed in HAEC treated with PLLA and curcumin by CCK-8, wound healing assay, ELISA, and Western blot. Significant inhibition of cell migration, remarkable dysfunction, and inflammatory responses were found in HAEC treated with PLLA degradation extract, and these effects were alleviated by Cur treatment. These findings indicated that cautious evaluation of biodegradable polymers should be performed, and Cur represents a promising anti-inflammatory agent for alleviating endothelial dysfunction and inflammation caused by PLLA degradation. In addition, Cur should be further studied experimentally in in vivo experiments on animal models as a potential therapeutic to reduce thrombosis of biodegradable polymer stents.

Evaluation of the internal fixation effect of nano-calcium-deficient hydroxyapatite/poly-amino acid composite screws for intraarticular fractures in rabbits

Objective

To evaluate the internal fixation effect of nano-calcium-deficient hydroxyapatite/poly-amino acid (n-CDHA/PAA) composite screws in the intraarticular fracture model.

Materials and methods

A total of 35 New Zealand White rabbits were used in a bilateral femoral intercondylar fracture model and randomly divided into two groups. n-CDHA/PAA screws were used in the experimental group, and medical metal screws were used in the control group. The fracture condition, range of motion, and the screw push-out strength were assessed, and an arthroscopic examination of knee joint was performed at 4, 8, and 12 weeks after surgery. The biodegradation of the n-CDHA/PAA screws in vivo was tested through weighing, and changes in screw structure were assessed by X-ray diffraction at 12 weeks after surgery.

Results

The general situation of all animals was good and showed no incision infection and dehiscence after surgery. X-ray scanning showed that significant callus growth was present in both groups at 4 weeks after surgery, and there was no significant difference (P>0.05) in the Lane-Sandhu score between the experimental and control groups at all time points after surgery. There were no statistically significant differences (P>0.05) in the range of motion and Oswestry Arthroscopy Score of arthroscopic examination of the knee joints between the two groups. The screw push-out strength of the control group was stronger than that of the experimental group at 4 weeks after surgery (P<0.05), but after that, there was no significant difference between the groups (P>0.05). The degradation tests showed that the n-CDHA/PAA screws degraded gradually after implantation, and the weight loss rate was approximately 16% at 12 weeks after surgery. The X-ray diffraction results showed that the crystal structure of the outer surface of the n-CDHA/PAA screw has changed at 12 weeks after surgery.

Conclusion

The n-CDHA/PAA screw is an effective and safe implant as a potential internal fixation device for an intercondylar fracture of the femur, and its internal fixation effect was similar to that of medical metal screw.

[Experimental study of demineralized dentin matrix on osteoinduction and related cells identification]

OBJECTIVE

The aim of this study was to explore the theoretical framework of cells and the forms of osteogenesis in the mechanism by which demineralized dentin matrix (DDM) induces osteogenesis.

METHODS

A total of 24 New Zealand rabbits were used in this study. A total of 4 erector spinae bags were created in each animal. A total of 3 erector spinae bags were implanted with DDM by random selection, whereas the remaining one erector spinae bag was not implanted with DDM. The rabbits were sacrificed after 1, 2, 3, 4, 8, 12, 16, and 20 weeks, and the samples were obtained. The samples were examined by hematoxylin-eosin (HE), tartrate-resistant acid phosphatase (TRAP), and immunohistochemical staining to identify the mesenchymal stem cells, osteoblasts, chondrocytes, and osteoclasts.

RESULTS

The results of HE staining showed that in the third week, cartilage- and bone-like matrices, as well as the osteoblast-like cells, were observed. The results of immunohistochemical staining showed that the expressions of CD44, alkaline phosphatase (ALP), and collagen Ⅱ were statistically significant 
(P<0.05).

CONCLUSIONS

DDM has good histocompatibility and osteoinduction. In addition, induced ectopic osteogenesis mode mainly occurs in the endochondral bone.

Mechanistic analysis of triamcinolone acetonide release from PLGA microspheres as a function of varying in vitro release conditions

In vitro tests for controlled release PLGA microspheres in their current state often do not accurately predict in vivo performance of these products during formulation development. Here, we introduce a new mechanistic and multi-phase approach to more clearly understand in vitro-in vivo relationships, and describe the first "in vitro phase" with the model drug, triamcinolone acetonide (Tr-A). Two microsphere formulations encapsulating Tr-A were prepared from PLGAs of different molecular weights and end-capping (18kDa acid-capped and 54kDa ester-capped). In vitro release kinetics and the evidence for controlling mechanisms (i.e., erosion, diffusion, and water-mediated processes) were studied in four release media: PBST pH 7.4 (standard condition), PBST pH 6.5, PBS+1.0% triethyl citrate (TC), and HBST pH 7.4. The release mechanism in PBST was primarily polymer erosion-controlled as indicated by the similarity of release and mass loss kinetics. Release from the low MW PLGA was accelerated at low pH due to increased rate of hydrolysis and in the presence of the plasticizer TC due to slightly increased hydrolysis and much higher diffusion in the polymer matrix. TC also increased release from the high MW PLGA due to increased hydrolysis, erosion, and diffusion. This work demonstrates how in vitro conditions can be manipulated to change not only rates of drug release from PLGA microspheres but also the mechanism(s) by which release occurs. Follow-on studies in the next phases of this approach will utilize these results to compare the mechanistic data of the Tr-A/PLGA microsphere formulations developed here after recovery of microspheres in vivo. This new approach based on measuring mechanistic indicators of release in vitro and in vivo has the potential to design better, more predictive in vitro release tests for these formulations and potentially lead to mechanism-based in vitro-in vivo correlations.

Subdermal implants of poly(L-lactic acid) with plasticizer: an ultrastructural study in rats

Poly(L-lactic acid) (PLLA) membranes containing 7% triethylcitrate plasticizer were implanted in the subcutaneous tissue of rats, and the cellular reaction was evaluated over a period of 2-180 days. The samples were processed for conventional transmission electron microscopy. Polymorphonuclear-type cells and a fibrin network were seen within membrane pores 2 days after implantation. In subsequent samples, there was cellular infiltration, which consisted mainly of fibroblasts, macrophages and multinuclear giant cells embedded in an abundant extracellular matrix containing a network of collagen fibers and blood vessels. At 90 and 180 days after implantation, a high density of voluminous phagocytic cells with a large number of endocytic polymer fragments within their cytoplasm was seen. These results show that PLLA membranes can support connective tissue proliferation and remodeling, which are important properties for successful bio-protheses.

Bone tissue engineering: a review in bone biomimetics and drug delivery strategies

Critical-sized defects in bone, whether induced by primary tumor resection, trauma, or selective surgery have in many cases presented insurmountable challenges to the current gold standard treatment for bone repair. The primary purpose of a tissue-engineered scaffold is to use engineering principles to incite and promote the natural healing process of bone which does not occur in critical-sized defects. A synthetic bone scaffold must be biocompatible, biodegradable to allow native tissue integration, and mimic the multidimensional hierarchical structure of native bone. In addition to being physically and chemically biomimetic, an ideal scaffold is capable of eluting bioactive molecules (e.g., BMPs, TGF-betas, etc., to accelerate extracellular matrix production and tissue integration) or drugs (e.g., antibiotics, cisplatin, etc., to prevent undesired biological response such as sepsis or cancer recurrence) in a temporally and spatially controlled manner. Various biomaterials including ceramics, metals, polymers, and composites have been investigated for their potential as bone scaffold materials. However, due to their tunable physiochemical properties, biocompatibility, and controllable biodegradability, polymers have emerged as the principal material in bone tissue engineering. This article briefly reviews the physiological and anatomical characteristics of native bone, describes key technologies in mimicking the physical and chemical environment of bone using synthetic materials, and provides an overview of local drug delivery as it pertains to bone tissue engineering is included.

In vivo cytokine-associated responses to biomaterials

Cytokines, chemokines, and growth factors were analyzed periodically over eight weeks from the wound exudate fluid surrounding biomaterials implanted subcutaneously within stainless steel mesh cages. TNF-alpha, MCP-1, MIP-1alpha, IL-2, IL-6, IL-1beta, VEGF, IL-4, and IL-10 were measured from exudate samples collected from cages containing specimens of polyethylene (PE), polyurethane (PU), or organotin polyvinyl chloride (ot-PVC). Empty cages served as negative controls, and lipopolysaccharide (LPS) served as a positive control. Cytokine, chemokine, and growth factor concentrations decreased from the time of implantation to eight weeks post-implantation, and there was an overall increase in cytokine, chemokine, and growth factor production for material-containing cages compared to empty cages. However, cytokine production was only modestly affected by the different surface chemistries of the three implanted polymeric materials.

The microscopical characterization of membranes poly (L-glycolic-co-lactic acid) with and without added plasticizer: an in vivo study

The development of biodegradable materials has lead to renewed interest in the study of their interactions with the host organism in order to make the resulting products appropriate for use as temporary materials in clinical research, as well as important therapeutic applications. The copolymer poly (L-lactic-co-glycolic acid) or PLGA membranes have been used for several purposes. The physical properties of these materials can be modified by the addition of a plasticizer, such as the triethylcitrate, to provide flexibility and porosity to the implants, and enhance control of the polymer degradation time. Membranes with 7% plasticizer and without plasticizer (triethylcitrate) were compared. Membranes without plasticizer were denser and more compact than those with plasticizer. Two days and 30 days after implantation, the membranes with and without plasticizer showed little degradation. Sixty days and 120 days after implantation, the membranes with 7% plasticizer showed more cell invasion, and tissue adherence, as well as rapid degradation when compared to membranes without plasticizer.

Application of polylactides in spinal cages: studies in a goat model

Spinal cages are currently made of non-resorbable materials, but they only have a temporary function: after fusion, resorption is desirable both from a biological and mechanical point of view. We studied different polylactides in stand-alone condition in a goat model. Cages were made of 100% poly(L-lactic acid) (PLLA) or 70/30 poly(L/DL-Lactic acid) (PLDLLA); titanium served as control. After six months, all titanium cages showed non-unions comparable to that observed in a clinical retrieval, thus showing validity of the goat model. PLLA cages maintained their mechanical integrity for six months, enough to allow fusion. After that, the material resorbed within 48 months without adverse tissue reactions. Bone formation was faster in PLDLLA cages, but these already failed within three months, thus losing their stabilising function: 50% ended in pseudo-arthrosis. Additional internal fixation provided enough stability for fusion (83%). Biocompatibility of both PLLA and PLDLLA was excellent. The long-term results show that PLLA cages can be used for stand-alone interbody fusion, and that PLLA is an improvement over titanium in terms of fusion rate. PLDLLA showed enhanced bone formation, but also earlier failure of the implant. Chances for spinal fusion were better with additional internal fixation.

The influence of triethylcitrate on the biological properties of poly (L-lactic-co-glycolic acid) membranes

Biodegradable polymers have a variety of uses in basic and clinical research, as well as important therapeutic applications. The most commonly used are poly (lactic acid), poly (glycolic acid) and their copolymer, poly (L-lactic-co-glycolic acid) or PLGA. The incorporation of a plasticizer into a polymer can be used to obtain a product with specific properties. In this work, we examined the influence of a plasticizer (triethylcitrate) on the properties of PLGA membrane implants for human clinical uses. Membranes with and without plasticizer were dense and compact and contained no pores. The incorporation of 7% plasticizer enhanced the degradation the polymer when compared to polymer without plasticizer. In membranes without plasticizer, the initiation of degradation was very slow and was seen only 60 days after implantation, should allow the use of this material in the repair of damage tissue. In both cases, macroscopic analysis showed that there was no adhesion of the membrane to capsule fibrous, and this adversely affected preservation of the polymer. With time, the adherence of the polymer to surrounding tissue increased. Overall there was little degradation of membranes without plasticizer compared to those containing plasticizer.

Morphometrical analysis of multinucleated giant cells in subdermal implants of poly-lactic acid in rats

The use of bioabsorbable polymers in (bio)medical applications has increased greatly in recent years, mainly because of their good bioreabsorption and biocompatibility. In this work, we examined the development of foreign body giant cells in intimate contact with porous membranes of poly L-lactic acid containing 7% of plasticizer triethylcitrate implanted in the backs of rats. The membranes were removed 2, 7, 14, 21, 28, 60, 90 and 180 days after implantation, along with a portion of the tissue around the implant. Histological analysis of the implant and tissue revealed the formation of a fibrous capsule from the seventh day of implantation onwards. Foreign body giant cells appeared from the seventh day and increased in number up to the twenty-eighth day and then up to the ninetieth day of implantation, remaining constant up to the end of the study onwards, and increased in number up to the ninetieth day after implantation and then remained constant. The number of nuclei in these cells increased from the seventh day of implantation up to the ninetieth day and then up to the end of the study.

Evaluation of biodegradable synthetic scaffold coated on arterial prostheses implanted in rat subcutaneous tissue

Polyester arterial prostheses impregnated with various synthetic biodegradable materials and with gelatin were implanted subcutaneously in rats for 3-180 days. The inflammation was assessed by quantifying the activity of alkaline phosphatase and by histology. The degradation of the scaffold materials was determined by scanning electron microscopy (SEM), size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). The alkaline phosphatase activity induced by the polymer-impregnated grafts was similar to that induced by the non-impregnated controls during most of the post-implantation periods. Histological studies revealed that the acute inflammatory response was moderate to mild and was similar for all types of specimens, except for the gelatin-impregnated grafts that induced a severe acute inflammation during the first 2 weeks post-implantation. At 4 and 6 months, significant disintegration of the scaffold was observed, accompanied by enhanced tissue infiltration and a reactivation of the acute inflammatory phase. Linear and exponential degradation rates of the synthetic polymers were described. The relative degradation rates of the biodegradable polymers were ranked as following: PLLACL > PDLLA > PLLA > PCEL. In conclusion, biodegradable polymers may provide an option as sealant/scaffolding materials for vascular prosthesis. It is suggested that the degradation rate of the polymer scaffolding materials should be higher to achieve early healing while without inducing strong inflammation.

The long-term behavior of poly-L-lactide screws in a minipig fracture model: preliminary report

The long-term degradation tissue response to poly-L-lactide (PLLA) screw was investigated for a minipig tibia fracture. As a bone-fracture model, three PLLA screws per animal were used to fix a tibia that had been subjected to a crank-shaped osteotomy. A total of 12 nine-month-old male minipigs were used. In time period from 1 month to 3 years, clinical, radiographic, and pathological studies were conducted. On macroscopic examination, no clear granuloma or fistula formation was noted for 3 years. On microscopic examination, no osteoclasts or giant cells were detected around the screws during the 3 years postoperatively. A substantial degradation of PLLA screw was observed between 2 and 3 years. At 3 years only slight residual breakdown products were found in macrophages. On electric microscopic examination, numerous degraded polymers were seen in a small number of macrophages around the screws. In this model, fixation of tibia fractures using PLLA screws was not associated with any side effects, and was safe and useful for up to 3 years.

In vivo leukocyte cytokine mRNA responses to biomaterials are dependent on surface chemistry

An in vivo mouse cage implant system was used to determine whether leukocyte cytokine mRNA responses to implanted biomaterials were dependent on surface chemistry. Surfaces displaying various chemistries (hydrophobic, hydrophilic, anionic, and cationic) were placed into stainless steel cages and implanted subcutaneously. Semiquantitative RT-PCR analyses revealed that hydrophilic surfaces showed a decreased expression of proinflammatory cytokines, IL-6 and IL-8, and pro-wound healing cytokines, IL-10 and TGF-beta by adherent cells, and mRNA levels of the proinflammatory cytokine, IL-1beta, and the pro-wound healing cytokine IL-13 were decreased in surrounding, exudate cells. Cytokine responses by adherent and exudate cells to hydrophobic, anionic and cationic surfaces were similar and indicative of a strong inflammatory response at the earliest time point followed by a wound healing response at later time points. However, no differences in the types or levels of exudate cells for any of the surfaces or the empty cage at each of the respective time points were observed, indicating their respective biocompatibility. These studies identify hydrophilic surface chemistries as having significant effects on leukocyte cytokine responses in vivo by decreasing the expression of inflammatory and wound healing cytokines by inflammatory cells adherent to the biomaterial as well as present in the surrounding exudate.

Characterization of the inflammatory response to biomaterials using a rodent air pouch model

Using a rodent air pouch, the inflammatory responses to biomaterials with distinct physical properties and chemical compositions were compared. The polymers examined were expanded poly(tetrafluoroethylene) (ePTFE), silicone, low-density polyethylene (LDPE), poly(L-lactic acid) (PLLA), poly(desaminotyrosyl-tyrosine ethyl carbonate) [poly(DTE carbonate)], and poly(desaminotyrosyl-tyrosine benzyl carbonate) [poly(DTBzl carbonate)]. We found that implantation of disks (4.5-4.8 mm) of these materials into rodent air pouches for 2 days had no effect on the number or type of cells recovered relative to sham controls. With each of the materials, macrophages were the predominant cell type identified (60-75%), followed by granulocytes (20-25%) and lymphocytes (10%). Implantation of poly(DTE carbonate), ePTFE, LDPE, or poly(DTBzl carbonate) into the pouches for 2 days caused an increase in release of superoxide anion by the pouch cells. Cells from pouches containing poly(DTE carbonate) also released more hydrogen peroxide and were more phagocytic. In contrast, PLLA and silicone had no effect on the functional activity of cells recovered from the pouches. Prolonging the implantation time of poly(DTE carbonate) or PLLA to 7 days did not alter the number or type of cells isolated from the pouches. However, cells from pouches containing poly(DTE carbonate) for 7 days continued to produce increased quantities of superoxide anion relative to sham control pouch cells. These results suggest that the air pouch model is a highly sensitive method and therefore useful for evaluating the functional responses of inflammatory cells to biomaterials.

Preparation of bioabsorbable nerve guide tubes

The use of bioabsorbable polymers in applications as temporary structural function, recovering damage in live tissues, is a promising research area. Membranes of poly(lactic acid) (PLA) may act as support to adhesion and cellular invasion or as devices for guided tissue regeneration (GTR). In this study, the same casting technique used to prepare membranes was used to prepare PLA tubes. These tubes can be used for tests in nerve guided regeneration (NGR). To improve flexibility of the device, a bioabsorbable plasticizer was added to the polymer. The initial results showed that the proposed technique allowed the preparation of flexible tubes that can be used for NGR.

Tissue reactions to polypyrrole-coated polyesters: A magnetic resonance relaxometry study

The electrically conductive properties of polypyrrole (PPy) as a coating on polyester material are very attractive for the manufacture of small diameter blood conduits. However, before these PPy-coated materials can be investigated for their capacity to generate endothelialized luminal surfaces, they must first be studied for their innocuousness in a living environment. The specific goal of the present study was to investigate the in vivo interactions of PPy-coated and noncoated woven polyester materials implanted subcutaneously in rats for prescheduled periods of 2, 5, 10, 20, and 30 days. The in vivo magnetic resonance (MR) relaxation times were computed for a small area of muscle tissue adjacent to the implants. A correlation was concurrently attempted with blood monocyte activation studies as well as histological observations of the tissue-material interface. The progressive pattern of the slower transversal relaxation time (T2s) values revealed a more persistent tissue reaction for the most conductive PPy-coated materials and a shorter acute tissue response as the surface resistivity increased. Similarly, the blood monocyte activation studies indicated that the thickness of the PPy coating, which correlated with the conductivity, was directly related to tissue response. Furthermore, both the MR and biological studies showed that the PPy-coated material with a high surface resistivity displayed the lowest tissue reaction over the entire period of implantation. The results obtained from the blood monocyte activation studies and histological observations correlate well with the noninvasive MR measurements of the body's healing process. The conductive materials with high surface resistivities must be further investigated. Finally, the noninvasive nature of MR relaxometry reveals its outstanding potential for future in vivo investigations of the body's tissue interactions with polymers and nonferromagnetic biomaterials.

Comparative histological evaluation of new tyrosine-derived polymers and poly (L-lactic acid) as a function of polymer degradation

Previous studies demonstrated that poly(DTE carbonate) and poly (DTE adipate), two tyrosine-derived polymers, have suitable properties for use in biomedical applications. This study reports the evaluation of the in vivo tissue response to these polymers in comparison to poly(L-lactic acid) (PLLA). Typically, the biocompatibility of a material is determined through histological evaluations as a function of implantation time in a suitable animal model. However, due to changes that can occur in the tissue response at different stages of the degradation process, a fixed set of time points is not ideal for comparative evaluations of materials having different rates of degradation. Therefore the tissue response elicited by poly(DTE carbonate), poly(DTE adipate), and PLLA was evaluated as a function of molecular weight. This allowed the tissue response to be compared at corresponding stages of degradation. Poly(DTE adipate) consistently elicited the mildest tissue response, as judged by the width and lack of cellularity of the fibrous capsule formed around the implant. The tissue response to poly(DTE carbonate) was mild throughout the 570 day study. However, the response to PLLA fluctuated as a function of the degree of degradation, exhibiting an increase in the intensity of inflammation as the implant began to lose mass. At the completion of the study, tissue ingrowth into the degrading and disintegrating poly(DTE adipate) implant was evident while no comparative ingrowth of tissue was seen for PLLA. The similarity of the in vivo and in vitro degradation rates of each polymer confirmed the absence of enzymatic involvement in the degradation process. A comparison of molecular weight retention, water uptake, and mass loss in vivo with two commonly used in vitro systems [phosphate-buffered saline (PBS) and simulated body fluid (SBF)] demonstrated that for the two tyrosine-derived polymers the in vivo results were equally well simulated in vitro with PBS and SBF. However, for PLLA the in vivo results were better simulated in vitro using PBS.