Polymeric Materials and Artificial Organs - American Chemical Society

4 The Basics of Biomedical Polymers: Interfacial Factors R O B E R T E. BAIER

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on April 4, 2018 | https://pubs.acs.org Publication Date: June 8, 1984 | doi: 10.1021/bk-1984-0256.ch004

Advanced Technology Center, Calspan Corporation, Buffalo, N Y 14225

I n t e r f a c i a l phenomena, i n c l u d i n g initial a d s o r p t i o n of macromolecular f i l m s , attachment of cells, and t r i g g e r i n g of cellular aggregation and exudation, often d i c t a t e the suitability of m a t e r i a l s f o r b i o medical a p p l i c a t i o n s . These f a c t o r s can be b e t t e r understood, c o n t r o l l e d and p r e d i c t e d if the chemistry of the i n t e r f a c i n g m a t e r i a l s i s w e l l c h a r a c t e r i z e d i n advance. This i s p a r t i c u l a r l y true in implant environments where a p p l i c a t i o n of such d i a g n o s t i c t o o l s as i n t e r n a l r e f l e c t i o n spectroscopy, contact angle checks, f i l m thickness determinations, and surface electrical p o t e n t i a l measurements can a i d considerably i n s e l e c t i n g m a t e r i a l s for p r o s t h e t i c devices that promote good t i s s u e i n c o r p o r a t i o n while remaining passive to blood elements. The p r e d i c t i v e patterns developed serve w e l l across a l a r g e span of bioadhesive problems from those i n t i s s u e and blood to those i n s a l i v a and the sea. Specific application of the concept of critical surface tension has l e d to s i g n i f i c a n t success i n the design and clinical acceptance of new human arterial g r a f t s , and is a i d i n g i n the development of artificial h e a r t s , and subp e r i o s t e a l dental implants. With these data i n hand, m a t e r i a l s d e f i c i e n c i e s become l e s s of a l i m i t i n g f a c tor i n biomedical device c o n s t r u c t i o n . A significant research need i s f o r s p e c i f i c a t i o n of the mechanical shear forces that are r e q u i r e d to assure r e l i a b l e detachment of even weakly bound b i o f o u l i n g f i l m s from the l e a s t adherent substrata now a v a i l a b l e .

0097-6156/84/0256-0039$06.00/0 © 1984 American Chemical Society

Gebelein; Polymeric Materials and Artificial Organs ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

POLYMERIC MATERIALS AND ARTIFICIAL ORGANS


40

I n t e r f a c i a l phenomena o f t e n d i c t a t e the s u i t a b i l i t y of b i o m a t e r i a l s f o r _in v i v o use. In p a r t i c u l a r , the surface c h a r a c t e r i s t i c s of v a r i o u s implants c o n t r o l the r e l a t i v e adhesive strengths obtained between b i o m a t e r i a l s and the l i v i n g t i s s u e s they touch. While great adhesive strength and immobility are d e s i r e d f o r orthopedic and dental implants, minimal bioadhesion i s c r i t i c a l to preventing thrombus formation i n c a r d i o v a s c u l a r devices, or plaque buildup on o r a l prostheses. T h i s overview addresses the p r i n c i p l e s of surface phenomena i n b i o l o g i c a l environments, d e s c r i b e s u s e f u l methods f o r s e n s i t i v e a n a l y s i s of the e a r l i e s t i n t e r f a c i a l events, and provides i l l u s t r a t i o n s of t h e i r use f o r c h a r a c t e r i z i n g m a t e r i a l s placed i n the human body. Scope of the Problem A t t e n t i o n i s d i r e c t e d to bioadhesive phenomena i n the o r a l e n v i ronment that present improved surface c o n d i t i o n i n g methods to promote e x c e l l e n t bonding between t i s s u e and implanted p r o s t h e t i c devices (1). Other important surface phenomena i n c l u d e those necessary to the safe and e f f e c t i v e f u n c t i o n of c a r d i o v a s c u l a r appliances such as the a r t i f i c i a l heart and s u b s t i t u t e blood v e s s e l s (2,3). Impressive s i m i l a r i t i e s e x i s t with b i o l o g i c a l f o u l i n g of m a t e r i a l s i n the sea (4) . The primary i n t e r f a c i a l events i n these d i v e r s e s y s t e m s — a l l wet, s a l t y , and b i o c h e m i c a l l y a c t i v e — a r e s i m i l a r enough to suggest that Nature has been most conservative i n accommodating encounters with strange boundaries. Research Premise A major d i f f i c u l t y i n many p r i o r s t u d i e s of biomedical implants i n the d e n t a l , orthopedic, or c a r d i o v a s c u l a r environment, has been the tendency to focus on long term behavior of the m a t e r i a l s — from weeks to months to years p o s t - i m p l a n t a t i o n . There has s e l dom been proper implant c h a r a c t e r i z a t i o n or even knowledge of t h e i r surface s t a t e s at the time of placement or of the e a r l y bioadhesive sequelae (within minutes, hours and days) changing the surface p r o p e r t i e s to others that can promote or i n h i b i t adhesion of formed b i o l o g i c a l elements (such as t i s s u e c e l l s or b a c t e r i a l organisms) (5). In more t r a d i t i o n a l engineering studi e s , f o r example those d e a l i n g with the r a t e of b i o l o g i c a l f o u l i n g of heat exchange m a t e r i a l s (as i n power p l a n t condenser tubes) and i t s consequences, an analogous ignorance of the i n i t i a t i n g events has been commonly dismissed with the l a b e l " i n d u c t i o n p e r i o d . " (6) In such engineering systems, as with biomedical implants, s i g n i f i c a n t gains i n our understanding of the performance and c o n t r o l of the devices i s h i g h l y dependent upon b e t t e r knowledge of the a c t u a l , i n i t i a l m i c r o f o u l i n g events. The f i r s t adhesive l a y e r s prepare the devices f o r grosser b i o f o u l i n g , with consequent d e t e r i o r a t i o n , f u n c t i o n a l l o s s e s , and degraded performance.


4.

BAIER

The Basics of Biomedical Polymers

41


Improved Methods f o r A n a l y s i s of I n t e r f a c i a l F a c t o r s Test p l a t e s a l l o w i n g s e n s i t i v e i n s p e c t i o n of the f i r s t organic l a y e r s accumulating on t h e i r faces are among the more u s e f u l t o o l s of the i n t e r f a c i a l s c i e n t i s t i n t e r e s t e d i n bioadhesive phenomena. In r e l e v a n t b i o l o g i c a l l o c a t i o n s and during a c t u a l use, these are most v a l u a b l e i n c h a r a c t e r i z i n g the f i r s t adsorbed or adherent l a y e r s . The primary technique p e r m i t t i n g i n s p e c t i o n of the " i n t e r f a c e conversion l a y e r s " spontaneously adsorbed to a l l known m a t e r i a l s exposed to the environments of the month, t i s s u e (whether i n l i v i n g animal or human hosts or i n c u l t u r e i n l a b o r a t o r y c o n t a i n e r s ) , blood, or the sea, i s known as i n t e r n a l r e f l e c t i o n i n f r a r e d spectroscopy ( 7 ) . I n essence, the technique p l a c e s the a n a l y s t i n s i d e the t e s t m a t e r i a l t h a t serves as a " l i g h t p i p e " f o r probing beams of electromagnetic energy. The s p e c t r o s c o p i c " f i n g e r p r i n t " of the m a t e r i a l f i r s t adsorbing a t the p l a t e s u r f a c e may be recorded during the primary adhesive phase ( 8 ) . Such t e s t p l a t e s have been incubated i n the mouths of human v o l u n t e e r s (9) and s i m i l a r s t u d i e s have been completed i n broths c o n s i s t i n g of n u t r i e n t medium i n o c u l a t e d w i t h s p e c i f i c microorganisms o r i g i n a l l y taken by micromanipulation techniques from the adherent plaque of human t e e t h ( 1 0 ) . The p l a t e s o b v i o u s l y experience d i f f e r e n t events on t h e i r f a c e s , d i c t a t e d by s p e c i f i c s u r f a c e property d i f f e r e n c e s . Some p l a t e s emerge from the plaque forming c h a l l e n g e as c l e a n and shiny as upon f i r s t immersion. Others accumulate t y p i c a l d e n t a l "brown s t a i n s " from m i c r o b i a l c o l o n i z i n g f i l m s (11). M e t a l l i c t e s t p l a t e s such as germanium or s i l i c o n are o f t e n used because t h e i r conductive p r o p e r t i e s prevent e l e c t r i c charge accumulation d u r i n g scanning e l e c t r o n m i c r o s c o p i c i n s p e c t i o n . T h i s e l i m i n a t e s the need f o r a d d i t i o n a l m e t a l l i c overcoatings u s u a l l y a p p l i e d to SEM samples p r i o r to m i c r o s c o p i c v i e w i n g . Absence of the u n i f o r m l y electron-dense m e t a l l i c overcoat on the i n t r i n s i c a l l y organic c o n d i t i o n i n g f i l m s (and attached c e l l u l a r l a y e r s ) then a l l o w s the r e l a t i v e t h i c k n e s s e s and l o c a t i o n s of the organic masses to be d i s t i n g u i s h e d by the d i f f e r e n c e s i n t h e i r a b i l i t y to suppress secondary e l e c t r o n e m i s s i o n — t h e process that provides the image of the common scanning e l e c t r o n m i c r o g r a p h — o f the h i g h - e l e c t r o n - d e n s i t y m e t a l l i c s u b s t r a t a . The t e s t p l a t e s can be made i n almost any shape and s i z e , and placed i n s p e c i a l i n t r a o r a l holders worn i n mouths of human v o l u n t e e r s . Such h o l d e r s provide means to analyze the " s k i n " on one's t e e t h , the p e l l i c l e acquired by s p e c i f i c a d s o r p t i o n of s a l i v a r y components before any s u c c e s s f u l c o l o n i z a t i o n by m i c r o b i a l f l o r a i s noted (12). I n f r a r e d s p e c t r a l t r a c e s obtained by the i n t e r n a l r e f l e c t i o n method a p p l i e d through t e s t p l a t e s exposed f o r o n l y a few moments i n the human mouth, demonstrate the presence of r a p i d l y adsorbed proteinaceous matter. Thus, the r e a l i t y of the " s k i n " on one's t e e t h , or on any other o b j e c t immersed even momentarily i n t h i s r i c h b i o l o g i c a l environment, can be documented. I t i s made of the



42

POLYMERIC MATERIALS A N D ARTIFICIAL ORGANS

same s u b s t a n c e — p r o t e i n — t h a t other n a t u r a l " s k i n s " are made o f . The s p e c t r a r e v e a l t h a t the p r o t e i n present i n the a c q u i r e d p e l l i c l e s i s g l y c o p r o t e i n i n the main. In a d d i t i o n t o the i n t e r n a l r e f l e c t i o n s p e c t r o s c o p i c t e c h nique, there i s a host of supporting methods. They range from techniques that estimate p r e c i s e f i l m t h i c k n e s s and r e f r a c t i v e index to techniques t h a t measure s u r f a c e e l e c t r i c a l property and w e t t a b i l i t y changes t h a t are a s s o c i a t e d w i t h p r o t e i n f i l m d e p o s i t i o n (13). Use o f these n o n d e s t r u c t i v e methods, a p p l i e d s e q u e n t i a l l y and r o u t i n e l y t o t e s t m a t e r i a l s exposed i n b i o l o g i c a l environments of concern, has been i l l u s t r a t e d p r e v i o u s l y i n s t u d i e s o f the f o u l i n g of food p r o c e s s i n g equipment (14). Typical Results Simple m o d i f i c a t i o n o f the s u r f a c e chemistry of immersed s o l i d m a t e r i a l s , s p e c i f i c a l l y t o provide low s u r f a c e energy ranges as i n d i c a t e d by c r i t i c a l s u r f a c e tensions between 20 and 30 dynes/cm, prevents permanent i n t e r f a c e conversion by spontaneously adsorbing glycoproteinaceous macromolecules. T h i s i n d u c t i o n of a poor "primer coat" i n h i b i t s the adhesion o f b i o l o g i c a l c e l l s ; even those elements such as blood p l a t e l e t s s p e c i a l i z e d f o r the purpose of s u r f a c e c o l o n i z a t i o n are prevented from g e t t i n g a s u c c e s s f u l " g r i p " on the s u b s t r a t a . Conversely, upward adjustment of a m a t e r i a l ' s s u r f a c e energy promotes stronger b i o l o g i c a l i n t e r a c t i o n s (15). With knowledge o f the zones o f s u r f a c e energy t h a t e i t h e r f a v o r o r minimize adhesion i n b i o l o g i c a l environments, i t i s now p o s s i b l e t o design and develop improved p r o s t h e t i c m a t e r i a l s f o r a number of important a p p l i c a t i o n s . Elsewhere, we have reviewed many o f the areas of c u r r e n t research i n bioadhesive phenomena: d e n t a l r e s t o r a t i v e s , p r o s t h e t i c implants, s u r g i c a l adhesives, and even improved c o a t i n g s f o r the p r e v e n t i o n of marine f o u l i n g on commercial ships (16).

Literature Cited 1. Natiella, J.R., Meenaghan, M.A., Flynn, H.E., Carter, J.M., Baier, R.E., and Akers, C.K., Unilateral Superiosteal Implants in Primates, Journal of Prosthetic Dentistry, 48:68-77, 1982. 2.

Baier, R.E., The Organization of Blood Components Near Interfaces, Annals of the New York Academy of Sciences, 283:17-36, 1977.

3.

Baier, R. E., Akers, C. K., Natiella, J. R., Meenaghan, M.A., and Wirth, J., Physiochemical Properties of Stabilized Umbilical Vein, Vascular Surgery, 14:145-157, 1980.


4.

BAIER

The Basics of Biomedical Polymers

43

4. Goupil, D.W., DePalma, V.A., and Baier, R.E., Physical/ Chemical Characteristics of the Macromolecular Conditioning Film in Biological Fouling, Proceedings of the Fifth International Congress on Marine Corrosion and Fouling, Graficas Orbe, S.L., Padill, 82, Madrid, Spain, pp 401-410, 1980.


5. Baier, R.E., Surface Properties Influencing Biological Adheaion, Chapt. 2 in Adhesion in Biological Systems (R.S. Manly, ed.), Academic Press, NY pp 15-48, 1970. 6. DePalma, V.A. and Baier, R.E., Microfouling of Metallic and Coated Metallic Flow Surfaces in Model Heat Exchange Cells, Proceedings of the Ocean Thermal Energy Conversion (OTEC) Biofouling and Corrosion Symposium (R.H. Gray, ed.), PNL-SA7115, U.S. Department of Energy, Washington, D. C. 20545, pp 89-106, 1978. 7. Harrick, N.J., Internal Reflection Spectroscopy, Interscience Publishers, NY, 1967. 8. Baier, R.E., Loeb, G.I., and Wallace, G.T., Role of an Artificial Boundary in Modifying Blood Proteins, Federation Proceedings, 30:1523-1538, 1971. 9. Baier, R.E. and Glantz, P.O., Characterization of Oral In Vivo Films Formed on Different Types of Solid Surfaces," Acta Odontol. Scand., 36:289-301, 1978. 10. Baier, R.E., "Adhesion to Different Types of Biosurfaces," in Dental Plaque and Surface Interactions in the Oral Cavity (S.A. Leach, ed.), Information Retrieval Inc., Arlington, VA, pp 31-47, 1980. 11.

Baier, R.E., "Substrata Influences on the Adhesion of Microorganisms and Their Resultant New Surface Properties," in Adsorption of Microorganisms to Surfaces (G. Bitton and K.C. Marshall, eds.), Wiley-Interscience Publishers, NY, pp 59104, 1980.

12. Baier, R.E., "Occurrence, Nature and Extent of Cohesive and Adhesive Forces in Dental Integuments," Chapt. 5, Surface Chemistry and Dental Integuments (A. Lasslo and R.P. Quintana, eds.), C.C. Thomas, Publisher, Springfield, IL, pp 337-391, 1973. 13.

Baier, R.E. and Loeb, G.I., "Multiple Parameters Characterizing Interfacial Films of a Protein Analogue, Polymethylglutamate," in Polymer Characterization: Interdisciplinary Approaches (C.D. Craver, ed.), Plenum Press, NY, pp 75-96, 1971.


POLYMERIC MATERIALS A N D ARTIFICIAL ORGANS

44


14. Baier, R.E., "Modification of Surfaces to Reduce Fouling and/ or Improve Cleaning," in Fundamentals and Applications of Surface Phenomena Associated with Fouling and Cleaning in Food Processing (B. Hallstrom, D.B. Lund, and Ch. Tragardh, eds.), Division of Food Engineering, Lund University, Alnarp, Sweden, pp 168-189, 1981. 15. Baier, R.E. and Meyer, A.E., "Surface Energetics and Biological Adhesion," Proceedings, International Symposium on Physiochemical Aspects of Polymer Surfaces (K. L. Mittal, ed.) Plenum Press, NY, 1982. 16. Baier, R.E., "Conditioning Surfaces to Suit the Biomedical Environment: Recent Progress," Journal of Biomechanical Engineering, 104:257-271, 1982. RECEIVED

April 23,

1984


Polymeric Materials and Artificial Organs - American Chemical Society

Recommend Documents